Investigating starch gelatinization through Stokes vector resolved second harmonic generation microscopy

Interaction of polarized light with healthy and abnormal regions of tissue reveals structural information associated with its pathological condition. Even a slight variation in structural alignment can induce a change in polarization property, which can play a crucial role in the early detection of abnormal tissue morphology. We propose a transmission-based Stokes-Mueller microscope for quantitative analysis of the microstructural properties of the tissue specimen. The Stokes-Mueller based polarization microscopy provides significant structural information of tissue through various polarization parameters such as degree of polarization (DOP), degree of linear polarization (DOLP), and degree of circular polarization (DOCP), anisotropy (r) and Mueller decomposition parameters such as diattenuation, retardance and depolarization. Further, by applying a suitable image processing technique such as Machine learning (ML) output images were analysed effectively. The support vector machine image classification model achieved 95.78% validation accuracy and 94.81% testing accuracy with polarization parameter dataset. The study's findings demonstrate the potential of Stokes-Mueller polarimetry in tissue characterization and diagnosis, providing a valuable tool for biomedical applications.

Characterization of pathological thyroid tissue using polarization-sensitive second harmonic generation microscopy

Effect of liquid fraction and bubble size distribution on the polarised light scattering characteristics of Casein foam

The visibility of inverted domain structures using the second harmonic generation (SHG) microscope is discussed based upon the three-wave coupling equations. Without reference second harmonic (SH) waves (non-interference case), the SHG intensity at a domain boundary decreases steeply along the perpendicular direction to the domain wall, which is observed as a dark line. Thus the non-interference SHG microscope reveals the location of domain boundaries but not the domain polarity which the SHG interference microscope can do. In the case of periodically poled domain structures, the clear observation criterion is expressed with the wave-number offset between the fundamental and SH waves.

We describe a Stokes polarimetry imaging technique that quantifies the polarization properties of remitted light backscattered from a sample. Right- and left-circularly polarized near-infrared light was used to illuminate rat-tail tissue embedded in turbid gelatin. The degree of linear polarization (DoLP) and degree of circular polarization (DoCP) image-maps indicate that increasing the depth of the rat tail within the turbid medium and varying the rat-tail geometry and orientation relative to the light source affected the contrast between structures and adjacent tissue layers. Stokes polarimetry imaging shows that the intervertebral discs and soft tissue regions of rat tails strongly depolarize incident circularly polarized light. Tendon regions remit light with a more linear form due to birefringence. Both DoLP and DoCP image-maps provide contrast between tissue structures. When differentiating between unpolarized light and light with low DoCP or DoLP, the polarization of backscattered light from the turbid medium must to be taken into consideration.

We have investigated the diffusion of the photosensitizer Chlorin-p(6) (Cp(6)) across a egg lecithin lipid bilayer at different pH by the Second Harmonic Generation (SHG) method. Cp(6) has three ionizable carboxylic acid groups, and consequently, neutral and several ionic forms of Cp(6) are expected to be present in the pH range 3-8. The absorption spectra of Cp(6) get considerably modified in the presence of liposomes as the pH is decreased indicating that the drug liposome binding is pH dependent. The first pK(a) of interconversion (D-C) has been identified at pH ~7.0 by fluorescence measurement in an earlier work. In this work, the second pK(a) of interconversion (C-B) has been identified at pH ~4.8 by the hyper-Rayleigh scattering method. At acidic pH (3, 4, and 5), where species A, B, and C are dominant, the addition of liposomes to a Cp(6) solution generates an instantaneous rise (less than 1 s) in the second harmonic (SH) signal followed by decays whose time constants ranged from ten to hundreds of seconds. The instantaneous rise is attributed to the adsorption of Cp(6) to the outer lipid bilayer, and the decay is attributed to the diffusion of the neutral and charged (A and B) species of the drug. The observed fast and slow time constants for diffusion in the pH range 3-5 are attributed to the neutral (A) and ionic form (B) of Cp(6), respectively. At pH 6, the intensity of the generated SH signals on the addition of liposome reduced, and at physiological pH, it was too weak to be detected. These results are consistent with previous studies that show that the interaction between Cp(6) and egg-PC liposomes is pH dependent. At lower pH due to the presence of the hydrophobic species (A and B) of Cp(6), its interaction with liposomes is strong, and at higher pH, the abundance of the negatively charged hydrophilic species (C and D) decreases the interaction with the like charged liposomes. We have also studied the effect of increasing the bilayer rigidity by decreasing the temperature of the medium or by incorporating 50 mol % cholesterol in the lipid bilayer and observed that lowering of temperature has more profound effect on the diffusion rates. The characteristics of the SH signal changed significantly when liposomes incorporating 50 mol % cholesterol were used at a low (3 °C) temperature. Under these conditions, the SH signal consisted of an instantaneous (<1s) followed by a slower rise (10-90s), and then, it decayed on a much longer time scale. This slow rise of the SH signal at pH 3 and 4 may be attributed to the temperature dependent adsorption of the anionic species (B) of Cp(6) with the liposomes. Further investigations are required in order to understand clearly the pH dependent diffusion of this drug across lipid bilayers.

