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介绍了几种LD泵浦Nd∶YAG双频激光器 ,均应用双折射原理实现。一类是利用自然双折射效应 ,在激光谐振腔内加入自然双折射元件 ;另一类则是对YAG晶片加压力 ,使YAG晶片本身成为应力双折射元件。由于双折射效应使激光在谐振腔内产生偏振方向互相垂直的寻常光 (o光 )和非寻常光 (e光 )两种成分。因为o光和e光在双折射元件中有着不同的折射率 ,因此一个激光谐振腔变成了具有两个物理长度的谐振腔 ,从而产生双频激光。改变自然双折射元件或对YAG晶片施加的压力 ,可调谐频差。实验中获得 10 9Hz量级的大频差 ,合成波长可到几十毫米 ,适用于绝对距离干涉测量
Several LD-pumped Nd:YAG dual-frequency lasers are introduced, both of which are implemented using the principle of birefringence. One is the use of natural birefringence effect, adding natural birefringence elements in the laser resonator; the other is the pressure on the YAG wafer, the YAG wafer itself become stress birefringence elements. Due to the birefringence effect, the laser generates two components of ordinary light (o light) and extraordinary light (e light) whose polarization directions are perpendicular to each other in the resonant cavity. Because o and e light have different refractive indices in the birefringent element, one laser cavity becomes a two-length cavity with two physical lengths, producing a dual-frequency laser. Tunable frequency difference can be tuned by changing the natural birefringence element or the pressure applied to the YAG wafer. Experiments to obtain the magnitude of 109Hz large frequency difference, the synthesis wavelength can be tens of millimeters, for absolute distance interferometry