Absolute measurement of a long, arbitrary distance to less than an optical fringe.

A scheme is proposed for high-precision, absolute length measurement for an arbitrary optical distance of a few meters to beyond 10(6) m. The approach utilizes a phase-stabilized femtosecond laser to provide both incoherent, time-of-flight information and coherent, fringe-resolved interferometry. Such a combined measurement capability allows an optical wavelength resolution to be achieved for absolute length measurement over a large dynamic range.