Objective: The optical information change of beams acted with biological tissue can get an insight into the new optical effects of tissue, even can provide a theoretical basis for the development of biphotonic medical diagnosis and therapy technologies. Polarization technology is also widely used in the field of biological detection own to its advantages of non-contact, rich information and without staining markers. In this work, the polarization behaviors of partially coherent screw-linear edge mixed dislocation beam transmitting in biological tissue have been analyzed and explored. Simultaneously, in order to gain a clearer and more intuitive understanding of the mixed dislocation beam, both the normalized intensity and phase distribution at source plane for different parameters a and b also have been discussed. We hope that the obtained results will provide theoretical and experimental foundation for expanding the application of singularity beams in biological tissue imaging technology.
Method: By combining the Schell term with the field distribution of the screw-linear edge mixed dislocation beam at the source plane, and based on the generalized Huygens-Fresnel principle, the analytical expressions of the cross-spectral density matrix elements of partially coherent screw-linear edge dislocation beam propagating in biological tissues are derived. Adopting the unified theory of coherence and polarization, the polarization behaviors of the beams can be investigated in detailed.
Results: At the source plane, the intensity is non axisymmetric distribution, and there exists a coherent vortex with a topological charge size of 1 and a linear edge dislocation. The sign of a is related to the rotation direction of the phase singularity. The larger the value of b, the farther the linear edge dislocation is from the origin (Figs. 1-4). At the source plane, the degree of polarization and ellipticity between the same two points are independent of the four parameters, including dimensionless parameter a, the off-axis distance of edge dislocation b, the spatial self-correlation length σ_yy, the spatial mutual-correlation length σ_xy (Figs. 5(a), 7(a), 8(a), 10(a), 11(a), 13(a), 14(a), 16(a)), the orientation angle is only independent of a and σ_xy (Figs. 6(a), 12(a)); the polarization of different two points is independent of a and b (Figs. 5(b)-10(b)), but is related to σ_yy and σ_xy (Figs. 11(b)-13(b)). In transmission, the polarization degree and ellipticity of different two points fluctuate greatly (Figs. 5, 7, 8, 10, 11, 13, 14, 16) and the orientation angle displays less fluctuation (Figs. 6, 9, 12, 13). Finally, all the polarization state parameters tend to be a certain value, respectively.
Conclusions: The results show that when b is smaller, the linear edge dislocation is paraxial and plays an important role in the polarization state change; when b is larger, the polarization state changes of the screw-linear edge mixed dislocation beam will tend to be the pattern of spiral beams. The absolute value of the difference between σ_yy and σ_xy is also one of main factors of influencing the polarization state. The sign of a does not affect the change in polarization state, but its magnitude affects the changes speed. Due to more complex factors determining the correlation fluctuations between different points in the light field, the changes of different two points are more sensitive than those of the same two points in shallow biological tissue. Beams with different parameters can be selected for different application requirements.