Akhtar - Spatially Partially Coherent Beams that Carry Orbital Angular Momentum

Most studies of laser beams that carry orbital angular momentum (OAM) have analyzed only coherent beams. We propose to study spatially partially coherent beams that carry OAM and propagate through complex media. We will focus on underwater optical turbulence created by Rayleigh-Benard natural convection. Refractive index is influenced by fluctuations of temperature along the propagation path in this environment, resulting in distorted amplitude and phase of the beam at the reception. It has been theoretically shown that spatially partially coherent beams have less scintillation on propagation through complex media than coherent beams. Theoretical findings suggest that beams carrying OAM are resilient on propagation as well. Our objective is to combine control of spatial partial coherence and topological charge for OAM to achieve reduction in scintillation. First, we will focus on generating spatially partially coherent beams that carry OAM using the method proposed by Olga Korotkova on the spatial light modulator (SLM). Once we achieve the proposed coherence level, we will propagate beams through a physical Rayleigh-Benard tank and measure the scintillation. We will measure normalized variance at the reception. Our objective is to find the optimal partial coherence for maximizing scintillation reduction for a series of beams that carry OAM. We plan to explore the impact of different topological charges, wavelengths, and polarization on scintillation reduction.

The slides below model preliminary spatial partial coherence by varying only the order of the OAM beam. The parameter ξ (zeta) exists where 0 < ξ < 1, and ξ = 0 is coherent and ξ = 1 is incoherent.