Average Degree Of Polarization Research Articles

Studying geometry of the ultraluminous X-ray pulsar Swift J0243.6+6124 using X-ray and optical polarimetry

Discovery of pulsations from a number of ultra-luminous X-ray (ULX) sources proved that accretion onto neutron stars can produce luminosities exceeding the Eddington limit by several orders of magnitude. The conditions necessary to achieve such high luminosities as well as the exact geometry of the accretion flow in the neutron star vicinity are, however, a matter of debate. The pulse phase-resolved polarization measurements that became possible with the launch of the Imaging X-ray Polarimetry Explorer (IXPE) can be used to determine the pulsar geometry and its orientation relative to the orbital plane. They provide an avenue to test different theoretical models of ULX pulsars. In this paper we present the results of three IXPE observations of the first Galactic ULX pulsar Swift J0243.6+6124 during its 2023 outburst. We find strong variations in the polarization characteristics with the pulsar phase. The average polarization degree increases from about 5<!PCT!> to 15<!PCT!> as the flux dropped by a factor of three in the course of the outburst. The polarization angle (PA) as a function of the pulsar phase shows two peaks in the first two observations, but changes to a characteristic sawtooth pattern in the remaining data set. This is not consistent with a simple rotating vector model. Assuming the existence of an additional constant polarized component, we were able to fit the three observations with a common rotating vector model and obtain constraints on the pulsar geometry. In particular, we find the pulsar angular momentum inclination with respect to the line of sight of $i_ p the magnetic obliquity of $ p and the pulsar spin position angle of $ p which significantly differs from the constant component PA of about 10 Combining these X-ray measurements with the optical PA, we find evidence for at least a 30 misalignment between the pulsar angular momentum and the binary orbital axis.

Ultrasoft state of microquasar Cygnus X-3: X-ray polarimetry reveals the geometry of the astronomical puzzle

Cygnus X-3 is an enigmatic X-ray binary that is both an exceptional accreting system and a cornerstone for population synthesis studies. Prominent X-ray and radio properties follow a well-defined pattern, and yet the physical reasons for the state changes observed in this system are not known. Recently, the presence of an optically thick envelope around the central source in the hard state was revealed using the X-ray polarization data obtained with the Imaging X-ray Polarimetry Explorer (IXPE). In this work we analyse IXPE data obtained in the ultrasoft (radio quenched) state of the source. The average polarization degree (PD) of 11.9 ± 0.5% at a polarization angle (PA) of 94° ±1° is inconsistent with the simple geometry of the accretion disc viewed at an intermediate inclination. The high PD, the blackbody-like spectrum, and the weakness of fluorescent iron line imply that the central source is hidden behind the optically thick outflow, similar to the hard-state geometry, and its beamed radiation is scattered, by the matter located along the funnel axis, towards our line of sight. In this picture the observed PD is directly related to the source inclination, which we conservatively determine to lie in the range 26° < i < 28°. Using the new polarimetric properties, we propose a scenario that can be responsible for the cyclic behaviour of the state changes in the binary.

Probing the enpolarization phenomenon in a speckle pattern using a microwave photonics-inspired approach.

We report how Stokes polarimetry of a highly resolved optical speckle pattern coupled to an original microwave photonics-inspired experimental approach allows new light to be shaded on the so-called enpolarization phenomenon, which consists in the local increase of the light degree of polarization (DOP) inducing a high average DOP value after interaction of unpolarized light with a totally depolarizing sample.

