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New Measurement and Diagnostic Technologies
Published in N. H. Malik, A. A. Al-Arainy, M. I. Qureshi, Electrical Insulation in Power Systems, 2018
N. H. Malik, A. A. Al-Arainy, M. I. Qureshi
An image intensifier directly intensifies electronically, images at extremely low light levels. It is made up of a photocathode, an electron lens, micro-channel plates (MCP) and a phosphor screen. When an optical image is focused onto the photocathode (Figure 11.17), it emits electrons in accordance with the intensity of the input optical image, thereby converting the input optical image into an electronic image. The electronic image is then focused on the MCP where it is intensified, and then strikes the phosphor screen of the intensifier where an intensified optical image is reproduced. The result of this process is ~104 to 105 intensification of the original incident light. The MCP normally used acts as a secondary electron multiplier and consists of an array of millions of glass capillaries fused into the form of a disk. When an electron enters and hits the capillary wall, secondary electrons are produced from the wall. These electrons are then accelerated by an electric field and strike the opposite wall to produce additional electrons, thereby providing the overall image amplification. Besides gain, spectral response and photocathode luminous sensitivity, the other parameters that influence the performance of an image intensifier are phosphor screen material, which influences phosphor’s spectral emission and decay characteristics, image magnification, limiting resolution and distortion. For investigations of fast electrical discharge phenomena or to image weak intensity discharges, image intensifiers play an important role.
Electro-Optical and Acousto-Optical Devices
Published in Daniel Malacara-Hernández, Brian J. Thompson, Advanced Optical Instruments and Techniques, 2017
Another important imaging tube, referred to as an image intensifier, is of significant importance in the transmittal of images. In principle, it is vacuum photodiode equipped with a photocathode on the input window and a phosphor layer on the output window. Image intensifiers are devices in which the primary optical image is formed on a photocathode surface (with an S20 phosphor layer backing), and the resulting photocurrent from each of the image points is intensified by increasing the energy of the electrons, as shown in Figure 11.21. The windows are made of the fiber-optic plates, so that the plane image surface of the input can be transformed to the curve object and the image surfaces of a simple electrostatic lens. The electrons strike a luminescent screen and the intensified image is produced by cathodoluminescent. It is possible to cascade more than one such intensifier with fiber-optic coupling between them, making sure that an accelerating potential is applied between the photocathode and the screen. Such a cascade device, along with an objective lens and an eyepiece, is used in the direct-view image intensifier. In any event, it is possible to achieve a luminance gain of up to 1000 with each image intensifier. An image intensifier, such as this, can also be designed by increasing the number of electrons (as in a photomultiplier).
A four-channel ICCD framing camera with nanosecond temporal resolution and high spatial resolution
Published in Journal of Modern Optics, 2021
Yuman Fang, Minrui Zhang, Junfeng Wang, Lehui Guo, Xueling Liu, Yu Lu, Jinshou Tian
The image intensifier operates by focusing an image onto a photocathode coated on the input window. The incident light drives the photocathode to launch photoelectrons proportional to the intensity of the light. Then, these photoelectrons are accelerated by an applied electric field and enter the microchannel plate (MCP). In the MCP, the photoelectrons collide with the channel walls to release secondary electrons, which produces a multiplication effect of many orders of magnitude. After exiting the MCP, the electrons are accelerated by an electric field again, this time impacting against the phosphor screen. The phosphor emits light, producing an output image that can be viewed by the CCD [13].