Enhanced gain and narrow linewidth of an optical cavity by the Doppler effect in a four-level atomic system

Abstract

A scheme for high gain and narrow linewidth of an optical cavity with a four-level atomic system is proposed by the Doppler effect via active Raman gain (ARG) process. Atomic motion leads to Doppler frequency shift which induces constructive interference for the linear susceptibility. The enhanced normal dispersion greatly narrows the cavity linewidth, and the amplified gain gives rise to a high cavity transmission. Simulation results show that the cavity linewidth based on ARG is about one order of magnitude narrower than that based on electromagnetically-induced transparency under the same conditions, and the cavity transmission intensity could be enhanced by nearly 30 times.