论文标题

飞秒X射线吸收光谱中的平衡检测到达到最终灵敏度极限

Balanced Detection in Femtosecond X-ray Absorption Spectroscopy to Reach the Ultimate Sensitivity Limit

论文作者

Schlotter, W. F., Beye, M., Zohar, S., Coslovich, G., Dakovski, G. L., Lin, M. -F., Liu, Y., Reid, A., Stubbs, S., Walter, P., Nakahara, K., Hart, P., Miedema, P. S., LeGuyader, L., Hofhuis, K., Le, Phu Tran Phong, Elshof, Johan E. ten, Hilgenkamp, H., Koster, G., Verbeek, X. H., Smit, S., Golden, M. S., Durr, H. A., Sakdinawat, A.

论文摘要

X射线吸收光谱(XAS)是一种强大且建立的技术,对元素和化学组成敏感。尽管有这些优势,但其实施并没有跟上超快脉冲X射线源的发展,XAS可以捕获飞秒化学过程。 X射线自由电子激光器(XFELS)传递飞秒,窄带宽($ \ frac {δe} {e} {e} <0.5 \%$)脉冲,其中包含$ \ sim 10^{10} $ photons。但是,每个脉冲中包含的能量会波动,从而使脉冲努力量化光子数量使脉搏变得复杂。计算每个脉冲中光子的改进已定义了XAS灵敏度的最新技术。在这里,我们通过平衡检测方法来证明这些改进的最后一步,该方法接近光子计数射击噪声限制。为此,我们从vo $ _2 $中的绝缘体 - 金属过渡中获得了高质量的吸收光谱,并解锁了一种探索具有超快X射线的稀释系统,微妙过程和非线性现象的方法。该方法对X射线光源特别有益,在X射线光源中,集成和平均是提高灵敏度的可行选择。

X-ray absorption spectroscopy (XAS) is a powerful and well established technique with sensitivity to elemental and chemical composition. Despite these advantages, its implementation has not kept pace with the development of ultrafast pulsed x-ray sources where XAS can capture femtosecond chemical processes. X-ray Free Electron Lasers (XFELs) deliver femtosecond, narrow bandwidth ($\frac{ΔE}{E} < 0.5\%$) pulses containing $\sim 10^{10}$ photons. However, the energy contained in each pulse fluctuates thus complicating pulse by pulse efforts to quantify the number of photons. Improvements in counting the photons in each pulse have defined the state of the art for XAS sensitivity. Here we demonstrate a final step in these improvements through a balanced detection method that approaches the photon counting shot noise limit. In doing so, we obtain high quality absorption spectra from the insulator-metal transition in VO$_2$ and unlock a method to explore dilute systems, subtle processes and nonlinear phenomena with ultrafast x-rays. The method is especially beneficial for x-ray light sources where integration and averaging are not viable options to improve sensitivity.

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