开放系统的无粒子数反转激光的时间演化分析

Transient analysis of laser without inversion in an open system

对开放的V型三能级系统,通过微分方程的数值运算,分析了该系统的无粒子数反转激光(laser without inversion,LWI)产生的机制,讨论了探测场和驱动场的失谐、驱动场的Rabi频率、粒子初始状态对系统LWI时间演化的影响。结果显示:驱动场耦合的两个能级上的粒子数分布以相同的频率振荡,位相差π;在探测场和驱动场皆共振(△=△_0=0)时,原子对探测场色散的响应为零,双光子相干项ρ_(ca)是实量;驱动场的Rabi频率Ω增大时,增益、相干项和粒子数差的振荡周期减小;粒子数的初始状态主要影响增益、相干项和粒子数差的振荡幅度,并不影响最后的稳定状态。

In an open V-type system, by numerical results of differential equations, the physical mechanism of laser without inversion （LWI） was analyzed, and the effects of the probe and driving fields detunings, the Rabi frequencies of the driving fields, and the initial values of the populations on LWI transient were discussed. The conclusions show that the populations of the two levels coupled by the driving field have the same oscillation frequency, however, exist a phase difference π. The dispersion equals to zero and two- photon coherent item is real number when the driving and the probe fields are both resonant. Oscillation period of the gain, coherent item and population difference reduce with the increase of the Rabi frequencies of the driving field. The initial values of the populations mainly affect the oscillation amplitudes of the gain, coherent item and population difference but don＇t affect their values in the steady state.