IR optics are devices capable of registering, displaying or emitting infrared (IR) radiation. The means by which such instruments gather this invisible energy is typically optical, a curved glass that focuses on the target source. Optics, however, are not the only means. IR technology is primarily a development of sensor mediums and analytic display.
Infrared is electromagnetic radiation just beyond the human range of the so-called visible spectrum from violet to red. Its wavelength — the measurement from peak to peak of any wave of energy — is longer than red. Infrared waves are both reflections of ordinary light off objects, as well as emissions from objects that generate heat. It is popularly used interchangeably with the term “thermal radiation.”
The human eye is an optical device which actually can “see” infrared rays. Its sensor, however — a layer of light-sensitive cells within the eye called the retina — cannot detect the infrared rays. The invention of the camera was simply a mechanical replication of the eye. Infrared photography was enabled by its sensor, a sheet of plastic coated with light-sensitive chemicals and additionally coated with a chemical that detects and blocks the passage of infrared rays.
Modern IR optics are used in many military, industrial and scientific applications. They are also employed in many consumer gadgets. Handheld remote controllers emit pulses of infrared light focused through a small lens toward appliances such as TV’s equipped with sensors. Non-contact infrared kitchen thermometers focus the infrared radiation emitted by food and other hot household objects onto a sensor for conversion into corresponding temperature display. Externally attached filters which block infrared light are available for digital cameras.
One military use of IR optics is the “heat-seeking” missile, which detects the infrared signature of a target such as an enemy plane’s exhaust and automatically maneuvers the missile’s flight toward it. Another well-known optical product, also available for other professions, is “night-vision” goggles or binoculars. Military grade models can see infrared sources. Most commercial models, however, are not true IR devices and only employ the basic technology of amplifying visible light.
At its most basic purpose, infrared technology is the detection and analytic display of heat, which humans can crudely feel but not see. IR optics is most widely applied in thermography, the graphic display or recording of temperature differences. A camera is built with an array of infrared sensors, whose collected data is digitized and uploaded to a computer. The computer analyzes the information and reconstructs the displayed image into a graduated representation of visible colors that is easily interpreted by a human. Thermography is used to study heat dissipation in biological animals or mechanical systems, as well as to analyze the integrity and stress of structural materials.
The most complex and precise IR optics are found in astronomical telescopes. Some are on orbiting satellites directed toward earth for climate study. All are located at high altitudes, such as on mountaintops or aboard jet airliners, because water vapor in the atmosphere readily absorbs infrared radiation. Their technological sophistication is needed in part to see extremely distant and dim objects. They are also designed to isolate the hot, infrared radiation from stars and other stellar objects for analysis — that is, to eliminate all other radiation, including visual light.