Linear Diattenuation Research Articles

Multiple scattering in turbid media containing chiral components: A Monte Carlo simulation

A Monte Carlo simulation was performed for an infinite plane medium containing spherical particles as well as a chiral component. The optical activity shifts patterns in the two-dimensional map of the effective scattering Mueller matrix in the azimuthal direction. The reduced effective matrix obtained by the simulation approximately satisfies reciprocity in spite of the theoretical prediction. The pattern shifts are explained by the mixing of elements of the reduced effective Mueller matrix owing to multiplication of two rotation matrices. The reduced effective matrix was factorized using the Lu-Chipman polar decomposition affording the polarization components as a function of the distance. The functions as a retarding linear diattenuator of the medium decreases, whereas the optical rotation increases, as the distance increases. The estimated specific rotation on the medium surface is 1.6 times larger than the specific rotation in the medium used in the simulation.

Corneal birefringence measured by spectrally resolved Mueller matrix ellipsometry and implications for non-invasive glucose monitoring.

A good understanding of the corneal birefringence properties is essential for polarimetric glucose monitoring in the aqueous humor of the eye. Therefore, we have measured complete 16-element Mueller matrices of single-pass transitions through nine porcine corneas in-vitro, spectrally resolved in the range 300…1000 nm. These ellipsometric measurements have been performed at several angles of incidence at the apex and partially at the periphery of the corneas. The Mueller matrices have been decomposed into linear birefringence, circular birefringence (i.e. optical rotation), depolarization, and diattenuation. We found considerable circular birefringence, strongly increasing with decreasing wavelength, for most corneas. Furthermore, the decomposition revealed significant dependence of the linear retardance (in nm) on the wavelength below 500 nm. These findings suggest that uniaxial and biaxial crystals are insufficient models for a general description of the corneal birefringence, especially in the blue and in the UV spectral range. The implications on spectral-polarimetric approaches for glucose monitoring in the eye (for diabetics) are discussed.

Noninvasive optical diagnostic of breast cancer using depolarization of light

Abstract In this study we implemented depolarization on whole blood samples of 20 adult breast cancer patients as well as 20 normal healthy persons and recorded Mueller matrix based polarization parameters. The most useful polarization parameter on the basis of which we can distinguish the breast cancer disease from normal is depolarization index. We have used a wavelength range of light from 400 to 800 nm wavelength at a fixed transmission window of 0.18 - 0.19 for all the samples. In case of Breast cancer 90% – 70% light is depolarized in the spectral range of 420 – 480 nm. For normal blood less light is depolarized i.e., 78% – 55%. For second spectral range 500 – 560 nm measure depolarization index is 23% – 20% for breast cancer but 15% – 14% for normal blood. Similarly, other polarization parameters like linear retardence, circular retardence, and linear diattenuation for breast cancer differ from normal blood samples.

Compound dichroic polarizers with wavelength-dependent transmission axes.

Compound dichroic polarizers using liquid crystal polymers and dichroic dyes have been studied for their variation of polarization with wavelength. Compound dichroic polarizers are composed of multilayer polarizers, where each layer has a different orientation and absorption spectrum. Several wavelength-dependent transmission axes configurations are proposed and investigated. Polarization properties, such as linear and circular diattenuation of the compound dichroic polarizers, for different wavelengths are measured and compared with simulation. Depending on the configuration, the compound dichroic polarizers can convert polarization signatures into color coding in unique ways.

Ex vivocharacterization of normal and adenocarcinoma colon samples by Mueller matrix polarimetry

Mueller matrix polarimetry along with polar decomposition algorithm was employed for the characterization of ex vivo normal and adenocarcinoma human colon tissues by polarized light in the visible spectral range (425-725 nm). Six derived polarization metrics [total diattenuation (DT ), retardance (RT ), depolarization(ΔT ), linear diattenuation (DL), retardance (δ), and depolarization (ΔL)] were compared for normal and adenocarcinoma colon tissue samples. The results show that all six polarimetric properties for adenocarcinoma samples were significantly higher as compared to the normal samples for all wavelengths. The Wilcoxon rank sum test illustrated that total retardance is a good candidate for the discrimination of normal and adenocarcinoma colon samples. Support vector machine classification for normal and adenocarcinoma based on the four polarization properties spectra (ΔT , ΔL, RT ,and δ) yielded 100% accuracy, sensitivity, and specificity, while both DTa nd DL showed 66.6%, 33.3%, and 83.3% accuracy, sensitivity, and specificity, respectively. The combination of polarization analysis and given classification methods provides a framework to distinguish the normal and cancerous tissues.

