A semiadiabatic treatment of the matter-field coupling is presented that accounts for the nonlinear variations affecting the widths and positions of laser-induced resonances in photodissociation as a function of the electromagnetic-field intensity. The procedure developed here goes beyond the widely used decoupled electronic-plus-field adiabatic treatment by retaining two ‘‘semiadiabatic’’ potentials that result from partial diagonalization of several blocks in the Floquet Hamiltonian. All closed channels lead to a unique multiphoton-dressed adiabatic closed channel that crosses a unique dressed adiabatic open channel. The remaining nondiagonal interaction is treated diabatically within a two-coupled-channel frame. The relative merits of diabatic approximations and of the semiadiabatic scheme are discussed within a large range of laser intensities and wavelengths on the example of ${\mathrm{H}}_2^{+}$(1s${\mathrm{\sigma }}_{\mathit{g}}$, v=0, J=1→2p${\mathrm{\sigma }}_{\mathrm{u}}$) photodissociation. Uniformally accurate results are reached for the semiadiabatic approach. This is very promising for studying field-induced nonlinearities for very intense lasers operating at rather short wavelengths where many electronic states including rotational structures may play a role.

• Received 3 May 1990

DOI:https://doi.org/10.1103/PhysRevA.42.1585