Two large-aperture tiled-grating (1.5 m) compressors, each consisting of four sets of tiled-grating assemblies, have been built for the OMEGA EP high-energy petawatt-class laser system. The techniques used for tiling individual tiled-grating assemblies and for optimizing the overall performance of a tiled-grating compressor are described. Both compressors achieved subpicosecond pulse duration without tiling-induced temporal degradation. A ray-tracing model predicted that the static wavefront of the grating tiles dominated focal-spot degradations when submicroradian tiling accuracy is achieved. The tiled-grating compressors delivered a tighter focal spot compared with subaperture grating compressors with single central tiles.

A grating-inspection system and a damage-analysis method have been developed to measure in situ laser-induced damage on a 1.5-m tiled-grating assembly of the OMEGA EP pulse compressor during a 15-ps, 2.2-kJ energy ramp. The beam fluence at which significant damage growth occurred was determined. This is the first report on beam fluence versus laser-induced-damage growth of meter-sized multilayer-dielectric-diffraction gratings. This result was correlated to the damage-probability measurement conducted on a small grating sample and is consistent with the fluence, corresponding to 100% damage probability.

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