Light-induced atom desorption for cesium loading of a magneto-optical trap: Analysis and experimental investigations

With the help of light-emitting diodes at the center wavelength of 470 nm, we demonstrate that light-induced atom desorption (LIAD) can be used for flexibly controlling the loading of magneto-optical traps (MOT) of cesium atoms. Under an ultralow background pressure in a quartz cell without any wall coating, we show that low intensity blue light can be used to control the loading rates (from 200 to 4000 atoms/s) and the number of cesium atoms (on the order of 10(4) in our experiment) in a MOT without the use of dispensers or any secondary atom source. A theoretical model based on an atom loading rate equation is built which can simulate the magneto-optical trap loading process with LIAD. The theoretical results are in agreement with experimental data. Some important parameters of the vacuum system are determined accordingly. The decay time of the vacuum pressure is about 70 ms, which is much shorter than the usual vacuum system for experiments on atomic ensembles. It is very difficult to measure such short times by the traditional fluorescence detection of cold atoms due to the slow loading process. The change of desorption rate (on the order of 10(13) atoms/s) for the different desorption intensities is also determined based on the background pressure caused by noncesium atoms in the cell. According to the experimental data and theoretical calculations, we obtain a partial pressure of about 1.4x10(-10) Torr for the untrapped cesium atoms and about 6.4x10(-10) Torr for the noncesium atoms at the moment the desorption light is turned off. The system is almost an ideal vacuum system for transferring atoms into another region for further experiments.