Effect of laser intensity on quantum trajectories in the macroscopic high-order harmonic generation**Project supported by the National Key Research and Development Program of China (Grant No. 2017YFA0403300), the National Natural Science Foundation of China (Grant Nos. 11627807, 11774175, 11534004, 11774129, and 11604119), the Fundamental Research Funds for the Central Universities of China (Grant No. 30916011207), the Jilin Provincial Research Foundation

Abstract

We macroscopically investigate the effect of the laser intensity and gas density on quantum trajectories in the high-order harmonic generation of Ne atoms irradiated by few-cycle, 800-nm laser pulses. The time–frequency profile of the harmonics shows that the long quantum trajectory is dominant at both lower and higher gas densities for a low laser intensity. At high laser intensities, the long quantum trajectory plays an important role for lower gas densities, while the short quantum trajectory is dominant at higher gas densities. An analysis of the phase mismatch for high-order harmonic generation shows that the primary emission of the quantum trajectories is determined by dynamic changes in the laser electric field during the propagation process.