Phase-contrast imaging of a dense atomic cloud

We demonstrate that phase-contrast imaging (PCI) can reliably reconstruct the in situ density profile even for highly spatially and optically dense samples. In our experiment, we achieve high spatial densities of up to 7.9 × 10¹³ atoms/cm³ and optical depths up to 64 in a dense cold atomic cloud of ⁸⁸Sr atoms. The use of a spatial light modulator instead of a fixed phase plate in the PCI setup provides enhanced flexibility and control of imaging parameters, making this imaging technique robust against imaging artifacts and adaptable to varying experimental conditions. Moreover, we quantify the conditions under which the standard single-atom polarizability model remains accurate for PCI in a density regime where collective effects should modify the atomic response of the system. We experimentally validate our statements by showing excellent agreement with time-of-flight measurements even at the highest densities. Our results establish PCI as a reliable and versatile method for characterizing spatially dense atomic clouds.