利用Ⅱ类相位匹配实现稳定倍频输出

Research on the Method to Stabilize Second Harmonic Generation Using Type Ⅱ Phase Matching

提出利用Ⅱ类相位匹配方法实现稳定倍频输出,并对该方法进行了理论分析和数值模拟。数值模拟是对KTP晶体xy平面内的Ⅱ类相位匹配倍频过程进行的。数值计算结果表明,Ⅱ类相位匹配倍频过程中,当基频光以除最佳入射偏振角之外的偏振方向入射时,倍频强度曲线随倍频晶体长度增加而呈周期性变化;由于这种周期性变化的存在,当基频光起伏变化时,倍频强度曲线会交叉汇聚,出现倍频稳定区;当偏离角(入射偏振角与最佳入射偏振角差值)一定时,随着基频光入射强度的增大,实现稳定倍频输出所需的倍频晶体长度减小,稳定输出时倍频效率不变;当基频光强度一定时,随着偏离角的增大,倍频输出稳定性提高,倍频效率稍有下降。

The method to stabilize the second harmonic generation （SHG） using type Ⅱ phase matching is put forward. The theoretical and numerical analysis has been done. Numerical simulation on type Ⅱphase matching SHG course in KTP shows that when the fundamental frequency （1ω） light is incident in the SHG crystal deviating the optimal polarizing angle, the second harmonic output （2ω） intensity changes periodically with the length of SHG crystal length increasing. With this kind of periodically changing, when input 1ω intensity fluctuates, the output 2ω intensity curves converge at a certain value of the SHG crystal length. At this point the fluctuation of output 2ω intensity becomes much smaller than that of the input 1ωintensity. With the deviating angle being confined to a certain vaiue, when the input 1ω intensity increases, the required nonlinear crystal length to stabilize 2ω intensity decreases and the energy conversion efficiency does not change. With the input 1ω intensity being confined to a certain value, when the deviating angle increases, the required nonlinear crystal length to stabilize 2ω intensity also decreases and the energy conversion efficiency remains high.