Imaging birefringence at sub-micrometre resolution has demonstrated its potential as a powerful label-free method to get insight into the structure of biological tissues, both for fundamental research and for biomedical applications. However, achieving sensitive birefringence imaging in real-time is a challenge. Recently our laboratory has successfully demonstrated real-time Mueller laser-scanning microscopy based on the idea of spectrally encoded light polarization. This method implements a very fast swept-wavelength laser source in combination with passive polarization optics, enabling high-speed polarization modulation (<MHz) and thus fast polarization measurements. However, as a Jones/Mueller method, it is operating off null (far from extinction) so its sensitivity is intrinsically limited. Here, we report a new version of the spectrally encoded light polarization microscope dedicated to weak linear retardance measurements and combining the high sensitivity of a null method with the speed of the spectrally encoded light polarization method. We expect that the superior performances of this new device will open the gate for real-time imaging of very weak birefringent structures within biological samples.
Mueller microscopes enable imaging of the optical anisotropic properties of biological or non-biological samples, in phase and amplitude, at sub-micrometer scale. However, the development of Mueller microscopes faces instrumental challenges: whilst adjusting the microscope, the operator needs a polarimetric image as guidance and the production of polarimetric parameters must be sufficiently quick to ensure fast imaging. To mitigate this issue, in this paper, a full Mueller scanning microscope based on spectral encoding of polarization is presented. The spectrum collected every 10 ms for each position of the optical beam on the specimen, incorporates all the information needed to produce the full Mueller matrix, which allows simultaneous images of all the polarimetric parameters at the unequalled rate of 1.5 Hz (for an image of 256×256 pixels). The design of the optical blocks allows for the real-time display of linear birefringent images which serve as guidance for the operator. In addition, the instrument has the capability to easily switch its functionality from a Mueller to a Second Harmonic Generation (SHG) microscope, providing a pixel-to-pixel matching of the images produced by the two modalities. The device performance is illustrated by imaging various unstained biological specimens.
A new setup was recently proposed to perform Mueller matrix polarimetry at 100 kHz using a swept laser source, high order retarders and a single channel photodetector. In this communication, we present the implementation of this setup on a laser scanning microscope to perform high speed scanning Mueller microscopy in transmission. Calibration of the instrument is briefly described and precision and stability over time are evaluated. Finally, Mueller images of a manufactured scene are reported. To our best knowledge, this is the first time that Mueller polarimetry is performed using a laser scanning microscope. We further plan to develop confocal/nonlinear/Mueller microscopy from the same setup in order to produce multimodal contrast images of biological samples.
We investigated the layer dynamics of a conventional surface-stabilized ferroelectric liquid crystal (SSFLC) using a full-optical snapshot Mueller matrix polarimeter (SMMP) based on wavelength polarization coding. Time-resolved polarimetric measurements were performed with different SSFLC samples, and a strong correlation between the polarimetric parameters and the SSFLC under electric field at different exposure times was found. It has been shown that the SMMP polarimeter is able to determine the evolution of the trajectory of the liquid crystal director between the two addressed states, the reversible motion of the smectic layer while switching, as well as the irreversible transition from chevron to bookshelf texture.
Human liver biopsy samples, consisting into a 16 μm thickness biomaterial chemically fixed into a formaldehyde
matrix, and stained by red picrosirius dye, are analysed for different states of fibrosis degeneration. Polarimetric
methods, and specially Mueller polarimetry based on wavelength coding, have been qualified as an efficient tool
to describe many different biological aspects. The polarimetric characteristics of the media, extracted from a Lu
and Chipman decomposition1, 2 of their Mueller Matrix (MM), are correlated with the degeneracy level of tissue.
Different works and results linked to the clinical analysis will be presented and compared to previous performed
works.3 Polarimetric imaging will be presented and compared with SHG measurements. A statistical analysis of
the distribution of polarimetric parameters (such as the retardance R and depolarisation Pd) will be presented
too, in order to characterise the liver fibrosis level into the biomaterial under study.
This paper describes a snapshot Mueller matrix polarimeter by wavelength polarization coding. This device encodes
polarization states in the spectral domain through use of a broadband source and high-order retarders. This allows one to
measure a full Mueller matrix from a single spectrum whose acquisition time only depends on the detection system
aperture. The theoretical fundamentals of this technique are developed prior to validation by experiments. The setup
calibration is described as well as optimization and stabilization procedures. Then, the polarimeter is used to study, by
time-resolved Mueller matrix polarimetry, the switching dynamics within a ferroelectric liquid crystal cell.
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