Polarization Dependence Research Articles

Modeling photomolecular effect using generalized boundary conditions for Maxwell equations

We recently demonstrated via experiments in hydrogels and at a single air-water interface the photomolecular effect: photons directly cleaving off water molecular clusters in the visible spectrum where bulk water has negligible absorption. To model single interface experiments, here we re-derive generalized boundary conditions for Maxwell equations by assuming a transition region of the electromagnetic fields across the interface, leading naturally to the Feibelman parameters used before to describe surface photoelectric and surface plasmon effects on metals. This generalization leads to modifications of the Fresnel coefficients and an expression for the surface absorptance that can reasonably explain trends in our single-interface experimental data on the angle and polarization dependence of the beam deflection. Our work provides further support for the existence of the photomolecular effect, suggests that surface absorption should exist in many materials, and lays a foundation for assessing the impacts of such surface absorption based on the Maxwell equations.

Demonstration of 4-quadrant analog in-memory matrix multiplication in a single modulation

Analog in-memory computing (AIMC) leverages the inherent physical characteristics of resistive memory devices to execute computational operations, notably matrix-vector multiplications (MVMs). However, executing MVMs using a single-phase reading scheme to reduce latency necessitates the simultaneous application of both positive and negative voltages across resistive memory devices. This degrades the accuracy of the computation due to the dependence of the device conductance on the voltage polarity. Here, we demonstrate the realization of a 4-quadrant MVM in a single modulation by developing analog and digital calibration procedures to mitigate the conductance polarity dependence, fully implemented on a multi-core AIMC chip based on phase-change memory. With this approach, we experimentally demonstrate accurate neural network inference and similarity search tasks using one or multiple cores of the chip, at 4 times higher MVM throughput and energy efficiency than the conventional four-phase reading scheme.

Spatial imaging of polarized deuterons at the Electron-Ion Collider

We study diffractive vector meson production at small-x in the collision of electrons and polarized deuterons e+d↑. We consider the polarization dependence of the nuclear wave function of the deuteron, which results in an azimuthal angular dependence of the produced vector meson when the deuteron is transversely polarized. The Fourier coefficients extracted from the azimuthal angular dependence of the vector meson differential cross-section exhibit notable differences between longitudinally and transversely polarized deuterons. The angular dependence of the extracted effective deuteron radius provides direct insight into the structure of the polarized deuteron wave function. Furthermore, we observe slightly increased gluon saturation effects when the deuteron is longitudinally polarized compared to the transversely polarized case. The small-x observables studied in this work will be accessible at the future Electron-Ion Collider.

Impact of polarization pulling on optimal spectrometer design for stimulated Brillouin scattering microscopy.

Brillouin spectroscopy has become an important tool for mapping the mechanical properties of biological samples. Recently, stimulated Brillouin scattering (SBS) measurements have emerged in this field as a promising technology for lower noise and higher speed measurements. However, further improvements are fundamentally limited by constraints on the optical power level that can be used in biological samples, which effectively caps the gain and signal-to-noise ratio (SNR) of SBS biological measurements. This limitation is compounded by practical limits on the optical probe power due to detector saturation thresholds. As a result, SBS-based measurements in biological samples have provided minimal improvements (in noise and imaging speed) compared with spontaneous Brillouin microscopy, despite the potential advantages of the nonlinear scattering process. Here, we consider how a SBS spectrometer can circumvent this fundamental trade-off in the low-gain regime by leveraging the polarization dependence of the SBS interaction to effectively filter the signal from the background light via the polarization pulling effect. We present an analytic model of the polarization pulling detection scheme and describe the trade-space unique to Brillouin microscopy applications. We show that an optimized receiver design could provide >25× improvement in SNR compared to a standard SBS receiver in most typical experimental conditions. We then experimentally validate this model using optical fiber as a simplified test bed. With our experimental parameters, we find that the polarization pulling scheme provides 100× higher SNR than a standard SBS receiver, enabling 100× faster measurements in the low-gain regime. Finally, we discuss the potential for this proposed spectrometer design to benefit low-gain spectroscopy applications such as Brillouin microscopy by enabling pixel dwell times as short as 10 μs.

