Geometric alignment of CH3I in an intense femtosecond laser field

Strong anisotropic angular distributions of the atomic ions Im+ (m = 1-6) and Cn+ (n = 1-2) have been observed when CH3I is irradiated by 110 fs, 810 nm laser pulses at an intensity of 1015 W/cm2. A comparison was made of the fragmental ions between the linearly polarized laser pulses and circularly polarized laser pulses, and the variation of the angular widths for different charged exploding ions was studied. Moreover, a double pulse experiment with crossed polarization was also performed. The results clearly demonstrate that a geometric alignment is the dominant mechanism for CH3I under the experimental conditions.