Electrophysics Night Vision
Glossary
How Night Vision Works
Glossary of Night Vision Terms
Atmospheric Transmission | Electromagnetic Spectrum | Generations of Image Intensifiers | Image Intensifier Tube | Infrared | Microbolometer
Atmospheric Transmission
Absorption of the infrared energy by the atmosphere. High transmission ranges are known as “atmospheric windows” through which infrared imaging over very long distances can be performed.
 
Electromagnetic Spectrum

The electromagnetic spectrum divides up the regions of electromagnetic radiation into different ranges having unique characteristics. This radiation is divided up rather arbitrarily into a number of regions based on wavelength: Gamma <10 nanometers, Ultraviolet radiation, Visible light 0.4 to 0.7 micrometers, Infrared Radiation, Microwaves, Radio waves. The following is a sub-categorization for the infrared range relevant for night vision:

Short wave infrared range (SWIR): Also known as the Near infrared range, that portion of the infrared spectrum from 750nm to 2500nm.
Mid wave infrared range (MWIR): That portion of the infrared spectrum from about 3 microns to 5 microns.
Long wave infrared range (LWIR): That portion of the infrared spectrum from about 8 microns to 12 microns.
 
Generations of Image Intensifiers
The different paradigms of image intensifier technology have been identified by “generations” of technology (also known as “Gen”). Generation 0 technology first developed in the 1950s depended on near infrared illumination to produce reasonable night vision images. After the light was converted to electrons, these electrons were accelerated so they hit a phosphor screen with greater energy, creating a visible image. Unfortunately, the accelerated electrons were somewhat distorted and vision with this method was impaired. Generation 1 image intensifiers were then developed that used a photocathode material that was better than Gen 0 in converting light to electrons. These units were able to operate at lower light levels than the Gen 0 and, became known as "starlight scopes" since near infrared illumination was not required. When three tubes were cascaded together, the sensitivity was sufficient for most night vision applications, but distortion existed. Generation 2 image intensifiers marked the development of a microchannel plate which multiplies the number of electrons by the thousands. A single unit of a Generation 2 image intensifier produced the same sensitivity as a 3-tube cascaded Generation 1 device but in a much small package and without distortion. Generation 3 is the most sophisticated night vision technology available today. The image intensifier's photocathode is coated with sensitive gallium arsenide, which allows for a more efficient conversion of light to electrical energy at extremely low levels of light. Generation 3 provides the clearest, sharpest night vision image available.
 
Image Intensifier Tube
An electro-optical device which converts photons to electrons, amplifies them, then converts them back to photons so the user can see at light levels that are normally too low.
 
Infrared
The range of electromagnetic radiation having a wavelength longer than that of visible light and shorter than that of microwave radiation. The name “infrared” translates to "below red", where red is the color of visible light of longest wavelength. Infrared radiation spans the wavelengths between approximately 750nm (0.75 microns) and 1mm (1000 microns).
 
Microbolometer
An infrared detector that absorbs the IR radiation and warms slightly; the electrical resistance across the bolometer changes as a function of temperature, which can be measured and made into a thermal image. See also our White Paper about Uncooled Microbolometers.
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Electrophysics Night Vision
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