Basic properties of infrared radiation. Infrared rays: properties, applications, effects on humans. Infrared radiation sources

> Infrared waves

What's happened infrared waves: Infrared wavelength, infrared wave range and frequency. Study infrared spectrum patterns and sources.

Infrared light(IR) - electromagnetic rays, which in terms of wavelengths exceed the visible (0.74-1 mm).

Learning Objective

• Understand the three ranges of the IR spectrum and describe the processes of absorption and emission by molecules.

Basic moments

• IR light accommodates most of the thermal radiation produced by bodies at approximately room temperature. Emitted and absorbed if changes occur in the rotation and vibration of molecules.
• The IR part of the spectrum can be divided into three regions according to wavelength: far infrared (300-30 THz), mid-infrared (30-120 THz) and near-infrared (120-400 THz).
• IR is also called thermal radiation.
• It is important to understand the concept of emissivity to understand IR.
• IR rays can be used to remotely determine the temperature of objects (thermography).

Terms

• Thermography is the remote calculation of changes in body temperature.
• Thermal radiation is electromagnetic radiation generated by a body due to temperature.
• Emissivity is the ability of a surface to emit radiation.

Infrared waves

Infrared (IR) light is electromagnetic rays whose wavelengths exceed visible light (0.74-1 mm). The infrared wavelength range converges with the 300-400 THz frequency range and accommodates enormous amounts of thermal radiation. IR light is absorbed and emitted by molecules as they change in rotation and vibration.

Here are the main categories of electromagnetic waves. Dividing lines differ in some places, and other categories may overlap. Microwaves occupy the high-frequency portion of the radio section of the electromagnetic spectrum

Subcategories of IR waves

The IR portion of the electromagnetic spectrum occupies the range from 300 GHz (1 mm) to 400 THz (750 nm). There are three types of infrared waves:

• Far IR: 300 GHz (1 mm) to 30 THz (10 µm). The lower part can be called microwaves. These rays are absorbed due to rotation in gas-phase molecules, molecular motions in liquids and photons in solids. Water in the earth's atmosphere is absorbed so strongly that it becomes opaque. But there are certain wavelengths (windows) used for transmission.
• Mid-IR range: 30 to 120 THz (10 to 2.5 µm). The sources are hot objects. Absorbed by molecular vibrations (various atoms vibrate in equilibrium positions). This range is sometimes called a fingerprint because it is a specific phenomenon.
• Nearest IR range: 120 to 400 THz (2500-750 nm). These physical processes resemble those that occur in visible light. The highest frequencies can be found with a certain type of photographic film and sensors for infrared, photography and video.

Heat and thermal radiation

Infrared radiation is also called thermal radiation. IR light from the Sun captures just 49% of the Earth's heating, with the rest being visible light (absorbed and re-reflected at longer wavelengths).

Heat is energy in a transitional form that flows due to differences in temperature. If heat is transferred by conduction or convection, then radiation can propagate in a vacuum.

To understand IR rays, we need to take a close look at the concept of emissivity.

IR Wave Sources

Humans and most of the planetary environment produce heat rays at 10 microns. This is the boundary separating the mid- and far-IR regions. Many astronomical bodies emit detectable amounts of IR rays at non-thermal wavelengths.

IR rays can be used to calculate the temperature of objects at a distance. This process is called thermography and is most actively used in military and industrial applications.

Thermographic image of a dog and cat

IR waves are also used in heating, communications, meteorology, spectroscopy, astronomy, biology and medicine, and art analysis.

Translation by Dmitry Viktorov

Abbreviation: IR radiation
Definition: invisible radiation with wavelengths from approximately 750 nm to 1 mm.

Infrared radiation- this is radiation with a wavelength greater than 700 - 800 nm, the upper limit of the visible wavelength range. This limit does not determine how the sensitivity of the eye to visible radiation in a given spectral region decreases.