High Precision Stokes Polarimetry for Scattering Light using Wide Dynamic Range Intensity Detector

This paper proposes a Stokes polarimetry for scattering light from a sample surface. To achieve a high accuracy measurement two approaches of an intensity detector and analysis algorism of a Stokes parameter were proposed. The dynamic range of this detector can achieve up to 10 10 by combination of change of neutral-density (ND) filters having different density and photon counting units. Stokes parameters can be measured by dual rotating of a retarder and an analyzer. The algorism of dual rotating polarimeter can be calibrated small linear diattenuation and linear retardance error of the retarder. This system can measured Stokes parameters from −20° to 70° of its scattering angle. It is possible to measure Stokes parameters of scattering of dust and scratch of optical device with high precision. This paper shows accuracy of this system, checking the polarization change of scattering angle and influence of beam size.

Polarization lidar observations of backscatter phase matrices from oriented ice crystals and rain.

Oriented particles can exhibit different polarization properties than randomly oriented particles. These properties cannot be resolved by conventional polarization lidar systems and are capable of corrupting the interpretation of depolarization ratio measurements. Additionally, the typical characteristics of backscatter phase matrices from atmospheric oriented particles are not well established. The National Center for Atmospheric Research High Spectral Resolution Lidar was outfitted in spring of 2012 to measure the backscatter phase matrix, allowing it to fully characterize the polarization properties of oriented particles. The lidar data analyzed here considers operation at 4°, 22° and 32° off zenith in Boulder, CO, USA (40.0°N,105.2°W). The HSRL has primarily observed oriented ice crystal signatures at lidar tilt angles near 32° off zenith which corresponds to an expected peak in backscatter from horizontally oriented plates. The maximum occurrence frequency of oriented ice crystals is measured at 5 km, where 2% of clouds produced significant oriented ice signatures by exhibiting diattenuation in their scattering matrices. The HSRL also observed oriented particle characteristics of rain at all three tilt angles. Oriented signatures in rain are common at all three tilt angles. As many as 70% of all rain observations made at 22° off zenith exhibited oriented signatures. The oriented rain signatures exhibit significant linear diattenuation and retardance.

Quantitative Mueller matrix fluorescence spectroscopy for precancer detection

Quantitative fluorescence spectroscopic Mueller matrix measurements from the connective tissue regions of human cervical tissue reveal intriguing fluorescence diattenuation and polarizance effects. Interestingly, the estimated fluorescence linear diattenuation and polarizance parameters were considerably reduced in the precancerous tissues as compared to the normal ones. These polarimetry effects of the autofluorescence were found to originate from anisotropically organized collagen molecular structures present in the connective tissues. Consequently, the reduction of the magnitude of these polarimetric parameters at higher grades of precancer was attributed to the loss of anisotropic organization of collagen, which was also confirmed by control experiments. These results indicate that fluorescence spectral diattenuation and polarizance parameters may serve as potentially useful diagnostic metrics.

Evaluation of anisotropic chitosan hydrogels using analytical Mueller matrix method and scanned laser pico-projector

Chitosan has excellent biodegradable, biocompatible and bio-absorbable properties and has been found increasing use in the biomedical field in recent decades. The linear birefringence (LB), linear diattenuation (LD), circular birefringence (CB), circular diattenuation (CD), and depolarization properties of chitosan hydrogel films crosslinked in citrate acid buffer solution (CBS) are extracted using an analytical Mueller matrix method. It is shown that the optical phase retardance property of the hydrogel films provides a reliable indication of both the chitosan concentration of the film and the pH value of the CBS crosslinking environment. In addition, chitosan hydrogel suspension with low-concentration crosslinked in CBS environments with various pH values are studied by the speckle contrast of the projected images obtained when illuminating the suspension with a scanned laser pico-projector (SLPP). It is found that for the samples crosslinked in an acidic environment, the speckle contrast decreases with an increasing pH value. By contrast, for the samples crosslinked in an alkaline CBS environment, the speckle contrast increases as the pH value increases. It is concluded that both the phase retardance and the speckle contrast enable the pH value of the CBS crosslinking solution to be reliably determined. However, of the two methods, the SLPP method yields improved measurement sensitivity. Overall, the results presented in this study show that the analytical Mueller matrix method and SLPP method provide an effective means of characterizing the optical properties, concentration and crosslinking environment of chitosan hydrogel films and suspensions.

