Veyrinas K, Vábek J, Valentin C, Descamps D, Péjot C, Burgy F, Constant E, Mével E, Catoire F
Opt Express. 2021 Sep 13;29(19):29813-29827. doi: 10.1364/OE.436086.
Controlling the wavefront of an extreme ultraviolet (XUV) high-order harmonic beam during the generation process offers the capability of modifying the beam properties without resorting to any XUV optics. By characterizing the XUV intensity profile and wavefront, we quantitatively retrieve both the size and the position of the waist of each harmonic generated in an argon jet. We show that optics-free focusing can occur under specific generating conditions leading to XUV focii of micrometer size. We also demonstrate that each focus is located at distinct longitudinal positions. Using this remarkable XUV wavefront control combined with near focus spatial selection, we experimentally demonstrate efficient and adjustable spectral filtering of the XUV beam, along with a strong rejection of the fundamental beam, without using any XUV optics. The experimental results are compared with simulations providing the impact of the filtering on the temporal profile of the XUV field. It shows that the attosecond structure is preserved and that the beam is more homogeneous after the filtering, thereby reducing the longitudinal focii shift. This is a major step to achieve high XUV intensity and probing ultrafast processes with an improved resolution.
在极紫外（XUV）高次谐波光束的产生过程中控制其波前，能够在不借助任何XUV光学元件的情况下改变光束特性。通过对XUV强度分布和波前进行表征，我们定量地获取了在氩气喷流中产生的各谐波的束腰尺寸和位置。我们表明，在特定的产生条件下会出现无光学元件聚焦，从而产生微米尺寸的XUV焦点。我们还证明每个焦点位于不同的纵向位置。利用这种卓越的XUV波前控制并结合近焦点空间选择，我们通过实验证明了在不使用任何XUV光学元件的情况下，对XUV光束进行高效且可调节的光谱滤波，同时强烈抑制基波光束。将实验结果与模拟结果进行了比较，模拟给出了滤波对XUV场时间分布的影响。结果表明，阿秒结构得以保留，并且滤波后光束更加均匀，从而减少了纵向焦点的偏移。这是实现高XUV强度并以更高分辨率探测超快过程的重要一步。
