Chirped synthetic-wavelength interferometry

We demonstrate distance measurement by varying, or chirping, the synthetic wavelength in a two-color laser diode interferometer. An absolute accuracy of 3 microm is achieved over a 200-mm range, without the phase ambiguities or optical complexities normally associated with synthetic-wavelength interferometry. The fibercoupled experimental system uses a 25-microW, 0.25-mm-diameter collimated object beam and can be used for dimensional gauging and rough-surface profiling.