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.
Highlights
Frequency conversion efficiency of laser radiation in nonlinear-optical crystals is governed by a phase matching condition [1]
There are versatile experimental techniques for registration of piezoelectric resonances in the wide frequency range of 10−3 – 1010 Hz. We have employed these techniques in an experimental setup, which we developed for measurement of piezoelectric resonances of nonlinear-optical crystals during their interaction with single-mode laser radiation
It was observed that the change in the resonance line shape measured in the experiment with uniform ambient temperature change and under non-uniform laser heating were identical. Basing on this fact we introduce a novel notion of the equivalent heating temperature of the crystal, which can characterize its non-uniform heating caused by laser radiation
Summary
Frequency conversion efficiency of laser radiation in nonlinear-optical crystals is governed by a phase matching condition [1]. One of the essential requirements for providing the phase matching condition is crystal temperature control. Until now there are no precision methods developed for crystal temperature control for high-power laser frequency conversion applications. The main reason for that is lack of a simple noncontact technique of the real-time crystal temperature determination during nonlinear-optical conversion process. During nonlinear-optical conversion process the heat exchange conditions of the crystal-air boundaries may vary. The main goal of our present research is the development of the precise method for crystal temperature control during laser heating. After conducting preliminary experiments it became evident that a theoretical model is needed for the laser heating process description This model is based on direct independent measurements of the sur-
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