A symmetrical method of optical heterodyning of the doppler shifted signal has been developed possessingminimal instrumental spectral broadening and high SNR. These advantages can be gainfully employed in measuringturbulence structure using a cw laser. The method employs two beams incident on the moving scatterer. Thedoppler signal frequency is independent of the scattering angle and the signal possesses no receiving aperturebroadening. Typical values of signal-to-noise ratio are around 30 dB for a signal strength of 3 × 10-9 W. Optical alignment is simple. Relative merits of this technique compared to the localoscillator heterodyning method are briefly described.
M. K. Mazumder and D. L. Wankum, "SNR and Spectral Broadening in Turbulence Structure Measurement Using a cw Laser," Appl. Opt. 9, 633-637 (1970)