Measuring beat frequency variations between two single mode lasers for distance measurement - sweeping wavelength of at least one laser and measuring and evaluating resulting phase angle change

摘要

The method involves influencing the frequencies of the lasers using acoustic optical modulators to operate a superheterodyne interferometer whose periodic output signal's phase depends on the reflector distance and beat frequency. The wavelength of at least one laser is tuned monotonically over a defined range to cause a monotonic change in beat frequency. The resulting phase angle variations and the total phase change are recorded. The beat frequency change is obtained using a simple algorithm taking account of signal propagation speed. An absolute distance measurement is obtained using two interferometers. USE/ADVANTAGE - For exact measurement of beat frequency of two single mode lasers and high resolution distance measurement.