Observation of laser-assisted elastic electron scattering by Ar in circularly polarized femtosecond laser fields

Laser-assisted electron scattering (LAES) by argon atoms driven by circularly polarized femtosecond near-infrared laser fields was studied using 1 keV electrons in the single-collision regime. Energy- and angle-resolved LAES signals were recorded with an angle-resolved time-of-flight spectrometer. A direct comparison of experimental results using linear, left-circular, and right-circular polarized lasers revealed a systematic decrease in LAES intensity under circular polarization. Numerical simulations based on Mittleman's extension of the Kroll-Watson theory reproduced the observed polarization dependence in both energy and angular distributions. No significant difference was found between left- and right-circular polarization within experimental uncertainty, in line with the theoretical prediction that the helicity-dependent contribution is negligible compared to the main term. These agreements confirm that the measured behavior is consistent with Mittleman's theory.