Equivalent temperature of nonlinear-optical crystals interacting with laser radiation

Abstract

Temperature calibrated piezoelectric resonances of internal acoustic vibration modes of a nonlinear-optical crystal during its heating by high-power laser radiation are used for noncontact measurements of both the non-uniform temperature distribution in the crystal volume and in the surrounding air. A novel notion of equivalent temperature of a crystal heated by laser radiation is introduced in laser physics. The true non-uniform crystal thermodynamic temperature at a given laser power is substituted by the measured equivalent crystal temperature, which is constant at that laser power. Using appropriate laser heating model the measured value of the equivalent crystal temperature allows one to calculate the unknown linear and nonlinear optical absorption coefficients as well as the heat transfer coefficient of the crystal with the surrounding air.

Self-Action of Second Harmonic Generation and Longitudinal Temperature Gradient in Nonlinear-Optical Crystals

“…As follows crystal equivalent temperature change due to heating by laser radiation of P power can be obtained by measuring resonance frequency shift (see Ref. [4] for details):…”

“…It is well known that in first approximation piezoelectric resonance frequencies linearly depend on temperature. Earlier we introduced application of impedance spectroscopy technique for precise temperature measurement of crystal heated by laser radiation [4]. Experimental determination of equivalent temperature of nonlinear-optical crystal in course of laser radiation frequency conversion was also demonstrated [5].…”

Piezoelectric periodically polled resonators for nonlinear-optical conversion of laser radiation

“…It was demonstrated that such important properties as ionic conductivity [11,12] and optical absorption [13][14][15] can be precisely measured using crystal piezoelectric resonances. Recently novel method based on the piezoelectric resonance spectroscopy technique was proposed for the accurate temperature determination of nonlinear-optical crystals interacting with laser radiation [14,15].…”

Crystal equivalent temperature model in process of nonlinear conversion of laser radiation

“…When we consider interaction with laser radiation the crystal is heated due to optical absorption and commonly its temperature is nonuniformly distributed in correspondence with laser intensity profile. It was proved experimentally [2,3] and theoretically [4] that for the last case nonuniform temperature distribution can be characterized using notion of crystal equivalent temperature. Crystal equivalent temperature is directly determined from measured resonance frequency shift ΔRf n (P) caused by laser irradiation of P power taking into account prt n K value of the resonance.…”

“…As refractive indices of the crystal and therefore phase velocities of waves to a considerable extent depend on crystal temperature the last one should be accurately measured and controlled for efficient radiation conversion. Recently noncontact impedance spectroscopy method has been proposed for precise temperature measurement of nonlinear-optical crystals interacting with laser radiation [2][3][4]. It is well known that all nonlinear-optical crystals are piezoelectrics.…”