In this paper, we investigated the second harmonic (SH) and the third harmonic (TH) generations in nanorods and nanotubes. Nonlinear free and bound electrons responses of metal combined with the third-order nonlinearity of dielectric core were utilized to study the nonlinear response of nanotubes made of noble metals such as gold. The impacts of the dielectric constant of core medium, thickness of metal shell, and size of nanotube on the SH and TH conversion efficiency are reported. The physical interpretations behind the results are discussed. Finally, we have shown that enhancement of the SH and TH generations are more noticeable and adjustable by varying the core-shell parameters compared to those of nanorods.

Second Harmonic Generation (SHG) has become a powerful tool for studying the surfaces of liquids and other centric systems [1], but due to the symmetry rule no Second Harmonic (SH) can be produced from their bulk. It is then of great interest that a number of recent experimental studies have shown strong SHG from randomly oriented suspension of finely fragmented purple membranes of Halobacterium halobium contain Bacteriorhodopsin (BR) [2 ], which belongs to the family of retinal proteins. The understanding of the nature of the SH signal itself still constitutes an obscure matter. Most of the mechanisms proposed for the description of this effect, have focused on the hyper-Rayleigh incoherent scattering, but some of them suggest also coherent nonlinear contributions into the SH signal.

Motivated by several observations of the degree of linear polarization of skylight in the oxygen A (O(2)A) band that do not yet have a quantitative explanation, we analyze the influence of aerosol altitude, microphysics, and optical thickness on the degree of linear polarization of the zenith skylight in the spectral region of the O(2)A band, between 755 to 775 nm. It is shown that the degree of linear polarization inside the O(2)A band is particularly sensitive to aerosol altitude. The sensitivity is strongest for aerosols within the troposphere and depends also on their microphysical properties and optical thickness. The polarization of the O(2)A band can be larger than the polarization of the continuum, which typically occurs for strongly polarizing aerosols in an elevated layer, or smaller, which typically occurs for depolarizing aerosols or cirrus clouds in an elevated layer. We show that in the case of a single aerosol layer in the atmosphere a determination of the aerosol layer altitude may be obtained. Furthermore, we show limitations of the aerosol layer altitude determination in case of multiple aerosol layers. To perform these simulations we developed a fast method for multiple scattering radiative transfer calculations in gaseous absorption bands including polarization. The method is a combination of doubling-adding and k-binning methods. We present an error estimation of this method by comparing with accurate line-by-line radiative transfer simulations. For the Motivated by several observations of the degree of linear polarization of skylight in the oxygen A (O(2)A) band that do not yet have a quantitative explanation, we analyze the influence of aerosol altitude, microphysics, and optical thickness on the degree of linear polarization of the zenith skylight in the spectral region of the O(2)A band, between 755 to 775 nm. It is shown that the degree of linear polarization inside the O(2)A band is particularly sensitive to aerosol altitude. The sensitivity is strongest for aerosols within the troposphere and depends also on their microphysical properties and optical thickness. The polarization of the O(2)A band can be larger than the polarization of the continuum, which typically occurs for strongly polarizing aerosols in an elevated layer, or smaller, which typically occurs for depolarizing aerosols or cirrus clouds in an elevated layer. We show that in the case of a single aerosol layer in the atmosphere a determination of the aerosol layer altitude may be obtained. Furthermore, we show limitations of the aerosol layer altitude determination in case of multiple aerosol layers. To perform these simulations we developed a fast method for multiple scattering radiative transfer calculations in gaseous absorption bands including polarization. The method is a combination of doubling-adding and k-binning methods. We present an error estimation of this method by comparing with accurate line-by-line radiative transfer simulations. For the O(2)A band, the errors in the degree of linear polarization are less than 0.11% for transmitted light, and less than 0.31% for reflected light. band, the errors in the degree of linear polarization are less than 0.11% for transmitted light, and less than 0.31% for reflected light.

