Propagation of Gaussian Schell-model vortex beams in biological tissues

The dependence of changes in the relative intensity and the spectral degree of coherence on the refractive-index C_n² of biological tissues, space correlation length σ₀ and wavelength λ of the Gaussian Schell-model (GSM) vortex and non-vortex beams in biological tissues has been studied. It is shown that the intensity distribution of GSM vortex beams passing through the biological tissues undergoes several stages. The bigger C_n² is, and the smaller σ₀ is, the quicker the intensity evolution is. The attenuation of intensity for GSM vortex beams is much slower than that of non-vortex beams, thus the beam quality of the former is better than the latter. When propagating through the biological tissue, the phase singularities of GSM vortex beams will appear. As the propagation distance increases, the position of the phase singularities will shift, and these points will disappear where the changes in the spectral degree of coherence of GSM vortex beams are consistent with those of GSM non-vortex beams. At the same propagation distance, the bigger C_n² is, and the smaller σ₀ and λ are, the shorter the distance between the phase singularities and the z axis is, when the propagation distance z is in the range of 0–50 μm.