Temperature dependence of the fluorescence lifetime and emission cross section of Tm:YLF in the 78–300 K range

Abstract

We have investigated the spectroscopic properties of Tm:YLF material around 1900 nm in detail to understand its amplification performance at cryogenic temperatures. Fluorescence lifetime and emission cross section (ECS) measurements are performed in the 78–300 K range using crystals with Tm doping levels of 0.5 and 2.5%. The radiative lifetime of the 3F4 level of Tm:YLF is found to be temperature dependent, and has a value of around 18 ms at 78 K, and 15.25 ms at 300 K, respectively. The emission measurements indicate the presence of rather strong and reasonably broadband peaks even at cryogenic temperatures. The 1877 nm emission peak of the E//c configuration has a strength of around 2.4 × 10−20 cm2 and a full-width half maximum (FWHM) of around 4 nm at 100 K. The E//a axis configuration possesses a broader emission around 1908 nm with a FWHM of around 19 nm at 100 K, but with a lower peak ECS value of 0.75 × 10−20 cm2. We have also investigated the temperature variation of fluorescence lifetime for the 3H4 level, and the results showed that the two-for-one cross-relaxation process is also quite effective at cryogenic temperatures. These findings clearly demonstrate that cryogenic Tm:YLF systems have the potential to reach kW level average powers and sub-1-ps pulsewidths.