Statistical spatio-temporal properties of the Laser MegaJoule speckle

Abstract

This paper investigates a statistical model to describe the spatial and temporal properties of hot spots generated by the superimposition of multiple laser beams. In the context of the Laser MégaJoule design, we introduce the formula for contrasts, trajectories and velocities of the speckle pattern. Single bundle of four beams, two-cones and three-cones configurations are considered. Statistical properties of the speckle in the zone where all the beams overlap are studied with different configurations of polarizations. These properties are shown to be very different from the case of one single bundle of four beams. The configuration of polarization has only a slight effect in the two-cones or three cones configuration. Indeed, the impact of the double polarization smoothing is reduced in the area in which all the beams overlap, while it is much more significant when they split. Moreover, the size of the hot-spots decreases as the number of laser beams increases, but we show that their velocity decreases. As a matter of fact, the maximal velocity of hot spots is found to be only about 10−5 of the velocity of light and the integrated contrast is about 15% when the beams overlap.

Faraday effect on stimulated Raman scattering in the linear region

“…Theoretical and numerical works were also performed [6][7][8][9]. To control the laser plasma interactions, many methods were put forward from the points of laser parameters and plasma parameters, such as laser smoothing technology [10], the spike train of uneven duration and delay [11][12][13][14], the alternating polarization [15], the multi-color light incident [16], changing the gas density in holhraum [17] and increasing the electron temperature. While these methods were considered with the un-magnetized plasma.…”