Programmable beam spatial shaping system for the National Ignition Facility

Abstract

A system of customized spatial light modulators has been installed onto the front end of the laser system at the National Ignition Facility (NIF). The devices are capable of shaping the beam profile at a low-fluence relay plane upstream of the amplifier chain. Their primary function is to introduce "blocker" obscurations at programmed locations within the beam profile. These obscurations are positioned to shadow small, isolated flaws on downstream optical components that might otherwise limit the system operating energy. The modulators were designed to enable a drop-in retrofit of each of the 48 existing Pre Amplifier Modules (PAMs) without compromising their original performance specifications. This was accomplished by use of transmissive Optically Addressable Light Valves (OALV) based on a Bismuth Silicon Oxide photoconductive layer in series with a twisted nematic liquid crystal (LC) layer. These Programmable Spatial Shaper packages in combination with a flaw inspection system and optic registration strategy have provided a robust approach for extending the operational lifetime of high fluence laser optics on NIF.

Progress of the injection laser system of SG-II

“…2.3% intensity distribution can be maintained. In addition, an optically addressed spatial modulator is used to pre-block the defect or damage site of the large aperture optics [60][61][62] . Given that the damage threshold of the binary mask with the chromate coat is low, we developed high damage threshold binary masks using dielectric films [63] .…”

“…Optically addressed spatial modulator can achieve high-energy availability without interferometric strips [60][61][62][64][65][66][67] . [60][61][62][64][65][66][67] As a transmission and amplitude type spatial light modulator, the optically addressable spatial light modulator has the advantages of high transmittance, high filling factor, no black gate and no diffraction spots in the follow-up optical path, compared with the existing TFT type transmission liquid crystal spatial light modulator. In high power laser systems, the use of modulators can optimize beam quality in real time.…”

Imaging of Phase Objects using Partially Coherent Illumination

“…Failing flaws can be reworked to mitigate their fratricide threat before installing the optic, either by applying a physical mitigation protocol [16][17][18] to the flaw itself, or by spot blocking [19] that location in the laser system before firing a high-power shot.…”

A Survey of Transparent Conducting Films and Optoelectrical Materials for High Optical Power Applications

“…Thus, there is a need to identify materials that can withstand the optical fluences of modern high‐repetition‐rate laser systems with high average and high peak power, while maintaining high conductance. Conductive films that are transparent to near IR (NIR) wavelengths are particularly important because of the ubiquitous use of neodymium‐doped yttrium aluminum garnet (Nd:YAG) lasers with a fundamental emission wavelength of 1064 nm; TCFs that are functional at this wavelength can also support plasmonic coupling from intraband transitions . To that end, this study surveys the lifetime laser damage threshold of a range of transparent and conductive materials with N e spanning five orders of magnitude from 10 18 to 10 23 cm −3 , sheet resistances <200 Ω sq −1 , and total transmission at 1064 nm ranging from 30% to 85%.…”