Polarization Anisotropy Research Articles

Effect of electronic nature of substituent position on the linear and nonlinear optical and physical properties of some quinoline derivatives. A computational study

In this work, we have performed a computational study of the linear and nonlinear optical, physical and chemical properties of some quinoline derivatives within density functional theory (DFT) using PBE/6-311G++(d, p) theoretical level . The molecular geometries have been analysed using the appropriate B3LYP/6-311++G(d,p) computational level. Linear optical such as the polarizability <α> and the polarizability anisotropy <Δα> and non-linear optical properties, namely the first hyperpolarizability βtot , electric field-induced second harmonic generation (EFISHG) β// have been calculated using COSMO model in DMSO solvent. The relation between electronic gap energy and the first hyperpolarisability β was also evaluated. Global conceptual reactivity descriptors and molecular electron potential analyses were performed, indicating that the electron density distribution along the studied structure makes it have a polar character, which leads to good non-linear optical properties. QTAIM analysis demonstrates that the presence of weak interaction in the 2-formyl-quinoline dimer may be the origin of the increases of the nonlinear optical properties. UV–Vis spectrum analysis indicates that 6-amino-2-formyl-quinoline may be used as a semiconductor organic material, which is considered a promising green energy organic material for possible future use as an alternative organic photovoltaic material in solar cells and other nonlinear optical applications.

Extending the FDTD GVADE method nonlinear polarization vector to include anisotropy.

In this paper the finite-difference time-domain general vector auxiliary differential equation method [Opt. Express14, 8305 (2006)10.1364/OE.14.008305], nonlinear polarization vector, the nonlinear electric dipole moment per unit volume, is extended to include anisotropy, in nonlinear isotropic media at optical frequencies. The theory is presented for extending the numerical method in 3D Cartesian coordinates, and then example simulation results are presented for two isotropic media. First, the simplified 2D transverse magnetic case is revisited for the fused silica example introduced in the 2006 paper, including the anisotropic part of the nonlinear polarization vector in the simulation; the simulation results including the anisotropic part of the polarization vector were compared with the purely isotropic polarization vector simulation results. Second, a simplified 2D transverse magnetic example was simulated in carbon disulfide, with its strong molecular re-orientation-induced polarization anisotropy.

Design and Synthesis of Two Sn-Centered Mixed Halide Crystals with Enhanced Birefringence.

Enhancing the optical anisotropy of compounds has attracted significant interest in the optical field. Sn-centered crystals, containing stereochemically active lone pairs, are widely regarded as promising birefringent materials. In this study, we successfully synthesized two novel Sn-centered mixed halide birefringent crystals, NaSn2F4Br and Na2Sn2F5I. These crystals, composed of Sn-centered mixed halide polyhedra, exhibit more than a 2-fold increase in birefringence from NaSn2F4Br to Na2Sn2F5I. Among all known Sn-centered halides, the Na2Sn2F5I crystal demonstrates the highest birefringence (Δn = 0.408@546 nm). Theoretical calculations indicate that the exceptional optical properties of Na2Sn2F5I arise from the large polarization anisotropy induced by the Sn-I bond within the Sn-centered polyhedra. These findings provide valuable insights for the development of high-quality birefringent crystal materials in Sn-centered mixed halide systems.

The Role of Polarizability in Isoelectronic Ions: The Case of Pseudohalides.

Specific ion effects are widespread and have been studied for over a century, yet they remain poorly understood. Terms like "kosmotropes" and "chaotropes" are convenient rules of thumb but the frequent reversal of the Hofmeister series implies their limitations. Polarizability is often used to classify ions, with kosmotropes considered low in polarizability and chaotropes high. However, for polyatomic ions, this framework becomes misleading. The anisotropic nature of polarizability in polyatomic ions plays a decisive role in shaping their behavior. In this work, we study pseudohalides (KOCN, KSCN, and KSeCN) aqueous solutions to explore these effects. We evaluate properties of these anions through experimental measurements of conductivity, density, viscosity, infrared spectra, and polarizability. Our results demonstrate that, even for linear isoelectronic polyatomic ions, the anisotropy of polarizability governs their hydration behavior.

