Polarization-dependent Behavior Research Articles

Holographic Multi-Notch Filters Recorded with Simultaneous Double-Exposure Contact Mirror-Based Method

This study presents a novel simultaneous double-exposure contact mirror-based method for fabricating holographic multi-notch filters with dual operational central wavelengths. The proposed method leverages coupled wave theory, the geometric relationships of K-vectors, and a reflection-type recording setup, incorporating additional reflecting mirrors to guide the recording beams. To validate the approach, a holographic notch filter was fabricated using photopolymer recording materials, resulting in operational wavelengths of 531.13 nm and 633.01 nm. The measured diffraction efficiencies at these wavelengths were ηs = 52.35% and ηp = 52.45% for 531.13 nm, and ηs = 67.30% and ηp = 67.40% for 633.01 nm. The component’s performance was analyzed using s- and p-polarized spectral transmission intensities at various reconstruction angles, revealing polarization-independent characteristics under normal incidence and polarization-dependent behavior under oblique incidence. The study also explored the relationships between recording parameters, such as incident angle, wavelength, emulsion expansion, and dispersion. The findings demonstrate that the first operational central wavelength is primarily influenced by the recording wavelength, while the second is primarily determined by the incident angle, covering a range from visible light to near-infrared. This method offers significant potential for cost-effective, mass-produced filters in optoelectronic applications.

Spin-Weighted Spherical Harmonics for Polarized Light Transport

The objective of polarization rendering is to simulate the interaction of light with materials exhibiting polarization-dependent behavior. However, integrating polarization into rendering is challenging and increases computational costs significantly. The primary difficulty lies in efficiently modeling and computing the complex reflection phenomena associated with polarized light. Specifically, frequency-domain analysis, essential for efficient environment lighting and storage of complex light interactions, is lacking. To efficiently simulate and reproduce polarized light interactions using frequency-domain techniques, we address the challenge of maintaining continuity in polarized light transport represented by Stokes vectors within angular domains. The conventional spherical harmonics method cannot effectively handle continuity and rotation invariance for Stokes vectors. To overcome this, we develop a new method called polarized spherical harmonics (PSH) based on the spin-weighted spherical harmonics theory. Our method provides a rotation-invariant representation of Stokes vector fields. Furthermore, we introduce frequency domain formulations of polarized rendering equations and spherical convolution based on PSH. We first define spherical convolution on Stokes vector fields in the angular domain, and it also provides efficient computation of polarized light transport, nearly on an entry-wise product in the frequency domain. Our frequency domain formulation, including spherical convolution, led to the development of the first real-time polarization rendering technique under polarized environmental illumination, named precomputed polarized radiance transfer, using our polarized spherical harmonics. Results demonstrate that our method can effectively and accurately simulate and reproduce polarized light interactions in complex reflection phenomena, including polarized environmental illumination and soft shadows.

Effect of electromagnetic radiation on the electronic and thermoelectric properties of armchair edge silicene nanoribbons

We theoretically investigate the influence of electromagnetic radiation on the electronic and thermoelectric properties of armchair edge silicene nanoribbons. Specifically, we study the effects of varying the polarization (s or p) and incident angle (0, 30, 45, 60, and 90°) of radiation on the band structure, transmission function, density of states, Seebeck coefficient, and electronic figure of merit (ZTe) of the nanoribbons. Our results demonstrate that the electronic properties are highly dependent on radiation conditions due to their influence on electron transport. We find that the transmission function and density of states exhibit distinct polarization-dependent behaviors that highlight the role of the radiation's electric field orientation. Importantly, the ZTe shows significant modulation with the incident angle for both polarizations, achieving optimized values up to 0.18. These findings provide insights into controlling the electronic and thermoelectric properties of silicene nanoribbons using electromagnetic radiation. Our work underscores opportunities for developing silicene-based nanophotonic devices with enhanced performance through all-optical means. The demonstrated tunability via irradiation paves the way for potential applications such as optical switches, sensors, and next-generation optoelectronics using silicene nanoribbons.

