Characteristics of dynamic alignment for diatomic and linear triatomic molecules in intense femtosecond laser fields

The process of dynamic alignment for diatomic and linear triatomic molecules is systematically investigated by solving numerically the rotation equation for angle θ between molecular axis and laser polarization direction in the high-frequency non-resonant regime. A two-step Coulomb explosion model of molecules in intense laser fields is used to determine the instant when molecular dynamic alignment is over. A counting approach and a fourth-order Runge-Kutta algorithm are used to calculate the angular distribution of molecules at a particular instant through solving numerically for a series of initial angle. Our computational results show that the majority of dynamic alignment for the light molecules N2, H2 and CO2 takes place before the molecule ionizes and begins to dissociate. However, for the heavy molecules Br2, I2 and CS2, the dynamic alignment occurs mainly during the process of molecular dissociation. The extent of molecular alignment tightly correlates not only with dynamic process of molecular Coulomb explosion, but also with molecular parameters and laser parameters. The effects of these factors to molecular dynamic alignment are extensively calculated and discussed.