Low-threshold diode-pumped 2.3-mu m Tm3+:YLF lasers

Abstract

We demonstrate low-threshold diode-pumped operation of a continuous-wave Tm3+:YLF laser near 2.3 mu m and provide a detailed experimental investigation of its lasing characteristics. A narrow-line, tunable Ti3+:sapphire laser was first used to measure the excitation spectrum and investigate the absorption saturation behavior of the 1.5 at.% Tm3+:YLF gain medium. A single-mode, 120-mW laser diode operating at 792 nm was then used as a pump source to demonstrate low-threshold lasing at 2.3 mu m. With a 1% output coupler, diode-pumped operation could be obtained with as low as 25 mW of incident threshold pump power. With 119 mW of pump power, as high as 10.5 mW of out-put power could be obtained at 2305 nm with a slope efficiency of 11.4%. By using a second, 250-mW laser diode, a resonator with variable output coupling was constructed to measure the threshold pump power and power slope efficiency as a function of output coupling. The minimum threshold pump power at output coupling levels approaching 0% was measured to be 4 mW. Results further showed that the slope efficiency decreased with increasing output coupling beyond 0.7%. The stimulated emission cross section at 2305 nm was further determined to be 0.68 x 10(-20) cm(2) from lasing threshold data.