Changes In Degree Of Polarization Research Articles

Change of polarization degree of light beams on propagation in curved space

Even in free space, which is commonly considered of as a flat space–time in most settings, the degree of polarization of a partially spatially coherent light beam changes as it travels. Similarly, the polarization degree would change when a partially spatially coherent light beam propagates in a curved space–time. The difference of the polarization degree between the curved space and flat space can reveal the essential structure of the curved space. In this work, we consider a simplest case of curved space known as Schwarzschild spacetime. We can simulate the Schwarzschild space–time as an optical material with an effective refractive index. The difference of the polarization degree of a light beam propagating in curved space and flat space can be achieved up to 5%, which is detectable in practical measurement. In addition, we have found that the partially spatially coherent light source is necessary for obtaining significant changes in polarization degree. Our results provide an alternative method to estimate the Schwarzschild radius of a massive object with the optical polarization degree measurement.

Multi-epoch spectropolarimetry for a sample of Type IIn Supernovae: persistent asymmetry in dusty circumstellar material

ABSTRACT We present multi-epoch spectropolarimetry and spectra for a sample of 14 Type IIn supernovae (SNe IIn). We find that after correcting for likely interstellar polarization, SNe IIn commonly show intrinsic continuum polarization of 1–3 per cent at the time of peak optical luminosity, although a few show weaker or negligible polarization. While some SNe IIn have even stronger polarization at early times, their polarization tends to drop smoothly over several hundred days after peak. We find a tendency for the intrinsic polarization to be stronger at bluer wavelengths, especially at early times. While polarization from an electron scattering region is expected to be grey, scattering of SN light by dusty circumstellar material (CSM) may induce such a wavelength-dependent polarization. For most SNe IIn, changes in polarization degree and wavelength dependence are not accompanied by changes in the position angle, requiring that asymmetric pre-SN mass loss had a persistent geometry. While 2–3 per cent polarization is typical, about 30 per cent of SNe IIn have very low or undetected polarization. Under the simplifying assumption that all SN IIn progenitors have axisymmetric CSM (i.e. disc/torus/bipolar), then the distribution of polarization values we observe is consistent with similarly asymmetric CSM seen from a distribution of random viewing angles. This asymmetry has very important implications for understanding the origin of pre-SN mass loss in SNe IIn, suggesting that it was shaped by binary interaction.

Mueller-matrix for non-ideal beam-splitters to ease the analysis of vectorial optical fields

Non-polarizing beam-splitters (BSs) are the heart of most optical experiments and instruments (optical coherence tomography, holography, optical communication, quantum cryptography, etc.). An ideal BS assumes polarization independence, rare to achieve in a realistic scenario due to BS’ intrinsic nature, which causes errors in polarization-sensitive experiments. This article identifies a solution to this problem by introducing a Mueller matrix (MM) for a realistic BS—which, to the best of our knowledge, is the only way to analyze the effect on vectorial fields. Simulations using the introduced MM assist in understanding modulations in the degree of polarization (DoP) of partially polarized fields after a BS. These changes in DoP by a BS are verified in an experiment by synthesizing a partially polarized beam. Further, the effects of BS on polarization singularities are studied using the matrices both theoretically and experimentally. It is observed that passing partially polarized polarization singular beams through a BS can cause a loss of axial symmetry in polarization features, which is verified through simulations using the introduced MM. This study may find useful applications in most optical experiments and instrumentation.

Polarimetry as a Tool for Observing Orographic Gravity Waves on Venus

Abstract Planet-wide stationary gravity waves have been observed with the thermal camera on the Akatsuki spacecraft. These waves have been attributed to the underlying surface topography and have successfully been reproduced using the Institut Pierre Simon Laplace (IPSL) Venus Mesoscale Model (VMM). Here, we use numerical radiative transfer computations of the total and polarized fluxes of the sunlight that is reflected by Venus under the conditions of these gravity waves to show that the waves could also be observed in polarimetric observations. To model the waves, we use the density perturbations computed by the IPSL VMM. We show the computed wave signatures in the polarization for nadir-viewing geometries observed by a spacecraft in orbit around Venus and as they could be observed using an Earth-based telescope. We find that the strength of the signatures of the atmospheric density waves in the degree of polarization of the reflected sunlight depends not only on the density variations themselves, but also on the wavelength and the cloud top altitude. Observations of such wave signatures on the dayside of the planet would give insight into the occurrence of the waves and possibly into the conditions that govern their onset and development. The computed change in degree of polarization due to these atmospheric density waves is about 1000 ppm at a wavelength of 300 nm. This signal is large enough for an accurate polarimeter to detect.

