A comparison of techniques for substrate birefringence measurement

State of the art techniques for measuring magneto optic disks birefringence are reviewed. As an illustration of one technique, we measured the birefringence of different magneto optic disk substrates by ellipsometry. The retardation data was fitted to an analytical expression as a function of the different indices of refraction. The variation of birefringence with the depth of the substrate is suspected to affect optimum focus and track error signal. A novel scanning micropolarimeter technique for measuring the index of refraction tensor through the depth of the magneto optic substrates is presented. Modeling to study the effects of typical birefringence profiles on the performance characteristics of magneto optic disks using the data from a scanning micropolarimeter is discussed.