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   Second generation Image intensifiers
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2nd generation is primarily used by law enforcement or for professional applications. This is because the cost of a 2nd gen unit is approximately $500.00 to $1000.00 more then a 1st gen. The main difference between a 1st and a 2nd generation unit is the addition of a micro-channel plate, commonly referred to as a MCP. The MCP works as an electron amplifier and is placed directly behind the photocathode. The MCP consists of millions of short parallel glass tubes. When the electrons pass through these short tubes, thousands more electrons are released. This extra process allows 2nd generation units to amplify the light many more times then 1st generation giving you a brighter and sharper image.

Figure 1 shows the structure of a typical image intensifier. A photocathode that converts light into photoelectrons, a microchannel plate (MCP) that multiplies electrons, and a phosphor screen that reconverts electrons into light are arranged in close proximity in an evacuated ceramic case. The close proximity design from the photocathode to the phosphor screen delivers an image with no geometric distortion even at the periphery. Types of image intensifiers are often broadly classified by "generation".

The first generation refers to image intensifiers that do not use an MCP and where the gain is usually no greater than 100 times. The second generation image intensifiers use MCPs for electron multiplication. Types using a single-stage MCP have a gain of about 10000, while types using a 3-stage MCP offer a much higher gain of more than 10 million.

A variety of photocathodes materials are currently in use. Of these, photocathodes made of semiconductor crystals such as GaAs and GsAsP are called "third generation". These photocathodes offer extremely high sensitivity. Among the first and second generation image intensifiers, there are still some inverter types in which an image is internally inverted by the electron lens, but these are rarely used now because of geometric distortion.

Main modifications of the 2nd plus generation image intensifiers: glass output, with inverter, non-invertor.

 
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