Orientation Of Linear Polarization Research Articles

Quarter-wave Pancharatnam-Berry phase gradient liquid crystal-enabled dual-polarization optical edge detection.

Here, we present a novel, to the best of our knowledge, optical edge detection scheme that can be operated in both linear and circular polarization modes, leveraging an optical spatial differentiator constructed by quarter-wave Pancharatnam-Berry (P-B) phase gradient element. After explaining the theoretical mechanism, we utilize a quarter-wave P-B phase liquid crystal polarization grating to validate the dual-polarization optical edge detection capability. We demonstrate that the orientation of linear polarization and the spin of circular polarization dictate the transition between edge and bright-field images. Besides, the linear and circular polarization modes exhibit broadband and monochromatic responsive properties, respectively. This mechanism, dependent on wavelength and polarization, holds promise for applications in color image processing, chiral sensing imaging, and polarization-entangled quantum imaging.

Dual-shot approach for polarization retrieval through a scattering medium

A dual-shot technique based on the field basis addition of two statistically independent speckle patterns is developed to recover an input polarization through a scattering layer. It is proposed theoretically, and demonstrated both numerically and experimentally that by tuning the linear polarization orientation of the reference speckle pattern to 0° and 45° w.r.t. the x-axis, polarization retrieval of an object beam through a scattering layer can be achieved by measuring the degree of polarization of the superposed speckle pattern. The proposed technique can have a wide range of applications in polarization sensing and biomedical imaging.

Control of Polarization Orientation Angle of Scattered Light Based on Metasurfaces: −90° to +90° Linear Variation

Metasurfaces can be used to precisely control polarization state of the scattered light. Here, we present a metasurface-based terahertz device. On the one hand, it serves as a high performance linear polarization converter in transmission of over 80% power with weak reflection. It is capable of rotating linear polarization orientation angle with respect to x-axis continuously from −90° to +90° at 0.84 THz. On the other hand, it serves as a circular polarizer. It can transform a linear polarized wave into a circular polarized wave at 2.49 THz. The transmitted and reflected field are both circular polarized with 50% power. The proposed device with dual functionalities can be applied to modulate the polarization state of the signal in THz wireless communication.

ALMA chemical survey of disk-outflow sources in Taurus (ALMA-DOT)

Context.Planets form in protoplanetary disks and inherit their chemical composition. It is therefore crucial to understand the molecular content of protoplanetary disks in their gaseous and solid components.Aims.We aim to characterize the distribution and abundance of molecules in the protoplanetary disk of DG Tau and to compare them with its dust distribution.Methods.In the context of the ALMA chemical survey of Disk-Outflow sources in the Taurus star forming region (ALMA-DOT) we analyze ALMA observations of the nearby disk-outflow system around the T Tauri star DG Tau in H2CO 31,2−21,1, CS 5−4, and CN 2−1 emission at an unprecedented resolution of ~0′′.15, which means ~18 au at a distance of 121 pc.Results.Both H2CO and CS emission originate from a disk ring located at the edge of the 1.3 mm dust continuum. CS probes a disk region that is slightly further out with respect to H2CO; their peaks in emission are found at ~70 and ~60 au, with an outer edge at ~130 and ~120 au, respectively. CN originates from an outermost and more extended disk/envelope region with a peak at ~80 au and extends out to ~500 au. H2CO is dominated by disk emission, while CS also probes two streams of material possibly accreting onto the disk with a peak in emission at the location where the stream connects to the disk. CN emission is barely detected and both the disk and the envelope could contribute to the emission. Assuming that all the lines are optically thin and emitted by the disk molecular layer in local thermodynamic equilibrium at temperatures of 20−100 K, the ring- and disk-height-averaged column density of H2CO is 2.4−8.6 × 1013cm−2, that of CS is ~1.7−2.5 × 1013cm−2, while that of CN is ~1.9−4.7 × 1013cm−2. Unsharp masking reveals a ring of enhanced dust emission at ~40 au, which is located just outside the CO snowline (~30 au).Conclusions.Our finding that the CS and H2CO emission is co-spatial in the disk suggests that the two molecules are chemically linked. Both H2CO and CS may be formed in the gas phase from simple radicals and/or desorbed from grains. The observed rings of molecular emission at the edge of the 1.3 mm continuum may be due to dust opacity effects and/or continuum over-subtraction in the inner disk, as well as to increased UV penetration and/or temperature inversion at the edge of the millimeter(mm)-dust which would cause enhanced gas-phase formation and desorption of these molecules. CN emission originates only from outside the dusty disk, and is therefore even more strongly anti-correlated with the continuum, suggesting that this molecule is a good probe of UV irradiation. The H2CO and CS emission originate from outside the ring of enhanced dust emission, which also coincides with a change in the linear polarization orientation at 0.87 mm. This suggests that outside the CO snowline there could be a change in the dust properties that manifests itself as an increase in the intensity (and change of polarization) of the continuum and of the molecular emission.

