Lasers have been successfully used in medicine for more than 50 years. Ophthalmology, gynecology, cosmetology, dermatology, physiotherapy, cardiology, rehabilitation, surgery, diagnostics - far from full list areas of medicine in which lasers are in demand.

From history to modern times

ABOUT healing potential The ancient Greeks knew about light and successfully used the energy of the sun in therapy. The founder of laser medicine was the American surgeon Leon Goldman. He was the first to use a laser generator for treatment skin diseases. This happened in 1961, a year after the invention of the device. Goldman's methods gave impetus to the development of new technology in dermatology.

Dermatology

Laser dermatology using low-intensity radiation can solve many skin problems faster and more effective than drug treatment.

Laser therapy sessions for treatment:

• Urticaria;
• Psoriasis;
• Eczema;
• Atopic dermatitis;
• Acne;
• Boils;
• Vitiligo;
• other diseases.

By affecting the superficial and deep layers of the skin, the stream of light destroys harmful bacteria, relieves pain, relieves inflammation, relieves pain and strengthens the skin's immunity. Not only the well-being improves, but also the condition of the patient’s skin.

Cosmetology

Laser cosmetology allows you to get rid of scars, scars, and age spots without pain. Can be easily removed with laser unwanted hair on the body, make wrinkles less pronounced, increase skin tone, make it more elastic.

The main advantages of laser cosmetology include:

• Selective influence. The doctor selects its parameters individually, depending on the problem and skin type.
• Minimal trauma. The laser beam affects certain areas without touching neighboring areas.
• Aesthetic result. It is noticeable after the first procedure.
• Persistence. The result obtained lasts for several years.

Gynecology

Lasers are used in gynecological practice in the treatment of diseases of the female reproductive system. Local impact light triggers biochemical reactions in the body - metabolic processes in the cells are activated, blood microcirculation improves, which is necessary for recovery.

Laser treatment is indispensable for cervical erosion and other diseases, the treatment of which requires accuracy, painlessness, and the absence of complications and contraindications from the gynecologist. Treatment is carried out in courses - 1-2 procedures per day for 10-14 days. If necessary, the doctor adjusts the duration, intensity, and frequency of sessions.

Ophthalmology

Laser technologies have proven themselves as effective therapeutic and surgical treatment of the visual organs. Laser beams are characterized by monochromaticity and parallel direction, which makes it possible to locally influence the biological tissues of the eye.

IN therapeutic purposes Laser stimulation is used, which is based on low-intensity red radiation. Its interaction with eye tissues has an anti-inflammatory, absorbable and stimulating effect. Laser stimulation is often included in complex therapy of patients diagnosed with keratitis, hemophthalmos, corneal erosion, opacification vitreous, as well as during the recovery period after operations.

Neurology

90% of Russians have problems with the spine. In modern neurology, laser treatment is increasingly used to treat osteochondrosis. Relief occurs after the first sessions. Laser radiation reduces symptoms and relieves patients from pain. The cause of severe back pain is considered to be a reflex syndrome - it disappears first.

Then the laser removes the radicular syndrome - it occurs due to swelling or due to constant compression of the root of the vertebral hernia. Radicular syndrome manifests itself in advanced stages of the disease and causes severe pain. Often a person cannot stand up, take a step, roll over, or sit down on his own.

Laser treatment for osteochondrosis can be multidirectional: on the source of inflammation or on bioactive points. The neuropathologist and physiotherapist select the intensity taking into account the symptoms and stage of the disease. Improvements appear after two courses of laser therapy, and for full recovery 5-6 courses are required.

Other Applications

In urology, lasers are used to treat the urethra, prostate, bladder stones, and warts. Dentists use laser radiation to treat periodontal disease, hygiene procedures, other pathologies. Laser therapy sessions are also prescribed for the prevention of diseases and strengthening the body's protective functions. This is especially true shortly before periods of mass incidence of influenza and viral infections.

The future is personalized therapy

Medical scientists from different countries The world agrees that laser medicine has good prospects. In the foreseeable future, it will be actively used in genetics and epigenetics and will allow treatment to be carried out on the scale of a single cell. Ultrashort pulses of a certain length will focus and generate pulses in thousandths of a second. This will be the first step towards introducing personalized treatment methods. The basis of such treatment is the human genome, which is individual for each person.

Currently, it is difficult to imagine progress in medicine without laser technologies, which have opened up new opportunities in solving numerous medical problems.

The study of the mechanisms of action of laser radiation of various wavelengths and energy levels on biological tissue makes it possible to create multifunctional laser medical devices, the range of which can be used in clinical practice has become so broad that it is very difficult to answer the question: what diseases are not treated with lasers?

The development of laser medicine follows three main branches: laser surgery, laser therapy and laser diagnostics.

Our area of ​​activity is lasers for applications in surgery and cosmetology, with sufficiently high power for cutting, vaporization, coagulation and other structural changes in biological tissue.

Sufficiently powerful lasers with an average radiation power of tens of watts are used, which are capable of strongly heating biological tissue, which leads to its cutting or evaporation. These and other characteristics of surgical lasers determine the use in surgery of various types of surgical lasers operating on different laser active media.

The unique properties of the laser beam make it possible to perform previously impossible operations using new effective and minimally invasive methods.

1. Surgical laser systems provide:

2. effective contact and non-contact vaporization and destruction of biological tissue;

3. dry surgical field;

4. minimal damage to surrounding tissues;

5. effective hemo- and aerostasis;

6. stopping of lymphatic ducts;

7. high sterility and ablasticity;

8. compatibility with endoscopic and laparoscopic instruments

This makes it possible to effectively use surgical lasers to perform a wide variety of surgical interventions in urology, gynecology, otorhinolaryngology, orthopedics, neurosurgery, etc.

Olga (Princess of Kyiv)

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Material from Wikipedia - the free encyclopedia

(Redirected from Princess Olga)Olga

V. M. Vasnetsov. "Duchess Olga"

3rd Princess of Kyiv

Predecessor: Igor Rurikovich

Successor: Svyatoslav Igorevich

Religion: Paganism, converted to Christianity

Birth: unknown

Dynasty: Rurikovich

Spouse: Igor Rurikovich

Children: Svyatoslav Igorevich

Princess Olga, baptized Elena († July 11, 969) - princess, ruled Kievan Rus after the death of her husband, Prince Igor Rurikovich, as regent from 945 to about 960. The first of the Russian rulers accepted Christianity even before the baptism of Rus', the first Russian saint.

About 140 years after her death, an ancient Russian chronicler expressed the attitude of the Russian people towards the first ruler of Kievan Rus, who was baptized: She was the forerunner of the Christian land, like the morning star before the sun, like the dawn before the dawn. She shone like the moon in the night; so she shone among the pagans, like pearls in the mud.

1 Biography

1.1 Origin

1.2 Marriage and beginning of reign

1.3 Revenge on the Drevlyans

1.4 Olga's reign

2 Olga’s baptism and church veneration

3 Historiography according to Olga

4 Memory of Saint Olga

4.1 In fiction

4.2 Cinematography

5 Primary sources

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Biography

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Origin

According to the earliest ancient Russian chronicle, the Tale of Bygone Years, Olga was from Pskov. The life of the holy Grand Duchess Olga specifies that she was born in the village of Vybuty in the Pskov land, 12 km from Pskov up the Velikaya River. The names of Olga’s parents have not been preserved; according to the Life, they were not of noble family, “from the Varangian language.” According to Normanists, Varangian origin is confirmed by her name, which has a counterpart in Old Norse as Helga. The presence of presumably Scandinavians in those places is noted by a number of archaeological finds, possibly dating back to the 1st half of the 10th century. On the other hand, in chronicles the name Olga is often rendered in the Slavic form “Volga”. The ancient Czech name Olha is also known.

Princess Olga at the Monument “1000th Anniversary of Russia” in Veliky Novgorod

The typographical chronicle (end of the 15th century) and the later Piskarevsky chronicler convey a rumor that Olga was the daughter of the Prophetic Oleg, who began to rule Kievan Rus as the guardian of the young Igor, the son of Rurik: “The Netsy say that Olga is Olga’s daughter.” Oleg married Igor and Olga.

The so-called Joachim Chronicle, the reliability of which is questioned by historians, reports Olga’s noble Slavic origins:

“When Igor matured, Oleg married him, gave him a wife from Izborsk, the Gostomyslov family, who was called Beautiful, and Oleg renamed her and named her Olga. Igor later had other wives, but because of her wisdom he honored Olga more than others.”

Bulgarian historians also put forward a version about the Bulgarian roots of Princess Olga, relying mainly on the message of the New Vladimir Chronicler (“Igor married [Oleg] in Bolgareh, and Princess Olga was killed for him.”) and translating the chronicle name Pleskov not as Pskov, but as Pliska is the Bulgarian capital of that time. The names of both cities actually coincide in the Old Slavic transcription of some texts, which served as the basis for the author of the New Vladimir Chronicler to translate the message of the “Tale of Bygone Years” about Olga from Pskov as Olga from the Bulgarians, since the spelling Pleskov to designate Pskov has long gone out of use.

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Marriage and beginning of reign

The first meeting of Prince Igor with Olga.

Hood. V. K. Sazonov

According to "The Tale of Bygone Years" Prophetic Oleg married Igor Rurikovich, who began to rule independently in 912, to Olga in 903. This date is questioned, since, according to the Ipatiev list of the same “Tale,” their son Svyatoslav was born only in 942.

Perhaps to resolve this contradiction, the later Ustyug Chronicle and the Novgorod Chronicle, according to the list of P. P. Dubrovsky, report Olga’s 10-year-old age at the time of the wedding. This message contradicts the legend set out in the Degree Book (2nd half of the 16th century), about a chance meeting with Igor at a crossing near Pskov. The prince hunted in those places. While crossing the river by boat, he noticed that the carrier was a young girl dressed in men's clothing. Igor immediately “flared with desire” and began to pester her, but received a worthy rebuke in response: “Why do you embarrass me, prince, with immodest words? I may be young and humble, and alone here, but know: it is better for me to throw myself into the river than to endure reproach.” Igor remembered about the chance acquaintance when the time came to look for a bride, and sent Oleg for the girl he loved, not wanting any other wife.

