Polarimetry Measurements Research Articles

HAWC+ Far-infrared Observations of the Magnetic Field Geometry in M51 and NGC 891

Abstract Stratospheric Observatory for Infrared Astronomy High-resolution Airborne Wideband Camera Plus polarimetry at 154 μm is reported for the face-on galaxy M51 and the edge-on galaxy NGC 891. For M51, the polarization vectors generally follow the spiral pattern defined by the molecular gas distribution, the far-infrared (FIR) intensity contours, and other tracers of star formation. The fractional polarization is much lower in the FIR-bright central regions than in the outer regions, and we rule out loss of grain alignment and variations in magnetic field strength as causes. When compared with existing synchrotron observations, which sample different regions with different weighting, we find the net position angles are strongly correlated, the fractional polarizations are moderately correlated, but the polarized intensities are uncorrelated. We argue that the low fractional polarization in the central regions must be due to significant numbers of highly turbulent segments across the beam and along lines of sight in the beam in the central 3 kpc of M51. For NGC 891, the FIR polarization vectors within an intensity contour of 1500 are oriented very close to the plane of the galaxy. The FIR polarimetry is probably sampling the magnetic field geometry in NGC 891 much deeper into the disk than is possible with NIR polarimetry and radio synchrotron measurements. In some locations in NGC 891, the FIR polarization is very low, suggesting we are preferentially viewing the magnetic field mostly along the line of sight, down the length of embedded spiral arms. There is tentative evidence for a vertical field in the polarized emission off the plane of the disk.

Enantioselective Crystallization of Chiral Inorganic Crystals of ϵ-Zn(OH)2 with Amino Acids.

Many inorganic materials can form crystals, but little is known about their enantioselective crystallization. Herein, we report on the enantioselective crystallization of ϵ-Zn(OH)2 (Wulfingite) chiral crystals by using amino acids. Crystals of ϵ-Zn(OH)2 were crystallized from supersaturated sodium hydroxide and zinc nitrate aqueous solutions in the presence of l- or d-arginine. All of the chiral measurements, such as selective chiral adsorption by circular dichroism (CD), chiral chromatography, and polarimetry measurements, clearly show chiral discrimination during the crystallization of ϵ-Zn(OH)2 . In addition, a new method has been developed for identifying chirality in crystals by using electron paramagnetic resonance (EPR). Although the values of chiral induction of the ϵ-Zn(OH)2 crystals obtained are somewhat low, these values are still significant because they demonstrate that enantioselectivity during the crystallization of chiral inorganic crystals with chiral additives can be achieved. The method can be applied to many chiral inorganic systems. Understanding and controlling the crystallization of chiral inorganic crystals is important for gaining knowledge on the interaction of chiral molecules with inorganic surfaces. This knowledge can lead to an understanding of basic scientific questions such as the evolution of homochirality in biomolecules and the development of chiral inorganic crystals for a variety of purposes such as asymmetric catalysis and optical applications.

Enantioselective Crystallization of Chiral Inorganic Crystals of ϵ‐Zn(OH)2 with Amino Acids

AbstractMany inorganic materials can form crystals, but little is known about their enantioselective crystallization. Herein, we report on the enantioselective crystallization of ϵ‐Zn(OH)2 (Wulfingite) chiral crystals by using amino acids. Crystals of ϵ‐Zn(OH)2 were crystallized from supersaturated sodium hydroxide and zinc nitrate aqueous solutions in the presence of l‐ or d‐arginine. All of the chiral measurements, such as selective chiral adsorption by circular dichroism (CD), chiral chromatography, and polarimetry measurements, clearly show chiral discrimination during the crystallization of ϵ‐Zn(OH)2. In addition, a new method has been developed for identifying chirality in crystals by using electron paramagnetic resonance (EPR). Although the values of chiral induction of the ϵ‐Zn(OH)2 crystals obtained are somewhat low, these values are still significant because they demonstrate that enantioselectivity during the crystallization of chiral inorganic crystals with chiral additives can be achieved. The method can be applied to many chiral inorganic systems. Understanding and controlling the crystallization of chiral inorganic crystals is important for gaining knowledge on the interaction of chiral molecules with inorganic surfaces. This knowledge can lead to an understanding of basic scientific questions such as the evolution of homochirality in biomolecules and the development of chiral inorganic crystals for a variety of purposes such as asymmetric catalysis and optical applications.

