Nonlinear variations affecting the widths and positions of laser-induced resonances in the molecular-dissociation process are discussed as a function of the electromagnetic field intensity. It is shown how the close-coupled equations of quantum scattering theory, taking into account multiphoton absorption and emission processes through the time-independent Floquet Hamiltonian, go beyond the widely used weak-field Fermi golden rule approximation. For the intermediate-field regime adiabatic electron-field channels can, in some cases, serve as a guide for the interpretation of nonlinearities, while for higher laser intensities very large field-induced mixings between molecular states predominate, requiring the introduction of an increasing number of Floquet blocks for converged calculations. The formalism is applied to the photodissociation of ${\mathrm{H}}_2^{+}$(1s${\mathrm{\sigma }}_{\mathrm{g}}$, v=0, J=1→2p${\sigma }_u$). Nonlinear effects appear for intensities larger than ${10}^{11}$ W/${\mathrm{cm}}^2$, for which experiments begin to be available.

• Received 1 March 1988

DOI:https://doi.org/10.1103/PhysRevA.38.5586