"Princess Olga meets the body of Prince Igor." Sketch by V. I. Surikov, 1915

The Novgorod First Chronicle of the younger edition, which contains in the most unchanged form information from the Initial Code of the 11th century, leaves the message about Igor’s marriage to Olga undated, that is, the earliest Old Russian chroniclers had no information about the date of the wedding. It is likely that the year 903 in the PVL text arose at a later time, when the monk Nestor tried to bring the initial ancient Russian history into chronological order. After the wedding, Olga’s name is mentioned again only 40 years later, in the Russian-Byzantine treaty of 944.

According to the chronicle, in 945, Prince Igor died at the hands of the Drevlyans after repeatedly collecting tribute from them. The heir to the throne, Svyatoslav, was only 3 years old at the time, so Olga became the de facto ruler of Kievan Rus in 945. Igor's squad obeyed her, recognizing Olga as the representative of the legitimate heir to the throne. The decisive course of action of the princess in relation to the Drevlyans could also sway the warriors in her favor.

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Revenge on the Drevlyans

After the murder of Igor, the Drevlyans sent matchmakers to his widow Olga to invite her to marry their prince Mal. The princess successively dealt with the elders of the Drevlyans, and then brought the people of the Drevlyans into submission. The Old Russian chronicler describes in detail Olga’s revenge for the death of her husband:

"Olga's vengeance against the Drevlyan idols." Engraving by F. A. Bruni, 1839.

1st revenge of Princess Olga: Matchmakers, 20 Drevlyans, arrived in a boat, which the Kievans carried and threw into a deep hole in the courtyard of Olga’s tower. The matchmaker-ambassadors were buried alive along with the boat. Olga looked at them from the tower and asked: “Are you satisfied with the honor?” And they shouted: “Oh! It’s worse for us than Igor’s death.”

Olga's second revenge on the Drevlyans. Miniature from the Radziwill Chronicle.

2nd revenge: Olga asked, out of respect, to send new ambassadors from the best men to her, which the Drevlyans willingly did. An embassy of noble Drevlyans was burned in a bathhouse while they were washing themselves in preparation for a meeting with the princess.

3rd revenge: The princess with a small retinue came to the lands of the Drevlyans to, according to custom, celebrate a funeral feast at her husband’s grave. Having drunk the Drevlyans during the funeral feast, Olga ordered them to be chopped down. The chronicle reports 5 thousand Drevlyans killed.

Olga's fourth revenge on the Drevlyans. Miniature from the Radziwill Chronicle.

4th revenge: In 946, Olga went with an army on a campaign against the Drevlyans. According to the First Novgorod Chronicle, the Kiev squad defeated the Drevlyans in battle. Olga walked through the Drevlyansky land, established tributes and taxes, and then returned to Kyiv. In the PVL, the chronicler made an insert into the text of the Initial Code about the siege of the Drevlyan capital of Iskorosten. According to the PVL, after an unsuccessful siege during the summer, Olga burned the city with the help of birds, to whose feet she ordered lit tow with sulfur to be tied. Some of the defenders of Iskorosten were killed, the rest submitted. A similar legend about the burning of the city with the help of birds is also told by Saxo Grammaticus (12th century) in his compilation of oral Danish legends about the exploits of the Vikings and the skald Snorri Sturluson.

Over the past half century, lasers have found application in ophthalmology, oncology, plastic surgery and many other areas of medicine and biomedical research.

The possibility of using light to treat diseases was known thousands of years ago. The ancient Greeks and Egyptians used solar radiation in therapy, and the two ideas were even linked to each other in mythology - the Greek god Apollo was the god of the sun and healing.

It was only with the invention of the coherent radiation source more than 50 years ago that the potential for using light in medicine was truly revealed.

Due to their special properties, lasers are much more effective than radiation from the sun or other sources. Each quantum generator operates in a very narrow range of wavelengths and emits coherent light. Lasers in medicine also make it possible to create high powers. The beam of energy can be concentrated in a very small point, thereby achieving high density. These properties have led to lasers being used in many fields today. medical diagnostics, therapy and surgery.

Treatment of skin and eyes

The use of lasers in medicine began with ophthalmology and dermatology. The quantum generator was discovered in 1960. And just a year after that, Leon Goldman demonstrated how a ruby ​​red laser in medicine could be used to remove capillary dysplasia, a type birthmarks, and melanoma.

This application is based on the ability of coherent radiation sources to operate at a specific wavelength. Coherent radiation sources are now widely used for the removal of tumors, tattoos, hair and moles.

In dermatology, lasers of different types and wavelengths are used, due to the different types of lesions being treated and the main absorbing substance within them. also depends on the patient's skin type.

Today, you cannot practice dermatology or ophthalmology without lasers, as they have become the primary tools for treating patients. Application of quantum generators for vision correction and wide range Ophthalmic applications have grown since Charles Campbell in 1961 became the first physician to use a red laser in medicine to heal a patient with a detached retina.

Later, ophthalmologists began to use argon sources of coherent radiation in the green part of the spectrum for this purpose. The properties of the eye itself, especially its lens, were used here to focus the beam in the area of ​​retinal detachment. The highly concentrated power of the device literally welds it together.

Patients with some forms of macular degeneration may benefit from laser surgery - laser coagulation and photodynamic therapy. In the first procedure, a beam of coherent radiation is used to seal blood vessels and slow their abnormal growth under the macula.

Similar studies were carried out in the 1940s with sunlight, but for their successful completion, doctors needed the unique properties of quantum generators. The next use of the argon laser was to stop internal bleeding. Selective absorption of green light by hemoglobin - the pigment of red blood cells - has been used to block bleeding blood vessels. To treat cancer, the blood vessels entering the tumor and supplying it with nutrients are destroyed.

This cannot be achieved using sunlight. Medicine is very conservative, as it should be, but coherent radiation sources have gained recognition in various fields. Lasers in medicine have replaced many traditional instruments.

Ophthalmology and dermatology have also benefited from excimer sources of coherent ultraviolet radiation. They have become widely used in corneal reshaping (LASIK) for vision correction. Lasers in aesthetic medicine are used to remove spots and wrinkles.

Profitable Cosmetic Surgery

Such technological developments are inevitably popular among commercial investors as they have enormous profit potential. The analytical company Medtech Insight in 2011 estimated the market size of laser cosmetic equipment to be worth more than $1 billion. Indeed, despite the decline in overall demand for medical systems during the global recession, cosmetic surgeries, based on the use of quantum generators, continue to be in constant demand in the United States - the dominant market for laser systems.

Imaging and diagnostics

Lasers in medicine play an important role in early detection cancer, as well as many other diseases. For example, in Tel Aviv, a group of scientists became interested in IR spectroscopy using infrared coherent radiation sources. The reason for this is that cancer and healthy tissue may have different infrared permeability. One promising application of this method is the detection of melanomas. For skin cancer early diagnosis very important for patient survival. Currently, detection of melanoma is done by eye, so you can only rely on the skill of the doctor.

In Israel, once a year, everyone can go for free melanoma screening. Several years ago, studies were conducted in one of the large medical centers, as a result of which it became possible to visually observe the difference in the infrared range between potential, but harmless signs, and real melanoma.

Katzir, organizer of the first SPIE conference on biomedical optics in 1984, and his group in Tel Aviv also developed optical fibers transparent to infrared wavelengths, allowing the technique to be extended to internal diagnostics. In addition, it can be a quick and painless alternative to a cervical smear in gynecology.

Blue in medicine has found application in fluorescent diagnostics.

Systems based on quantum generators are also beginning to replace X-rays, which were traditionally used in mammography. X-rays present doctors with a difficult dilemma: high intensity is needed to reliably detect cancer, but increased radiation itself increases the risk of cancer. As an alternative, the possibility of using very fast laser pulses to take pictures of the breast and other parts of the body, such as the brain, is being explored.

OCT for the eyes and more

Lasers in biology and medicine have found application in optical coherence tomography (OCT), which has caused a wave of enthusiasm. This imaging technique uses the properties of a quantum generator and can produce very clear (on the order of microns), cross-sectional and three-dimensional images of biological tissue in real time. OCT is already used in ophthalmology, and can, for example, allow an ophthalmologist to see a cross-section of the cornea to diagnose retinal diseases and glaucoma. Today, the technique is also beginning to be used in other areas of medicine.

One of the largest areas emerging from OCT is fiber optic imaging of arteries. can be used to assess the condition of an unstable plaque prone to rupture.

Microscopy of living organisms

Lasers in science, technology, and medicine also play a key role in many types of microscopy. A large number of developments have been made in this area, the goal of which is to visualize what is happening inside the patient's body without the use of a scalpel.

The hardest part about removing cancer is the need to constantly use a microscope so that the surgeon can make sure everything is done correctly. The ability to perform microscopy “live” and in real time is a significant advance.

A new application of lasers in engineering and medicine is near-field scanning optical microscopy, which can produce images with a resolution much greater than that of standard microscopes. This method is based on optical fibers with notches on the ends, the dimensions of which are smaller than the wavelength of light. This enabled subwavelength imaging and laid the foundation for imaging biological cells. The use of this technology in IR lasers will allow us to better understand Alzheimer's disease, cancer and other changes in cells.

PDT and other treatment methods

Developments in optical fibers are helping to expand the use of lasers in other areas. In addition to the fact that they allow diagnostics to be carried out inside the body, the energy of coherent radiation can be transferred to where it is needed. This can be used in treatment. Fiber lasers are becoming much more advanced. They will radically change the medicine of the future.

