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阐述了具有双下能级四能级结构的激光介质产生双波长激光的原理,介绍了二镜腔内两个波长同时振荡所要满足的阈值公式,数值计算发现空间烧孔效应的存在使阈值条件从一条曲线拓宽为一个区域,使两个波长更容易同时起振.然后,计算了激光晶体长度和泵浦功率对双波长阈值条件的影响,结果发现在增益饱和前晶体越长,泵浦功率越高,越容易出现双波长激光.最后,计算了几种常用掺钕激光晶体的双波长阈值曲线,对比发现Nd∶YAP晶体由于具有两个相近的发射截面而更适合于产生双波长激光.“,”The principle of producing dual-wavelength laser was presented in laser crystals of four energy level system with double lower level.The threshold formulas of dual-wavelength simultaneous oscillation in two-mirror cavity were introduced.It was found by calculation that the existence of space holeburning effect made the threshold condition widened to a region from a curve,which was helpful for dual-wavelength oscillation.Moreover,the effect of the crystal length and pump power on the dualwavelength threshold were calculated,results show that,before the gain saturation happens,the longer the crystal length is and the higher the pump power is,the more easily the dual-wavelength laser will appear.Finally,the dual-wavelength threshold curves of several common Nd-doped laser crystals were calculated,which showed by comparison that Nd∶YAP crystal is more suitable for producing dualwavelength laser due to its two similar emission cross sections.