Two-Dimensional Magnetic Exciton Polariton with Strongly Coupled Atomic and Photonic Anisotropies.

Anisotropy is a fundamental property of both material and photonic systems. The interplay between material and photonic anisotropies, however, has hardly been explored due to the vastly different length scales. Here we demonstrate exciton polaritons in a 2D antiferromagnet, CrSBr, coupled with an anisotropic photonic crystal cavity, where the spin, atomic, and photonic anisotropies are strongly correlated. Atomic anisotropy led to exceptionally strong coupling between anisotropic exciton and optical modes, which are stable against excitation densities a few orders of magnitude higher than polaritons in isotropic materials. The resulting polaritons feature anisotropic polarizations determined by the interplay of not only the anisotropies but also the dissipations and coupling of both exciton and photon modes, tunable by tens of degrees via many parameters. The work provides insights of excitons in CrSBr and demonstrates a prototype where atomic- and photonic-scale orders strongly couple, giving rise to unconventional properties in quantum materials and photonic devices.

Giant Ultrabroadband Bulk Photovoltaic Effect Engendered by Two-Photon Absorption in α-In2Se3 for Chiral Terahertz Wave Generation.

Bulk photovoltaic effect (BPVE) can break the Shockley-Queisser limit by leveraging the inherent asymmetry of crystal lattice without a junction. However, this effect is mainly confined to UV-vis spectrum due to the wide-bandgap nature of traditional ferroelectric materials, thereby limiting the exploration of the infrared light-driven efficient BPVE. Herein, giant two-photon absorption (TPA) driven BPVE is uncovered from visible to infrared in ferroelectric α-In2Se3 utilizing wavelength-tunable terahertz (THz) emission spectroscopy. Remarkably, α-In2Se3 exhibits exceptional THz emission efficiency in the infrared region, surpassing renowned THz emitters like p-InAs and achieving an efficiency approximately eight times the magnitude of standard ZnTe. The power exponent-type pump fluence and quadruple polarization features reveal a unique TPA-driven BPVE, corroborated by a fourth-order nonlinear oscillator model. Notably, TPA-engendered BPVE efficiency approaches 68% of that observed in the single-photon absorption process. Moreover, the TPA responses display clear polarization anisotropy, with considerably relative phase and amplitude driven by synchronous in-plane and out-of-plane polarization, leading to chiral THz waves with high efficiency, tunable orientation, and controllable ellipticity. This work highlights the advantages of TPA-induced BPVE responses in narrow-bandgap ferroelectric semiconductors, enhancing spectral utilization efficiency, aiding high-performance devices based on BPVE, and guiding chiral THz wave design.

Computational studies of the optical properties of 4-cyano-4-hexyl biphenyl using a combination of DFT and molecular dynamics simulation

ABSTRACT In this study, we predicted the optical properties of the liquid crystal 4-cyano-4-hexylbiphenyl (6CB) by employing a combination of Density Functional Theory (DFT) and Molecular Dynamics simulation. We obtained the polarisability and anisotropy of polarisability of the liquid crystal through DFT calculations by employing a variety of basis sets and implementing them in Gaussian 09. The density and order parameters of the liquid crystal at different temperatures were determined from Molecular Dynamics simulations and implemented in NAMD. The extraordinary and ordinary refractive indices were then predicted from the Vuks equation. The effect of long-range corrected DFT calculations on polarisability and anisotropy of polarisability was also explored with the functionals LC-BLYP and CAM-B3LYP. We found that at static frequencies, the basis set B3LYP 6–31 G (2d,p) produced excellent results in determining refractive indices with maximum errors of 4.1% and 3% in the nematic and isotropic phases, respectively. However, the B3LYP functional was unsuitable for determining refractive indices at a wavelength of 589 nm. In contrast, the long-range functional CAM-B3LYP combined with the basis set 6–31 G (2d,p) resulted in maximum errors of 3.7% in the nematic phase and 2.5% in the isotropic phase when determining refractive indices at 589 nm.

