Coherent correlation between nonadiabatic rotational excitation and angle-dependent ionization of NO in intense laser fields

Itakura, Ryuji; Hasegawa, Hirokazu*; Kurosaki, Yuzuru; Yokoyama, Atsushi; Oshima, Yasuhiro*

When neutral NO molecules are partly ionized in intense laser fields ( 35 TW/cm), a hole in the rotational wave packet of the remaining neutral NO is created by the ionization, whose rate depends on the alignment angle of the molecular axis with respect to the laser polarization direction. Rotational state distributions of NO are experimentally observed and then the characteristic feature that the population at higher levels is increased by the ionization can be identified. Numerical calculation for solving time-dependent rotational Schrodinger equations including the effect of the ionization is carried out. The numerical results suggest that NO molecules aligned perpendicular to the laser polarization direction are dominantly ionized at the peak intensity of = 42 TW/cm, where the multiphoton ionization is preferred rather than the tunneling ionization.