Sub-micron focusing of soft x-ray free electron laser beam
Sub-micron focusing of soft x-ray free electron laser beam
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软 X 射线自由电子激光束的亚微米聚焦
DOI：
10.1117/12.822498
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发表时间：
2009
期刊：
影响因子：
--
通讯作者：
T. Tschentscher
中科院分区：
文献类型：
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作者：
S. Bajt;H. Chapman;A. Nelson;R. Lee;S. Toleikis;P. Mirkarimi;J. Alameda;S. Baker;H. Vollmer;R. Graff;A. Aquila;E. Gullikson;J. Meyer Ilse;E. Spiller;J. Krzywiński;L. Juha;J. Chalupský;V. Hájková;J. Hajdu;T. Tschentscher
一个多层涂层的27厘米焦距抛物线，优化反射13.5 nm的波长，在正常的入射，被用于多个FLASH实验，并聚焦到亚微米光束尺寸的光束。光束的强度是从FLASH光束在PMMA涂覆的基底上留下的凹坑的深度间接测量的。比较模拟和实验的陨石坑形状，我们发现最佳匹配的波前误差为0.45 nm，或λ/30。我们进一步估计焦斑的FWHM为350 nm，焦点中的强度为1018 W/cm 2。亚微米的闪光光束提供了极端强度的条件下，必不可少的温暖致密物质的实验。相同的光学元件被用于多个实验中，并在光束中幸存下来。然而，经过几天的第一次测量后，光学表面被污染了。这种污染降低了反射镜的反射率，这是部分恢复的氧等离子体清洗。然而，即使是部分清洁的多层涂层光学器件仍然是衍射限制的，并且可以在未来的实验中将光束聚焦到亚微米光束尺寸。
A multilayer-coated 27-cm focal length parabola, optimized to reflect 13.5 nm wavelength at normal incidence, was used in multiple FLASH experiments and focused the beam to a sub-micron beam size. The intensity of the beam was measured indirectly from the depths of craters left by the FLASH beam on PMMA-coated substrates. Comparing simulated and experimental shapes of the craters we found the best match for a wavefront error of 0.45 nm, or λ/30. We further estimated that the FWHM of the focal spot was 350 nm and that the intensity in the focus was 1018 W/cm2. The sub-micron FLASH beam provided extreme intensity conditions essential for warm dense matter experiments. The same optic was used in multiple experiments and survived the beam. However, after the first measurements, which took place over several days, the optical surface was contaminated. This contamination reduced the mirror reflectivity, which was partially recovered by oxygen plasma cleaning. However, even the partially cleaned multilayer-coated optic is still diffraction limited and can focus the beam in future experiments to a sub-micron beam size.