非均匀激光场中氢分子离子高次谐波的增强

Enhancement of high-order harmonic generation from H_2^+ in near plasmon-enhanced laser field

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摘要通过数值求解非波恩-奥本海默近似下的一维含时薛定谔方程,研究了蝴蝶结型纳米结构基元中氢分子离子高次谐波的产生.研究表明,在蝴蝶结型纳米结构基元内部产生的非均匀场的空间位置对高次谐波的发射有较大影响.当非均匀场的空间位置从30 a.u.平移到-30 a.u.时,高次谐波的截止位置被延展且形成光滑的超连续的谐波谱,并应用时频分析方法、经典三步模型以及电离概率等解释了高次谐波发射的物理机理.研究了高次谐波谱对非均匀场空间位置的依赖性与载波包络值的关系,发现随着载波包络值的变化,非均匀场在不同空间位置处的高次谐波谱变化趋势相同. High-order harmonic generation （HHG） from the interaction among intense laserfields and atoms and molecules has attracted much attention. It is of the paramount importance and is still a rapidly growing field due to its potential to produce coherent and bright light within the uv and soft X-ray region and to generate attosecond pulses. Generally speaking, a typical spectrum of HHG shows that for the first few harmonics decrease rapidly, then present by a broad plateau of almost constant conversion e-ciency, and end up with a sharp cutoff. In a recent experiment, it is verified that the field enhancement induced around the bow-tie elements with a 20-nm gap allows the generation of extreme-ultraviolet light directly from the output of a single femtosecond oscillator of 100-kW peak power. With the development of the HHG in the vicinity of metallic nanostructure from atomic responses, the harmonic generation in the vicinity of metallic nanostructure from molecules has also been investigated. In this paper, HHG from H＋2 in bowtie-shaped nanostructure is investigated by solving the one-dimensional time-dependent Schr-dinger equation within the non-Born-Oppenheimer approximation by the splitting-operator fast-Fourier transform technique. We find that the spatial position of the inhomogeneous field inside the nanostructure has a great influence on the harmonic spectrum. When the spatial position of the inhomogeneous field is translated from 30 a.u. to-30 a.u., the cutoff of the HHG can be extended and the smoother supercontinuum harmonic spectrum is formed. The underlying physical mechanism can be well demonstrated by the time-frequency distribution, the three-step model, the ionization probability and electric field of the driving laser. The harmonic order as a function of the ionization time and emission time can be given by the semi-classial three-step model. The trajectory with an earlier ionization time but a later emission time as a long electronic trajectory, and the trajectory with a later ionization time b

作者罗香怡刘海凤贲帅刘学深

机构地区白城师范学院物理与电子信息学院吉林大学原子与分子物理研究所