Multiphysics model of liquid-cooled Nd:phosphate split-slabs in large aperture optical amplifiers

Abstract

High repetition rates in high energy solid-state laser systems can yield to a rise of temperature in amplifiers despite the use of cooling systems. This effect can significantly impact the performance of amplifiers by inducing thermal stress, birefringence or thermal lensing. Here, we develop a multiphysics model to support the design, optimization and commissioning of a liquid-cooled large aperture split-slab laser glass amplifier. This multiphysics model includes optical pumping in the amplifying medium, heat loading, hydraulic effects induced by the liquid coolant, mechanical deformation and their potential coupled effects on the optical wavefront. The accuracy of each model is assessed by carrying out specific experimental measurements and characterizations. We show that this set of models allows the prediction of performance of a liquid-cooled amplifier from the flash-lamp emission to the amplified wavefront at a repetition rate of one shot per minute.

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

“…Liquid-cooled amplifiers are currently used in facilities as pump laser or main beam amplifiers [ 7 , 19 , 20 ] , which has motivated developments for improving their performances. In particular, (i) a thermo-hydraulic-mechanical-optical model was developed to provide a complete and multi-physics model of these amplifiers [ 21 ] . During the first step, the gain and heat generated by optical pumping are calculated using a combination of a phenomenological lamp model [ 22 ] , heat transport and calculation of the population of the different atomic levels.…”

“…During the first step, the gain and heat generated by optical pumping are calculated using a combination of a phenomenological lamp model [ 22 ] , heat transport and calculation of the population of the different atomic levels. In the second step, the spatial distribution of the heat is used in a COMSOL software model that includes the computer-aided design of the amplifier cell and the description of the coolant flow to compute by ray tracing the laser wavefront deformation induced by thermo-mechanical-hydraulic effects [ 21 ] . (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 ] .…”

Monolithic edge-cladding process for the elliptical disk of N31-type Nd-doped high-power laser glass

“…In particular, such a process cannot be applied at the present time when the amplifier glass slabs need to be immersed in organic and/or inorganic coolants for a high repetition rate [22][23][24][25] . The coolants would easily dissolve the bonding agent, such as the used epoxy structural adhesive, that combines the edge-cladding glass strip with the laser glass slab.…”

“…Although this is a very good and commonly used edge-cladding process, it is not suitable for special-shaped laser glass components, such as elliptical and circular disks. And especially such a process could not be applied at present time when the amplifier glass slabs need to be immersed in organic and/or inorganic coolants for a high repetition rate [22][23][24][25] . The coolants would easily dissolve the bonding agent such as the used epoxy structural adhesive that combines edge-cladding glass strip with laser glass slab.…”