Shack-Hartmann Wavefront Sensing of Ultrashort Optical Vortices

Abstract

Light beams carrying Orbital Angular Momentum (OAM), also known as optical vortices (OV), have led to fascinating new developments in fields ranging from quantum communication to novel light–matter interaction aspects. Even though several techniques have emerged to synthesize these structured-beams, their detection, in particular, single-shot amplitude, wavefront, and modal content characterization, remains a challenging task. Here, we report the single-shot amplitude, wavefront, and modal content characterization of ultrashort OV using a Shack-Hartmann wavefront sensor. These vortex beams are obtained using spiral phase plates (SPPs) that are frequently used for high-intensity applications. The reconstructed wavefronts display a helical structure compatible with the topological charge induced by the SPPs. We affirm the accuracy of the optical field reconstruction by the wavefront sensor through an excellent agreement between the numerically backpropagated and experimentally obtained intensity distribution at the waist. Consequently, through Laguerre–Gauss (LG) decomposition of the reconstructed fields, we reveal the radial and azimuthal mode composition of vortex beams under different conditions. The potential of our method is further illustrated by characterizing asymmetric Gaussian vortices carrying fractional average OAM, and a realtime topological charge measurement at a 10Hz repetition rate. These results can promote Shack-Hartmann wavefront sensing as a single-shot OV characterization tool.

Arbitrary-Order and Multichannel Optical Vortices with Simultaneous Amplitude and Phase Modulation on Plasmonic Metasurfaces

“…Compared with the spin angular momentum (SAM) with only two states, the OAM of photons implies more available modes of field states [5], which are orthogonal to each other [6]. Therefore, vortex beams have been widely used in the fields of high-capacity optical communication [7], nanophotonic detectors [8], optical manipulation of nanoparticles [9], near-field optical trapping [10], quantum memory [11], imaging [12], the phenomenon of bound states in the continuum [13], etc. In recent years, many methods have been proposed for the generation of OVs, such as using a spiral phase plate [14], nano resonant ring [15], plasmonic spiral shapes [16], metal nanorods, and grating nonstaggered metasurfaces [17].…”