Combination of surface plasmon resonance and differential Mueller matrix formalism for noninvasive glucose sensing

A novel technique is proposed for circular birefringence (CB) sensing using a surface plasmon resonance (SPR) prism coupler and differential Mueller matrix polarimetry. In the proposed system, the SPR prism coupler is placed in front of the sample in order to generate a weak-scattering medium model and enhance the sensitivity of the measurement process. The CB properties of the sample are then extracted using a dynamic Stokes-Mueller matrix polarimetry measurement system in the reflectance mode. The practical feasibility of the system is demonstrated by measuring the CB properties of aqueous glucose solutions and glucose phantom solutions containing 2% lipofundin. The oral glucose tolerance tests pilot study was performed on four healthy human volunteers aged between 20 and 25 years old. The experimental results show that the proposed method has a resolution of just 10 mg/dL. In general, the results confirm that the proposed polarimetry-SPR system provides a fastand reliable approach for CB detection and has significant potential for noninvasive glucose monitoring device (NIGMD) applications.

Observation of topologically enabled unidirectional guided resonances.

Unidirectional radiation is important for various optoelectronic applications, such as lasers, grating couplers and optical antennas. However,almost all existing unidirectional emitters rely on the use of materials or structures that forbid outgoing waves-that is, mirrors, which are oftenbulky, lossy and difficult to fabricate. Here we theoretically propose and experimentally demonstrate a class of resonances in photonic crystal slabs that radiate only towards one side of the slab, with no mirror placed on the other side. These resonances, which we name 'unidirectional guided resonances', are found to be topological in nature: they emerge when a pair of half-integer topological charges1-3 in the polarization field bounce into each other in momentum space. We experimentally demonstrate unidirectional guided resonances in the telecommunication regime by achieving single-side radiative quality factors as high as 1.6×105. We further demonstrate their topological nature through far-field polarimetry measurements. Our work represents a characteristic example of applying topological principles4,5 to control optical fields and could lead to energy-efficient grating couplers and antennas for light detection and ranging.

Direct control of magnetic chirality in NdMn2O5 by external electric field

Detailed investigation of the incommensurate magnetic ordering in a single crystal of multiferroic NdMn2O5 has been performed using both non-polarized and polarized neutron diffraction techniques. Below TN = 30.5 K magnetic Bragg reflections corresponding to the non-chiral type magnetic structure with propagation vector k1 = (0.5 0 kz1) occurs. Below about 27 K a new distorted magnetic modulation with a similar vector kz2 occurs, which is attributed to the magnetization of the Nd3+ ions by the Mn-sub-lattice. Strong temperature hysteresis in the occurrence of the incommensurate magnetic phases in NdMn2O5 was observed depending on the cooling or heating history of the sample. Below about 20 K the magnetic structure became of a chiral type. From spherical neutron polarimetry measurements, the resulting low-temperature magnetic structure kz3 was approximated by the general elliptic helix. The parameters of the magnetic helix-like ellipticity and helical plane orientation in regard to the crystal structure were determined. A reorientation of the helix occurs at an intermediate temperature between 4 K and 18 K. A difference between the population of right- and left-handed chiral domains of about 0.2 was observed in the as-grown crystal when cooling without an external electric field. The magnetic chiral ratio can be changed by the application of an external electric field of a few kV/cm, revealing strong magnetoelectric coupling. A linear dependence of the magnetic chirality on the applied electric field in NdMn2O5 was found. The results are discussed within the frame of the antisymmetric super-exchange model for Dzyaloshinsky-Moria interaction.

Mapping of real-time morphological changes in the neuronal cytoskeleton with label-free wide-field second-harmonic imaging: a case study of nocodazole.

.We demonstrate the use of wide-field high-throughput second-harmonic (SH) microscopy for investigating cytoskeletal morphological changes on the single-cell level. The method allows for real-time, in vitro, label-free measurements of cytoskeletal changes that can, under certain conditions, be quantified in terms of orientational distribution or in terms of changes in the number of microtubules. As SH generation is intrinsically sensitive to noncentrosymmetrically structured microtubules, but not to isotropic or centrosymmetric materials, we use it to probe the microtubule structure in the cytoskeleton when it undergoes dynamic changes induced by the application of nocodazole, a well-known microtubule-destabilizing drug that reversibly depolymerizes microtubules. In addition, the orientational directionality of microtubules in neurites and cell bodies is determined label-free using SH polarimetry measurements. Finally, we use spatiotemporal SH imaging to show label-free, real-time nocodazole-induced morphological changes in neurons of different age and in a single axon.

