Fig. 1. Calculated energy distribution of free electrons in the case of (a) linearly (ε=0) and (b) circularly (ε=1.0) polarized laser pulses with an intensity of 1.4×1014  W/cm2, and the average electron energy with varying laser intensities with (c) linear and (d) circular polarizations.

Fig. 2. Fluorescence emission due to the decay of excited molecule N2 (380.4 nm) and molecular ion N2+ (391.3 nm) generated by linearly (black line) and circularly (red dot line) polarized laser pulses for intensities of (a) 0.1×1014 and (b) 1.0×1014  W/cm2, respectively. (c) and (d) show the intensity of the fluorescence emission at 380.4 and 391.3 nm generated by linearly (square black solid line) and circularly (circle red dot line) polarized laser pulses with varying intensities, respectively.

Fig. 3. Intensity ratio γ at 380.4 and 391.3 nm with varying laser intensities from Ip=0.1×1014 to 2.4×1014  W/cm2.