Infrared radiation is the electromagnetic radiation found between the visible spectrum redness and the shortwave radio radiation. It is not visible to the human eye, however, it is sensible warmth. IR waveband waves are between 760 nm and 10000 nm and are divided into three sub-ranges:
- the shortwave infrared radiation:
760 – 2000 nm (IR-A),
- the medium-wave infrared radiation:
2000 – 4000 nm (IR-B),
- the long-wave infrared radiation:
4000 – 10000 nm (IR-C).
Earth's atmosphere transmits infrared range of 400–700 nm which is called the atmosphere window. Infrared rays are strongly absorbed by certain constituents of the atmosphere. The spectrum of the infrared as well as ultraviolet or visible light may be linear or continuous strip. Linear spectrum of excited atoms emit when crossing between close electron levels. For example, mercury atoms are sending a number of lines lying in the near infrared ( λ = 1,01-2,32μm ) and serve to calibrate the instrument mass spectrometry. Airlines hydrogen Paschen series, Brackett and Pfund are also in the infrared range.
- Natural – the source of all materials heated, like human body or sun.
- Incandescent lamps with high power, i.e. 250-1000 W tungsten thread. Bubble lamps in addition to a special shape are coated with a special reflective layer which allows to focus the radiation in a narrow solid angle (beam direction). The thread temperature is ca 2200oK and the maximum radiation is: λ = 1.2 μm. To obtain shortwave infrared radiation of 760 - 2000 nm (IR-A), lamp with the tungsten ribbon can be used.
To obtain the medium-wave infrared radiation of 2000 - 4000 nm (IR-B), the Nernst burner can be used in the sphere of λ=25-100 μm – using the web-coated platinum oxides of rare earths metals ( thorium, zirconium, cerium etc.) incandescent by current. And the long-wave infrared radiation 4000 - 10000 nm (IR-C) are obtained through a quartz high-pressure mercury lamp.
3. Secondary, for example, pre-warmed earth is also a source of infrared light.
Application of the infrared is large. It has huge application in all kinds of military equipments such as short and medium range missile homing systems. Any device that is in motion is the emitter of such waves. Infrared enables seeing in the darkness using the night vision devices. In the sphere of IT and telecommunications using the IR receivers and transmitters enables the data transfers without the necessity of cable connection.
IR thermometers enable to measure the temperature without the direct contact with the object.
In the forensics technique the infrared waves find the false documents and works of art.
Infrared radiation is used at taking the astronomic pictures as the infrared gets smaller impairment than the visible spectrum during the transition through the layer of clouds and mist, which makes possible to photograph the objects that are far away. Infrared detectors are used in order to find infrared radiation. Searching the infrared radiation spectrum is used to determine the particle structure and in the chemical analyze. Besides, infrared radiation is also used in therapeutic (short-wave diathermy), biology (infrared microscopy), therm location, drying, heating, and to the air photography. The therm vision camera operation is based on infrared radiation, too.