Pattern generation with an extended focal depth.

The depth of focus of light patterns can be extended, within given tolerances, beyond the classical limits. For a quantitative evaluation we introduce a degree of depth-of-focus extension and a three-dimensional energy-distribution efficiency. The basic limitations involved in depth-of-focus extension are discussed. A coherent system in which the input is optimized for a desired output pattern is presented. An example of a pattern containing diffraction-limited line segments and a 4 times improvement in depth of focus is demonstrated. This task is much more difficult than generating patterns of isolated light spots in which the depth of focus is extended beyond an order of magnitude.