RUI: Space Charge Effects in Laser Photoelectron Devices

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The goals of this project are to understand the effects of space charge on the resolution of photoelectron microscopes operating at high current densities, to improve their resolution, and to exploit the space charge nonlinearity for pulse measurements and other applications. The photoelectron microscope is an instrument in which light induces electron emission from a sample and the electrons are focussed to form a highly magnified image of the sample surface. Its uses are in crystal growth, biology, catalysis, and microelectronics. Earlier theoretical and experimental studies of space charge limited resolution are in poor agreement. Illuminators now used are almost entirely incoherent sources rather than lasers because of performance difficulties encountered with the latter. In this project a spherical-potential electron optical system will be used with various types of laser illumination to evaluate resolution as a function of emission current density. The theory of space charge aberrations will be extended to this case and compared with experimental results. Space charge effects provide an adjustable, very fast nonlinearity which may be used for pulse duration measurements and other signal processing applications.