Displacement measurements of technical surfaces with a synchronously pumped external cavity diode laser

A novel principle for absolute position measurements of rough surfaces is presented. A measurement object with a rough surface acts as an external reflector for an antireflection coated laser diode. Determining the longitudinal mode spacing yields the distance from the laser diode to the measurement object. Synchronous pumping of the laser diode results in locking of the modes of the built-up Fabry-Perot resonator. Due to resonance enhancement the mode locked external cavity laser sensor allows highly resolved displacement measurements of rough surfaces. The influence of the object as well as the active gain medium on the accuracy of the measurements is investigated by experiments and simulations.