Characterization of Pancreatic Cancer Tissue Using Multiphoton Excitation Fluorescence and Polarization-Sensitive Harmonic Generation Microscopy.

Thin tissue sections of normal and tumorous pancreatic tissues stained with hematoxylin and eosin were investigated using multiphoton excitation fluorescence (MPF), second harmonic generation (SHG), and third harmonic generation (THG) microscopies. The cytoplasm, connective tissue, collagen and extracellular structures are visualized with MPF due to the eosin stain, whereas collagen is imaged with endogenous SHG contrast that does not require staining. Cellular structures, including membranous interfaces and nuclear components, are seen with THG due to the aggregation of hematoxylin dye. Changes in the collagen ultrastructure in pancreatic cancer were investigated by a polarization-sensitive SHG microscopy technique, polarization-in, polarization-out (PIPO) SHG. This involves measuring the orientation of the linear polarization of the SHG signal as a function of the linear polarization orientation of the incident laser radiation. From the PIPO SHG data, the second-order non-linear optical susceptibility ratio, χ(2)zzz'/χ(2)zxx', was obtained that serves as a structural parameter for characterizing the tissue. Furthermore, by assuming C6 symmetry, an additional second-order non-linear optical susceptibility ratio, χ(2)xyz'/χ(2)zxx', was obtained, which is a measure of the chirality of the collagen fibers. Statistically-significant differences in the χ(2)zzz'/χ(2)zxx' values were found between tumor and normal pancreatic tissues in periductal, lobular, and parenchymal regions, whereas statistically-significant differences in the full width at half maximum (FWHM) of χ(2)xyz'/χ(2)zxx' occurrence histograms were found between tumor and normal pancreatic tissues in periductal and parenchymal regions. Additionally, the PIPO SHG data were used to determine the degree of linear polarization (DOLP) of the SHG signal, which indicates the relative linear depolarization of the signal. Statistically-significant differences in DOLP values were found between tumor and normal pancreatic tissues in periductal and parenchymal regions. Hence, the differences observed in the χ(2)zzz'/χ(2)zxx' values, the FWHM of χ(2)xyz'/χ(2)zxx' values and the DOLP values could potentially be used to aid pathologists in diagnosing pancreatic cancer.

ARE INTERNETWORK MAGNETIC FIELDS IN THE SOLAR PHOTOSPHERE HORIZONTAL OR VERTICAL?

ABSTRACT Using many observations obtained during 2007 with the Spectro-Polarimeter of the Hinode Solar Optical Telescope, we explore the angular distribution of magnetic fields in the quiet internetwork regions of the solar photosphere. Our work follows from the insight of Stenflo, who examined only linear polarization signals in photospheric lines, thereby avoiding complications of the analysis arising from the differing responses to linear and circular polarization. We identify and isolate regions of a strong polarization signal that occupy only a few percent of the observed quiet Sun area yet contribute most to the net linear polarization signal. The center-to-limb variation of the orientation of linear polarization in these strong signal regions indicates that the associated magnetic fields have a dominant vertical orientation. In contrast, the great majority of the solar disk is occupied by much weaker linear polarization signals. The orientation of the linear polarization in these regions demonstrates that the field orientation is dominantly horizontal throughout the photosphere. We also apply our analysis to Stokes profiles synthesized from the numerical MHD simulations of Rempel as viewed at various oblique angles. The analysis of the synthetic data closely follows that of the observations, lending confidence to using the simulations as a guide for understanding the physical origins of the center-to-limb variation of linear polarization in the quiet Sun area.

