Alexandrite laser on-peak pumped by a frequency doubled Raman Yb-fiber laser at 589 nm

Abstract

An Alexandrite laser on-peak pumped by a frequency doubled Raman Yb-fiber laser at 589 nm, which matches well with the absorption peak of Alexandrite crystal along b-axis, is demonstrated for the first time. With a pump power of 7.7 W, a maximum average output power of 2.51 W at 755 nm was achieved, with a beam quality factor better than 1.25. The slope efficiency was 41%, which is not the highest but moderate due to the experimentally confirmed high roundtrip loss of 2.3% resulting from the imperfect crystal coating quality and crystal quality. In addition, wide wavelength tuning from 727.2 nm to 787.3 nm was demonstrated by employing a 1 mm thick single plate birefringent filter (BRF). With the help of a 6 mm thick BRF, dual-wavelength operation was achieved at 755.2 nm and 764.2 nm, with a maximum average output power of 1.8 W. It is believed that much higher power Alexandrite laser with high beam quality and high efficiency could be expected considering the fact that 100-W level 589 nm laser is available now.