High-order harmonic generation of CO and N₂ molecules under linearly- and bi circularly-polarized laser pulses by TD-DFT

Abstract

We present a method for high-order harmonics generation of N 2 and CO molecules under two-color circularly polarized counter-rotating laser pulses at frequencies of ω 0 and 2ω 0 . Pulse envelope in this investigation is sin-squared and the intensity of each laser beam is 2 × 10 14 W • cm −2 with ten-optical cycle (o.c.). We show that an isolated pulse with a pulse duration shorter than 20 attosecond from the superposition of several harmonics can be generated. Both two-color linearly-and bicircularly-polarized laser pulses are considered. Our results have also been compared with the outcomes of the previous theoretical works as well as experiment observations. It is found that for CO molecule, the bicircularly-polarized laser pulses are superior and more efficient, and it can generate narrower attosecond pulses than the linearly-polarized pulses. While for N 2 molecule, the two-color linearly-polarized pulses are more efficient, and it can generate narrower attosecond pulses than the bicircularlypolarized pulses. Furthermore, in order to demonstrate the origin of red-and blue-shifts in high-harmonic spectra, the effect of pulse duration on the high-order harmonics spectra is investigated. In addition, to obtain imaging on the temporal dependence of the electron densities, the time dependent electron localization function is used. Moreover, in order to study of the quantum trajectory of electrons, time-frequency analysis is utilized.

Symmetry analyses of high-order harmonic generation in monolayer hexagonal boron nitride

“…For the case of gas phase, circular harmonics can be generated by using counter-rotating bicircular laser fields for single atom and molecule [54,55] or by a single circularly polarized pulse for multiple-center molecules of proper symmetries [26]. Kfir et al [56] have reported that when the isotropic gas in a hollowcore waveguide is ionized by bichromatic counterrotating circularly polarized laser pulses, one can observe bright phase-matched circularly polarized harmonics with the disappearance of 3mth harmonics.…”

Influence of intensity ratio of the two driving laser fields on the cutoff of the high-order harmonics

“…To investigate the cutoff positions of HHG, we numerically solve a two-dimensional time-dependent Schrödinger equation (TDSE) of the helium atom driven by a BCCP laser field [20][21][22] (atomic units are used throughout this paper unless otherwise stated):…”