Analysis of lasing in gain medium based on four-energy level atomic model

With the present interest in metamaterial, gain medium shows promise for complex system due to their amplification effect and wide potential application area. In this paper we present a model that simulates lasing in gain medium by using a model of four-energy level atomic system based on the finite-difference time-domain method.Meanwhile we propose a new pump mechanism, i.e., Gaussian Pump. It is found that results of the spectra, lasing threshold and population dynamics of the new pump mechanism are in good agreement with theoretical results. The results can also provide reference for caculating more complex metamaterial system.