Optical mask for laser-cooled atoms

An optical mask is a standing wave of light in resonance with an open atomic transition. The mask depletes the population of the initial internal state everywhere except in a narrow vicinity of the nodes. We have experimentally explored the optical mask as a tool for creating a periodic pattern in the density of cold rubidium atoms (in a particular hyperfine ground state) and also as an instrument for imaging the density in situ. The instrumental width of the imaging technique is a small fraction of the optical wavelength and is limited due to an effect of the dipole force rather than the initial velocity spread.