Noise reduction in absorption imaging for quantum gases experiments

Abstract

In many experiments with quantum gases, the information about the final state of the system is extracted by the density profile of the cloud. One of the most common techniques used to image the cloud is absorption imaging, which is limited by various kinds of noise. One of the main sources of noise is the presence of fringes that originates from vibrations in the experiment. In our case, the problem is increased by the presence of an optical cavity around the atoms which diffracts the imaging light. These fringes can be eliminated by appropriate fringe-removal algorithms. We show that these algorithms reduce the noise down to being close to the limit imposed by the CCD camera. We also analyse some patterns that persist in the optical density after removing the fringes. We relate these patterns to shifts of the atomic cloud or of the imaging system between different runs of the experiment and to diffraction by the atoms and the cavity.