Despite the fact that the eye's sensitivity to visible radiation, for example, at 700 nm is already very weak, radiation from some laser diodes with a wavelength above 750 nm can still be seen if this radiation is sufficiently intense. Such radiation can be harmful to the eyes, even if it is not perceived as very bright. The upper limit of the infrared spectrum in terms of wavelength is also not clearly defined, but is usually understood to be approximately 1 μm.

To "see" in infrared light, night vision devices are used.

For areas of the infrared spectrum, the following classification is used:

• - near infrared region of the spectrum (also called IR-A) is ~ from 700 to 1400 nm. Lasers emitting in this wavelength range are especially dangerous to the eyes, since near-infrared radiation is transmitted and focused on the sensitive retina in the same way as visible light, but at the same time does not trigger the protective blink reflex. Appropriate eye protection is required.
• - shortwave infrared (IR-B) propagates from 1.4 to 3 µm. This range is relatively safe for the eyes, since such radiation will be absorbed by the substance of the eye before it can reach the retina. Erbium-doped fiber amplifiers for fiber optic communications operate in this range.
• - mid-wave infrared range (IR-C) from 3 to 8 µm. The atmosphere experiences strong absorption in this range. There are many absorption lines, for example for carbon dioxide (CO2) and water vapor (H2O). Many gases have strong and characteristic absorption lines of mid-IR radiation, which makes this spectral region interesting for highly sensitive gas spectroscopy.
• - long wave IR varies from 8 to 15 µm, following the far-infrared, which extends down to 1 mm, in the literature it sometimes starts as early as 8 µm. The long-wave IR region of the spectrum is used for thermal imaging.

However, it should be noted that the definitions of these terms vary significantly in the literature. Most glasses are transparent to near-infrared radiation, but strongly absorb radiation at longer wavelengths, and photons from this radiation can be directly converted into phonons. For quartz glass used in quartz fibers, strong absorption occurs after 2 µm.

Infrared radiation is also called thermal radiation, since thermal radiation from heated bodies is mostly in the infrared region. Even at room temperature and below, bodies emit significant amounts of mid- and far-infrared radiation, which can be used for thermal imaging.
For example, infrared images of a winter-heated home can reveal heat leaks (for example, in windows, the roof, or in poorly insulated walls behind radiators) and thus help take effective improvement measures.

Based on materials from the Internet portal

Infrared radiation- electromagnetic radiation, occupying the spectral region between the red end of visible light (with wavelength λ = 0.74 μm) and microwave radiation (λ ~ 1-2 mm).

The optical properties of substances in infrared radiation differ significantly from their properties in visible radiation. For example, a layer of water of several centimeters is opaque to infrared radiation with λ = 1 μm. Infrared radiation makes up most of the radiation from incandescent lamps, gas-discharge lamps, and about 50% of the radiation from the Sun; Some lasers emit infrared radiation. To register it, they use thermal and photoelectric receivers, as well as special photographic materials.

Now the entire range of infrared radiation is divided into three components:

• short-wave region: λ = 0.74-2.5 µm;
• mid-wave region: λ = 2.5-50 µm;
• long-wave region: λ = 50-2000 µm;

Recently, the long-wave edge of this range has been separated into a separate, independent range of electromagnetic waves - terahertz radiation(submillimeter radiation).

Infrared radiation is also called “thermal” radiation, since infrared radiation from heated objects is perceived by the human skin as a sensation of heat. In this case, the wavelengths emitted by the body depend on the heating temperature: the higher the temperature, the shorter the wavelength and the higher the radiation intensity. The radiation spectrum of an absolutely black body at relatively low (up to several thousand Kelvin) temperatures lies mainly in this range. Infrared radiation is emitted by excited atoms or ions.

Discovery history and general characteristics

Infrared radiation was discovered in 1800 by the English astronomer W. Herschel. While studying the Sun, Herschel was looking for a way to reduce the heating of the instrument with which the observations were made. Using thermometers to determine the effects of different parts of the visible spectrum, Herschel discovered that the “maximum of heat” lies behind the saturated red color and, possibly, “beyond visible refraction.” This study marked the beginning of the study of infrared radiation.

