Near-infrared Polarization Research Articles

Distortion of Magnetic Fields in a Starless Core. V. Near-infrared and Submillimeter Polarization in FeSt 1-457

The relationship between submillimeter (submm) dust emission polarization and near-infrared (NIR) $H$-band polarization produced by dust dichroic extinction was studied for the cold starless dense core FeSt 1-457. The distribution of polarization angles ($90^{\circ}$-rotated for submm) and degrees were found to be very different between at submm and NIR wavelengths. The mean polarization angles for FeSt 1-457 at submm and NIR wavelengths are $132.1^{\circ} \pm 22.0^{\circ}$ and $2.7^{\circ} \pm 16.2^{\circ}$, respectively. The correlation between $P_H$ and $A_V$ was found to be linear from outermost regions to relatively dense line of sight of $A_V \approx 25$ mag, indicating that NIR polarization reflects overall polarization (magnetic field) structure of the core at least in this density range. The flat $P_H/A_V$ versus $A_V$ correlations were confirmed, and the polarization efficiency was found to be comparable to the observational upper limit (Jones 1989). On the other hand, as reported by Alves et al., submm polarization degrees show clear linearly decreasing trend against $A_V$ from $A_V \approx 20$ mag to the densest center ($A_V \approx 41$ mag), appearing as "polarization hole" structure. The power law index for the $P_{\rm submm}$ versus $A_V$ relationship was obtained to be $\approx -1$, indicating that the alignment for the submm sensitive dust is lost. These very different polarization distributions at submm and NIR wavelengths suggest that (1) there is different radiation environment at these wavelengths or (2) submm-sensitive dust is localized or the combination of them.

Conversion of near-infrared polarization characteristics by rotation of the upper layer in a three-layer structure

In this paper, a three-layer chiral structure is proposed to achieve the conversion of its performance between broadband circular polarization asymmetric transmission and broadband circular dichroism by rotating the upper layer of the structure. For circular polarization asymmetric transmission, its asymmetric transmission parameters can reach a maximum of 0.89 and over 0.5 from 134 to 225 THz. For circular dichroism, the co-polarized transmission coefficient of right-handed circularly polarized wave is above 0.8 and the co-polarized transmission coefficient of left-handed circularly polarized wave is lower than 0.25 from 137 to 214 THz. The above results have not been reported in previous papers. This structure provides potential applications for circular polarization converters and circular polarizers.

Magnetic field structures in star-forming regions revealed by imaging polarimetry at multi-wavelengths

AbstractMagnetic fields are ubiquitous in various scales of astronomical objects, and they are considered as playing significant roles from star to galaxy formations. However, the role of the magnetic fields in star forming regions is less well understood because conventional optical polarimetry is hampered by heavy extinction by dust. We have been conducting extensive near-infrared polarization survey of various star-forming regions from low- and intermediate-mass to high-mass star-forming regions, using IRSF/SIRPOL in South Africa. Not only linear but also circular polarizations have been measured for more than a dozen of regions. Both linear and circular polarimetric observations at near-infrared wavelengths are useful tools to study the magnetic fields in star forming regions, although infrared circular polarimetry has been less explored so far. In this presentation, we summarize our results of the near-infrared polarization survey of star forming regions and its comparison with recent submillimeter polarimetry results. Such multi-wavelength approaches can be extended to the polarimetry using ALMA, SPICA in future, and others. We also present our recent results of the first near-infrared imaging polarimetry of young stellar objects in the Circinus molecular cloud, which has been less studied but a very intriguing cluster containing numerous signs of active low-mass star formation.

