Abstract

A spectroscopic investigation is reported for a sample of Cesium atoms which are cooled and confined in a Zeeman shift spontaneous force optical trap.^(1'2) From measured absorption spectra for a weak probe beam both in steady state and under transient conditions, we infer that the sample consists of approximately 10⁶ atoms trapped in a spherical volume of radius 400µm and cooled to roughly 300µK. To explore the spectral response of this sample under conditions of strong excitation by the trapping laser beams ("pump" waves), we record transmission as a function of frequency for a low intensity "probe" wave focussed through the trap. As might be expected, we observe probe spectra with broad regions of absorption and amplification characteristic of the Autler-Townes splitting for a "dressed" two-state atom. However, additional narrow features around the pump frequency have linewidths of several hundred kilohertz (well-below the natural linewidth of 5MHz) and exhibit appreciable single pass gain (≥30%) . Our preliminary attempts to describe these features theoretically provide limited qualitative agreement with experiment. In an effort to correlate the spectroscopic characteristics of the trap with its mechanical properties, we have observed recoil of the trapped atoms either along or opposite to the direction of propagation of the probe beam depending upon whether the probe experiences absorption or gain. The direction of recoil can be switched with a change in probe detuning of less than 300kHz.

© 1990 Optical Society of America