CD Focusing Based on Astigmatism
A cylindrical lens introduces astigmatism into the optics.
The shape of the cross section of the beam changes on moving through the
principal focus. The different relative intensities on the four-quandrant detector
generates a signal which is used to correct the focus of the objective lens.
Source: "The physics of the compact disc" by John A. Cope, Physics Education 28, 1993.
Last updated May 17, 1999.
Copyright George Watson, Univ. of Delaware, 1996.