Pulsed infrared LED radiation. Infrared rays: properties, applications, impact on humans

> Infrared waves

What infrared waves: infrared wavelength, infrared wavelength 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 task

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 generated by bodies at about room temperature. It is 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 by wavelength: far infrared (300-30 THz), middle (30-120 THz) and near (120-400 THz).
IR is also referred to as thermal radiation.
It is important to understand the concept of emissivity in order to understand IR.
IR rays can be used to remotely determine the temperature of objects (thermography).

Terms

Thermography - remote calculation of changes in body temperature.
Thermal radiation is electromagnetic radiation produced by a body due to temperature.
Emissivity is the ability of a surface to radiate.

infrared waves

Infrared (IR) light - electromagnetic rays, which in terms of wavelengths are superior to visible light (0.74-1 mm). The infrared wave band converges with the frequency range of 300-400 THz and accommodates a huge amount 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. The dividing lines differ in some places, while other categories may overlap. Microwaves occupy the high-frequency section of the radio section of the electromagnetic spectrum

Subcategories of IR Waves

The infrared part of the electromagnetic spectrum covers 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. The water in the earth's atmosphere is so strongly absorbed that it makes it opaque. But there are certain wavelengths (windows) used for transmission.
Mid-IR: 30 to 120 THz (10 to 2.5 µm). The sources are hot objects. Absorbed by vibrations of molecules (various atoms vibrate in equilibrium positions). Sometimes this range is referred to as a fingerprint because it is a specific phenomenon.
Closest IR: 120 to 400 THz (2500-750 nm). These physical processes resemble those that occur in visible light. The highest frequencies can be found with certain types 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 covers only 49% of the earth's heating, and the rest is visible light (absorbed and re-bounced 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, the concept of emissivity must be carefully considered.

IR Wave Sources

Humans and most of the planetary environment create heat rays at 10 microns. This is the boundary that separates the mid and far infrared regions. Many astronomical bodies emit a detectable amount of IR 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 use.

Thermographic image of dog and cat

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

Infrared radiation- electromagnetic radiation occupying the spectral region between the red end of visible light (with a wavelength λ = 0.74 microns and a frequency of 430 THz) and microwave radio radiation (λ ~ 1-2 mm, frequency 300 GHz).

The entire range of infrared radiation is conditionally divided into three areas:

The long-wave edge of this range is sometimes distinguished into a separate range of electromagnetic waves - terahertz radiation (submillimeter radiation).

Infrared radiation is also called “thermal radiation”, since infrared radiation from heated objects is perceived by human skin as a sensation of warmth. 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 emission 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.

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History of discovery and general characteristics

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

Previously, laboratory sources of infrared radiation were exclusively incandescent bodies or electrical discharges in gases. Now, on the basis of solid-state and molecular gas lasers, modern sources of infrared radiation with adjustable or fixed frequency have been created. To register radiation in the near infrared region (up to ~1.3 μm), special photographic plates are used. A wider sensitivity range (up to about 25 microns) is possessed by photoelectric detectors and photoresistors. Radiation in the far infrared region is recorded by bolometers - detectors sensitive to heating by infrared radiation.

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

Since infrared spectra are associated with rotational and vibrational motions in a molecule, as well as with electronic transitions in atoms and molecules, IR spectroscopy provides important information about the structure of atoms and molecules, as well as the band structure of crystals.

Infrared bands

Objects typically emit infrared radiation across the entire wavelength spectrum, but sometimes only a limited region of the spectrum is of interest because sensors typically only collect radiation within a certain bandwidth. Thus, the infrared range is often subdivided into smaller ranges.

