Temperature‐Dependent Spectroscopy and Laser Performance of Yellow Tb:YLF Lasers with 36% Slope Efficiency at Room Temperature and 61% at 100 K

An efficient cryogenic and room‐temperature yellow and cryogenic red Tb3+:LiYF4 laser is presented and a detailed analysis of the relevant temperature‐dependent spectroscopic properties from room temperature to liquid helium temperature for this gain medium is provided. Cooling from room temperature to 78 K increases the peak absorption cross sections in the pump band at 486 nm in the cyan‐blue significantly and the peak emission cross sections in the yellow by a factor of five, while slightly increasing the fluorescence lifetime. An improved growth procedure of the laser crystal enables an increased room‐temperature slope efficiency of 36% at 587.4 nm. At 100 K, slope efficiencies of up to 61% are obtained and optical‐to‐optical efficiencies of 55% at a wavelength of 581.4 nm, doubling all values previously reported for yellow Tb3+:LiYF4 lasers and establishing this system as the most efficient yellow laser source to date. During these experiments, continuous‐wave laser operation at 624 nm is realized as well with a slope efficiency of 47% at 78 K. The study enhances the understanding of the processes currently limiting the room‐temperature performance of Tb3+ lasers, which facilitates improved laser performance by tailored gain materials even in the temperature range accessible to Peltier cooling.