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 topological charges (TCs) of Laguerre–Gaussian vortex beams, including the magnitude and the sign, by analyzing the interference intensity patterns. The magnitude is determined by analyzing the interference intensity patterns between the vortex beam and its conjugate beam, and using an improved Mach–Zehnder interferometer with a dove prism. Counting the number of interference bright petals attests to the magnitude of high-order TCs through half of the bright petal number. After the TC is modulated by a spiral phase plate, the sign is acquired by comparing the counting results of two charge-coupled devices. Just by this method, we have been able to measure both the magnitude and the sign of the TCs up to l=±90. Our experimental results are in good agreement with the numerical simulations.