3D scattering-enabled vectorial holographic projection with a binary amplitude hologram

Empowered by wavefront shaping (WFS) techniques, scattering materials (SMs) hold significant potential in high-capacity, high-fidelity, and crosstalk-free 3D holographic projections. Here, we present an optimal accumulation algorithm (OAA) to generate binary amplitude holograms that enable simultaneous control of 3D intensity and polarization distributions through SMs. In particular, OAA is efficient for creating binary holograms since only addition and comparison operations are required. Using such a binary hologram, we demonstrate complete polarization control on four planes simultaneously, and an average degree of polarization over 95% is achieved. Moreover, a 3D holographic projection of polarization-multiplexed images on multiple planes is also presented with an average Pearson correlation coefficient over 0.80. By exploiting the rapid switching ability of a digital micromirror device, we further demonstrate dynamic 3D vectorial holographic projections with reconfigurable binary amplitude holograms. Our proposed approach offers a competitive way to generate holograms for 3D scattering-enabled vectorial holographic projections.

All-optical polarization scrambler based on polarization beam splitting with an amplified fiber ring

Optical-fiber-based polarization scramblers can reduce the impact of polarization sensitive performance of various optical fiber systems. Here, we propose a simple and efficient polarization scrambler based on an all-optical Mach-Zehnder structure by combining a polarization beam splitter and an amplified fiber ring. To totally decoherence one polarization split beam, a fiber ring together with an amplifier is incorporated. The ratio of two orthogonal beams can be controlled by varying the amplification factor, and we observe different evolution trajectories of the output state of polarizations on the Poincaré sphere. When the amplification factor exceeds a certain threshold, the scrambler system exhibits nearly ideal polarization scrambling behavior. A commercial single wavelength laser with a linewidth of 3 MHz is utilized to characterize the scrambling performance. We found that when the sampling rate is 1.6 MSa/s, a scrambling speed up to 2000krad/s can be obtained for the average degree of polarization being less than 0.1. We also exploit these random polarization fluctuations to generate random binary numbers, indicating that the proposed technique is a good candidate for a random bit generator.

Polarized QED cascades over pulsar polar caps

ABSTRACT The formation of e± plasmas within pulsar magnetospheres through quantum electrodynamics (QED) cascades in vacuum gaps is widely acknowledged. This paper aims to investigate the effect of photon polarization during the QED cascade occurring over the polar cap of a pulsar. We employ a Monte Carlo-based QED algorithm that accurately accounts for both spin and polarization effects during photon emission and pair production in both single-particle and particle-in-cell (PIC) simulations. Our findings reveal distinctive properties in the photon polarization of curvature radiation (CR) and synchrotron radiation (SR). CR photons exhibit high linear polarization parallel to the plane of the curved magnetic field lines, whereas SR photons, on average, demonstrate weak polarization. As the QED cascade progresses, SR photons gradually dominate over CR photons, thus reducing the average degree of photon polarization. Additionally, our study highlights an intriguing observation: the polarization of CR photons enhances e± pair production by approximately 5 per cent, in contrast to the inhibition observed in laser–plasma interactions. Our self-consistent QED-PIC simulations in the corotating frame reproduce the essential results obtained from single-particle simulations.

X-Ray Polarimetry of the Dipping Accreting Neutron Star 4U 1624–49

We present the first X-ray polarimetric study of the dipping accreting neutron star 4U 1624−49 with the Imaging X-ray Polarimetry Explorer. We report a detection of polarization in the nondip time intervals with a confidence level of 99.99%. We find an average polarization degree (PD) of 3.1% ± 0.7% and a polarization angle of 81° ± 6° east of north in the 2–8 keV band. We report an upper limit on the PD of 22% during the X-ray dips with 95% confidence. The PD increases with energy, reaching from 3.0% ± 0.9% in the 4–6 keV band to 6% ± 2% in the 6–8 keV band. This indicates the polarization likely arises from Comptonization. The high PD observed is unlikely to be produced by Comptonization in the boundary layer or spreading layer alone. It can be produced by the addition of an extended geometrically thin slab corona covering part of the accretion disk, as assumed in previous models of dippers, and/or a reflection component from the accretion disk.

Lead-Free Chiral Perovskite for High Degree of Circularly Polarized Light Emission and Spin Injection.

