Use of a multimode short-external-cavity laser diode for absolute-distance interferometry

The author considers the resonant-mode structure of a three-wall Fabry-Perot laser-diode cavity in the context of multiple-color interferometric techniques for determining absolute distance. It is found that the theoretical emission spectrum for a dispersive gain medium such as GaAIAs in such a cavity can be used to generate synthetic wavelengths from less than 200 µm to more than a meter with a single laser diode. The emission characteristics and their use in distance measurements are then illustrated experimentally by using a commercially available short-external-cavity device operated near threshold.