Opt Lett. 2018 Jul 15;43(14):3285-3288. doi: 10.1364/OL.43.003285.
The beam smoothing technology, smoothing by spectral dispersion, plays an important role in improving the illumination uniformities of the lasers in inertial confinement fusion facilities. However, due to the limitations of the modulation frequency of the electro-optic modulator, the uniformity of the lasers approaches an asymptotic value after tens of picoseconds that are much longer than the response time of laser plasma instabilities. To the best of our knowledge, this is the first time that an ultrafast smoothing approach for improving the uniformity of a laser quad in both radial and azimuthal directions in the picosecond scale was proposed. Among the four individual beams in a quad, two of them were smoothed by independent ultrafast focal zooming, and the rest were transformed into Laguerre-Gaussian (LG) beams that carry same topological charges with opposite signs. The focal spots of these two LG beams were coherent superposed, and their intensity distributions rotated rapidly in a period of several picoseconds. As a result of the focal zooming and rotation, an ultrafast and significant improvement of the uniformity of a laser quad was achieved.
光束平滑技术，通过光谱色散进行平滑，在提高惯性约束聚变设施中激光的照明均匀性方面发挥着重要作用。然而，由于电光调制器的调制频率限制，激光的均匀性在几十皮秒后接近渐近值，这远长于激光等离子体不稳定性的响应时间。据我们所知，这是首次提出在皮秒量级上在径向和角向两个方向上提高激光四极子均匀性的超快平滑方法。在四极子的四个单独光束中，其中两个通过独立的超快聚焦变焦进行平滑，其余两个转换为携带相反符号的相同拓扑电荷的拉盖尔-高斯（LG）光束。这两个 LG 光束的焦点相干叠加，它们的强度分布在几个皮秒的周期内快速旋转。由于聚焦变焦和旋转，激光四极子的均匀性得到了超快且显著的改善。
