Abstract

The data pattern on the recording surface can be thought of as collections of cosinusoidal gratings, no matter what the technique used for modulating the reflected light. Reflected light from a focused beam contains a zero order and ± 1st diffracted orders, as shown in Figure 1. The separation angle between the diffracted orders depends on the spatial frequency of the grating. High spatial frequencies yield large separation of the diffracted orders. Light collected by the objective lens contains the zero order and portions of the diffracted orders. The signal amplitude received from the detectors depends on the modulation of the interference between the diffracted orders and the zero order. The amount of modulation depends on the overlap area. At low frequencies, the overlap area is most of the collection aperture. At high frequencies the overlap area reduces, so the signal amplitude decreases.

© 1994 Optical Society of America