Development of ultra-short pulse, single coherent spike for SASE X-ray FELs
Development of ultra-short pulse, single coherent spike for SASE X-ray FELs
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DOI：
10.1016/j.nima.2008.04.061
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发表时间：
2008-08
影响因子：
1.4
通讯作者：
S. Reiche;P. Musumeci;C. Pellegrini;J. Rosenzweig
中科院分区：
文献类型：
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作者：
S. Reiche;P. Musumeci;C. Pellegrini;J. Rosenzweig
人们对生产用于原子物理和其他应用的高功率、超短、1fs 或更短的相干 X 射线脉冲非常感兴趣。然而，目前 X 射线 SASE FEL 的设计导致 X 射线脉冲长约 100 倍。 X射线脉冲的时间结构由几个因素决定，主要是电子束长度和FEL配合长度。到目前为止，所有自由电子激光器都工作在电子束长度远大于合作长度的状态。在 X 射线 SASE FEL 的情况下，这意味着 X 射线脉冲由一系列尖峰组成，在 LCLS 的情况下有几百个尖峰，并且束长度约为 200fs。已经提出了几种将束长度减少到 10-1fs 区域的方法。这些方法基于电子束操纵，将电子束的激光部分切割至总长度的一小部分，从而减少 X 射线脉冲长度。我们在这里考虑一种不同的方法，使用超短、电荷非常低的电子束，其长度等于或小于 FEL 合作长度。在这种情况下，在波荡器中放大后的X射线脉冲长度是电子束团长度的几倍。我们的模拟表明，在 LCLS 和 SPARX 的情况下，使用 1pC 电子束操作，我们获得短至 300as 的 X 射线脉冲，在 SPARX 情况下变换受限，在 LCLS 情况下几乎变换受限。与产生短 X 射线束的其他模式相比，这种模式具有背景信号非常小的优点，因为所有电子都用于产生激光，并且电荷非常小。
There is a large interest in the production of high power, ultra-short, 1fs or less, coherent X-ray pulses, for atomic physics and other applications. However, the present design of X-ray SASE FELs leads to an X-ray pulse about 100 times longer. The time structure of the X-ray pulse is determined by several factors, mainly the electron bunch length and the FEL cooperation length. Until now all FELs have been working in the regime where the electron bunch length is much larger than the cooperation length. In the case of an X-ray SASE FEL this means that the X-ray pulse consists of a series of spikes, a few hundred in the case of the LCLS, and the bunch length is of the order of 200fs. Several methods to reduce the bunch length to the 10-1fs region have been proposed. These methods are based on electron bunch manipulation to cut the lasing part of the bunch to a fraction of the total length, thus reducing the X-ray pulse length. We are considering here a different method, using ultra-short, very low charge electron bunches, with a length of the order or shorter than the FEL cooperation length. In this case the X-ray pulse length after amplification in the undulator is a few times the electron bunch length. Our simulations show that in the case of LCLS and SPARX, operating with a 1pC electron beam, we obtain X-ray pulses as short as 300as, transform limited in the SPARX case, and almost transform limited in the LCLS case. Compared to other modes of producing short X-ray bunches this one offers the advantage of very small background signal, since all electrons are used to lase, and the charge is very small.