Interaction of atoms with electromagnetic radiation

K. T. Hecht

J. Michael Hollas

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.

Umberto Lucia, Giulia Grisolia

In the environment, there exists a continuous interaction between electromagnetic radiation and matter. So, atoms continuously interact with the photons of the environmental electromagnetic fields. This electromagnetic interaction is the consequence of the continuous and universal thermal non-equilibrium, that introduces an element of randomness to atomic and molecular motion. Consequently, a decreasing of path probability required for microscopic reversibility of evolution occurs. Recently, an energy footprint has been theoretically proven in the atomic electron-photon interaction, related to the well known spectroscopic phase shift effect, and the results on the irreversibility of the electromagnetic interaction with atoms and molecules, experimentally obtained in the late sixties. Here, we want to show how this quantum footprint is the "origin of time". Last, the result obtained represents also a response to the question introduced by Einstein on the analysis of the interaction between radiation and molecules when thermal radiation is considered; he highlighted that in general one restricts oneself to a discussion of the energy exchange, without taking the momentum exchange into account. Our result has been obtained just introducing the momentum into the quantum analysis.

Robert P. Lucht

The subject of this chapter is the quantum mechanical analysis of the interaction of electromagnetic radiation with atomic transitions. The analysis is based on the Schrödinger wave equation, and in the first section, the gauge-invariant form of the external electromagnetic field is introduced. The electric dipole interaction and the long-wavelength approximation for the analysis of this interaction are discussed. The perturbative analysis of both single-photon and two-photon electric dipole interactions is presented, and density matrix analysis is introduced. The interaction of radiation with the resonances of atomic hydrogen is then discussed. The analysis is performed for both coupled and uncoupled representations. In the last section of the chapter, the radiative interactions for multielectron atoms are discussed. The Wigner–Eckart theorem and selection rules for transitions between levels characterized by coupling are developed. The effect of hyperfine splitting on radiative transitions is also briefly discussed.

Igor I Sobel'man