The field of photomedicine, which uses light-sensitive chemicals that interact with the body in specific ways, could use quantum generators to both diagnose and treat patients. In photodynamic therapy (PDT), for example, a laser and a photosensitive drug can restore vision in patients with the “wet” form of age-related macular degeneration, the leading cause of blindness in people over the age of 50.

In oncology, some porphyrins accumulate in cancer cells and fluoresce when illuminated at a certain wavelength, indicating the location of the tumor. If these same compounds are then illuminated with a different wavelength, they become toxic and kill the damaged cells.

Red gas helium-neon laser is used in medicine in the treatment of osteoporosis, psoriasis, trophic ulcers etc., since this frequency is well absorbed by hemoglobin and enzymes. Radiation slows down inflammatory processes, prevents hyperemia and swelling, improves blood circulation.

Personalized treatment

Two other areas where lasers could be used are genetics and epigenetics.

In the future, everything will happen at the nanoscale, allowing medicine to be practiced on the cellular scale. Lasers that can generate femtosecond pulses and tune to specific wavelengths are ideal partners for medical professionals.

This will open the door to personalized treatments based on a patient's individual genome.

Leon Goldman - the founder of laser medicine

When talking about the use of quantum generators in treating people, one cannot fail to mention Leon Goldman. He is known as the "father" of laser medicine.

Within a year of inventing the coherent radiation source, Goldman became the first researcher to use it to treat a skin disease. The technique that the scientist used paved the way for the subsequent development of laser dermatology.

His research in the mid-1960s led to the use of the ruby ​​quantum generator in retinal surgery and to discoveries such as the ability of coherent radiation to simultaneously cut skin and seal blood vessels, limiting bleeding.

Goldman, a dermatologist at the University of Cincinnati for much of his career, founded the American Society of Lasers in Medicine and Surgery and helped lay the foundation for laser safety. Died 1997

Miniaturization

The first 2-micron quantum generators were the size of a double bed and cooled with liquid nitrogen. Today there are diodes that fit in the palm of your hand, and even smaller ones. These kinds of changes pave the way for new areas of application and development. Future medicine will have tiny lasers for brain surgery.

Thanks to technological progress, costs are constantly being reduced. Just as lasers have become commonplace in household appliances, they have begun to play a key role in hospital equipment.

If previously lasers in medicine were very large and complex, today's production of them from optical fiber has significantly reduced the cost, and the transition to the nanoscale will reduce costs even further.

Other Applications

Using lasers, urologists can treat urethral stricture, benign warts, urinary stones, bladder contracture and prostate enlargement.

The use of lasers in medicine has allowed neurosurgeons to make precise cuts and perform endoscopic monitoring of the brain and spinal cord.

Veterinarians use lasers for endoscopic procedures, coagulation of tumors, making incisions, and photodynamic therapy.

Dentists use coherent radiation for hole making, gum surgery, antibacterial procedures, dental desensitization, and orofacial diagnostics.

Laser tweezers

Biomedical researchers around the world use optical tweezers, cell sorters, and a variety of other tools. Laser tweezers promise better and faster cancer diagnosis and have been used to capture viruses, bacteria, small metal particles and strands of DNA.

Optical tweezers use a beam of coherent radiation to hold and rotate microscopic objects, similar to how metal or plastic tweezers can pick up small and fragile objects. Individual molecules can be manipulated by attaching them to micron-sized pieces of glass or polystyrene beads. When the beam hits the ball, it bends and has a small impact, pushing the ball right into the center of the beam.

This creates an "optical trap" that can trap a small particle in a beam of light.

Laser in medicine: pros and cons

Coherent radiation energy, the intensity of which can be modulated, is used to cut, destroy or alter the cellular or extracellular structure of biological tissues. In addition, the use of lasers in medicine, in short, reduces the risk of infection and stimulates healing. The use of quantum generators in surgery increases the accuracy of dissection; however, they pose a danger to pregnant women and there are contraindications for the use of photosensitizing drugs.

The complex structure of tissues does not allow for an unambiguous interpretation of the results of classical biological tests. Lasers in medicine (photo) are an effective tool for destroying cancer cells. However, powerful sources of coherent radiation act indiscriminately and destroy not only the affected tissue, but also the surrounding tissue. This property is an important tool of the microdissection technique, used to perform molecular analysis at a site of interest with the ability to selectively destroy excess cells. The goal of this technology is to overcome the heterogeneity present in all biological tissues to facilitate their study in a well-defined population. In this sense, laser microdissection has made a significant contribution to the development of research, to the understanding of physiological mechanisms that can now be clearly demonstrated at the population and even single cell level.

Tissue engineering functionality has become a major factor in the development of biology today. What happens if you cut actin fibers during division? Will the Drosophila embryo be stable if the cell is destroyed during folding? What are the parameters involved in the meristem zone of a plant? All these issues can be solved with the help of lasers.

Nanomedicine

IN Lately A variety of nanostructures have emerged with properties suitable for a range of biological applications. The most important of them are:

• quantum dots - tiny nanometer-sized light-emitting particles used in highly sensitive cellular imaging;
• magnetic nanoparticles, which have found application in medical practice;
• polymer particles for encapsulated therapeutic molecules;
• metal nanoparticles.

The development of nanotechnology and the use of lasers in medicine have, in short, revolutionized the way drugs are administered. Nanoparticle suspensions containing drugs can increase the therapeutic index of many compounds (increase solubility and efficacy, reduce toxicity) by selectively targeting affected tissues and cells. They deliver active substance, and also regulate the release of the active ingredient in response to external stimulation. Nanotheranostics is a further experimental approach that provides dual use of nanoparticles, drug compounds, therapeutics and diagnostic imaging tools, paving the way for personalized treatment.

The use of lasers in medicine and biology for microdissection and photoablation has made it possible to understand the physiological mechanisms of disease development at different levels. The results will help determine the best methods for diagnosing and treating each patient. The development of nanotechnology in close connection with advances in imaging will also be indispensable. Nanomedicine is a promising new form of treatment for certain types of cancer, infectious diseases or diagnostics.

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Introduction

1. Lasers and their use in medicine

2. Use of high-intensity laser radiation in surgery (general principles)

3. Light breakdown

Conclusion

List of used literature

Introduction

Lasers or optical quantum generators are modern sources of coherent radiation that have a number of unique properties. The creation of lasers was one of the most remarkable achievements of physics in the second half of the 20th century, which led to revolutionary changes in many areas of science and technology. To date, a large number of lasers with different characteristics- gas, solid-state, semiconductor, emitting light in various optical ranges. Lasers can operate in pulsed and continuous modes. The radiation power of lasers can vary from fractions of a milliwatt to 10 12 -10 13 W (in pulsed mode). Lasers are widely used in military equipment, materials processing technology, medicine, optical navigation, communication and location systems, in precision interference experiments, in chemistry, just in everyday life, etc.

One of the most important properties of laser radiation is its extremely high degree of monochromaticity, which is unattainable in the radiation of non-laser sources. This and all other unique properties of laser radiation arise as a result of the coordinated, cooperative emission of light quanta by many atoms of the working substance.

To understand the principle of laser operation, you need to more carefully study the processes of absorption and emission of light quanta by atoms. An atom can be in different energy states with energies E 1, E 2, etc. In Bohr's theory, these states are called stable. In fact, a stable state, in which an atom can remain indefinitely in the absence of external disturbances, is only the state with the lowest energy. This condition is called basic. All other states are unstable. An excited atom can remain in these states only very a short time, about 10 - 8 s, after which it spontaneously goes into one of lower states, emitting a quantum of light, the frequency of which can be determined from Bohr's second postulate. Radiation emitted during the spontaneous transition of an atom from one state to another is called spontaneous. An atom can remain at some energy levels for a much longer time, on the order of 10 - 3 s. Such levels are called metastable.

The transition of an atom to a higher energy state can occur through resonant absorption of a photon, the energy of which is equal to the difference between the energies of the atom in the final and initial states.

Transitions between atomic energy levels do not necessarily involve the absorption or emission of photons. An atom can gain or give up some of its energy and move into another quantum state as a result of interactions with other atoms or collisions with electrons. Such transitions are called non-radiative.

In 1916, A. Einstein predicted that the transition of an electron in an atom from an upper energy level to a lower one can occur under the influence of an external electromagnetic field, whose frequency is equal to the natural frequency of the transition. The resulting radiation is called forced or induced. Stimulated emission has amazing property. It differs sharply from spontaneous emission. As a result of the interaction of an excited atom with a photon, the atom emits another photon of the same frequency, propagating in the same direction. In the language of wave theory, this means that the atom emits an electromagnetic wave whose frequency, phase, polarization and direction of propagation are exactly the same as that of the original wave. As a result of the stimulated emission of photons, the amplitude of the wave propagating in the medium increases. From the point of view of quantum theory, as a result of the interaction of an excited atom with a photon, the frequency of which is equal to the transition frequency, two completely identical twin photons appear.

It is stimulated radiation that is the physical basis for the operation of lasers.

1 . Lasers and their use in medicine

Despite the common nature of light and radio waves, for many years optics and radio electronics developed independently, independently of each other. It seemed that the light sources - excited particles and radio wave generators - had little in common. Only in the middle of the 20th century did work appear on the creation of molecular amplifiers and radio wave generators, which marked the beginning of a new independent field of physics - quantum electronics.

Quantum electronics studies methods for amplifying and generating electromagnetic oscillations using stimulated emission of quantum systems. Advances in this area of ​​knowledge are found by everyone greater application in science and technology. Let's get acquainted with some of the phenomena underlying quantum electronics and the operation of optical quantum generators - lasers.

