A perturbative description of coherent multiphoton resonant processes

Nikolai B. Delone

The most important results of study of multiphoton ionization of atoms are reviewed. Discussions are presented of specific features of the process, theoretical methods of description of ionization of atoms in a strong light field, the basic principles of design of experiments in which intense laser radiation is used, results of investigation of direct and resonance processes of multiphoton ionization, and the mutual relation between multiphoton processes (multiphoton excitation and ionization) and various phenomena leading to perturbation of the spectrum of bound states of an electron in an atom under the influence of a strong light field.

A. T. Georges, P. Lambropoulos

Deepak Srivastava

A recently proposed collisional time-correlation function method for resonance laser–target interactions in molecular targets is modified and extended to include time-delayed multiphoton processes in the dynamics. The explicitly time-dependent laser and target dynamics in this method is separated into laser electric field and molecular target dipole/susceptibility correlation functions. The first and second order laser field correlation functions, also known as Glauber field correlation functions, are evaluated in a continuum mode description of photon number representation for both resonance and time-delayed multiphoton processes. We show that such a description allows for the incorporation of laser pulse shape and phase coherence in the formalism, while the laser–target interaction dynamics is still described similarly to the resonance single- and multiphoton processes. As an example, the transition rates for a two-photon Gaussian pump–probe dynamics are derived in which we show that the phase coherence between the Gaussian pump and probe pulses can be incorporated and controlled through a single delay-time-dependent parameter.

Michele Crance

R. Wallace

Ashat M. Basharov

Resonant interactions of a coherent field with an anharmonic oscillator are classified based on the established analogy with multiphoton interactions of light with atoms. It is shown that interference interactions in which the absorption of a single coherent field quantum induces a multiphoton transition in the anharmonic oscillator are superpositions of resonances of the “cascade” and “lambda-V” types, and a general description of these resonances is given. For the third- and fourth-order nonlinearities, the general expressions are applicable to a resonant process with the absorption of a single photon and the double excitation of the oscillator. Resonant processes of the second harmonic generation and “rectification” of radiation are predicted and described; experimental investigation of these processes will provide information about anharmonicity parameters in the proposed model.