HYPERSONIC STUDIES AND REFRACTIVE-INDEXES OF CSTIOASO4 AND KTIOASO4 SINGLE-CRYSTALS

The longitudinal Brillouin backscattering spectra along the [001] phon on direction have been measured as a function of temperature (24-896 d egrees C) for both CsTiOAsO4 (CTA) and KTiOAsO4 (KTA). As the temperat ure approaches the ferroelectric transition temperature T-c, the acous tic phonon frequencies of both CTA and KTA show a strong softening (wh ich reaches a minimum at T-c similar to 688 degrees C for CTA). For bo th CTA and KTA, a broad damping peak was observed and can be attribute d to the dynamic order-parameter fluctuations. This anomaly implies th at an eta(2) mu-type coupling is the dominant mechanism for the acoust ic soft modes in CTA and KTA. Here eta is the order parameter and mu i s the strain. The refractive indices (n(x),n(y),n(z)) and Cauchy's equ ations were obtained as a function of wavelength (0.4-1.7 mu m) for KT A. The phase matching angles (theta phi) of second harmonic generation for the fundamental wavelengths of 1.064 (type I) and 1.32 (types I a nd II) were also calculated.