Generation of negative group velocity Lamb waves by a moving laser source.

Analytical existence conditions for negative group velocity (NGV) of an arbitrary mode Lamb waves in elastic plate was obtained. Experimentally, NGV waves were excited by means of a thermoelastic laser source moving across the sample plate with a controllable velocity. Such source is coupled with modes which phase velocity component parallel to the surface coincides with the source speed.

Specific directions of ultrasound propagation in double potassium tungstates for light modulation.

Acousto-optical characteristics of double potassium tungstates are analyzed and specific directions for light modulation are found. First, an important subgroup of elasto-optic coefficients of KYb(WO) and KLu(WO) crystals are calculated with use of experimental data. It is revealed that with proper choice of ultrasound direction the acousto-optical figure-of-merit approximately 2 times exceeds the maximum value detected in previous experiments.

Achromatic optical elements.

The principles of wavefront reconstruction by means of a geometric-optical reflection of radiation from surfaces of interference fringe maxima are discussed. The optical elements based on these principles should be achromatic. Two methods of the optical elements design are proposed.