Fiber Optic Sensor’s Performance Enhancement by Tuning NIR Wavelength, Polarization, and 2D Material

Fiber optic evanescent wave sensor consisting of chalcogenide core, silica clad, and 2D material (graphene and MoS2) monolayer is simulated and analyzed in near infrared (NIR) aiming at highly sensitive and reliable detection of malignancies in human liver tissues. Dispersion relations of normal and malignant human liver tissues are considered. The sensor’s performance is examined in terms of sensitivity and resolution. The analysis indicates that using MoS2 as 2D material provides enhanced (nearly two-fold) performance compared with graphene. At 1200-nm wavelength, the sensitivity achieved is nearly 93.7 mW/RIU (real index) and 548.30 mW/RIU (imaginary index) whereas resolution achievable is of the order of 10−9 RIU (real index) and 10−10 RIU (imaginary index). Longer NIR wavelength should be used and p-polarization provides significantly better performance compared with s-polarization. With lesser photodamage and reduced Rayleigh scattering (due to being operated in NIR), the proposed sensor probe also has the ability to deliver considerably finer resolution than the current lot of fiber optic sensors based on different techniques. The limitations of the proposed sensor model are also discussed.

Multiwavelength Stellar Polarimetry of the Filamentary Cloud IC5146. I. Dust Properties

Abstract We present optical and near-infrared stellar polarization observations toward the dark filamentary clouds associated with IC5146. The data allow us to investigate the dust properties (this paper) and the magnetic field structure (Paper II). A total of 2022 background stars were detected in the R c , , H, and/or K bands to mag. The ratio of the polarization percentage at different wavelengths provides an estimate of , the wavelength of the peak polarization, which is an indicator of the small-size cutoff of the grain size distribution. The grain size distribution seems to significantly change at mag, where both the average and dispersion of decrease. In addition, we found μm for mag, which is larger than the ∼0.55 μm in the general interstellar medium (ISM), suggesting that grain growth has already started in low-A V regions. Our data also reveal that polarization efficiency ( ) decreases with A V as a power law in the R c , , and K bands with indices of −0.71 ± 0.10, −1.23 ± 0.10, and −0.53 ± 0.09. However, H-band data show a power index change; the PE varies with A V steeply (index of −0.95 ± 0.30) when mag, but softly (index of −0.25 ± 0.06) for greater A V values. The soft decay of PE in high-A V regions is consistent with the radiative alignment torque model, suggesting that our data trace the magnetic field to mag. Furthermore, the breakpoint found in the H band is similar to that for A V , where we found the dispersion significantly decreased. Therefore, the flat PE–A V in high-A V regions implies that the power-index changes result from additional grain growth.

A Curved Magnetic Field in the Ring-like Shell of Bubble N4

Abstract We report the detection of a curved magnetic field in the ring-like shell of the bubble N4, derived from near-infrared polarization of reddened diskless stars located behind this bubble. The magnetic field in the shell is curved and parallel to the ring-like shell, and its strength is estimated to be in the plane of the sky. The magnetic field strength in the shell is significantly enhanced compared to the local field strength. We calculate the mass-to-flux ratio for the submillimeter clumps in the shell and find that they are all magnetically subcritical. Our results demonstrate that the magnetic field strengthens as the interstellar medium is compressed into a shell, and suggest that the magnetic field has the potential to hinder star formation triggered by H ii region expansion.

Comparing Submillimeter Polarized Emission with Near-infrared Polarization of Background Stars for the Vela C Molecular Cloud

Abstract We present a large-scale combination of near-infrared (near-IR) interstellar polarization data from background starlight with polarized emission data at submillimeter wavelengths for the Vela C molecular cloud. The near-IR data consist of more than 6700 detections probing a range of visual extinctions between 2 and in and around the cloud. The submillimeter data were collected in Antarctica by the Balloon-borne Large Aperture Submillimeter Telescope for Polarimetry. This is the first direct combination of near-IR and submillimeter polarization data for a molecular cloud aimed at measuring the “polarization efficiency ratio” ( ), a quantity that is expected to depend only on grain-intrinsic physical properties. It is defined as , where p 500 and p I are polarization fractions at and the I band, respectively, and is the optical depth. To ensure that the same column density of material is producing both polarization from emission and from extinction, we conducted a careful selection of near-background stars using 2MASS, Herschel, and Planck data. This selection excludes objects contaminated by the Galactic diffuse background material as well as objects located in the foreground. Accounting for statistical and systematic uncertainties, we estimate an average value of 2.4 ± 0.8, which can be used to test the predictions of dust grain models designed for molecular clouds when such predictions become available. The ratio appears to be relatively flat as a function of the cloud depth for the range of visual extinctions probed.

