Application of optical frequency shifting by means of amplitude modulation in laserhyphen;Doppler velocimetry

摘要

A simple method of optical frequency shifting a laserhyphen;Doppler signal is described. The method employs a localhyphen;oscillator heterodyne system where the signal beam is modulated in amplitude by either a light chopper or a rotating linear polarizer disk. Photomixing the signal and reference beams at the photodetector will yield an output that will contain, among other terms, a term at the sum frequency of the Doppler and amplitude modulation frequencies. Due to the low frequency of amplitude modulation, this method is uniquely suited for frequency biasing of Doppler signals from scatterers moving at very low speeds.