Optical Circular Polarization Research Articles

Optical evaluation of internal damage to human hair based on second near-infrared window polarization microscopy.

Hair beauty treatments glorify human life. As a side effect, there is a risk of deteriorating the health of the hair. Optically polarized microscopy has been used for many decades to evaluate hair conditions owing to its ease of use and low operating costs. However, the low biopermeability of light hinders the observation of detailed structures inside hair. The aim of this study is to establish an evaluation technique of internal damages in a hair by utilizing a near-infrared (NIR) light with a wavelength of 1000-1600 nm, called "second NIR window". We built a laser scanning transmission microscope system with an indium gallium arsenide detector, a 1064 nm laser source, and optical circular polarization to visualize the anisotropy characterization of keratin fibres in hair. Samples of Asian black hair before and after bleaching, after permanent-waving, after lithium bromide (LiBr) treatment, and after heating was observed. Some parameters reflecting intra-hair damage were quantitatively compared with the parameters in digitally recorded images with analytical developments. The light transmittance of black hair was dramatically improved by utilizing the second NIR window. Numerical analysis of circular polarization in hair quantified the internal damage in chemically or thermally treated hair and found two different types of damage. The present method enabled quantitative evaluation of the condition changes in the cortex; for example, a decrease in circular polarizability by LiBr treatment and restoration by replacing the LiBr solution with water. In addition, black speckles were observed after the heat treatment. Longer heating and wetting times increased the appearance probability and size of the speckles. According to quantitative analyses, the emergence of black spots was independent of polarizability changes, indicating that they were not pores. Circular polarization microscopy based on near-infrared optics in the second NIR window provides an effective evaluation method for quantifying intra-hair damage caused by cosmetic treatments. The present method provides noninvasive, easy, and inexpensive hair evaluation and has potential as a gold standard in hair care research/medical fields.

High-resolution spectroscopy of the intermediate polar EX Hydrae. II. The inner disk radius

is one of the best studied, but still enigmatic intermediate polars. We present phase-resolved blue VLT/UVES high-resolution ($ 16.000$) spectra of taken in January 2004. Our analysis involves a unique decomposition of the Balmer line profiles into the spin-modulated line wings that represent streaming motions in the magnetosphere and the orbital-phase modulated line core that represents the accretion disk. Spectral analysis and tomography show that the division line between the two is solidly located at $ rad defining the inner edge of the accretion disk at $r_ in $\,cm or $ (WD radii). This large central hole allows an unimpeded view of the tall accretion curtain at the lower pole with a shock height up to that is required by X-ray and optical observations. Our results contradict models that advocate a small magnetosphere and a small inner disk hole. Equating $r_ in $ with the magnetospheric radius in the orbital plane allows us to derive a magnetic moment of the WD of $ and a surface field strength $B_1\! Given a polar field strength $B_ p optical circular polarization is not expected. With an accretion rate $ M\!=\! the accretion torque is $G_ acc The magnetostatic torque is of similar magnitude, suggesting that is not far from being synchronized. We measured the orbital radial-velocity amplitude of the WD, $K_1=58.7 and found a spin-dependent velocity modulation as well. The former is in perfect agreement with the mean velocity amplitude obtained by other researchers, confirming the published component masses $M_1 and $M_2 msun.

Optical circular polarization of blazar S4 0954+65 during high linear polarized states

Optical circular polarization observations can directly test the particle composition in black hole jets. We report the first observations of the BL Lac-type object S4 0954+65 in high linear polarized states. While no circular polarization was detected, we were able to place upper limits of < 0.5% at 99.7% confidence. Using a simple model and our novel optical circular polarization observations, we can constrain the allowed parameter space for the magnetic field strength and composition of the emitting particles. Our results favor models that require magnetic field strengths of only a few Gauss and models in which the jet composition is dominated by electron-positron pairs. We discuss our findings in the context of typical magnetic field strength requirements for blazar emission models.