Optical and near-infrared linear polarization of low and intermediate-gravity ultracool dwarfs

We aim to study the optical and near-infrared linear polarimetric properties of a sample of young M7-L7 dwarfs ($\approx$1-500 Myr) with spectroscopic signatures of low- and intermediate-gravity atmospheres. We collected optical ($RIZ$) and near-infrared ($YJHK_{\rm s}$) linear polarimetry images on various time scales from $\sim$0.2 h to months. Linear polarization degrees in the interval 0-1.5\% ($I$- and $J$-bands) were measured with accuracies ranging from $\pm$0.1 $\%$ to $\pm$0.9 $\%$ depending on the observing filter and the target brightness. We found that the young field dwarfs in our sample show similar polarimetric degrees at both $I$- and $J$-bands, and that there is no obvious trend with the spectral type. The two Taurus sources in our sample show intense levels of $J$-band linear polarization probably due to surrounding disks. By compiling data from the literature for high-gravity M7-L7 dwarfs with likely ages $\ge$500 Myr, we did not observe any apparent difference in the linear polarimetry intensity between the young and old samples that could be ascribed to differing atmospheric gravities. Polarimetric variability with peak to peak amplitudes up to 1.5 $\%$ is detected on scales of about a rotation in two out of four targets that were monitored over several hours. Long-term polarimetric variability is also detected in nearly all dwarfs of the sample with data spanning months to years.

THE MAGNETIC FIELD OF L1544. I. NEAR-INFRARED POLARIMETRY AND THE NON-UNIFORM ENVELOPE

ABSTRACT The magnetic field (B-field) of the starless dark cloud L1544 has been studied using near-infrared (NIR) background starlight polarimetry (BSP) and archival data in order to characterize the properties of the plane-of-sky B-field. NIR linear polarization measurements of over 1700 stars were obtained in the H band and 201 of these were also measured in the K band. The NIR BSP properties are correlated with reddening, as traced using the Rayleigh–Jeans color excess (H–M) method, and with thermal dust emission from the L1544 cloud and envelope seen in Herschel maps. The NIR polarization position angles change at the location of the cloud and exhibit their lowest dispersion there, offering strong evidence that NIR polarization traces the plane-of-sky B-field of L1544. In this paper, the uniformity of the plane-of-sky B-field in the envelope region of L1544 is quantitatively assessed. This allows evaluation of the approach of assuming uniform field geometry when measuring relative mass-to-flux ratios in the cloud envelope and core based on averaging of the radio Zeeman observations in the envelope, as done by Crutcher et al. In L1544, the NIR BSP shows the envelope B-field to be significantly non-uniform and likely not suitable for averaging Zeeman properties without treating intrinsic variations. Deeper analyses of the NIR BSP and related data sets, including estimates of the B-field strength and testing how it varies with position and gas density, are the subjects of later papers in this series.

Angle resolved photoelectron spectroscopy of two-color XUV–NIR ionization with polarization control

Electron emission caused by extreme ultraviolet (XUV) radiation in the presence of a strong near infrared (NIR) field leads to multiphoton interactions that depend on several parameters. Here, a comprehensive study of the influence of the angle between the polarization directions of the NIR and XUV fields on the two-color angle-resolved photoelectron spectra of He and Ne is presented. The resulting photoelectron angular distribution strongly depends on the orientation of the NIR polarization plane with respect to that of the XUV field. The prevailing influence of the intense NIR field over the angular emission characteristics for He(1s) and Ne(2p) ionization lines is shown. The underlying processes are modeled in the frame of the strong field approximation (SFA) which shows very consistent agreement with the experiment reaffirming the power of the SFA for multicolor-multiphoton ionization in this regime.

