Absolute optical ranging with 200-nm resolution

Absolute optical ranging has been demonstrated by wavelength-multiplexed interferometry with a range resolution of 200 nm, well below the single-wavelength ambiguity. Two current- and temperature-tunable GaAlAs laser diodes (850 nm) provide an equivalent wavelength below 100 microm and a resolution of less than 200 nm. The achievement of such resolution provides the means for combining single- and multiple-wavelength interferometric measurements to achieve unambiguous distance measurement with nanometer resolution. The ranging system is also used to profile unambiguously an integrated circuit structure with a 2.5-microm surface topography.