When decay rate in the coupling channel is greater than that in the probe channel, the incoherent population pumping in the probe channel can create the gain without inversion.
当耦合路径上的衰变率大于探测路径上的衰变率时，探测路径上的抽运导致了非逆转增益现象的产生。
2
Using rate equation theory, the equation group including the population inversion density of the gain medium, photon density and the absorber ground state population density is acquired.