of the target object from the laser diode where a is a parameter associated with the system operation in this case the modulation comprises the chirp induced modulation frequency and the spatial information computed includes the distance range of the target from the diode the range is computed easily from the frequency modulation in the laser emission the parameter a 2f cx dx dt where f is the optical frequency x is cavity length and dx dt refers to the slope of the triangular wave oscillation of the reflector the parameter is readily determined empirically by observing the modulation frequency f r for a known target distance as pointed out above it may be necessary to tune the system to prevent mode switching also the chirp frequency may be detected but is not necessarily of direct interest and may be discarded by the processor a system breadboard for range was composed of a 40 mw maximum rated power index guided diode a 8 6 mm focal length 0 5 numerical aperture lens 48 a piezo actuated external cavity mirror of 40 reflectively and a 750 mm focal length simple lens 52 of 18 mm clear aperture the 10 cm external cavity length was varied over 0 6 microns at 20 hz using a piezoelectric transducer driven by a triangle wave voltage modulation a spectrum analyzer measured the frequency content of the signal produced by the photodetector the diode was operated near threshold to take advantage of the modulation depth enhancement the integrated output power of the radar breadboard under these conditions was 0 5 mw despite the low power level and the small size 18 mm of the collection aperture 56 the radar operated reliably for a wide variety of target materials up to.