Erskine David J
Lawrence Livermore National Laboratory, L-487, Livermore, California 94550, USA.
Rev Sci Instrum. 2020 Apr 1;91(4):043103. doi: 10.1063/1.5143246.
When near-instantaneous shocks are recorded by using a Doppler velocity interferometer velocity interferometer system for any reflector (VISAR), they typically exceed the detector's ability to react and "skipped fringes" result, where its visibility briefly reduces. Traditionally, replacing skipped fringes required guesswork in analysis, which increased arrival time errors. Second, the use of long but velocity-sensitive interferometer delays with fast detectors which can resolve the delay has traditionally been avoided because of the fear of confusing the arrival time signal. However, shorter delays produce smaller fringe phase shifts per velocity and, thus, can decrease velocity precision. We realize that while some loss of fringe information occurs at shock events, this is often just a partial loss and the residual fringe information can still hold valuable information. We describe a forward model (FM) of the interferometer action and detector blurring that assists with VISAR fringe analysis at skipping events: (1) more precise shock arrival times, (2) arrival time precision not limited by long delays, and (3) improved ghost subtraction, which improves accuracy over a broad time region. We demonstrate the utility of a FM on National Ignition Facility and Laboratory for Laser Energetics Omega shots and discuss data process methods to increase the high time resolution of VISAR systems despite their limitations and complexities.
当使用多普勒速度干涉仪（VISAR）对任何反射器记录近瞬间冲击时，它们通常会超出探测器的反应能力，从而产生“跳条纹”现象，即条纹可见度会短暂降低。传统上，分析中要替换跳条纹需要猜测，这会增加到达时间误差。其次，传统上一直避免使用长但对速度敏感的干涉仪延迟以及能够分辨延迟的快速探测器，因为担心会混淆到达时间信号。然而，较短的延迟在单位速度下产生的条纹相移较小，因此会降低速度精度。我们认识到，虽然在冲击事件中会出现一些条纹信息丢失的情况，但这通常只是部分丢失，残余的条纹信息仍然可能包含有价值的信息。我们描述了一种干涉仪作用和探测器模糊的正向模型（FM），它有助于在跳条纹事件时进行VISAR条纹分析：（1）更精确的冲击到达时间；（2）到达时间精度不受长延迟限制；（3）改进的重影减除，这在较宽的时间区域内提高了精度。我们展示了FM在国家点火装置和激光能量学实验室欧米伽实验中的效用，并讨论了尽管VISAR系统存在局限性和复杂性，但仍能提高其高时间分辨率的数据处理方法。
