Opt Lett. 2018 Sep 15;43(18):4433-4436. doi: 10.1364/OL.43.004433.
We extend a recently demonstrated scheme [Optica4, 976 (2017)OPTIC82334-253610.1364/OPTICA.4.000976] to overcome the limit of conventional harmonic cutoff for different pulse durations, laser wavelengths, and gas targets. By tuning the truncation of long wavelength lasers, we show that the defocusing-assisted phase matching (DAPM) can be achieved in a tightly focused beam and highly ionized short gas cell, and can be used to effectively extend the harmonic cutoff energy and optimize its yield. An analysis of phase matching reveals that at longer wavelengths, greater cutoff extension to the water window region is achieved because of the larger harmonic intrinsic phase (proportional to the cube of laser wavelength), and because DAPM works at relatively higher laser intensities using a Ne target. This scheme provides a promising method for efficiently generating intense attosecond light sources in the extreme ultraviolet to x-rays.
我们扩展了最近提出的一种方案[Optica4, 976 (2017) OPTIC82334-253610.1364/OPTICA.4.000976]，以克服传统谐波截止限制，实现不同脉冲持续时间、激光波长和气体靶的应用。通过调整长波长激光的截断，我们表明，在强聚焦光束和高离化短气体池中可以实现离焦辅助相位匹配（DAPM），并可用于有效扩展谐波截止能量并优化其产率。相位匹配的分析表明，在较长波长下，由于更大的谐波固有相位（与激光波长的立方成正比），以及使用氖靶时 DAPM 在相对较高的激光强度下工作，因此可以实现更大的水窗区域截止延伸。该方案为在极紫外到 X 射线区域高效产生强阿秒光源提供了一种有前途的方法。
