|
Induced beam scattering at small angles in the acoustic resonator has been experimentally discovered and theoretically explained. For a single-mode, excitation scattering angle as well as the acoustic vibration frequency are proportional to the emission intensity and the area of the longitudinal section of resonator. The higher beam divergence is the higher is the initial field and acoustic vibrations intensity in the resonator. For rather high longitudinal dimensions of the acoustic resonators a theory has been summarized in case of multi-mode excitation of acoustic waves during Mandelstam-Brillouin stimulated scattering (MBSS). If it happens an angular spectrum of scattered waves must be excited which is located near angle Bregg corresponding to the lowest space frequency of acoustic vibrations. In case of considerable energy pumping into the scattering light, Bregg peak of angular distribution will be close to the half-divergence angle of pumping or priming. During the experimental studies of wave- front (WF) structure (by Hartmann method) of the emissions formed by ORU (optical resonator unit) with various magnifications and lengths of 'cold' focusing, the hartmonogrammes gave triplet crosses over the vertical which is the result of the presence of several beams with different wave fronts in the Hartmann matrix plane (HM). It may be shown indeed that for the emission lambda equals 10.6 micrometer primary energy transition into scattered light in the vertical plane may be done for very small acoustic waves reflection ratios, ro greater than 10-2. When a camera with face walls having windows for the beams path, the magnification of beams divergence was also detected, which coincides with the scattering angle calculated from the criterion of multimode excitation. The effect was not detected without the face walls. Conditions are determined under which wave-front distortions of the beams are minimal.
|
