Image intensifiers

Image intensifier tubes (IITs) are vacuum tubes that amplify a low light-level image to observable levels. The incoming light is converted into photoelectrons by to photocathode of the tube. Next, highly intensified photoelectrons strike the phosphor screen (anode) and a bright image is created that human can easily see.

Image intensifier tubes are the most important component of night vision devices and typical classification of night vision devices is based on tube classification. IITs are typically divided into several generations in dependence of the method to amplify incoming light (photocathode material, tube design structure) as the basic criterion. IITs can be also classified using other criteria like type of input optics, type of output optics, phosphor screen, photocathode size, or tube performance.
   NVDs for defense applications form the most important segment of night vision market. Therefore it is not surprising that both general concept and methods for testing IITs were developed by military. These recommendations have been presented in a long series of MIL SPEC standards that regulate testing image intensifier tubes. A set of almost thirty parameters was proposed to characterize IITs. However, practically a smaller set of no more than fourteen parameters (resolution, Modulation Transfer Function (MTF), Signal To Noise Ratio (SNR), Halo, blemishes (dark spots, bright spots, Multi to Multi Noise, Multi Boundary Noise, Chicken Wire), Image Non Alignment, Gross Distortion, Shear Distortion, Non-Uniformity, Photocathode Useful Diameter, Luminance Gain, Saturation Level, Equivalent Background Illumination (EBI), tube current) is measured during typical acceptance tests of potted, ready to use IITs. Nowadays, MIL standards are at least partially accepted by both manufacturers, test laboratories and final users of NVDs all over the world.
Learn more:
  1. Chrzanowski K., Computerized Station For Semi-Automated Testing Image Intensifier Tubes, Metrology and Measurement Systems, Vol. 22, No 3, 2015
  2.  Chrzanowski K., Review of night vision metrology, Opto-Electronics Review, 22 (1), 2015 
  3. Chrzanowski  K., Review of night vision technology, Opto-Electronics Review, 21 (2), p. 153-181, 2013   

Image is often worth more than thousand of words. Therefore a visit to another section of this website that presents computer simulators developed by Inframet is recommended.  These are  computer programs that simulate an imaging system by generating on computer screen images similar to images generated by the simulated imaging system. One of such programs - Nightmet -  simulates a small part of an image intensifier tube seen using a microscope during measurement of resolution of an image intensifier tube at different light intensity levels.