Theory of the Line Shape of Resonance Scattering of Strong Radiation by a Two-Level Particle

Zhifang Deng, Shaul Mukamel

A non-Markovian microscopic theory for the spontaneous emission spectrum of a two-level atom driven by a strong laser field and undergoing dephasing via the interaction with a thermal bath is developed. The present theory is valid for an arbitrary correlation time scale of the bath relative to the linewidth and interpolates from the Markovian to the static limits. Model calculations using the stochastic line-shape function of Kubo show how the characteristic triplet spectrum is modified by the interaction with the bath. The present results generalize our previous studies of resonance Raman scattering in a three-level system in a strong radiation field.

R.Q. Hackett, George William Series

P. A. Hackett, R. A. Back

Shaul Mukamel, Danielle Grimbert, Yitzhak Rabin

We develop an expansion for the resonance Raman line shape of a three-level system $|a〉$, $|b〉$, and $|c〉$ in an arbitrary strong radiation field, being perturbed by dephasing collisions with foreign gas particles. The microscopic information relevant to the line broadening is expresssed in terms of a hierarchy of $n$-time correlation functions of the transition dipole operator ($n=2,4,6,\dots{}$). To lowest order ($n=2$) the spectrum is expressed in terms of the three ordinary line-shape functions corresponding to the $\mathrm{ab}$, $\mathrm{bc}$, and $\mathrm{ac}$ transitions. The present theory is not restricted to the impact limit and, depending on the collision time scale, may yield very different results from the well-known impact spectra. Explicit calculations of the predicted spectra are presented for a model system.

J L Steward, Ralph W. Parsons

A microwave bridge is described which permits radiation from two sources to be propagated through a gas and to be detected separately even when the sources are operating at the same frequency. This bridge is used to study the shape of the (J,K)=(3,3) inversion line in N 14 H 3 when the molecules are subjected to a strong resonant or near-resonant pumping field. The shape of the line is studied by measuring the absorption of a much weaker probe field. For sufficiently strong pump fields, power can be removed from the pump and transferred to the probe field, causing the latter to be amplified. The results are in quantitative agreement with theory. However, the development of a theory which satisfactorily includes the consequences of the degeneracy of the molecular energy levels has not yet been accomplished.

Oleg N. Gadomsky, V. R. Nagibarov