Orbital angular momentum spectrum of partially coherent vortex beams in slant atmospheric turbulence

Cross-spectral density function of partially coherent Laguerre–Gaussian (LG) beam propagation in slant atmospheric turbulence is derived based on the extended Huygens–Fresnel principle. Using the Markov approximation, the power expression of different spiral harmonic components of partially coherent LG beam in a slant atmospheric turbulence is obtained. The effects of source coherence parameters, propagation distance and zenith angles on transverse coherent lengths and orbital angular momentum (OAM) spectrum of beams are analysed. Finally, the Young's double-slit interference phenomena of fully coherent and partially coherent vortex beams are compared experimentally. If the propagation distance is fixed, then large source coherence parameters result in small transverse coherent lengths. If the zenith angle is fixed, then the relative power of initial OAM state is reduced, and different spiral harmonic components increase with increasing propagation distance. Slant atmospheric turbulence has great effects on the OAM characteristics of high order beams. These results may serve as experimental and theoretical bases for practical applications of OAM of partially coherent vortex beams.