Polarization dependence of intensities Raman peaks in twisted graphene bilayer

The polarization dependence of the Raman 2D peak intensity and the polarization independence of the G Raman peak intensity have already been established in single-layer and AB-stacked bilayer graphene. Nevertheless, this study has not been conducted for twisted bilayers. In this study, we investigate the polarization properties of Raman peaks in three distinct twisted bilayer graphene samples, each exhibiting unique characteristics: G peak resonance, the presence of R′ peaks, and D-like peaks, respectively. Our analysis reveals anisotropic behavior in the G peak only under resonance enhancement conditions and consistent polarization-dependent behavior in the 2D peak across all twisted bilayers. Furthermore, we observe a pronounced symmetric and asymmetric polarization dependence in the intensity of R′ and D-like peaks, respectively. These observations have been attributed to the strong coupling between the two layers resulting from the resonance between the van Hove singularities, which affects the behavior of the G peak, and to a double resonance effect that enhances the coupling between the nodal structure and the electron–phonon anisotropy in the intravalley and intervalley regions for R′ and D-like peaks, respectively. These findings contribute to the advancement of our understanding of twisted bilayer systems and offer opportunities for exploring more profound studies.

Effect of laser polarization on atomic and ionic emissions in Laser-Induced Breakdown Spectroscopy (LIBS)

Laser-Induced Breakdown Spectroscopy (LIBS) is attracting a great deal of interest in qualitative and quantitative analysis of materials. Close observation reveals that developments in the science that underpins LIBS as an analytical technique are limited to either signal enhancement strategies or newer data analysis techniques that facilitate better interpretation of raw LIBS data. Developments related to the excitation part of LIBS have been restricted to the effects of laser beam characteristics or the effect of ambient experimental conditions. The influence, if any, of the polarization state of the excitation laser has largely remained unexplored. We address this lacuna by probing the influence of different polarization states of the excitation laser on LIBS spectra of metals (copper and silver) and non-metals (polyethylene) by analyzing the polarization-dependent behavior of both atomic and ionic emission lines. Our observations open the possibility of tackling the problem of relatively faint emissions from ionic species in the plasma by appropriately manipulating the polarization state of the incident laser beam; this may lead to easy-to-implement improvement in the performance of LIBS instruments.Graphical abstract

Tunable ultrafast thermionic emission from femtosecond-laser hot spot on a metal surface by control of laser polarization and angle of incidence: A numerical investigation

Ultrafast laser induced thermionic emission from metal surfaces has several applications. Here, we investigate the role of laser polarization and angle of incidence on the ultrafast thermionic emission process from laser driven gold coated glass surface. The spatio-temporal evolution of electron and lattice temperatures are obtained using an improved three-dimensional (3D) two-temperature model (TTM) which takes into account the 3D laser pulse profile focused obliquely onto the surface. The associated thermionic emission features are described through the modified Richardson-Dushman equation, including dynamic space-charge effects and are included self-consistently in our numerical approach. We show that temperature-dependent reflectivity influences laser energy absorption. The resulting peak electron temperature on the metal surface monotonically increases with the angle of incidence for the P polarization, while for the S polarization it shows the opposite trend. We observe that thermionic emission duration shows a strong dependence on the angle of incidence and contrasting polarization dependent behavior. The duration of the thermionic current shows strong correlation to the intrinsic electron-lattice thermalization time, in a fluence regime well below the damage threshold of gold. The observations and insights have important consequences in designing ultrafast thermionic emitters using a metal based architecture.

Pyrimidine-based azo dyes: Synthesis, photophysical investigations, solvatochromism explorations and anti-bacterial activity