The usual division scheme

The most common division into smaller ranges is as follows:

Abbreviation	Wavelength	Photon energy	Characteristic
Near-infrared, NIR	0.75-1.4 µm	0.9-1.7 eV	Near IR, limited on one side by visible light, on the other - by water transparency, which deteriorates significantly at 1.45 µm. Widespread infrared LEDs and lasers for fiber and airborne optical communication systems operate in this range. Video cameras and night vision devices based on image intensifier tubes are also sensitive in this range.
Short-wavelength infrared, SWIR	1.4-3 µm	0.4-0.9 eV	The absorption of electromagnetic radiation by water increases significantly at 1450 nm. The 1530-1560 nm range dominates the long-distance region.
Mid-wavelength infrared, MWIR	3-8 µm	150-400 meV	In this range, bodies heated to several hundred degrees Celsius begin to radiate. In this range, thermal heads homing of air defense systems and technical thermal imagers are sensitive.
Long-wavelength infrared, LWIR	8-15 µm	80-150 meV	In this range, bodies with temperatures around zero degrees Celsius begin to radiate. In this range, thermal imagers for night vision devices are sensitive.
Far-infrared, FIR	15 - 1000 µm	1.2-80 meV

CIE scheme

International Commission on Illumination International Commission on Illumination ) recommends the division of infrared radiation into the following three groups:

IR-A: 700 nm - 1400 nm (0.7 µm - 1.4 µm)
IR-B: 1400 nm - 3000 nm (1.4 µm - 3 µm)
IR-C: 3000 nm - 1 mm (3 µm - 1000 µm)

ISO 20473 schema

thermal radiation

Thermal radiation or radiation is the transfer of energy from one body to another in the form of electromagnetic waves radiated by bodies due to their internal energy. Thermal radiation is mainly in the infrared region of the spectrum from 0.74 microns to 1000 microns. A distinctive feature of radiant heat transfer is that it can be carried out between bodies located not only in any medium, but also in vacuum. An example of thermal radiation is light from an incandescent lamp. The thermal radiation power of an object that meets the criteria of an absolutely black body is described by the Stefan-Boltzmann law. The ratio of the radiative and absorptive abilities of bodies is described by the law radiation Kirchhoff. Thermal radiation is one of the three elementary types of thermal energy transfer (in addition to thermal conductivity and convection). Equilibrium radiation is thermal radiation that is in thermodynamic equilibrium with matter.

Application

Night-vision device

There are several ways to visualize an invisible infrared image:

Modern semiconductor video cameras are sensitive in the near infrared. To avoid color errors, ordinary household video cameras are equipped with a special filter that cuts off the IR image. Cameras for security systems, as a rule, do not have such a filter. However, at night there are no natural sources of near-IR, so without artificial illumination (for example, infrared LEDs), such cameras will not show anything.
Image intensifier tube - a vacuum photoelectronic device that amplifies light in the visible spectrum and near infrared. It has high sensitivity and is able to give an image in very low light. They are historically the first night vision devices, widely used and currently in cheap night vision devices. Since they work only in the near IR, they, like semiconductor video cameras, require lighting.
Bolometer - thermal sensor. Bolometers for technical vision systems and night vision devices are sensitive in the wavelength range of 3..14 microns (mid-IR), which corresponds to the radiation of bodies heated from 500 to -50 degrees Celsius. Thus, bolometric devices do not require external illumination, registering the radiation of the objects themselves and creating a picture of the temperature difference.

thermography

Infrared thermography, thermal image or thermal video is a scientific method for obtaining a thermogram - an image in infrared rays that shows a picture of the distribution of temperature fields. Thermographic cameras or thermal imagers detect radiation in the infrared range of the electromagnetic spectrum (approximately 900-14000 nanometers or 0.9-14 µm) and, based on this radiation, create images that allow you to determine overheated or supercooled places. Since infrared radiation is emitted by all objects that have a temperature, according to Planck's formula for black body radiation, thermography allows you to "see" the environment with or without visible light. The amount of radiation emitted by an object increases as its temperature rises, so thermography allows us to see differences in temperature. When we look through a thermal imager, warm objects are seen better than those cooled to ambient temperature; humans and warm-blooded animals are more easily visible in the environment, both during the day and at night. As a result, the promotion of the use of thermography can be attributed to the military and security services.

infrared homing

Infrared homing head - a homing head that works on the principle of capturing infrared waves emitted by a captured target. It is an optical-electronic device designed to identify a target against the surrounding background and issue a capture signal to an automatic sighting device (APU), as well as to measure and issue a signal of the angular velocity of the line of sight to the autopilot.

