High Degree Of Polarization Research Articles

Circular bioeconomy: Actors and dynamics of knowledge co-production in Finland

The circular bioeconomy is a highly scrutinized concept in Finland and internationally, with a high degree of polarization regarding forest utilization rates and distrust between certain actors. This offers an interesting case for an exploratory analysis of issues associated with knowledge co-production. Knowledge co-production entails the integration of different knowledge types and collaboration across multiple societal actors with potentially conflicting viewpoints and agendas. We interviewed key organizations operating at the nexus of science and policy in the processes of knowledge co-production regarding the circular bioeconomy in Finland, including representatives from ministries, universities, research institutes, innovation promoters, and interest organizations. Using qualitative content analysis, we assessed the actors' tacit knowledge and perceptions regarding 1) their role in knowledge co-production across knowledge types; 2) elements enabling knowledge co-production; and 3) tensions and needs/opportunities of knowledge co-production. To frame our data collection and analysis, we particularly draw from recent sustainability science literature on knowledge types in co-production. The findings reveal that the three main knowledge types – lay, expert, and scientific – are acknowledged by all actors, but are dealt with, to different extents, according to the roles played by different actors in the process of knowledge generation. Collaboration was reported to be largely project-oriented, enabled by funding, similar mindsets, and organizational/individual networks. Tensions included conflicting ideological positions held by various actors in the circular bioeconomy, mainly hampering the co-production of normative/target knowledge; funding-induced gaps and risks in inter-actor cooperation, mainly affecting process/system knowledge of the circular bioeconomy; and gaps and difficulties in cross-sectoral and cross-discipline engagement, mainly affecting predictive/transformative knowledge. Knowledge synthesis, policy-supporting knowledge, and transformative knowledge were perceived by several interviewees to be important avenues towards improving the sustainability potential of the Finnish forest sector.

The future is humanistic: Infusing compassion in the systems thinking world—Circles, dialogue and RoundTables as levers for individual and community emancipation

AbstractIn this age of isolation, exacerbated by an increased number of natural disasters and their associated impact, we are faced with a deepening poverty of social connections and a high degree of polarisation on multiple counts. Designed for contexts ranging from workplaces to spiritual discourse, more and more instances of intentional conversations are surfacing across the world. It is only when we are able to appreciate the view of ‘another’, that we are truly able to step beyond the boundary of the self. In this paper, we explore a practitioner's perspective on three formats of gathering that are currently practiced at the International Society for the Systems Sciences. Using social and humanistic values, we outline how these three simple yet powerful techniques embody inclusivity, with the intention of inspiring its readers to consider hosting alternate forms of meetings in academic and organisational settings, thus creating grounds for compassionate understanding.

Enhanced room-temperature spin-valley coupling in V-doped MoS2

Achieving room-temperature valley polarization in two-dimensional (2D) atomic layers (2D materials) by substitutional doping opens new avenues of applications. Here, monolayer ${\mathrm{MoS}}_{2}$, when doped with vanadium at low (0.1 atomic %) concentrations, is shown to exhibit high spin-valley coupling, and hence a high degree of valley polarization at room-temperature. The atomic layers of ${\mathrm{MoS}}_{2}$ (MS) and V-doped ${\mathrm{MoS}}_{2}$ (VMS) are grown via the chemical vapor deposition-assisted method. The formation of new energy states near the valence band is confirmed from band gap calculations and also from the density functional theory--based band structure analyses. Time-reversal symmetry broken energy shift in the equivalent valleys is predicted in VMS, and the room-temperature chirality-controlled photoluminescent (PL) excitation measurements indicate such a shift in valley exciton energies (\ensuremath{\sim}35 meV). An enhanced valley polarization in VMS (\ensuremath{\sim}42%) is observed in comparison to that in MS (12%), while in MS, the chirality-controlled excitations did not show the difference in emission energies. Spin Hall effect of light--based optical rotation measurements indicate the asymmetric absorption among the two different chiralities of the incident light, hence supporting the existence of room-temperature valley polarization. This study opens possibilities of room-temperature opto-spintronics using stable 2D materials.

