Scalable design for a high energy cryogenic gas cooled diode pumped laser amplifier

In this paper we present details of a scalable design for a cryogenic helium gas cooled DPSSL amplifier based on a multislab Yb:YAG geometry. A prototype amplifier design capable of efficient amplification of 10 ns pulses to 10 J at 10 Hz is presented, which has been derived from computational fluid dynamic calculations and thermal modeling. Model predictions have also been used to design a suitable cryogenic gas cooling system, details of which are also presented. Experimental testing has confirmed stable amplifier temperatures are achievable from room temperature down to 88 K, with a gas coolant temperature stability of ±0.2 K. Single-pass transmission wave front measurements are in reasonable agreement with model predictions derived from thermal maps for two different YAG slab geometries. Slabs with a narrower width Cr-doped YAG absorptive cladding, added to suppress ASE, demonstrated a wave front error of ∼0.2 waves at 1030 nm (peak-to-valley) over the 20 mm×20 mm pumped region within the amplifier. The low level of optical distortion confirms that the amplifier design provides an acceptable level of temperature and flow uniformity and demonstrates the merit of a multislab geometry.