Large-area, broadband and high-efficiency near-infrared linear polarization manipulating metasurface fabricated by orthogonal interference lithography

Manipulation of the polarization state using electromagnetic metasurface has attracted considerable attention in recent years. However, most previously demonstrated single-layer polarization conversion metasurfaces suffer from low polarization conversion efficiency, narrow operation bandwidth, or huge fabrication challenges, especially for the visible and near-infrared frequencies. In this letter, a broadband and high-efficiency reflective linear polarization converter composed of ellipse-shaped plasmonic planar resonator was demonstrated in the near-infrared region. A polarization conversion ratio in power larger than 91.1% is achieved from 730 nm to 1870 nm. Furthermore, orthogonal interference lithography is adopted to prepare the large-area optical polarization conversion metasurface. The fabrication strategy unplugs the bottleneck of the fabrication of the large-area metasurface in the optical regime, promising an unprecedented progress for optical communication and integrated optics.

Theory of effect of near-infrared laser polarization direction on high-order terahertz sideband generation in semiconductors

In a semiconductor illuminated by a strong terahertz (THz) field, the electron-hole pairs excited by linear polarized near-infrared (NIR) laser can recombine to emit high-order THz sideband. Previous experimental results have shown, under the same condition of excitation intensity, the polarization direction of the NIR laser could affect the sideband intensity. In this letter, we theoretically investigate the effect of the NIR laser polarization direction on high-order terahertz sideband generation in bulk GaAs.

FIRST OPTICAL AND NEAR-INFRARED POLARIMETRY OF A MOLECULAR CLOUD FORMING A PROTO-BROWN DWARF CANDIDATE

LDN 328 is cited as an example of a fairly isolated clump contracting to form multiple sub-cores, possibly through gravitational fragmentation. In one of these sub-cores, a proto-brown dwarf (L328-IRS) candidate is in the process of formation through the self-gravitating contraction, similar to the formation scenario of a low-mass star. We present results of our optical and near-infrared polarization observations of regions toward LDN 328. This is the first observational attempt to map the magnetic field geometry of a cloud harboring a proto-brown dwarf candidate associated with a sub-parsec-scale molecular outflow. On a parsec scale, the magnetic field is found to follow the curved structure of the cloud showing a head–tail morphology. The magnetic field is found to be well ordered over a 0.02–0.2 pc scale around L328-IRS. Taking into account the uncertainties in the determination of position angles, the projected angular offset between the magnetic field direction and the outflow axis is found to be in the range of 0°–70°. Considering outflow to be the proxy for the rotation axis, the result obtained in this study implies that the rotation axis in L328 is preferably parallel to the local magnetic field. The magnetic field strength estimated in the close vicinity of L328-IRS is ∼20 μG. Results from the present study suggest that the magnetic field may be playing a vital role even in the cores that are forming sub-stellar sources.

Near-infrared optical constants and optical polarization properties of ZnO thin films

The optical characteristics of ZnO thin films deposited on Si (111) and quartz at temperature <50°C using reactive RF sputtering deposition were examined within the near-infrared (NIR) region. From the X-ray diffraction observations, it was found that the films show a polycrystalline structure. X-ray photoelectron spectroscopy analysis shows the chemical bonding states of zinc and oxygen in the surface of the films and confirms the formation of Zn–O bonds. The field emission scanning electron microscopy and the atomic force microscopy images of the films shown an almost uniform distribution and the surfaces are smooth with grains of the order of 40–60nm. The average surface roughness was in the range of 3.15–24.33nm. Over a wavelength range 700–2500nm, the optical constants of the films were obtained by analysis of the measured ellipsometric spectra using the Cauchy–Urbach model. Refractive indices and extinction coefficients of the ZnO films were determined to be in the range n=1.65–1.73 and κ=0.0060–0.029, respectively. Also, the s- and p-polarized optical properties (transmittance and reflectance) of the films have been measured at different angles of incidence in the UV–Vis–NIR spectral range. In addition, calculations have been carried out in order to determine the optical absorptance by using the conservation of energy. The films reveal a high transmittance (85%–95%), low reflectance (5%–15%), and very low absorptance (<1%) at normal incidence. This means that the sputtered polycrystalline ZnO films could be good candidates for antireflection (AR) optical coatings.

