Alignment effects of NO in femtosecond laser field

The laser-induced alignment effects of NO in linearly polarized femtosecond laser field within the intensity order of 1014 W/cm2 at 820 nm have been investigated experimentally by using velocity mapping technique. The angular and velocity distributions of fragment ions with different charge numbers are measured. The alignment degrees increased with the charge numbers, and were nearly independent of the laser intensities. Our results indicate the geometric alignment dominates before the ionization of NO into NO2+, while the dynamic alignment of the molecular ions dominates after the ionization.