<title>Optical-Mechanical Design Of The IBM 6670 Laser Printhead</title>

Abstract

A laser printhead is described that uses an 18 facet rotating mirror to produce a scanning spot of red light from a 5 milliwatt, HeNe laser. The scan has a high duty-cycle in a direction parallel to the irtruni axis of a conventional ellectrophotog.raphic processing system. The beam is modulated by an 80-megahertz, acoustooptic modulator that allows dot-switching times of 100 nanoseconds. The dot matrix is 240 x 240 per inch over an 8½- x 14-inch document area. Positional timing of the scanning spot is determined by a reference beam scanning a Ronchi grating. This beam is split from the fixed laser b a thin Wedge prism and passes through the same optical system as the scanning beam,. The reference beam is at a slightly different angle than the Bragg angle as it goes into the acoustooptic crystal, so is not affected by the acoustic waves that are transduced. The laser printhead has been designed as a hand-carried, compact, modular-component assembly that allows field replacement of several of its components including the laser.