Propagation of light in a circular array of elliptical fibres

We have studied transformation of discrete light beams in circular arrays of elliptical fibres, in which the orientation of ellipses’ axes linearly depends on the angular position of the fibre in the array and makes an half-integer number p of full rotations while tracing along its contour. We have derived analytical expressions for the spectra and supermodes that allow for evanescent coupling between the fibres in the next-neighbour approximation. We have studied the transformative properties of such an array and shown that it can generate cylindrical vector beams (CVBs) of TE and TM types. We have shown that the type of generated beam depends on the orientation of linear polarization of the incident beam. In this way, the circular array of strongly elliptical fibres enables polarization control over the type of the generated CVB. We have also shown that such arrays can change the topological charge of an incoming discrete optical vortex by the doubled array’s index p.

Double-sided structured mask for sub-micron resolution proximity i-line mask-aligner lithography.

Diffractive mask-aligner lithography allows printing structures that have a sub-micrometer resolution by using non-contact mode. For such a purpose, masks are often designed to operate with monochromatic linearly polarized light, which is obtained by placing a spectral filter and a polarizer in the beam path. We propose here a mask design that includes a wire-grid polarizer (WGP) on the top side of a photo-mask and a diffractive element on the bottom one to print a 350 nm period grating by using a classical mask-aligner in proximity exposure mode. Linearly polarizing locally an unpolarized incident beam is only possible by using a WGP on the top side of the mask. This configuration opens the possibility to use different linear polarization orientation on a single mask and allows to print high resolution structures with different orientation within one exposure.

Erbium-doped slot waveguides containing size-controlled silicon nanocrystals

Silicon based slot waveguides with a slot containing Si nanocrystals (Si-nc) and Erbium ions (Er3+) inside a silica matrix were prepared using sputter deposition and low-energy ion implantation. This sequence enabled independent optimization of nanocrystal formation and Er3+ incorporation parameters. Using a superlattice approach, the size of the Si-nc inside the slot could be controlled and optimized for maximum Er3+ luminescence yield at 1.54 μm. Er3+ is found to be efficiently pumped by Si-nc of sizes around 3 to 4 nm. Increasing Er3+ photoluminescence at 1.54 μm with increasing post-implantation annealing temperatures up to 1000 °C is attributed to annealing of matrix or Si-nc interface defects mainly. Additionally, a dependence of the Er3+ luminescence intensity on both the excitation and emission linear polarization orientation is shown, which demonstrates efficient field enhancement in sputtered slot waveguide structures.

Nonlinear Photoluminescence Imaging of Isotropic and Liquid Crystalline Dispersions of Graphene Oxide

We report a visible-range nonlinear photoluminescence (PL) from graphene oxide (GO) flakes excited by near-infrared femtosecond laser light. PL intensity has nonlinear dependence on the laser power, implying a multiphoton excitation process, and also strongly depends on a linear polarization orientation of excitation light, being at maximum when it is parallel to flakes. We show that PL can be used for a fully three-dimensional label-free imaging of isotropic, nematic, and lamellar liquid crystalline dispersions of GO flakes in water. This nonlinear PL is of interest for applications in direct label-free imaging of composite materials and study of orientational ordering in mesomorphic phases formed by these flakes, as well as in biomedical and sensing applications utilizing GO.