Previously, laboratory sources of infrared radiation were exclusively hot bodies or electrical discharges in gases. Nowadays, modern sources of infrared radiation with adjustable or fixed frequency have been created based on solid-state and molecular gas lasers. To record radiation in the near-infrared region (up to ~1.3 μm), special photographic plates are used. Photoelectric detectors and photoresistors have a wider sensitivity range (up to approximately 25 microns). Radiation in the far infrared region is recorded by bolometers - detectors that are sensitive to heating by infrared radiation.

IR equipment is widely used in both military technology (for example, for missile guidance) and civilian technology (for example, in fiber-optic communication systems). IR spectrometers use either lenses and prisms or diffraction gratings and mirrors as optical elements. To eliminate the absorption of radiation in air, spectrometers for the far-IR region are manufactured in a vacuum version.

Since infrared spectra are associated with rotational and vibrational movements in the molecule, as well as with electronic transitions in atoms and molecules, IR spectroscopy allows one to obtain important information about the structure of atoms and molecules, as well as the band structure of crystals.

Application

Medicine

Infrared rays are used in physiotherapy.

Remote control

Infrared diodes and photodiodes are widely used in remote controls, automation systems, security systems, some mobile phones (infrared port), etc. Infrared rays do not distract human attention due to their invisibility.

Interestingly, the infrared radiation from a household remote control is easily recorded using a digital camera.

When painting

Infrared emitters are used in industry for drying paint surfaces. The infrared drying method has significant advantages over the traditional convection method. First of all, this is, of course, an economic effect. The speed and energy consumed during infrared drying is less than the same indicators with traditional methods.

Food Sterilization

Infrared radiation is used to sterilize food products for disinfection.

Anti-corrosion agent

Infrared rays are used to prevent corrosion of surfaces coated with varnish.

Food industry

A special feature of the use of IR radiation in the food industry is the possibility of penetration of an electromagnetic wave into capillary-porous products such as grain, cereals, flour, etc. to a depth of up to 7 mm. This value depends on the nature of the surface, structure, material properties and frequency characteristics of the radiation. An electromagnetic wave of a certain frequency range has not only a thermal, but also a biological effect on the product, helping to accelerate biochemical transformations in biological polymers (starch, protein, lipids). Conveyor drying conveyors can be successfully used when storing grain in granaries and in the flour-grinding industry.

In addition, infrared radiation is widely used to heat indoor and outdoor spaces. Infrared heaters are used to organize additional or main heating in rooms (houses, apartments, offices, etc.), as well as for local heating of outdoor space (outdoor cafes, gazebos, verandas).

The disadvantage is the significantly greater unevenness of heating, which is completely unacceptable in a number of technological processes.

Checking money for authenticity

An infrared emitter is used in devices for checking money. Applied to the banknote as one of the security elements, special metameric inks can be seen exclusively in the infrared range. Infrared currency detectors are the most error-free devices for checking the authenticity of money. Applying infrared marks to a banknote, unlike ultraviolet ones, is expensive for counterfeiters and therefore not economically profitable. Therefore, banknote detectors with a built-in IR emitter are, today, the most reliable protection against counterfeiting.

Health Hazard

Strong infrared radiation in hot areas may cause eye hazard. It is most dangerous when the radiation is not accompanied by visible light. In such places it is necessary to wear special eye protection.

see also

Other heat transfer methods

Methods for registering (recording) IR spectra.

Notes

Links

William Herschel first noticed that behind the red edge of the prism-derived spectrum of the Sun there was invisible radiation that caused the thermometer to heat up. This radiation was later called thermal or infrared.

Near-infrared radiation is very similar to visible light and is detected by the same instruments. Mid- and far-IR uses bolometers to detect changes.

