Spectral Narrowing due to Elastic Collisions

V. A. Ulybin, V. P. Chebotaev

Veniamin P. Chebotayev, V. A. Ulybin

Jenny Lam, Duncan G. Steel, R. A. McFarlane

Mehmet Özgür Oktel, Leonid S Levitov

Optical excitations in a Bose gas are demonstrated to be sensitive to many-body effects. At low temperature the momentum relaxation is provided by momentum exchange collisions, rather than by elastic collisions. A collective excitation mode forms, which in a nondegenerate gas is manifest in a collision shift and dramatic narrowing of spectral lines. In the Bose-Einstein condensate state, each spectral line splits into two components. The doubling of the optical excitations results from the physics analogous to that of the second sound. We present a theory of the line doubling, and calculate optical absorption spectrum for a uniform density system.

А. П. Коузов

Решетов Владимир Александрович

Abstract Collision-induced stimulated photon echoes formed in a gaseous medium on the transition with the angular momentum change J a = 0 → J b = 1 under the action of ‘strong’ longitudinal magnetic field, when the echo pulse becomes unpolarized, are considered with an account of elastic depolarizing collisions. In the case of narrow spectral line the explicit expressions for the echo polarization density matrix and the degree of polarization are obtained. In the case of broad spectral line the results of the numeric calculations reproduce qualitatively the curve obtained in the experiments with ytterbium vapor.