Use of the 5P3/2→6P3/2 electric dipole forbidden transition in Rb as a non-perturbing probe of atom dynamics in an operating magneto-optical trap

Abstract Results of spectroscopy experiments using the $5P_{3/2} \to 6P_{3/2}$ electric dipole forbidden transition in cold rubidium atoms are presented. Production of this forbidden transition is detected by observing the emission of the $420 $ nm fluorescence photons that result from the decay of the $6P_{3/2} $ state into the ground state. The experiments are performed under the steady state operation conditions of a magneto-optical trap (MOT), and thus provide non-perturbing information on the atom-light system. The hyperfine structure of the $6P_{3/2}$ level is completely resolved, and the fluorescence peaks show the expected Autler-Townes (AT) splitting of the emission lines. This hyperfine structure is used to calibrate the frequency scale of all spectra recorded. A combination of this absolute frequency scale and an expression for the AT profile allows an absolute determination of the effective Rabi frequency and detuning of the MOT. The behavior of these AT doublets is studied as a function of frequency detuning and also as a function of the trapping light intensity.
The experiments also take full advantage of the strong polarization dependence of the relative intensities of the hyperfine fluorescence components.
This study results in a sensitive probe of the relative populations of the magnetic sublevel projections relative to the trapping magnetic field gradient.
An almost isotropic population distribution was found, but small deviations from isotropy could be determined with this electric dipole forbidden probe.

Tunneling Barrier Thickness Dependence of Spin Polarization of Ferromagnet in Magnetic Tunnel Junctions

Abstract For designing low-impedance magnetic tunnel junctions (MTJs), it has been found that tunneling magnetoresistance strongly correlates with the insulating barrier thickness, imposing a fundamental problem about the relationship between spin polarization of ferromagnet and the insulating barrier thickness in MTJs. Here, we investigate the influence of alumina barrier thickness on tunneling spin polarization (TSP) through a combination of theoretical calculations and experimental verification. Our simulating results reveal a significant impact of barrier thickness on TSP, exhibiting an oscillating decay of TSP with the barrier layer thinning. Experimental verification is realized on FeNi/AlO x /Al superconducting tunnel junctions to directly probe the spin polarization of FeNi ferromagnet using Zeeman-split tunneling spectroscopy technique. These findings provide valuable insights for designs of high-performance spintronic devices, particularly in applications such as magnetic random access memories, where precise control over the insulating barrier layer is crucial.

High-accuracy direction measurement and high-resolution computational spectral reconstruction based on photonic crystal array.

Portable and wearable miniaturized spectrometers play a crucial role in various fields. In this paper, we present a method for simultaneously realizing high-accuracy direction measurement and high-resolution computational spectral reconstruction based on the angle sensitivity of conventional photonic crystals (PCs), wherein an optical filter array is composed of multiple one-dimensional PCs. The high-angle sensitivity of PCs results in angle-dependent optical spectra. When these spectra with different angles are used to reconstruct the target spectra in an unknown direction and the interval between adjacent angles is sufficiently small, the accurate direction of the target can be automatically identified. Moreover, the computational spectra still have high resolution over a wide range of incidences. The computational spectra under arbitrary polarizations can also be recognized based on the polarization dependence of the PCs at an oblique incidence. Our research results are significant for engineering a new miniaturized comprehensive computational spectrometer with target-direction perception and omnidirectional spectral reconstruction abilities.

Ultra-wideband solar absorber via vertically structured GDPT metamaterials

We explore a new solar absorber via vertically structured metamaterials integrating 2D graphene, dielectric layers of silica (SiO2), aluminum oxide (Al2O3), and phase-transition vanadium dioxide (VO2) graphene, dielectric, phase transition (GDPT), achieving broadband absorption and polarization independence. Applying the finite-difference time-domain (FDTD) method, the optical performance of the absorber is analyzed under the normal incidence of a plane wave spanning wavelengths from 250 to 4000 nm. Particularly, our investigation reveals a broad bandwidth exceeding 90 % absorption, spanning 3559 nm from 250 to 3809 nm, with an impressive average absorption efficiency of over 95.9 %. Significantly, the absorber demonstrates polarization independence and insensitivity to large angles of incidence, enhancing its practical capability. We illuminate the important role of Fabry-Perot resonance in absorption by precisely tuning layer thicknesses to induce interference effects. The integration of graphene, dielectric layers, and VO2, augmented by Fabry-Perot resonance, provides a vital foundation for high-performance solar energy conversion technology. This technology has important applications in efficient and broadband solar absorbers, and these absorbers can maintain high performance under different conditions. Our goal is to solve current technological challenges and contribute to the development of next-generation solar energy conversion for various photon technologies, such as energy harvesting, electromagnetic wave capture, and photovoltaic devices.

