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Statistical Brightness Gain of a Channeltron Image Intensifier
Abstract
A mathematical calculation of the statistical brightness gain of a postulated image intensifier is achieved. Two general cases for the signal-to-noise ratio are formulated: (1) owing to an inevitable nonadditive quantum noise, and (2) owing to the sum of a quantum noise and a postulated additive Poisson noise. The former is found to be somewhat higher than the latter. However, if either the brightness gain of the imaging system or the input photon rate increases, the signal-to-noise ratio of the latter case will asymptotically approach that of the former case. The minimum required scintillation for the two general cases is also determined and is found to be directly proportional to the brightness gain of the imaging system. The illumination of the image screen for the two cases is also calculated. Finally, it is concluded that the brightness gain does not improve the signal-to-noise ratio of the imaging system, which is due to the inevitable quantum noise. However, if the gain of the image illumination could affect the integration time and the perceptive area of the human eye, a substantial change of the signal-to-noise ratio and the required minimum scintillation would be expected.
First proximity voltage is the voltage between the cathode of Low Light Level image intensifier and the input surface of
Micro-channel plate（MCP）. There are so many factors influencing the image intensifier performance, and the first
proximity voltage is one of the most important factors that can not be ignored. Based on the theory analysis and test of
different proximity voltage on the gain、signal-to-noise ratio and equivalent background noise, this test has studied on the
important performance of Gen III image intensifier effected by the proximity voltage. By the experimental study, the
increase of first proximity voltage to a certain extent can improve gain、signal-to-noise ratio and equivalent background
noise at the same time. The main cause of this phenomenon is that the increase of proximity voltage can enlarge the
incident electron energy, and then improve the quantum efficiency of the incident electron; meantime, stray electron
produced by field emission at the action of the electric field of filmed-MCP will lead to equivalent background
deterioration. Ultimately we conclude that: 1) Signal to noise is proportional to the square of he cathode sensitivity,
increases with the first collision energy of the incident electron, especially at 200-500ev. 2)In the increasing process of
voltage from 300v to 800v, the gain of filmed-MCP increases rapidly, but lower again when Upk increases further because
of gain self-saturation; lgG and lgUpk are linear relationship, thus the curve can intuitively demonstrate the relationship
between them. 3) Stray electron produced by field emission at the action of the electric field of filmed-MCP will lead to
equivalent background deterioration, but will not exceed the requirements of technical specifications（2.5×10-7lx）.
Zusammenfassung Die Bedingungen für den Betrieb eines Rohrvervielfacher-Rasters (RVR) werden untersucht. Der Bereich linearer Verstärkung wird unter Berürcksichtigung der Wärmeentwicklung im RVR angegeben. Die Bildübertragung wird frequenzmässig analysiert und Messbedingungen zur Bestimmung der Modulations-und der Kontrastübertragungfunktion werden abgeleitet.
The theoretical performance limit of an imaging device may in many cases depend upon the quantum fluctuation noise of the signal itself. Experiments on the ability of the eye to recognize a regular pattern delineated by randomly fluctuating scintillations are described, and the data are used to calculate the resolving power of an ideal image intensifier used with an x-ray fluoroscope. It is shown that the ultimate resolving power in such a system may ideally exceed even that of ordinary screen-film radiography.
The major ideas of modern probability theory are presented without assuming a mathematical background necessary for a rigorous discussion. The first 6 chapters deal with: basic theory; dependence and independence; distribution and moment generating functions; and the normal, Poisson, and related probability laws. Chapters 7 and 8 deal with random variables and their expectations and may be included with the first 6 chapters as a part of a one quarter undergraduate course. Chapters 9 and 10 introduce limit theorems and characteristic functions. Over 160 worked examples, 120 exercises requiring proof, and 480 numerical problems with 1/2 of them answered in the back. (PsycINFO Database Record (c) 2012 APA, all rights reserved)
An absolute scale of performance is set up in terms of the performance of an ideal picture pickup device, that is, one limited only by random fluctuations in the primary photo process. Only one parameter, the quantum efficiency of the primary photo process, locates position on this scale. The characteristic equation for the performance of an ideal device has the form BC2α2 = constant where B is the luminance of the scene, and C and α are respectively the threshold contrast and angular size of a test object in the scene. This ideal type of performance is shown to be satisfied by a simple experimental television pickup arrangement. By means of the arrangement, two parameters, storage time of the eye and threshold signal-to-noise ratio are determined to be 0.2 seconds and five respectively. Published data on the performance of the eye are compared with ideal performance. In the ranges of B(10-6 to 102 footlamberts), C(2 to 100 percent) and α(2' to 100'), the performance of the eye may be matched by an ideal device having a quantum efficiency of 5 percent at low lights and 0.5 percent at high lights. This is of considerable technical importance in simplifying the analysis of problems involving comparisons of the performance of the eye and man-made devices. To the extent that independent measurements of the quantum efficiency of the eye confirm the values (0.5 percent to 5.0 percent), the performance of the eye is limited by fluctuations in the primary photo process. To the same extent, other mechanisms for describing the eye that do not take these fluctuations into account are ruled out. It is argued that the phenomenon of dark adaptation can be ascribed only in small part to the primary photo-process and must be mainly controlled by a variable gain mechanism located between the primary photo-process and the nerve fibers carrying pulses to the brain.
San Fran-cisco, 1962), p. 300ff. CHANGES OF ADDRESS Changes of address should be sent to APPLIED OPTICS SUB-SCRIPTION HANDLING
- E Parzen
- Stochastic
E. Parzen, Stochastic Processes (Holden Day, Inc., San Fran-cisco, 1962), p. 300ff. CHANGES OF ADDRESS Changes of address should be sent to APPLIED OPTICS SUB-SCRIPTION HANDLING, American Institute of Physics, 335 East 45th Street, New York, New York 10017, as far in advance as possible. Eight weeks should be allowed to effect such change.