Unified Optical Scanning Technology

Chapter 4.8 - Scanner Devices and Techniques: Acousooptic Scanners

4.8 ACOUSTOOPTIC SCANNERS

This device, utilizing the acoustooptic effect (sound wave induction of refractive index variation in a medium), is one of the most diverse of low-inertia scanners. With appropriate material selection, it serves a wide range of optical wavelengths. Transmission ranges of several materials overlap to cover substantial portions of the ultraviolet-visible-infrared spectrum; exemplified by lithium niobate (LiNbO3, 0.04-4.5μm), telurium dioxide (TeO2, 0.35-5μm), and germanium (Ge, 2-20μm). Although acoustooptic devices are also designed for and suited ideally to intensity modulation of laser beams, this work concentrates on its scanning characteristics. Before the advent of economical and well-controlled modulatable laser diodes, almost every "laser printer" utilized an acoustooptic modulator. It is noteworthy, too, that almost no laser printer utilized acoustooptic deflection. This illustrates one of the trade-offs of low-inertia devices: limited capability for forming adequate resolution along a contiguous scan line of typical page width. [It may be recognized that a similar limitation exists for the broadband galvanometer (Section 4.5.1), while scanning at a sufficiently high rate.] If the limitation of scan line continuity is relaxed, one may compose and join narrower subraster columns to form the full width. This technique (called stitching) is, however, seldom implemented because of the exacting requirements for assembling the columns to such accuracy in position and image density that their joints are practically imperceptible under loupe scrutiny.

 

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