Lasers are light sources that operate on the basis of the process of forced (stimulated, induced) emission of photons by excited atoms or molecules under the influence of radiation photons having the same frequency. A distinctive feature of this process is that the photon produced during stimulated emission is identical in frequency, phase, direction and polarization to the external photon that caused it. This determines the unique properties of quantum generators: high coherence of radiation in space and time, high monochromaticity, narrow directivity of the radiation beam, huge concentration of power flow and the ability to focus into very small volumes. Lasers are created on the basis of various active media: gaseous, liquid or solid. They can produce radiation in a very wide range of wavelengths - from 100 nm (ultraviolet light) to 1.2 microns (infrared radiation) - and can operate in both continuous and pulsed modes.

The laser consists of three fundamentally important components: an emitter, a pump system and a power source, the operation of which is ensured with the help of special auxiliary devices.

The emitter is designed to convert pump energy (transfer the helium-neon mixture 3 into an active state) into laser radiation and contains an optical resonator, which is generally a system of carefully manufactured reflective, refractive and focusing elements, in the internal space of which a certain type of electromagnetic waves is excited and maintained fluctuations in the optical range. The optical resonator must have minimal losses in the working part of the spectrum, high precision in the manufacture of components and their mutual installation.

The creation of lasers turned out to be possible as a result of the implementation of three fundamental physical ideas: stimulated emission, the creation of a thermodynamically nonequilibrium inverse population of atomic energy levels, and the use of positive feedback.

Excited molecules (atoms) are capable of emitting luminescence photons. Such radiation is a spontaneous process. It is random and chaotic in time, frequency (there may be transitions between different levels), direction of propagation and polarization. Another radiation - forced or induced - occurs when a photon interacts with an excited molecule if the photon energy is equal to the difference in the corresponding energy levels. With forced (induced) emission, the number of transitions performed per second depends on the number of photons entering the substance during the same time, i.e., on the intensity of light, as well as on the number of excited molecules. In other words, the higher the population of the corresponding excited energy states, the higher the number of forced transitions.

Induced radiation is identical to incident radiation in all respects, including in phase, so we can talk about coherent amplification of an electromagnetic wave, which is used as the first fundamental idea in the principles of laser generation.

The second idea, implemented when creating lasers, is to create thermodynamically nonequilibrium systems in which, contrary to Boltzmann's law, there are more particles at a higher level than at a lower one. The state of the medium in which for at least two energy levels it turns out that the number of particles with higher energy exceeds the number of particles with lower energy is called a state with inverted population of levels, and the medium is called active. It is the active medium in which photons interact with excited atoms, causing their forced transitions to a lower level with the emission of quanta of induced (stimulated) radiation, that is the working substance of the laser. A state with an inverse population of levels is formally obtained from the Boltzmann distribution for T< О К, поэтому иногда называется состоянием с "отрицательной" температурой. По мере распространения света в активной среде интенсивность его возрастает, имеет место явление, обратное поглощению, т. е. усиление света. Это означает, что в законе Бугера kX < 0, поэтому инверсная населенность соответствует среде с отрицательным показателем поглощения.

A population inversion state can be created by selecting particles with lower energy or by specially exciting the particles, for example, with light or an electrical discharge. By itself, a state of negative temperature does not exist for a long time.

The third idea used in the principles of laser generation originated in radiophysics and is the use of positive feedback. During its implementation, part of the generated stimulated emission remains inside the working substance and causes stimulated emission by more and more excited atoms. To implement such a process, the active medium is placed in an optical resonator, usually consisting of two mirrors, selected so that the radiation arising in it repeatedly passes through the active medium, turning it into a generator of coherent stimulated radiation.

The first such generator in the microwave range (maser) was designed independently in 1955 by Soviet scientists N.G. Bason and A.M. Prokhorov and American - C. Townes and others. Since the operation of this device was based on stimulated emission of ammonia molecules, the generator was called molecular.

In 1960, the first quantum generator in the visible range of radiation was created - a laser with a ruby ​​crystal as a working substance (active medium). In the same year, the helium-neon gas laser was created. The huge variety of currently created lasers can be classified according to the type of working substance: gas, liquid, semiconductor and solid-state lasers are distinguished. Depending on the type of laser, the energy to create a population inversion is supplied in different ways: excitation with very intense light - “optical pumping”, electric gas discharge, in semiconductor lasers - electric shock. Based on the nature of their glow, lasers are divided into pulsed and continuous.

Let's consider the operating principle of a solid-state ruby ​​laser. Ruby is a crystal of aluminum oxide Al 2 0 3 containing approximately 0.05% chromium ions Cr 3 + as an impurity. Excitation of chromium ions is carried out by optical pumping using high-power pulsed light sources. One of the designs uses a tubular reflector with an elliptical cross-section. Inside the reflector there is a direct xenon flash lamp and a ruby ​​rod located along lines passing through the foci of the ellipse (Fig. 1). Inner surface aluminum reflector is well polished or silver plated. The main property of an elliptical reflector is that the light coming out of one of its focus (xenon lamp) and reflected from the walls enters the other focus of the reflector (ruby rod).

The ruby ​​laser operates according to a three-level scheme (Fig. 2 a). As a result of optical pumping, chromium ions move from the ground level 1 to the short-lived excited state 3. Then a non-radiative transition occurs to the long-lived (metastable) state 2, from which the probability of a spontaneous radiative transition is relatively small. Therefore, the accumulation of excited ions in state 2 occurs and an inverse population is created between levels 1 and 2. Under normal conditions, the transition from the 2nd to the 1st level occurs spontaneously and is accompanied by luminescence with a wavelength of 694.3 nm. The laser cavity has two mirrors (see Fig. 1), one of which has a reflection coefficient R of the intensity of the light reflected and incident on the mirror), the other mirror is translucent and transmits part of the radiation incident on it (R< 100 %). Кванты люминесценции в зависимости от направления их движения либо вылетают из боковой поверхности рубинового стержня и теряются, либо, многократно отражаясь от зеркал, сами вызывают вынужденные переходы. Таким образом, пучок, перпендикулярный зеркалам, будет иметь наибольшее развитие и выходит наружу через полупрозрачное зеркало. Такой лазер работает в импульсном режиме. лазер пробой медицинское биологическое

Along with the ruby ​​laser operating according to a three-level scheme, four-level laser schemes based on ions of rare earth elements (neodymium, samarium, etc.) embedded in a crystalline or glass matrix have become widespread (Fig. 24, b). In such cases, a population inversion is created between two excited levels: the long-lived level 2 and the short-lived level 2."

A very common gas laser is the helium-neon laser, which is excited by an electrical discharge. The active medium in it is a mixture of helium and neon in a ratio of 10:1 and a pressure of about 150 Pa. Neon atoms are emitting, helium atoms play a supporting role. In Fig. 24, c shows the energy levels of helium and neon atoms. Generation occurs during the transition between levels 3 and 2 of neon. In order to create an inverse population between them, it is necessary to populate level 3 and empty level 2. The population of level 3 occurs with the help of helium atoms. During an electrical discharge, electron impact excites helium atoms into a long-lived state (with a lifetime of about 10 3 s). The energy of this state is very close to the energy of level 3 of neon, therefore, when an excited helium atom collides with an unexcited neon atom, energy is transferred, as a result of which level 3 of neon is populated. For pure neon, the lifetime at this level is short and the atoms move to levels 1 or 2, and the Boltzmann distribution is realized. Depletion of level 2 of neon occurs mainly due to the spontaneous transition of its atoms to the ground state upon collisions with the walls of the discharge tube. This ensures a stationary inverse population of levels 2 and 3 of neon.

The main structural element of a helium-neon laser (Fig. 3) is a gas-discharge tube with a diameter of about 7 mm. Electrodes are built into the tube to create a gas discharge and excite helium. At the ends of the tube at the Brewster angle there are windows, due to which the radiation is plane-polarized. Plane-parallel resonator mirrors are mounted outside the tube, one of them is translucent (reflection coefficient R< 100 %). Таким образом, пучок вынужденного излучения выходит наружу через полупрозрачное зеркало. Это лазер непрерывного действия.

The resonator mirrors are made with multilayer coatings, and due to interference, the required reflection coefficient is created for a given wavelength. The most commonly used lasers are helium-neon lasers, which emit red light with a wavelength of 632.8 nm. The power of such lasers is low, it does not exceed 100 mW.

The use of lasers is based on the properties of their radiation: high monochromaticity (~ 0.01 nm), sufficiently high power, beam narrowness and coherence.

The narrowness of the light beam and its low divergence made it possible to use lasers to measure the distance between the Earth and the Moon (the resulting accuracy is about tens of centimeters), the rotation speed of Venus and Mercury, etc.

Their use in holography is based on the coherence of laser radiation. Gastroscopes have been developed based on a helium-neon laser using fiber optics, which make it possible to holographically form a three-dimensional image of the internal cavity of the stomach.

The monochromatic nature of laser radiation is very convenient for exciting Raman spectra of atoms and molecules.

Lasers are widely used in surgery, dentistry, ophthalmology, dermatology, and oncology. The biological effects of laser radiation depend on both the properties of the biological material and the properties of the laser radiation.

All lasers used in medicine are conventionally divided into 2 types: low-intensity (intensity does not exceed 10 W/cm2, most often about 0.1 W/cm2) - therapeutic and high-intensity - surgical. The intensity of the most powerful lasers can reach 10 14 W/cm 2; in medicine, lasers with an intensity of 10 2 - 10 6 W/cm 2 are usually used.

Low-intensity lasers are those that do not cause a noticeable destructive effect on tissue directly during irradiation. In the visible and ultraviolet regions of the spectrum, their effects are caused by photochemical reactions and do not differ from the effects caused by monochromatic light received from conventional, incoherent sources. In these cases, lasers are simply convenient monochromatic light sources that provide precise localization and dosage of exposure. Examples include the use of helium-neon laser light for the treatment of trophic ulcers, coronary heart disease, etc., as well as krypton and other lasers for photochemical damage to tumors in photodynamic therapy.

