High Degree Of Circular Polarization Research Articles

Lasing Polarization Characteristics in 1.55- $\mu \text{m}$ Spin-Injected VCSELs

Circular polarization characteristics in vertical-cavity surface-emitting lasers (VCSELs) with InAlGaAs quantum wells injected by spin-polarized electrons were investigated. A degree of circular polarization of 10% was obtained in a reduced birefringence VCSEL at a lasing wavelength of 1544 nm at room temperature under optical pumping of spin-polarized electrons. Strong birefringence originally introduced to stabilize the lasing polarization was confirmed to be undesirable for a high degree of circular polarization in spin-injected VCSELs. A spin-flip rate equation analysis fairly reproduced the experimental results and supported our conclusions.

Modeling of light interaction with exoskeletons of scarab beetles.

Some beetles of the family Scarabaeidae produce brilliant metallic-looking colors by their pure dielectric exoskeletons and reflect light with a high degree of circular polarization. In the present work, we discuss three models for simultaneously describing scattering, spectral, and polarization characteristics of scarab beetles. Each model consists of three slabs: an outer thin epicuticle, an exocuticle having a helicoidal structure, and a thick uniform slightly absorbing endocuticle. Scattering features are defined by rough interfaces of the epicuticle and/or nonuniformities of the exocuticle. As an example, a slightly modified model of an earlier study of Chrysina aurata is considered. The modification is aimed at including surface and volume nonuniformities that affect not only spectral and polarization properties but also scattering. Another example of using the proposed models is based on the analysis of image formations of a specimen of the species Mimela chinensis, which was studied in a polarizing microscope at different magnifications. The results show that the proposed models can be applied for explanation of light interaction with the exoskeletons of scarab beetles.

Controlling the Polarization State of Light with Plasmonic Metal Oxide Metasurface.

Conventional plasmonic materials, namely, noble metals, hamper the realization of practical plasmonic devices due to their intrinsic limitations, such as lack of capabilities to tune in real-time their optical properties, failure to assimilate with CMOS standards, and severe degradation at increased temperatures. Transparent conducting oxide (TCO) is a promising alternative plasmonic material throughout the near- and mid-infrared wavelengths. In addition to compatibility with established silicon-based fabrication procedures, TCOs provide great flexibility in the design and optimization of plasmonic devices because their intrinsic optical properties can be tailored and dynamically tuned. In this work, we experimentally demonstrate metal oxide metasurfaces operating as quarter-waveplates (QWPs) over a broad near-infrared (NIR) range from 1.75 to 2.5 μm. We employ zinc oxide highly doped with gallium (Ga:ZnO) as the plasmonic constituent material of the metasurfaces and fabricate arrays of orthogonal nanorod pairs. Our Ga:ZnO metasurfaces provide a high degree of circular polarization across a broad range of two distinct optical bands in the NIR. Flexible broad-band tunability of the QWP metasurfaces is achieved by the significant shifts of their optical bands and without any degradation in their performance after a post-annealing process up to 450 °C.

NEAR-INFRARED CIRCULAR AND LINEAR POLARIMETRY OF MONOCEROS R2

ABSTRACT We have conducted simultaneous JHK s -band imaging circular and linear polarimetry of the Monoceros R2 (Mon R2) cluster. We present results from deep and wide near-infrared linear polarimetry of the Mon R2 region. Prominent and extended polarized nebulosities over the Mon R2 field are revisited, and an infrared reflection nebula associated with the Mon R2 cluster and two local reflection nebulae, vdB 67 and vdB 69, is detected. We also present results from deep imaging circular polarimetry in the same region. For the first time, the observations show relatively high degrees of circular polarization (CP) in Mon R2, with as much as approximately 10% in the K s band. The maximum CP extent of a ring-like nebula around the Mon R2 cluster is approximately 0.60 pc, while that of a western nebula, around vdB 67, is approximately 0.24 pc. The extended size of the CP is larger than those seen in the Orion region around IRc2, while the maximum degree of CP of ∼10% is smaller than those of ∼17% seen in the Orion region. Nonetheless, both the CP size and degree of this region are among the largest in our infrared CP survey of star-forming regions. We have also investigated the time variability of the degree of the polarization of several infrared sources and found possible variations in three sources.

