Polarization imaging of biological samples with spatial filtering

Polarization measurement technology can detect the microscopic structure information from biological samples. However, for biological samples with weak scattering effect, the optical signal obtained by the detector will contain a large amount of zero-frequency light without scattering, which makes it difficult to effectively extract the polarization information of the samples with weak scattering effect. Therefore, in this study, we introduce spatial filtering technique into polarization measurement. In the experimental setup, a spatial filter is placed in the rear focal plane of the objective lens to block the zero-frequency light, so as to realize the selection of scattered photons. A red LED with the wavelength of 633nm was used as the lighting source. The measurement of polarization information is based on the dual-rotating quarter-wave plate method. Considering the widespread presence of spherical and columnar scatterers in biological systems, Hacat cells and biological fibers were selected for the experiment. By comparing with the polarization data without spatial filtering, we found that the polarization parameter obtained after the high pass filtering measurement can better characterize the samples.