Deng Yunpei, Zerdane Serhane, Xie Xinhua, Divall Edwin, Johnson Philip J M, Arrell Christopher, Lemke Henrik Till, Mankowsky Roman, Oggenfuss Alex, Svetina Cristian, Erny Christian, Cirelli Claudio, Milne Christopher, Knopp Gregor, Beaud Paul, Johnson Steven L
Opt Express. 2020 Apr 13;28(8):11117-11127. doi: 10.1364/OE.388911.
Many of the scientific applications for X-ray free-electron lasers seek to exploit the ultrashort pulse durations of intense X-rays to obtain femtosecond time resolution of various processes in a "pump-probe" scheme. One of the limiting factors for such experiments is the timing jitter between the X-rays and ultrashort pulses from more conventional lasers operating at near-optical wavelengths. In this work, we investigate the potential of using X-ray-induced changes in the optical second harmonic generation efficiency of a nonlinear crystal to retrieve single-shot arrival times of X-ray pulses with respect to optical laser pulses. Our experimental results and simulations show changes to the efficiency of the second harmonic generation of 12%, approximately three times larger than the measured changes in the transmission of the 800 nm center-wavelength fundamental pulse. Further experiments showing even larger changes in the transmission of 400 nm center-wavelength pulses show that the mechanism of the second harmonic generation efficiency modulation is mainly the result of X-ray-induced changes in the linear absorption coefficients near 400 nm. We demonstrate and characterize a cross-correlation tool based on this effect in reference to a previously demonstrated method of X-ray/optical cross-correlation.
许多X射线自由电子激光的科学应用试图利用强X射线的超短脉冲持续时间，通过“泵浦-探测”方案获得各种过程的飞秒时间分辨率。此类实验的限制因素之一是X射线与来自工作在近光学波长的更传统激光器的超短脉冲之间的定时抖动。在这项工作中，我们研究了利用X射线引起的非线性晶体光学二次谐波产生效率的变化来获取X射线脉冲相对于光学激光脉冲的单次到达时间的潜力。我们的实验结果和模拟表明，二次谐波产生效率变化了12%，大约是800nm中心波长基频脉冲传输测量变化的三倍。进一步的实验表明，400nm中心波长脉冲的传输有更大的变化，这表明二次谐波产生效率调制的机制主要是X射线引起的400nm附近线性吸收系数的变化。我们参照先前展示的X射线/光学互相关方法，展示并表征了基于这种效应的互相关工具。
