Influence of polarization on speckle patterns in the Laser MegaJoule configuration

This paper investigates hot spot characteristics generated by the superimposition of multiple laser beams in the Laser MegaJoule configuration. First, properties of speckle statistics are studied in the context of the superimposition of several laser beams. The case of a single quadruplet is studied. Values of the speckle width and of the speckle length as well as of the abundance of the speckles are compared to the results given by numerical simulations. Application to the speckle patterns generated in the Laser MegaJoule configuration in the zone where all the beams overlap is then presented. The case of three different polarizations is investigated: P polarization, S polarization and the case of Double Polarization smoothing (DPS). It is found that the sizes of the speckles and their abundance depend on the choice of the polarization and that DPS seems to be the best option.