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This review considers the factors which influence the exciton behavior at the semiconductor surface and, consequently, are revealed through excitonic optical spectra. The basic knowledge of excitons in semiconductors is first presented. The experimental exciton reflectance spectra of CdS and CdSe crystals are discussed followed by an analysis of the results which make use of the near-surface “dead-layer” model. In particular, the effect of the electron irradiation on the exciton reflectance lineshape and exciton photoluminescence is considered with reference to the physical factors which control optical spectra. Various mechanisms of localization of excitons in a semiconductor surface region are presented. Relevant experiments on low-temperature photoluminescence and reflectance are discussed. Finally, the effect on the exciton reflectance of the electric field of the space-charge layer is considered in detail.

The analytical and numerical investigations of trajectories of the probe beam electrons in the two dimensional wakefield, excited in plasma by a dense bunch of relativistic electrons with Gauss longitudinal and transverse distribution of density is carried out. On the basis of calculations of probe beam deviations, the diagnostic instrument is developed for parameters of experiments conducted in NSC KIPT. The diagnostic instruments consist of an electron gun forming the electron beam with energy 10 KeV, current 10 /spl mu/A and diameter 2 mm which passes through the chamber of interaction and falls on a collector of diameter 10 mm. A collector (screen) is placed in front of the first plate of a microchannel amplifier which consists of three microchannel plates (MCP) with sizes 20-30 mm. The voltage of 3 kV was applied to each plate. Total amplification of MCP amplifier is 10/sup 4/-10/sup 5/ in dependence on quantity of particles, falling on the first plate. As a result the deviations of probe beam by excited wakefield the electrons fall on the first plate of the amplifier and are registered by the anode of the amplifier, located behind the third plates. Calculated probe beam deviations and obtained amplification of MCP amplifier permit investigation of the electrical wakefields, excited by the sequence of relativistic bunches (number of particles in bunch is 2/spl middot/10/sup 9/, energy is 14 MeV) in plasma of density 10/sup 11/-10/sup 13/ cm/sup -3/. The maximal value of the fields registered by such a technique is not less 2 kV/cm.