Approximate solutions of polarization state evolution in tokamak plasma polarimetry and their precision

Polarimetry measurement results are used in tokamak plasma equilibrium codes as a constraint, decreasing the measurement uncertainty in determination plasma current, safety factor and density profile. In numerical codes, instead of solving rigorous equation of polarimetric state evolution, approximate analytical expression could be used to increase computing efficiency. In this paper is analyzed the precision of three different models compared with exact solution of polarization state evolution equation. Calculations are made for circular plasma model, with plasma parameters representative for operating domain of tokamak device. The obtained results define the limits of applicability of the separate proposed approximated methods in equilibrium codes for plasma in configuration similar to considered in the paper.

Advances in the simulation of light-tissue interactions in biomedical engineering.

Monte Carlo (MC) simulation for light propagation in scattering and absorbing media is the gold standard for studying the interaction of light with biological tissue and has been used for years in a wide variety of cases. The interaction of photons with the medium is simulated based on its optical properties and the original approximation of the scattering phase function. Over the past decade, with the new measurement geometries and recording techniques invented also the corresponding sophisticated methods for the description of the underlying light-tissue interaction taking into account realistic parameters and settings were developed. Applications, such as multiple scattering, optogenetics, optical coherence tomography, Raman spectroscopy, polarimetry and Mueller matrix measurement have emerged and are still constantly improved. Here, we review the advances and recent applications of MC simulation for the active field of the life sciences and the medicine pointing out the new insights enabled by the theoretical concepts.

Mueller matrix polarimetry of bianisotropic materials [Invited

Mueller matrix polarimetry is a powerful optical technique for characterization of both anisotropic and bianisotropic materials. This review emphasizes methods for the interpretation of measured Mueller matrices, from the meanings of matrix symmetries, to ab initio calculations of Mueller matrices that begin with Maxwell’s equations operating on materials with permittivity, permeability, and magnetoelectric constitutive tensors. We present an overview of polarimetry measurements in crystals as well as metamaterials that have optically responsive features on the order of the wavelength of visible light. Examples of the full measurement of the constitutive tensors of bianisotropic media from the analysis of their Mueller matrices, collected in either transmission or reflection, are illustrated for natural crystals, polycrystals, and nanofabricated metamaterials. Experimental and theoretical research into the complex optical responses of bianisotropic materials with polarized light is best expressed in terms of the Mueller matrix, as it offers an unambiguous and mathematically robust platform for analysis of light–matter interactions.

Single-incidence polarimetry for optical characteristics

In this paper, we propose a simplified measurement called single-incidence polarimetry measurement (SPM) to obtain optical characteristics such as di-attenuationP, variation of phase difference Δ and depolarization index d on material surface. Compared with tradition Mueller matrix polarimetry which needs multiple (at least 4) Stokes vectors as incidences in experiments, SPM only needs single polarized light as incidence, which simplifies experimental procedures tremendously and increases experimental efficiency. In addition, SPM is suitable for complicated materials such as thick lump samples, uneven surfaces, powder and liquid which are not available on traditional ellipsometers, e.g., the variable-angle spectroscopic ellipsometer (VASE) produced by J. A. Woollam Company. The objectivity and lower complexity of SPM are verified by the contrast experiments with Mueller matrix polarimetry. The advantage that SPM is more suitable for complicated experimental condition is demonstrated by the contrast experiments with VASE. All the analyses and discussions are realized by the root mean squared error (RMSE) between referenced values and experimental results. In conclusion, SPM can realize low-cost and easy-assembled measurements on complicated and depolarized surfaces rather than obtaining higher precision data on smooth and thin surfaces. In the aspect of efficiency and convenience, SPM is useful to analyze optical characteristics qualitatively.