Infrared heater

Data transfer

The spread of infrared LEDs, lasers and photodiodes made it possible to create a wireless optical data transmission method based on them. In computer technology, it is usually used to connect computers with peripheral devices (IrDA interface). Unlike the radio channel, the infrared channel is insensitive to electromagnetic interference, and this allows it to be used in industrial conditions. The disadvantages of the infrared channel include the need for optical windows on the equipment, the correct relative orientation of devices, low transmission rates (usually does not exceed 5-10 Mbit / s, but when using infrared lasers, significantly higher rates are possible). In addition, secrecy of information transfer is not ensured. In line-of-sight conditions, an infrared channel can provide communication over distances of several kilometers, but it is most convenient for connecting computers located in the same room, where reflections from the walls of the room provide a stable and reliable connection. The most natural type of topology here is the “bus” (that is, the transmitted signal is simultaneously received by all subscribers). The infrared channel could not be widely used, it was replaced by the radio channel.

Thermal radiation is also used to receive warning signals.

Remote control

Infrared diodes and photodiodes are widely used in remote control panels, automation systems, security systems, some mobile phones (infrared port), etc. Infrared rays do not distract a person's attention due to their invisibility.

Interestingly, the infrared radiation of a household remote control is easily captured using a digital camera.

The medicine

The most widely used infrared radiation in medicine is found in various blood flow sensors (PPGs).

Widespread pulse rate (HR, HR - Heart Rate) and blood oxygen saturation (Sp02) meters use green (for pulse) and red and infrared (for SpO2) radiation LEDs.

Infrared laser radiation is used in the DLS (Digital Light Scattering) technique to determine the pulse rate and blood flow characteristics.

Infrared rays are used in physiotherapy.

Influence of long-wave infrared radiation:

Stimulation and improvement of blood circulation. When exposed to long-wave infrared radiation on the skin, skin receptors are irritated and, due to the reaction of the hypothalamus, the smooth muscles of the blood vessels relax, as a result, the vessels dilate.
Improvement of metabolic processes. The thermal effect of infrared radiation stimulates activity at the cellular level, improves the processes of neuroregulation and metabolism.

Food sterilization

With the help of infrared radiation, food products are sterilized for the purpose of disinfection.

food industry

A feature of the use of infrared radiation in the food industry is the possibility of penetration of an electromagnetic wave into such capillary-porous products as grain, cereals, flour, etc. to a depth of up to 7 mm. This value depends on the nature of the surface, structure, properties of the material and the frequency response of the radiation. An electromagnetic wave of a certain frequency range has not only a thermal, but also a biological effect on the product, it helps to accelerate biochemical transformations in biological polymers (

Infrared light is visually inaccessible to human vision. Meanwhile, long infrared waves are perceived by the human body as heat. Infrared light has some properties of visible light. Radiation of this form lends itself to focusing, is reflected and polarized. Theoretically, IR light is more interpreted as infrared radiation (IR). Space IR occupies the spectral range of electromagnetic radiation 700 nm - 1 mm. IR waves are longer than visible light and shorter than radio waves. Accordingly, IR frequencies are higher than microwave frequencies and lower than visible light frequencies. The IR frequency is limited to the range of 300 GHz - 400 THz.

Infrared waves were discovered by the British astronomer William Herschel. The discovery was registered in 1800. Using glass prisms in his experiments, the scientist in this way explored the possibility of dividing sunlight into separate components.

When William Herschel had to measure the temperature of individual flowers, he discovered a factor in the increase in temperature when successively passing through the following series:

violet,
blue,
greenery,
yolk,
orange,
red.