Polarizability of exohedral lithium derivatives of fullerene C60

We have calculated mean polarizabilities of lithium–C60 exohedral derivatives and found that the depression of polarizability is typical for them as for covalent adducts of C60. This phenomenon implies the decreasing growth of the mean polarizability with the increasing number of the addends, attached to the fullerene core. Our previously developed model of the additive scheme, accounting this depression, works for lithium compounds only qualitatively, as the C60…Li contacts are non-covalent. Anisotropy of polarizability of C60Li n correlates with Li…Li distances in the molecules and almost independent of their symmetry.

Designing a Heteroleptic Tetrahedral Group with an Ultrahigh Polarizability Anisotropy by Optimizing the Bonding Electrons Activity and Their Distribution

Designing a Heteroleptic Tetrahedral Group with an Ultrahigh Polarizability Anisotropy by Optimizing the Bonding Electrons Activity and Their Distribution

Piezoelectric Property Amplification in 0.46PNN-0.23PIN-0.31PT Ceramics via Optimized Low-Temperature Sintering and Defect Chemistry

The sintering temperature of piezoelectric ceramics plays a pivotal role in their cost and efficacy within the realm of multilayer actuator applications. While being conducive to piezoelectric capabilities of ceramics, the increase in sintering temperature entails higher fabrication costs. In contrast, a lower sintering temperature can reduce costs, but the performance of the actuator may be compromised. To address these issues, the Li-Sc co-doped 0.46PNN-0.23PIN-0.31PT ceramics were produced in the present work. At a relatively low sintering temperature (950 °C), the synergy of multiple ferroelectric phases and defect polarization could be achieved, thereby augmenting the electromechanical properties of the material. At an optimal doping ratio of 0.6 mol% for both Li and Sc, the ceramics demonstrated superior performance metrics, including d33 = 1000 pC/N, d33* = 1050 pm/V, kp = 0.53, and εr = 8001. Applying the Rietveld refinement and Rayleigh analysis, it was established that the incorporation of Li is essential in the formation of a rhombohedral phase-dominated morphotropic phase boundary (MPB), which decreases polarization anisotropy amidst the coexisting phases, facilitating polarization rotation and significantly enhancing the piezoelectric properties of ceramics. The nanodomains within the material were detected through SS-PFM and PFM testing. Notably, Sc3+-induced defects disrupted the extended ferroelectric domains, fostering the emergence of nanodomains with higher activity, which in turn enabled to markedly improve the electromechanical performance of the ceramics even at the lower sintering temperature. This investigation not only provides a viable strategy for curtailing the manufacturing costs of multilayer actuators but also opens up new prospects for the low-temperature fabrication of piezoelectric materials and their applications.

Lone Pair‐Electrons‐ and Aromaticity‐Dependent Optical Nonlinearity Responses of (ƞ5‐Cp)Fe(η5‐P5), Fe(ƞ5‐P5)2, and [Fe(η4‐P4)2]2− Ferrocene Analogs

AbstractDriven by their unique electronic structures and geometries, quantum chemistry and wavefunction analyses are conducted to explore the effects of aromaticity and lone pair‐electrons on the linear and nonlinear optical (NLO) responses of four ferrocene analogs. Aromaticity indicators reveal that the stability of (η5‐Cp)Fe(η5‐P5) and [Fe(η4‐P4)2]2− is primarily due to their σ‐aromaticity. In contrast, Fe(η5‐P5)2 exhibits π‐aromaticity, characterized by significant diamagnetic ring currents and electron delocalization facilitated by both out‐of‐plane and in‐plane π‐conjugation, distinguishing it from planar systems like C18. Fe(η5‐P5)2, with the largest surface area (234.60 Å2), displays the strongest van der Waals (vdW) attraction in its central region (−0.95 kcal/mol), surpassing that of [Fe(η4‐P4)2]2−. Further analysis of second‐order NLO responses underscores the critical role of cyclo P4 and cyclo P5 lone pair‐electrons in enhancing polarization anisotropy and optical nonlinearity. Fe(η5‐P5)2 achieves maximum NLO dispersion at γxxxx(λ = 588 nm), showing a 12‐fold increase over Fe(ƞ5‐Cp)2 in the static regime. Real‐space function analyses, hyperpolarizability density, and tensor maps further support these findings, emphasizing the potential of cyclo P5 lone pair‐electrons for the development of high‐performance NLO materials.

