The discovery that light beams with a helical phase front carry orbital angular momentum (OAM) has enabled applications in many fields ranging from optical manipulation to quantum information processing and, recently, free-space information transfer and communications. Here, a novel three-dimensional fabrication process by electron beam lithography was finely tuned in order to realize high-quality spiral phase plates (SPPs) for the generation of OAM-carrying optical beams. Single-and multi-step SPPs have been realized for the generation of high-order Laguerre-Gaussian beams with different values of topological charge and radial index. The optical response of these optical elements was experimentally investigated and compared with theoretical models. (C) 2015 Optical Society of America
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