ИСТИНА

One of the most important characteristics of any acousto-optical device is its dynamic range. The dynamic range is determined by maximal side lobe level of the transmission function. It is known that for a typical acousto-optical cell, the maximal side lobe level is equal –9.3 dB in case of strong interaction and –14 dB for weak interaction. It was theoretically shown that a general view of the transmission function in a cell depends on distribution of acoustic amplitude along the region of the acousto-optical interaction. In order to optimize the shape of the characteristics with the goal to suppress the side lobes, it is necessary to control the distribution of sound amplitude over the interaction length. Theoretical analysis considered during this research is based on a step-function distribution. This type of the amplitude distribution may be obtained by means of subdivision of a piezotransducer of an acousto-optical cell into separate sections. Each section is controlled by corresponding voltage with the specially chosen amplitude. It is theoretically shown that, in the case of the optimal distribution of the sound amplitude along 3 equal sections, the maximal side lobe level may be decreased to – 14.5 dB. The distribution along 6 equal parts results in –20 dB and 10 parts give the decrease up to –24 dB. The acousto-optical cell on the base on dense flint glass with division into 8 equal parts was chosen for the experimental research. The optimal distribution of sound amplitude along these sections was calculated. The distribution was also measured by means of AO methods. The experimentally measured distribution occurred qualitatively close to the optimal distribution predicted theoretically. The transmission functions were obtained experimentally when the dependence of the diffracted light intensities on the angle of optic incidence on the ultrasonic column was measured. The transmission functions of the experimental cell were evaluated in the wide range of frequencies (60–90 MHz) because the amplitude distribution depended on the acoustic frequency. The intensity of a maximal side lobe did not exceed –18 dB, i.e. sufficiently lower than – 13 dB characteristic for a typical acousto-optic cell.