A radio-frequency impedance spectroscope for studying the interaction of high-power laser radiation with nonlinear optical crystals has been developed. It has been revealed that the shape of the piezoelectric resonance line of a crystal heated with laser radiation is identical under both uniform heating in the absence of laser radiation and nonuniform heating resulting from the action of laser radiation. This allows introduction of the notion of the equivalent crystal temperature characterizing the nonuniform temperature distribution in a crystal exposed to laser radiation.

We present the results of measurements of low optical absorption and scattering coefficients in lithium triborate crystals using the method of piezoelectric resonance laser calorimetry under the action of polarised single-mode laser radiation at wavelengths of 1070 and 532 nm in the power ranges of 50 – 300 and 5 – 50 W, respectively. It is shown that when radiation propagates along the crystal axis a, these coefficients remain constant in the specified power ranges and do not depend on the direction of laser radiation polarisation. The measured optical scattering coefficients are compared with the results obtained by the method of integrating spheres.

Temperature gradient of PPLN crystal in process of SHG was measured using transparent tiny piezoelectric crystals as thermal sensors. Temperature of each sensor was determined directly by measuring induced frequency shifts of its piezoelectric resonances.