Collinear acousto-optic diffraction using two nearby sound frequencies

Collinear acousto-optic spectrometers with sound consisting of one frequency have a spectral transfer function with many good characteristics, such as a narrow bandwidth, ... the side lobes, however, are rather high. To reduce these side lobes, one can try to apodize the sound in the acousto-optic cell by using a sound wave consisting out of two frequencies. At certain times, this produces a more smoothened sound field in the cell than in the one-frequency case. The resulting transfer function will contain lower side lobes. Also, the influence of all the sound field parameters--the amplitude, frequency difference, and time--on the transmission function is studied. Out of these results, better-performing collinear spectrometers can be designed.     

New system of Kravchenko orthogonal wavelets $$ \{ \widetilde{up(t)}\} $$

Doklady Mathematics -     

Automatized System for Measuring the Surface Density of Current Carriers and Electrical Permittivity of Conducting Materials

An automatised system for analyzing the electron topography of a conducting surface (semiconductors, metals, ferrites or conductor ceramics) is represented. The function of the system is based on the recently observed surface photo-charge effect. The investigation is express and contactless. The system allows visualisations of different formations on the surface such as defects, ion-implanted areas, etc. on a computer screen. The structure of the system is described. The results from investigations with GaP and Cu are reported.     

Contactless Spectroscopy of Deep Levels in Semiconducting Materials: Gaas

Abstract

The surface photo voltage (SPV) and photocurrent (PC) transients as a result of the excitation by the short high-intensity light pulses from semiconductor's intrinsic absorption spectral region are investigated in semi-insulating GaAs. It is shown that the mathematical convolution of SPV transients and arbitrary form double-pulse integrator (lock-in, double-boxcar) in a wide temperature range allows to receive the deep-level (DL) spectrum without the need to form electrical contacts to the crystal investigated. The use of such a procedure while scanning the crystal surface with a light spot at a temperature, corresponding to some DL maximum in the spectrum, makes possible the con tactless determination of this DL density distribution profile along the scanning direction.