Interaction of laser radiation with gold metal film deposited onto the lithium niobate substrate was investigated by means of piezoelectric resonance spectroscopy. Such metal-dielectric heterostructure has eigenmodes which can be excited by application of the probe radiofrequency electric field due to the piezoelectric nature of lithium niobate. Frequencies of these piezoelectric resonances are extremely sensitive to the temperature. During interaction with laser radiation the temperature of the film is determined as a solution of the nonstationary heat conduction equation relying on the experimentally measured induced shifts of piezoelectric resonance frequencies, which were preliminary calibrated in uniform heating conditions.
A novel method of optical image registration using matrix of piezoelectric crystals is introduced. This technique allows measurement of beam profiles without using attenuation systems even at high power levels of incident radi- ation. Each element of the sensor matrix is the crystal piezoelectric resonator that has its own set of eigenmodes, which frequencies strongly depend on temperature. Due to an inverse piezoelectric effect the eigenmodes can be excited noncontactly via the application of the probe radiofrequency electric field providing that its frequency corresponds to any of the crystal eigenmode frequencies. Due to the residual optical absorption each element is heated in compliance with the incident radiation power. A calibration procedure is preliminary performed by transmitting collimated laser radiation separately through each single matrix element.
Longitudinal temperature distribution at the surface of the end-pumped Nd:YAG laser crystal was measured using tiny piezoelectric crystals as the temperature sensors. Temperature of each sensor was determined directly by measuring the frequency of its piezoelectric resonance that was noncontactly excited by probe ac electric field. Crystal sensors are transparent to the scattered radiation and can have very small size.
Novel piezoelectric resonance laser calorimetry technique, based on impedance spectroscopy, is introduced for measuring low optical absorption coefficients of nonlinear-optical crystals. This method exploits dependence of crystal piezoelectric resonance frequencies on its temperature. Nonuniform temperature of the crystal heated by laser radiation is characterized by equivalent temperature that is directly determined by measuring frequency shift of certain piezoelectric resonance calibrated on temperature. Kinetics of crystal equivalent temperature during its interaction with laser radiation is obtained by measuring frequency kinetics of piezoelectric resonance. It is demonstrated that optical absorption coefficient can be determined from the linear slope of initial part of temperature kinetics. Basing on experiments with LiB3O5 and LiNbO3 crystals it was proved that values of optical absorption coefficients determined from initial part and full time kinetics of equivalent temperature have almost the same values.
Novel method is proposed for determination of nonlinear-optical crystal both heat transfer and optical absorption coefficients by measuring kinetics of the laser-irradiated crystal temperature-dependent piezoelectric resonance frequency. When laser radiation propagates through the crystal its temperature evaluation with time is directly determined from crystal piezoelectric resonance frequency shift, which is precisely measured by analyzing crystal response to the applied ac electric voltage. Heat transfer and optical absorption coefficients are obtained using measured characteristic time of crystal laser heating kinetics by solving nonstationary heat conduction equation. Experiments were performed with nonlinear-optical α-quartz, lithium triborate (LBO) and periodically poled lithium niobate (PPLN) crystals.
Novel method of piezoelectric resonance spectroscopy is introduced for nonlinear-optical crystals equivalent temperature measurement during frequency conversion of laser radiation. Equivalent temperature of the crystal heated by laser radiation is directly determined from its strongly temperature sensitive piezoelectric resonance frequencies. Method was applied for PPLN crystal temperature measurement during second harmonic generation of CW ytterbium fiber laser radiation. Temperature tuning curves of PPLN and its phase matching temperature dependence on pump power were precisely measured using concept of the equivalent temperature. Hysteresis of PPLN temperature and optical bistability of second harmonic power in respect to pump power were observed.
Nonuniform temperature distribution inside the nonlinear-optical crystal heated by the high-power laser radition is
characterised by the equivalent crystal temperature, which is directly determined from the measured frequency of the
crystal piezoelectric resonance.
A model of nonlinear-optical crystal heating is proposed that enables one to determine temperature distribution
inside the sample under action of laser radiation from the measurements of internal crystal temperature. Absorption and
heat transfer coefficient at crystal-air boundary are also determined. Crystal temperature is measured by analyzing
changes of piezoelectric resonance frequencies of the sample.
Influence of the high-power laser radiation on the piezoelectric resonance in the nonlinear-optical KTiOPO4 crystal was
observed. Equivalent crystal temperature can be directly determined from the piezoelectric resonance frequency during
interaction of the laser radiation with crystals. Frequency kinetics of the different piezoelectric resonances of the
KTiOPO4 crystal were observed for the different pump laser powers up to 20 W. The KTiOPO4 optical absorption
coefficient and the amplitude of the crystal inhomogeneous temperature distribution were obtained from the kinetics
data. A theoretical model of the piezoelectric resonances on the basis of the Rayleigh-Ritz method is proposed.
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