Fig. 1
From: Universal orbital angular momentum spectrum analyzer for beams
Diagram to show the principles of the universal OAM spectrum analyzer. We introduce a reference Gaussian beam ER to coaxially interfere with the analyzed beam. In addition to the intensity of the analyzed beam I, we also capture the intensity patterns of the reference beam IR, the coaxial combined beam Icos, and the coaxial combined beam with π/2 phase delay Isin. Note that here all the four intensity patterns are expressed as two-dimensional real matrices, from which one can recover the complex amplitude, and then do the helical harmonic decomposition to acquire the OAM spectrum. The whole analyzing process is done based on the definition of OAM spectrum. Thus this propose is universal for any laser beams