A significant enhancement of high-order harmonic generation by using a dipole gas

This paper presents an analytical study of high-order harmonic generation ( HHG) by quantum systems possessing permanent dipole moments (PDMs), such as atoms/molecules placed in a static electric field or polar molecules. HHG by conventional, non-PDM systems typically demonstrated a plateau in the en velope of harmonics followed by a steep fall in harmonic intensities when t he harmonic number exceeds a certain threshold. This paper shows that the H HG by PDM systems results in a significant extension of the plateau to high er frequencies and a slower decline of intensities at frequencies higher th aw the end of the plateau. Moreover. there occurs a substantial growth of t he total, summed intensity of all components of the scattering spectrum. Ot her physically interesting distinctive features of the HHG by PDM systems a re: the presence of both odd and even harmonics of the laser frequency in t he scattering spectrum; a tripler structure of both odd and even harmonics; and the appearance of a component at the doubled Rabi frequency (i.e. at a frequency much lower than the laser frequency). The results are obtained b y using the adiabatic basis for the analysis of a multi-quantum resonance i n a two-level system possessing PDMs.