Optical fiber-based full Mueller polarimeter for endoscopic imaging using a two-wavelength simultaneous measurement method.

This paper reports a technique based on spectrally differential measurement for determining the full Mueller matrix of a biological sample through an optical fiber. In this technique, two close wavelengths were used simultaneously, one for characterizing the fiber and the other for characterizing the assembly of fiber and sample. The characteristics of the fiber measured at one wavelength were used to decouple its contribution from the measurement on the assembly of fiber and sample and then to extract sample Mueller matrix at the second wavelength.

Self-organized arrays of dislocations in thin smectic liquid crystal films.

Combining optical microscopy, synchrotron X-ray diffraction and ellipsometry, we studied the internal structure of linear defect domains (oily streaks) in films of a smectic liquid crystal 8CB with thicknesses in the range of 100-300 nm. These films are confined between air and a rubbed PVA polymer substrate which imposes hybrid anchoring conditions (normal and unidirectional planar, respectively). We show how the presence or absence of dislocations controls the structure of highly deformed thin smectic films.

Differential Mueller matrix of a depolarizing homogeneous medium and its relation to the Mueller matrix logarithm.

The different z-dependence and non-commutativity of the two components of the differential Mueller matrix of a homogeneous depolarizing medium prevent its formal identification with the Mueller matrix logarithm. By using a classic linear differential equation expansion, we advance a procedure for the extraction of the elementary polarization properties, in terms of mean values and variances-covariances, from the Mueller matrix logarithm. The approximate solution, based on the immediate identification of the differential matrix with the matrix logarithm, turns out to remain satisfactory up to relatively high depolarization levels.

Optimization of Picrosirius red staining protocol to determine collagen fiber orientations in vaginal and uterine cervical tissues by Mueller polarized microscopy.

Polarized microscopy provides unique information on anisotropic samples. In its most complete implementation, namely Mueller microscopy, this technique is well suited for the visualization of fibrillar proteins orientations, with collagen in the first place. However, the intrinsic optical anisotropy of unstained tissues has to be enhanced by Picrosirius Red (PR) staining to enable Mueller measurements.

Demonstration of full 4×4 Mueller polarimetry through an optical fiber for endoscopic applications.

A novel technique to measure the full 4 × 4 Mueller matrix of a sample through an optical fiber is proposed, opening the way for endoscopic applications of Mueller polarimetry for biomedical diagnosis. The technique is based on two subsequent Mueller matrices measurements: one for characterizing the fiber only, and another for the assembly of fiber and sample. From this differential measurement, we proved theoretically that the polarimetric properties of the sample can be deduced.

Determination of collagen fiber orientation in histological slides using Mueller microscopy and validation by second harmonic generation imaging.

We studied the azimuthal orientations of collagen fibers in histological slides of uterine cervical tissue by two different microscopy techniques, namely Mueller polarimetry (MP) and Second Harmonic Generation (SHG). SHG provides direct visualization of the fibers with high specificity, which orientations is then obtained by suitable image processing. MP provides images of retardation (among other polarimetric parameters) due to the optical anisotropy of the fibers, which is enhanced by Picrosirius Red staining.

Polarimetric imaging of uterine cervix: a case study.

We present a preliminary investigation of macroscopic polarimetric imaging of uterine cervix. Orthogonal state contrast (OSC) images of healthy and anomalous cervices have been taken in vivo at 550 nm. Four ex vivo cervix samples have been studied in full Muller polarimetry, at 550 nm and 700 nm, and characterized in detail by standard pathology.

Multispectral Mueller polarimetric imaging detecting residual cancer and cancer regression after neoadjuvant treatment for colorectal carcinomas.

This work is devoted to a first exploration of Mueller polarimetric imaging for the detection of residual cancer after neoadjuvant treatment for the rectum. Three samples of colorectal carcinomas treated by radiochemotherapy together with one untreated sample are analyzed ex vivo before fixation in formalin by using a multispectral Mueller polarimetric imaging system operated from 500 to 700 nm. The Mueller images, analyzed using the Lu-Chipmann decomposition, show negligible diattenuation and retardation.

