Recent advances in ultrafast extreme ultraviolet (EUV) and x-ray light sources provide direct access to fundamental time and length scales for biology, chemistry, and materials physics. However, such light pulses are challenging to measure due to the need for femtosecond time resolution at difficult-to-detect wavelengths. Also, single-shot measurements are needed because severe pulse-to-pulse fluctuations are common. Here we demonstrate single-shot, complete field measurements by applying a novel version of frequency resolved optical gating. An EUV free electron laser beam creates a transient grating containing the pulse’s electric field information, which is read out with a 400 nm probe pulse. By varying the time delay between two copies of the EUV pump, rather than between the pump and the probe, we separate the needed coherent wave mixing from the slow incoherent response. Because this approach uses photoionization, it should be applicable from the vacuum ultraviolet to hard x rays.

中文翻译：

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极紫外自由电子激光脉冲的全光学单脉冲全电场测量

超快极紫外（EUV）和X射线光源的最新进展为生物学，化学和材料物理领域的基本时间和长度尺度提供了直接途径。然而，由于在难以检测的波长上需要飞秒时间分辨率，因此这种光脉冲难以测量。另外，由于严重的脉冲间波动是常见的，因此需要单次测量。在这里，我们通过应用新型的频率分辨光学选通演示了单次完整场测量。EUV自由电子激光束会创建一个包含脉冲电场信息的瞬态光栅，该瞬态光栅会通过400 nm探测脉冲读出。通过改变两个EUV泵之间的时间延迟，而不是改变泵和探头之间的时间延迟，我们从慢的非相干响应中分离出所需的相干波混合。由于此方法使用光电离，因此应适用于从真空紫外线到硬X射线。