Intracavity frequency-doubled high power blue laser by suppressing the photorefractive effect in $BiB_3O_6$ crystals

Abstract

This study aims to realize a diode pumped solid-state continuous wave (CW) intracavity frequency doubling blue laser with high efficiency and high power using a new nonlinear optical crystal bismuth triborate ($BiB_3O_6$, BIBO) which has large second-order nonlinear coefficients and a high transmission coefficient in the UV region. Firstly, a photoinduced birefringence change was observed in the BIBO crystals during intracavity frequency doubling of the 912 nm wavelength, H5which would cause an adverse effect on efficient intracavity frequency doubling. The birefringence change, which was measured using a Senarmont compensator, was $1.87 \times 10^{-3}$ when irradiated by a focused 488 nm Ar-ion laser beam of 300 mW with a radius of 35 um for an hour. The BIBO crystal was recovered completely from the birefringence change after being annealed at $300\degC$ for 24 hours. This finding was applied to the suppression of the optical damage during intracavity second-harmonic generation. Secondly, a diode pumped solid-state CW quasi-three-level laser of 912 nm wavelength was demonstrated using neodymium-doped gadolinium vanadate ($Nd:GdVO_4$) as a laser crystal in Z-fold cavity geometry. The internal losses were measured by the Findlay-Clay method to optimize the pump waist position. The maximum output power of 912 nm radiation was 1.28 W at the pump power of 18.7 W. The slope efficiency was 11.6% with respect to the input power. The mechanisms and parameters that affect the performance of the quasi-three-level laser were investigated. Finally, an efficient CW blue intracavity frequency doubling at the 456 nm wavelength was demonstrated using the BIBO crystal while maintaining its temperature at $150\degC$ to prevent photorefractive damage. The maximum blue laser output power of 1.24 W was achieved at the diode laser pump power of 21.0 W. The slope efficiency was 8.8 %.