Exploration of spectral and temporal fine structures of high-order harmonic generation

Synopsis We present an ab initio precision investigation of the time-frequency characteristics of high-order harmonic generation (HHG) calculated by solving accurately and efficiently the time-dependent Schrodinger equation by means of the time-dependent generalized pseudospectral method. We extend a new synchrosqueezing transform (SST) to obtain the time-frequency spectra of the HHG and the dynamical phase associated with the dipole-emission time profile. The SST time-frequency analysis allows us to explore the in depth dynamics and contributions of the multi-rescattering trajectories and resonant trajectories in HHG. It also exhibits the subtle details of the spectral and temporal fine structures of the HHG, providing novel insights regarding the dynamical origin of the HHG in below-and above-threshold regimes.