Doppler展宽的四能级系统无反转激光的传播效应

Propagation effects on inversionless lasing in a Doppler-broadened four-level system

在考虑Doppler效应下,通过理论分析和数值模拟研究了传播效应对开放四能级系统中的无反转激光特性的影响。研究发现:探测场和驱动场同向传输对系统获得无反转激光更为有利,要想提高探测激光的增益不仅要选取合适的入口处驱动场Rabi频率值,而且选取适当的驱动场和探测场初始失谐值对于提高激光增益也极为关键;随传播距离的增大,探测场上下能级粒子数一直满足无反转,而探测场上能级和驱动场上能级间的粒子数随传播距离的增大发生了Raman反转。

Propagation effects of lasing without inversion （LWI） in a Doppler-broadened open four-level system are studied and simulated numerically. The results of numerical calculation for theoretical equations with considering propagation effect and Doppler effect in the open LWI system show that： 1） It is more advantageous to obtain LWI in the open system when the probing and driving fields are copropagating. 2） It is necessary for raising the probe gain that not only the driving field intensity at the entrance of the active medium needs be selected a proper value, but also the nominal detunings of driving and probe fields need be given suitable values. 3） With propagation length increase, population inversion cannot happen always in the upper and lower levels of the probed transition, and Raman inversion can be achieved in the upper level of the probed transition and upper level of optical transition which an intense external field drives.