Advances on the measurement of orbital angular momentum spectra for laser beams (Invited)

Since Allen et al. have shown that laser beams with helical wavefront carry orbital angular momentums (OAMs), great advances have been achieved for manipulating beams’ OAMs, and contribute to lots of novel structured beams as optical phase and polarization vortices, laser beam lattices. Such structured fields can find applications in lots of domains including large-capacity data-transmission, remote detection, laser manufacture, high-resolution imaging. One of the important bases of above scenarios is diagnose the OAM spectrum. In the early stage, researchers concentrate more on the measurement of OAM distributions, and afterwards expanded gradually to the intensity proportion measurement of each OAM component, namely the orbital angular momentum spectrum. In this paper, the recent advances of OAM spectrum measurement for laser beams were systematically reviewed and summarized, covering approaches of OAM spectrum measurement based on diffraction, mode sorting and other novel methods.