Boulder distribution, circular polarization, and optical maturity: A survey of example lunar polar terrains for future landing sites

Boulder occurrence at the southern polar regions of the Moon was analysed to see connections between optical, radio, spectral, and topography-related roughness datasets. On optical images, boulders tend to concentrate in groups (the groups are 0.9–1.8 km diameter and cover about 9% of the surveyed regions; while boulders inside these groups have up to 6 boulder/100 m2, e.g., 60,000 boulder/km2 (54% of areal coverage), while outside these groups around 7 boulder/km2 (0.06% areal coverage). The correlation between optical boulder density and Circular Polarization Ratio: CPR (0.26) and Optical Maturity: OMAT (0.38) values are weak, while CPR and OMAT distribution patterns are elevated around fresh craters with elevated boulder density. While fresh craters with boulders coincide with elevated CPR values, but in some cases, elevated CPR is without elevated surface boulder occurrence, indicating shallow subsurface boulders. A good correlation between CPR values and surface roughness (0.68) indicates boulder exhumation at topographic differences of craters. OMAT and CPR values of fresh craters (with elevated and sharp rims) show elevated values above the adjacent regions. OMAT is elevated up to 1–3 times the crater diameter, while CPR is elevated at a smaller area than OMAT values. The CPR might partly come from boulders that could not be ejected as far as smaller regolith grains indicated by OMAT-related freshness. Boulder occurrence at fresh impact craters indicates a thickness of the loose top porous regolith layer of 6–11 m, not far from those gained by another author (5–18 m) for terrain areas.

Optical circular polarization induced by axionlike particles in blazars

We propose that the interaction between the axionlike particles (ALPs) and photons can be a possible origin of optical circular polarization (CP) in blazars. Given that there is no definite detection of optical CP at $\sim0.1\%$ level, a rough limit on ALP-photon coupling can be obtained, specifically $g_{a\gamma}\cdot B_\mathrm{T0}\lesssim7.9\times10^{-12}~\mathrm{G\cdot GeV}^{-1}$ for $m_{a}\lesssim 10^{-13}~\mathrm{eV}$, depending on the magnetic field configuration of the blazar jet. Obviously, for the blazar models with a larger magnetic field strength, such as hadronic radiation models, this constraint could be more stringent. We also perform a dedicated analysis of the tentative observations of optical CP in two blazars, namely 3C 66A and OJ 287, and we find that these observations could be explained by the ALP-photon mixing with $g_{a\gamma} \sim 10^{-11}~\mathrm{GeV}^{-1}$. As an outlook, our analysis can be improved by further research on the radiation models of blazars and high-precision joint measurements of optical CP and linear polarization.

Linear and Circular Polarimetry of the Optically Bright Relativistic Tidal Disruption Event AT 2022cmc

Tidal disruption events (TDEs) occur when a star orbiting a massive black hole is sufficiently close to being tidally ripped apart by the black hole. AT 2022cmc is the first relativistic TDE that was observed (and discovered) as an optically bright and fast transient, showing signatures of nonthermal radiation induced by a jet that is oriented toward the Earth. In this work, we present optical linear and circular polarization measurements, observed with the Very Large Telescope/FORS2 in the R band (which corresponds to the blue/UV part of the spectrum in the rest frame), ∼7.2 and ∼12.2 rest-frame days after the first detection, respectively, when the light curve of the transient had settled in a bright blue plateau. Both linear and circular polarizations are consistent with zero, p lin = 0.14% ± 0.73%, and p cir = −0.30% ± 0.53%. This is the highest signal-to-noise ratio linear polarization measurement obtained for a relativistic TDE and the first circular polarimetry for such a transient. The nondetection of the linear and circular polarizations is consistent with the scenario of AT 2022cmc being a TDE where the thermal component (disk+outflows) is viewed pole-on, assuming an axially symmetric geometry. The presence and effect of a jet and/or external shocks are, however, difficult to disentangle.

Constraints on magnetic field and particle content in blazar jets through optical circular polarization

ABSTRACT Polarization offers a unique view in the physical processes of astrophysical jets. We report on optical circular polarization (CP) observations of two famous blazars, namely 3C 279 and PKS 1510−089, at high linearly polarized states. This is the first time PKS 1510−089 is observed in optical CP. While only upper limits can be extracted from our observing campaign, the non-detection of optical CP allows us to provide meaningful constraints on their magnetic field strength and jet composition. We find that high-energy emission models requiring high magnetic field strength and a low positron fraction can be excluded.

Broadband chiral silicon photonic circuits based on fork-type inversely tapered nanowire waveguides.

