Coherence properties of a random electromagnetic vortex beam propagating in biological tissues

Abstract

ABSTRACTBased on the extended Huygens-Fresnel principle and the unified theory of polarization and coherence, the coherence properties of random electromagnetic Gaussian Schell model (GSM) vortex beams propagating through biological tissues were investigated. It was shown that with an increasing propagation distance, the change in the spectral degree of coherence |μ(ρ, −ρ, z)| is more complex than that of μ(0, ρ, z). If the change in |μ(ρ, −ρ, z)| is divided into the preceding and latter stages, then the change in μ(0, ρ, z) is similar to that of |μ(ρ, −ρ, z)| at the latter stage. The wavelength of the far-infrared beam (λ = 10.6 µm) is similar to that emitted by the biological tissues, and a resonance with water molecules occurs in the biological tissues. At the initial plane, the larger ρx corresponds to a smaller value of |μ(ρ, −ρ, z)|, and during the propagation process, the spatial coherent interval is wider for |μ(ρ, −ρ, z)| than for μ(0, ρ, z). The fluctuation change depth of |μ(ρ, −ρ, z)| in the biological tissues is somewhat shallower than that of μ(0, ρ, z) under the same conditions, such as the same biological tissue, the same wavelength, or the same interval between two field points. In addition, the spatial self-correlation length σyy has an effect on |μ(ρ, −ρ, z)| and on μ(0, ρ, z) to a different extent, while the changes in these two quantities are independent of the spatial mutual-correlation length σxy of the random electromagnetic GSM vortex beam.