Qualitatively new phenomena are observed when using visible or ultraviolet radiation from high-intensity lasers. In laboratory photochemical experiments with conventional light sources, as well as in nature under the influence of sunlight, single-photon absorption usually occurs. This is stated in the second law of photochemistry, formulated by Stark and Einstein: every molecule involved in chemical reaction, coming under the influence of light, absorbs one quantum of radiation, which causes a reaction. The single-photon nature of absorption, described by the second law, is fulfilled because at ordinary light intensities it is practically impossible for two photons to simultaneously enter a molecule in the ground state. If such an event were to take place, the expression would take the form:

2hv = E t - E k ,

which would mean the summation of the energy of two photons for the transition of a molecule from the energy state E k to a state with energy E g. There is also no absorption of photons by electronically excited molecules, since their lifetime is short, and the irradiation intensities usually used are low. Therefore, the concentration of electronically excited molecules is low, and their absorption of another photon is extremely unlikely.

However, if the light intensity is increased, two-photon absorption becomes possible. For example, irradiation of DNA solutions with high-intensity pulsed laser radiation with a wavelength of about 266 nm led to ionization of DNA molecules similar to that caused by y-radiation. Exposure to low-intensity ultraviolet radiation did not cause ionization. It has been established that upon irradiation aqueous solutions nucleic acids or their bases with picosecond (pulse duration 30 ps) or nanosecond (10 ns) pulses with intensities above 10 6 W/cm 2 led to electronic transitions resulting in the ionization of molecules. With picosecond pulses (Fig. 4, a), the population of high electronic levels occurred according to the scheme (S 0 -> S1 -> S n), and with hv hv nanosecond pulses (Fig. 4, b) - according to the scheme (S 0 -> S1 -> T g -> T p). In both cases, the molecules received energy exceeding the ionization energy.

The absorption band of DNA is located in the ultraviolet region of the spectrum at< 315 нм, видимый свет нуклеиновые кислоты совсем не поглощают. Однако воздействие высокоинтенсивным лазерным излучением около 532 нм переводит ДНК в электронно-возбужденное состояние за счет суммирования энергии двух фотонов (рис. 5).

The absorption of any radiation leads to the release of a certain amount of energy in the form of heat, which is dissipated from the excited molecules into the surrounding space. Infrared radiation is absorbed mainly by water and causes mainly thermal effects. Therefore, the radiation of high-intensity infrared lasers causes a noticeable immediate thermal effect on tissue. The thermal effect of laser radiation in medicine is mainly understood as evaporation (cutting) and coagulation of biological tissues. This applies to various lasers with intensities from 1 to 10 7 W/cm 2 and with irradiation durations from milliseconds to several seconds. These include, for example, a gas C 0 2 laser (with a wavelength of 10.6 μm), Nd:YAG laser (1.064 μm) and others. Nd:YAG laser is the most widely used solid-state four-level laser. Generation is carried out on transitions of neodymium ions (Nd 3+) introduced into Y 3 Al 5 0 12 yttrium aluminum garnet (YAG) crystals.

Along with heating the tissue, some of the heat is removed due to thermal conductivity and blood flow. At temperatures below 40 °C, irreversible damage is not observed. At a temperature of 60 °C, protein denaturation, tissue coagulation and necrosis begin. At 100-150 °C dehydration and charring are caused, and at temperatures above 300 °C the tissue evaporates.

When radiation comes from a high-intensity focused laser, the amount of heat generated is large, creating a temperature gradient in the tissue. At the point where the beam hits, the tissue evaporates, and charring and coagulation occurs in the adjacent areas (Fig. 6). Photoevaporation is a method of layer-by-layer removal or cutting of tissue. As a result of coagulation, the blood vessels are sealed and bleeding stops. Thus, a focused beam of a continuous C 0 2 laser () with a power of about 2 * 10 3 W/cm 2 is used as a surgical scalpel for cutting biological tissues.

If you reduce the duration of exposure (10-10 s) and increase the intensity (above 10 6 W/cm 2), then the sizes of the charring and coagulation zones become negligible. This process is called photoablation (photoremoval) and is used to remove tissue layer by layer. Photoablation occurs at energy densities of 0.01-100 J/cm 2 .

With a further increase in intensity (10 W/cm and higher), another process is possible - “optical breakdown”. This phenomenon is that due to the very high electric field strength of laser radiation (comparable to the strength of intra-atomic electric fields), matter ionizes, plasma is formed and mechanical shock waves are generated. Optical breakdown does not require the absorption of light quanta by a substance in the usual sense; it is observed in transparent media, for example, in air.

2. Application of high-intensity laser radiation in surgery (general principles)

The main method of treating surgical diseases is operations involving the dissection of biological tissues. The impact of highly concentrated light energy on biological tissue leads to its strong heating, followed by evaporation of interstitial and intracellular fluid, compaction and coagulation of tissue structures. At low exposures, the surface layers of biological tissue are destroyed. With increasing exposure, the depth and volume of destruction increase.

Surgical lasers are either continuous or pulsed, depending on the type of active medium. Conventionally, they can be divided into three groups according to power level:

coagulating: 1-5 W;

evaporating and shallow cutting: 5-20 W;

deep cutting: 20-100 W.

Of course, this division is largely arbitrary, since the radiation wavelength and operating mode greatly influence the requirements for the output power of a surgical laser

When using high-power laser radiation, a very rapid increase in tissue temperature occurs at the point of contact of the laser beam with the biological tissue. This leads to the effect of reversible denaturation of the protein (40-53 °C), a further increase in temperature (55-63 °C) leads to irreversible destruction of protein structures. An increase in temperature from 63 to 100 °C leads to coagulation, and from 100 °C or more to evaporation and carbonization of biological tissue.

The operation, performed using a non-contact method, provides a pronounced hemostatic effect. The impact is carried out practically bloodless or with minimal blood loss, which simplifies its implementation and is accompanied by minor trauma to surrounding tissues.

The depth of penetration of laser radiation into tissue depends on the exposure time and the degree of tissue hydration. The higher the hydrophilicity, the lower the penetration depth, and vice versa, the lower the degree of tissue hydration, the deeper the radiation penetrates. With pulsed laser radiation, biological tissue is not heated to the required depth as a result of significant surface absorption, and therefore evaporation does not occur, but only coagulation takes place. With prolonged exposure after charring, the tissue absorption parameters change and evaporation begins.

Laser surgery uses high-intensity laser radiation (HILI), which is obtained using CO 2, EnYAG laser and argon laser.

Laser surgical instruments have high precision and accuracy in producing destructive effects on the operated organs and tissues. This is relevant and sometimes is always the missing link in key stages of operations, especially operations performed on tissues and organs with intense blood supply, in order to cause coagulation of the destruction front and avoid hemorrhage. Also, the use of a laser scalpel ensures absolute sterility of the operation. Here you can cite the medical complexes “Scalpel-1”, “Kalina”, “Parsing”, “Lancet-1” - CO models, lasers intended for surgical operations V various areas medical practice. Laser surgical devices are a universal cutting tool and can be used at key stages of surgical interventions. Indications for the use of laser radiation during surgery are: the need to perform operations on organs that are richly supplied with blood, when complete hemostasis is required, and its implementation is accompanied by conventional methods large blood loss; the need to sterilize purulent wounds and prevent possible microbial contamination of clean surgical wounds (this circumstance is extremely important in regions with a tropical climate); the need for precision surgical techniques; surgical interventions in patients with blood clotting disorders.

There are no universal laser treatment modes for various tissues. Therefore, the selection of optimal parameters and modes of exposure is carried out by the surgeon independently, based on the basic methods of using laser surgical units in medical practice. For surgical treatment, these techniques were developed by employees of the Russian State Scientific Center for Laser Medicine and MMA named after. THEM. Sechenov, Tverskoy medical academy based on a generalization of clinical experience in various fields of medicine: dental and maxillofacial surgery, abdominal surgery, lung and pleural surgery, plastic surgery, cosmetology, purulent surgery, burn surgery, anorectal surgery, gynecology, urology, otolaryngology.

The nature of the interaction of laser radiation with biological tissue depends on the power density of the laser radiation and the interaction time. The speed of cutting tissue with a laser beam is different stages The operation is selected experimentally by the surgeon depending on the type of tissue and the desired quality of the cut with the selected parameters of laser radiation. Slowing the cutting speed can lead to increased tissue carbonation and the formation of a deep coagulation zone. In the superpulse mode and especially in the pulse-periodic mode, carbonization and necrosis associated with overheating of surrounding tissues are practically eliminated at any speed of the laser beam. Let us present the main characteristics of the devices used in medical practice. The radiation wavelength is 10.6 microns. Output radiation power (adjustable) - 0.1-50 W. Power in the "medipulse" mode - 50 W. The power density of laser irradiation is limited from above by a conditional value of 50-150 W/cm 2 for pulsed lasers and a value of 10 W/cm 2 for continuous lasers. Diameter of laser beam on fabric (switchable) - 200; 300; 500 microns. Guidance of the main radiation by a diode laser beam - 2 mW, 635 nm. Radiation modes (switchable) - continuous, pulse-periodic, medipulse. Radiation exposure time (adjustable) - 0.1-25 min. The duration of the radiation pulse in the pulse-periodic mode (adjustable) is 0.05-1.0 s. The duration of the pause between pulses is 0.05-1.0 s. Remote control panel. Turning the radiation on and off - foot pedal. Removal of combustion products - smoke evacuation system. The radius of the operating space is up to 1200 mm. The cooling system is autonomous, air-liquid type. Placement in the operating room is floor or tabletop. Power supply (AC) - 220 V, 50 Hz, 600 W. Overall dimensions and weight vary. As you can see, the main difference between a laser for surgery and other medical lasers is the high radiation power, especially in the pulse. This is necessary so that during the pulse the tissue substance has time to absorb the radiation, heat up and evaporate into the surrounding air space. Basically, all surgical lasers operate at medium infrared region optical range.

