Comparison Study On Atomic And Molecular Ellipticity Dependence Of High-Order Harmonic Generation

We systematically investigate ellipticity dependence of high-order harmonic generation of Ar and N-2 in intense elliptically polarized laser fields. The experimental normalized ratios of low-order harmonic intensity to high-order harmonic intensity increase with ellipticity for both Ar and N-2, and quantitatively depend on targets and trajectory paths. The experimental results are well reproduced by a nonadiabatic semiclassical simulation and explained by trajectory-based analysis. In addition, the influence of nuclear distance on the ratios is theoretically investigated. Our work reveals that the difference between atoms and molecules can be attributed to the influence of different ionic potentials, which depends on the molecular structure (internuclear distance) and alignment, on the evolution of the photoelectron.