Phase locked laser diode interferometry for surface profile measurement

We propose a new type phase locked interferometer which uses tunability of the wavelength of a laser diode. The phase lock is achieved by controlling the injection current of the laser diode. A CCD image sensor is used as a photodetector to scan electrically a measuring point along the surface of the object. Since this interferometer uses no mechanical elements such as a piezoelectric transducer and galvanomirror, the measurement accuracy is not limited by the mechanical properties. The characteristics of the feedback control system for the phase lock are examined through measurements of surface profiles of the diamond-turned aluminum disks.