We report a zero-dimensional (0D) lead-free chiral perovskite (S-/R-MBA)4Bi2I10 with a high degree of circularly polarized light (CPL) emission. Our 0D lead-free chiral perovskite exhibits an average degree of circular polarization (DOCP) of 19.8% at 78 K under linearly polarized laser excitation, and the maximum DOCP can reach 25.8%, which is 40 times higher than the highest DOCP of 0.5% in all reported lead-free chiral perovskites to the best of our knowledge. The high DOCP of (S-/R-MBA)4Bi2I10 is attributed to the free exciton emission with a Huang-Rhys factor of 2.8. In contrast, all the lead-free chiral perovskites in prior reports are dominant by self-trapped exciton in which the spin relaxation reduces DOCP dramatically. Moreover, we realize the manipulation of the valley degree of freedom of monolayer WSe2 by using the spin injection of the 0D chiral lead-free perovskites. Our results provide a new perspective to develop lead-free chiral perovskite devices for CPL light source, spintronics, and valleytronics.

First X-Ray Polarization Measurement Confirms the Low Black Hole Spin in LMC X-3

X-ray polarization is a powerful tool to investigate the geometry of accreting material around black holes, allowing independent measurements of the black hole spin and orientation of the innermost parts of the accretion disk. We perform X-ray spectropolarimetric analysis of an X-ray binary system in the Large Magellanic Cloud, LMC X-3, that hosts a stellar-mass black hole, known to be persistently accreting since its discovery. We report the first detection of the X-ray polarization in LMC X-3 with the Imaging X-ray Polarimetry Explorer, and find the average polarization degree (PD) of 3.2% ± 0.6% and a constant polarization angle of −42° ± 6° over the 2–8 keV range. Using accompanying spectroscopic observations by NICER, NuSTAR, and the Neil Gehrels Swift observatories, we confirm previous measurements of the black hole spin via the X-ray continuum method, a ≈ 0.2. From polarization analysis only, we found consistent results with low black hole spin, with an upper limit of a < 0.7 at a 90% confidence level. A slight increase in the PD with energy, similar to other black hole X-ray binaries in the soft state, is suggested from the data but with a low statistical significance.

Mueller-Polarimetry of Barley Leaves I: Depolarization Metrics

In this paper, Mueller polarimetry is applied to study the three groups of common barley leaf samples (Hordeum vulgare) in the visible spectrum (λ = 632.8 nm): Chlorina mutant, Chlorina etiolated mutant and Cesaer varieties. These samples differed in internal leaf structure from genetic mutation or by illumination during growth. Our main concern is to discriminate and characterize these three groups of leaf samples by depolarization metrics: degree of polarization (DoP), average degree of polarization (Average DoP), depolarization index (DI(M)), and Q(M) and R(M) metrics. The results obtained show that all depolarization metrics are sensitive to the sample’s polarization properties. The most effective observable is the Q(M) metric in both forward and backward scattering. The DoP metric showed presence of depolarization anisotropy, which is significantly different for forward and backward scattering for all three groups of samples. Dichroism is observed for both forward and backward scattering, with lower dichroism in forward scattering.

Magnetic Structures and Turbulence in SN 1006 Revealed with Imaging X-Ray Polarimetry

Young supernova remnants strongly modify the surrounding magnetic fields, which in turn play an essential role in accelerating cosmic rays (CRs). The X-ray polarization measurements probe magnetic field morphology and turbulence at the immediate acceleration site. We report the X-ray polarization distribution in the northeastern shell of SN 1006 from a 1 Ms observation with the Imaging X-ray Polarimetry Explorer. We found an average polarization degree of 22.4% ± 3.5% and an average polarization angle of −45.°4 ± 4.°5 (measured on the plane of the sky from north to east). The X-ray polarization angle distribution reveals that the magnetic fields immediately behind the shock in the northeastern shell of SN 1006 are nearly parallel to the shock normal or radially distributed, similar to that in the radio observations, and consistent with the quasi-parallel CR acceleration scenario. The X-ray emission is marginally more polarized than that in the radio band. The X-ray polarization degree of SN 1006 is much larger than that in Cas A and Tycho, together with the relatively tenuous and smooth ambient medium of the remnant, favoring that CR-induced instabilities set the magnetic turbulence in SN 1006, and CR acceleration is environment-dependent.