Controlled transportation of mesoscopic particles by enhanced spin-orbit interaction of light in an optical trap

We study the effects of the spin orbit interaction (SOI) of light in an optical trap and show that the propagation of the tightly focused trapping beam in a stratified medium can lead to significantly enhanced SOI. For a plane polarized incident beam the SOI manifests itself by giving rise to a strong anisotropic linear diattenuation effect which produces polarization-dependent off-axis high intensity side lobes near the focal plane of the trap. Single micron-sized asymmetric particles can be trapped in the side lobes, and transported over circular paths by a rotation of the plane of input polarization. We demonstrate such controlled motion on single pea-pod shaped single soft oxometalate (SOM) particles of dimension around $1\times 0.5\mu$m over lengths up to $\sim$15 $\mu$m . The observed effects are supported by calculations of the intensity profiles based on a variation of the Debye-Wolf approach. The enhanced SOI could thus be used as a generic means of transporting mesoscopic asymmetric particles in an optical trap without the use of complex optical beams or changing the alignment of the beam into the trap.

Probing the fractal pattern and organization ofBacillus thuringiensisbacteria colonies growing under different conditions using quantitative spectral light scattering polarimetry

Development of methods for quantification of cellular association and patterns in growing bacterial colony is of considerable current interest, not only to help understand multicellular behavior of a bacterial species but also to facilitate detection and identification of a bacterial species in a given space and under a given set of condition(s). We have explored quantitative spectral light scattering polarimetry for probing the morphological and structural changes taking place during colony formations of growing Bacillus thuringiensis bacteria under different conditions (in normal nutrient agar representing favorable growth environment, in the presence of 1% glucose as an additional nutrient, and 3 mM sodium arsenate as toxic material). The method is based on the measurement of spectral 3×3 Mueller matrices (which involves linear polarization measurements alone) and its subsequent analysis via polar decomposition to extract the intrinsic polarization parameters. Moreover, the fractal micro-optical parameter, namely, the Hurst exponent H, is determined via fractal-Born approximation-based inverse analysis of the polarization-preserving component of the light scattering spectra. Interesting differences are noted in the derived values for the H parameter and the intrinsic polarization parameters (linear diattenuation d, linear retardance δ, and linear depolarization Δ coefficients) of the growing bacterial colonies under different conditions. The bacterial colony growing in presence of 1% glucose exhibit the strongest fractality (lowest value of H), whereas that growing in presence of 3 mM sodium arsenate showed the weakest fractality. Moreover, the values for δ and d parameters are found to be considerably higher for the colony growing in presence of glucose, indicating more structured growth pattern. These findings are corroborated further with optical microscopic studies conducted on the same samples.

Quantitative polarimetry of plasmon resonant spheroidal metal nanoparticles: A Mueller matrix decomposition study

Quantitative polarization characteristics of plasmon resonant spheroidal metal (silver) nanoparticles are investigated using polar decomposition of scattering Mueller matrices. The decomposition analysis on the scattering matrices (computed using T-matrix approach) of preferentially oriented spheroidal silver nanoparticles showed enhanced linear retardance (δ) and diattenuation (d) effects in their surface plasmon resonance bands, with intriguing spectral characteristics. While the magnitude of δ (λ) peaked around the spectral overlap region of the transverse and the longitudinal dipolar plasmon resonance bands, d (λ) peaked at wavelengths corresponding to the peaks of these two bands. The observed linear retardance and diattenuation effects were attributed to the inherent differences in phases and amplitudes respectively, of the two orthogonal dipolar plasmon polarizabilities of the spheroidal metal nanoparticles, which were confirmed further by studying their angular dependence. Further, when averaged over all possible ( random) orientation, addition of the individual retardance matrices having random orientation of axes manifests as stronger depolarization (Δ) in spheroidal metal nanoparticles as compared to their dielectric counterparts. Consequently, the spectral variations of Δ (λ) for the randomly oriented nanoparticles resembled that for the variation of δ (λ) for the preferentially oriented ones. Derivation, quantification and unique interpretation of the intrinsic plasmon polarization characteristics (and their spectral behavior) aided by Mueller matrix decomposition may have important implications for contrast enhancement in nanoparticle-based biomedical imaging, as well as in other applications involving nano-plasmonics.