JIM-10, a laser surgical device "Lasermed" - the latest achievement in the field of laser technology, is suitable for carrying out operations in a mobile version. Built on the basis of semiconductor lasers emitting at a wavelength of 1.06 microns, the device is highly reliable, small in size and weight. Output radiation power - 0-7(10) W, packaged dimensions 470 x 350 x 120 mm, weight no more than 8 kg. This device is designed in the form of a suitcase, which, if necessary, can be transformed into a working position.

Also among the products of other domestic manufacturers, the following surgical complexes can be mentioned: ALOD-OBALKOM "Surgeon" (near-IR surgical laser device with adjustable radiation power). There are 5 modifications available, differing in the maximum laser radiation power - 6 W, 9 W, 12 W, 15 W, 30 W. Used for PT therapy (coagulation, removal of tumors, tissue cutting), installations based on carbon dioxide, YAG-neodymium (general surgery) and argon (ophthalmology) lasers of the company, as well as many others based on both gas, solid-state and semiconductor active avg.

There are many foreign and domestic analogues, the principles of use of which are similar to those stated above.

3. Light breakdown

Light breakdown (optical breakdown, optical discharge, laser spark), the transition of a substance as a result of intense ionization to the plasma state under the influence of electromagnetic fields of optical frequencies. Light breakdown was first observed in 1963 when radiation from a high-power pulsed ruby ​​crystal laser operating in the Q-switched mode was focused in air. When a light breakdown occurs, a spark appears at the focus of the lens; the effect is perceived by the observer as a bright flash, accompanied by a strong sound. For the breakdown of gases at optical frequencies, huge electric fields of the order of 106-107 V/cm are required, which corresponds to the intensity of the light flux in the laser beam = 109-1011 W/cm 2 (for comparison, microwave breakdown of atmospheric air occurs at a field strength = 104 V/cm). There are two possible mechanisms: Light breakdown of a gas under the influence of intense light radiation. The first of them does not differ in nature from the breakdown of gases in fields of not very high frequencies (this also includes the microwave range). The first seed electrons, which appear for one reason or another in the field, first gain energy by absorbing photons in collisions with gas atoms. This process is the opposite of the bremsstrahlung emission of quanta during electron neutron scattering. excited atoms. Having accumulated energy sufficient for ionization, the electron ionizes the atom, and instead of one, two slow electrons appear, and the process repeats. This is how an avalanche develops (see AVALANCHE DISCHARGE). In strong fields, this process occurs quite quickly and a breakdown breaks out in the gas. The second mechanism for the occurrence of light breakdown, characteristic specifically for optical frequencies, is of a purely quantum nature. Electrons can be torn away from atoms as a result of the multiquantum photoelectric effect, i.e., with the simultaneous absorption of several photons at once. A single-quantum photoelectric effect in the case of frequencies in the visible range is impossible, since the ionization potentials of atoms are several times higher than the energy of the quantum. So, for example, the photon energy of a ruby ​​laser is 1.78 eV, and the ionization potential of argon is 15.8 eV, i.e., 9 photons are required to remove an electron. Typically, multiphoton processes are unlikely, but their speed increases sharply with increasing photon number density, and at those high intensities at which Light Breakdown is observed, their probability reaches a significant value. In dense gases, at pressures on the order of atmospheric pressure and higher, avalanche ionization always occurs; multiphoton processes here are only the cause of the appearance of the first electrons. In rarefied gases and in fields of picosecond pulses, when electrons fly out of the field action area without having had time to experience many collisions, the avalanche does not develop and Light breakdown is possible only due to the direct ejection of electrons from atoms under the influence of light. This is only possible with very strong light fields >107 V/cm. At high pressures Light breakdown is observed in much weaker fields. The entire mechanism of Light Breakdown is complex and diverse.

Basic light quantities

Light breakdown is also observed in condensed media when powerful laser radiation propagates through it and can cause destruction of materials and optical parts of laser devices.

The use of a semiconductor laser opens up new possibilities in the quality and timing of treatment. This high-tech surgical instrument and apparatus can be used for prevention and wound management in the postoperative period. This becomes possible through the use of physiotherapeutic properties of infrared laser radiation, which has a pronounced anti-inflammatory effect, bacteriostatic and bactericidal effect, and has a stimulating effect on tissue immunity and regeneration processes. It is also worth mentioning the possibility of using a diode laser to whiten teeth by 3-4 shades in one visit. However, the most common areas of laser application are surgery and periodontics.

The results obtained when working with a laser give reason to assert: a diode laser is an almost indispensable doctor’s assistant in everyday work, which is confirmed by positive reviews from patients. In their opinion, the use of this type of treatment is justified and comfortable. The operation is bloodless, quick, and the postoperative stage is easier to bear.

Objectively, a decrease in healing time by 2 times is observed, less painful sensations during and after operations, allowing you to do without anesthetics, faster regeneration, absence of edema - it is not surprising that an increasing number of patients prefer laser manipulation. But that's not all - the developed technique for managing patients with periodontal disease allows us to reduce the number and delay flap operations. Encouraging results have also been obtained in endodontics - treatment of canals with laser light seems very promising.

Areas of use. Diode lasers perfectly dissect, disinfect, coagulate and reconstruct soft tissues, making it possible to successfully perform the following manipulations:

* Gum correction during pre-prosthetic preparation makes it easier to work with materials. The bloodless field gives direct access to surfaces covered by the mucous membrane.

* Plastic frenulum - short frenulum of the tongue and upper lip is eliminated, plastic surgery of the vestibule of the oral cavity. In most cases, complete removal of the frenulum is successful. During the healing process, minimal swelling is observed - significantly less than wounds from intervention with a scalpel.

* Treatment of periodontal pockets for gingivitis and initial periodontitis. After a course of radiation, a quick and good result is achieved. It has also been noted that hard dental deposits are easier to remove after exposure to laser radiation.

* Gingivoplasty. Gingival hyperplasia resulting from orthodontic treatment and mechanical irritation is becoming increasingly common. It is known that stimulation of mucous tissues leads to pathological coating of the tooth. The tissue response is permanent and usually requires removal of excess tissue. Laser surgery presents effective method removal of excess tissue, restoring the normal appearance of the mucosa.

* Treatment of aphthous ulcers and herpes hyperesthesia. The physiotherapeutic capabilities of the diode laser are used. Laser energy in the form of an unfocused beam directed at the surface of these lesions affects nerve endings(for hyperesthesia). More difficult cases require light surface contact.

* Cosmetic reconstruction of the mucous membrane. This manipulation is a perfect aesthetic treatment method. Lasers make it possible to remove tissue layer by layer. The absence of bleeding allows these operations to be performed with greater accuracy. Gum tissue is easily evaporated, leaving clear edges. The parameters of the width, length of the incisions and height of the gingival contours are easily achievable.

* Periodontal treatment. In this situation, the most successful is an integrated approach combining surgery and physical therapy. There are treatment programs that lead to long-term remission if the patient follows oral hygiene recommendations. At the first visit, the acute process is stopped, then the pathological pockets are sanitized, and, if necessary, surgical manipulations are performed using additional bone materials. Next, the patient undergoes a maintenance course of laser therapy. The treatment period takes on average 14 days.

* Endodontic treatment. The traditional use of laser in endodontics is the evaporation of pulp residues and disinfection of canals. Special endodontic tips allow you to work directly in the open canal up to the apex. Using a laser, tissue remains are ablated, bacteria are destroyed, and the canal walls are glazed. If there is a fistula, the laser beam passes through the fistula channel towards the source of inflammation. At the same time, the spread of infection is stopped for some time and the symptoms are suppressed, but relapse is obvious if the root canal is not fully processed.

* Whitening. One should not ignore the fact that this is one of the most popular aesthetic procedures among patients. With the help of a diode laser, a significant whitening effect can be achieved in just one visit. The procedure itself is extremely simple and consists of activating a pre-applied whitening gel with laser radiation.

Advantages. In surgical dentistry and periodontology, the advantages of a laser are determined by factors such as accuracy and ease of access to the surgical field. At the same time, there is no bleeding during the operation, which allows the surgical field to remain dry, and this naturally provides a better overview - as a result, the operation time is reduced. Additionally, it is worth noting that during the operation the vessels are coagulated, thereby minimizing postoperative swelling.

Also, due to the anti-inflammatory and bacteriostatic effects of laser radiation, the risk of complications is reduced. Wound healing occurs faster compared to traditional techniques.

With laser conservative treatment of gingivitis and periodontitis with pocket depths up to 5 mm, there is no bleeding and inflammatory phenomena; in some cases, regeneration is observed bone tissue, which is confirmed by x-ray studies.

When carrying out bleaching, in addition to the short procedure time (about 1 hour), a significant advantage is the minimal manifestation of hypersensitivity after the bleaching procedure.

Domestic developments. As you can see, there are many advantages of using diode lasers. There is truth and one serious drawback inherent in all innovative developments in all areas of human knowledge - a high price. Indeed, the cost of such devices, especially those produced by well-known Western brands, is significant. Fortunately, there are Russian developments in this area, and this is quite rare case(when it comes to high-tech developments), when “Russian” does not mean “worst”. Since Soviet times, domestic developments in the field of laser technologies are not only not inferior to Western analogues, but often surpass them - many prototypes of modern laser systems were developed in our country.

There is also a domestic semiconductor dental laser - this is the Lamy S device (a joint development of the Denta-Rus Medical Center and the Opttekhnika Research and Production Center), which some Western companies have already become interested in, because among other things, its indisputable advantage is the fact that the cost of the laser is 3 times lower compared to imported analogues.

The device uses semiconductor laser crystals operating from low-voltage low-power (350 W) power sources, rather than gas-discharge tubes that require a special high-voltage power source. This design allows you to solve several problems at once - the absence of high voltage is a certain guarantee of safety for the doctor and the patient, there are no harmful electromagnetic fields, and no special cooling is required.