Optical Polarimetry of the Tidal Disruption Event AT2019DSG

Abstract We present time-series imaging polarimetry observations of a nearby tidal disruption event (TDE) AT2019DSG at z = 0.0512 to probe the disruption mechanism and shed light on the accretion process. We obtain linear polarimetry using the Alhambra Faint Object Spectrograph and Camera on board the 2.5 m Nordic Optical Telescope. Our observations showed a polarization at the 9.2% ± 2.7% level early on, decreasing to less than 2.7% (at the 68% confidence level) one month later. While the high level of polarization in the early epoch is similar to that of Swift J164449.3+573451 and Swift J2058+0516, the low level of polarization in the later epoch is in agreement with that of OGLE16aaa. Our results thus show the temporal evolution of optical polarization from a TDE. As the degree of polarization changes over time, it is unlikely to be attributed to host galaxy dust, but may originate from a non-isotropic accreting disk, or associated with the relativistic jet emission.

不同湿度环境下可见光波段激光偏振特性研究

Haze weather interferes with the visible light imaging effect, and the polarization characteristic of visible light can effectively improve the detection efficiency. Haze environment is affected by aerosol particle humidity, which is an important physical parameter of haze environment. In order to obtain the polarization characteristics of visible light in haze environment, the influence of humidity in haze environment on polarization characteristics was analyzed. Based on the single particle scattering characteristics of non-polarized light aerosol, the polarization transmission model was established by improved Monte Carlo method, research on transmission characteristics of polarized light in visible bands under different humidity and water mist was conducted, the influence of humidity change in water mist environment on polarization characteristics of polarized light in different visible bands was analyzed, and a near-real water mist environment was built. The polarization model was verified by laboratory experiments, the change of polarization degree and polarization state of linear polarized light on 450, 532 and 671 nm was compared and analyzed under different humidity conditions, the confidence of simulation model was more than 60%. The results show that the polarization degree of polarized light decreases with the increase of humidity of water-fog environment. With the increase of the wavelength, the polarization tends to be flat, while the exit polarization degree increases with the increase of wavelength. The humidity values of the descending point of polarization degree are 50%, 70% and 90% when the laser wavelengths are 450, 532, 671 nm, respectively. For water mist, which is easily affected by humidity, polarized light with longer wave length should be selected as far as possible for transmission detection in visible band. Because humidity has a greater influence on shorter wavelengths than longer wavelengths, circularly polarized light with longer wavelengths has the best polarization retention characteristics in environments with higher humidity. In the environment with high humidity, polarized light imaging with long wavelength should be selected as far as possible to achieve better imaging effect.

Warped disks during type II outbursts in Be/X-ray binaries: evidence from optical polarimetry

Context. Current models that explain giant (type II) X-ray outbursts in Be/X-ray binaries (BeXB), are based on the idea of highly distorted disks. They are believed to occur when a misaligned and warped disk becomes eccentric, allowing the neutron star to capture a large amount of material. The BeXB 4U 0115+63 underwent two major outbursts in 2015 and 2017. Aims. Our aim is to investigate whether the structural changes in the disk expected during type II outbursts can be detected through optical polarimetry. Methods. We present the first optical polarimetric observations and new optical spectra of the BeXB 4U 0115+63 covering the period 2013–2017. We study in detail the shape of the Hα line profile and the polarization parameters before, during, and after the occurrence of a type II X-ray outburst. Results. We find significant changes in polarization degree and polarization angle and highly distorted line profiles during the 2017 X-ray outburst. The degree of polarization decreased by ∼1%, while the polarization angle, which is supposed to be related with the disk orientation, first increased by ∼10° in about two months and then decreased by a similar amount and on a similar timescale once the X-ray activity ceased. Conclusions. We interpret the polarimetric and spectroscopic variability as evidence for the presence of a warped disk.