Synthesis of Cesium Copper Bromide Nanorods with Strong Linearly Polarized Emission

AbstractSemiconductor nanorods have often been observed to emit polarized light. This property can be useful for emission applications such as displays, optical communications, and biological labeling. Recently, many researchers have tried to replace nanocrystals containing toxic metals, such as Cd or Pb, with alternatives that can also demonstrate polarized emission. Here a low temperature injection (LTI) method with a relatively short chain octylammonium bromide ligand precursor is used to slow down the nanorod formation reaction and the controlled anisotropic growth of Cs3Cu2Br5 nanorods is realized, producing more uniform samples of nanorods with higher aspect ratios than those previously reported. Such nanorods exhibit a very high degree of polarization (DOP) of 0.88 ± 0.04 for single rods, and a corresponding polarization anisotropy of 0.26 for the sample population, both the highest yet reported for any perovskite‐like material. Further this method can be extended to produce Cs3Cu2Cl5 nanorods as well, allowing for broad tuning of their optical properties.

Enhancement of valley polarization in CVD grown monolayer MoS2 films

The development of future valley based electronics or valleytronics requires a high degree of valley polarization (VP) in large area monolayer (1L)-MoS2. Though it is possible to synthesize 1L-MoS2 films with large area coverage, VP property of as-grown films is found to be very poor. Here, we investigate the role of physisorbed air molecules and strain on the luminescence and the VP characteristics of large area monolayer MoS2 grown on various substrates by a microcavity based chemical vapor deposition (CVD) technique. The study shows that the removal of adsorbates from sulfur vacancy (VS) sites not only suppresses the broad sub-bandgap luminescence feature that typically dominates low temperature photoluminescence (PL) spectra of these films but also significantly enhances VP. Post-growth transfer of the 1L-MoS2 film from sapphire to a SiO2/Si substrate by a polystyrene assisted process is found to be highly effective in improving the polarization characteristic (∼80%) of K-valleys through relaxation of the biaxial tensile strain and the removal of physisorbed air molecules from the VS sites. The process is also found to provide long lasting protection for MoS2 films from air. The finding, thus, creates much needed opportunity to use CVD grown large area 1L-MoS2 for realization of valleytronics of the future.

Investigation of spin rotators in CEPC at the Z-pole

PurposeLongitudinal polarization is an important design aspect of the future 100 km-scale Circular Electron Position Collider (CEPC). Spin rotators are needed in the CEPC collider rings to make the beam polarization along the longitudinal direction at the interaction points (IPs). This paper focuses on the design of spin rotators for CEPC at the Z-pole (45.6 GeV).MethodsThe design of spin rotators in the CEPC at the Z-pole is based on solenoid magnets and horizontal bending magnets sections. The coupling of transverse motion introduced by solenoids is compensated with quadrupole lenses. Adjustments have been made to the layout to implement the spin rotators into the collider rings.ResultsLongitudinal polarized beam can be achieved at the IPs with the spin rotators. High degree of polarization is attainable, while the effect of spin rotators on orbital motion is acceptable. The detailed simulation results will be presented.ConclusionA solenoid-based spin rotator configuration is designed and integrated into the CEPC collider ring lattice. According to the simulation results, the polarization requirements can be satisfied.

Optical birefringence changes in myelinated and unmyelinated nerves: A comparative study.

The measurement of birefringence variations related to nerve activity is a promising label-free technique for sensing compound neural action potentials (CNAPs). While widely applied in crustaceans, little is known about its efficiency on mammal peripheral nerves. In this work, birefringence recordings to detect CNAPs, and Stokes parameters measurements were performed in rat and lobster nerves. While single-trial detection of nerve activity in crustaceans was achieved successfully, no optical signal was detected in rats, even after extensive signal filtering and averaging. The Stokes parameters showed that a high degree of polarization of light is maintained in lobster sample, whereas an almost complete light depolarization occurs in rat nerve. Our results indicate that depolarization itself is not sufficient to explain the absence of birefringence signals in rats. We hypothesize that this absence comes from the myelin sheets, which constraint the birefringence changes to only take place at the nodes of Ranvier.

