An interferometer (100, 200, 500) for sensing the displacement of an object, the interferometer comprising: a laser and optics portion including, a master laser (102, 214, 430, 602, 702) configured to generate a master laser beam, a slave laser (110, 212, 432, 604, 704) configured to generate a slave laser beam, and optical elements configured and arranged to direct only one of the master laser beam and the slave laser beam off of the object (152, 275, 452, 640, 770) and combine the master laser beam and slave laser beam to provide a sensing beat signal to a beat signal phase measurement loop (131, 261) and a reference beat signal to a reference phase lock loop (127, 255), the reference beat signal used at least in part to control the phase of the slave laser (110, 212, 432, 604, 704); and an electronic circuit portion coupled to receive the sensing beat signal and the reference beat signal, the electronic circuit portion including, a clock (142, 804), at least one numerically controlled oscillator (140, 144, 230, 220, 802) having a clock input coupled to the clock (142, 804), a first mixer (146, 240) having a first input coupled to receive the reference beat signal, a second input coupled to receive an output of the at least one numerically controlled oscillator (144, 220) and an output used to at least in part control the slave laser (110, 212, 604, 704), a second mixer (136, 540, 810) having a first input to receive the sensing beat signal and a second input to receive an output of the at least one numerically controlled oscillator (140, 230, 802), an interferometer output coupled to receive an output of the second mixer; at least one sensing heterodyne detector (124, 252, 253, 414, 610, 612, 734, 736, 730, 731), configured and arranged to provide the sensing beat signal; and at least one reference heterodyne detector (126, 250, 251, 420, 250, 251, 614, 616, 754, 756) configured and arranged to provide the reference beat signal. a laser and optics portion including, a master laser (102, 214, 430, 602, 702) configured to generate a master laser beam, a slave laser (110, 212, 432, 604, 704) configured to generate a slave laser beam, and optical elements configured and arranged to direct only one of the master laser beam and the slave laser beam off of the object (152, 275, 452, 640, 770) and combine the master laser beam and slave laser beam to provide a sensing beat signal to a beat signal phase measurement loop (131, 261) and a reference beat signal to a reference phase lock loop (127, 255), the reference beat signal used at least in part to control the phase of the slave laser (110, 212, 432, 604, 704); and an electronic circuit portion coupled to receive the sensing beat signal and the reference beat signal, the electronic circuit portion including, a clock (142, 804), at least one numerically controlled oscillator (140, 144, 230, 220, 802) having a clock input coupled to the clock (142, 804), a first mixer (146, 240) having a first input coupled to receive the reference beat signal, a second input coupled to receive an output of the at least one numerically controlled oscillator (144, 220) and an output used to at least in part control the slave laser (110, 212, 604, 704), a second mixer (136, 540, 810) having a first input to receive the sensing beat signal and a second input to receive an output of the at least one numerically controlled oscillator (140, 230, 802), an interferometer output coupled to receive an output of the second mixer; at least one sensing heterodyne detector (124, 252, 253, 414, 610, 612, 734, 736, 730, 731), configured and arranged to provide the sensing beat signal; and at least one reference heterodyne detector (126, 250, 251, 420, 250, 251, 614, 616, 754, 756) configured and arranged to provide the reference beat signal.