We present a novel phase-based filtering algorithm designed to retrieve the Degree of Linear Polarization (DoLP) and Angle of Linear Polarization (AoLP) by leveraging the intrinsic properties of a pixelated polarization camera. Unlike conventional intensity-based filters, our approach utilizes complex phase values to estimate polarization parameters, offering a flexible and computationally efficient alternative. Each point is treated as an independent measurement, dependent solely on the kernel size, which enables the potential for real-time processing. Experimental and simulation evaluations under Gaussian noise conditions validate the robustness of our approach, demonstrating a high degree of consistency with standard methods. The ANOVA analysis results reflect this consistency across datasets, as indicated by the sum of squares (SS), mean squares (MS), and F-statistic values. This reinforces the reliability of the proposed algorithm and highlights its practical applicability in noise-affected environments. Our findings suggest that the proposed method provides a stable and adaptable solution for polarization parameter extraction, making it well-suited for applications in fields such as biomedical imaging, remote sensing, and industrial inspection, where real-time performance and noise resilience are critical.

A number of liquid crystalline cyclic pentamethylsiloxane compounds were synthesized containing high concentrations of covalently attached disperse red 1(4-[N-ethyl, N- hydroxyethylamino]-4'-nitroazobenzene) pendant groups. Corona poling (1.0 (mu) A/-5 kV) was used to align these pendant groups in thin films (1 - 2 micrometers ) produced by spin coating onto ITO covered glass substrates. The measured second harmonic (SH) intensities of these films were comparable to 1 mm thick, y-cut quartz. The initial rise in the SH signal at 25 degree(s)C occurred in less than 10 seconds. This was followed by an additional 20 - 50% increase in the signal over the next 1 - 15 minutes to a final equilibrium value. The SH signal of compounds in the smectic or nematic phase increased to a value of 0.7 - 1.0 X the quartz standard upon heating. An upper temperature limit for each material was observed prior to the dielectric breakdown of the film. The SH intensity typically decayed back to its prepoling value within one hour for films that were poled at 25 degree(s)C. Long term SH stability was observed in films that were poled at elevated temperatures. The intensity of the SH signal was found to be a function of the composition, liquid crystalline phase, and temperature.

In this work, we present the experimental phase function and degree of linear polarization of twosets of samples consisting of forsterite and spinel particles. The size distributions of the studiedsamples span over a broad range in the scattering size parameter domain. This work is part ofan ongoing experimental project devoted to understand photopolarimetric observations of asteroidsand comets. In particular, we study the effect of the size on the scattering matrix elements, findinga strong dependence of characteristic parameters, e.g. maximum of polarization and inversion angle,on particles size.IntroductionPolarimetric observations of dust clouds are a powerful tool in planetary science. They allow usinvestigating the nature and properties of solar system bodies and planetary systems in differentstages of evolution, e.g. asteroids, comets, and protoplanetary disks. For example, they can beused as a reference to refine the taxonomic classification of asteroids [1, 2] or they can help in thediscrimination of objects with cometary origin [3]. Some dust materials, like olivine and spinel,are remarkably interesting for the investigation and characterization of solar system small bodies.In particular, olivine is an extensively diffuse silicate mineral and spinel, a magnesium/aluminummineral, is a characteristic component of the unusual class of presumably ancient Barbarian asteroidsas well as an important component of Calcium Aluminium rich Inclusions (CAI) found in primitivemeteorites [6, 7]. Physical and optical properties of the dust, such as their refractive index, size,composition, and structure define their ability to scatter the light. Therefore, in order to study thesematerials, we need to experimentally characterize their photopolarimetric curves.MeasurementsWe analyze six samples of olivine and spinel with different sizes. The samples denoted as Pebbleconsist of millimeter-sized grains and lie in the geometrical optics regime. Further, two sizedistributions consisting of particles smaller than 30 and 100 micrometers are produced out of theolivine and spinel bulk samples. The measurements have been performed at the IAA Cosmic DustLaboratory (CODULAB), Granada, Spain [4]. The instrument allows to measure the scatteringmatrix of a cloud of particles and can be set also to retrieve the scattering matrix of single mm-sizedparticles [5]. The measurements have been obtained at 520 nm for the mm-sized grains and at 514nm for the micron-sized samples. The scattering angle covers the range from 3&amp;#176; to 177&amp;#176;.ResultsFigures 1 and 2 show the phase function and degree of linear polarization (DLP) respectively ofolivine and of spinel samples.The phase function curves show a strong dependence on particle size. We see that the micron-sizedsamples have lower values with a rather flat trend at side- and back-scattering regions and a strongincrease in the forward direction. In contrast, the pebbles show u-shaped phase functions. The slopeof the phase function at side- and back-scattering regions is stronger in the case of the spinel.The DLP curves also show a dependence on the size. They have the typical bell shape with anegative branch at low phase angles. Spinel Pebble shows the higher maximum of polarization. Thethree spinel samples show a well-defined negative polarization branch with an inversion angle locatedaround 28&amp;#176; regardless of the particle size. It is interesting to note in the case of the olivine samplesthe inversion angle is highly dependent on particle size. The high inversion angle of Barbarianasteroids polarization curves could be related to the presence of spinel in the form of millimetergrains of regolith.Figure 1: Phase function curves (left) and degree of linear polarization (right) for the three olivinesamples.Figure 2: Phase function curves (left) and degree of linear polarization (right) for the three spinelsamples.&amp;#160;References[1] Belskaya I.N. et al., Refining the asteroid taxonomy by polarimetric observations. ICARUS, Vol.284, pp. 30-42, 2017.[2] L&amp;#243;pez-Sisterna C. et al., Polarimetric survey of main-belt asteroids. VII. New results for 82main-belt objects. A&amp;amp;A, Vol. 626, A42, 2019.[3] Cellino A. et al., Unusual polarimetric properties of (101955) Bennu: similarities with F-classasteroids and cometary bodies. MNRAS, Vol.481, pp.L49-L53, 2018.[4] Mu&amp;#241;oz O. et al., Experimental determination of scattering matrices of dust particles at visiblewavelengths: The IAA light scattering apparatus. JQSRT, Vol. 111, 187 196, 2009.[5] Mu&amp;#241;oz O. et al., Experimental Phase Function and Degree of Linear Polarization Curves ofMillimeter sized Cosmic Dust Analogs ApJSS, Vol. 247, pp.19, 2020.[6] Cellino A. et al., A successful search for hidden Barbarians in the Watsonia asteroid family.MNRAS, Vol. 439, L75-L79, 2014.[7] Devog&amp;#233;le M. et al., New polarimetric and spectroscopic evidence of anomalous enrichment inspinel-bearing calcium-aluminium-rich inclusions among L-type asteroids. ICARUS, Vol. 304,pp. 31-57. 2018.&amp;#160;

