<title>Precision, Post-Objective, Two-Axis, Galvanometer Scanning</title>

Using a laser beam and galvanometer scanners with mirrors in an orthogonal configuration is a simple, low cost way to scan an X-Y flat field in a raster or vector mode. The major drawback in the method has been the geometric distortions inherent in two-axis, flat-field scanning, primarily pincushion, tangent, and focus errors of the imaged beam on the field. Until now the problem has been resolved by pre-objective scanning in which a corrective lens is placed between the scanners and the field. Use has been limited, however, to small fields (20 cm) where corrective lenses are practical. Accurate corrections with multiple wavelengths are difficult, if not impossible. Small fields with large radii also have been used to minimize geometric errors, but long focus distances create a number of optical problems. General Scanning now has a post-objective scanning system which solves these problems in virtually any field size or scan radius configuration. By positioning simple lenses and dynamic focusing before the scanners, a post-objective scanning system is created. In this system, the scanning and focus servos are under precise control of a digital correction computer. This paper discusses the theory of correction and the hardware available, as well as the implementation and performance, of a post-objective scanning system.