Significance: Reflection Mueller matrix imaging is suitable for characterizing the microstructure of bulk specimens and probing dynamic processes in living animals, there are always demands for speed and accuracy for such applications to avoid possible artifacts and reveal a sample’s intrinsic properties.Aim: To demonstrate a design of collinear reflection Mueller matrix fast imaging microscope based on dual division of focal plane (DoFP) polarimeters (DoFPs-CRMMM) which has high measurement speed and accuracy.Approach: In DoFPs-CRMMM, to improve the measurement speed, we applied the dual DoFP polarimeters design on the collinear reflection system for the first time to achieve fast imaging in about 2 s. To improve the measurement accuracy, we improved the double-pass eigenvalue calibration method (dp-ECM) by background light correction, and explored the optimization of the set of reference samples.Results: DoFPs-CRMMM was applied to measure the standard polarization samples and monitor the tissue optical clearing process of an artificial layered bulk tissue. Results show that the system has satisfactory performance which can capture the variation of polarization properties during the dynamic process.Conclusions: We present the establishment and demo application of DoFPs-CRMMM. The measurement speed can be further accelerated for potential applications in monitoring dynamic processes or living biomedical systems.
Polarization parameters derived from Mueller matrix (MM) can describe different structural and optical properties of the media. Anisotropy of light-structure interactions are useful in many fields like biomedical research, but can be affected by the orientation relationship between samples and detection systems. In this paper, we used backscattering MM imaging systems with different backscattering angles to obtain MMs and several anisotropic parameters. The angle between backscattering and the normal of the sample surface changes from 180° to 110° while the incident light is parallel to the normal. Concentrically aligned fibers sample is used as scattering media. It has fibers of complete 360° directions. The experimental results showed the colinear backscattering MM imaging system can provide anisotropic parameters with better periodical variation than non-colinear backscattering MM imaging system does. The amplitude of signal attenuates with the scattering angle declines. The collinear backscattering MM imaging system has better detection ability measuring anisotropy of samples. However, further studies are still necessary to analyze the additional information obtained from non-collinear backscattering MM imaging system.
In a recent attempt, we developed a colinear backscattering Mueller matrix microscope by adding polarization state generator (PSG) and polarization state analyzer (PSA) into the illumination and detection optical paths of a commercial metallurgical microscope. It is found that specific efforts have to be made to reduce the artifacts due to the intrinsic residual polarizations of the optical system, particularly the dichroism due to the 45 degrees beam splitter. In this paper, we present a new calibration method based on numerical reconstruction of the instrument matrix to remove the artifacts introduced by beam splitter. Preliminary tests using a mirror as a standard sample show that the maximum Muller matrix element error of the colinear backscattering Muller matrix microscope can be reduced to a few percent.
It has been demonstrated in many biomedical applications that polarization imaging is capable of probing the characteristic microstructural features of complex biological specimens quantitatively and non-invasively. In a recent study, we carried on backscattering Muller matrix imaging on living nude mice skin using oblique illumination by a 633nm LED light source. We quantitatively measured how the anisotropy properties of the living mice skin changes as functions of the UV exposure time. The time course features provide vital clue for the mechanism of UV damage and the effectiveness of sunscreen for reducing such damage. In this work, we report an upgraded system with LED light sources of five different colors ranging from blue to red. The system is calibrated by taking multi-color Mueller matrix images using a single set of rotating achromatic quarter-wave plates. In both in situ applications on living nude mice skin and ex vivo imaging of thick fresh tissue samples, we demonstrated that the multi-color polarized light backscattering measurements are able to reveal more details on the microstructure of the sample, particularly helpful in separating different effects due to photon scattering and propagation.
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