Ranging and velocimetry signal generation in a backscatter-modulated laser diode.

A compact self-aligning laser radar has been constructed for coheren ranging and velocimetry using a laser diode modulated by feedback from light scattered from a diffusing target. The phenomenology of beat-signal generation in the device is discussed from both experimental and theoretical points of view. The ac-coupled modulation waveform is asymmetric (similar to a sawtooth) and different for the two propagation directions of the light leaving the diode. Atheoreticalmodel, based on the mode structure ofathree-mirrorFabry-Perot cavity, describes signal generation in these experiments and accounts for the asymmetric waveform.