Detailed Characterization of Electron Plasma Waves Produced by Stimulated Raman Scattering

Modeling of the competition of stimulated Raman and Brillouin scatter in multiple beam experiments

“…The LULI experimental conditions have been described in several publications. [1][2][3][4][5][6][7] A six laser beam facility was used with three heater beams at 0.53 µm with random phase plates (RPP) to produce and heat an underdense plasma from a CH foil. Two or three f/ 6 laser interaction beams at 1.053 µm also with random phase plates (RPP) were used to study laser plasma interactions making relative angles 22.5˚, 45˚, and 67.5˚.…”

“…Thus, with SBS observed to occur farther out in the plasma, pump depletion in the most intense speckles (which are the most active for SRS and SBS) due to SBS can account for why SRS (either absolute or convective) is not observed in the same speckle until SBS quenches. 2 Another consideration for LULI plasma conditions is whether ponderomotive and thermal filamentation can occur. The linear convective gain for the growth of electron density perturbations in ponderomotive filamentation over a 300µm speckle is significant: [9][10][11][12]40 Im…”

“…Laser-plasma experiments at the Laboratoire pour L'Utilisation des Lasers Intenses (LULI) [1][2][3][4][5][6][7] have yielded a number of interesting observations bearing on the physics of stimulated Brillouin (SBS) and Raman (SRS) scattering. Of particular interest have been observations of the anti-correlation of SBS and SRS in multiple-beam experiments with exploding CH (carbon and hydrogen plastic) foils.…”

“…Moreover, with the addition of a second and a third interaction laser beam, the tendency was for the SBS direct backscatter to saturate sooner in time and at a lower amplitude (both in the ion acoustic wave's electron density perturbation and the reflectivity), and for the SRS backscatter to onset sooner and at a higher amplitude (Figs. [1][2][3][4][5]. With two interaction beams at 22.5˚ relative angle, the observed SBS ion acoustic wave's electron density perturbation associated with the ion wave bisecting the laser propagation directions (the mutually resonant ion wave) increased in amplitude with increasing intensity of the two driving waves.…”

“…More generally, the study of and control of SBS and SRS have received continuous theoretical and experimental attention for many years in laser fusion research. [1][2][3][4][5][6][7][8][9][10][11][12][13][14] The symmetric compression of fusion targets in either direct drive or indirect drive can be affected by SBS and SRS, and there is the potential for damage to plasma-facing optics from direct backscatter unless these instabilities are controlled. 15 Furthermore, the optimization of the fusion performance of experiments in multiple beam facilities like the National Ignition Facility (NIF) 16 requires careful control over both the timing and relative amplitudes of the crossing beams, which sets limits on how much SBS and SRS can be tolerated.…”