硅漂移探测器在LCLS的最佳脉冲处理、堆积分解和应用
Optimal pulse processing, pile-up decomposition and applications of silicon drift detectors at LCLS
摘要：
硅漂移探测器（SDD）彻底改变了地质学和牙科学等领域的光谱学。对于超快X射线自由电子激光（FEL）实验的一个子集，SDD可以做出重大贡献。通常，未知的光谱是有趣的，携带科学数据，或者背景测量有助于识别意外信号。许多测量仅涉及几个先验已知的离散光子能量，允许堆积和光谱光子计数的单事件分解。我们设计了一个脉冲函数，并证明了通过拟合获得每个脉冲的信号幅度和上升时间，从而消除了脉冲整形的需要。通过避免脉冲整形，数十纳秒的上升时间导致减少的脉冲堆积，并允许在光子分离时间下将剩余脉冲堆积分解到数百纳秒，同时产生精度为10纳秒的到达时间信息。波形拟合同时产生高能量分辨率和高计数率（比当前数字脉冲处理器高2个数量级）。结果表明，叠加谱拟合相对简单，优于叠加谱反褶积。我们开发了一个光子堆积的统计模型，恒定强度的源，扩展到可变强度的源（典型的自由电子激光），并用它来适应一个复杂的堆积光谱。随后，我们开发了贝叶斯堆积分解方法，该方法允许以99%的准确度从6条单色线分解具有多达6个光子的单个事件的堆积。SDD的实用性将持续到X射线自由电子激光科学时代。他们的继任者ePixS混合像素探测器已经提供了数百个像素，每个像素都具有与SDD相似的性能，并且具有紧凑，坚固和实惠的封装
英文摘要：
Silicon drift detectors (SDDs) revolutionized spectroscopy in fields as diverse as geology and dentistry. For a subset of experiments at ultra-fast, x-ray free-electron lasers (FELs), SDDs can make substantial contributions. Often the unknown spectrum is interesting, carrying science data, or the background measurement is useful to identify unexpected signals. Many measurements involve only several discrete photon energies known a priori, allowing single event decomposition of pile-up and spectroscopic photon counting. We designed a pulse function and demonstrated that the signal amplitude and rise time are obtained for each pulse by fitting, thus removing the need for pulse shaping. By avoiding pulse shaping, rise times of tens of nanoseconds resulted in reduced pulse pile-up and allowed decomposition of remaining pulse pile-up at photon separation times down to hundreds of nanoseconds while yielding time-of-arrival information with precision of 10 nanoseconds. Waveform fitting yields simultaneously high energy resolution and high counting rates (2 orders of magnitude higher than current digital pulse processors). We showed that pile-up spectrum fitting is relatively simple and preferable to pile-up spectrum deconvolution. We developed a photon pile-up statistical model for constant intensity sources, extended it to variable intensity sources (typical for FELs) and used it to fit a complex pile-up spectrum. We subsequently developed a Bayesian pile-up decomposition method that allows decomposing pile-up of single events with up to 6 photons from 6 monochromatic lines with 99% accuracy. The usefulness of SDDs will continue into the x-ray FEL era of science. Their successors, the ePixS hybrid pixel detectors, already offer hundreds of pixels, each with similar performance to an SDD, in a compact, robust and affordable package
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