A portion of a first portion of light (13, 90, 90′) from a source of light (11) is masked by a mask (138), and the resulting masked first portion of light (90″) is combined using a beam splitter optic (136) with at least one second portion of the light (30) that had been subject to scattering by a medium (20, 20′, 20″). The mask (138) is configured so that interference patterns (104, 47) generated from the first and at least one second portions of light are substantially mutually exclusive even though those interference patterns (104, 47) would otherwise overlap one another absent the mask (138).