Changes in the degree of polarization of random electromagnetic GSM vortex beams in biological tissues

Based on the Huygens-Fresnel principle, the analytic expressions of the cross-spectral density matrix elements of the random electromagnetic Gaussian Schell model (GSM) vortex beams in biological tissues are derived, and used to study the changes in the on-axis degree of polarization P(0, 0, z), one point degree of polarization P(ρ, ρ, z) and two points (generalized) degree of polarization P(0, ρ, z) of random electromagnetic GSM vortex beams. The results show that with the increment of the propagation distance z, the bigger Cn2 is, the earlier appearance of the inflexion points in P(0, 0, z) and P(ρ, ρ, z) are, but the changes in P(0, ρ, z) are related to the propagation distance. The smaller σxy is, the greater σyy is, the more smooth the change curves of P(0, 0, z), P(ρ, ρ, z) and P(0, ρ, z) are. Besides, the difference values between σxx and σyy also influence the changes in P(0, 0, z), P(ρ, ρ, z) and P(0, ρ, z). On the same conditions, the changes in P(0, ρ, z) are more complicate than those in P(ρ, ρ, z), and the changes in P(ρ, ρ, z) are more complex than those in P(0, 0, z).

Imaging polarimetry of comets C/2013 V1 (Boattini) and 290P/Jager before and after perihelion

We report the results obtained from the optical polarimetric study of the light scattered by comets C/2013 V1 (Boattini) and 290P/Jager at lower phase angles. The polarimetric observations of two comets have been performed with the 1.04-m Sampurnanand telescope of Aryabhatta Research Institute of observational sciencES near Nainital in India on 2013 December 4 and 5 and on 2014 April 24 using R photometric band ($\lambda$ = 630 nm, $\Delta$$\lambda$ =120nm). We covered observations in both the pre and post perihelion passage of comets C/2013 V1 (Boattini) and 290P/Jager at two phase angles $\sim$ 13$^\circ$ and 27$^\circ$. The degree of polarization changes from ($-1.4$$\pm 0.3$)per cent to (+2.8$\pm 0.5$)per cent for comet C/2013 V1 (Boattini) and ($-1.6$$\pm 0.5$)per cent to (+2.5$\pm 0.5$)per cent for comet 290P/Jager at phase angles $\sim$ 13$^\circ$ and 27$^\circ$ respectively. The change in the physical properties of cometary dust is being well studied from the polarization maps obtained for both the period of observations. It is found that the aperture polarization values are comparable to those of other comets. The variation in the brightness profile of both the comets from the standard canonical nature is also being observed in both the solar and anti-solar direction during this phase which suggests the various physical evolution influencing the cometary comae.

Polarized emission of quantum dots in microcavity and anisotropic Purcell factors

We study the polarization properties of quantum dot (QD) emission coupled with the fundamental cavity modes. A rotation of polarization axis and a change of polarization degree are observed as the coupling is varied. To explain this observation, we derive an analytical model considering the polarization misalignment between QD dipole and cavity mode field. Our model also provides a new approach to extract the anisotropic Purcell factors by analyzing the polarization of detected quantum dot emission coupled to the cavity mode, which paves the way to develop high-efficiency polarized single photon sources.

Effect of source parameters on polarization characteristics of electromagnetic beam propagating in atmospheric turbulence

According to the theory of beam spreading and taking electromagnetic Gaussian Shell-model beam as an object of research, the change in its spectral degree of polarization is studied by numerical analysis. Based on the numerical results, the mechanism that governs the change in polarization of an electromagnetic beam on propagation is discussed. The results show that the beam spreading of two components of an electromagnetic beam results in the change in polarization of beam directly, and the beam spreading is determined by source parameters and atmospheric turbulence. The difference between beam spreading of two components induced by coherence leads to the change in polarization in free space. The change in degree of polarization is influenced by source parameters and turbulence on propagation in atmosphere. The result is similar to that in free space over relatively short distance, which is mainly governed by source parameters. With the enhancement of turbulence over a sufficiently long distance, the change in polarization in atmosphere is different from that in free space.

Depolarization of light in magnetooptical crystals under magnetomechanical resonance conditions

Taking into account multiple reflections inside a magnetooptical crystal under conditions of magnetomechanical resonance, we determine the change of polarization degree of light passing through the sample using methods of Muller matrices and of the Stokes vector.

Correlation between in-plane strain and optical polarization of Si-doped AlGaN epitaxial layers as a function of Al content and Si concentration

We have investigated the relationship between in-plane strain and optical polarization in AlGaN epitaxial layers as a function of Al content and of Si concentration. Al content and in-plane strain were measured by reciprocal space mapping using a simple relationship from the tensor of elastic moduli. The change of valence band energy separation based on the measured in-plane strain was in good agreement with the change of polarization degree as a function of Al content. The dependence of polarization degree on Si concentration was also explained by the change of in-plane strain, and polarization switching occurred around the Al content and strain as calculated by the k · p approach with the cubic approximation.

