Guang Pu Xue Yu Guang Pu Fen Xi
February 2012
Based on the theoretical models of computing the photocathode optical performance, quantum yield and integral sensitivity, the photoemission characteristics of the domestic and ITT's transmission-mode extended blue GaAs photocathodes, namely the cathode optical properties and performance parameters, were respectively investigated. The compared results show that the integral sensitivity of the domestic transmission-mode extended blue photocathode has achieved 2,100 microA x lm(-1), still falling behind the ITT's integral sensitivity of 2,750 μA x m(-1). The reasons for the difference in quantum yield curves are that, on one hand, the thickness of GaAlAs window-layer and the Al mole fraction play a critical role in the short-wavelength response, especially in the extended blue region.
View Article and Find Full Text PDFGuang Pu Xue Yu Guang Pu Fen Xi
October 2011
GaN photocathode has a wide applicaion in ultraviolet detection because of the outstanding performance. GaN photocathode was activated in ultrahigh vacuum (UHV) system by Cs/O, and the reflection-mode quantum efficiency (QE) was analyzed. The QE is 30%-10% corresponding to the wavelength 240-350 nm, and the QE curve is flat.
View Article and Find Full Text PDFGuang Pu Xue Yu Guang Pu Fen Xi
August 2011
High temperature annealing and Cs/O activation are external incentives, while the property of GaN material is internal factor in the preparation of negative electron affinity GaN photocathode. The similarities and differences of the performance of the two structure photocathodes are analysed based on the difference of the structure between uniform-doping and gradient-doping negative electron affinity GaN photocathodes and the changes in photocurrents in activation and the quantum yield after successfully activated of GaN photocathodes. Experiments show that: the photocurrent growth rate is slower in activation, activation time is longer and quantum efficiency is higher after successfully activated of gradient-doping GaN photocathode than those of uniform-doping photocathode respectively.
View Article and Find Full Text PDFGuang Pu Xue Yu Guang Pu Fen Xi
August 2010
Mechanism about the change of GaAs phtotocathode's surface barrier during Cs activated process was studied. Ionized Cs and p type doping impurity(Be) form a dipole that decreases the vacuum level of GaAs. Generally, Cs activated GaAs photocathode could achieve zero electron affinity state.
View Article and Find Full Text PDFGuang Pu Xue Yu Guang Pu Fen Xi
November 2009
For a quantitative analysis of the effect of varied doping structure on the quantum efficiency of cathode, two kinds of reflective gradient doping GaAs photocathode samples were designed and grown respectively. After activation, the dynamic spectral response curves of the two samples were obtained. The spectral response curves were transformed into quantum efficiency curves.
View Article and Find Full Text PDFBy combining X-ray imaging technology and low light level imaging technology, the authors' research group designed the novel combined X-ray image intensifier. Different from the imported conventional one, it is an X-ray screen lens coupled with a brightness intensifier, and is a non-vacuum device. In this paper, the novel combined X-ray image intensifier is described in terms of its structure, imaging principle and imaging performance, and the comparisons of the structure, imaging principle and imaging performance between the novel combined one and the conventional one are given in detail.
View Article and Find Full Text PDFIn the intelligent traffic system, the automatic recognition system of the car plate is an important development field. This system must satisfy the requirement of all-day long inspection. In the course of inspection, the lack of natural light(such as at night, in rainy day.
View Article and Find Full Text PDFThis paper mainly introduces the principles of a type of circuit for measuring frequency & duty cycle of low-frequency signals, and its applications in neuron-threshold stimulator. The circuit has the advantages of simple structure and accurate measurement.
View Article and Find Full Text PDFZhongguo Yi Liao Qi Xie Za Zhi
March 2002
It is always very difficult to process the bioelectrical signals, sampling, amplifying and quantifying because of the different sources it comes from and the mechanism it depends on. This paper mainly introduces a method of measuring the peak value of bioelectrical signals, expatiates on the structure, testing result, analysis for error and measure taken for improvement of the circuit designed by this method. At last, the paper also points out that the method is wonderful, simple, easy to carry out, and can be used in many medical systems.
View Article and Find Full Text PDFSpace Med Med Eng (Beijing)
December 2002
Objective. To design a new type of circuit for measuring frequency & duty cycle of stimulated bioelectrical signal for the project of "the map of neuron-threshold in human brain and its clinical application". Method.
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