With analog scanning, time-domain low-coherence interferometry lacks precise depth information, and optical carrier generation demands a linear scanning speed. Full-field heterodyne low-coherence interferometry that uses a logarithmic complementary metal-oxide semiconductor camera, acousto-optic modulation, and digital depth stepping is reported, with which random regions of interest, lateral and axial, can be accessed. Furthermore, nanometer profilometry is possible through heterodyne phase retrieval of the interference signal. The approach demonstrates inexpensive yet high-precision functional machine vision offering true digital random access in three dimensions. © 2006 Optical Society of America OCIS codes: 040.2840, 120.3180, 150.6910, 230.1040 In low-coherence interferometry (LCI), 1 typically consisting of a Michelson interferometer with a lowcoherence light source, interference is achieved only when the path lengths of the two interferometer arms are matched within the coherence length of the source. If the path length of one arm is linearly scanned, the result is an interference envelope with an optical carrier of maximum amplitude centered at the point of path length matching. Thus depth scanning and optical carrier generation are facilitated in one operation, and profiling is obtained by detection of the intensity envelope.Decoupling depth scanning from optical carrier generation by use of digital depth stepping and frequency shifting between two interferometer arms ( Fig. 1) by acousto-optic modulators (AOMs) offers improved functionality over its analog scanning counterparts in LCI. Random regions of interest (ROIs) can be directly accessed in depth and their precise axial positions known within the resolution of the digital stepper. Furthermore, a high-fidelity optical carrier, generated without electromechanical movement, permits the utilization of full-field interferometric phase measurement inside the coherence gate of the light source. Thus, further to the micrometer depth selectivity of LCI, full-field profilometry on a nanometer scale is achieved within the coherence envelope through phase retrieval of the interferometric signal.Heterodyne LCI was demonstrated, 2 but the system was single point and used analog depth scanning. A full-field phase-stepping approach to LCI was reported 3 ; however, in addition to burdensome calibration procedures, perturbations owing to electromechanical scanning are highly undesirable in nanoscale measurement. The use of differential phase contrast 4 in LCI has furthered the ability of optical coherence tomography 5 to achieve subwavelength cellular measurement. However, phase measurement through heterodyne interferometry offers superior precision and robustness against system temperature drift, vibrations, and random noise. 6 Previously, 7 this logarithmic complementary metal-oxide semiconductor (CMOS) camera was utilized in full-field LCI with analog depth scanning. The camera features random ROI pixel access in space and time at fast frame rates, and lateral...