Unveiling the Unusual Electron–Phonon Interaction and Quasi‐Particle Dynamics in type‐II Weyl Semimetal NbIrTe4

AbstractLayered ternary type‐II Weyl semimetals demonstrate promising applications in high‐performance and broadband optoelectronics, therefore it is crucial to gain insights into their photocarriers’ dynamics. In this work, the probing polarization dependence of non‐equilibrium dynamics in NbIrTe4 is investigated by using transient reflectivity spectroscopy. Following photoexcitation at 3.18 eV, the dynamical response of 1.59 eV probe pulse exhibits a strong dependence on probe polarization. The relaxation comprises two components: a rapid recovery of ≈0.6 ps attributed to the electron–phonon scattering, and an anomalous slow recovery spanning hundreds of picoseconds attributed to the photoinduced quasi‐particle. The polarization dependence of rapid relaxation time τ is indicative of the in‐plane anisotropy of electron–phonon coupling in NbIrTe4. The slow relaxation modulated by a latest reported 16 cm−1 coherent phonon also shows strong probing polarization dependence, further revealing the anisotropic nature of electron–phonon coupling and the possibility of anisotropic lattice distortion, as well as photoinduced polaron, under ultrafast photoexcitation in NbIrTe4. The dynamical anisotropy in NbIrTe4 has provided valuable guidance for the application of NbIrTe4 in polarization‐sensitive nonlinear optics or optoelectronic devices and offers insights into the unique carrier transport as well as phonon transport properties of this newly established topological material.

Observation of Circular Dichroism Induced by Electronic Chirality.

Chiral phases of matter, characterized by a definite handedness, abound in nature, ranging from the crystal structure of quartz to spiraling spin states in helical magnets. In 1T-TiSe_{2} a source of chirality has been proposed that stands apart from these classical examples as it arises from combined electronic charge and quantum orbital fluctuations. This may allow its chirality to be accessed and manipulated without imposing either structural or magnetic handedness. However, direct bulk evidence that broken inversion symmetry and chirality are intrinsic to TiSe_{2} remains elusive. Here, employing resonant elastic x-ray scattering technique, we reveal the presence of circular dichroism, i.e., polarization dependence of the resonant diffraction intensity, up to ∼40% at forbidden Bragg peaks that emerge at the charge and orbital ordering transition. The dichroism varies dramatically with incident energy and azimuthal angle. Comparison to calculated scattering intensities traces its origin to bulk chiral electronic order in TiSe_{2} and establishes resonant elastic x-ray scattering as a sensitive probe to electronic chirality.

Large Orbital Moment and Dynamical Jahn-Teller Effect of AlCl-Phthalocyanine on Cu(100).

Submonolayer amounts of chloroaluminum-phthalocyanine on Cu(100) were studied with scanning tunneling spectroscopy. The molecule can be prepared in a fourfold symmetric state whose conductance spectrum exhibits a zero-bias feature similar to a Kondo resonance. In magnetic fields, however, this resonance splits far more than expected from the spin of a single electron. Density functional theory calculations reveal a charge transfer of 1.3 electrons to the degenerate lowest unoccupied molecular orbitals. These orbitals are mixed by the orbital momentum operator L[over ^]_{z} with a large matrix element corresponding to m_{L}≈2.7. Dehydrogenation of a ligand lifts the degerenracy of the lowest unoccupied molecular orbital, reduces the splitting in magnetic fields, and induces a polarity dependence of the spectra. Using model calculations of the spin, orbital, and vibrational degrees of freedom we show that a dynamical Jahn-Teller effect reproduces the main experimental observations.