First-principles-integrated Study of Blazar Synchrotron Radiation and Polarization Signatures from Magnetic Turbulence

Blazar emission is dominated by nonthermal radiation processes that are highly variable across the entire electromagnetic spectrum. Turbulence, which can be a major source of nonthermal particle acceleration, can widely exist in the blazar emission region. The Turbulent Extreme Multi-Zone (TEMZ) model has been used to describe turbulent radiation signatures. Recent particle-in-cell (PIC) simulations have also revealed the stochastic nature of the turbulent emission region and particle acceleration therein. However, radiation signatures have not been systematically studied via first-principles-integrated simulations. In this paper, we perform combined PIC and polarized radiative transfer simulations to study synchrotron emission from magnetic turbulence in the blazar emission region. We find that the multiwavelength flux and polarization are generally characterized by stochastic patterns. Specifically, the variability timescale and average polarization degree (PD) are governed by the correlation length of the turbulence. Interestingly, magnetic turbulence can result in polarization angle swings with arbitrary amplitudes and duration, in either direction, that are not associated with changes in flux or PD. Surprisingly, these swings, which are stochastic in nature, can appear either bumpy or smooth, although large-amplitude swings (>180°) are very rare, as expected. Our radiation and polarization signatures from first-principles-integrated simulations are consistent with the TEMZ model, except that in the latter, there is a weak correlation, with zero lag, between flux and degree of polarization.

Highly polarized light emission from hybrid of quantum dots and plasmons in the intermediate coupling regime.

Colloidal semiconductor quantum dots (QDs), with a size tunable bandgap and remarkably high quantum efficiency, have been recognized as ideal light sources in quantum information and light emitting devices. For light sources, besides the emission intensity and spectral profile, the degree of polarization (DoP) is an essential parameter. Here, by embedding a monolayer of QDs inside the nanogap between a bottom Au mirror and a top Ag nanowire, we have demonstrated highly polarized light emission from the QDs with an average DoP of 0.89. In addition to the anisotropic photoluminescence (PL) intensity, the PL spectra are distinct at different polarizations, with an asymmetric spectral shape or even two-peak features. Such an anisotropic emission behavior arises from the coupling between the QDs and the largely confined and polarization-dependent gap-plasmons in the Au/QD/Ag nanocavities in the intermediate coupling regime. Our results demonstrate the possibility of achieving highly polarized light sources by coupling spherical QDs to single anisotropic plasmonic nanocavities, to provide new opportunities in the future design of polarized QD-based display devices.

Polarized X-Rays from Windy Accretion in Cygnus X-1

Recent X-ray polarimetric data on the prototypical black hole X-ray binary Cyg X-1 from the Imaging X-ray Polarimetry Explorer present tight constraints on accretion geometry in the hard spectral state. Contrary to general expectations of a low, ≲1% polarization degree (PD), the observed average PD was found to be a factor of 4 higher. Aligned with the jet position angle on the sky, the observed polarization favors geometry of the X-ray emission region stretched normally to the jet in the accretion disk plane. The high PD is, however, difficult to reconcile with the low orbital inclination of the binary i ≈ 30°. We suggest that this puzzle can be explained if the emitting plasma is outflowing with a mildly relativistic velocity ≳0.4 c. Our radiative transfer simulations show that Comptonization in the outflowing medium elongated in the plane of the disk and radiates X-rays with the degree and direction of polarization consistent with observations at i ≈ 30°.