Wave and frequency range of IR radiation

Based on the wavelength, scientists conditionally divide infrared radiation into several spectral parts. However, there is no single definition of the boundaries of each individual part.

Scale of electromagnetic radiation: 1 - radio waves; 2 - microwaves; 3 - IR waves; 4 - visible light; 5 - ultraviolet; 6 - x-ray rays; 7 - gamma rays; B is the wavelength range; E - energy

Theoretically, three wave ranges are designated:

Near
Average
Further

The near infrared range is marked by wavelengths close to the end of the visible light spectrum. The approximate calculated wave segment is indicated here by the length: 750 - 1300 nm (0.75 - 1.3 microns). The radiation frequency is approximately 215-400 Hz. Short IR range will emit a minimum of heat.

Middle IR range (intermediate), covers wavelengths of 1300-3000 nm (1.3 - 3 microns). Frequencies are measured here in the range of 20-215 THz. The level of radiated heat is relatively low.

The far infrared range is closest to the microwave range. Alignment: 3-1000 microns. Frequency range 0.3-20 THz. This group consists of short wavelengths at the maximum frequency interval. This is where the maximum heat is emitted.

Application of infrared radiation

IR rays have been used in various fields. Among the most famous devices are thermal imagers, night vision equipment, etc. Communication and network equipment IR light is used in both wired and wireless operations.

An example of the operation of an electronic device - a thermal imager, the principle of operation of which is based on the use of infrared radiation. And this is just one example out of many others.

The remote controls are equipped with a short-range IR communication system, where the signal is transmitted through IR LEDs. Example: common household appliances - TVs, air conditioners, players. Infrared light transmits data over fiber optic cable systems.

In addition, infrared radiation is actively used by research astronomy to study space. It is thanks to infrared radiation that it is possible to detect space objects that are invisible to the human eye.

Little-Known Facts About IR Light

Human eyes really cannot see infrared rays. But the skin of the human body is capable of “seeing” them, reacting to photons, and not just to thermal radiation.

The surface of the skin actually acts as an "eyeball". If you go outside on a sunny day, close your eyes and stretch your palms up to the sky, you can easily find the location of the sun.

In winter, in a room where the air temperature is 21-22ºС, being warmly dressed (sweater, trousers). In summer, in the same room, at the same temperature, people also feel comfortable, but in lighter clothes (shorts, T-shirt).

It is easy to explain this phenomenon: despite the same air temperature, the walls and ceiling of the room in summer emit more far-IR waves carried by sunlight (FIR - Far Infrared). Therefore, the human body at the same temperature, in the summer perceived more heat.

IR heat is reproduced by any living organism and inanimate object. On the screen of the thermal imager, this moment is noted more than clearly.

Pairs of people sleeping in the same bed are involuntarily transmitters and receivers of FIR waves in relation to each other. If a person is alone in bed, he acts as a transmitter of FIR waves, but no longer receives the same waves in return.

When people talk to each other, they involuntarily send and receive FIR wave vibrations from one another. Friendly (love) hugs also activate the transmission of FIR radiation between people.

How does nature perceive infrared light?

Humans are unable to see infrared light, but snakes of the viper or viper family (such as rattlesnakes) have sensory "pits" that are used to image in infrared light.

This property allows snakes to detect warm-blooded animals in complete darkness. Snakes with two sensory pits are thought to have some infrared depth perception.

Properties of the IR snake: 1, 2 - sensitive zones of the sensory cavity; 3 - membrane cavity; 4 - internal cavity; 5 - MG fiber; 6 - outer cavity

Fish successfully use Near Infrared (NIR) light to capture prey and navigate in water areas. This sense of NIR helps the fish navigate accurately in low light conditions, in the dark or in murky water.