Polarization-independent and high-efficiency 2D dielectric transmission grating under Littrow incidence

In this paper, a transmission two-dimensional (2D) all-dielectric grating with cuboid arrays is proposed, which has high diffraction efficiency and good polarization independence under Littrow mounting conditions at an incident wavelength of 780 nm. The optimization results indicate that when the incident wavelength is 780 nm, the diffraction efficiency of the (−1, 0) order of transverse electric (TE) and transverse magnetic (TM) polarizations can reach 98.62% and 98.23%, respectively, with the polarization-dependent loss (PDL) of 0.017 dB. To the best of our knowledge, high-efficiency polarization-independent 2D transmission grating with a simpler and more effective structure is proposed for the first time, which demonstrates significant enhancements in bandwidth and manufacturing tolerances while maintaining high diffraction efficiency. The results suggest that the grating has great potential for applications in high-precision displacement measurements such as grating interferometers.

Optical and electrical studies on the TS defect in 4H-SiC

Abstract When annealing a 4H silicon carbide (SiC) crystal, a sequence of optically active defect centers
occurs among which the TS center is a prominent example. Here, we present low-temperature photoluminescence
analyses on the single defect level. They reveal that the three occurring spectral
signatures TS1, TS2 and TS3 originate from one single defect. Their polarization dependences expose
three different crystallographic orientations in the basal plane, which relate to the projections of
the nearest neighbor directions. Accordingly, we find a three-fold level-splitting in ensemble studies,
when applying mechanical strain. This dependency is quantitatively calibrated. A complementary
electrical measurement, deep level transient spectroscopy, reveals a charge transition level of the TS
defect at 0.6 eV above the valence band. For a future identification, this accurate characterization
of its optical and electronic properties along with their response to mechanical strain is a milestone.

Hunting for Monolayer Black Phosphorus with Photoluminescence Microscopy

Monolayer black phosphorus (BP) holds great promise for naturally hyperbolic polaritons and correlated states in rectangular moiré superlattices. However, preparing and identifying high-quality monolayer BP are challenging due to its instability and high transparency, which limits extensive studies. In this study, we developed a method for rapidly and nondestructively identifying monolayer BP and its crystal orientation simultaneously using modified photoluminescence (PL) microscopy. The optical contrast of monolayer BP has been significantly increased by at least twenty times compared to previous reports, making it visible even on a transparent substrate. The polarization dependence of optical contrast also allows for the in situ determination of crystal orientation. Our study facilitates the identification of monolayer BP, expediting more extensive research on and potential industrial applications of this material.

A dual-band polarization independent dielectric metasurface-based absorber for sensing application in the visible light regime

We present a dual-band, polarization-independent dielectric terahertz absorber exhibiting near-perfect absorption and minimal reflection at frequencies of f 1 = 419 THz and f 2 = 528 THz. Using electromagnetic theory, we modeled the structure to derive the surface electric admittance and magnetic impedance of the metasurface, elucidating the conditions required for perfect absorption in terms of inverse electric and magnetic polarizabilities. The absorber features a tunable symmetrical design, facilitating precise frequency adjustment by modifying structural parameters and ensuring polarization independence for perpendicularly incident electromagnetic waves. This scalable and versatile absorber, constructed from readily available materials, is optimally suited for applications in resource detection, imaging, sensing, and medical diagnostics, attributed to its simplicity, cost-effectiveness, and high performance.

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Asymmetric bi-level dual-core mode converter for high-efficiency and polarization-insensitive O-band fiber-chip edge coupling: breaking the critical size limitation.

