Quasi-intrinsic angular momentum

In this work we pointed out that the orbital AM has an intermediate and distinct character between intrinsic and extrinsic, it is quasi-intrinsic. We propose a device to measure directly the variance as well as the angular spectrum of any optical field. This device consists of an interferometer with a pair of Dove prisms (DP) in its arms, azimuthally rotated to a relative angle thetas, and a pi/2 phase plate (PP). The novelty of this device, when compared to holographic measurements, lies in the fact that the measurement spans the angle space and provides the exact OAM spectrum -via a Fourier transform-for any spatial profile of the input beam. A second important use of this interferometer is to access directly the variance V, by measuring M(thetas) for small angles, with limited experimental effort.