Theoretical Simulation of the High-Order Harmonic Generated from Neon Atom Irradiated by the Intense Laser Pulse

Based on the strong field approximation theory and numerical solution of Maxwell's propagation equations, the high-order harmonic is generated from a neon (Ne) atom irradiated by a high-intensity laser pulse whose central wavelength is 800 nm. In the harmonic spectrum, it is found that in addition to the odd harmonics of the driving laser, a new frequency peak appeared. By examining the time-dependent behavior of the driving laser, it is found that the symmetry of the laser field is broken. We demonstrated that these new spectrum peaks are caused by the intensity reduction and frequency blue shift of the high-intensity laser during propagation. Our results reveal that it is feasible to modulate the harmonics of the specific energy to produce high-intensity harmonic emission by changing the gas density and the position of the gas medium interacting with the laser pulse.