High Speed All-Optical Polarization Scrambler Based on Polarization Beam Splitting Delayed Fiber Loop

Polarization scramblers are widely employed to mitigate polarization fluctuation-related effects for optical signals propagating in fiber systems. We propose an all-optical polarization scrambler configuration based on a polarization beam splitting delayed fiber loop. By deteriorating the coherence of one beam, and controlling the intensity ratio of two orthogonal beams, the polarization scrambler operates in a chaotic regime. The effect on polarization scrambling of loop structure is tested by a home-made narrow-linewidth laser with linewidth of 500 Hz. We investigate the polarization scrambling performance for a commercial distributed feedback laser with linewidth of 3 MHz in various operating regimes. Scrambling speeds under chaotic regime reach 42 Mrad/s with a degree of polarization <0.1 at the maximum sampling rate of 100 MSa/s. We also characterize the dependence of the scrambling speed and average degree of polarization on delay fiber length and wavelengths within the C-band. The output performance of the proposed scrambler for scrambling 40 MHz and 6 GHz modulated signals are tested and waveform distortions are identified due to polarization scrambling.

Detection of Underwater Targets Using Polarization Laser Assisted Echo Detection Technique

At present, polarization imaging detection experiments of underwater objects mainly focus on the degree of polarization but lack of Stokes vector imaging effect of each element. Based on the principle that the polarization characteristics of different materials are different, the experiment of underwater target detection by laser pulse polarization is carried out in this paper, and the influence of different depths of an underwater object and material factors on polarization imaging detection is studied. The results show that in air, the average degree of polarization of iron sheet is 0.56, that of ceramic tile is 1.00, and that of plastic is 0.48. In water, the average degree of polarization of iron sheet is 0.3625 at 7.5 m, the average degree of polarization of ceramic tile at 7.5 m is 0.359, and that of plastic at 7.5 m is 0.3805. The medium will change the degree of polarization of the measured object. The targets made of different materials have different polarization characteristics, and the polarization information is of great value in improving the detection performance of man-made targets. Polarization detection can obtain better information about underwater objects than traditional radiation intensity detection and can effectively suppress the absorption and scattering of light by water.

Compact Polarized X-Ray Source Based on All-Optical Inverse Compton Scattering

Polarized x-ray source is a useful probe for many fields, such as fluorescence imaging, magnetic microscopy, and nuclear physics research. All-optical inverse Compton scattering source (AOCS) based on a laser wakefield accelerator (LWFA) has drawn great attention in recent years due to its compact scale and high performance, especially its potential to generate polarized x rays. Here, polarization-tunable AOCS x rays are generated by a plasma-mirror-based scheme. The linearly and circularly polarized AOCS x rays are measured to have the mean photon energy of $60(\ifmmode\pm\else\textpm\fi{}5)/64(\ifmmode\pm\else\textpm\fi{}3)$ keV and the single-shot photon yield of approximately $1.1/1.3\ifmmode\times\else\texttimes\fi{}{10}^{7}$. A Compton polarimeter is designed to diagnose the x-ray polarization states, demonstrating the polarization tunability of AOCS, and indicating that the average polarization degree of the linearly polarized AOCS is $75(\ifmmode\pm\else\textpm\fi{}3)\mathrm{%}$ within 18.2 mrad x-ray divergence.