Infrared radiation plays an important role in shaping the Earth's weather and climate, just like sunlight. The total mass of sunlight absorbed by the Earth, in an equal amount of IR radiation, must travel from the Earth back into space. Otherwise, global warming or global cooling is inevitable.

There is an obvious reason why the air cools quickly on a dry night. The low level of humidity and the absence of clouds in the sky open up a free path for infrared radiation. Infrared rays enter outer space faster and, accordingly, carry away heat faster.

A significant part of what comes to the Earth is infrared light. Any natural organism or object has a temperature, which means it releases infrared energy. Even objects that are a priori cold (such as ice cubes) emit infrared light.

Technical potential of the infrared zone

The technical potential of IR rays is limitless. Lots of examples. Infrared tracking (homing) is used in passive missile control systems. Electromagnetic radiation from the target, received in the infrared part of the spectrum, is used in this case.

Target tracking systems: 1, 4 - combustion chamber; 2, 6 - relatively long flame exhaust; 5 - cold flow bypassing the hot chamber; 3, 7 - assigned important IR signature

Weather satellites equipped with scanning radiometers produce thermal images, which then allow analytical methods to determine cloud heights and types, calculate land and surface water temperatures, and determine ocean surface features.

Infrared radiation is the most common way to remotely control various devices. Based on FIR technology, many products are being developed and produced. The Japanese excelled here. Here are just a few examples popular in Japan and around the world:

special pads and heaters FIR;
FIR plates to keep fish and vegetables fresh for a long time;
ceramic paper and ceramics FIR;
fabric FIR gloves, jackets, car seats;
hairdresser's FIR-dryer, which reduces damage to hair;

Infrared reflectography (art conservation) is used to study paintings, helping to reveal the underlying layers without destroying the structure. This technique helps to reveal the details hidden under the artist's drawing.

In this way, it is determined whether the current painting is an original work of art or just a professionally made copy. The changes associated with the restoration work on works of art are also determined.

IR rays: impact on human health

The beneficial effects of sunlight on human health have been scientifically proven. However, excessive exposure to solar radiation is potentially dangerous. Sunlight contains ultraviolet rays, the action of which burns the skin of the human body.

Infrared saunas of mass use are widespread in Japan and China. And the trend towards the development of this method of healing is only intensifying.

Meanwhile, far infrared provides all the health benefits of natural sunlight. This completely eliminates the dangerous effects of solar radiation.

By applying IR beam reproduction technology, full temperature control (), unlimited sunlight is achieved. But these are not all known facts about the benefits of infrared radiation:

Far infrared rays strengthen the cardiovascular system, stabilize heart rate, increase cardiac output, while reducing diastolic blood pressure.
The stimulation of cardiovascular function with far infrared light is an ideal way to maintain a normal cardiovascular system. There is an experience of American astronauts during a long space flight.
Far-infrared IR rays with temperatures above 40°C weaken and eventually kill cancer cells. This fact is confirmed by the American Cancer Association and the National Cancer Institute.
Infrared saunas are often used in Japan and Korea (hyperthermia therapy or Waon therapy) for the treatment of cardiovascular diseases, especially chronic heart failure and peripheral arterial disease.
Research results published in the journal Neuropsychiatric Disease and Treatment show infrared rays as a "medical breakthrough" in the treatment of traumatic brain injury.
Infrared sauna is considered seven times more effective in removing heavy metals, cholesterol, alcohol, nicotine, ammonia, sulfuric acid and other toxins from the body.
Finally, FIR-therapy in Japan and China came out on top among the effective ways to treat asthma, bronchitis, colds, flu, sinusitis. It is noted that FIR-therapy removes inflammation, swelling, mucous blockages.

Infrared light and a lifespan of 200 years

Infrared radiation is a type of electromagnetic radiation that borders on the red part of the visible light spectrum on one side and microwaves on the other. Wavelength - from 0.74 to 1000-2000 micrometers. Infrared waves are also called "thermal". Based on the wavelength, they are classified into three groups:

shortwave (0.74-2.5 micrometers);

medium wave (longer than 2.5, shorter than 50 micrometers);

longwave (more than 50 micrometers).

