Temperature dependence of the emission cross-section and fluorescence lifetime in Cr:LiCAF, Cr:LiSAF, and Cr:LiSGaF between 78 K and 618 K

Cr:Colquiriites (Cr:LiCAF, Cr:LiSAF, and Cr:LiSGaF) are well-known for their broad emission bands in the near-infrared region. Unfortunately, due to their relatively weak thermomechanical strength, average powers from Cr:Colquiriite lasers have been so far limited to sub-5 W level in continuous-wave operation at room temperature. In this study, the promise of cryogenic operation, which shows significant power scalability in Yb-based systems, is investigated in detail for Cr-doped Colquiriite crystals in terms of the temperature dependence of the fluorescence lifetime and emission cross-section (sigma e) in the 78-618 K range. The lifetime measurements showed that the fluorescence, as well as the radiative lifetimes of Cr:Colquiriites are temperature dependent. The emission cross-section measurements revealed that while cooling the crystals from 300 K to 78 K, the peak sigma e in E| |c polarization increases moderately for all crystals: from around 1.3 x 10-20 cm2 to 1.6 x 10-20 cm2 in Cr:LiCAF, from around 4.5 x 10-20 cm2 to 6.3 x 10-20 cm2 in Cr:LiSAF and from around 3.1 x 10-20 cm2 to 3.95 x 10-20 cm2 in Cr:LiSGaF. We provide analytical formulas describing the measured temperature dependence of all relevant quantities such as fluorescence/radiative lifetime, peak emission wavelength, peak emission cross-section, and emission full-width at half-maximum. Overall, the reported results constitute a solid basis for the modeling of Cr:Colquiriite-based laser and amplifier systems, especially for the assessment of their potential at cryogenic temperatures.