Influence of Finite Lower-level Lifetime on the Performance in CW Four-level Laser

在考虑了有限的下能级寿命和激光能级与晶格场的相互作用的基础上，对四能级激光的速率方程组进行了求解。结果表明由于这个有限寿命的存在，激光阈值升高，输出与输入之间出现了非线性。与下能级瞬时跃迁的理想情况不同，泵浦功率增大时，四能级激光器的输出趋向于一个极限值，并且，下能级寿命越长，激光器所能获得的最大输出越小。

Influence of Finite Lower level Lifetime on the Performance in CW Four level Laser

The rate equations for a continuous four level laser are solved in this letter,taking into account the finite lower level lifetime and the crystal field splitting of the laser levels.It is shown that the existence of this finite lower level lifetime raises the threshold,nonlinearizes the in and out relationship and acts as an ultimate role in limiting the achievable output power for a four level laser,instead of the ideal case of infinite achievable power while the relaxation from the lower level is regarded as instantaneous. Key Workds:Lower lewel lifetime,Crystal field splitting,Boltzmann occupation factor$$$$ The Study of High Reflecting Coatings for GaAs Semiconductor Laser Cavity Surface$$$$ Yang Xiaoyan (Changchun Institute of Optics and Fine Mechanics,Changchun 130022) Liu Jie (Changchun Institute of Optics and Fine Mechanics, Chinese Academy of Sciences ,Changchun 130022) Abstract Through the technology process of evaporating SiO Au high reflecting coatings on GaAs laser back cavity surface,we analysed the coating characteristics.The reflectivity have been increased from 32%,in the case of no coatings,to above 94%.By this,the device cavity surfaces have been protected.The laser output power and working lifetime have been enhanced.