Helicity-selective phase-matching and quasi-phase matching of circularly polarized high-order harmonics: towards chiral attosecond pulses

Phase matching of circularly polarized high-order harmonics driven by counter-rotating bi-chromatic lasers was recently predicted theoretically and demonstrated experimentally. In that work, phase matching was analyzed by assuming that the total energy, spin angular momentum and linear momentum of the photons participating in the process are conserved. Here we propose a new perspective on phase matching of circularly polarized high harmonics. We derive an extended phase matching condition by requiring a new propagation matching condition between the classical vectorial bi-chromatic laser pump and harmonics fields. This allows us to include the influence of the laser pulse envelopes on phase matching. We find that the helicity dependent phase matching facilitates generation of high harmonics beams with a high degree of chirality. Indeed, we present an experimentally measured chiral spectrum that can support a train of attosecond pulses with a high degree of circular polarization. Moreover, while the degree of circularity of the most intense pulse approaches unity, all other pulses exhibit reduced circularity. This feature suggests the possibility of using a train of attosecond pulses as an isolated attosecond probe for chiral-sensitive experiments.

Spectrum splitting for fast polarization switching ofundulator radiation.

A simple scheme to quickly switch the polarity of circular radiation is proposed, which is based on spectrum splitting of undulator radiation. In this scheme, two helical undulators with opposite helicities are placed tandem in one straight section, both of which are divided into several segments. The optical phases between segments are tuned so that light waves from one of the two undulators are out of phase, while those from the other are in phase. Then the radiation spectrum of the former is split and the intensity at the fundamental photon energy vanishes. As a consequence, the monochromated photon beam at the fundamental energy is circularly polarized with the helicity specified by the in-phase undulator, which can be quickly flipped by tuning the optical phase. Numerical calculations carried out to demonstrate the feasibility of the proposed scheme show that a relatively high degree of circular polarization is expected if the angular acceptance of the beamline is not too large.

Plasmon-mediated circularly polarized luminescence of GaAs in a scanning tunneling microscope

The electroluminescence from p-type GaAs(110) in a scanning tunneling microscope has been investigated at 6 K. Unexpectedly, high degrees of circular polarization have often been observed with ferromagnetic Ni tips and also with paramagnetic W and Ag tips. The data are interpreted in terms of two distinct excitation mechanisms. Electron injection generates intense luminescence with low polarization. Plasmon-mediated generation of electron-hole pairs leads to less intense emission, which, however, is highly polarized for many tips.

Chiral nanostructures producing near circular polarization

Optical properties of chiral nanostructured films made of Al1−xInxN using a new growth mechanism — curved-lattice epitaxial growth — are reported. Using this technique, chiral films with right-and left-handed nanospirals were produced. The chiral properties of the films, originating mainly from an internal anisotropy and to a lesser extent from the external helical shape of the nanospirals, give rise to selective reflection of circular polarization which makes them useful as narrow-band near-circular polarization reflectors. The chiral nanostructured films reflect light with high degree of circular polarization in the ultraviolet part of the spectrum with left- and right-handedness depending on the handedness of the nanostructures in the films.

Polarization control of an X-ray free-electron laser with a diamond phase retarder.

A diamond phase retarder was applied to control the polarization states of a hard X-ray free-electron laser (XFEL) in the photon energy range 5-20 keV. The horizontal polarization of the XFEL beam generated from the planar undulators of the SPring-8 Angstrom Compact Free-Electron Laser (SACLA) was converted into vertical or circular polarization of either helicity by adjusting the angular offset of the diamond crystal from the exact Bragg condition. Using a 1.5 mm-thick crystal, a high degree of circular polarization, 97%, was obtained for 11.56 keV monochromatic X-rays, whereas the degree of vertical polarization was 67%, both of which agreed with the estimations including the energy bandwidth of the Si 111 beamline monochromator.