Quantum chemical study of new oxadiazoles as efficient optical and nonlinear optical and photovoltaic materials under gas, PCM and COSMO solvent effects

The science of organic optical and nonlinear optical (NLO) materials has been captivating the scientific community owing to their extensive applications in optoelectronics, OLEDs, and telecommunications. This study presents the design and investigation of novel organic compounds of pyrene and 1,3,4-oxadiazole derivatives (1-oxza to 6-oxza), featuring various push–pull combinations. Quantum chemical calculations were employed to determine linear polarizabilities (α) and third-order NLO polarizabilities (γ). Notably, the largest average third-order NLO polarizability value was found to be 254.9 × 10−36 esu for the finely tuned push–pull system 6-oxza, which is ∼35 times greater than that of the prototype NLO molecule of p-nitroaniline (p-NA). Among the derivatives, 1-oxza exhibits the highest linear isotropic polarizability (αiso) value of 61.59 × 10−24 esu, while 5-oxza displays the highest linear anisotropic polarizability (αaniso) value of 60.09 × 10−24 esu. A notable increase of approximately ∼1 to ∼2 times in < γ > is observed for selected compounds (1-oxza, 4-oxza, 6-oxza), indicating that the Conductor-like Screening Model (COSMO) overestimates the values compared to the polarizable continuum model (PCM) and gas phases. Solvent significantly enhances third-order NLO polarizability amplitudes depending upon solvent polarity and strength of substitution groups. We calculated the frequency-dependent third-order NLO polarizability of 6-oxza at laser wavelengths ranging from 1400 to 1970 nm. The second hyperpolarizability EFISHG process (γ(−2ω; ω, ω, 0)) was calculated at a laser wavelength of 1400 nm, and the γ-amplitude was found to be 400.1 × 10−36 esu. The remarkable hyperpolarizability response in the gas phase is corroborated by TD-DFT calculations, which reveal a larger transition dipole moment of 3.062 and a lower transition energy of 3.780 eV as origin of larger hyperpolarizability for 6-oxza. A comprehensive analysis was performed based on FMOs for designed compounds to elucidate the intramolecular charge transfer (ICT) mechanisms and observed a notable reduction in energy band gap 4.89 eV for 6-oxza, which is responsible for enhanced NLO response. Additionally, DOS maps revealed the quantitative contributions of HOMOs and LUMOs for crucial electronic states related to the efficient ICT process. Additionally, we analyzed the photovoltaic properties and found that 6-oxza has the highest dye regeneration and the lowest open-circuit voltages of 1.89 eV and 2.22 eV, respectively. Our designed model compounds can put real-time such compounds under spotlight of scientific interests which seeks more efficient optical and NLO properties.

Achieving Phase-Matching in Nonlinear Optical Materials CsM2In2S6 (M = Cd/In, Hg/In) by the Incorporation of Unprecedented Trigonal Planar MS3 Motifs.

