Numerical Simulation On High-order Harmonic Generation Of A Neon Atom Under The Intense Laser Pulse

As laser technology develops,it has been experimentally possible to produce high-intensity ultrashort laser pulse.By using such a strong laser pulse to interact with atoms and molecules,novel experimental phenomena,such as non-sequential double ionization,above threshold ionization,and high-order harmonic generation can be observed.The unique’platform’structure in the high-order harmonic generation is used to generate desktop coherent XUV light sources and generate optical pulses on ultra-short time scales.At present,influenced by low harmonic efficiency,its further application is limited,so it’s essential to do further research on the generation process.Based on the theory of strong field approximation and Maxwell’s equation system,this paper gives a systematic study of the high-order harmonic generation under the interaction between high-intensity laser pulse and the Ne atom.And the main contents are as follows:（1）The high-order harmonic emission spectrum of the Ne atom under laser pulse irradiation with a laser intensity of 1×10¹⁵W/cm²,a driving laser pulse width of 30 fs,and a wavelength of800nm was calculated.In addition to the odd harmonics that drive the laser frequency,new frequency peaks can be observed in the harmonic spectrum.Built on the analysis of the time-dependent evolution of the driving laser and the generation of harmonic at different spatial locations,it is found that these new spectral peaks are the results of intensity and frequency blueshift reduction during the propagation of the driving laser.By changing the position of the interaction of the gas medium and laser pulse,the gas density,and the length of the laser interaction with the gas,it’s found that it could be regulated for the specific energy harmonics and produce high-intensity harmonic generation at that frequency.（2）Under high-intensity laser irradiation,the harmonic emission spectrum of Ne atoms changes in steps with the pulse width of the driving laser.It was found that the new frequency of the harmonic emission spectrum deviated from the odd harmonic frequency and decreased with increasing pulse duration.The analysis of the driving laser at different transmission positions gives some evidence for this change.It indicates that by giving the shorter driving laser pulse,its frequency can see more changes after transmission.Therefore,it’s necessary to further study the influence of the changes of the driving laser wavelength on the harmonic emission spectrum.It was found that the harmonic emission spectrum did not change much under a 400 nm laser.But for a1200 nm driving laser,the harmonic emission spectrum showed a multi-peak structure.Through the analysis of the transmission of the driving laser field,it can be found that the 1200 nm driving laser is more moderately distributed in the radial direction after propagating,which in turn leads to the broadening of the harmonic spectrum.