Real time grating clock for galvanometer scanners in laser scanning systems

摘要

A scanning system which utilizes a resonant mechanical oscillator, such as a galvanometer, to scan a laser beam across a surface of a medium responsive to said laser beam. The laser beam scan velocity across the surface normally would vary sinusoidally because of the resonant nature of the drive system. The data flow, or bit density, of information to be recorded on or read out from the surface, would have a corresponding sinusoidal variation. In order to compensate for this, a grating is provided adjacent the galvanometer and a second laser beam is simultaneously incident on the mirror portion of the rotating galvanometer. As the galvanometer is caused to oscillate, two scanning beams are generated, one scanning the surface and the other scanning across the grating. The grating is arranged to provide a plurality of timing or clocking pulses which are generated in response to the scanning thereof by the laser beam whereby in the writing mode, the writing laser beam is accurately clocked as it is modulated and in the read mode, the timing pulses matches the bit density of the output data, causing the data to be entered into a storage device at the proper time sequence.