CD-R groove measurement by phase stepping interferometry

The interferometric CD-R groove measurements in transmission and reflection mode with HeNe and Ar+ lasers are presented. The phase micro-inhomogeneities on the surface relief of polycarbonate substrates are compared with the surface relief of a stamping onto copper layer metal master for rainbow holograms, used as a test object. The grid density of the test object is about 60% higher than the density of the CD-R groove at a similar relief depth. The reason for the phase inhomogeneities is due to the refractive index variations of the polymer substrate. The RMS of the measurements is not higher than 0.1rad.