Innovative applications of semiconductor laser diodes

Non-contact, non-incremental, and highly accurate distance measurements over both short and extended ranges are required by a number of industrial and medical applications where compact and robust measuring devices suitable for in-field usage are needed. We can find applications in dimensional quality control systems; in both macro and micro profilometry, in wide structure monitoring, in robot tracking, in high precision machining, optical tomography etc.. In this context, we show that new commercial semiconductor laser diodes are suitable for non-incremental absolute distance measurements based on low-coherence and optical frequency modulation. Even if the knowledge of the coherence properties of these device is of great importance, this information is usually not available in the standard device data sheets. Therefore we present a thorough characterisation of the coherence properties of some commercial visible and near-infrared laser diodes performed using basically a Michelson interferometer. As example two interferometric systems, based on laser diode sources, are proposed; the main characteristics of these systems are (i) high accuracy combined with an extended measuring range, (ii) simple optical layout, (iii) small dimensions, (iv) low cost.