Resonant interactions of diatomic molecules with intense laser fields: time-independent multi-channel Green function theory and application to experiment

The resonant interactions of diatomic molecules with UV and VUV intense laser radiation are investigated within an original non-perturbative approach of multi-channel nuclear wave functions and Greenʹs functions. The interactions are considered in a quantum-electrodynamic picture where the laser field and molecule are treated as quantum objects. The presented theoretical approach is formulated as a multi-quantum technique to calculate analytically the resonant laser–molecule interactions and molecular photoprocesses. The method permits to include the non-linear impact of a resonant laser upon intra-molecular motion beyond an adiabatic approximation and may be applied for laser intensities until 1015 W cm−2. The theory of wave functions and Greenʹs functions of multi-channel Schrödinger equation is elaborated without perturbative restrictions on inter-channel couplings. The multi-channel quasi-classical approximation is developed to integrate the coupled equations for nuclear motion in simple matrix form. The theoretical approach proposed is used to study the intense-field photodissociation and photoabsorption, multi-photon resonant ionization and dissociation, dynamic polarizability and resonance Raman scattering from rotating diatomic molecules. The well-known laser-induced hardening and softening of intra-molecular bonds are reformulated. The new resonances in the molecular absorption, ionization and dissociation, arisen in resonant laser fields, are examined too. The phenomena of resonant laser field selective orientation and alignment of non-dipole diatomic molecules, laser-induced molecular dipole moment, temperature-dependent polarization of molecular gases, non-perturbative amplification of scattered laser radiation in resonant medium are analysed in detail. The known experimental observations of laser-induced non-linear effects and circumstances for new strong-field experiments are discussed.