Retrieving the OAM spectrum and the spatial distribution of structured optical fields

摘要

Helical modes of light, that is those optical spatial modes carrying a definite amount of orbital angular momentum,are proving a crucial resource in modern photonics. In all applications that rely on these modes and on theircombination, a fundamental role is played by the scheme that is used to characterise the complex structure ofthe light beam. Here we describe a technique that applies the concept of digital holography to the study ofthe orbital angular momentum content of structured light [1]. In particular, the interference pattern formed bythe light beam under investigation and a reference field is analysed digitally, and the complete electric field isobtained. A decomposition in term of helical modes allows one to get the orbital angular momentum spectrumof the beam in a few steps, with the possibility of retrieving also the complex radial profile associated witheach mode. Requiring a simple setup and a limited number of measurements, this technique could provide aconvenient strategy for the characterisation of structured light beams.