The entire planet Earth and all objects on it, even ice, shine in the mid-IR range. Due to this, the Earth is not overheated by solar heat. But not all infrared radiation passes through the atmosphere. There are only a few windows of transparency; the rest of the radiation is absorbed by carbon dioxide, water vapor, methane, ozone and other greenhouse gases that prevent the Earth from rapidly cooling.

Due to atmospheric absorption and thermal radiation from objects, mid- and far-IR telescopes are taken into space and cooled to the temperature of liquid nitrogen or even helium.

The infrared range is one of the most interesting for astronomers. It contains cosmic dust, important for the formation of stars and the evolution of galaxies. IR radiation passes through clouds of cosmic dust better than visible radiation and allows one to see objects that are inaccessible to observation in other parts of the spectrum.

Sources

A fragment of one of the so-called Hubble Deep Fields. In 1995, a space telescope collected light coming from one part of the sky for 10 days. This made it possible to see extremely faint galaxies up to 13 billion light years away (less than one billion years from the Big Bang). Visible light from such distant objects undergoes a significant red shift and becomes infrared.

The observations were carried out in a region far from the galactic plane, where relatively few stars are visible. Therefore, most of the registered objects are galaxies at different stages of evolution.

The giant spiral galaxy, also designated M104, is located in a cluster of galaxies in the constellation Virgo and is visible to us almost edge-on. It has a huge central bulge (a spherical thickening in the center of the galaxy) and contains about 800 billion stars - 2-3 times more than the Milky Way.

At the center of the galaxy is a supermassive black hole with a mass of about a billion solar masses. This is determined by the speed of movement of stars near the center of the galaxy. In the infrared, a ring of gas and dust is clearly visible in the galaxy, in which stars are actively being born.

Receivers

Main mirror diameter 85 cm made of beryllium and cooled to a temperature of 5.5 TO to reduce the mirror's own infrared radiation.

The telescope was launched in August 2003 under the program NASA's four great observatories, including:

• Compton Gamma-ray Observatory (1991–2000, 20 keV-30 GeV), see Sky at 100 MeV gamma rays,
• Chandra X-ray Observatory (1999, 100 eV-10 keV),
• Hubble Space Telescope (1990, 100–2100 nm),
• Spitzer infrared telescope (2003, 3–180 µm).

The Spitzer telescope is expected to have a lifespan of about 5 years. The telescope received its name in honor of astrophysicist Lyman Spitzer (1914–97), who in 1946, long before the launch of the first satellite, published the article “Advantages for Astronomy of an Extraterrestrial Observatory,” and 30 years later convinced NASA and the American Congress to begin developing a space telescope. Hubble."

Sky Reviews

Near-infrared sky 1–4 µm and in the mid-infrared range 25 µm(COBE/DIRBE)

In the near-infrared range, the Galaxy is visible even more clearly than in the visible.

But in the mid-IR range the Galaxy is barely visible. Observations are greatly hampered by dust in the solar system. It is located along the ecliptic plane, which is inclined to the galactic plane at an angle of about 50 degrees.

Both surveys were obtained by the DIRBE (Diffuse Infrared Background Experiment) instrument on board the COBE (Cosmic Background Explorer) satellite. This experiment, begun in 1989, produced complete maps of infrared sky brightness ranging from 1.25 to 240 µm.

Terrestrial Application

The device is based on an electron-optical converter (EOC), which allows one to significantly (from 100 to 50 thousand times) amplify weak visible or infrared light.

The lens creates an image on the photocathode, from which, as in the case of a PMT, electrons are knocked out. Then they are accelerated by high voltage (10–20 kV), are focused by electron optics (an electromagnetic field of a specially selected configuration) and fall onto a fluorescent screen similar to a television. On it, the image is viewed through eyepieces.

Acceleration of photoelectrons makes it possible in low light conditions to use literally every quantum of light to obtain an image, but in complete darkness a backlight is required. In order not to reveal the presence of an observer, they use a near-infrared illuminator (760–3000 nm).