Efficient coupling between optical fibers and on-chip photonic waveguides has long been a crucial issue for photonic chips used in various applications. Edge couplers (ECs) based on an inverse taper have seen widespread utilization due to their intrinsic broadband operation. However, it still remains a big challenge to realize polarization-insensitive low-loss ECs working at the O-band (1,260-1,360 nm), mainly due to the strong polarization dependence of the mode coupling/conversion and the difficulty to fabricate the taper tip with an ultra-small feature size. In this paper, a high-efficiency and polarization-insensitive O-band EC is proposed and demonstrated with great advantages that is fully compatible with the current 130-nm-node fabrication processes. By introducing an asymmetric bi-level dual-core mode converter, the fundamental mode confined in the thick core is evanescently coupled to that in the thin core, which has an expanded mode size matched well with the fiber and works well for both TE/TM-polarizations. Particularly, no bi-level junction in the propagation direction is introduced between the thick and thin waveguide sections, thereby breaking the critical limitation of ultra-small feature sizes. The calculated coupling loss is 0.44-0.56/0.48-0.61 dB across the O-band, while achieving 1-dB bandwidths exceeding 340/230 nm for the TE/TM-polarization modes. For the fabricated ECs, the peak coupling loss is ∼0.82 dB with a polarization dependent loss of ∼0.31 dB at the O-band when coupled to a fiber with a mode field diameter of 4 μm. It is expected that this coupling scheme promisingly provides a general solution even for other material platforms, e.g., lithium niobate, silicon nitride and so on.

Spin chain orientation and magneto-optical coupling in twisted NiPS3 homostructures

Magnetic two-dimensional (2D) materials have garnered significant attention due to their unique electronic, magnetic, and optical properties and their potential applications in next-generation electronic and optoelectronic devices. However, the magneto-optical effects of oligolayer antiferromagnetic materials remain inadequately understood. Here, we investigate the magnetic properties of few-layer nickel phosphorus trisulfide (NiPS3) and its twisted heterostructures, emphasizing the observation of optical phenomena at low temperatures (1.65 K). By stacking few-layer NiPS3 to fabricate twisted homostructures, we probe their magnetic characteristics using photoluminescence (PL) spectroscopy. Our results reveal that sharp exciton peaks emerge at low temperatures and that the spin chain orientation in oligolayer NiPS3 can be discerned through the polarization dependence of exciton PL intensity. Notably, fewer-layered NiPS3 exhibits a significant magneto-optical effect under an applied magnetic field, allowing the modulation of the polarization angle of its exciton PL spectrum. Additionally, the polarization-dependent Raman spectrum of NiPS3 shows substantial changes under the influence of a magnetic field. These findings underscore the potential of few-layer NiPS3 for future magneto-optical device applications.

Phonon Directionality Impacts Electron-Phonon Coupling and Polarization of the Band-Edge Emission in Two-Dimensional Metal Halide Perovskites.

Two-dimensional metal halide perovskites are highly versatile for light-driven applications due to their exceptional variety in material composition, which can be exploited for the tunability of mechanical and optoelectronic properties. The band-edge emission is defined by the structure and composition of both organic and inorganic layers, and electron-phonon coupling plays a crucial role in the recombination dynamics. However, the nature of the electron-phonon coupling and what kind of phonons are involved are still under debate. Here we investigate the emission, reflectance, and phonon response from single two-dimensional lead iodide microcrystals with angle-resolved polarized spectroscopy. We find an intricate dependence of the emission polarization with the vibrational directionality in the materials, which reveals that several bands of low-frequency phonons with nonorthogonal directionality contribute to the band-edge emission. Such complex electron-phonon coupling requires adequate models to predict the thermal broadening of the emission and provides opportunities to design polarization properties.

Multifunctionality in vanadium dioxide-integrated metamaterials for switching between dual-band perfect absorption and asymmetric transmission

In this work, we present a theoretical proposal for an actively tunable metamaterial design that integrates vanadium dioxide (VO2). This VO2-integrated design demonstrates the ability to switch between dual-band perfect absorption and asymmetric transmission (AT) functionalities in the near-infrared and mid-infrared spectral ranges. By utilizing the unique properties of VO2, our proposed device achieves broadband absorption across approximately 2.47 μm with polarization independence when VO2 is in its metallic state. Furthermore, it exhibits narrowband absorption with polarization correlation, reaching a linear dichroism value of approximately 0.704. On the other hand, when VO2 is in its insulating state, the metamaterial structure realizes AT of 0.418 for circularly polarized light. We provide physical insight into the operating mechanisms through impedance matching analysis and electric field distributions. The integration of VO2 in this dynamically tunable, multifunctional metamaterial design offers a novel approach to developing reconfigurable nanophotonic and nanosystem technologies.