外腔式双波长喇曼激光器的耦合波理论

Coupled wave theory of extracavity pumped dual-wavelength Raman lasers

为了对基于喇曼晶体的主要喇曼频移模和次级喇曼频移模的外腔式双波长喇曼激光器进行理论分析,采用光场的波动方程和喇曼晶体中振动波的阻尼谐振子波方程推导出了描述基频光、喇曼光1和喇曼光2的耦合波方程组,通过引入归一化参量对耦合波方程组进行了归一化,并数值分析了输出镜反射率和归一化参量对外腔式双波长喇曼激光器性能的影响。结果表明,选择对主要频移模反射率小于0.5且对次级频移模反射率大于0.5的输出镜、两个喇曼振动模的增益系数相差不大的喇曼晶体,适当提高入射基频光的脉冲宽度可以提高次级喇曼频移模的转化效率,可实现有效双波长运转。所提出的归一化耦合波理论可以作为分析外腔式双波长喇曼激光器的辅助工具。

The extracavity pumped dual-wavelength Raman laser based on the main and the secondary Raman shifts of Raman crystal was theoretically analyzed.From the wave equation of the light field and the damped harmonic oscillator wave equation for the vibrational wave in Raman crystal,a group of coupled wave equations were deduced to describe the fundamental laser,Raman laser 1 and Raman laser 2 were then derived.The coupled wave equations were normalized by introducing several normalized parameters.The effects of the normalized Raman gain coefficient,normalized fundamental pulse width and output mirror reflectivities on the performance of extracavity dual-wavelength Raman lasers were numerically analyzed.It is found that selecting the output mirror with reflectivity less than 0.5 for the main frequency shift and larger than 0.5 for the secondary frequency shift,and the Raman crystal with small difference gain coefficients of the two Raman modes,and properly increasing the pulse width of the incident fundamental frequency light can improve the conversion efficiency of the secondary Raman frequency shift and achieve effective dual wavelength operation.The theoretical derivation and numerical calculation of this paper can be used as a theoretical tool for the design and analysis of extracavity dual-wavelength Raman lasers,and can provide a reference for the experimental research of this kind of lasers.