Optical spin or circular polarization provides a new degree of freedom to control light-matter interaction in the fundamentals and applications of light. To broaden the bandwidth of chiral (spin-controlled) coupling in photonic integrated circuits, we propose fork-type inversely tapered nanowire waveguides to compensate for the out-of-step phase evolution of adiabatic coupling between ${{\rm TE}_0}$ and ${{\rm TM}_0}$ (${{\rm TE}_1}$) modes excited from the $x$- and $y$-polarization components of spin polarized light in free space, respectively. We design and simulate two kinds of devices based on air and ${{\rm Si}_3}{{\rm N}_4}$ up-claddings to show the feasibility of broadening the bandwidth of chiral silicon photonic circuits by using fork-type inverse tapers. Numerical results show that the bandwidth can approach 70 nm under high directionality of above 0.90. This broadband chiral coupling via the new phase synchronizing technique with fork-type inverse tapers may pave the way to develop on-chip spin photonics or polarization-based photonic integrated devices.

Cross-polarization induced crosstalk impact analysis on the BER performance of 100-Gbps CPDM 8-QAM CO-FOC system over unrepeatered 100-km SSMF link

This proposed article presents a comprehensive investigation of a coherent optical (CO) circular-polarization division multiplexed (CPDM) 8-quadrature amplitude modulation (8-QAM) for the fiber optic communication (FOC) system over an unrepeatered 100 km SSMF link to find the impact of cross-polarization (XPol) induced crosstalk by arbitrary misalignment of the states of polarization (SOPs) on the bit error rate (BER) performance. A thorough study with a mathematical analysis is demonstrated, considering the Maxwellian distribution for the mean misalignment angle, to acquire the output expression of the signal to cross-talk plus noise ratio (SCNR) and average BER for a CO homodyne CPDM 8-QAM receiver. Numerical simulations exhibit that BER performance deteriorates due to the XPol effects. Results show that the system experiences a power penalty for the mean misalignment angle to acquire a definite BER of 10−9 for a fixed local oscillator power. Besides, a detailed comparison between the existing PDM-QPSK and our proposed CPDM 8-QAM model is elucidated where our proposed model is significantly better than the existing model in terms of SCNR-BER performances, spectral-efficiency (SE) and capacity of the system as well.

High‐Performance Circularly Polarized Light‐Sensing Near‐Infrared Organic Phototransistors for Optoelectronic Cryptographic Primitives

AbstractChiral photonics has emerged as a key technology for future optoelectronics, such as quantum information and encryption, by making use of photonic waves from enantiomeric structures. An inevitable challenge for realizing such chiral optoelectronics is the development of near‐infrared circularly polarized (NIR CP) light‐sensing photodetectors that convert optical power and circular polarization direction into distinguishable electrical signals. Herein, a simple and promising strategy for high‐performance NIR CP light‐sensing organic phototransistors (NIR CPL‐OPTRs) applicable to highly secure optoelectronic encryption is proposed. By directly assembling a standalone cholesteric liquid‐crystal network film in a thin‐film NIR CPL‐OPTR, remarkable responsivity and distinguishability are achieved. The synergetic effect of amplification of the photocurrent signal by the applied electric field and improved light absorption by the reduced reflection in the multilayered structure leads to high responsivity. As a proof‐of‐concept, the chiral phototransistor arrays are demonstrated as a physically unclonable function device and exhibit enhanced cryptographic characteristics.

Effects of environment variation of glycerol smoke particles on the persistence of linear and circular polarization.

Environment variation is an important factor affecting the polarization propagation through the smoke. In this paper, we investigate the effects of the relative humidity and optical thickness on polarization transmission character, as well as the persistence of the linear and circular polarization of artificial smoke particles with simulations and experiments. We develop an environment modulation system to control the environment variation and measure the transmission degree of polarization (DOP). Correspondingly, by building the relation between the smoke filling time and optical thickness, as well as between the relative humidity and particle size and refractive index, we utilize the Monte Carlo program to track photon scattering process through varying the radius, refractive index and optical thickness. Both the simulation and the experimental results show that the DOP of both linear and circular polarizations are constantly decreased with the increasing of the optical thickness. However, at the same optical thickness, both the linear and circular polarization's persistence benefits with the increasing of the relative humidity. Moreover, circular polarization persists better than linear polarization in the larger optical thickness and the higher humidity environment under the wavelength of 532 nm. These works can verify the persistence of circular polarization and broaden the application range of polarized lights in a variable artificial smoke environment.

