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 gener ation and multiphoton ionization is investigated when the laser polari zation changes from linear to elliptical. The ellipticity dependence o f 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 compare d to that of the harmonics. This phenomenon is due to the fact that hi gh-harmonic generation is more strongly affected by the selection rule s than ionization, when polarization changes.