Blueshifted outflow from 24.329+0.145

New studies of an hydroxyl (OH) maser site that has puzzled astronomers for more than 40 yr demonstrate that its emission arises in a unique strong blueshifted outflow. Measurements with the Australia Telescope Compact Array (ATCA) locate this enigmatic OH 1667-MHz maser at 24.329+0.145 (Galactic coordinates). This is coincident (to arcsecond accuracy) with maser emission at the 6668-MHz transition of methanol and a newly discovered maser at the 22-GHz transition of water. The methanol maser establishes the site as one of high-mass star formation, and the small spread of methanol features about a median velocity of +113 km s−1 defines its systemic velocity. The water maser shows a combination of some emission arising near this systemic velocity, and the remainder arising in the blueshifted outflow. The 1667-MHz OH emission extends over more than 20 km s−1, and our demonstrated association with the methanol maser reveals that this is offset from the systemic velocity by as much as 50 km s−1. The implied energetic blueshifted outflow is unprecedented in OH masers of this class. Our spectral studies using the ATCA, with a new high-resolution spectrometer, achieve full polarization observations of the 1665- and 1667-MHz OH ground-state transitions. The dominance of 1667-MHz emission, with no detection at 1665 MHz, suggests unusual physical properties in the ouflow region. Likewise, the prevalence of linear polarization may be a consequence of emission arising in a fast-moving outflow, with perhaps a link between linear polarization orientation and outflow orientation. We also present new observations of maser sites 24.494−0.039 and 24.790+0.083. These close neighbours of 24.329+0.145, with methanol maser emission at a similar systemic velocity, are also accompanied by masers of water and OH, but have no unusual maser properties. The velocity and Galactic longitude of all three sites, and of the H ii complex W42, correspond to an especially interesting Galactic location near the tangent point of the 3-kpc arm (expanding ring), at a distance of 7.7 kpc.

Experimental Study of Hard X‐Ray Production at Sub‐Relativistic Intensities: Effect of Polarization and Nanosecond Pre‐Pulse

For the plasma formed under interaction of femtosecond laser radiation with the surface of a target electronvelocity distribution has fundamentally non-maxwellian shape: besides thermal electrons, taking their originfrom classical collisional mechanisms, hot electron component is formed. In particular such important effects asgeneration of hard X-rays with high spectral intensity and small pulse duration, protons and multicharged ionsacceleration to high energies, nuclear reactions in plasma and so on, are closely linked with hot electrons.Generation of the hot electron component is related to additional, non-collisional mechanisms of electronsheating; its mean energy exceeds mean energy of thermal component by 1-2 orders [1]. Orientation of lin-ear polarization of radiation with respect to plasma’s electron density gradient plays important role at moderateintensities (10

Generation of circular polarization of the cosmic microwave background

The standard cosmological model, which includes only Compton scattering photon interactions at energy scales near recombination, results in zero primordial circular polarization of the cosmic microwave background. In this paper we consider a particular renormalizable and gauge-invariant standard model extension coupling photons to an external vector field via a Chern-Simons term, which arises as a radiative correction if gravitational torsion couples to fermions. We compute the transport equations for polarized photons from a Boltzmann-like equation, showing that such a coupling will source circular polarization of the microwave background. For the particular coupling considered here, the circular polarization effect is always negligible compared to the rotation of the linear polarization orientation, also derived using the same formalism. We note the possibility that limits on microwave background circular polarization may probe other photon interactions and related fundamental effects such as violations of Lorentz invariance.

X-ray polarimetry by means of Compton scattering in the sensor of a hybrid photon counting pixel detector

For the first time a hybrid semiconductor photon counting pixel detector has been used for measurements of linear X-ray polarization by exploiting the Compton effect in the silicon sensor layer. The time-to-shutter mode of the X-ray imaging detector Timepix was used to identify Compton-scattering events in the sensor layer by the analysis of coincidences. For irradiation with polarized X-ray photons of energies between 27 and 84 keV we were able to measure a large modulation factor of μ meas = ( 68.1 ± 16.4 ) % for this type of X-ray polarimeter. Degree and orientation of linear polarization can be determined. This publication describes the experimental setup, data analysis method, measurement and simulation results, and gives first estimations on the polarimetric performance for an application in X-ray astronomy.

Pulse-to-pulse polarization-switching method for high-repetition-rate lasers

We report a method that enables dynamic switching of the pulse-to-pulse linear polarization orientation of a high-pulse-rate laser. The implications for laser micromachining, where polarization direction can be important, are also discussed.

