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Abstract

The present invention encompasses a scanning optical system such as internal drum photoplotters that has a raster scanner for advancing a circularly polarized optical beam across a substrate surface in a first direction to form a scan line and for advancing the optical beam in a second direction substantially perpendicular to the first direction. There is a curved platen for receiving a substrate and an apparatus for switching the optical beam polarization between first and second directions in response to polarization control signals;. An encoder generates signals indicative of the position of the optical beam along a current scan line. There is a controller that receives the encoder signals and generates the advancement signals and the modulator control signals. The controller further provides the optical beam polarization switching signals in dependence on the encoder signals such that the optical beam polarization is switched after the completion of the current scan line. The system is characterized by a spinner which uses polarization switching to generate two scan lines per spinner rotation.

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First Claim