光声喇曼效应中光束的空间耦合与几何匹配

Light Beam Spatial Coupling and Geometry Match in Photoacoustic Raman Effect

推导出在两束高斯光束作用下相干喇曼跃迁几率的空间分布函数 ,讨论了聚焦作用以及泵浦光束和斯托克斯光束间的空间耦合、几何参数匹配对光声喇曼信号的影响。结果表明 ,光声喇曼光谱 (PARS)信号主要产生于两激光束焦面附近的相互作用区域 ;当两光束的共焦参数相等时 ,喇曼转换效率最高 ,随着两光束几何参数失匹配度的增加 ,PARS信号将减弱。另外 ,光束间的空间耦合需要精确调整以获得最佳的 PARS信号输出 ,尤其是横向偏差的影响特别敏感。

We calculate the overlap integral for two focused Gaussian beams to derive the Raman transition probability as a function of spatial location within the interaction region in the photoacoustic Raman process.The effects of laser focusing and the influences of spatial coupling and geometry match between the pump and the Stokes beams on the generation of photoacoustic Raman signal are discussed in detail,and numerical estimates using typical values of the relevant parameters are presented.The results indicate that,the photoacoustic Raman spectrum(PARS) signal is produced mainly in the interaction region in the vicinity of the beams focal plane,it reaches the peak magnitude when the two beams have equal focusing parameters,and will decrease as the degree of geometry mismatch between the pump and the Stokes beams increases.Furthermore,accurate adjustment for spatial coupling between the two beams is needed to achieve an optimal output of PARS signal,which is especially more sensitively affected by the transverse maladjustment.