Abstract
This paper investigates statistical properties of hot spots when speckle patterns are generated by the superimposition of multiple laser beams in a 2 cone and a 3 cone Laser MegaJoule configuration in the zone where all the beams overlap. Three different cases of polarizations are investigated: P polarization, S polarization and the case of Double Polarization Smoothing (DPS). It is found that the sizes of the speckles depend on the choice of the polarization and that DPS seems to be the best option in both configurations. It is shown that the longitudinal radius of the hot spots in a 2 cone configuration is bigger than in a 3 cone configuration.
Highlights
INTRODUCTIONIrradiation uniformity is a key issue for multiple laser beam facilities such as the National Ignition Facility (NIF) in the US [1] or the Laser Megajoule (LMJ) in France [2]
This paper investigates statistical properties of hot spots when speckle patterns are generated by the superimposition of multiple laser beams in a 2 cone and a 3 cone Laser MegaJoule configuration in the zone where all the beams overlap
Irradiation uniformity is a key issue for multiple laser beam facilities such as the National Ignition Facility (NIF) in the US [1] or the Laser Megajoule (LMJ) in France [2]
Summary
Irradiation uniformity is a key issue for multiple laser beam facilities such as the National Ignition Facility (NIF) in the US [1] or the Laser Megajoule (LMJ) in France [2]. We investigate the effect of the polarization configuration and of the number of cones on hot spot properties in the LMJ configuration in the zone where all the beams overlap. This is especially important since it has been recently shown in NIF experiments that non linear mechanisms that can take place in this zone such as energy transfer from one quad to another or multi-beam effects on backscatter could alter symetry [6] or energy coupling to the target [7]. We first remind analytical estimates for the speckle sizes and the statistical properties of the speckles in multiple beams configuration [9] We apply these formula to the case of a 2 cone and a 3 cone configuration for a LMJ irradiation scheme in these three cases of polarization.
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