NEAR-INFRARED CIRCULAR POLARIZATION SURVEY IN STAR-FORMING REGIONS: CORRELATIONS AND TRENDS

We have conducted a systematic near-infrared circular polarization (CP) survey in star-forming regions, covering high-mass, intermediate-mass, and low-mass young stellar objects. All the observations were made using the SIRPOL imaging polarimeter on the Infrared Survey Facility 1.4 m telescope at the South African Astronomical Observatory. We present the polarization properties of ten sub-regions in six star-forming regions. The polarization patterns, extents, and maximum degrees of linear and circular polarizations are used to determine the prevalence and origin of CP in the star-forming regions. Our results show that the CP pattern is quadrupolar in general, the CP regions are extensive, up to 0.65 pc, the CP degrees are high, up to 20 %, and the CP degrees decrease systematically from high- to low-mass young stellar objects. The results are consistent with dichroic extinction mechanisms generating the high degrees of CP in star forming regions.

Interference in the angular distribution of photoelectrons in superimposed XUV and optical laser fields

The angular distribution of photoelectrons ejected during the ionization of Ne atoms by extreme ultraviolet (XUV) free-electron laser radiation in the presence of an intense near infrared (NIR) dressing field was investigated experimentally and theoretically. A highly nonlinear process with absorption and emission of more than ten NIR photons results in the formation of numerous sidebands. The amplitude of the sidebands varies strongly with the emission angle and the angular distribution pattern reveals clear signatures of interferences between the different angular momenta for the outgoing electron in the multi-photon process. As a specific feature, the central photoelectron line is characterized at the highest NIR fields by an angular distribution, which is peaked perpendicularly to both the XUV and NIR polarization directions. Experimental results are reproduced by a theoretical model based on the strong field approximation.

Glucose content detection in aqueous solutions with near-infrared polarization spectrometry

The absorbance using diffuse reflectance in the polarization spectroscopy was expressed using the empirical expressions that fitted the Monte Carlo simulation results. The absorbance spectra of glucose solutions indicated that the partition among H2O molecular species changed partly to the other ones depending on the glucose content. In saline water and phosphate-buffered saline water, there appears an action opposite to the transition in dissolution of glucose by the destruction of water species due to the presence of Na+ and Cl− ions. The sensitivity of glucose concentration in them was found to be higher in the cross-polarization than in the parallel one owing to the increased travelling distance caused by multiscattering.

