Polarimetric response of second harmonic generation in microscopy of partially oriented chiral fibrillar structures

Polarimetric second harmonic generation (SHG) microscopy is employed to study partially oriented fibrillar structures. The polarimetric SHG parameters are influenced by three-dimensional (3D) configuration of C6 symmetry fibrilar structures in the focal volume (voxel) of a microscope. The achiral and chiral susceptibility tensor components ratios (R and C, respectively) are extracted from the linear polarization-in polarization-out (PIPO) measurements. The analytical derivations along with the polarimetric SHG microscopy results obtained from rat tail tendon, rabbit cornea, pig cartilage and meso-tetra (4-sulfonatophenyl) porphine (TPPS4) cylindrical aggregates demonstrate that SHG intensity is affected by parallel/antiparallel arrangements of the fibers, and R and C ratio values change by tilting the fibers out of image plane, as well as by crossing the fibers in 2D and 3D. The polarimetric microscopy results are consistent with the digital microscopy modeling of fibrillar structures. These results facilitate the interpretation of polarimetric SHG microscopy images in terms of 3D organization of fibrilar structures in each voxel of the samples. Statement of SignificancePolarimetric second harmonic generation (SHG) microscopy is used to study partially oriented C6 symmetry chiral fibrillar structures. The linear polarization-in polarization-out (PIPO) SHG imaging is performed on rat tail tendon, rabbit cornea, pig cartilage tissues and meso-tetra (4-sulfonatophenyl) porphine (TPPS4) cylindrical aggregates. The study demonstrates that SHG intensity is affected by parallel/antiparallel arrangements of the fibers, and the achiral and chiral susceptibility component ratio values change by tilting the fibers out of image plane, as well as by crossing the fibers in 2D and 3D. The polarimetric microscopy results are consistent with the digital microscopy modeling of fibrillar structures. These results facilitate the interpretation of polarimetric SHG microscopy images in terms of 3D organization of fibrillar structures in each voxel of the samples.