Direct and reciprocal spin-orbit interaction effects in a graded-index medium

Spin-orbit interactions (SOI) arising due to the propagation of a paraxial light beam, with spin-angular momentum and intrinsic- and extrinsic-orbital angular momentum degrees of freedom, along a curved trajectory and their mutual interactions is investigated due to several fundamental effects of interest. We demonstrate here all six direct and reciprocal SOI effects due to the propagation of light in an inhomogeneous-anisotropic medium, such as a graded-index rod. We show that each of light’s angular momentum component impacts the other in such a way as to have a unique effect, characterized using interferometry, polarimetry, and weak measurement methods. The results are expected to have significant impact on the basic understanding of light-matter interaction and its applications.

Approximate analytic expressions using Stokes model for tokamak polarimetry and their range of validity

The analysis of the polarimetry measurements has the aim of validating models (De Marco and Segre 1972 Plasma Phys. 14 245), with a careful attention to the clarification of their limits of application. In this paper a new approximation method is introduced, the so-called special constant Omega direction (SCOD), which gives an analytical solution to the polarimetry exact Stokes model equations. The available approximate solutions (including SCOD) of the polarimetry propagation equations are presented, compared and their application limits determined, using a reference tokamak configuration, which is a simplified equilibrium for a circular tokamak. The SCOD approximation is compared successfully to the Stokes model in the context also of equilibria evaluated for two JET discharges. The approximation methods are analytical or very simple mathematical expressions which can also be used in equilibrium codes for their optimization.

The wavelength dependence of interstellar polarization in the Local Hot Bubble

The properties of dust in the interstellar medium (ISM) nearest the Sun are poorly understood because the low column densities of dust toward nearby stars induce little photometric reddening, rendering the grains largely undetectable. Stellar polarimetry offers one pathway to deducing the properties of this diffuse material. Here we present multi-wavelength aperture polarimetry measurements of seven bright stars chosen to probe interstellar polarization near the edge of the Local Hot Bubble (LHB) - an amorphous region of relatively low density interstellar gas and dust extending ~70-150 pc from the Sun. The measurements were taken using the HIgh Precision Polarimetric Instrument (HIPPI) on the 3.9-m Anglo-Australian Telescope. HIPPI is an aperture stellar polarimeter with a demonstrated sensitivity of 4.3 parts-per-million (ppm). Of the stars observed two are polarized to a much greater degree than the others; they have a wavelength of maximum polarization ($\lambda_{max}$) of ~550 $\pm$ 20 nm - similar to that of stars beyond the LHB - and we conclude that they are in the wall of the LHB. The remaining five stars have polarizations of ~70 to 160 ppm, of these four have a much bluer $\lambda_{max}$, ~350 $\pm$ 50 nm. Bluer values of $\lambda_{max}$ may indicate grains shocked during the evolution of the Loop I Superbubble. The remaining star, HD 4150 is not well fit by a Serkowski curve, and may be intrinsically polarized.

Correlation polarimetry for broadband magnetic fluctuation measurements.

Correlation techniques have been successfully utilized for plasma diagnostics like electron cyclotron emission to reduce measurement noise. We present the first application of such a technique to Faraday-effect polarimetry measurements on the Madison Symmetric Torus (MST). The MST far infrared (FIR) interferometer-polarimeter diagnostic utilizes 11 vertical chords with a chord separation of 7-8 cm and a heterodyne detection system for fluctuation measurements up to several hundred kHz. The planar-diode mixers viewing each chord represent independent noise sources; modifying the optical setup so that two different mixers view the same chord allows cross correlation between the two independent signals to reduce the noise floor in fluctuation measurements. In this manner, the noise floor in both interferometry and polarimetry measurements in reversed-field pinch discharges has been reduced by a factor of 20-30. The correlation polarimeter provides a sensitive measurement of broadband magnetic fluctuations.

Equilibrium reconstruction at JET using Stokes model for polarimetry

This paper presents the first application to real JET data of the new equilibrium code NICE which enables the consistent resolution of the inverse equilibrium reconstruction problem in the framework of non-linear free-boundary equilibrium coupled to the Stokes model equation for polarimetry. The conducted numerical experiments enable first of all to validate NICE by comparing it to the well-established EFIT code on 4 selected high performance shots. Secondly the results indicate that the fit to polarimetry measurements clearly benefits from the use of Stokes vector measurements compared to the classical case of Faraday measurements, and that the reconstructed and profiles are better constrained with smaller error bars and are closer to the profiles reconstructed by EFTM, the EFIT JET code using internal MSE constraints.

