We present local profile measurements of inner mirrorlike and external front-end polycarbonate surfaces at the same spot of assembled optical storage devices, a CD and a DVD, performed with a heterodyne scanning interferometer that uses Gaussian beams. We show that the heterodyne interferometer can reproduce the profiles of both surfaces with accurate precision. We describe a procedure for calibrating the instrument based on the measurement of reflecting calibrated gratings. To show the advantages that the heterodyne interferometer represents as a valuable tool for the characterization of optical disks, we include a comparison of experimental results obtained with a confocal microscope under similar working conditions.