The experimental results of a study of the equivalent temperature of quartz crystals in the presence of a controlled linear gradient of the thermodynamic temperature are presented. Under conditions of non-uniform heating, the equivalent temperature of crystals was determined by measuring the frequencies of the eigenmodes of acoustic resonances on the basis of the preliminary calibration of the resonance frequencies under uniform heating. It is shown that the equivalent temperature determined in this way characterizes the average thermodynamic temperature of the crystal. Non-uniform heating of a crystal, including the use of laser radiation, was simulated.

We have introduced an approach for low optical absorption coefficient measurement of piezoelectric materials based on the piezoelectric resonance laser calorimetry (PRLC) method. An RF oscillator circuit provides a convenient way to track the piezoelectric resonance frequency during laser irradiation. In this work, the optical absorption coefficient of lithium triborate crystal under high-power IR laser irradiation was measured using the oscillator circuit and the conventional PRLC technique.

The results of study of the influence of ionic conductivity on the optical absorption coefficient of lithium triborate crystals exposed to continuous wave high-power laser radiation at 1070 nm wavelength are presented.

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.

The bulk of the LiNa₅Mo₉O₃₀ (LNM) crystals were successfully grown in the [010] and [001] directions without internal inclusions and cracks, using the Czochralski method with a low temperature gradient. The crystal grown in the [010] direction showed a tendency to twinning. The crystal grown in the [001] direction demonstrated high structural perfection (FWHM = 13″) for the (001) plane and high optical quality Δn ≈ 2 × 10⁻⁵. The laser-induced damage threshold was measured along a, b and c axes and was 12.2, 27.0 and 27.5 J/cm², respectively. The thermo-optical coefficient dn/dT was measured for the main crystallographic axes, which was −5.75 × 10⁻⁶, −20.2 × 10⁻⁶ and 3.65 × 10⁻⁶ K⁻¹ along the a, b and c axes, respectively. The second harmonic generation (SHG) was conducted in the crystalline LNM sample. The maximum efficiency value of 3.5% at a pump power of 12 W was achieved.

The bulk LiNa5Mo9O30 (LNM) crystals were successfully grown in the [010] and [001] directions without internal inclusions and cracks by the Czochralskii method with low temperature gradient. The crystal grown in the [010] direction showed a tendency to twinning. The crystal grown in the [001] direction demonstrated high structural perfection (FWHM=13'') for the (001) plane and high optical quality Δn≈210-5. The laser induced damage threshold was measured along a, b and c axes and was 15.7, 27.0 and 27.5 J/cm2 respectively. The thermo-optical coefficient dn/dT was measured for the main crystallographic axes, which was -5.7510-6, -2.0210-5 and 3.6510-6 K-1 along the a, b and c axes, respectively. The second harmonic generation (SHG) is conducted in crystalline LNM sample. The maximum efficiency value of 3.5% at pump power of 12 W had been achieved.