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Image Intensifiers(I.I.)
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Image Intensifiers
OVERVIEW
Image intensifiers (often abbreviated as I. I.) were primarily developed for nighttime viewing and surveillance under moonlight or starlight. Image intensifiers are capable of detecting and amplifying low-light-level images (weak emissions or reflected light) for bringing them into view as sharp contrast images. Image intensifier applications have spread from nighttime viewing to various fields including industrial product inspection and scientific research, especially when used with CCD cameras (intensified CCD or ICCD). Gate operation models are also useful for observation and motion analysis of high-speed phenomena (high-speed moving objects, fluorescence lifetime, bioluminescence and chemiluminescence images). Some major image intensifier applications are introduced here.
FEATURES
Wide Variations
A wide variety of characteristics is presented including spectral response by choosing a photocathode and window material combination, photocathode size, the number of MCPs (gain) and gate time. You are sure to find the device that best matches your application from our complete lineup of standard or custom products.
High Resolution
Clear, sharp images can be obtained with no chicken wire.
Compact and Lightweight
Proximity-focused configuration is more compact and lightweight than inverter type.
No Distortion
Images without distortion can be obtained even at periphery.
High-speed Gate Operation
High-speed gated image intensifiers are available for imaging and motion analysis of high-speed phenomena.
High Sensitivity GaAsP Photocathode
Excellent image intensification with an even higher signal-to-noise ratio is achieved by combining our filmless MCP fabrication technology with the high-sensitivity GaAsP photocathode that delivers a typical quantum efficiency of 50 % at 530 nm (see lower left graph).
APPLICATIONS
STRUCTURE
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.
OPERATING PRINCIPLE
Figure 2 shows how light focused on the photocathode is converted into photoelectrons. The number of photoelectrons emitted at this point is proportional to the input light intensity. These electrons are then accelerated by a voltage applied between the photocathode and the MCP input surface (MCP-in) and enter individual channels of the MCP. Since each channel of the MCP serves as an independent electron multiplier, the input electrons impinging on the channel wall produce secondary electrons. This process is repeated hundreds of times by the potential gradient across the both ends of the MCP and a large number of electrons are in this way released from the output end of the MCP. The electrons multiplied by the MCP are further accelerated by the voltage between the MCP output surface (MCP-out) and the phosphor screen, and strike the photocathode which emits light according to the amount of electrons. Through this process, an input optical image is intensified about 10 000 times (in the case of a one-stage MCP) and appears as the output image on the phosphor screen.
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