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A semi-classical optimization model is introduced for controlling the high-order harmonic generation process and extending the cutoff frequency. This method is capable of defining the driving laser shape interact with the F2 molecule for maximizing the cutoff frequency properly. This optimization procedure is evaluated by examining the high harmonic spectrum from the F­2 molecule irradiated by a two-color laser field. High harmonic spectrum is done using time-dependent density functional theory in a three-dimensional space. The results showed that adding two driving laser pulses with optimization could enhance the cutoff frequency by 96% compared to two driving laser pulses without optimization. In addition, this model for the F2 molecule is capable of reducing the output attosecond pulse duration from 200 as not optimized two-color laser to 135 as the optimized two-color laser.

In this paper, high-order harmonic generation by a bicircular field, which consists of two coplanar counterrotating circularly polarized fields of frequency ω and 3ω, is investigated for bromine (Br2) molecule. This field possesses dynamical symmetry, which can be adapted to the symmetry of the highest occupied molecular orbital (HOMO) and used to investigate the molecular symmetry. An accurate three dimensional(3D) calculation of molecular dynamics through time dependent density- functional theory (TDDFT)is considered to explore broad harmonic plateau with high efficiency. We show that an attosecond pulse with a pulse duration of 349as from the superposition of several optimum harmonics is generated. Furthermore, in order to study of the quantum trajectory of electrons, time-frequency analysis is utilized. This work is proved to be a potential way for applications in coherent imaging and photoelectron spectroscopy.