Sources of infrared radiation

On our planet, infrared radiation is by no means uncommon. Almost any heat is the effect of exposure to infrared rays. It doesn't matter what it is: sunlight, the heat of our bodies, or the heat coming from heating appliances.

The infrared part of the electromagnetic radiation does not heat the space, but directly the object itself. It is on this principle that the work of infrared lamps is built. And the Sun heats the Earth in the same way.

Impact on living organisms

At the moment, science does not know the confirmed facts of the negative impact of infrared rays on the human body. Unless due to too intense radiation, the mucous membrane of the eyes can be damaged.

But we can talk about the benefits for a very long time. Back in 1996, scientists from the US, Japan and Holland confirmed a number of positive medical facts. Thermal Radiation:

destroys some types of hepatitis virus;

inhibits and slows down the growth of cancer cells;

has the ability to neutralize harmful electromagnetic fields and radiation. Including radioactive;

helps diabetics produce insulin;

can help with dystrophy;

improving the condition of the body with psoriasis.

Under the state of health improves, the internal organs begin to work more efficiently. Muscle nutrition is increased, the strength of the immune system is greatly increased. It is a well-known fact that in the absence of infrared radiation, the body ages noticeably faster.

Infrared rays are also called "rays of life". It was under their influence that life was born.

The use of infrared rays in human life

Infrared light is used no less widely than it is common. Perhaps it will be very difficult to find at least one area of the national economy where the infrared part of electromagnetic waves has not found application. We list the most famous areas of application:

warfare. The homing of missile warheads or night vision devices are all the result of the use of infrared radiation;

thermography is widely used in science to determine the overheated or supercooled parts of the object under study. Infrared images are also widely used in astronomy, along with other types of electromagnetic waves;

household heaters. Unlike convectors, such devices use radiant energy to heat all objects in the room. And already further, interior items give off heat to the surrounding air;

data transmission and remote control. Yes, all remotes for TVs, tape recorders and air conditioners use infrared rays;

disinfection in the food industry

the medicine. Treatment and prevention of many different types of diseases.

Infrared rays are a relatively small part of electromagnetic radiation. Being a natural way of heat transfer, not a single life process on our planet can do without it.

INFRARED RADIATION (IR radiation, IR rays), electromagnetic radiation with wavelengths λ from about 0.74 μm to about 1-2 mm, that is, radiation occupying the spectral region between the red end of visible radiation and shortwave (submillimeter) radio radiation. Infrared radiation refers to optical radiation, but unlike visible radiation, it is not perceived by the human eye. Interacting with the surface of bodies, it heats them up, so it is often called thermal radiation. Conventionally, the region of infrared radiation is divided into near (λ = 0.74-2.5 microns), middle (2.5-50 microns) and far (50-2000 microns). Infrared radiation was discovered by W. Herschel (1800) and independently by W. Wollaston (1802).

Infrared spectra can be line (atomic spectra), continuous (condensed matter spectra) or striped (molecular spectra). Optical properties (transmission, reflection, refraction, etc.) of substances in infrared radiation, as a rule, differ significantly from the corresponding properties in visible or ultraviolet radiation. Many substances that are transparent to visible light are opaque to infrared radiation of certain wavelengths, and vice versa. For example, a layer of water several centimeters thick is opaque to infrared radiation with λ > 1 µm, so water is often used as a heat-shielding filter. Plates of Ge and Si, opaque to visible radiation, are transparent to infrared radiation of certain wavelengths, black paper is transparent in the far infrared region (such substances are used as light filters when infrared radiation is isolated).

The reflectivity of most metals in infrared radiation is much higher than in visible radiation, and increases with increasing wavelength (see Metal Optics). Thus, the reflection of Al, Au, Ag, Cu surfaces of infrared radiation with λ = 10 μm reaches 98%. Liquid and solid non-metallic substances have selective (depending on the wavelength) reflection of infrared radiation, the position of the maxima of which depends on their chemical composition.

