不同2×2集束聚焦方式下高功率激光靶面光强分布特性

Light intensity distribution of high-power laser beams on target plane under different focus system of 2 × 2 beam array

大口径高功率激光装置为提高激光靶面的光强强度,通常采用2×2集束聚焦的模式进行打靶.大口径楔形透镜是组成2×2集束聚焦系统的核心元件,可分为二维离轴楔形透镜、一维离轴楔形透镜和非离轴楔形透镜3类.为了获得理想靶面光强分布,基于这3类楔形透镜,对比研究相应2×2集束聚焦系统下的靶面光强分布特性.研究结果表明:相比离轴楔形透镜,采用基于非离轴楔形透镜的2×2集束聚焦系统时,容易在激光靶面获得更窄的主瓣宽度、更强的峰值强度、更高的能量集中度.研究结果对高功率激光靶场聚焦系统的配置选择有重要参考价值.

Large aperture high-power laser drivers usually focus the high power laser beams in 2 × 2 quads to the target chamber center in order to increase the light intensity on the target plane. The large aperture wedged focus lenses are the core components in the focus system of quadruplets of beams, and it is thought possible to use four two-dimensional off-axis wedged focus lenses as four sub-lenses to make up a larger aperture wedged focus lens in form to focus the four beams. Given that the large aperture two-dimensional off-axis wedged focus lenses are processed and used difficultly,the wedged focus lenses are divided into three categories： the two-dimensional off-axis wedged focus lenses, the onedimensional off-axis wedged focus lenses, and the non-off-axis wedged focus lenses. On the basis of the three modes of the wedged focus lenses and the corresponding specific incidence angles of each sub-beam, the three focus schemes for the 2 × 2 beam array are put forward to comparatively research the light intensity distribution on the target plane.Research results show that from a perspective of the coherence among the four sub-beams, the phase factors of each sub-beam respectively introducing by the three focus systems with the two-dimensional off-axis, one-dimensional off-axis,and non-off-axis wedged focus lenses are asymmetric, asymmetric and symmetric inside each sub-beam, and symmetric,asymmetric and symmetric among the four sub-beams. Therefore, the wave front consistency of the four sub-beams decreases in the order of the focus systems with the non-off-axis, two-dimensional off-axis, and one-dimensional off-axis wedged focus lenses. The focus schemes with the non-off-axis wedged focus lenses for 2 × 2 beam array can get the narrowest main-lobe, the strongest peak-value intensity, the highest energy concentration ratio on the target plane,followed by the one-dimensional off-axis and two-dimensional off-axis wedged focus lenses. The off-axis mode of the wedged focus lenses not only increases the complexity in the course of processing and using, but also increases the main-lobe size, decreases the peak-value intensity and the energy concentration ratio, which obtains a weaker focusing characteristics than that of the non-off-axis mode of the wedged focus lenses. Research results can provide an important reference for the design of the focus system in the target area of high-power laser drivers.