Magnetic Structure of a Dark Bok Globule

The thermal dust continuum emission at 848 μm from the globule CB 068, a Class 0 young stellar object (YSO), reveals strong linear polarization percentage values (up to 11%) in two polarized-intensity regions located on either side of the center, away from the twin CO outflows. At the 5% polarized intensity level, the two highly polarized regions have a radial separation of 0.01 pc from the center of the Bok globule. The two polarized regions are located on either side of the axis of the twin CO outflows, with polarization contours paralleling the outflows. The linear polarization orientation leads us to deduce that, in the inner part of the polarized-intensity regions, the electric field vector roughly follows the boundary of a pseudodisk or bar (the pseudodisk or bar was previously detected both in dust and in ammonia emission). The linear polarization orientation, within a radius of 0.03 pc, can be matched roughly to an infalling halo-to-disk magnetic field morphology, excluding the regions of the external envelope and near the CO outflows. On a 0.04 pc scale, our model predictions for CB 068 give a pseudodisk diameter of about 8800 AU. We predict a magnetic field strength (over 0.03 pc) of about 150 μG, which comes about from the Chandrasekhar-Fermi method (via the ratio of the line of sight velocity dispersion to the polarization angle dispersion).

Optical Kerr coefficient measurement in coiled high-birefringent fibers

The optical Kerr effect in coiled high-birefringent fibers was measured based on a double-beam polarimetric method. A Q-switched Nd:YAG laser, operating at 1.064 mum (FWHM of 80 ns at 1 kHz), was used as the pump beam and a cw 0.633-mum He-Ne laser was used as the probe beam with its polarization fixed at 45 degrees with respect to the birefringent axis whereas orientation of the linearly polarized pump light varied. The phase shifts induced by an intense pump beam in a short bow-tie high-birefringent fiber were determined for different fiber lengths coiled into 15- and 30-cm-diameter drums. It was found that the induced phase shift changes drastically with the state of polarization of the pump light. A strong dependence of the phase shift on orientations of linear pump polarization is attributed to differential losses of eigenmodes peculiar to birefringent axes. Therefore, optical Kerr coefficients remain unchanged regardless of the dependence of the nonlinear response of the coiled high-birefringent fibers on pump polarization.

Gaussian beam transmission and reflection from a general anisotropic multilayer structure

Transmission and reflection of Gaussian beams from a general anisotropic multilayer structure are investigated. The principal axes of the layers are oriented arbitrarily with respect to each other and with respect to a fixed reference coordinate system. The Gaussian beam is assumed to have an arbitrary angle of incidence and linear polarization orientation. Two numerical examples are presented: a single slab of uniaxial calcite and a multilayer structure of biaxial 4-(N, N-dimethylamino)-3-acet amidonitrobenzene with antireflection coatings on the input and output faces. Results show the distortions of the beam caused by the anisotropy of the structure.

Intensity dependent four-wave-mixing polarization rules in quantum wells

The self-diffraction four wave mixing signal from excitonic transitions in GaAs quantum wells is investigated experimentally as a function of arbitrary linear polarization orientation of the incident light pulses. The polarization of the diffracted signal, and the phase of quantum beats between light and heavy hole excitons, are shown to strongly dependent on the magnitude of excitation intensity. The experimental results observed for excitation densities above 2 × 10 9 cm −2 are in accordance with theoretical conceptions of the polarization selection rules for light and heavy hole exciton transitions in a quantum well. For lower excitation, remarkable deviations from the predictions of the theoretical model occur.

Interferometric stress birefringence measurement

We describe a sensitive method for measuring the stress birefringence of an optical window that utilizes a phase-measuring Fizeau interferometer incorporating a variable retarder and a nonpolarizing beam splitter. When we test a material in an interferometer cavity, the wave front transmitted through the material is deviated by the surfaces, inhomogeneity, and birefringence of the material. Birefringence causes the transmitted wave front to have different optical path difference (OPD) profiles for the vertical and horizontal orientations of linear polarization. Subtracting these OPD profiles reveals the amount of phase difference between the fast and slow axes of the material. Hence, birefringence may be calculated. Phase-measurement techniques and a computer-controlled interferometer employing a variable liquid-crystal retarder provide a fully automated instrument for measuring stress birefringence. The theoretical derivation, discussion of the instrument, and experimental results are presented.