Azo dyes are widely recognized for their diverse applications, including colorants, sensors, and imaging agents. The unique molecular structure of pyrimidine-based azo dyes offers intriguing possibilities for tuning their optical properties through strategic modifications. The synthesis of a series of pyrimidine-based azo dyes was carried out using well-established methods, and the chemical structures were confirmed by various spectroscopic techniques. To the best of our knowledge, for the first time such type of electron-rich azo dyes with a pyrimidine-based framework were probed for their solvatochromism and fluorescent behaviors. Subsequently, their photophysical properties were investigated using UV–visible absorption and fluorescence spectroscopy. The solvatochromic effect revealed significant changes in the dyes' absorption and emission wavelengths, providing valuable information about their polarity-dependent behavior. To establish correlations between molecular structure and optical properties, a thorough analysis of the obtained data was conducted. Their emission characteristics were also analyzed to assess their suitability as fluorescent probes. Azo dyes (7-12) demonstrate a remarkable ability to efficiently convert absorbed energy into emitted light, as indicated by their high quantum yield values. Biological investigations have demonstrated significant efficacy against a wide range of bacterial strains, with their performance comparable to that of commercially available antibiotics such as Cefixime. Structure-activity & -property relationships were delineated, highlighting the impact of specific molecular modifications on the biological and photophysical behaviors of the reported dyes.

K-Space Hyperspectral Imaging by a Birefringent Common-Path Interferometer.

Fourier-plane microscopy is a powerful tool for measuring the angular optical response of a plethora of materials and photonic devices. Among them, optical microcavities feature distinctive energy-momentum dispersions, crucial for a broad range of fundamental studies and applications. However, measuring the whole momentum space (k-space) with sufficient spectral resolution using standard spectroscopic techniques is challenging, requiring long and alignment-sensitive scans. Here, we introduce a k-space hyperspectral microscope, which uses a common-path birefringent interferometer to image photoluminescent organic microcavities, obtaining an angle- and wavelength-resolved view of the samples in only one measurement. The exceptional combination of angular and spectral resolution of our technique allows us to reconstruct a three-dimensional (3D) map of the cavity dispersion in the energy-momentum space, revealing the polarization-dependent behavior of the resonant cavity modes. Furthermore, we apply our technique for the characterization of a dielectric nanodisk metasurface, evidencing the angular and spectral behavior of its anapole mode. This approach is able to provide a complete optical characterization for materials and devices with nontrivial angle-/wavelength-dependent properties, fundamental for future developments in the fields of topological photonics and optical metamaterials.

Optically imprinted polarization gratings with a twisted nematic liquid crystal as a photomask

Liquid crystal Pancharatnam–Berry phase optical elements (LCPBOEs) are becoming increasingly attractive elements to be used to enhance near-eye displays or manipulate light beams, owing to their flatness and circular polarization-dependent behavior. The optical imprinting technique that is one of the commonly used methods for fabricating LCPBOEs is considered to be the most promising technique for mass production at a low cost, but the design of the photomask must be improved. In this work, a photomask that is based on a twisted nematic liquid crystal polarization grating (TNLCPG) cell, acting as a broadband linear polarization rotator, is designed. This TNLCPG cell, with a predefined alignment profile of a polarization grating, can convert linearly polarized light into a light field with spatially varying linear polarization and exhibits broadband operation over the entire visible spectrum. The designed TNLCPG photomask is used to demonstrate a liquid crystal polarization grating (LCPG) film using a white flashlight as a writing source. A high diffraction efficiency of greater than 95% is obtained. With its simple design and fabrication, the proposed TNLC-based photomask can potentially be used in the fabrication of LCPBOEs.

Spatial and polarization-resolved exciton–photon coupling in quasi-whispering-gallery mode ZnO microrod cavity

Whisper gallery mode (WGM) resonances and the coupling of excitons and WGMs are measured from ZnO microrod cavity in the visible and ultraviolet spectral ranges. The coupling of excitons and WGMs leads to split modes which exhibit a clear spatial dependence due to the uneven field distribution of WGM on ZnO microrod surface. Polarization dependent behavior together with a blueshift of the upper polariton branch mode are observed owing to the transition polarization of different types of excitons in the ZnO microcavity. Numerical simulations are carried out using finite element method to support the experimental results. This work reveals the spatial and polarization dependent exciton–photon coupling in a ZnO microrod which implies promising applications in photonic polariton field ranging from ultraviolet lasers, high-sensitivity detectors to optoelectronic devices

Ultracompact silicon-based polarization splitter and rotator based on asymmetric directional couplers with subwavelength gratings