Examining the dust of the tailless Oort-cloud comet C/2020 T2

We report our latest analysis of the Oort-cloud comet C/2020 T2 (also named Palomar or T2) observed at 2.06 au from the Sun (phase angle of 28.°5) roughly two weeks before perihelion. It lacks a significant dust tail in scattered light, showing a strong central condensation of the coma throughout the apparition that is reminiscent of so-called Manx comets. Its spectral slope of polarized light increases and decreases in the J (1.25 μm) and H (1.65 μm) bands, respectively, resulting in an overall negative (blue) slope (−0.31 ±0.14% μm−1 ) in contrast to the red polarimetric color of active comets observed at similar geometries. The average polarization degree of T2 is 2.86±0.17% for the J and 2.75±0.16% for the H bands. Given that near-infrared wavelengths are sensitive to the intermediate-scale structure of cometary dust (i.e., dust aggregates), our light-scattering modeling of ballistic aggregates with different porosities and compositions shows that the polarimetric properties of T2 are compatible with low-porosity (~66%), absorbing dust aggregates with negligible ice contents on a scale of 10–100 μm (density of ~652 kg m−3). This is supported by the coma morphology of T2 which has a viable β (the relative importance of solar radiation pressure on dust particles) range of ≲10−4. The secular evolution of r-band activity of T2 from archival data reveals that the increase in its brightness accelerates around 2.4 au pre-perihelion, with its overall dust production rate that is about 100 times smaller than those of active Oort-cloud comets. We also found an apparent concentration of T2 and Manx comets toward ecliptic orbits. This paper underlines the heterogeneous nature of Oort-cloud comets, which may be investigated in the near future with dedicated studies of their dust characteristics.

X-Ray Polarization Detection of Cassiopeia A with IXPE

We report on a ∼5σ detection of polarized 3–6 keV X-ray emission from the supernova remnant Cassiopeia A (Cas A) with the Imaging X-ray Polarimetry Explorer (IXPE). The overall polarization degree of 1.8% ± 0.3% is detected by summing over a large region, assuming circular symmetry for the polarization vectors. The measurements imply an average polarization degree for the synchrotron component of ∼2.5%, and close to 5% for the X-ray synchrotron-dominated forward shock region. These numbers are based on an assessment of the thermal and nonthermal radiation contributions, for which we used a detailed spatial-spectral model based on Chandra X-ray data. A pixel-by-pixel search for polarization provides a few tentative detections from discrete regions at the ∼ 3σ confidence level. Given the number of pixels, the significance is insufficient to claim a detection for individual pixels, but implies considerable turbulence on scales smaller than the angular resolution. Cas A’s X-ray continuum emission is dominated by synchrotron radiation from regions within ≲1017 cm of the forward and reverse shocks. We find that (i) the measured polarization angle corresponds to a radially oriented magnetic field, similar to what has been inferred from radio observations; (ii) the X-ray polarization degree is lower than in the radio band (∼5%). Since shock compression should impose a tangential magnetic-field structure, the IXPE results imply that magnetic fields are reoriented within ∼1017 cm of the shock. If the magnetic-field alignment is due to locally enhanced acceleration near quasi-parallel shocks, the preferred X-ray polarization angle suggests a size of 3 × 1016 cm for cells with radial magnetic fields.

Interstellar Extinction and Polarization of Stars in the Open Cluster NGC 6709

We present BVRI polarimetric measurements of 23 stars in the direction of the open cluster NGC 6709. Fifteen stars display wavelength-dependence of polarization which is typically due to selective extinction in the interstellar medium and could be fitted to the Serkwoski equation. Based on these stars, we obtained an average maximum degree of polarization of 0.722 ± 0.022% and an average wavelength at a maximum polarization of 0.615 ± 0.011 μm. The observed low polarization may be due to the alignment of grains along a more longitudinally-directed magnetic field in this region which would cause the aspect ratio of the grains to be reduced. This would have the observational consequence of decreased polarization as well as shifting toward longer wavelengths. Using the expression proposed by Whittet & van Breda we calculated the ratio of total-to-selective extinction as , higher than the nominal value of 3.1 for the general ISM. The remaining eight sample stars display an unusual wavelength-dependence that is similar to some Be stars. However, there are only two Be stars currently listed in this cluster, yet, based on our data, they both present reliable fits within the Serkowski equation. The overall alignment of the V-band polarization vectors implies polarization by selective extinction due to foreground dust. Using the Planck 353 GHz channel we find there is an agreement between polarization by emission and selective extinction. Since the optical polarization traces a magnetic field, this suggests that the magnetic field in this region is inclined to the Galactic plane, with an overall average Galactic position angle of 104 ± 12 (st. dev.) degrees.