Experimental investigation of the ellipticity dependence of high-harmonic generation and ionization in argon in the multiphoton regime

In the multiphoton regime, the correlation between high-harmonic generation and multiphoton ionization is investigated when the laser polarization changes from linear to elliptical. The ellipticity dependence of high harmonics and ion signal is measured experimentally. Both high harmonics and ion signal decrease with increased ellipticity at fixed laser intensity, but the decrease in ion signal is much slower compared to that of the harmonics. This phenomenon is due to the fact that high-harmonic generation is more strongly affected by the selection rules than ionization, when polarization changes.