Intensity Distribution And Coherent Vortex Evolution Of Partially Coherent Beams Propagating In Biological Tissue

Laser is an important invention with milestone significance in the history of optics and even the entire history of scientific and technological development.It has the advantages of high coherence,high monochromaticity,high directivity and high brightness that traditional light sources cannot match.The advent of laser led to the emergence of new disciplines,such as tissue optics,biomedical photonics,singularity optics and so on.Among them,singularity optics is mainly studied in completely coherent,monochromatic and scalar wave fields,which studies the optical wave field structures such as optical vortices,coherent vortices and wavefront dislocations in the optical wave field near the phase singularity and related problems..Tissue optics is a research field in which optics and life sciences intersect and integrate with each other,which has developed rapidly with the application of modern optical technology in disease diagnosis and treatment,which is of great significance for the development and application of biomedical spectral detection and imaging technology.This paper is based on the generalized Huygens-Fresnel principle and the phase distribution method.It takes the circular edge dislocation beam and the Laguerre-Gaussian beam as the research objects,and studies the intensity distribution,phase evolution and transmission trajectory of the two beams.The effects of beam parameters on the propagation characteristics and anti-turbulence ability of the two beams in biological tissue propagation were analyzed.The main research contents are as follows:(1)The dynamic evolution of partially coherent circular edge dislocation beams in biological tissues is studied.Based on the generalized Huygens-Fresnel principle,the analytical expression of the cross spectral density function for partially coherent circular edge dislocation beams propagating in the deep dermis of mouse tissue is derived.According to the beam propagation theory and numerical simulation calculations,the effects of the initial beam parameters(beam wavelength and the number of circular edge dislocations)and the propagation distance on the normalized light intensity distribution,phase evolution and propagation trajectory of the beam are studied.The results show that the partially coherent circular edge dislocation beam propagating in the deep dermis of mouse tissue,with the increase of the propagation distance,the intensity distribution gradually evolves from multi-peak shape to single-peak shape.With the change of beam parameters,the evolution speed of the light intensity distribution profile is different.In the initial propagation,the n-order circular edge dislocation splits into n pairs of coherent vortices with topological charges "+1" and "-1",respectively.As the propagation distance increases,n pairs of coherent vortices with topological charges "+1" and "-1" are regenerated,and finally 2n pairs of coherent vortices are annihilated.(2)The propagation behavior of partially coherent Laguerre-Gaussian beams in biological tissues is studied.Based on the generalized Huygens-Fresnel principle,the analytical expression of the cross-spectral density function for the partially coherent Laguerre-Gaussian beam propagating in biological tissues is derived,and study the effect of propagation distance,topological charge,radial index,spatial coherence length,and wavelength on the normalized intensity and phase evolution of this beam in the dermis of mouse tissue.The results show that the partially coherent Laguerre-Gaussian beam with topological charge m and radial index n propagating in the deep dermis of mouse tissue,with the increase of propagation distance,a certain beam parameter changes,the beam intensity distribution changes and the evolution speed of coherent vortex are different,and the influence of beam parameters on the beam propagation characteristics is discussed.