Ganeev Rashid A, Boltaev Ganjaboy S, Kim Vyacheslav V, Guo Chunlei
The Guo China-US Photonics Laboratory, State Key Laboratory of Applied Optics, Changchun Institute of Optics, Fine Mechanics and Physics, Chinese Academy of Sciences, Changchun 130033, China.
The Institute of Optics, University of Rochester, Rochester, NY 14627, USA.
Nanomaterials (Basel). 2019 Apr 8;9(4):572. doi: 10.3390/nano9040572.
The application of nanoparticles (NPs) and quasi-phase matching (QPM) each play an important role in the enhancement of high-order harmonics (HHG) of ultrashort laser pulses. We analyze various regimes of nanoparticle plasma formation for the creation conditions for maximal QPM-induced enhancement of the groups of harmonics in the extreme ultraviolet (XUV). Laser plasmas were formed on the surfaces of NPs- and microparticle (MPs)-contained targets using ablation by nanosecond, picosecond, and femtosecond pulses. Different conditions of laser plasma formation (extended and perforated plasma) and variable concentrations of free electrons in these three cases of laser ablation led to modifications of QPM conditions. We demonstrate novel approaches in the optimization of QPM at the conditions of laser ablation of NPs and MPs by pulses of different durations. The formation of QPM conditions using femtosecond and picosecond heating pulses during HHG in such plasmas allowed the growth of conversion efficiency of the groups of harmonics, with the enhancement factors exceeding 25× in different ranges of XUV, contrary to less efficient QPM in the case of nanosecond pulse-induced ablation.
纳米颗粒（NPs）的应用和准相位匹配（QPM）在增强超短激光脉冲的高次谐波（HHG）方面均发挥着重要作用。我们分析了纳米颗粒等离子体形成的各种状态，以确定在极紫外（XUV）波段实现由QPM引起的最大谐波群增强的产生条件。利用纳秒、皮秒和飞秒脉冲烧蚀，在含有NPs和微粒（MPs）的靶材表面形成激光等离子体。在这三种激光烧蚀情况下，不同的激光等离子体形成条件（扩展等离子体和穿孔等离子体）以及自由电子的可变浓度导致了QPM条件的改变。我们展示了在不同持续时间脉冲对NPs和MPs进行激光烧蚀的条件下优化QPM的新方法。在这种等离子体中的高次谐波产生过程中，使用飞秒和皮秒加热脉冲形成QPM条件，可使谐波群的转换效率提高，在不同的XUV波段增强因子超过25倍，这与纳秒脉冲诱导烧蚀情况下效率较低的QPM情况相反。
