光受激发射的稳定性

本文推导出描述三能级Laser工作过程的准经典方程组,并分析了输出振动的稳定性。在阈值以上,当T₁?T₂,q^-1时,只在1/(qT₂)>1时,输出振幅是稳定的(其中T₁,T₂,q^-1分别是分子纵向、横向及谐振腔的弛豫时间)。在稳定区域,趋向平衡的时间与T₁成正比。当分子线宽小于谐振腔宽度时,输出是不稳定的,而在1/(qT₂)减小时,平衡点由稳定变到不稳定时产生一个稳定的极限环,即输出振幅逐渐开始振动。关于稳定性的结论在气体Laser中是可以检验的。本文指出,在红宝石Laser中看到的输出不稳定,可能就是谐振腔的q很大的结果。

OUTPUT STABILITY OF LASERS

The semiclassical equations which describe the behaviours of three-level lasers were derived. The method of nonlinear mechanics was used to treat the electromagnetic oscillations coupled with the dipole moments of molecules. It is shown that when the pumping power is larger than the critical value, the amplitude of output oscillations is stable (corresponding to a stable equilibrium point in phase space), only if the homogeneous line width of molecules (1/T₂) is larger than the damping width of the resonan-tor (q). The appearance of instability of output oscillations is due to the effect of coherence. Furthermore, a stable limit cycle was shown to appear when the above mentioned equilibrium point becomes unstable as qT₂ increases. Therefore, it seems true that there is no limit cycle near the equilibrium point when it is stable. These results may account for the instability of amplitude of output oscillations observed by some authors in ruby lasers, and should be checked in detail with gas lasers.