Measuring topological charges of Laguerre–Gaussian vortex beams using two improved Mach–Zehnder interferometers

Abstract. We demonstrate, theoretically and experimentally, a new method to measure high-order topologicalcharges (TCs) of Laguerre–Gaussian vortex beams, including the magnitude and the sign, by analyzing theinterference intensity patterns. The magnitude is determined by analyzing the interference intensity patternsbetween the vortex beam and its conjugate beam, and using an improved Mach–Zehnder interferometerwith a dove prism. Counting the number of interference bright petals attests to the magnitude of high-orderTCs through half of the bright petal number. After the TC is modulated by a spiral phase plate, the sign isacquired by comparing the counting results of two charge-coupled devices. Just by this method, we havebeen able to measure both the magnitude and the sign of the TCs up to l ¼ 90. Our experimental resultsare in good agreement with the numerical simulations. © 2016 Society of Photo-Optical Instrumentation Engineers (SPIE)[DOI: 10.1117/1.OE.55.3.035104] Keywords: topological charge; interference; spiral phase plate; measurement.Paper 160085 received Jan. 18, 2016; accepted for publication Mar. 1, 2016; published online Mar. 22, 2016.