Timing control in acousto-optic scanner based on acoustic velocity of traveling wave lens

Abstract

Pixel clock and beam scan timing of an acousto-optic scanner are controlled by an acoustic velocity-driven, phase locked loop containing an adjustable voltage controlled pixel clock generator, which is controlled by a detector that produces delayed and attenuated replica of the excitation waveform applied to an ATWL scanner used to scan a light beam across a workpiece. In a first embodiment of the invention, an end-of-cell transducer converts the pressure induced traveling lens into an electrical signal replica of the excitation input. In a second embodiment, an end-of-scan optical pick-off monitor is employed to detect the scanned optical spot as it crosses its field of view. Each pixel is spatially invariant to propagation velocity changes in the ATWL medium, so that as variations in temperature change the speed of the pressure-induced lens traveling from the excitation transducer to the end of the ATWL cell on each scan, the pixel clock is correspondingly slowed down or speeded up by the same proportional amount, to maintain registration in time and space.