There are also devices that detect objects’ own thermal radiation in the mid-IR range (8–14 µm). Such devices are called thermal imagers; they allow you to notice a person, animal or heated engine due to their thermal contrast with the surrounding background.

All the energy consumed by an electric heater ultimately turns into heat. A significant part of the heat is carried away by air, which comes into contact with the hot surface, expands and rises, so that mainly the ceiling is heated.

To avoid this, heaters are equipped with fans that direct warm air, for example, to a person’s feet and help mix the air in the room. But there is another way to transfer heat to surrounding objects: infrared radiation from a heater. The hotter the surface and the larger its area, the stronger it is.

To increase the area, radiators are made flat. However, the surface temperature cannot be high. Other heater models use a spiral heated to several hundred degrees (red heat) and a concave metal reflector that creates a directed stream of infrared radiation.

Infrared radiation is electromagnetic radiation that lies on the border with the red spectrum of visible light. The human eye is not able to see this spectrum, but we feel it on our skin as heat. When exposed to infrared rays, objects heat up. The shorter the wavelength of infrared radiation, the stronger the thermal effect will be.

According to the International Organization for Standardization (ISO), infrared radiation is divided into three ranges: near, mid and far. In medicine, pulsed infrared LED therapy (LEDT) uses only near-infrared wavelengths because it does not scatter from the skin surface and penetrates subcutaneous structures.

The spectrum of near-infrared radiation is limited from 740 to 1400 nm, but with increasing wavelength, the ability of the rays to penetrate tissue decreases due to the absorption of photons by water. “RIKTA” devices use infrared diodes with a wavelength in the range of 860-960 nm and an average power of 60 mW (+/- 30).

The radiation of infrared rays is not as deep as laser radiation, but it has a wider range of effects. Phototherapy has been shown to accelerate wound healing, reduce inflammation and relieve pain by affecting subcutaneous tissue and promoting cell proliferation and adhesion in tissue.

LEDT intensively promotes heating of the tissue of surface structures, improves microcirculation, stimulates cell regeneration, helps reduce the inflammatory process and restore the epithelium.

EFFECTIVENESS OF INFRARED RADIATION IN TREATING HUMANS

LEDT is used as an addition to low-intensity laser therapy with RIKTA devices and has therapeutic and preventive effects.

Exposure to infrared radiation helps accelerate metabolic processes in cells, activates regenerative mechanisms and improves blood supply. The effect of infrared radiation is complex and has the following effects on the body:

increasing the diameter of blood vessels and improving blood circulation;

activation of cellular immunity;

relieving tissue swelling and inflammation;

relief of pain syndromes;

improvement of metabolism;

relieving emotional stress;

restoration of water-salt balance;

normalization of hormonal levels.

When exposed to the skin, infrared rays irritate receptors, transmitting a signal to the brain. The central nervous system responds reflexively, stimulating overall metabolism and increasing overall immunity.

The hormonal response promotes the expansion of the lumen of microcirculatory growth vessels, improving blood flow. This leads to normalization of blood pressure and better transport of oxygen to organs and tissues.

SAFETY

Despite the benefits of pulsed infrared LED therapy, exposure to infrared radiation must be dosed. Uncontrolled irradiation can lead to burns, redness of the skin, and overheating of tissues.

The number and duration of procedures, frequency and area of ​​infrared radiation, as well as other treatment features should be prescribed by a specialist.

APPLICATION OF INFRARED RADIATION

LEDT therapy has shown high effectiveness in the treatment of various diseases: pneumonia, influenza, sore throat, bronchial asthma, vasculitis, bedsores, varicose veins, heart disease, frostbite and burns, some forms of dermatitis, diseases of the peripheral nervous system and malignant skin tumors.

Infrared radiation, along with electromagnetic and laser radiation, has a restorative effect and helps in the treatment and prevention of many diseases. The Rikta device combines multi-component radiation and allows you to achieve maximum effect in a short time. You can buy an infrared radiation device at.