1. An apparatus, comprising: an array of radiation-absorbing regions supported on a substrate and having first and second pluralities of radiation-absorbing regions, wherein, for each radiation-absorbing region of the first plurality, the region's position with respect to the substrate is responsive to an amount of radiation incident on the region; and an array of reflecting regions, each reflecting region being rigidly fixed to one of the radiation-absorbing regions and being adapted to reflect a respective portion of an interrogating beam of light to form a respective portion of a reflected beam, the array of reflecting regions being adapted to impart onto the reflected beam a spatial phase modulation pattern that corresponds to a spatial intensity pattern of the radiation incident on the array of radiation-absorbing regions.