Human atherosclerotic samples collected by carotid endarterectomy were investigated using electronic paramagnetic resonance imaging (EPRI) for visualization of reactive oxygen species, and nonlinear optical microscopy (NLOM) to study structural features. Regions of strong EPRI signal, indicating a higher concentration of reactive oxygen species and increased inflammation, were found to colocalize with regions dense in cholesterol crystals as revealed by NLOM.
A method for measuring three-dimensional (3-D) direction images of collagen fibers in biological tissue is presented. Images of the 3-D directions are derived from the measured transmission Mueller matrix images (MMIs), acquired at different incidence angles, by taking advantage of the form birefringence of the collagen fibers. The MMIs are decomposed using the recently developed differential decomposition, which is more suited to biological tissue samples than the common polar decomposition method. Validation of the 3-D direction images was performed by comparing them with images from second-harmonic generation microscopy. The comparison found a good agreement between the two methods. It is envisaged that 3-D directional imaging could become a useful tool for understanding the collagen framework for fibers smaller than the diffraction limit.
The collagen meshwork in articular cartilage of chicken knee is characterized using Mueller matrix imaging and multiphoton microscopy. Direction and degree of dispersion of the collagen fibers in the superficial layer are found using a Fourier transform image-analysis technique of the second-harmonic generated image. Mueller matrix images are used to acquire structural data from the intermediate layer of articular cartilage where the collagen fibers are too small to be resolved by optical microscopy, providing a powerful multimodal measurement technique. Furthermore, we show that Mueller matrix imaging provides more information about the tissue compared to standard polarization microscopy. The combination of these techniques can find use in improved diagnosis of diseases in articular cartilage, improved histopathology, and additional information for accurate biomechanical modeling of cartilage.
We present the application of a near infra red Mueller matrix imaging ellipsometer to the characterization of
plasmonic polarizers. The samples are prepared by evaporation of Au onto SiO2 ripples. The nanostructured
ripple surface has been produced by ion beam sputtering at an off normal angle of incidence. Au was thereafter
evaporated onto the surface at an grazing angle. As a result, thin lines of nearly connected Au nanoparticles
form along the illuminated side of the ripples, resulting in a large in-plane anisotropy of the structure. Mueller
matrix imaging is used to determine the lateral uniformity of the optical signal in correlation to the real space
topography of the sample, and to determine to what degree the nanoparticles tend to form a connected wire, or
whether there are well separated Au particles. The success of this method in order to produce polarizers, lies
in controlling the process to allow well connected lines of Au particles along the ripples, with a high degree of
homogeneity. Mueller Matrix images of the sample recorded at normal incidence are shown, and the information
that can be extracted from such images is discussed.
A Mueller Matrix Imaging Ellipsometer system is operated in transmission and used to study nematic textures
in colloidal dispersions of synthetic Na-fluorohectorite clay platelets in solution. It is clearly observed that the
anisometric particles organize into phases with strong birefringence, which results in a strong retardance. The
Mueller matrix imaging technique supplies an image of the retardance matrix, even in the presence of other
effects such as light scattering and diattenuation. The spatial variation of the absolute value of the retardance,
the orientation of the fast axis of the retardance, the total diattenuation and the orientation of the diattenuation
are presented. In particular, from knowledge of the anisotropic shape of the particles, the orientation of the
particles within ordered domains, and the density of the particles within the domains are spatially determined.
The experiments are based on adding synthetic clay particles into a solution contained in a thin rectangular glass
container. Upon letting gravitation act on the sample, different phases appear after a few weeks. One phase
contains nematic textures and we are able to determine the ordering and also estimate the density of the
domains/texture within the phase, in addition to estimating the local order within a domain with an image
resolution of 12 μm.
We report on the design and performance test of a multiple laser Mueller matrix ellipsometer (MME). The MME is well conditioned due to the integration of the recently reported achromatic 132-deg compensators based on biprisms, in combination with high-quality Glan-Thompson polarizers. The system currently operates between 300 and 2700 nm, without the need to change any optical components except for the detector. Four lasers are employed as light sources (405, 532, 633, and 1570 nm) to test the performance in both reflection and transmission modes. Thus, the system is used to determine the Mueller matrices and associated optical constants of known optical systems: 1. optical rotatory power of D-glucose in solution, 2. reflection of a native oxide c-Si wafer, and 3. the properties of a liquid crystal spatial light modulator. The results show that the system matrices of the MME have condition numbers between the optimal and 2 during operation, resulting in small experimental errors. To the best of our knowledge, there is no other MME reported with such good conditioning over a comparably wide spectral range.
The optimal design over a broad spectral range of Liquid Crystal (LC) based Polarisation State Generators (PSG) and
Polarisation State Analyzers (PSA), requires detailed knowledge of the spectral behaviour of the LCs. The full Mueller
matrix measurement formalism based on the Eigenvalue Calibration Method, does in principle not require an exact
modelling of the polarizing components, however, it is required that the condition number for both the PSG and the PSA
is close to optimum over a wide spectral range. Two LC technologies are investigated here, Ferroelectric LC (FLC), and
Liquid Crystal Variable Retarders (LCVR). In the case of a FLC based PSG, additional components, such as fixed
retarders also need to be properly characterised in order for a proper broad spectral optimal design. These issues are here
studied by characterizing the FLCs, the LCVRs and the fixed retarders with the help of a commercial visible Mueller
matrix ellipsometer, and a polarizer-rotating sample-rotating analyzer near infra red set-up. The results are analyzed in
the framework of the optimal condition number over a broad spectral range.
Real time monitoring and control, by multiwavelength phase modulated ellipsometry of the growth of plasma deposited optical structures is presented. The transparent layers consists of SiO2 SiNx and oxynitrides. We present an efficient method for the estimation of the optical parameters based on a sliding window containing the last acquired measurements. This method is used to monitor the deposition of multilayer coatings with homogenous deposition conditions, and is also used in feedback control of such coatings. The sliding window method is further developed to follow slowly time-varying parameters such as the deposition rate. A preliminary study of a fast novel method based on the same principle for real time monitoring of refractive index gradients is described. As an example, the real time monitoring of the growth of a linear gradient index is demonstrated.
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