Tests of a full-scale ITER toroidal interferometer and polarimeter (TIP) prototype on the DIII-D tokamak (invited).

A full-scale ITER toroidal interferometer and polarimeter (TIP) prototype, including an active feedback alignment system, has been installed and tested on the DIII-D tokamak. In the TIP prototype, a two-color interferometry measurement of line-integrated density is carried out at 10.59 μm and 5.22 μm using a CO2 and quantum cascade laser, respectively, while a separate polarimetry measurement of the plasma-induced Faraday effect is made at 10.59 μm. The TIP prototype is equipped with a piezo tip/tilt stage active feedback alignment system that minimizes noise in the measurement and keeps the diagnostic aligned throughout DIII-D discharges. The measured phase resolution for the polarimeter and interferometer is 0.05° (100 Hz bandwidth) and 1.9° (1 kHz bandwidth), respectively. The corresponding line-integrated density resolution for the vibration-compensated interferometer is δnL = 1.5 × 1018 m-2, and the magnetic field-weighted line-integrated density from the polarimeter is δnBL = 1.5 × 1019 Tm-2. Both interferometer and polarimeter measurements during DIII-D discharges compare well with the expectations based on calculations using Thomson scattering measured density profiles and magnetic equilibrium reconstructions. Additionally, larger bandwidth interferometer measurements show that the diagnostic is a sensitive monitor of core density fluctuations with demonstrated measurements of Alfvén eigenmodes and tearing modes.

Impact of the Cotton–Mouton effect on Faraday polarimetry measurements using circular polarization

A comprehensive understanding of the impact of the Cotton–Mouton effect on Faraday polarimetry measurements using counter-rotating circular polarization (CP) probe beams has been developed. By using the Jones theory, an analytic study shows that the Cotton–Mouton effect cancels to first order with coupling into the Faraday measurement only at higher orders. A Jones-based numerical study shows the coupling effect strongly depends on the Cotton–Mouton effect, Faraday effect, and wavelength chosen for the measurement. For realistic DIII-D plasma conditions and far-infrared wavelength, numerical calculation suggests the measurement is dominated by the Faraday effect while the coupling effect leads to a small but finite correction. By statistical comparison between the experimental measurement and the Jones-based numerical calculation under various plasma parameters, the impact of the Cotton–Mouton effect has been verified. Proper treatment of the coupling effect is essential in the data analysis under certain conditions for polarimetric measurement using CP in present devices and beyond.

Feasibility of a far infrared laser based polarimeter diagnostic system for the JT-60SA fusion experiment

JT-60SA is the large Tokamak device that is being built in Japan under the Broader Approach Satellite Tokamak Programme and the Japanese National Programme and will operate as a satellite machine for ITER. The main goal of the JT-60SA Programme is to provide valuable information for the ITER steady-state scenario and for the design of DEMO, where the real-time control of the safety factor profile is very important, in connection with both MHD stability and plasma confinement. It has been demonstrated in this work that to this end polarimetry measurements are necessary, in particular in order to reconstruct the safety factor profile in reversed shear scenarios. In this paper we present the main steps of a conceptual feasibility study of a multi-channel polarimeter diagnostic and the resulting optimised geometry. In this study, magnetic scenario modelling, a realistic CAD-driven design and long-term operation requirements, rarely even considered at this stage, have been considered. It is shown that a far infrared polarimeter system, with a laser operating at a wavelength of 194.7 μm and up to twelve channels can be envisaged for JT-60SA. The top requirements can be attained, i.e., that the polarimeter, together with other diagnostic measurements, should provide q-profile reconstruction with an accuracy of 10% for the entire plasma cycle and suitable time resolution for real-time applications, in particular in high density and ITER-relevant plasma scenarios.

A TPC as high performance gamma-ray telescope and polarimeter: polarisation measurement in a beam between 1.7 and 74MeV with HARPO

We presented in 2014 the very first data from a polarised gamma-ray beam between 1.7 and 74MeV. We now show the results of their analysis, and in particular the polarimetry measurements. With these results, we are establishing a new, high-performance way to do gamma-ray astronomy and, for the first time, polarimetry, in the e+e- pair regime.