Image processing and control of a programmable spatial light modulator for spatial beam shaping

Abstract

Programmable spatial shapers using liquid-crystal-based spatial-light-modulators in the National Ignition Facility lasers enable spatial shaping of the beam profile so that power delivered to the target can be maximized while maintaining system longevity. Programmable spatial shapers achieve three objectives: Introduce obscurations shadowing isolated flaws on downstream optical elements that could otherwise be affected by high fluence laser illumination; Spatial shaping to reduce beam peak-to-mean fluence variations to allow the laser to operate at higher powers so that maximum power can be delivered to the target; And finally gradually exposing the optical regions that have never seen laser light because they have always had shadowing from a blocker that is no longer needed. In this paper, we describe the control and image processing algorithms that determine beam shaping and verification of the beam profile. Calibration and transmittance mapping essential elements of controlling the PSS are described along with spatially nonlinear response of the device such as scale and rotation.

Beam shaping in the high-energy kW-class laser system Bivoj at the HiLASE facility

“…There is great effort to either pre-compensate or improve the spatial beam profile or wavefront in order to avoid optics damage in the amplifiers and to achieve the most uniform output. For this purpose, various types of spatial light modulator (SLM)-based beam shapers have been deployed at several laser facilities in their laser systems [6][7][8][9][10][11] or in test experiments [12][13][14][15] .…”

“…If the SLM is placed between crossed polarizers, each pixel can vary attenuation by rotating linear polarization between the polarizers [ 9 , 10 ] . There are also techniques based on computer-generated holograms [ 15 ] , optically addressable transmissive light valves [ 6 ] or binary beam shapers using error diffusion [ 14 , 16 ] . Probably the most used are the methods that incorporate diffraction gratings and spatial filters for removing the unwanted diffraction orders.…”

Hundred-Joule-level, nanosecond-pulse Nd:glass laser system with high spatiotemporal beam quality

“…However, these are all passive shaping methods used for particular laser system, which is not suitable for achieving high spatial beam quality in complex high-power lasers applied in accurate physics experiments. In recent years, programmable liquid-crystal spatial light modulator (SLM) has been used for adaptive spatial beam shaping and it has been installed onto some large laser systems, such as the National Ignition Facility (NIF) [41] and the OMEGA EP laser [42] . However, there have been only a limited number of reports on spatial beam shaping for high-power lasers using an SLM, especially for medium-scale 100-J lasers [43] .…”