An ultrasmall polarization splitter and rotator (PSR) on a silicon-on-insulator (SOI) platform is proposed based on an asymmetric directional coupler (ADC) consisting of a bridged subwavelength grating (BSWG) and a strip silicon waveguide with another SWG embedded in the middle slot. The inputting TE mode is tightly confined in BSWG and directly passes through a bar port with little coupling to the adjacent waveguide because of the phase mismatch, while the phase-matching condition allows the injected TM mode to be evanescently decoupled from BSWG and simultaneously converted into the TE mode supported by a SWG slot waveguide before propagating out through the cross port. Both polarization-dependent behaviors within the proposed PSR can be readily realized and efficiently manipulated by independently controlling the attributes of the ADC waveguides, which are distinctly engineered by different SWG segments. We have verified what we believe, to the best of our knowledge, is the first combination of BSWG and a SWG slot waveguide that provides an additional degree of freedom in the design and a stronger modal hybridization due to the doubled effects from jointly used SWGs. Further, the increasing number of inserted SWGs in the present device drastically reduces the device footprint, leading to a coupling length of only 5.5 µm. From the results, the conversion loss of − 0.28 d B (polarization conversion ratio of 93.7%) has been obtained for a TM-to-TE conversion at 1.55 µm. The TM mode of the resulting PSR shows its cross talk is less than − 14.3 d B and the conversion loss is better than − 0.63 d B in a 95 nm bandwidth that has covered the entire C and L bands. The cross talk and insertion loss of the TE mode are lower than − 29 d B and − 0.42 d B , respectively, as the operating wavelength varies.

Unusual ferroelectric-dependent birefringence in 2D trilayered perovskite-type ferroelectric exploited by dimensional tailoring

<h2>Summary</h2> Ferroelectrics with switchable spontaneous polarization have taken a dominant position as the nonlinear optical candidates, of which birefringence is an essential merit to optical devices. Despite the increasing advance of hybrid perovskite ferroelectrics, it remains a great challenge to control and tune their birefringence, thus hindering their practical optical applications. Here, we present a 2D trilayered hybrid perovskite-type ferroelectric obtained by 3D-to-2D dimensional tailoring, [(CH₃)₂CH(CH₂)₂NH₃]₂(CH₃NH₃)₂Pb₃Cl₁₀, showing biaxial polarizations of ∼5 μC/cm² and a relatively wide optical band gap. The intrinsic 2D architecture results in highly anisotropic principal refractive indices, namely, the optical birefringence. Interestingly, its birefringence can be reversibly switched through ferroelectric-to-paraelectric symmetry breaking. The birefringence tuning is further established by virtue of pretransitional modulation of ferroelectricity, exhibiting unusual polarization-dependent behaviors. In our judgment, this study on the polarization-dependent birefringence of hybrid perovskite ferroelectrics will provide a new pathway toward modulating nonlinear optical properties for smart devices.

Morphological and Orientational Controls of Self-Assembly of Gold Nanorods Directed by Evaporative Microflows.

Evaporative self-assembly of noble metal nanoparticles into ordered structures holds great promise for fabricating optical and plasmonic devices by virtue of its low cost, high efficiency, and ease of operation. However, poor control of Marangoni flows is one of the challenges accounting for realizing a well-defined assembly. Herein, based on the theoretical analysis of the influence of evaporative intensity on the assembly, two simple but reliable flow-field-confinement platforms are designed to control the evaporative microflows and to work concurrently with depletion forces to enable the regulated self-assembly of gold nanorods. Orientationally ordered assemblies are realized by the designed strong unidirectional microflow in a capillary, and a device-scale assembly of monolayer membrane is obtained by the created weak convection in homemade glass cells. Morphologically diversified superstructure assemblies, such as spherulite-like, boundary-twisted, chiral spiral assemblies, and merging membranes with a π-twisted domain wall, are obtained due to the spontaneous symmetry breaking or in the presence of defects, such as surface steps and screw dislocations. Optical anisotropy and polarization-dependent behaviors of these assemblies are further revealed, implying the potential applications in plasmonic coupling devices and optoelectronic components. An understanding of the entropy-driven assembly behaviors and control of evaporative microflows to guide the self-assembly of gold nanorods provides insights into the general bottom-up approach that is helpful for constructing complex yet robust nanosuperstructures.

