关键词: 中红外飞秒激光/
高次谐波/
分子多轨道干涉
English Abstract
Signature of multi-channel interference in high-order harmonic generation from N2 driven by intense mid-infrared pulses
Li Gui-Hua1,Xie Hong-Qiang2,
Yao Jin-Ping3,
Chu Wei3,
Cheng Ya3,
Liu Xiao-Jun4,
Chen Jing5,
Xie Xin-Hua6
1.School of Science, East China Jiatong University, Nanchang 330013, China;
2.School of Science, East China University of Technology, Nanchang 330013, China;
3.State Key Laboratory of High Field Laser Physics, Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, Shanghai 201800, China;
4.State Key Laboratory of Magnetic Resonance and Atomic and Molecular Physics, Wuhan Institute of Physics and Mathematics, Chinese Academy of Sciences, Wuhan 430071, China;
5.Institute of Applied Physics and Computational Mathematics, Beijing 100088, China;
6.Photonics Institute, Vienna University of Technology, A-1040 Vienna, Austria, EU
Fund Project:Project supported by National Basic Research Program of China (Grant Nos. 2014CB921300, 2013CB922201), the National Natural Science Foundation of China (Grant Nos. 11127901, 11134010, 61575211, 11304330, 11404357, 61405220, 11274050, 11334009, 61605227), and the Shanghai Sailing Program, China (Grant Nos. 14YF1406100, 16YF1412700).Received Date:30 August 2016
Accepted Date:13 October 2016
Published Online:05 November 2016
Abstract:Recently, three major types of minima (i.e., Cooper-like minimum, two-center interference minimum and multi-channel interference minimum) have been observed in high-order harmonic generation (HHG) spectra. Identification of the origin of the minimum in a HHG spectrum is critical for self-probing of the molecular structures and dynamics, which has been an important subject in attosecond physics. In this paper, we report the investigation of the multi-electron dynamics in HHG from N2 molecules driven by intense mid-infrared laser pulses. Based on a pump-probe experimental setup, clear spectral minima in the cutoff region of high harmonic spectra from N2 molecules are observed in measurements with mid-infrared laser pulses at three wavelengths (i.e., 1300, 1400 and 1500 nm). A systematic investigation has been carried out for clarifying the origin of these minima. We carefully measured the spectral minima under three different experimental conditions:1) different alignment angles of molecules; 2) various peak laser intensities; 3) tunable driving laser wavelengths. Experimental results show that the positions of the spectral minima do not depend on the alignment angles of molecules. In addition, the measured spectral minima shift almost linearly with the laser intensity for all three wavelengths, and the positions of the spectral minima strongly depend on the wavelengths of the driven field. These findings are in conflict with the Cooper-like and two-center interference minima predictions, providing strong evidences on the dynamic multi-channel interference origin of these minima. Besides, we theoretically calculated the positions of multi-channel interference minima by using a classical three-step model and found out perfect agreements between the experimental results and theoretical calculations, which again strongly support the multi-channel interference picture. Moreover, the advantages of the observed dynamic multi-channel interference based on HHG driven by long wavelength lasers are discussed. The long wavelength driver lasers are attractive for not only generating coherent XUV radiation and attosecond pulses, but also investigating structures and dynamics of molecules in strong laser fields.
Keywords: mid-infrared femtosecond laser pulses/
high-order harmonic generation/
multi-channel interference of molecules
