Guiding of cold atoms by a red-detuned laser beam of moderate power

Abstract

We report measurements on the guiding of cold 87Rb atoms from a magneto-optical trap by a continuous light beam over a vertical distance of 6.5 mm. For moderate laser power (<85 mW) we are able to capture around 40% of the cold atoms. We systematically study the guided fraction as a function of laser power and detuning, and give an analytical expression that agrees well with our results. Although the guide is red detuned, the optical scattering rate at this detuning (≈70 GHz) is acceptably low. For lower detuning (<30 GHz) a larger fraction is guided but radiation pressure starts to push the atoms upward, effectively lowering the acceleration due to gravity.