We present first experimental results of a novel method to study the energy chirp of the electron beam lasing window at a free-electron laser operating in self-amplified spontaneous emission mode. The method requires a single magnetic chicane splitting the FEL undulator into two parts of several gain lengths each. Undulator segments should have variable gaps. By scanning both the delay in the chicane and detuning in a part of the undulators, one can retrieve the linear component of both the radiation frequency chirp and the electron energy chirp. In addition, such scan improves the accuracy of the previously proposed autocorrelation-based pulse duration measurement technique. The proposed method targets facilities that lack direct diagnostics of the electron beam longitudinal phase space distribution. It also can be extended to diagnose transverse tilts of the beam.

中文翻译：

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延迟失谐扫描在自由电子激光器上表征纵向电子束

我们目前提出一种新方法的第一实验结果，该方法研究以自放大自发发射模式工作的自由电子激光器的电子束激光窗口的能量window。该方法需要单个磁锥将FEL波动器分成两个部分，每个部分具有几个增益长度。起伏器段应具有可变的间隙。通过扫描斜角的延迟和一部分波荡器的失谐，可以获取辐射频率线性调频和电子能量线性调频的线性分量。另外，这种扫描提高了先前提出的基于自相关的脉冲持续时间测量技术的准确性。所提出的方法针对的设施缺乏对电子束纵向相空间分布的直接诊断。