Obtaining high degree of circular polarization at x-ray free electron lasers via a reverse undulator taper

Baseline design of a typical X-ray FEL undulator assumes a planar configuration which results in a linear polarization of the FEL radiation. However, many experiments at X-ray FEL user facilities would profit from using a circularly polarized radiation. As a cheap upgrade one can consider an installation of a short helical (or cross-planar) afterburner, but then one should have an efficient method to suppress powerful linearly polarized background from the main undulator. In this paper we propose a new method for such a suppression: an application of the reverse taper in the main undulator. We discover that in a certain range of the taper strength, the density modulation (bunching) at saturation is practically the same as in the case of non-tapered undulator while the power of linearly polarized radiation is suppressed by orders of magnitude. Then strongly modulated electron beam radiates at full power in the afterburner. Considering SASE3 undulator of the European XFEL as a practical example, we demonstrate that soft X-ray radiation pulses with peak power in excess of 100 GW and an ultimately high degree of circular polarization can be produced. The proposed method is rather universal, i.e. it can be used at SASE FELs and seeded (self-seeded) FELs, with any wavelength of interest, in a wide range of electron beam parameters, and with any repetition rate. It can be used at different X-ray FEL facilities, in particular at LCLS after installation of the helical afterburner in the near future.

NEAR-INFRARED CIRCULAR POLARIZATION IMAGES OF NGC 6334-V

We present results from deep imaging linear and circular polarimetry of the massive star-forming region NGC 6334- V. These observations show high degrees of circular polarization (CP), as much as 22 % in the Ks band, in the infrared nebula associated with the outflow. The CP has an asymmetric positive/negative pattern and is very extended (~80" or 0.65 pc). Both the high CP and its extended size are larger than those seen in the Orion CP region. Three-dimensional Monte Carlo light-scattering models are used to show that the high CP may be produced by scattering from the infrared nebula followed by dichroic extinction by an optically thick foreground cloud containing aligned dust grains. Our results show not only the magnetic field orientation of around young stellar objects but also the structure of circumstellar matter such as outflow regions and their parent molecular cloud along the line of sight. The detection of the large and extended CP in this source and the Orion nebula may imply the CP origin of the biological homochirality on Earth.

Curvature radiation for intermediate pitch angles

The radiation by a charged particle in a non-uniform magnetic field is analyzed when the particle’s trajectory forms a curved spiral. The case when the pitch angle is less than the inverse of the Lorentz factor is considered. It is shown that the spectral angular distribution of the radiation consists of two parts that are substantially separated in frequency. One of these components represents curvature radiation, which is primarily linearly polarized, while the other possesses the typical properties of undulatory radiation, with a high degree of circular polarization. The derived formulas can be used to analyze the radiation of pulsars.

A Broadband, Background-Free Quarter-Wave Plate Based on Plasmonic Metasurfaces

We demonstrate optically thin quarter-wave plates built with metasurfaces that generate high-quality circularly polarized light over a broad wavelength range for arbitrary orientation of the incident linear polarization. The metasurface consists of an array of plasmonic antennas with spatially varying phase and polarization responses. Experimentally demonstrated quarter-wave plates generate light with a high degree of circular polarization (>0.97) from λ = 5 to 12 μm, representing a major advance in performance compared to previously reported plasmonics-based wave plates.

Magnetoresistive switching and highly polarized electroluminescence from semimagnetic semiconductor bicrystals Zn1−xMnxTe

The Zn1−xMnxTe bicrystals grown by the high-pressure Bridgman method exhibit magnetic-field-sensitive current-voltage characteristics. The threshold voltage of avalanche breakdown decreases by 40% as the magnetic field increases from 0 to 14 T. In the postbreakdown regime, the Zn1−xMnxTe bicrystals emit an intense red and green electroluminescence. Under magnetic field, the green emission exhibits a high degree of circular polarization which reaches 0.95 and 0.78 at 1.8 K and 4.2 K, respectively. The relation between the photon energy of the green emission and the threshold voltage has been studied.

