近日，德国欧洲X射线自由电子激光装置(XFEL)的Gianluca Geloni及其研究小组取得一项新进展。经过不懈努力，他们研制出兆赫兹重复率下的级联硬X射线自种子自由电子激光器。相关研究成果已于2023年10月16日在国际知名学术期刊《自然—光子学》上发表。
该研究团队报道了安装在欧洲XFEL的级联HXRSS系统的研究成果，该系统目前是世界上唯一运行的高重复率硬X射线XFEL设施。通过高重复率与HXRSS的结合，该系统能够以每秒10序列的速率产生6-14 keV光子能量范围内带宽约为1 eV的毫焦耳级脉冲（(对应于大约1 mJeV-1峰值光谱密度)，每个序列包含数百个以兆赫兹重复率到达的脉冲。
在2.25 MHz的重复频率和6-7 keV的光子能量范围内，研究人员观察并表征了热负荷对HXRSS晶体的影响，这种影响会大大改变后续X射线脉冲的光谱。然而，研究人员证明了他们的级联自种子方案能够将这种有害影响降低到检测水平以下。这一重要突破为超快X射线光谱学、散射和成像技术在广泛科学领域的应用开辟了令人兴奋的新可能性。
据悉，为了在亚纳秒至飞秒时间范围内进行高分辨率X射线光谱学研究，需要超短X射线脉冲和比目前可用的更大的光谱X射线通量。虽然已经证明了硬X射线自种子（HXRSS）装置可以产生具有必要峰值通量特性的X射线自由电子激光（XFEL）辐射，但这些系统迄今为止无法提供高重复率，从而限制了平均通量的提高。
附：英文原文
Title: Cascaded hard X-ray self-seeded free-electron laser at megahertz repetition rate
Author: Liu, Shan, Grech, Christian, Guetg, Marc, Karabekyan, Suren, Kocharyan, Vitali, Kujala, Naresh, Lechner, Christoph, Long, Tianyun, Mirian, Najmeh, Qin, Weilun, Serkez, Svitozar, Tomin, Sergey, Yan, Jiawei, Abeghyan, Suren, Anton, Jayson, Blank, Vladimir, Boesenberg, Ulrike, Brinker, Frank, Chen, Ye, Decking, Winfried, Dong, Xiaohao, Kearney, Steve, La Civita, Daniele, Madsen, Anders, Maltezopoulos, Theophilos, Rodriguez-Fernandez, Angel, Saldin, Evgeni, Samoylova, Liubov, Scholz, Matthias, Sinn, Harald, Sleziona, Vivien, Shu, Deming, Tanikawa, Takanori, Terentiev, Sergey, Trebushinin, Andrei, Tschentscher, Thomas, Vannoni, Maurizio, Wohlenberg, Torsten, Yakopov, Mikhail, Geloni, Gianluca
Issue&Volume: 2023-10-16
Abstract: High-resolution X-ray spectroscopy in the sub-nanosecond to femtosecond time range requires ultrashort X-ray pulses and a spectral X-ray flux considerably larger than that presently available. X-ray free-electron laser (XFEL) radiation from hard X-ray self-seeding (HXRSS) setups has been demonstrated in the past and offers the necessary peak flux properties. So far, these systems could not provide high repetition rates enabling a high average flux. We report the results for a cascaded HXRSS system installed at the European XFEL, currently the only operating high-repetition-rate hard X-ray XFEL facility worldwide. A high repetition rate, combined with HXRSS, allows the generation of millijoule-level pulses in the photon energy range of 6–14 keV with a bandwidth of around 1eV (corresponding to about 1mJeV–1 peak spectral density) at the rate of ten trains per second, each train including hundreds of pulses arriving at a megahertz repetition rate. At 2.25 MHz repetition rate and photon energies in the 6–7 keV range, we observed and characterized the heat-load effects on the HXRSS crystals, substantially altering the spectra of subsequent X-ray pulses. We demonstrated that our cascaded self-seeding scheme reduces this detrimental effect to below the detection level. This opens up exciting new possibilities in a wide range of scientific fields employing ultrafast X-ray spectroscopy, scattering and imaging techniques.
DOI: 10.1038/s41566-023-01305-x
Source: https://www.nature.com/articles/s41566-023-01305-x