Energy transfer upconversion in Nd:YAG at cryogenic temperatures

The precise characterisation of the ground state absorption cross section around 800 nm for Nd:YAG from room temperature to liquid nitrogen temperature is presented. These results enabled the measurement of the energy transfer upconversion macroparameter over the same temperature range for 0.3at.%- and 0.6at.%-doped samples via a simple automated z-scan technique. The main absorption cross section peak at 808 nm is found to increase from (6.90 ± 0.30) pm2 at the highest, to (42.30 ± 2.10) pm2 at the lowest temperatures. Over the same range, the energy transfer upconversion parameter increases from (21.5 ± 2.3) 10−18cm3/s to (52.6 ± 2.5) 10−18cm3/s and from (36.0 ± 2.8) 10−18cm3/s to (65.7 ± 1.9) 10−18cm3/s, for the 0.3at.%- and 0.6at.%-doped crystals, respectively. Although energy transfer upconversion is known to limit room temperature operation on the 946 nm transition for this laser, we demonstrate that when the crystal is cooled to liquid nitrogen temperature, despite a twofold increase in the macroparameter, it has a negligible effect on performance.