A charge-coupled device ͑CCD͒ camera capable of taking high-quality images of ultracold atomic samples can often represent a significant portion of the equipment costs in atom trapping experiment. We have modified the commercial control software of a CCD camera designed for astronomical imaging to take absorption images of ultracold rubidium clouds. This camera is sensitive at 780 nm and has been modified to take three successive 16-bit images at full resolution. The control software can be integrated into a Matlab graphical user interface with fitting routines written as Matlab functions. This camera is capable of recording high-quality images at a fraction of the cost of similar cameras typically used in atom trapping experiments.

Multi-level gaseous atomic systems showing electromagnetically induced transparency (EIT) phenomenon also exhibit low light intensity nonlinear optical phenomena. This is primarily due to the supression of linear susceptibility for the probe light during EIT. Therefore under EIT, nonlinear interactions become appreciable even at very low light intensities. In particular, Kerr nonlinearity in N systems irradiated by three fields has been both experimentally and theoretically investigated. In this paper, we report an all optical observation of an absorptive three-photon resonance feature, of subnatural width, in a N level scheme of gaseous rubidium, at room temperature, in a novel geometry of three independent beams. The non-Doppler free configuration of the beam in which the absorption is seen is the first such feature reported in a beam that is not directly taking part in the transparency effect. We have demonstrated the velocity selective nature of this absorption and studied the contrast dependence on detuning from the fourth level. Density matrix calculations have been carried out for this geometry, the results of which are in qualitative agreement with the experiment.

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