(Invited, Digital Presentation) Circularly Polarized Photoluminescence from Nanostructured Arrays of Light Emitters

Metasurfaces offer compact routes to spatial and polarization control of luminescence from nearby emitters. The most common integration strategy is to coat a patterned metamaterial or metasurface with a film of light emitting material. For example, structures such as arrays of Au nanorods coated with achiral light emitters exhibit circularly polarized photoluminescence at specific outcoupled angles. However, the degree of circular polarization in these systems is limited to relatively low values, and does not coincide with the angles with high photoluminescence intensity.This talk will discuss an alternative strategy, where the light emitters are patterned instead. We show that this structure offers several advantages: rather than averaging over the contributions of emitters in many different locations, this system exhibits highly directional photoluminescence with high degrees of circular polarization. Most importantly, the photoluminescence intensity is high at the same angles where the degree of circular polarization is high.These patterned light-emitting nanostructures are formed using direct-write electron beam lithography on semiconductor nanocrystals. This versatile method is capable of forming structures with aspect ratios greater than 2 and feature sizes as small as 30 nm, photoluminescence is retained after patterning, and the system is robust to multiple patterning steps.

Optical Detection of Long Electron Spin Transport Lengths in a Monolayer Semiconductor.

Using a spatially resolved optical pump-probe experiment, we measure the lateral transport of spin-valley polarized electrons over very long distances (tens of micrometers) in a single WSe_{2} monolayer. By locally pumping the Fermi sea of 2D electrons to a high degree of spin-valley polarization (up to 75%) using circularly polarized light, the lateral diffusion of the electron polarization can be mapped out via the photoluminescence induced by a spatially separated and linearly polarized probe laser. Up to 25% spin-valley polarization is observed at pump-probe separations up to 20 μm. Characteristic spin-valley diffusion lengths of 18±3 μm are revealed at low temperatures. The dependence on temperature, pump helicity, pump intensity, and electron density highlight the key roles played by spin relaxation time and pumping efficiency on polarized electron transport in monolayer semiconductors possessing spin-valley locking.

Image-restoration algorithm based on an underwater polarization imaging visualization model.

The polarization bidirectional reflection distribution function theory of a target is combined with microfacet theory, and the Monte Carlo method is used to establish an underwater laser active-polarization imaging model based on Mie scattering theory. The model presented herein can simulate imaging of an underwater target with a high degree of polarization, and the effects of optical thickness and target surface roughness on active underwater laser imaging results are demonstrated by the simulation image. Combined with histogram equalization and the traditional polarization differential imaging algorithm, an algorithm is presented herein that globally estimates the mutual information value between the target polarization degree and the correction factor of backscattered light polarization degree. The images received from the simulation test can be restored, and results show that the algorithm can restore the target image with a high degree of polarization to some extent. Finally, the correctness of the active underwater laser polarization imaging model and the feasibility of global estimation based on the polarization differential restoration algorithm are verified experimentally.

Study of High Polarized Nanostructure Light-Emitting Diode

In this study, we investigated the characteristic difference between the two different configurations of the three-dimensional shell–core nanorod LED. We achieve a degree of polarization of 0.545 for tip-free core–shell nanorod LED and 0.188 for tip core–shell nanorod LED by combining the three-dimensional (3D) structure LED with photonic crystal. The ability of low symmetric modes generated by photonic crystals to enhance degree of polarization has been demonstrated through simulations of photonic crystals. In addition, light confinement in GaN-based nanorod structures is induced by total internal reflection at the GaN/air interface. The combination of 3D core–shell nanorod LED and photonic crystals cannot only produce a light source with a high degree of polarization, but also a narrow divergence angle up to 56°. These 3D LEDs may pave the way for future novel optoelectronic components.

High-Luminance Microsized CH3NH3PbBr3 Single-Crystal-Based Light-Emitting Diodes via a Facile Liquid-Insulator Bridging Route.

