Above-threshold-dissociation dynamics ofH2+with short intense laser pulses

Abstract

A rigorous time-dependent wave-operator method within the Bloch formalism is presented and applied to the calculation of the photodissociation rate of ${\mathrm{H}}_{2}^{+}$ in intense pulsed laser fields. The wave packet is simultaneously propagated on the radiatively coupled ground and electronically excited potential-energy surfaces of the ion, combining a Lanczos reduction technique at low orders and recursive time-dependent Bloch operators. Dissociation rates are extracted from an asymptotic-flow analysis in the momentum space. The energy distributions of the protons, resulting from multiphoton absorption above the dissociation threshold, consist of a sequence of peaks spaced by half of the photon energy. The distribution of higher-energy peaks decreases with increasing intensity, due to stimulated emission from dissociating fragments. Time-resolved dynamics reached by ultrashort intense pulses (\ensuremath{\simeq}20-fs duration and peak intensity varying in the range from 3.5\ifmmode\times\else\texttimes\fi{}${10}^{12}$ to 3.5\ifmmode\times\else\texttimes\fi{}${10}^{14}$ W/${\mathrm{cm}}^{2}$) leads to a thorough interpretation of photon-exchange mechanisms between the field and the ion during the excitation and fragmentation steps.