New technology for investigation of photoelastic properties of nontransparent crystals

Abstract

As is well known, in absolutely transparent crystals an acousto‐optical interaction is lacking. In this connection’s greatest interest acousto‐optical investigations are presented in optical range, in which the crystal is not transparent. In order to carry out similar experiments, it is necessary to use the crystal with a small light absorption coefficient at applied wavelength. Evidently, the geometry of experiment will be different from that for transparent crystal because the few‐millimeters‐thick crystal will absorb the incident light completely. The main problem is selection of an appropriate buffer crystal for the investigated crystal that the light beam penetrated into sample by Bragg angle at required frequency. In the present work the measurements of effective photoelastic constant have been done for Si crystal, which is not transparent at wavelength 632.8 nm. The crystal of lithium niobate was used as the buffer crystal because its refractive index (n=2.28) is not far from that for Si crystal. The results of executed investigations have shown the possibility of determination of photoelastic constants in nontransparent crystals by Bragg scattering method. At that rate, the very high intensity of scattered light can be obtained in comparison with that in transparent crystals.