Nondestructive Graphene Raman Detection of Optical Vortices

Orbital angular momentum (OAM) has garnered considerable attention for its potential in various applications, particularly in optical communications. However, efficient OAM detection remains a challenge, limiting its practical implementation. Here, we introduce a nondestructive, all-optical method for OAM detection based on coherent anti-Stokes Raman scattering (CARS) spectroscopy. By employing Laguerre-Gaussian modes for both the pump and Stokes beams, we take advantage of the doughnut-shaped intensity distribution of optical vortex beams (OVBs) to modulate the spatial structure of the CARS signal. We validate this approach through theoretical and experimental studies using graphene layers and polymer films under varying intensity conditions. The resulting CARS signal strength is directly correlated with the topological charge of the OVB, enabling precise identification. Since only the CARS signal is measured─rather than the OAM-carrying beam itself─information in the incident beams remains intact, offering a transformative solution for OAM analysis. This measurement via nonlinear beam interactions ensures that the method is both nondestructive and all-optical. Furthermore, the strong Raman response, optical uniformity, and well-characterized properties of atomically thin graphene make it particularly well-suited for efficient signal detection. We believe that this technique paves the way for advancements in optical communication and information processing.