Orientation-dependent strong-field dissociative single ionization of CO

The dissociative ionization of CO in orthogonally polarized femtosecond laser pulses are studied in a pump-probe scheme. The ionization of CO by the pump pulse and the dissociation of the created CO⁺ by the probe pulse can be fully disentangled by identifying the photoelectron momentum distributions. Different from the dissociative ionization by a single pulse in which the CO molecule mostly breaks along the field polarization, in this pump-probe strategy, the CO⁺ ion created from ionization by the pump pulse is favored to dissociate when it orients orthogonal to the polarization direction of the probe pulse. It is attributed to the laser-coupling of various electronic states of the molecular ion in the dissociation process, supported by the numerical simulation of a modeled time-dependent Schrödinger equation.