HOW INFRARED VIEWER WORKS
The Electrooptic’s Infrared viewer works by focusing the infrared light reflected by or emitted from a chosen
subject onto theimage tube. An electron image is generated in accordance with the incident intensity and the S-
1 spectral sensitivity of the photocathode material. The unit is powered by depressing and maintaining a pushbutton
switch conveniently located on the device. When powered, and internal high voltage 3V battery - based
power supply generates the 16-18 kV required to accelerate the electron image into the output phosphor screen.
The fluorescent green light output (550 nm) is observed.
The minimum detectable signal for a near-infrared viewer depends on:
· the power density;
· the wavelength of incident radiation (nm);
· the effective aperture of the objective lens;
· the distance between the spot and the viewer;
· the time duration of the signal (pulsed or continuous);
· the reflectivity of the diffusing surface;
· the sensitivity of the human eye or device used in viewing the output of the IR viewer.
Approximately minimum power densities required to view an infrared laser beam from a distance one meter:
· 20 μW/cm*cm for a 1,06 μm
· 500 μW/cm*cm for a 1,3 μm
The IR viewer with sensitivity 350...2000 nm has the photocathode S-1+ type that contains the increased concentration of oxygen that increases ensitivity of the photocathode and shifts it sensitivity in infrared area. The IR viewer can be used to view 2.0 μm laser beam at minimum power density 2 W/cm*cm. When operated in the 1500...2000 nm range, the IR viewer has a low spectral response; therefore observations can be performed when the following requirements are met:
Use an IR cut-off filter or interference filter and darken the room to reduce the external background.
Use a metallic surface for viewing the laser infrared reflective radiation, as any paper for these purposes will absorb infrared radiation.
IR viewer in comparison with a CCD camera.
Certain models of CCD cameras can be used to observe near-infrared radiation at wavelengths up to about 1,1 μm. However, because these cameras are designed for optimum performance in the visible wavelength range, as a result, they exhibit mediocre performance in the near-infrared range, image bleeding, blooming, low sensitivity and low contrast are some of the observed characteristics.
Visualization of infrared laser beam in «mid-air».
It is a misconception that an IR viewer can be used to view infrared laser beams in «mid-air». However, as with the beam from a flashlight, if dust particles are in the beam path, the beam will become partly visible. Ordinarly, 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.
Comparative parameters of infrared viewers the Abris-M and the SM-3R.
The Abris-M viewer is based on a first generation high-grade image converter that has an electro-static focusing system, photocathode S-1 with increased concentration of oxygen and screen of type P-20 with maximum of luminescence 550 nm. The SM-3R has the similar design. But in comparison with the SM-3R viewer the Abris-M has the best resolution, infrared sensitivity and factor of intensification. The infrared sensitivity of the Abris-M 2000 is approximately bigger in two times in comparison with the SM-3R 2000. As the Abris-M has a high-grade image, it can be used with a CCD camera adapter for PC and video
registration of the image. The SM-3R is a miniature viewer that fits comfortably in the palm of the hand or on face mask for hands free operation. This viewer is more preferable when important are sizes and weight of the device.
The IR viewer is visual device but not device for measuring. All similar visual devices is characterised by sensitivity in mA/W or mcA/lm. Plot of dependence of the power density from the wavelength can be built only for the single certain conditions of viewing.