A retroreflective array (RRA) is an assembly of identical small corner-cube reflectors. An RRA breaks a beam of light into many sub-beams and redirects each of them back to itself, with only a small displacement. In effect, the RRA approximates a phase conjugator. It has the advantage of being completely passive and useable with incoherent light. Commercial corner-cube arrays are available with element apertures of approximately 0.15 mm, as well as larger sizes.
You-Zung Hsieh, Richard D. Sacks, and Michael D. Morris, "Furnace Atomic Absorption Spectrometry with a Retroreflective Array Optical System," Appl. Spectrosc. 42, 524-525 (1988)
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