报告题目: Nonlinear propagation effects of high-order harmonics generated from a macroscopic gaseous medium

报告时间: 11月28日（周五）上午9：30

报告地点：1号楼1楼108会议室　　

Abstract:

　　High-order harmonic generation (HHG) has been a promising way to retrieve the atomic or molecular structure and to produce single attosecond pulse or attosecond pulse trains. In this talk, I will focus on a few hot topics of HHG from the theoretical point view. First, I will show that the harmonic yield can be enhanced by one to two orders of magnitude if the laser’s waveform is optimized by synthesizing two- or three-color fields compared to a sinusoidal wave without an increase in the total laser power [1]. The optimization scheme is carried out by genetic algorithm, which is accomplished by adjusting intensities of lasers and relative phase between them with the consideration of macroscopic propagation effects. This paves a way to make high harmonics feasible in the near future as general bright tabletop light sources. And then, I will show that for the first time the observed HHG spectra of atoms and molecules can be accurately reproduced theoretically when precise experimental conditions are known. The macroscopic HHG can be expressed as a produce of a macroscopic wave packet and a photorecombination cross section, where the former depends on laser experimental conditions while the latter is the property of target atoms or molecules. The factorization makes it possible to retrieve microscopically atomic or molecular structure information from the measured macroscopic HHG spectra [2]. In the end, I will discuss the contributions from multiple molecular orbitals of aligned N2 molecules when the generating pulse is perpendicular to the aligning one, the generation of a single attosecond pulse by using a spatial filter centered on axis to select the harmonics in the far field with different divergence at the saturation regime, and harmonic generation using a truncated Bessel spatial beam [2].

　　[1] C. Jin, G. Wang, H. Wei, A. T. Le, and C. D. Lin, Waveforms for optimal sub-keV high-order harmonics with synthesized two- or three-colour laser fields, Nature Communications 5, 4003 (2014).

　　[2] C. Jin, Theory of Nonlinear Propagation of High Harmonics Generated in a Gaseous Medium, Springer Theses, Springer (2013).

CV:

　　Cheng Jin received the B.S. and M.S. degrees in Physics from Northwest Normal University, Lanzhou, Gansu, China, in 2003 and 2006, respectively and the Ph.D. degree in Physics from Kansas State University, Manhattan, Kansas, USA, in 2012.

　　Dr. Jin is currently a Research Associate in the Department of Physics at Kansas State University. His research is mainly about the strong-field physics, attosecond science, and ultrafast optics from the theoretical aspects, specifically including the development of macroscopic propagation model for high harmonics, the waveform synthesis for improving harmonic efficiency, the generation of an isolated attosecond pulse, the harmonic generation in a hollow waveguide, the photoionization of aligned molecules with high-harmonic light, and the molecular tunneling ionization.