Abstract: Storage capacity of a magnetic recording medium is increased by providing a nonconductive layer over a magnetic layer on which magnetic data is writable in a series of recording tracks, and applying a pattern of electrostatic charges to the nonconductive layer above at least one of the recording tracks to write track-position-denoting servo information in overlying relation to magnetic data. The pattern may be applied by electrostatic charges selectively of negative or positive polarity that are imprinted while the medium is in a mold or advanced over an electro-photographic charge transfer drum, for thereby preprinting the pattern as a step in fabrication of the medium.

Abstract: Unwanted interference effects arising in those high speed laser scanning systems, particularly those used in printing, employing an acousto-optical modulator for scanning with a plurality of focussed beams simultaneously in order to reduce the required deflection scan rate, and to better the rise and fall times of the waveforms, are largely eliminated by arranging a pair of Bragg deflection cells one behind the other with the directions of propagation of the acoustic waves in the cells substantially 90 degrees apart with respect to each other. The undeflected beam of light is projected onto the cells at the Bragg angles for both cells. Substantially, the same results obtain as though a single Bragg cell were used but devoid of acoustical interference effects.