Hocquet Steve, Penninckx Denis, Gleyze Jean-François, Gouédard Claude, Jaouën Yves
CEA/CESTA, 15 avenue des Sablières, BP 2, 33114 Le Barp, France.
Appl Opt. 2010 Mar 1;49(7):1104-15. doi: 10.1364/AO.49.001104.
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%.
高功率激光器，如兆焦耳激光器（LMJ），必须进行相位调制，以避免受激布里渊散射（SBS），这种散射可能会严重损坏激光链末端的光学元件。目前，LMJ上的光谱展宽是通过正弦相位调制来实现的。这种纯正弦相位调制会导致光谱功率密度（SPD）不均匀。因此，对于相同的SBS功率阈值，正弦相位调制光谱必须大于具有等能量峰值的等效理想SPD。在本文中，我们提出了一种通过非正弦相位调制来生成能量平衡狄拉克峰光谱的技术。因此，我们可以用非正弦相位调制构建一个更窄的光谱，其具有与正弦相位调制相同的SBS阈值，并且我们表明可以大幅降低调频到调幅的转换，这对于LMJ激光性能非常重要，降低幅度高达40%。
