- Gradient-index rod lenses have been developed and ana- lyzed as imaging optical elements, but their capability as flux concentra- tors has not been explored. Both analytic methods and computer ray- trace simulations are used for a comprehensive evaluation of the concentration and efficiency of these rods. They appear to be well suited as concentrators for the distal end of laser fiber optic surgical units, toward improving surgical efficacy and reducing expensive laser power. © 2001 Society of Photo-Optical Instrumentation Engineers. (DOI: 10.1117/1.1347998) Subject terms: concentrators; biomedical optics; nonimaging optics; gradient in- dex; optical design; geometric optics.