But let’s return to the low price of the device - this allows you to recoup your financial investments much faster and start making a profit. Agree, in addition to improving the quality of patient care, this is also very important in a commercial setting.

Among other features of the Lamy devices, it makes sense to note the following - they do not require special conditions and special maintenance, are small in size and easily transported within the clinic, and are reliable and stable parameters. Service is organized in such a way that if a malfunction occurs, the doctor receives another device during repairs.

Conclusion

The main instruments that the surgeon uses for tissue dissection are a scalpel and scissors, i.e. cutting instruments. However, wounds and cuts made with a scalpel and scissors are accompanied by bleeding, requiring the use of special hemostasis measures. In addition, when in contact with tissue, cutting instruments can spread microflora and malignant tumor cells along the cut line. In this regard, for a long time, surgeons have dreamed of having at their disposal an instrument that would make a bloodless cut, while simultaneously destroying pathogenic microflora and tumor cells in the surgical wound. Interventions on a “dry surgical field” are ideal for surgeons of any profile.

Attempts to create an “ideal” scalpel date back to the end of the last century, when the so-called electric knife, operating using high-frequency currents, was designed. This device, in more advanced versions, is currently used quite widely by surgeons of various specialties. However, as experience has accumulated, the negative aspects of “electrosurgery” have been identified, the main one of which is too large a zone of thermal tissue burn in the area of ​​the incision. It is known that the wider the burn area, the worse the surgical wound heals. In addition, when using an electric knife, it becomes necessary to include the patient’s body in an electrical circuit. Electrosurgical devices have a negative impact on performance electronic devices and devices for monitoring the body’s vital functions during surgery. Cryosurgical machines also cause significant tissue damage, impairing the healing process. The speed of tissue dissection with a cryoscalpel is very low. In fact, this does not involve dissection, but tissue destruction. A significant burn area is also observed when using a plasma scalpel. If we take into account that the laser beam has pronounced hemostatic properties, as well as the ability to seal the bronchioles, bile ducts and pancreatic ducts, then the use of laser technology in surgery becomes extremely promising. Briefly listed some of the advantages of using lasers in surgery relate primarily to carbon dioxide lasers (C 0 2 lasers). In addition to them, lasers that operate on other principles and on other working substances are used in medicine. These lasers have fundamentally different qualities when affecting biological tissues and are used for relatively narrow indications, in particular in cardiovascular surgery, oncology, and for treatment surgical diseases skin and visible mucous membranes, etc.

WITHlist of used literature

1. A.N. Remizov "Medical and biological physics".

2. O.K. Skobelkin "Lasers in surgery, edited by professor."

3. S.D. Pletnev "Lasers in clinical medicine" edited.

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INTRODUCTION

The main instruments that the surgeon uses for tissue dissection are a scalpel and scissors, i.e. cutting instruments. However, wounds and cuts made with a scalpel and scissors are accompanied by bleeding, requiring the use of special hemostasis measures. In addition, when in contact with tissue, cutting instruments can spread microflora and malignant tumor cells along the cut line. In this regard, for a long time, surgeons have dreamed of having at their disposal an instrument that would make a bloodless cut, while simultaneously destroying pathogenic microflora and tumor cells in the surgical wound. Interventions on a “dry surgical field” are ideal for surgeons of any profile.

Attempts to create an “ideal” scalpel date back to the end of the last century, when the so-called electric knife was designed, operating using high-frequency currents. This device, in more advanced versions, is currently used quite widely by surgeons of various specialties. However, as experience has accumulated, the negative aspects of “electrosurgery” have been identified, the main one of which is too large a zone of thermal tissue burn in the area of ​​the incision. It is known that the wider the burn area, the worse the surgical wound heals. In addition, when using an electric knife, it becomes necessary to include the patient’s body in an electrical circuit. Electrosurgical devices negatively affect the operation of electronic devices and devices for monitoring the body's vital functions during surgery. Cryosurgical machines also cause significant tissue damage, impairing the healing process. The speed of tissue dissection with a cryoscalpel is very low. In fact, this does not involve dissection, but tissue destruction. A significant burn area is also observed when using a plasma scalpel. If we take into account that the laser beam has pronounced hemostatic properties, as well as the ability to seal the bronchioles, bile ducts and pancreatic ducts, then the use of laser technology in surgery becomes extremely promising. Briefly listed some of the advantages of using lasers in surgery relate primarily to carbon dioxide lasers (CO 2 lasers). In addition to them, lasers that operate on other principles and on other working substances are used in medicine. These lasers have fundamentally different qualities when affecting biological tissues and are used for relatively narrow indications, in particular in cardiovascular surgery, oncology, for the treatment of surgical diseases of the skin and visible mucous membranes, etc.

LASERS AND THEIR APPLICATION IN MEDICINE

Despite the common nature of light and radio waves, for many years optics and radio electronics developed independently, independently of each other. It seemed that the light sources - excited particles and radio wave generators - had little in common. Only in the middle of the 20th century did work appear on the creation of molecular amplifiers and radio wave generators, which marked the beginning of a new independent field of physics - quantum electronics.

Quantum electronics studies methods for amplifying and generating electromagnetic oscillations using stimulated emission of quantum systems. Advances in this area of ​​knowledge are increasingly being used in science and technology. Let's get acquainted with some of the phenomena underlying quantum electronics and the operation of optical quantum generators - lasers.

Lasers are light sources that operate on the basis of the process of forced (stimulated, induced) emission of photons by excited atoms or molecules under the influence of radiation photons having the same frequency. A distinctive feature of this process is that the photon produced during stimulated emission is identical in frequency, phase, direction and polarization to the external photon that caused it. This determines the unique properties of quantum generators: high coherence of radiation in space and time, high monochromaticity, narrow directivity of the radiation beam, huge concentration of power flow and the ability to focus into very small volumes. Lasers are created on the basis of various active media: gaseous, liquid or solid. They can produce radiation in a very wide range of wavelengths - from 100 nm (ultraviolet light) to 1.2 microns (infrared radiation) - and can operate in both continuous and pulsed modes.

The laser consists of three fundamentally important components: an emitter, a pump system and a power source, the operation of which is ensured with the help of special auxiliary devices.

The emitter is designed to convert pump energy (transfer the helium-neon mixture 3 into an active state) into laser radiation and contains an optical resonator, which is generally a system of carefully manufactured reflective, refractive and focusing elements, in the internal space of which a certain type of electromagnetic waves is excited and maintained fluctuations in the optical range. The optical resonator must have minimal losses in the working part of the spectrum, high precision in the manufacture of components and their mutual installation.

The creation of lasers turned out to be possible as a result of the implementation of three fundamental physical ideas: stimulated emission, the creation of a thermodynamically nonequilibrium inverse population of atomic energy levels, and the use of positive feedback.

Excited molecules (atoms) are capable of emitting luminescence photons. Such radiation is a spontaneous process. It is random and chaotic in time, frequency (there may be transitions between different levels), direction of propagation and polarization. Another radiation - forced or induced - occurs when a photon interacts with an excited molecule if the photon energy is equal to the difference in the corresponding energy levels. With forced (induced) emission, the number of transitions performed per second depends on the number of photons entering the substance during the same time, i.e., on the intensity of light, as well as on the number of excited molecules. In other words, the higher the population of the corresponding excited energy states, the higher the number of forced transitions.

Induced radiation is identical to incident radiation in all respects, including in phase, so we can talk about coherent amplification of an electromagnetic wave, which is used as the first fundamental idea in the principles of laser generation.

The second idea, implemented when creating lasers, is to create thermodynamically nonequilibrium systems in which, contrary to Boltzmann's law, there are more particles at a higher level than at a lower one. The state of the medium in which for at least two energy levels it turns out that the number of particles with higher energy exceeds the number of particles with lower energy is called a state with inverted population of levels, and the medium is called active. It is the active medium in which photons interact with excited atoms, causing their forced transitions to a lower level with the emission of quanta of induced (stimulated) radiation, that is the working substance of the laser. A state with an inverse population of levels is formally obtained from the Boltzmann distribution for T< О К, поэтому иногда называется состоянием с «отрицательной» температурой. По мере распространения света в активной сред интенсивность его возрастает, имеет место явление, обратное поглощению, т. е. усиление света. Это означает, что в законе Бугера kX < 0, поэтому инверсная населенность соответствует среде с отрицательным показателем поглощения.

A population inversion state can be created by selecting particles with lower energy or by specially exciting the particles, for example, with light or an electrical discharge. By itself, a state of negative temperature does not exist for a long time.

The third idea used in the principles of laser generation originated in radiophysics and is the use of positive feedback. During its implementation, part of the generated stimulated emission remains inside the working substance and causes stimulated emission by more and more excited atoms. To implement such a process, the active medium is placed in an optical resonator, usually consisting of two mirrors, selected so that the radiation arising in it repeatedly passes through the active medium, turning it into a generator of coherent stimulated radiation.

The first such generator in the microwave range (maser) was designed in 1955 independently by Soviet scientists N. G. Basoi and A. M. Prokhorov and American scientists - C. Townes and others. Since the operation of this device was based on stimulated emission ammonia molecules, the generator was called molecular.

In 1960, the first quantum generator of visible radiation was created - a laser with a ruby ​​crystal as a working substance (active medium). In the same year, the helium-neon gas laser was created. The huge variety of currently created lasers can be classified according to the type of working substance: gas, liquid, semiconductor and solid-state lasers are distinguished. Depending on the type of laser, the energy to create a population inversion is supplied in different ways: excitation with very intense light - “optical pumping”, electric gas discharge, and in semiconductor lasers - electric current. Based on the nature of their glow, lasers are divided into pulsed and continuous.

