Zeeman双频激光器频率分裂与纵模间隔变动一致性分析

激光谐振腔内相位各向异性会引起频率分裂,两分裂模的频差大小由表现出的相位延迟所决定.对于腔内相位延迟较小的He-Ne激光器,两分裂模很接近,处于烧孔重叠区,存在模式竞争而不能同时振荡,形成隐频率分裂.同时,使得激光器两正交偏振方向上的相邻级纵模产生固定的变动量,其大小等于隐频率分裂量的2倍.如果沿激光偏振方向施加横向磁场,Ne原子谱线发生横向Zeeman分裂,增益原子分成两群,分别为平行于磁场和垂直于磁场方向偏振的光提供增益,大大减弱模竞争,使得激光器的两分裂模可同时振荡并测得频差.在谐振腔内放入倾斜的石英晶体片或半波片,由两种方法分别测量频率分裂量并进行比较.实验表明两种方法测量的结果均与理论计算相符,平均相对偏差不超过1%.据此可以准确得到Zeeman双频激光器的频差大小,并为半波片测量提供了新方法.

Consistency of splitting frequency difference with longtudinal modes spacing variation in Zeeman dual-frequency laser

Phase anisotropy in laser resonant cavity will bring about an influence on laser frequency and polarization,such as laser frequency splitting,of which the frequency difference is determined by their introduced phase retardation.For a helium-neon laser with a small phase retardation in the cavity,the two split modes are very close to each other whose burned holes are overlapped.Then only one mode oscillates while the other is always in lock-in state due to strong mode competition,which forms hidden frequency split.Meanwhile the spacing between adjacent longitudinal modes deviates from original value and produces a certain variation equal to twice the hidden splitting frequency difference.As a result the longitudinal modes spacing variation is dominated by the phase retardation.On the other hand,by applying transverse magnetic field to a laser tube along the polarization direction,the neon atoms will undergo transverse Zeeman effect and be divided into two groups to provide the gain for polarized light beams parallel to the magnetic field and perpendicular to the magnetic field respectively.Then the laser mode competition is greatly weakened so that the two split modes can oscillate simultaneously to obtain the frequency difference.In order to make profound study of the consistency between longitudinal mode spacing variation and splitting mode frequency difference in the presence of transverse magnetic field,the samples of tilted quartz plate or half wave plate is placed into laser cavity to produce phase retardation.By the two mentioned methods,the splitting frequency difference varying with phase retardation of samples is deduced to make a comparison.Two measurements show that the average relative deviation is less than 1%,while the experimental results accord with theoretical analyses quite well.In this way splitting frequency difference of Zeeman dual-frequency laser can be determined accurately,and a new method to measure the phase retardation of half wave plate is provided.