Design of Polarization-Insensitive Optical Fiber Probe Based on Effective Optical Parameters

When using an optical fiber probe to measure the properties of anisotropic optical materials, some form of polarization controller is required to compensate for the inherent birefringence and diattenuation properties of the fiber. The experimental settings of the optical components within the polarization controller are generally determined on a trial-and-error basis; resulting in a lengthy experimentation process. Accordingly, in the present study, a method is proposed for calculating in advance the precise controller settings required to guarantee the formation of a free-space condition. In the proposed approach, the effective optical parameters of the optical fiber are determined using an analytical method, and the optimal settings of the polarization controller are then determined using a genetic algorithm. It is shown that the proposed approach enables a free-space condition to be achieved for the common polarization controller. The practical applicability of the proposed approach is demonstrated by remotely and absolutely measuring the linear birefringence and linear diattenuation properties of a quarter-wave plate and a polarizer, respectively.

Characterization on five effective parameters of anisotropic optical material using Stokes parameters—Demonstration by a fiber-type polarimeter

An analytical technique based on the Mueller matrix method and the Stokes parameters is proposed for extracting five effective parameters on the principal axis angle, phase retardance, diattenuation axis angle, diattenuation and optical rotation angle of anisotropic optical materials. The linear birefringence (LB) / circular birefringence (CB) properties and linear diattenuation (LD) properties are decoupled within the analytical model. The analytical method is then integrated with a genetic algorithm to extract the optical properties of samples with linear birefringence property using a fiber-based polarimeter. The result demonstrates the feasibility of analytical model in characterizing five effective parameters of anisotropic optical material. Also, it confirms that the proposed fiber-based polarimeter provides a simple alternative to existing fiber-based probes for parameter measurement in the near field or the remote environment. A low birefringence fiber-based polarimeter based on effective parameters and genetic algorithm without using a fiber polarization controller is first proposed confirmatively.

Using polarimeter and Stokes parameters for measuring linear birefringence and diattenuation properties of optical samples

A technique is proposed for measuring the linear birefringence and linear diattenuation of an optical sample using a polarimeter. In the proposed approach, the principal axis angle (α), phase retardance (β), diattenuation axis angle (θd ), and diattenuation (D ) are derived using an analytical model based on the Mueller matrix formulation and the Stokes parameters. The dynamic measurement ranges of the four parameters are shown to be α = 0~180°, β = 0~180°, θd = 0~180°, and D = 0~1, respectively. Thus, full-range measurements are possible for all parameters other than β. In this study, the proposed methodology does not require the principal birefringence axes and diattenuation axes to be aligned. In addition, the linear birefringence and linear diattenuation properties are decoupled within the analytical model, and thus the birefringence properties of the sample can be solved directly without any prior knowledge of the diattenuation parameters.

Polarized diffuse reflectance measurements on cancerous and noncancerous tissues

We report the measurement of polarization parameters (linear retardance, diattenuation and depolarization) of normal and malignant tissue from human oral cavity and breast over the spectral range 390 nm to 550 nm. These parameters were determined using the 3 x 3 Mueller matrix, the elements of which could be determined using linear polarization measurements only. The significant differences observed in the polarization parameters of the normal and malignant tissues appear to arise because of the changes in the collagen matrix in the two tissue types.

Measurement of linear birefringence and diattenuation properties of optical samples using polarimeter and Stokes parameters

A technique is proposed for measuring the linear birefringence and linear diattenuation of an optical sample using a polarimeter. In the proposed approach, the principal axis angle (alpha), phase retardance (beta), diattenuation axis angle (thetad), and diattenuation (D) are derived using an analytical model based on the Mueller matrix formulation and the Stokes parameters. The dynamic measurement ranges of the four parameters are shown to be alpha = 0 approximately 180 degrees, beta = 0 approximately 180 degrees, theta(d) = 0 approximately 180 degrees, and D = 0 approximately 1, respectively. Thus, full-range measurements are possible for all parameters other than beta. In this study, the proposed methodology does not require the principal birefringence axes and diattenuation axes to be aligned. In addition, the linear birefringence and linear diattenuation properties are decoupled within the analytical model, and thus the birefringence properties of the sample can be solved directly without any prior knowledge of the diattenuation parameters. Also, the characteristic parameters in the baked polarizer with linear birefringence are successfully extracted from an optically equivalent model and proved by the respective simulation and experiment introduced in this study.

