Investigation of tunable single frequency diode lasers for sensor applications

The coherence and tuning properties of tunable single-frequencies lasers used in coherent detection systems have been investigated. The use of a fixed external cavity was found to increase significantly the coherence length of such systems but simultaneously reduce the tunability. An essentially all-electronic phase-modulated external cavity was used to restore the tunability, and a tuning range coherence length product of ~500 GHz-m was achieved. The modulated external activity laser was used in a coherent lidar system that achieved a maximum range of 150 m and a fractional resolution of 0.5%. The system is also shown to be a powerful tool for mapping out the tuning and coherence properties of tunable single-frequency lasers