No abstract

High-power lasers, such as the Laser MegaJoule (LMJ), have to be phase modulated to avoid stimulated Brillouin scattering (SBS) that may strongly damage optics at the end of the laser chain. Current spectral broadening on LMJ is performed with a sinusoidal phase modulation. This pure sinusoidal phase modulation leads to inhomogeneous spectral power densities (SPD). Thus, for a same SBS power threshold, the sinusoidal phase-modulated spectrum has to be larger than the equivalent ideal SPD with isoenergetic peaks. We present in this paper a technique to generate energy-balanced Dirac peaks spectra thanks to nonsinusoidal phase modulations. Thus, we can build a narrower spectrum with a nonsinusoidal phase modulation that has the same SBS threshold as a sinusoidal phase modulation, and we show that FM-to-AM conversion can be strongly reduced, which is of great interest for LMJ laser performance, with reductions up to 40%.

Highly efficient parametric amplification and wavelength conversion have been demonstrated in the 1040–1090 nm band. A nonlinear photonic crystal fiber was used to provide the anomalous dispersion required for phase matching at 1 μm. A 40 dB maximum gain and +35 dB idler conversion efficiency have been achieved in the subnanosecond pulsed regime and by using a spectrally filtered supercontinuum source as a small signal.

Fiber-based optical-parametric chirped-pulse amplification is reported at 1μm in a microstructured fiber in the femtosecond regime. The signal has been highly stretched by an Öffner triplet and then amplified with an all-fiber, pulsed-pump, fiber optical-parametric amplifier. More than 30dB gain has been achieved over 8.3nm, and the amplified signal has been recompressed.