The transfer of polarized radiation in a medium containing size‐shape distributions of randomly oriented nonspherical particles is modeled by employing a prolate spheroidal particle model. The parameter characterizing the mean departure from sphericity of the shape‐distribution is the effective aspect ratio of the particle ensemble. The radiance, the degree of linear polarization and the degree of circular polarization are strongly sensitive to a variation of the effective aspect ratio. This shape‐sensitivity is observed consistently from size‐shape distributions containing mainly moderately aspherical particles to those containing predominantly highly aspherical particles. When the effective aspect ratio varies between 4 and 12, the degree of linear polarization changes by as much as 0.15. At certain angles from the sun, the radiance changes by as much as 60% within the same range of effective aspect ratios.

Electric field induced second harmonic measurements applying femtosecond laser pulses (1.59 eV, 80±5 fs, 80 MHz) to substantially boron doped p+-Si/SiO2 interfaces reveal a temporal evolution of the second harmonic (SH) signal, which differs drastically from that of weakly doped samples. A significant initial SH signal is observed in native p+-Si/SiO2 interfaces for boron doping concentrations &amp;gt;7.5×1017 cm−3. This SH signal is attributed to a built-in interfacial electric field E0 generated by the doping induced accumulation of charges at the Si/SiO2 interface following the ionization of interface defect states. A sign reversal is observed in the azimuthal SH anisotropy pattern of the initial SH signal relative to that of the saturated SH signal in p+-Si/SiO2 indicating that the doping related and electron induced interfacial field components oppose each other. Furthermore, the intensity dependence of the initial SH signal in p+-Si/SiO2 is found to be nonquadratic and, in particular, shows a nonmonotonic behavior at incident intensities above ∼60 GW/cm2. These observations are attributed to ultrafast screening of E0 caused by linearly as well as nonlinearly photoexcited electron-hole pairs.

We have examined, in earlier work, the relationship between naturally induced chlorophyll-a fluorescence and the underwater polarized oceanic light field. This shows the un-polarized fluorescence causes a reduction in the degree of polarization over the fluorescence spectral range. Theory shows that the peak of the reduction in polarization occurs at or near the fluorescence peak. Furthermore, it also shows that the magnitude of this reduction in degree of polarization can be related to both the magnitude of the fluorescence as well as the intensity of the underwater light field over the fluorescence spectral range. To examine this relationship in detail, a vector radiative transfer code (VRTE) for the coupled atmosphere-ocean system was employed for a variety of oligotrophic and eutrophic water conditions. The VRTE used measured inherent optical properties (IOPs) for these water conditions as inputs to simulate the complete elastic and inelastic components of the underwater light field, as well as the degree of linear polarization (DoLP) associated with it. These theoretical predictions were then compared with the results of DoLP measurements carried out using by our multiangular hyperspectral polarimeter. A comparison of the measured reduction in degree polarization of the underwater light field over the fluorescence spectral range, and the magnitude of the fluorescence causing it, confirmed the validity of our theoretical relationship, and the feasibility of determining the natural fluorescence existing in an underwater light field from polarization measurements.