Micro-/nanosized organic-inorganic hybrid perovskite single crystals (SCs) with appropriate thickness and high crystallinity are promising candidates for high-performance electroluminescent (EL) devices. However, their small lateral size poses a great challenge for efficient device construction and performance optimization, causing perovskite SC-based light-emitting diodes (PSC-LEDs) to demonstrate poor EL performance. Here, we develop a facile liquid-insulator bridging (LIB) strategy to fabricate high-luminance PSC-LEDs based on single-crystalline CH3NH3PbBr3 microflakes. By introducing a blade-coated poly(methyl methacrylate) (PMMA) insulating layer to effectively overcome the problems of leakage current and possible short circuits between electrodes, we achieve the reliable fabrication of PSC-LEDs. The LIB method also allows us to systematically boost the device performance through crystal growth regulation and device architecture optimization. Consequently, we realize the best CH3NH3PbBr3 microflake-based PSC-LED with an ultrahigh luminance of 136100 cd m-2 and a half-lifetime of 88.2 min at an initial luminance of ∼1100 cd m-2, which is among the highest for organic-inorganic hybrid perovskite LEDs reported to date. Moreover, we observe the strong polarized edge emission of the microflake-based PSC-LEDs with a high degree of polarization up to 0.69. Our work offers a viable approach for the development of high-performance perovskite SC-based EL devices.

Linearly polarized 2044-nm pulsed laser generation in Ho:YAG active medium

We demonstrated the efficient generation of a linearly polarized Ho:YAG laser pumped by a thulium fiber laser. Independent of the pumping power and without utilizing any dispersive optical element, the output radiation remained stable with a high degree of linear polarization. The output with 2044 nm wavelength and 0.12 nm bandwidth was measured. In the free-running generation, with respect to the incident pump power, we recorded more than 9 W of output power with 59% slope efficiency. In addition, in the pulsed generation, we obtained more than 2.2 mJ pulses with 50 ns time duration, and 44 kW peak power.

High-Power Q-Switched 1064 nm Output Light with High Polarization Degree and Efficient Depolarization Compensation

High-Power Q-Switched 1064 nm Output Light with High Polarization Degree and Efficient Depolarization Compensation

Circularly polarized radio emission from the repeating fast radio burst source FRB 20201124A

ABSTRACT The mechanism that produces fast radio burst (FRB) emission is poorly understood. Targeted monitoring of repeating FRB sources provides the opportunity to fully characterize the emission properties in a manner impossible with one-off bursts. Here, we report observations of the source of FRB 20201124A, with the Australian Square Kilometre Array Pathfinder (ASKAP) and the ultra-wideband low (UWL) receiver at the Parkes 64-m radio telescope (Murriyang). The source entered a period of emitting bright bursts during early 2021 April. We have detected 16 bursts from this source. One of the bursts detected with ASKAP is the brightest burst ever observed from a repeating FRB source with an inferred fluence of 640 ± 70 Jy ms. Of the five bursts detected with the Parkes UWL, none display any emission in the range 1.1–4 GHz. All UWL bursts are highly polarized, with their Faraday rotation measures (RMs) showing apparent variations. We obtain an average RM of −614 rad m−2 for this FRB source with a standard deviation of 16 rad m−2 in the UWL bursts. In one of the UWL bursts, we see evidence of significant circularly polarized emission with a fractional extent of 47 ± 1 per cent. Such a high degree of circular polarization has never been seen before in bursts from repeating FRB sources. We also see evidence for significant variation in the linear polarization position angle in the pulse profile of this UWL repeat burst. Models for repeat burst emission will need to account for the increasing diversity in the burst polarization properties.

Optical Dynamic Nuclear Polarization of 13C Spins in Diamond at a Low Field with Multi-Tone Microwave Irradiation.

