Abstract
When a non-cooperative target is at a distance within the coherence length of a laser, the backscattered light induces modulation signals in the laser power output that can be used for velocimetry and ranging. Backscatter modulation in semiconductor laser diodes has had little practical impact in laser radar because the coherence length of these devices has restricted their operational range to about 2 m. In the present work, we report experimental measurements of absolute range using a backscatter-modulation laser radar in an external cavity whose length is varied by piezo-electric transducers. The laboratory demonstration system operates at 0.5 mW, has an operational range of 40 m and is sensitive to backscattered light levels of less than 10 pW. The extended operational range and high sensitivity of the external-cavity geometry make this simple, compact, low-power laser radar a practical alternative to heterodyne detection for many applications.
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