Depolarization Mechanism For Polarized Light And Applications Of Polarized Light Scattering In Noninvasive Monitoring Of Biological Tissues

Growing applications of polarized light scattering in noninvasive monitoring of biological tissues have been developed since people have been investigating it deeplier and deeplier.However the propagation of polarized light in turbid medium is a quite complicated problem.Depolarization and change of polarization state will be influenced by the optical parameters of turbid medium and measurement configuration.Characterizing the influence precisely is of paramount importance for its applications in biological field.In addition,there exist many topics in blood monitoring which are worth to be further investigated.This dissertation focuses on the depolarization mechanisms of polarized light propagation in turbid medium and discusses several potential applications of polarized light scattering in blood tissues.Aiming at the depolarization mechanism,two depolarization calculation methods,Mueller polar decomposition and Mueller coherence matrix,were compared.It is found that the averge degree of polarization calculated from Mueller coherence matrix is closer to the standard value,which is obtained by integrating over the whole Poincare sphere,than the method of Mueller polar decomposition when depolarization anisotropy appears in turbid medium.Meanwhile,it is revealed that depolarization anisotropy can be indicated by both polarization memory rate and depolarization-entropy relation.In the turbid medium with optical rotation and birefringence,linear depolarization anisotropy factor should be introduced to depict the depolarization properties in a thorough sense.On this basis,depolarization anisotropy on the backscattering plane of Mie scatterers was studied.It is of note that circular depolarization is more serious than linear depolarization in a specific backscattering area near the illumination point,which is unexpected for Mie scatterers.Time-resolved Monte Carlo(MC)simulation shows the anomalous depolarization anisotropy is related to depolarization mechanism of circular polarization.Further investigation demonstrates that lateral scattering events happen with most propobility in this area.Helicity asymmetry of circular polarization decreases upon lateral scattering,which leads to the anomalous depolarization anisotropy in that specific area.Mueller matrix for infinitely narrow beam is convolved into the response for Gaussian beam by Gaussian transformation.On this basis several application examples in blood tissues have been discussed.Firstly,the polarization characteristics on the backscattering plane of erythrocytes suspensions were investigated.It is found that the cause for the nonmonotonic variations of degree of polarization and diattenuation with radial distance is that scattering angle and scattering number simultaneously affect them.Secondly,degree of polarization and diattenauation for erythrocyte suspensions in hemolysis were studied.It is demonstrated that the relationship between the two polarization properties and hemolysis rate were produced under the simultaneous effects from scattering and absorption.Interestingly,the threshold of hemolytic reaction can be distinguished by the relationship.Third,the backscattering Mueller matrices for intralipid suspensions with glucose were measured.Polarization memory rate is found to correlate positively with glucose concentration and turbidity will not influence it.In addition,the relationship between optical rotation pathlength and optical pathlength was discussed by MC simulation for turbid medium with optical active substances.As expected,optical rotation pathlength is larger than optical pathlength,and optical properties of the media affect the relationship.Based on the reference which combines near-infrared spectroscopy and tissue polarimetry to measure blood glucose noninvasively,chemometrics methods are discussed to extract glucose concentration by use of absorption spectrum,optical rotation spectrum and polarization spectrum.Backscattering polarization properties are researched by MC simulation in the spectral range of 530-1310nm.The method of 3×3 Mueller matrices is proposed to measure the spectral polarization.3 × 3 Mueller matrices on backscattering plane of turbid medium are measured when the wavelengths for the incident light are 632.8nm and 532nm by the use of waveplate rotation method.It is found that the linear degree of polarization variation between 632.8nm and 532nm is in agreement with simulation result.An experimental system incorporating polarization modulation and synchronous detection techniques is proposed to measure the 3 X 3 Mueller matrices.The system lays the foundation to measure the spectral polarization precisely,especially spectral optical rotation,for turbid medium with optical substances.