A method of 3-D optical metrology based on a triangulation system using holographic axilens to increase the depth-measuring range without any decrease in the axial or the lateral resolution is presented. The element is designed according to an analytic ray-tracing optimization approach and is recorded as a computer-generated hologram. A sixfold increase in the depth-measuring range is experimentally obtained while nearly diffraction limited light spots are completely maintained.
"Three-dimensional optical metrology with extended depth-measuring range using a holographic axilens," Optical Engineering 42(1), (1 January 2003). https://doi.org/10.1117/1.1524170