Nd:Phosphate Split-slab Liquid Cooled kJ Amplifier for High Power Laser at 1 Shot/Minute

Abstract

A liquid cooled Nd:Phosphate split-disk amplifier, operating at 1053nm and one shot/min, was designed and built. Good wavefront quality is obtained, in agreement with multi-physics modeling and with performance needs on high power laser systems.

Analysis of mid-spatial frequency wavefront distortions from a liquid-cooled flash-lamp pumped Nd:phosphate laser amplifier

“…As a guideline for large inertial confinement fusion (ICF) lasers, typical values of 2.5 nm root mean square (RMS) in the (1-10 mm) range for the transmitted wavefront are usually considered as an acceptable upper limit for individual amplifier slabs; in addition, a 1D power spectral density (PSD) specification in the form of aν −2.5 , where a is a constant and ν the frequency, is also used to avoid frequency peaks that are likely to be amplified by the Kerr effect [17,18] . In the case of a liquid-cooled amplifier slab, these distortions can be reduced below the nanometer RMS level in the (1-10 mm) range by optimizing the coolant distribution without optical pumping thanks to a knifeedge metrology [24] . Moreover, the same level of wavefront RMS deformation is present for spatial distortions below the millimeter scale, independent of the coolant distribution [24] .…”

“…In the case of a liquid-cooled amplifier slab, these distortions can be reduced below the nanometer RMS level in the (1-10 mm) range by optimizing the coolant distribution without optical pumping thanks to a knifeedge metrology [24] . Moreover, the same level of wavefront RMS deformation is present for spatial distortions below the millimeter scale, independent of the coolant distribution [24] .…”

“…Such distortions are induced by the coolant flow, as reported in Refs. [24,25]. However, whatever the repetition rate tested, the PSD stays below the acceptable upper limit represented by the broken purple line.…”

“…(ii) A liquid-cooled amplifier test-bed was designed and built to characterize mid-to large-scale spatial frequency distortions in amplified wavefronts and compare these with model predictions [23] . In addition, knifeedge Foucault measurements were also performed in a single-pass configuration to investigate (0.1-10 mm) smallto mid-scale spatial frequency distortions, in particular those induced by liquid flow [24] . Here we report on the amplified optical wavefront performances in the mid-to large-spatialscale range (1-100 mm) of a neodymium phosphate liquidcooled amplifier cell pumped by flash-lamps built as a test-bed for liquid-cooled amplification.…”