Low optical polarization at the core of the optically thin jet of M87

ABSTRACT We study the optical linear and circular polarization in the optically thin regime of the core and jet of M87. Observations were acquired two days before the Event Horizon Telescope (EHT) campaign in early 2017 April. A high degree (∼20 per cent) of linear polarization (Plin) is detected in the bright jet knots resolved at $\sim 10\,\mathrm{ to}\,23\, \rm {arcsec}$ ($0.8{-}1.8\, \rm {kpc}$) from the centre, whereas the nucleus and inner jet show Plin ≲ 5 per cent. The position angle of the linear polarization shifts by ∼90° from each knot to the adjacent ones, with the core angle perpendicular to the first knot. The nucleus was in a low level of activity (Plin ∼ 2–3 per cent), and no emission was detected from HST-1. No circular polarization was detected either in the nucleus or the jet above a 3 σ level of Pcirc ≤ 1.5 per cent, discarding the conversion of Plin into Pcirc. A disordered magnetic field configuration or a mix of unresolved knots polarized along axes with different orientations could explain the low Plin. The latter implies a smaller size of the core knots, in line with current interferometric observations. Polarimetry with EHT can probe this scenario in the future. A steep increase of both Plin and Pcirc with increasing frequency is expected for the optically thin domain, above the turnover point. This work describes the methodology to recover the four Stokes parameters using a λ/4 waveplate polarimeter.

Optical Chiral Induced Spin Selectivity XMCD Study.

The chiral induced spin selectivity (CISS) effect in which selective transport of electron spins through helical chiral molecules occurs, has attracted a lot of attention in recent years. This effect was used to magnetize ferromagnetic (FM) samples by utilizing adsorbed chiral molecules. The electron transfer through the molecules was generated optically or electrically. In the optical configuration, circularly polarized light induced efficient magnetization by spin torque transfer (STT), using a hybrid of quantum dots (QDs) and chiral molecule self-assembled monolayer (SAM). Here, we use X-ray magnetic chiral dichroism (XMCD) spectroscopy in order to probe the optically induced magnetization on thin FM films. The results show differences in the FM magnetization depending on the optical circular polarization, matching previous non-local Hall probe measurements.

Discovery of spin-modulated circular polarization from IGR J17014−4306, the remnant of Nova Scorpii 1437 AD

Polarimetry of IGR J1401−4306, a long-period (12.7 h) eclipsing intermediate polar and remnant of Nova Scorpii 1437 AD, reveals periodic variations of optical circular polarization, confirming the system as the longest-period eclipsing intermediate polar known. This makes it an interesting system from an evolutionary perspective. The circular polarization is interpreted as optical cyclotron emission from an accreting magnetic white dwarf primary. Based on the polarimetry, we propose that it is a disc-fed intermediate polar. The detection of predominantly negative circular polarization is consistent with only one of the magnetic poles dominating the polarized emission, while the other is mostly obscured by the accretion disc.

Polarized Emission from Gamma-Ray Burst Jets

I review how polarization signals have been discussed in the research field of Gamma-Ray Bursts (GRBs). I mainly discuss two subjects in which polarimetry enables us to study the nature of relativistic jets. (1) Jet breaks: Gamma-ray bursts are produced in ultra-relativistic jets. Due to the relativistic beaming effect, the emission can be modeled in a spherical model at early times. However, as the jet gradually slows down, we begin to see the edge of the jet together with polarized signals at some point. (2) Optical flash: later time afterglow is known to be insensitive to the properties of the original ejecta from the GRB central engine. However, a short-lived, reverse shock emission would enable us to study the nature of of GRB jets. I also briefly discuss the recent detection of optical circular polarization in GRB afterglow.

Complementary Y-shaped chiral metamaterial with giant optical activity and circular dichroism simultaneously for terahertz waves

A complementary Y-shaped chiral metamaterial (CYCMM) is proposed for the realization of giant optical activity and circular polarization with strong circular dichroism (CD) simultaneously for terahertz (THz) waves. It is demonstrated that the proposed CYCMM can achieve 90° linear polarization rotation around 2.13 THz and a giant CD effect at 2.38 THz through full-wave simulations. The mechanism of the giant CD effect and optical activity is illustrated by simulated surface current distribution. Due to strong optical activity and the CD effect, the proposed CYCMM is useful for the development of integrated terahertz spectroscopic and imaging devices.