Application of spectroscopic ellipsometry and Mueller ellipsometry to optical characterization.

This article provides a brief overview of both established and novel ellipsometry techniques, as well as their applications. Ellipsometry is an indirect optical technique, in that information about the physical properties of a sample is obtained through modeling analysis. Standard ellipsometry is typically used to characterize optically isotropic bulk and/or layered materials.

Ex vivo photometric and polarimetric multilayer characterization of human healthy colon by multispectral Mueller imaging.

Healthy human colon samples were analyzed ex vivo with a multispectral imaging Mueller polarimeter operating from 500 to 700 nm in a backscattering configuration with diffuse light illumination impinging on the innermost tissue layer, the mucosa. The intensity and polarimetric responses were taken on whole tissues first and after progressive exfoliation of the outer layers afterwards. Moreover, these measurements were carried out with two different substrates (one bright and the other dark) successively placed beneath each sample, allowing a reasonably accurate evaluation of the contributions to the overall backscattered light by the various layers.

Impact of model parameters on Monte Carlo simulations of backscattering Mueller matrix images of colon tissue.

Polarimetric imaging is emerging as a viable technique for tumor detection and staging. As a preliminary step towards a thorough understanding of the observed contrasts, we present a set of numerical Monte Carlo simulations of the polarimetric response of multilayer structures representing colon samples in the backscattering geometry. In a first instance, a typical colon sample was modeled as one or two scattering "slabs" with monodisperse non absorbing scatterers representing the most superficial tissue layers (the mucosa and submucosa), above a totally depolarizing Lambertian lumping the contributions of the deeper layers (muscularis and pericolic tissue).

Effect of speckle on APSCI method and Mueller Imaging.

The principle of the polarimetric imaging method called APSCI (Adapted Polarization State Contrast Imaging) is to maximize the polarimetric contrast between an object and its background using specific polarization states of illumination and detection. We perform here a comparative study of the APSCI method with existing Classical Mueller Imaging(CMI) associated with polar decomposition in the presence of fully and partially polarized circular Gaussian speckle. The results show a noticeable increase of the Bhattacharyya distance used as our contrast parameter for the APSCI method, especially when the object and background exhibit several polarimetric properties simultaneously.

Ex-vivo characterization of human colon cancer by Mueller polarimetric imaging.

Cancerous and healthy human colon samples have been analyzed ex-vivo using a multispectral imaging Mueller polarimeter operated in the visible (from 500 to 700 nm) in a backscattering configuration with diffuse light illumination. Three samples of Liberkühn colon adenocarcinomas have been studied: common, mucinous and treated by radiochemotherapy. For each sample, several specific zones have been chosen, based on their visual staging and polarimetric responses, which have been correlated to the histology of the corresponding cuts.

Mueller matrix imaging of human colon tissue for cancer diagnostics: how Monte Carlo modeling can help in the interpretation of experimental data.

Colon samples with both healthy and cancerous regions have been imaged in diffuse light and backscattering geometry by using a Mueller imaging polarimeter. The tumoral parts at the early stage of cancer are found to be less depolarizing than the healthy ones. This trend clearly shows that polarimetric imaging may provide useful contrasts for optical biopsy.

Experimental validation of the symmetric decomposition of Mueller matrices.

We experimentally assess the validity of the symmetric decomposition of Mueller matrices [R. Ossikovski, J. Opt.

Scattered light measurements on textured crystalline silicon substrates using an angle-resolved Mueller matrix polarimeter.

Dry plasma etching is a promising technique for crystalline silicon surface texturing aimed at improving solar cell efficiencies by reducing incident light reflection and backscattering at the cell front surface. In this work we present a new optical characterization technique for textured surfaces based on a Mueller polarimeter coupled with a high numerical aperture microscope operated either in real or in angular spaces. This tool provides both the specularly reflected and the angle-resolved backscattered intensities in a very efficient manner, due to the absence of moving parts.