Majority of dynamic nuclear polarization (DNP) experiments have been requiring helium cryogenics and strong magnetic fields for a high degree of nuclear polarization. In this work, we instead demonstrate an optical hyperpolarization of naturally abundant C nuclei in a diamond crystal at a low magnetic field and the room temperature. It exploits continuous laser irradiation for polarizing electronic spins of nitrogen vacancy centers and microwave irradiation for transferring the electronic polarization to C nuclear spins. We have studied the dependence of C polarization on laser and microwave powers. For the first time, a triplet structure corresponding to the N hyperfine splitting has been observed in the C polarization spectrum. By simultaneously exciting three microwave frequencies at the peaks of the triplet, we have achieved C bulk polarization of 0.113 %, leading to an enhancement of 90,000 over the thermal polarization at 17.6 mT. We believe that the multi-tone irradiation can be extended to further enhance the C polarization at a low magnetic field.

Valley polarization control in WSe2 monolayer by a single-cycle laser pulse

Abstract The valley degree of freedom in two-dimensional materials provides an opportunity to extend the functionalities of valleytronics devices. Very short valley lifetimes demand the ultrafast control of valley pseudospin. Here, we theoretically demonstrate the control of valley pseudospin in WSe2 monolayer by single-cycle linearly polarized laser pulse. We use the asymmetric electric field controlled by the carrier-envelope phase (CEP) to make the valley polarization between K and K'-point in the Brillouin zone (BZ). Time-dependent density functional theory with spin-orbit interaction reveals that no valley asymmetry and its CEP dependence is observed within the linear-optical limit. In the nonlinear-optical regime, linearly polarized pulse induces a high degree of valley polarization and this polarization is robust against the field strength. Valley polarization strongly depends and oscillates as a function of CEP. The carrier density distribution forms nodes as the laser intensity increases, our results indicate that the position of the carrier density in the BZ can be controlled by the laser intensity. From the analysis by the massive Dirac Hamiltonian model, the nodes of the carrier density can be attributed to the Landau-Zener-St\"uckelberg interference of wave packets of the electron wave function.

Two-dimensional quasi periodic structures for large-scale light out-coupling with amplitude, phase and polarization control.

Chip-scale light-atom interactions are vital for the miniaturization of atomic sensing systems, including clocks, magnetometers, gyroscopes and more. Combining as many photonic elements as possible onto a photonic chip greatly reduces size and power consumption, where the critical elements are those interfacing between the 2D circuit and the 3D vapor cell. We introduce a new design method for large scale two-dimensional converter structures, enabling out-coupling of radiation from the photonic chip into the atomic medium. These structures allow light intensity and phase spatial distribution and polarization control, without external light-manipulating elements. Large, 100 × 100 µm2 structures were designed generating low divergence optical beams with high degree of circular polarization. Simulations obtain mean circular polarization contrast of better than 30 dB.

Democracy and polarization in the National Assembly of the Republic of Korea

The median-voter hypothesis predicts convergence of party platforms across a one-dimensional political spectrum during majoritarian elections. Assuming that the convergence is reflected in legislative activity, we study the time evolution of political polarization in the National Assembly of the Republic of Korea for the past 70 years. By projecting the correlation of lawmakers onto the first principal axis, we observe a high degree of polarization from the early 1960s to the late 1980s before democratization. As predicted by the hypothesis, it showed a sharp decrease when party politics were revived in 1987. Since then, the political landscape has become more and more multi-dimensional under the action of party politics, which invalidates the assumption behind the hypothesis. For comparison, we also analyze co-sponsorship in the United States House of Representatives from 1979 to 2020, whose correlation matrix has been constantly high-dimensional throughout the observation period. Our analysis suggests a pattern of polarization evolving with democratic development, from which we can argue the power and the limitation of the median-voter hypothesis as an explanation of real politics.

Circularly Polarized Laser Emission from an Electrically Pumped Chiral Microcavity

The authors demonstrate a prototype of an electrically injected, circularly polarized near-infrared laser based on a specifically engineered chiral microcavity. Importantly, the high degree of polarization of the emitted coherent beam is determined by the chirality of the imprinted structure, which is based on an optical cavity with a gradually doped GaAs/AlAs distributed Bragg reflector. A two-step lithographic process was used to fabricate the chiral structures, in combination with electrical injectors. This device represents a key step toward utilizing chiral microcavities in real-world applications.