One-dimensional Molecular Alignment Induced By Femtosecond Laser Pulses

In this dissertation, post-pulse alignment of molecules irradiated by femtosecond laser pulse was studied both experimentally and theoretically. Intense laser pulses can align molecules due to the interaction between the laser electric field and the induced dipole moment of molecules. For femtosecond laser pulse, the laser pulse duration is shorter than the rotational period of the molecule, transient alignment can periodically be revived after the laser is off. Post-pulse alignment of a series of molecules was experimentally studied using the weak field polarization spectroscopy technique. An enhanced degree of alignment was also demonstrated by using two pulses with appropriate separation times. A pure heterodyne weak field polarization spectroscopy was developed to quantify the post-pulse molecular alignment. The pure heterodyne signal reflects the alignment parameter directly and its Fourier transform shows the population of rotational states. Finally multielectron ionization and Coulomb explosion of C2H4 irradiated by 110 fs, 800 nm laser pulses at an intensity of 1015 W/cm2 were studied and strong anisotropic angular distributions were observed for the atomic ions. Based on the results of two crossed linearly polarized laser pulses it is concluded that such anisotropic angular distributions result from dynamic alignment, in which the rising edge of the laser pulses aligns the neutral C2H4 molecules along the laser polarization direction before ionization.