光参量过程中的逆转换问题

Back conversion in optical parametric process

逆转换是影响光参量变换转换效率、参量光光束质量以及参量光输出稳定性的关键因素,随光斑分布和时间变化,逆转换现象很难消除.文中分析了光参量变换过程中的逆转换问题,研究了影响逆转换的关键因素.分析得出,适当的晶体长度、优化的抽运光斑截面类型、合适的谐振腔参数(对于振荡器)有利于降低逆转换,提高参量转换效率,改善参量光光束质量.根据理论分析结果,设计了脉冲砷酸钛氧钾(KTA)光参量振荡器,实验获得了270mJ信号光和150mJ闲频光输出,有效地抑制了逆转换的影响,参量转化效率达到了43%.

Back conversion is the key factor that affects the conversion efficiency,the beam quality of the parametric waves,and the stability of the output in the optical parametric process. For the reason of the variation of the back conversion with the distribution in the cross-section and with time,the back conversion cannot be eliminated thoroughly. We analyzed the problem of the back conversion in the optical parametric process,and established the models of the parametric process for the continuous waves and the pulsed waves,which help us study the key factors affecting the back conversion. According to the conclusion of our analysis,the proper length of the nonlinear crystals,the optimal distribution of the energy of the pump beam,and the proper parameters of the resonant cavity （ for optical parametric oscillators ） could reduce the back conversion and help to increase the conversion efficiency. According to the theoretical results,we designed an X-cut KTA （Potassium Titanyl Arsenate） optical parametric oscillator,and obtained the signal light with the energy of 270 mJ and the idler light with the energy of 150 mJ,which decreased the back conversion,and the efficiency reached 43% .