A programmable beam shaping system for tailoring the profile of high fluence laser beams

Abstract

Customized spatial light modulators have been designed and fabricated for use as precision beam shaping devices in fusion class laser systems. By inserting this device in a low-fluence relay plane upstream of the amplifier chain, "blocker" obscurations can be programmed into the beam profile to shadow small isolated flaws on downstream optical components that might otherwise limit the system operating energy. In this two stage system, 1920 × 1080 bitmap images are first imprinted on incoherent, 470 nm address beams via pixilated liquid crystal on silicon (LCoS) modulators. To realize defined masking functions with smooth apodized shapes and no pixelization artifacts, address beam images are projected onto custom fabricated optically-addressable light valves. Each valve consists of a large, single pixel liquid cell in series with a photoconductive Bismuth silicon Oxide (BSO) crystal. The BSO crystal enables bright and dark regions of the address image to locally control the voltage supplied to the liquid crystal layer which in turn modulates the amplitude of the coherent beams at 1053 nm. Valves as large as 24 mm x 36 mm have been fabricated with low wavefront distortion (<0.5 waves) and antireflection coatings for high transmission (>90%) and etalon suppression to avoid spectral and temporal ripple. This device in combination with a flaw inspection system and optic registration strategy represents a new approach for extending the operational lifetime of high fluence laser optics.

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

“…A subsequent polarizer converts the polarization modulation into amplitude modulation. Consequently, apodized patterns free from spurious pixelization artifacts are generated by this second stage, which transfers the desired blockers, gray level and beam profile to the coherent main laser beam [8].…”

“…In this paper, we describe the control and associated image processing of the PSS subsystem. Next we briefly describe the optical subsystem [8].…”

“…Exposure to high-fluence laser light can cause some optical flaws to grow over time and impact performance. The programmable spatial shaper (PSS) based on liquid-crystal spatial light modulators (SLM) was designed and implemented within the NIF laser to introduce arbitrarily shaped obscurations that act to reduce laser irradiation around selected flaw sites [8]. The OI system and Laser Performance Operations Model (LPOM) [9] supply the flaw site information, while the PSS system provides "blockers" that cast a shadow in the beam effectively reducing flaw irradiation exposure.…”

Image processing and control of a programmable spatial light modulator

“…In this paper, we describe the control and associated image processing of the PSS subsystem. Next we briefly describe the optical subsystem [5].…”

“…Exposure to high-fluence laser light can cause some optical flaws to deteriorate over time and impact performance. Recently a programmable spatial shaper (PSS) based on liquid-crystal spatial light modulators (SLM) was designed and implemented within the NIF laser for arbitrarily shaping obscurations that act to reduce laser irradiation around selected flaw sites [5]. The OI system supplies the flaw site information, while the PSS system provides "blockers" that cast a shadow in the beam effectively reducing flaw irradiation exposure.…”