Let's consider the operating principle of a solid-state ruby ​​laser. Ruby is a crystal of aluminum oxide Al 2 0 3 containing approximately 0.05% chromium ions Cr 3+ as an impurity. Excitation of chromium ions is carried out by optical pumping using high-power pulsed light sources. One of the designs uses a tubular reflector with an elliptical cross-section. Inside the reflector there is a direct xenon flash lamp and a ruby ​​rod located along lines passing through the foci of the ellipse (Fig. 1). The inner surface of the aluminum reflector is highly polished or silver plated. The main property of an elliptical reflector is that the light coming out of one of its focus (xenon lamp) and reflected from the walls enters the other focus of the reflector (ruby rod).

The ruby ​​laser operates according to a three-level scheme (Fig. 2 a). As a result of optical pumping, chromium ions move from the ground level 1 to the short-lived excited state 3. Then a non-radiative transition occurs to the long-lived (metastable) state 2, from which the probability of a spontaneous radiative transition is relatively small. Therefore, the accumulation of excited ions in state 2 occurs and an inverse population is created between levels 1 and 2. Under normal conditions, the transition from the 2nd to the 1st level occurs spontaneously and is accompanied by luminescence with a wavelength of 694.3 nm. The laser cavity has two mirrors (see Fig. 1), one of which has a reflection coefficient R of the intensity of the light reflected and incident on the mirror), the other mirror is translucent and transmits part of the radiation incident on it (R< 100%). Кванты люминесценции в зависимости от направления их движения либо вылетают из боковой поверхности рубинового стержня и теряются, либо, многократно отражаясь от зеркал, сами вызывают вынужденные переходы. Таким образом, пучок, перпендикулярный зеркалам, будет иметь наибольшее развитие и выходит наружу через полупрозрачное зеркало. Такой лазер работает в импульсном режиме.

Along with the ruby ​​laser operating according to a three-level scheme, four-level laser schemes based on ions of rare earth elements (neodymium, samarium, etc.) embedded in a crystalline or glass matrix have become widespread (Fig. 24, b). In such cases, a population inversion is created between two excited levels: the long-lived level 2 and the short-lived level 2."

A very common gas laser is the helium-neon laser, which is excited by an electrical discharge. The active medium in it is a mixture of helium and neon in a ratio of 10:1 and a pressure of about 150 Pa. Neon atoms are emitting, helium atoms play a supporting role. In Fig. 24, c shows the energy levels of helium and neon atoms. Generation occurs during the transition between levels 3 and 2 of neon. In order to create an inverse population between them, it is necessary to populate level 3 and empty level 2. The population of level 3 occurs with the help of helium atoms. During an electrical discharge, electron impact excites helium atoms into a long-lived state (with a lifetime of about 10 3 s). The energy of this state is very close to the energy of level 3 of neon, therefore, when an excited helium atom collides with an unexcited neon atom, energy is transferred, as a result of which level 3 of neon is populated. For pure neon, the lifetime at this level is short and the atoms move to levels 1 or 2, and the Boltzmann distribution is realized. Depletion of level 2 of neon occurs mainly due to the spontaneous transition of its atoms to the ground state upon collisions with the walls of the discharge tube. This ensures a stationary inverse population of levels 2 and 3 of neon.

The main structural element of a helium-neon laser (Fig. 3) is a gas-discharge tube with a diameter of about 7 mm. Electrodes are built into the tube to create a gas discharge and excite helium. At the ends of the tube at the Brewster angle there are windows, due to which the radiation is plane-polarized. Plane-parallel resonator mirrors are mounted outside the tube, one of them is translucent (reflection coefficient R< 100%). Таким образом, пучок вынужденного излучения выходит наружу через полупрозрачное зеркало. Это лазер непрерывного действия.

The resonator mirrors are made with multilayer coatings, and due to interference, the required reflection coefficient is created for a given wavelength. The most commonly used lasers are helium-neon lasers, which emit red light with a wavelength of 632.8 nm. The power of such lasers is low, it does not exceed 100 mW.

The use of lasers is based on the properties of their radiation: high monochromaticity (~ 0.01 nm), sufficiently high power, beam narrowness and coherence.

The narrowness of the light beam and its low divergence made it possible to use lasers to measure the distance between the Earth and the Moon (the resulting accuracy is about tens of centimeters), the rotation speed of Venus and Mercury, etc.

Their use in holography is based on the coherence of laser radiation. Gastroscopes have been developed based on a helium-neon laser using fiber optics, which make it possible to holographically form a three-dimensional image of the internal cavity of the stomach.

The monochromatic nature of laser radiation is very convenient for exciting Raman spectra of atoms and molecules.

Lasers are widely used in surgery, dentistry, ophthalmology, dermatology, and oncology. The biological effects of laser radiation depend on both the properties of the biological material and the properties of the laser radiation.

All lasers used in medicine are conventionally divided into 2 types: low-intensity (intensity does not exceed 10 W/cm2, most often about 0.1 W/cm2) - therapeutic and high-intensity - surgical. The intensity of the most powerful lasers can reach 10 14 W/cm 2; in medicine, lasers with an intensity of 10 2 - 10 6 W/cm 2 are usually used.

Low-intensity lasers are those that do not cause a noticeable destructive effect on tissue directly during irradiation. In the visible and ultraviolet regions of the spectrum, their effects are caused by photochemical reactions and do not differ from the effects caused by monochromatic light received from conventional, incoherent sources. In these cases, lasers are simply convenient monochromatic light sources that provide precise localization and dosage of exposure. Examples include the use of helium-neon laser light for the treatment of trophic ulcers, coronary heart disease, etc., as well as krypton and other lasers for photochemical damage to tumors in photodynamic therapy.

Qualitatively new phenomena are observed when using visible or ultraviolet radiation from high-intensity lasers. In laboratory photochemical experiments with conventional light sources, as well as in nature under the influence of sunlight, single-photon absorption usually occurs. This is stated in the second law of photochemistry, formulated by Stark and Einstein: each molecule participating in a chemical reaction under the influence of light absorbs one quantum of radiation, which causes the reaction. The single-photon nature of absorption, described by the second law, is fulfilled because at ordinary light intensities it is practically impossible for two photons to simultaneously enter a molecule in the ground state. If such an event were to take place, the expression would take the form:

2hv = E t - E k ,

which would mean the summation of the energy of two photons for the transition of a molecule from the energy state E k to a state with energy E g. There is also no absorption of photons by electronically excited molecules, since their lifetime is short, and the irradiation intensities usually used are low. Therefore, the concentration of electronically excited molecules is low, and their absorption of another photon is extremely unlikely.

However, if the light intensity is increased, two-photon absorption becomes possible. For example, irradiation of DNA solutions with high-intensity pulsed laser radiation with a wavelength of about 266 nm led to ionization of DNA molecules similar to that caused by y-radiation. Exposure to low-intensity ultraviolet radiation did not cause ionization. It was established that irradiation of aqueous solutions of nucleic acids or their bases with picosecond (pulse duration 30 ps) or nanosecond (10 ns) pulses with intensities above 10 6 W/cm 2 led to electronic transitions resulting in the ionization of molecules. With picosecond pulses (Fig. 4, a), the population of high electronic levels occurred according to the scheme (S 0 --> S1 --> S n), and with hv hv nanosecond pulses (Fig. 4, b) - according to the scheme (S 0 --> S1 -> T g -> T p). In both cases, the molecules received energy exceeding the ionization energy.

The absorption band of DNA is located in the ultraviolet region of the spectrum at< 315 нм, видимый свет нуклеиновые кислоты совсем не поглощают. Однако воздействие высокоинтенсивным лазерным излучением около 532 нм переводит ДНК в электронно-возбужденное состояние за счет суммирования энергии двух фотонов (рис. 5).

The absorption of any radiation leads to the release of a certain amount of energy in the form of heat, which is dissipated from the excited molecules into the surrounding space. Infrared radiation is absorbed mainly by water and causes mainly thermal effects. Therefore, the radiation of high-intensity infrared lasers causes a noticeable immediate thermal effect on tissue. The thermal effect of laser radiation in medicine is mainly understood as evaporation (cutting) and coagulation of biological tissues. This applies to various lasers with intensities from 1 to 10 7 W/cm 2 and with irradiation durations from milliseconds to several seconds. These include, for example, a CO 2 gas laser (with a wavelength of 10.6 μm), Nd:YAG laser (1.064 μm) and others. Nd:YAG laser is the most widely used solid-state four-level laser. Generation is carried out on transitions of neodymium ions (Nd 3+) introduced into Y 3 Al 5 0 12 yttrium aluminum garnet (YAG) crystals.

Along with heating the tissue, some of the heat is removed due to thermal conductivity and blood flow. At temperatures below 40 °C, irreversible damage is not observed. At a temperature of 60 °C, protein denaturation, tissue coagulation and necrosis begin. At 100-150 °C dehydration and charring are caused, and at temperatures above 300 °C the tissue evaporates.

When radiation comes from a high-intensity focused laser, the amount of heat generated is large, creating a temperature gradient in the tissue. At the point where the beam hits, the tissue evaporates, and charring and coagulation occurs in the adjacent areas (Fig. 6). Photoevaporation is a method of layer-by-layer removal or cutting of tissue. As a result of coagulation, the blood vessels are sealed and bleeding stops. Thus, a focused beam of a continuous CO 2 laser () with a power of about 2 * 10 3 W/cm 2 is used as a surgical scalpel for cutting biological tissues.

If you reduce the duration of exposure (10 - 10 s) and increase the intensity (above 10 6 W/cm 2), then the sizes of the charring and coagulation zones become negligible. This process is called photoablation (photoremoval) and is used to remove tissue layer by layer. Photoablation occurs at energy densities of 0.01-100 J/cm 2 .

With a further increase in intensity (10 W/cm and above), another process is possible - “optical breakdown”. This phenomenon is that due to the very high electric field strength of laser radiation (comparable to the strength of intra-atomic electric fields), matter ionizes, plasma is formed and mechanical shock waves are generated. Optical breakdown does not require the absorption of light quanta by a substance in the usual sense; it is observed in transparent media, for example in air.