A highly efficient hybrid fiber optic laser using a cesium atom vapor cell as an optical gain medium

A new scheme of a highly efficient hybrid laser cavity is proposed and experimentally demonstrated utilizing a hot cesium (Cs) vapor cell as an optical gain medium. The laser cavity consists of a macroscopic concave reflector (> 99% reflectivity) and a 4% Fresnel-reflecting facet of a single mode fiber (SMF). The cesium gain cell is located between these two reflectors. The SMF serves multiple roles: (1) a passive mode-matching component to approximate the pump beam diameter to that of the laser cavity mode within the cesium cell, (2) an output coupler with a low reflectivity, and (3) a low loss laser delivery with a high beam-quality. Optimizing the pump beam waist diameter and the cesium vapor cell temperature, a high slope efficiency of 86% and an optical-to-optical conversion efficiency of 71% were achieved in the pump power range of 400-600 mW. The unique multi-functional role of the SMF in the hybrid cavity is fully described, which can also be applied to other high optical gain media.