Passing through the earth's atmosphere, infrared radiation is attenuated due to scattering and absorption by air atoms and molecules. Nitrogen and oxygen do not absorb infrared radiation and weaken it only as a result of scattering, which is much less for infrared radiation than for visible light. Molecules H 2 O, O 2 , O 3 , etc., present in the atmosphere, selectively (selectively) absorb infrared radiation, and the infrared radiation of water vapor is especially strongly absorbed. H 2 O absorption bands are observed in the entire IR region of the spectrum, and CO 2 bands - in its middle part. In the surface layers of the atmosphere there are only a small number of "transparency windows" for infrared radiation. The presence of particles of smoke, dust, small drops of water in the atmosphere leads to an additional attenuation of infrared radiation as a result of its scattering on these particles. At small particle sizes, infrared radiation is scattered less than visible radiation, which is used in infrared photography.

Sources of infrared radiation. A powerful natural source of infrared radiation is the Sun, about 50% of its radiation lies in the infrared region. Infrared radiation accounts for 70 to 80% of the radiation energy of incandescent lamps; it is emitted by an electric arc and various gas-discharge lamps, all types of electric space heaters. In scientific research, the sources of infrared radiation are tungsten tape lamps, a Nernst pin, a globe, high-pressure mercury lamps, etc. The radiation of some types of lasers also lies in the IR region of the spectrum (for example, the wavelength of neodymium glass lasers is 1.06 μm, helium-neon lasers - 1.15 and 3.39 microns, CO 2 lasers - 10.6 microns).

Receivers of infrared radiation are based on the conversion of radiation energy into other types of energy available for measurement. In thermal receivers, the absorbed infrared radiation causes an increase in the temperature of the temperature-sensitive element, which is recorded. In photoelectric receivers, the absorption of infrared radiation leads to the appearance or change in the strength of an electric current or voltage. Photoelectric receivers (unlike thermal ones) are selective, that is, they are sensitive only to radiation from a certain region of the spectrum. Photo registration of infrared radiation is carried out with the help of special emulsions, however, they are sensitive to it only for wavelengths up to 1.2 microns.

The use of infrared radiation. IR radiation is widely used in scientific research and for solving various practical problems. The emission and absorption spectra of molecules and solids lie in the IR region, they are studied in infrared spectroscopy, in structural problems, and are also used in qualitative and quantitative spectral analysis. In the far IR region lies the radiation that occurs during transitions between the Zeeman sublevels of atoms, the IR spectra of atoms make it possible to study the structure of their electron shells. Photographs of the same object taken in the visible and infrared ranges, due to the difference in the coefficients of reflection, transmission and scattering, can vary significantly; In IR photography, you can see details that are not visible in normal photography.

In industry, infrared radiation is used for drying and heating materials and products, in everyday life - for space heating. On the basis of photocathodes sensitive to infrared radiation, electron-optical converters have been created, in which the infrared image of an object, invisible to the eye, is converted into a visible one. On the basis of such converters, various night vision devices (binoculars, sights, etc.) are built, which make it possible to detect objects in complete darkness, to observe and aim, irradiating them with infrared radiation from special sources. With the help of highly sensitive infrared receivers, objects are located by their own infrared radiation and homing systems for projectiles and missiles are created. IR locators and IR rangefinders allow you to detect in the dark objects whose temperature is higher than the ambient temperature and measure the distance to them. The powerful radiation of infrared lasers is used in scientific research, as well as for terrestrial and space communications, for laser sounding of the atmosphere, etc. Infrared radiation is used to reproduce the meter standard.

Lit .: Schreiber G. Infrared rays in electronics. M., 2003; Tarasov VV, Yakushenkov Yu. G. Infrared systems of "looking" type. M., 2004.