Room temperature circularly polarized lasing in an optically spin injected vertical-cavity surface-emitting laser with (110) GaAs quantum wells

We fabricated a (110)-oriented vertical-cavity surface-emitting laser (VCSEL) with GaAs/AlGaAs quantum wells (QWs) and characterized the lasing properties of the VCSEL under optical spin injection. We demonstrated circularly polarized lasing at a high degree of circular polarization of 0.96 for our VCSEL at room temperature that originated from a long electron spin relaxation time of 0.7 ns in the (110) GaAs QWs despite a really small initial electron spin polarization of 0.04, which was well reproduced by using a rate equation analysis.

Control of Electron Spin Relaxation Dynamics and Circularly Polarized Lasing in Semiconductor Lasers

We investigated spin-controlled semiconductor lasers which can emit circularly polarized coherent light by utilizing electron spin polarization and the optical selection rule. We fabricated a (110)-oriented vertical-cavity surface-emitting laser (VCSEL) with GaAs/AlGaAs quantum wells (QWs) and characterized lasing properties of the VCSEL under optical spin injection. Circularly polarized lasing with a high degree of circular polarization of 0.96 in the VCSEL was demonstrated at room temperature originating from a long electron spin relaxation time in the (110) GaAs QWs. We also demonstrated a tenfold modulation of electron spin relaxation time from 4 to 0.3 ns in the (110) GaAs QWs through the Rashba spin-orbit coupling induced by applying an external electric field at room temperature.

Polarization Bistability and Resultant Spin Rings in Semiconductor Microcavities

The transmission of a pump laser resonant with the lower polariton branch of a semiconductor microcavity is shown to be highly dependent on the degree of circular polarization of the pump. Spin dependent anisotropy of polariton-polariton interactions allows the internal polarization to be controlled by varying the pump power. The formation of spatial patterns, spin rings with a high degree of circular polarization, arising as a result of polarization bistability, is observed. A phenomenological model based on effective semiclassical equations of motion provides a good description of the experimental results. Inclusion of interactions with the incoherent exciton reservoir, which provides spin-independent blueshifts of the polariton modes, is found to be essential.

Spin polarization of the neutral exciton in a single quantum dot

While efficient nuclear polarization has earlier been reported for the charged exciton in InAs/GaAs quantum dots at zero external magnetic field, we report here on a surprisingly high degree of circular polarization, up to ≈ 60 % , for the neutral exciton emission in individual InAs/GaAs dots. This high degree of polarization is explained in terms of the appearance of an effective nuclear magnetic field which stabilizes the electron spin. The nuclear polarization is manifested in experiments as a detectable Overhauser shift. In turn, the nuclei located inside the dot are exposed to an effective electron magnetic field, the Knight field. This nuclear polarization is understood as being due to the dynamical nuclear polarization by an electron localized in the QD. The high degree of polarization for the neutral exciton is also suggested to be due to separate in-time capture of electrons and holes into the QD.

Circular polarization—Another difference between quasars and BL Lac objects?

Analysis of VLBI data obtained on the VLBA reveals an absence of BL Lac objects with high degrees of circular polarization (>0.4%) detected among quasars. This cannot be due to observational selection effects: such objects should have been detected if the distributions of the degree of circular polarization for BL Lac objects and quasars were the same. This observational result provides new evidence for the existence of fundamental differences in the “central engines“ of objects in these two optical classes, which lead to different physical properties of their relativistic jets, such as the composition of the jet plasma (e −−e + or e −−p); the energy spectra of the particles; the magnitude, geometry and degree of order of the jet magnetic field; the angular momentum of the black hole; etc.

Near-field circular polarization probed by chiral polyfluorene

We demonstrate that a high degree of circular polarization can be delivered to the near field (NF) of an aperture at the apex of hollow-pyramid probes for scanning optical microscopy. This result is achieved by analyzing the dichroic properties of an annealed thin polymer film containing a chiral polyfluorene derivative, placed in close proximity to the optical probe. We also prove that the degree of circular polarization in the probe NF does not depend in a significant way on the shape of the aperture, at variance with the far-field behavior. These results demonstrate the feasibility of nano-optics applications exploiting circularly polarized NFs.