A recent change in the optical and γ-ray polarization of the Crab nebula and pulsar

We report on observations of the polarization of optical and {\gamma}-ray photons from the Crab nebula and pulsar system using the Galway Astronomical Stokes Polarimeter (GASP), the Hubble Space Telescope/Advanced Camera for Surveys (HST/ACS) and the International Gamma-Ray Astrophysics Laboratory satellite (Integral). These, when combined with other optical polarization observations, suggest that the polarized optical emission and {\gamma}-ray polarization changes in a similar manner. A change in the optical polarization angle has been observed by this work, from 109.5 \pm 0.7\deg in 2005 to 85.3 \pm 1.4 \deg in 2012. On the other hand, the {\gamma}-ray polarization angle changed from 115 \pm 11 \deg in 2003-2007 to 80 \pm 12 \deg in 2012-2014. Strong flaring activities have been detected in the Crab nebula over the past few years by the high energy {\gamma}-ray missions Agile and Fermi, and magnetic reconnection processes have been suggested to explain these observations. The change in the polarized optical and {\gamma}-ray emission of the Crab nebula/pulsar as observed, for the first time, by GASP and Integral may indicate that reconnection is possibly at work in the Crab nebula. We also report, for the first time, a non-zero measure of the optical circular polarization from the Crab pulsar+knot system.

Modeling and simulation of polarization errors in Sagnac fiber optic current sensor

Sagnac fiber optic current sensor (S-FOCS) is a kind of optical interferometer based on Sagnac structure, optical polarization states of sensing light wave in Sagnac fiber optic current sensor are limited. However, several factors induce optical polarization error, and non-ideal polarized light waves cause the interference signal crosstalk in sensor, including polarizer, quarter-wave retarder, splice angular, birefringence and so on. With these errors, linearly polarized light wave in PM fiber and circularly polarized light wave in sensing fiber become elliptically polarized light wave, then, nonreciprocal phase shift induced by magnetic field of the current is interrupted by wrong polarization state. To clarify characteristics of optical polarization error in fiber optic current sensor, we analyze the evolution process of random optical polarization state, linear optical polarization state and circular optical polarization state in Sagnac fiber optic current sensor by using Poincare sphere, then, build optical polarization error models by using Jones matrix. Based on models of polarization state in Sagnac fiber optic current sensor, we investigate the influence of several main error factors on optical polarization error characteristics theoretically, including extinction ratio in polarizer, phase delay in quarter-wave retarder, splice angular between quarter-wave retarder and polarization maintaining fiber. Finally, we simulate and quantify nonreciprocal phase shift to be detected in fiber optic current sensor related with optical polarization errors. In the end, we demonstrate S-FOCS in test. The results show that transfer matrix errors are induced by inaccurate polarization properties during polarization state conversion, then, the stability and accuracy of the S-FOCS are affected, and it is important to control the polarization properties at each step of the polarization state conversion precisely.

Optical circular polarization in quasars

We present new optical circular polarization measurements with typical uncertainties < 0.1% for a sample of 21 quasars. All but two objects have null circular polarization. We use this result to constrain the polarization due to photon-pseudoscalar mixing along the line of sight. We detect significant (> 3 sigma) circular polarization in two blazars with high linear polarization and discuss the implications of this result for quasar physics. In particular, the recorded polarization degrees may be indicative of magnetic fields as strong as 1 kG or a significant contribution of inverse Compton scattering to the optical continuum.

Zeeman tomography of magnetic white dwarfs

The magnetic fields of the accreting white dwarfs (WDs) in magnetic cataclysmic variables (mCVs) determine the accretion geometries, the emission properties, and the secular evolution of these objects. We determine the structure of the surface magnetic fields of the WDs primaries in magnetic CVs using Zeeman tomography. Our study is based on orbital-phase resolved optical flux and circular polarization spectra of the polars EF Eri, BL Hyi, and CP Tuc obtained with FORS1 at the ESO VLT. An evolutionary algorithm is used to synthesize best fits to these spectra from an extensive database of pre-computed Zeeman spectra. The general approach has been described in previous papers of this series. The results achieved with simple geometries as centered or offset dipoles are not satisfactory. Significantly improved fits are obtained for multipole expansions that are truncated at degree l(max)=3 or 5 and include all tesseral and sectoral components with 0<=m<=l. The most frequent field strengths of 13, 18, and 10MG for EF Eri, BL Hyi, CP Tuc and the ranges of field strength covered are similar for the dipole and multipole models, but only the latter provide access to accreting matter at the right locations on the WD. The results suggest that the field geometries of the WDs in short-period mCVs are quite complex with strong contributions from multipoles higher than the dipole in spite of a typical age of the WDs in CVs in excess of 1 Gyr. It is feasible to derive the surface field structure of an accreting WD from phase-resolved low-state circular spectropolarimetry of sufficiently high signal-to-noise ratio. The fact that independent information is available on the strength and direction of the field in the accretion spot from high-state observations helps in unraveling the global field structure.