New Lasing Mode of a Diode Laser: A 200-Picosecond Leading Edge of a Nanosecond Pulse

A unique rangefinder that, as far as we know, was not mentioned in previous publications has been studied. It is based on an injection diode laser with an eye-safe radiation density (below 1 μJ/cm2) and a single-photon avalanche diode (SPAD). A new lasing mode of the nanosecond laser with a 200-ps-long step at the leading edge of a 4-ns-long pulse with spatial extension of about 1.2 m has been implemented. It has been found that the discovered step of the optical pulse amplitude is initiated by a current avalanche in a field-effect transistor (FET) that switches capacitance discharge in the feed circuit of the diode laser. The detection of the 200-ps-long amplitude step by a quick-response SPAD detector (20 ns) improves the accuracy of the rangefinder by 12 times. The application of such rang finder to measure critical distances (shorter than the laser pulse extension), e.g., in the problems of space ship landing or docking and underwater robot rendezvous and approach has been discussed.