Analysis of multilevel spiral phase plates using a Dammann vortex sensing grating Zhang, N. ; Davis, Jeffrey A. ; Moreno, Ignacio ; Cottrell, Don M. ; Yuan, X. -C. Abstract Publication: Optics Express Pub Date: December 2010 DOI: 10.1364/OE.18.025987 Bibcode: 2010OExpr..1825987Z