Low-Threshold Diode-Pumped 2.3-$\mu$ m Tm3+:YLF Lasers

We demonstrate low-threshold diode-pumped operation of a continuous-wave Tm
³⁺
:YLF laser near 2.3 μm and provide a detailed experimental investigation of its lasing characteristics. A narrow-line, tunable Ti
³⁺
:sapphire laser was first used to measure the excitation spectrum and investigate the absorption saturation behavior of the 1.5 at.% Tm
³⁺
: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 μm. 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 output 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 × 10
^-20
cm
²
from lasing threshold data.