有像差情况下的全息光栅拼接研究

Study of Gratings Tiled by Holographic Exposure with Wave Aberration

激光约束核聚变系统需要大口径脉冲压缩光栅。全息光栅拼接法是制造大口径光栅的重要手段。针对有像差的全息曝光系统,提出了一种拼缝处光栅对准拼接方法。为研究像差对光栅拼接特性的影响,用随机波面进行了光栅模拟拼接,计算了远场衍射能量分布与拼接误差的关系。实验拼接了(150+150)×200 mm2口径光栅,其拼接均方根误差值为0.034λ,峰-峰误差值为0.110λ。利用光栅±1级衍射波面,计算得到了曝光系统像差,并模拟了拼缝处最小拼接误差,其均方根误差值为0.016λ,峰-峰误差值为0.105λ。结果表明,拼接误差与理论模拟结果相近。该误差不会造成远场衍射光斑能量明显下降。由此证明了该方法的可行性。

Large-aperture pulse compression gratings are needed by laser confinement fusion system. Tiled-grating made by holographic exposure is an important way to manufacture large aperture gratings. A method is proposed to align the gratings for the exposure system with wave aberration. In order to study the effect of the wave aberration on the characteristics of tiled-grating, the random wave fronts are used to simulate the tiled-gratings.The relationship between the distribution of far-field diffraction energy and the tiling-error is calculated. A grating of（150＋150）×200 mm2 is made experimentally. The root-mean-square value of the tiling-error is 0.034λ and the peak to peak value is 0.110λ. The ± 1st diffraction wave fronts of the grating are used to calculate wave aberration of the exposure system. The minimum value of the tiling-error is simulated theoretically. The root-mean-square value of the error is 0.016λ and the peak to peak value is 0.105λ. The results show that the tiling-error is close to the simulated data. The far-field diffraction intensity can not be decreased obviously by the tiling-error. It is proved that the method proposed in this article is feasible.