Sources of possible artefacts in the contrast evaluation for the backscattering polarimetric images of different targets in turbid medium.

It is known that polarization-sensitive backscattering images of different objects in turbid media may show better contrasts than usual intensity images. Polarimetric image contrast depends on both target and background polarization properties and typically involves averaging over groups of pixels, corresponding to given areas of the image. By means of numerical modelling we show that the experimental arrangement, namely, the shape of turbid medium container, the optical properties of the container walls, the relative positioning of the absorbing, scattering and reflecting targets with respect to each other and to the container walls, as well as the choice of the image areas for the contrast calculations, can strongly affect the final results for both linearly and circularly polarized light.

Spectroscopic ellipsometry and polarimetry for materials and systems analysis at the nanometer scale: state-of-the-art, potential, and perspectives.

This paper discusses the fundamentals, applications, potential, limitations, and future perspectives of polarized light reflection techniques for the characterization of materials and related systems and devices at the nanoscale. These techniques include spectroscopic ellipsometry, polarimetry, and reflectance anisotropy. We give an overview of the various ellipsometry strategies for the measurement and analysis of nanometric films, metal nanoparticles and nanowires, semiconductor nanocrystals, and submicron periodic structures.

Angle resolved Mueller polarimetry with a high numerical aperture and characterization of transparent biaxial samples.

We present a polarimetric instrument suitable for the simultaneous measurement of angle resolved normalized Mueller matrices for polar angles ranging from 0 degrees to 60 degrees and all azimuths. The polarimetric modulation and analysis are performed by means of an optimized polarization state generator and analyzer based on nematic liquid crystals. A high numerical aperture (0.

Experimental evidence for naturally occurring nondiagonal depolarizers.

We report on two Stokes nondiagonalizable Mueller matrices experimentally observed in a biological and in an organic sample. These matrices are examples of naturally occurring nondiagonal depolarizers whose unique property is to preserve the degree of polarization of all but one totally polarized light state. The description of the experimental matrices within the theory of Bragg scattering on cholesteric liquid crystals, as well as their interpretation in physical and structural terms, are likewise addressed.

Adapted polarization state contrast image.

We propose a general method to maximize the polarimetric contrast between an object and its background using a predetermined illumination polarization state. After a first estimation of the polarimetric properties of the scene by classical Mueller imaging, we evaluate the incident polarized field that induces scattered polarization states by the object and background, as opposite as possible on the Poincar e sphere. With a detection method optimized for a 2-channel imaging system, Monte Carlo simulations of low flux coherent imaging are performed with various objects and backgrounds having different properties of retardance, dichroism and depolarization.

Experimental implementation and properties of Stokes nondiagonalizable depolarizing Mueller matrices.

We report on the experimental realization of a family of depolarizing Mueller matrices that are Stokes nondiagonalizable. We likewise demonstrate a unique characteristic property of Stokes nondiagonalizable matrices consisting in the preservation of the degree of polarization of a single totally polarized input and illustrate it on our experimental example.

Registration scheme suitable to Mueller matrix imaging for biomedical applications.

Most Mueller matrix imaging polarimeters implement sequential acquisition of at least 16 raw images of the same object with different incident and detected light polarizations. When this technique is implemented in vivo, the unavoidable motions of the subject may shift and distort the raw images to an extent such that the final Mueller images cannot be extracted. We describe a registration algorithm which solves this problem for the typical conditions of in vivo imaging, e.

Metrology of replicated diffractive optics with Mueller polarimetry in conical diffraction.

The feasibility of metrological characterization of the one-dimensional (1D) holographic gratings, used in the nanoimprint molding tool fabrication step, by spectroscopic Mueller polarimetry in conical diffraction is investigated. The studied samples correspond to two different steps of the replicated diffraction grating fabrication process. We characterized master gratings that consist of patterned resist layer on chromium-covered glass substrate and complementary (replica) gratings made of nickel.