Intensity Enhancement Investigation Of The High Harmonic Generated From Atom Irradiated By The Combined Laser Pulse

High-order harmonic generation(HHG)results from the radiation of high-intensity laser pulses of atoms or molecules.Currently,obtaining coherent light sources and synthesize attosecond pulses in the soft X-ray region can be accomplished successfully using HHG.The low radiation intensity of HHG is one of the major reasons limiting its application.Therefore,based on the numerical solution to the time-dependent Schrodinger equation method,this paper proposes to use a two-color field or a three-color field to improve the harmonic efficiency in a specific order or frequency range by controlling the motion of the ionized electrons that generate harmonics.Specifically includes the following two aspects :(1)Using two-color driving laser pulses with wavelengths of 1600 nm and 800 nm controls the efficiency of specific order harmonics.The 192 th harmonic efficiency can be seen to be 20 times better than the adjacent harmonic efficiency when the full width at half maximum(FWHM)is 310 and the amplitude ratio is 1.3: 1.The "three-step" model and time-dependent ionization probability analysis reveal that the reason for this improvement is that the combined field’s electron ionization rate is high at a particular moment and quickly returns to the parent ion recombination.On this basis,the effects of the phase of the two-color field,the FWHM,the amplitude ratio,the ionization probability and the wavelength on the harmonic enhancement are further analyzed.(2)Using three-color driving laser pulses with wavelengths of 1600 nm,800 nm,and 533 nm,the multi-order harmonic efficiency improvement is controlled.It is found that under the same FWHM,the 69 th order and 348 th order harmonic efficiencies are enhanced by nearly two orders of magnitude compared with the adjacent harmonic efficiency when the peak amplitudes of the three-color electric field are 0.13,0.1 and 0.086,respectively.Harmonic efficiency enhancements of approximately 150 harmonic orders in the frequency range from 299 to 443 are observed with a peak amplitude of 0.14 for the 533 nm laser and all other conditions held constant,an enhancement of 1 to 2 magnitudes over the neighbouring harmonics.The mechanism was examined using the "three-step" model and time-dependent ionization probability.Based on this,more analysis is done on how the driving laser’s wavelength,amplitude ratio,FWHM,and phase affect harmonic intensity.