High-Order Resonant Peaks and Polarization Dependence of Microphotoluminescence in Whispering-Gallery Mode ZnO Microrod Cavity

High order phenomena in the visible range and with polarization dependence in the ultraviolet (UV) region of the microphotoluminescence (micro-PL) spectrum in whispering-gallery mode (WGM) ZnO microrod cavity have been thoroughly studied at room temperature. WGM ZnO microrod cavity with good crystallinity is produced by the CVD growth method, and the ZnO microrod structures are characterized by structural and optical methods. Through the micro-PL spectrum measurement of the ZnO microrod, it is found that high-order resonance peaks appeared in the visible region. The different polarization conditions can be adjusted by rotating the angles of the polarizer, and it is proved that the micro-PL spectrum has strong polarization-dependent behavior in the UV region. Our results imply broad application potentials in the study of ZnO microrod-based photonic cavity devices.

Frequency Tripling via Sum-Frequency Generation at the Nanoscale

High refractive index dielectric nanostructures can be exploited to enhance nonlinear optical processes via the strong light confinement by their resonant modes. The sensitive dependence of these modes on the geometry and material composition offers ample opportunities for tailoring the optical response of the system. Here we report sum-frequency generation (SFG) by individual AlGaAs nanocylinders, pumped by two pulsed beams at a telecommunication frequency, ω, and its duplicate, 2ω. Under such a scheme, the SFG at 3ω = ω + 2ω is degenerate with the third-harmonic generation (THG) seeded by the input at ω, thereby tripling its frequency via the second-order permittivity χ(2), rather than via χ(3) as in THG. The concurrent detection of THG and SFG enables us to determine χ(3) = 7 × 10–20 m2/V2 by comparing experiments to numerical simulations and based on the known value of χ(2). We observe a rich size- and polarization-dependent behavior that gives appeal to the studied system as a key component of miniaturized photonic devices.

Dynamical control of directional nonlinear scattering from metallic nanoantennas by three-dimensional focal polarization orientation

We demonstrate that the directionality of far-field second harmonic (SH) emission generated from individual gold nanosphere can be flexibly engineered by manipulating three-dimensional (3D) focal polarization orientation of the excitation field, which is explained by the coherent interference between SH dipolar and quadrupolar emission modes. The SH dipolar emission mode is independent of the polarization direction of the fundamental field whereas the evolution of the focal polarization orientation can dramatically modify the quadrupolar emission pattern. Therefore, the resultant SH emission pattern has a polarization-dependent behavior and side scattering almost perpendicular to the propagation direction of the incident light can be observed under a specific condition. Our findings provide a novel degree of freedom for all-optical control of directional nonlinear scattering from single nanoantenna, thereby opening new possibilities for future potential applications.

Raman spectroscopy polarization dependence analysis in two-dimensional gallium sulfide

Group-III post-transition-metal monochalcogenides like gallium sulfide (GaS) are layered semiconductors with weakly interacting adjacent layers, which allow them to be reduced to the two-dimensional nanometric thickness level by different exfoliation approaches, similar to graphene. Here, we investigate the intensity polarization dependence of the Raman modes for a different number of GaS layers and use symmetry analysis and density-functional perturbation theory to provide further information on these structures. The Raman polarization-dependent behaviors of the bulk relative modes ${\mathrm{A}}_{1g}$ and ${\mathrm{E}}_{2g}$ were found to be independent of the number of layers, being proportional to ${cos}^{2}(\ensuremath{\theta})$ for ${\mathrm{A}}_{1g}$ modes and constant for ${\mathrm{E}}_{2g}$ modes. The computational calculations for two and three layers show Raman active modes emerging at Raman shifts near the bulk Raman modes, with ${\mathrm{A}}_{1g}$ (${\mathrm{A}}_{1}^{\ensuremath{'}}$) and ${\mathrm{E}}_{g}$ (${\mathrm{E}}^{\ensuremath{'}}$) symmetries for an even (odd) number of layers, some of them being observed as ``shoulders'' in the experimental Raman spectra. These phonon modes present Raman tensors with components similar to those observed in bulk, thus explaining the same polar dependencies for different GaS thicknesses. The Raman intensity calculations were made by implementing the specific experimental geometry used here, thus resulting in good qualitative agreement. These results are fundamental for the understanding of the structural and vibrational changes when GaS is reduced to the few-layer limit, layer-number differentiation, and for further symmetry-lowering studies by strain manipulation or substrate interaction, which are routine issues in both fundamental research and device fabrication.

