腔内倍频准三能级与四能级激光器噪声特性的比较

利用同种激光晶体Nd∶YAG和同种倍频晶体LiB₃O₅(LBO)分别构成蓝光(473 nm)与绿光(532 nm)激光器并进行了噪声特性研究。分析了腔内倍频准三能级与四能级激光器噪声的不同机理。实验发现:在输出功率为50 mW的情况下,腔内倍频准三能级激光系统的倍频光噪声为120%,比腔内倍频四能级激光器噪声大得多,后者在输出功率为60 mW的情况下,激光噪声在5%以下。针对准三能级倍频激光器的这种特点,采用耦合微分方程组模型进行了分析。结果指出,问题的根源在于准三能级激光系统中具有较大的再吸收损耗,如果能够适当控制该损耗,准三能级激光系统的倍频噪声问题便会得以改善。

Comparison of noise properties in intracavity-doubling quasi-three-level and four-level solid state lasers

Based on the different noise machanisms of the intracavity-doubling quasi-three-level and four-level lasers,the blue(473 nm) and green (532 nm)lasers are made to study their noise characteristics using the same laser crystal (Nd∶YAG) and the same doubling crystal(LiB₃O₅). The magnitude of the noise is >120% at output power of 50 mW in a intracavity-doubling quasi-three-level laser, but in a similar intracavity-doubling four-level laser,it is <5% at output power of 60 mW. It is shown that the noise in intracavity-doubling quasi-three-level laser is larger than that in four-level laser system. These properties of high-frequency noise in intracavity-doubling laser have been analysed through coupled-differential equation models and analysis results point out that these properties are caused by the reabsorption losses in quasi-three-level intracavity-doubling laser system.The noise in tracavity-doubling quasi-three-level laser will be decreased if reabsorption losses are controlled.