Abstract: The disclosure is directed to a method and apparatus for precisely controlling the frequency of a laser, and for precise control of distance. In a disclosed embodiment, a laser beam is split, modulated to obtain a frequency differential, and coupled to an interferometer which is designed to produce two processed beams having intensities that vary at the same ac frequency, but at a phase difference that is indicative of the laser frequency. The processed beams are converted to ac electrical signals which are coupled to phase control circuitry. The phase control circuitry determines the phase between the electrical signals and produces a control signal for controlling the laser frequency. Phase offset increments are introduced in the phase detection process, these phase offset increments resulting in controlled changes in the laser frequency. The laser frequency can be computed and read out as a function of the phase offset increments.