Multimodal sensing of underwater optical turbulence using beams carrying orbital angular momentum, part 1:...

We present a comprehensive experimental study investigating orbital angular momentum (OAM) beams for sensing underwater optical turbulence strength using multimodal optical measurements. Synchronized measurements of pupil plane intensity, focal plane intensity, and mode-sorter spectra were collected in a Rayleigh-Bénard convection tank across three turbulence strengths, ranging from Cn2=1.96×10^-10 to 2.06×10^-9m^-2/3. The pupil plane scintillation index provided the best discrimination between turbulence conditions, with comparable performance across OAM modes. Focal plane beam wander showed a monotonic increase with turbulence strength across all OAM modes. The mode-sorter results varied with the OAM mode, with modes ℓ=2 and ℓ=4 yielding greater separation in the mode spreading due to the turbulence. Our results demonstrate that the pupil plane scintillation across all OAM modes tested captures the most relevant information for discriminating between optical turbulence strengths, validating structured light as a versatile probe for environmental sensing.