针对常温工作条件下利用磷酸氧钛钾（KTP）晶体对钇铝石榴石（NdYAG）晶体1319 nm激光三倍频产生440 nm蓝色激光的实验，对三倍频KTP晶体的相位匹配角进行了理论计算和实验研究。通过多组色散方程得到KTP晶体的相位匹配角，并计算出相应的有效非线性系数。选取一组结果（θ=84.6°，φ=0°）对KTP晶体切割，利用一台1319 nm激光器，将晶体放入腔中，采用旋转晶体偏角和调节温度的方法寻找出三倍频KTP晶体最佳匹配角度（θ=85.04°，φ=0°）。该晶体经过重新切割，440 nm蓝色激光输出的光束强度有了明显的提高，最佳工作温度为18 ℃。

For the aim of third harmonic generation (THG) experiment of NdYAG 1319 nm laser to produce 440 nm blue laser using KTP crystal at room temperature, theoretical calculation and experimental study have been carried out for the THG phase-matching angle of KTP crystal. Using several sellmeier equations, phase-matching angles are derived, and corresponding effective nonlinear coefficients are calculated. One result (θ=84.6°, φ=0°) of the angles is chosen to cut KTP crystal, and then by using a laser of 1319 nm, crystals are carried into the cavity, methods of rotating the crystal and adjusting the temperature to find out optimum phase matching angle of the KTP crystal for THG (θ=85.04°, φ=0°) are applied. After re-cutting KTP crystal, the beam intensity of outputting 440 nm blue laser has a significant improvement and the optimum operating temperature is 18 ℃.