The trigonal planar unit possesses significant hyperpolarizability and polarizability anisotropy, which makes it useful for optimizing nonlinear optical (NLO) materials, however, chalcogenide with this unit has seldom been reported. In this work, a novel approach is introduced by integrating the unprecedented trigonal planar MS3 (M=Cd/In, Hg/In) motifs into the nearly optically isotropic tetrahedral units, resulting in two novel chalcogenides CsM2In2S6 (M=Cd/In, 1; Hg/In, 2). Notably, structures 1 and 2 feature nearly planar triangular units at the center, encircled by three trimers, further interconnecting each other to create 3D frameworks. Importantly, phases 1 and 2 display phase-matching (PM) capabilities, primarily attributed to incorporating trigonal planar MS3 units that additionally enhance polarizability anisotropy. Furthermore, compounds 1 and 2 demonstrate moderate second-harmonic generation (SHG) signals (0.70 and 0.84 × AgGaS2@1.7µm). This study pioneers an efficient strategy for the design of infrared NLO crystals with PM capabilities.

Electric-field-induced polarization anisotropy of interband photoluminescence in GaAs

Near-infrared photoluminescence spectra of the n-doped gallium arsenide epilayer under heating lateral electric field conditions are studied. The field dependences of hot electron and hole temperatures are determined from photoluminescence spectra and from solving the power balance equation using current–voltage characteristic. Polarization anisotropy of the photoluminescence radiation arising due to the anisotropy of hot electron distribution function and angular dependence of the interband optical matrix element in the momentum space is observed and investigated. The obtained experimental data are in satisfactory agreement with the theoretical model.

Enhanced Control of Single-Molecule Emission Frequency and Spectral Diffusion.

The Stark effect provides a powerful method to shift the spectra of molecules, atoms, and electronic transitions in general, becoming one of the simplest and most straightforward ways to tune the frequency of quantum emitters by means of a static electric field. At the same time, in order to reduce the emitter sensitivity to charge noise, inversion symmetric systems are typically designed, providing a stable emission frequency with a quadratic-only dependence on the applied field. However, such nonlinear behavior might be reflected in correlations between the tuning ability and unwanted spectral fluctuations. Here, we provide experimental evidence of this trend using molecular quantum emitters in the solid state cooled down to liquid helium temperatures. We finally combine the electric field generated by electrodes, which is parallel to the molecule's induced dipole, with optically excite long-lived charge states acting in the perpendicular direction. Based on the anisotropy of the molecule's polarizability, our two-dimensional control of the local electric field allows us not only to tune the emitter's frequency but also to sensibly suppress the spectral instabilities associated with field fluctuations.

Strong Anisotropy and Giant Photothermoelectricity of 1D Alloy Nb3Se12I-Based Photodetector for Ultrabroadband Light-Detection and Encryption Imaging Application.

Securing high-capacity and safe communication holds great potential for ushering in the new era of digital society. In this study, a wide-band photodetector based on the quasi-1D niobium selenide compounds (Nb3Se12I), showing up photothermoelectric (PTE) dominated multiple synergistic effects with high responsivity across a wide wavelength range from deep-ultraviolet (254nm) to terahertz (0.30 THz), providing an efficient strategy for high-capacity optical processing is introduced. Combined with the polarized-sensitive property of the Nb3Se12I photodetector, an encrypted imaging technology using polarization-resolved PTE current is developed. This technology is capable of transforming encrypted messages into polarization states, which can be restored through a specially designed decryption algorithm, greatly enhancing the concealment and security of the information transmission process. Overall, the Nb3Se12I-based detector manifests in terms of high responsivity (283.2 A W-1 to 520nm, 1632.4 A W-1 to 980nm, and 1868.1 A W-1 for short-wave infrared light of 2200nm), suitable response speed of 43 µs for 0.30 THz wave and polarization anisotropy ratio of 1.83. The versatile abilities of photodetector in the realm of ultrabroadband polarized detection and encryption imaging may advance the use of anisotropic thermoelectric materials in high-capacity and secure information communication applications.

Carbonatoperoxovanadates with Strong Second-Harmonic Generation: Insights from First-Principles Calculations on Anisotropic Structures and Optical Parameters.

