Holographic optical scanning elements with minimum aberrations

An analytical method to design holographic optical elements for focusing laser scanners, especially disk scanners, with minimum aberrations and optimum scan line definition is reported. The results reveal that the focused spot constraint to a straight line is always astigmatic. However, by accepting small deviations from the straight line, the astigmatism can be eliminated. The second-order analytical solutions are examined with the help of geometrical ray tracing and compared with experimental results. By extending the method to higher-order approximations, it was found that the correction of the aberrations is essentially limited to the direction perpendicular to the scan line.