Investigation of dust properties of the proto-planetary nebula IRAS 18276−1431

We investigate the circumstellar dust properties of the oxygen-rich bipolar proto-planetary nebula (PPN) IRAS 18276−1431 by means of two-dimensional radiative transfer simulations of the circumstellar dust shell. The model geometry is assumed to have a torus and an envelope which consists of a pair of bipolar lobes and a spherical asymptotic giant branch shell. The parameters of the dust and the dust shell are constrained by comparing the spectral energy distribution (SED) and near-infrared intensity and polarization data with the models. The polarization in the envelope reaches 50–60 per cent and is nearly constant in the H and KS bands in the observations. This weak wavelength dependence of the polarization can be reproduced with a grain-size distribution function for the torus: 0.05 μm ≤ a with n(a)∝a− (p = 5.5)exp ( − a/ac = 0.3 μm). The power index p is significantly steeper than that for interstellar dust (p ∼ 3). Similar results have also been found in some other PPNs and suggest that mechanisms that grind down large particles, such as sputtering, may also have acted when the dust particles formed. The spectral opacity index β is found to be 0.6 ± 0.5 from the 760 μm to 2.6 mm fluxes, which is characterized by the dust in the torus. This low value (<2) indicates the presence of large dust grains in the torus. We discuss two possible dust models for the torus. One has a size distribution function of 1.0 ≤ a ≤ amax = 5 000.0 μm with n(a) ∝ a−(p = 2.5) and the other is 1.0 μm ≤ a ≤ amax = 10 000.0 μm with n(a) ∝ a−(p = 3.5). The former has β of 0.633, but we are not able to find reasonable geometry parameters to fit the SED in the infrared. The latter has β of 1.12, but reproduces the SED better over a wide wavelength range. With this dust model, the geometric parameters are estimated as follows: the inner and outer radii are 30 and 1000 au and the torus mass is 3.0 M⊙. Given that the torii are generally not found to be rotating, a large fraction of the torus material is likely to be expanding. Assuming an expansion velocity of 15 km s−1, the torus formation time and mass-loss rate are found to be ∼300 yr and ∼10−2 M⊙ yr−1, respectively.

Near-Infrared Imaging Polarization Study of M 17

Abstract We conducted wide-field ($ \sim$ 8$ '$$ \times$ 8$ '$ ) $ \textit{JHK}_{\rm s}$ imaging polarimetric observations toward the massive star-formation region M 17. The southern H II bar is identified as large-scale infrared reflection nebula (IRN) illuminated by OB stars in the cluster center, while the northern bar shows polarization originating from dichroic extinction. Three small-scale bipolar IRN with centro-symmetric polarization patterns were identified, and their illuminating sources, embedded young stellar objects (YSOs), are most likely the driving sources of bipolar outflows. $ \textit{JHK}_{\rm s}$ polarizations of point sources in M 17 show a wavelength dependence of the polarization of dichroic extinction in the general interstellar medium, indicating $ \alpha$$ \sim$ 1.8 for the empirical relation $ P$$ \propto$$ \lambda^{-\alpha}$ of interstellar polarization. The distribution of the polarization angle shows two peaks at 170$ ^{\circ}$ and 110$ ^{\circ}$ , indicating a non-uniform magnetic field structure in M 17. The direction of the magnetic field in the cluster region is south-north. However, the magnetic field in the H II region is roughly between 100$ ^{\circ}$ –140$ ^{\circ}$ , roughly perpendicular to the Galactic disk. Such a configuration indicates that the magnetic field in the cluster region is twisted from the primordial orientation in the cluster formation. The magnetic field in the southern bar has a total strength of $ \sim$ 230$ \ \mu$ G, and is 40$ ^{\circ}$ inclined to the plane of the sky. The outflows driven by YSOs in M 17 show a poor relation with the surrounding magnetic fields. This fact implies that the magnetic field in M 17 does not dominate the orientations of protostars formed inside.

Magnetic Field Structure in Molecular Clouds by Polarization Measurements

AbstractWe report on a program to delineate magnetic field structure inside molecular clouds by optical and infrared polarization observations. An ordered magnetic field inside a dense cloud may efficiently align the spinning dust grains to cause a detectable level of optical and near-infrared polarization of otherwise unpolarized background starlight due to dichroic extinction. The near-infrared polarization data were taken by SIRPOL mounted on IRSF in SAAO. Here we present the SIRPOL results in RCW 57, for which the magnetic field is oriented along the cloud filaments, and in Carina Nebula, for which no intrinsic polarization is detected in the turbulent environment. We further describe TRIPOL, a compact and efficient polarimer to acquire polarized images simultaneously at g', r', and i' bands, which is recently developed at Nagoya University for adaption to small-aperture telescopes. We show how optical observations probe the translucent outer parts of a cloud, and when combining with infrared observations probing the dense parts, and with millimeter and submillimeter observations to sutdy the central embedded protostar, if there is one, would yield the magnetic field structure on different length scales in the star-formation process.