Abstract

High power lasers such as the Laser MégaJoule (LMJ) under construction near Bordeaux (France) require phase modulations of the pulses in order to smooth the beam and to avoid stimulated Brillouin scattering in large optics which may cause damages. For anti-Brillouin, the phase modulation chosen for the LMJ is a sine-wave at a frequency of 2 GHz and a modulation index of 7 inducing a spectral broadening of 32 GHz. For smoothing, the broadening is larger (171 GHz) because the phase modulation is a 14.25 GHz sine-wave having a modulation index of 5. Anti-Brillouin is always activated while smoothing may be activated or not (see the optical spectral power distributions (SPD) in Figures 1 and 2).

© 2007 IEEE