On radiation emission by an atom under a sudden perturbance

S. Rajasekar, R. Velusamy

This chapter discusses the time-dependent perturbation theory applicable for small time-dependent perturbation. The incident electromagnetic wave makes the electric and magnetic potentials to oscillate and the perturbation is usually very small compared with the static Hamiltonian. The theory of time-dependent perturbation was developed by Dirac in 1927. Approximation methods are developed for systems where the time dependence of the Hamiltonian is small, slowly varying or rapidly varying. These correspond to perturbation, adiabatic and sudden approximations. An interesting consequence of sudden approximation is that the system can undergo an adiabatic change due to the sudden approximation. The rate of spontaneous emission is proportional to the number of atoms in the excited state. In the stimulated emission, an incident radiation of appropriate frequency induces an atom in an excited state to emit radiation. In the case of time-dependent perturbations, the system undergoes transition from one state to another during the action of the perturbation.

G.E. Notkin, Sergey G. Rautian, A. A. Feoktistov

M. D. Anosov

V. I. Matveev

A general expression for the spectrum of photons emitted by atom at sudden perturbation is obtained. Some concrete examples of application of the obtained result are considered. The conclusion about the coherence of radiation of the atomic electrons under the such influences is made. PACS numbers: 32.30.*

V. I. Matveev

Electron transitions and the spectrum of radiation emitted by an atom interacting with an ultrashort electromagnetic pulse are studied based on the sudden perturbation approximation. The excitation and ionization probabilities, the spectra of pulse reradiation by the atom, and the reradiation cross sections are calculated. It is concluded that the reradiation of ultrashort electromagnetic pulses by multielectron atoms is of a coherent nature.

E.I. Aliskenderov, A. S. Shumovskiǐ, Ho Trung Dung