Characterization of high energy, high average power, cryogenic laser amplifier head cooled using the reversed Brayton cycle

We present a high power, high energy cryogenic Yb:yttrium aluminum garnet laser head cooled by a reversed Brayton cycle-based gaseous helium system. The temperature of the helium is roughly 120 K and, typically, to reach such temperatures, liquid nitrogen is used. By utilizing a reversed Brayton cycle in the cooling circuit, the system can reach such cryogenic temperatures using only room temperature water to cool the helium. We demonstrate cooling to the level of 120 K and measure the optical properties of the laser head to show that it is suitable for high energy, high average power laser operation.