Thermal Effect in KTP Crystals During High Power Laser Operation

We report the theoretical and experimental studies of the thermal effect of the KTP crystal during high power operation. From the dependence of the refractive index temperature coefficients on wavelength, the dependence of the optimum phase-matching angles on temperature is derived. In the experiment, the angle of the frequency-doubled KTP crystal is tilted to compensate for the thermal effect and to obtain ΔФ = 0.7°when the green laser output power is 30W and the KTP crystal temperature about 80°C. We obtained the highest stable output power greater than 40W with an L-shape flat-flat intracavity frequency-doubled Nd:YAG laser. The experimental results are very consistent with the theoretical analysis.