Assessment of magneto-optic Faraday effect-based drift on interferometric single-mode fiber optic gyroscope (IFOG) as a function of variable degree of polarization (DOP)

In this study, a novel interferometric fiber optic gyroscope (IFOG), which has a different depolarizer structure, is designed in TUBITAK UME (National Metrology Institute of Turkey) to experimentally and relatively evaluate the effect of the degree of polarization on the Faraday effect-based drift of the light waves injected into both arms of a Sagnac interferometer. In order to observe whether or not any change occurs in the Faraday-based drift, depending on the variations in degree of polarization (DOP), a triple structure-depolarizer IFOG possessing adjustable DOP is firstly designed and prototyped. The minimum DOP achieved with triple structure-depolarizers is typically 0.15% for both clockwise (CW) and counterclockwise (CCW) light waves at both arms of the Sagnac interferometer. The experimental evaluations about the drift are given for DOP changes extending from 78.00% to 0.15% together with two main and different theoretical approaches in the literature. According to the experimental evaluations given herein, it is experimentally proved that the Faraday-based drift does not change depending on DOP values of both CW and CCW light waves injected into the single-mode (SM) sensing coil and it is impossible to state a concept of a depolarized IFOG by considering the polarization state at the entrance arms of the SM sensing coil.

厄米-高斯电磁光束在杨氏干涉实验中的偏振度变化

厄米-高斯电磁光束在杨氏干涉实验中的偏振度变化

Turbulence-induced changes in degree of polarization, degree of coherence and spectrum of partially coherent electromagnetic beams

Based on a recently formulated unified theory of coherence and polarization, a method is described to study turbulence-induced changes in the polarization, the coherence and the spectrum of partially coherent electromagnetic beams on propagation. The electromagnetic Gaussian Schell-model beam is taken as a typical example of partially coherent electromagnetic beams, and the closed-form expressions for the degree of polarization, the degree of coherence and the spectrum of electromagnetic Gaussian Schell-model beams propagating through atmospheric turbulence are derived in the quadratic approximation of Rytov's phase structure function. Some interesting results are obtained, which are illustrated by numerical examples and are explained in physics.

Changes in the spectral degree of polarization of stochastic spatially and spectrally partially coherent electromagnetic pulses in dispersive media

Based on the theory of coherence and polarization of stochastic electromagnetic pulses, the analytical expression for the spectral degree of polarization of stochastic spatially and spectrally partially coherent electromagnetic pulses propagating in dispersive media is derived. Numerical calculations are performed to show the dependence of spectral degree of polarization on the spatial correlation length, temporal coherence length, pulse duration, pulse frequency, and medium dispersion. The results are interpreted physically.

Birefringence Measurements of Photonic Liquid Crystal Fibre by Use of the Depolarization Method

In the paper we present the results of investigating the effective birefringence of prototype photonic crystal fibre, partially infiltrated with “1550” liquid crystal mixture. We use the modified Mueller matrix method with an additional depolarization matrix to calculate degree of polarization changes of the light propagating in the liquid-crystal infiltrated microstructured optical fibres. We conducted the research for red and infrared semiconductor laser diodes. The research may lead to construction of temperature controlled depolarizer.

Stokes parameters and degree of polarization of nonparaxial stochastic electromagnetic beams

On the basis of angular spectrum representation and the stationary-phase method, far-field expressions for generalized Stokes parameters of nonparaxial stochastic electromagnetic beams are derived, which permits us to study the changes in the ordinary Stokes parameters upon propagation, and the changes in the spectral degree of polarization of partially polarized nonparaxial stochastic electromagnetic beams. It is shown that the spectral degree of polarization changes across the section on beam propagation.

Depolarization of light in microstructured fibers filled with liquid crystals

AbstractIn the paper we analyze microstructured optical fibers filled with typical nematic liquid crystals, i.e., 5CB and 6CHBT under influence of external electric field or temperature. We use the modified Mueller matrix method with an additional depolarization matrix to calculate degree of polarization changes of the light propagating in the liquid-crystal infiltrated microstructured optical fibers. Preliminary experimental results of light depolarization measurements during propagation in these microstructured fibers are also presented.