8| IRV3 SERIES USER MANUAL
7 Visualization
7..1 Photosensitivity
The minimum detectable signal for a near-infrared viewer depends on:
• Power density
• Wavelength of incident radiation
• Effective aperture of the objective lens
• Distance between observed target and the viewer
• Time duration of the signal (pulsed or continuous)
• Reflectivity of the diffusing surface
• Sensitivity of human eye or device used in viewing the output of the IR viewer
Approximate minimum of power densities required for observing an infrared laser source from a
distance of one meter:
20 µW/cm2 for a 1060 nm; 500 µW/cm2 for a 1300 nm. The IR viewer with sensitivity 350-2000
nm has the photocathode S-1+ type which contain the increased concentration of oxygen. It
increases sensitivity of the photocathode. IR viewer can be used to view 2.0 µm laser beam at
minimum power density 2 W/cm2. When operated in the 1500-2000 nm range, IR viewer has a
low spectral response, therefore observations can be performed when the following
requirements are met:
1. Use an IR cut-off filter or interference filter and darken the room to reduce the external
background.
2. Use a metallic surface for observation of reflected radiation, as any other material
might absorb infrared radiation.
7..2 Black Spots on Screen
Black spots on the screen are cosmetic blemishes in the image converter which do not affect the
performance or reliability of infrared viewers. Some spots are inherent in the manufacturing processes.
7..3 Visualization of Beam in Mid-Air
It is a misconception that an IR viewer can be used to view infrared laser beams in “mid-air” (1100 –
2000 nm). However, if dust particles are in the beam path, the beam will become partly visible.
Basically, IR viewers can be used to see the projection of the infrared beam spot on a flat diffusing
surface such as a white card or metallic surface.