Anisotropy of Excitons in Two-Dimensional Perovskite Crystals.

Two-dimensional (2D) perovskites show great potential for optoelectronic applications due to their bandgap tunability, extremely large excition binding energy, and large crystal anisotropy compared with their three-dimensional counterparts. To fully explore exciton-based applications and improve their performance, it is essential to understand the exciton behavior in 2D perovskites. Here, we investigate exciton anisotropy within the crystallographic plane and cross plane of (C4H9NH3)2PbI4 2D perovskite crystals by polarization-resolved photoluminescence, reflection, and photoconductivity studies. We observe a polarization-dependent emission evolution and an enhanced self-trapped exciton emission with an oblique incident excitation from the cross plane. Furthermore, the anisotropy of excitons in (C4H9NH3)2PbI4 2D perovskite crystals is identified by polarization-resolved photoluminescence and photoconductivity measurement, and a completely opposite polarization-dependent behavior was observed for free excitons and self-trapped excitons. We attribute this different anisotropy to the existence of out-of-plane excitons and different optical selection rule for free excitons and self-trapped excitons. Our findings will shed light on designing and improving the performance of exciton-based optoelectronic devices in 2D perovskites.

3D polarization-dependent waveguide arrays in LiNbO3 crystal produced by femtosecond laser writing

Waveguide arrays are basic photonic elements in integrated optics. We propose a 3D hybrid-integrated waveguide array based on the femtosecond laser writing of lithium niobate (LiNbO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> ) crystals by engineering the layout of laser-induced tracks. The cross section of the structure is a cross-shaped geometry. The light propagation through this waveguide array shows polarization-dependent behaviors, which enables mode-coupling along either the vertical or the horizontal direction under excitation of linearly polarized light. This work opens new way to produce polarization-dependent optical devices in photonic systems by using femtosecond laser writing of LiNbO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> .

Intramolecular charge-transfer state of carotenoids siphonaxanthin and siphonein: function of non-conjugated acyl-oxy group.

We used ultrafast transient absorption spectroscopy to study excited-state dynamics of two keto-carotenoids, siphonaxanthin and siphonein. These two carotenoids differ in the presence of dodecanoyl-oxy group in siphonein, which is attached to the C19 carbon on the same side of the molecule as the conjugated keto group. We show that this dodecanoyl-oxy group, though not in conjugation, is still capable of modifying excited state properties. While spectroscopic properties of siphonein and siphonaxanthin are nearly identical in a non-polar solvent, they become markedly different in polar solvents. In a polar solvent, siphonein, having the dodecanoyl-oxy moiety, exhibits less pronounced vibrational bands in the absorption spectrum and has significantly enhanced characteristic features of an intramolecular charge-transfer (ICT) state in transient absorption spectra compared to siphonaxanthin. The presence of the dodecanoyl-oxy moiety also alters the lifetimes of the S1/ICT state. For siphonaxanthin, the lifetimes are 60, 20, and 14ps in n-hexane, acetonitrile, and methanol, whereas for siphonein these lifetimes yield 60, 11, and 10ps. Thus, we show that even a non-conjugated functional group can affect the charge-transfer character of the S1/ICT state. By comparison with fucoxanthin acyl-oxy derivatives, we show that position of the acyl-oxy group in respect to the conjugated keto group is the key feature determining whether the polarity-dependent behavior is enhanced or suppressed.