Carbonatoperoxovanadates are considered as promising functional materials in optoelectronic devices due to their excellent optical properties, particularly strong second-harmonic generation (SHG) response. However, the relationship between their geometric structures and optical properties remains unclear. Herein, the structural, electronic, and optical properties of carbonatoperoxovanadates A3VO(O2)2CO3 (A=K, Rb, and Cs) were investigated using first-principles calculation. Results suggest that high-density and parallel arrangement of nonlinear optical active [VO(O2)2CO3] units are conducive to generating large SHG response in A3[V(O2)2O]CO3. Optical anisotropy was observed. Birefringence values for A3[V(O2)2O]CO3 were comparable to those of commonly used infrared nonlinear optical materials. Specifically, results of tiny optical characteristics (local dipole moments, HUMO-LUMO gap, polarizability anisotropy, and hyperpolarizability) indicate that asymmetry [VO(O2)2CO3] is an excellent nonlinear optical active functional unit, owing to the synergistic effect between its non-centrosymmetric nonlinear optical elements. This study elucidates the structure-property relationship of carbonatoperoxovanadates, offering valuable insights for designing novel high-performance SHG materials.

Measuring the circular polarization of gravitational waves with pulsar timing arrays

The circular polarization of the stochastic gravitational wave background (SGWB) is a key observable for characterizing the origin of the signal detected by Pulsar Timing Array (PTA) collaborations. Both the astrophysical and the cosmological SGWB can have a sizeable amount of circular polarization, due to Poisson fluctuations in the source properties for the former, and to parity violating processes in the early universe for the latter. Its measurement is challenging since PTA are blind to the circular polarization monopole, forcing us to turn to anisotropies for detection. We study the sensitivity of current and future PTA datasets to circular polarization anisotropies, focusing on realistic modelling of intrinsic and kinematic anisotropies for astrophysical and cosmological scenarios respectively. Our results indicate that the expected level of circular polarization for the astrophysical SGWB should be within the reach of near future datasets, while for cosmological SGWB circular polarization is a viable target for more advanced SKA-type experiments. Published by the American Physical Society 2024

Implications of scattering for CMB foreground emission modelling

Context. The extreme precision and accuracy of forthcoming observations of the cosmic microwave background (CMB) temperature and polarisation anisotropies, aiming to detect the tiny signatures of primordial gravitational waves or of light relic particles beyond the standard three light neutrinos, requires commensurate precision in the modelling of foreground Galactic emission that contaminates CMB observations. Aims. We evaluate the impact of second-order effects in Galactic foreground emission due to Thomson scattering off interstellar free electrons and to Rayleigh scattering off interstellar dust particles. Methods. We used existing sky survey data and models of the distribution of free electrons and dust within the Milky Way to estimate the amplitude and power spectra of the emission originating from radiation scattered either by free electrons or by dust grains at CMB frequencies. Results. Both processes generate corrections to the total emission that are small compared to direct emission and are small enough not to pose problems for current-generation observations. Conclusions. However, B modes generated by Thomson scattering of incoming radiation off interstellar free electrons at CMB frequencies are within an order of magnitude compared to the sensitivity of the most advanced forthcoming CMB telescopes, and might require more precise evaluation in the future.

Strong Non-Reciprocal Chiroptical Properties in Thin Films of Chiral Alkylthio-Decorated 1,4-Phenylene/Thiophene Dyes.

In the context of chiral π-conjugated materials, the use of enantiopure alkylthio appendages represents a valid alternative to conventional alkoxy groups: sulphur atom is bigger and more electron-rich than oxygen, thus allowing for higher polarizability, greater flexibility, larger bulkiness and lower structural anisotropy. In light of these considerations, here we report two new chiral alkylthio-decorated 1,4-phenylene/thiophene dyes, obtained by simple synthetic strategies involving Pd-catalyzed cross-coupling protocols, looking for strong non-reciprocal chiroptical features in thin films. In particular, for the chiral alkylthio-decorated 1,4-phenylene-bis(thiophenylpropynone) (Thio-PTPO) dye, which proved to be the most promising for our purpose, a detailed investigation in thin films was carried out, involving optical and chiroptical spectroscopies in absorption and emission, as well as optical microscopy techniques.