Polarimetry in turbid, birefringent, optically active media: A Monte Carlo study of Mueller matrix decomposition in the backscattering geometry

Determination of the intrinsic polarization properties of a complex turbid medium such as biological tissue in the backscattering geometry (a geometry that is convenient for in situ applications) is complicated due to the confounding influence of scattering, and due to simultaneous occurrence of several polarization effects. We have investigated the polar decomposition approach of Mueller matrices to delineate individual intrinsic polarization parameters (specifically linear retardance δ and optical rotation ψ) of a birefringent, chiral, turbid medium in the backscattering geometry, using Mueller matrices generated with polarization-sensitive Monte Carlo simulations. The results show that near the exact backscattering direction, the interplay of the scattering-induced linear retardance and diattenuation on the intrinsic values for δ and ψ is coupled in a complex interrelated way, due to contribution of the backscattered photons. In contrast, these effects were significantly reduced for detection positions at distances larger than a transport length away from the point of illumination. Simultaneous determination of the intrinsic values for δ and ψ of a birefringent, chiral, turbid medium in the backward detection geometry can thus be accomplished by decomposing the Mueller matrices recorded at distances larger than a transport length away from the point of illumination. Determination of the intrinsic values for these polarization parameters in backscattering geometry could be significant in, for example, for quantification of tissue structural anisotropy and for noninvasive blood glucose measurements of diabetic patients.

Spectroscopic Mueller matrix polarimeter using four-channeled spectra

A Mueller matrix polarimeter acquired for four-channeled spectra is proposed. Both the polarizing and analyzing optics of this system consist of a linear polarizer and a high-order retarder. The polarizing elements can modulate the polarization states in the wavenumber space. By applying a Fourier transform method to a single-channeled spectrum, nine elements of the Mueller matrix can be deconvoluted without modifying the configuration of either the polarizing or analyzing optics. It is thus possible to determine the wavelength dependence of all the Mueller matrix elements from four-channeled spectra obtained using four different configurations for the polarizing and analyzing optics. The performance of this method is evaluated by measuring polarization properties, such as retardance, azimuthal angle, and linear diattenuation, from the obtained Mueller matrix in wavenumber space.

Mueller matrix decomposition for extraction of individual polarization parameters from complex turbid media exhibiting multiple scattering, optical activity, and linear birefringence

Linear birefringence and optical activity are two common optical polarization effects present in biological tissue, and determination of these properties has useful biomedical applications. However, measurement and unique interpretation of these parameters in tissue is hindered by strong multiple scattering effects and by the fact that these and other polarization effects are often present simultaneously. We have investigated the efficacy of a Mueller matrix decomposition methodology to extract the individual intrinsic polarimetry characteristics (linear retardance delta and optical rotation psi, in particular) from a multiply scattering medium exhibiting simultaneous linear birefringence and optical activity. In the experimental studies, a photoelastic modulation polarimeter was used to record Mueller matrices from polyacrylamide phantoms having strain-induced birefringence, sucrose-induced optical activity, and polystyrene microspheres-induced scattering. Decomposition of the Mueller matrices recorded in the forward detection geometry from these phantoms with controlled polarization properties yielded reasonable estimates for delta and psi parameters. The confounding effects of scattering, the propagation path of multiple scattered photons, and detection geometry on the estimated values for delta and psi were further investigated using polarization-sensitive Monte Carlo simulations. The results show that in the forward detection geometry, the effects of scattering induced linear retardance and diattenuation are weak, and the decomposition of the Mueller matrix can retrieve the intrinsic values for delta and psi with reasonable accuracy. The ability of this approach to extract the individual intrinsic polarimetry characteristics should prove valuable in diagnostic photomedicine, for example, in quantifying the small optical rotations due to the presence of glucose in tissue and for monitoring changes in tissue birefringence as a signature of tissue abnormality.