Absorption Anisotropy Research Articles

Empirical model of the total transmission of light in turbid media

The objective of this study is to develop an empirical model for the total transmission in turbid media, which will use the optical properties such as the absorption coefficient, scattering coefficient, and anisotropy factor to predict the total transmission. An empirical model based on the relationship between the total transmission and collimated transmission, integrating an error term to account for discrepancies arising from scattering and absorption effects, is introduced. Monte Carlo simulations were employed to generate data across varying optical properties. The model’s parameters were determined through fitting algorithms and further refined using Bayesian inference, ensuring independence among variables. The results demonstrate that while the total transmission can be accurately described across a range of refractive indices, the quality of the model deteriorates with increasing scattering coefficients. This empirical model offers a rapid and reasonably accurate estimation of the total transmission, with potential applications in fields requiring quick assessments of light propagation in turbid media.

How does goldene stack?

The recent synthesis of goldene, a 2D atomic monolayer of gold, has opened new avenues in exploring novel materials. However, the question of when multilayer goldene transitions into bulk gold remains unresolved. This study used density functional theory calculations to address this fundamental question. Our findings reveal that multilayer goldene retains an AA-like stacking configuration of up to six layers, with no observation of Bernal-like stacking as seen in graphene. Goldene spontaneously transitions to a bulk-like gold structure at seven layers, adopting a rhombohedral (ABC-like) stacking characteristic of bulk face-centered cubic (FCC) gold. The atomic arrangement converges entirely to the bulk gold lattice for more than ten layers. Quantum confinement significantly impacts the electronic properties, with monolayer and bulk goldene exhibiting levels with linear dispersion at the X-point of the Brillouin zone. In contrast, multilayer goldene shows levels with linear dispersions at the X- and Y-points. Monolayer goldene exhibits anisotropic optical absorption, which is absent in bulk gold. This study provides a deeper understanding of multilayer goldene's structural and electronic properties and stacked 2D materials in general.

Angle-resolved Raman scattering study of anisotropic two-dimensional tellurium nanoflakes

As an elemental crystal, anisotropic two-dimensional (2D) tellurium (Te) flakes have recently garnered significant attention due to their exceptional chemical stability, tunable bandgap, low thermal conductivity, and high carrier mobility. To further investigate the anisotropic properties of Te nanoflakes, a rapid and effective method of determining their crystal axes is essential. In this study, it is demonstrated that the intensity of the Raman-active mode in Te nanoflakes exhibits a laser-polarization-dependence, varying periodically with the polarization angle. The crystal axis in two-dimensional Te nanoflakes can be identified using angle-resolved polarized Raman spectroscopy. Specifically, the Raman intensity of the A1 mode is the highest when the incident light is polarized along the [12¯10] direction and the lowest when polarized along the [0001] direction. This identification of the crystal axis via Raman spectroscopy is further verified by transmission electron microscopy measurements. In addition, theoretical simulations reveal that anisotropic Raman scattering is closely associated with the interference effect in a multilayer stacking system, as well as anisotropic absorption and anisotropic electron–phonon coupling in Te nanoflakes. This discovery not only provides a rapid method for locating the crystal axes in Te nanoflakes but also offers new insights into the scattering phenomenon in anisotropic materials beyond Te nanoflakes.

A Gradient Disordered Cellular Porous Ti-6Al-4V Alloy Fabricated by Powder Bed Fusion with High Energy Absorption and Low Anisotropy

A Gradient Disordered Cellular Porous Ti-6Al-4V Alloy Fabricated by Powder Bed Fusion with High Energy Absorption and Low Anisotropy

Features of magnetically induced exceptional points in cholesteric liquid crystals

Abstract In this work, the photonic properties of cholesteric liquid crystals (CLCs) in an external magnetic field parallel to the helix axis are investigated for the first time in the short-wavelength band of the spectrum, where exceptional points (EPs) are found. It was shown that at EP the real parts of two of four wave numbers touch each over, and their imaginary parts intersect. Here the reflection, transmission and absorption show the same values for two eigenmodes of CLC layer. At anisotropic absorption near the EP there appear points where the magnetically induced transmittance and absorption are observed. The light localization peculiarities as well as photonic density of states (PDOS) peculiarities near these points were also investigated. Near EPs, PDOS for two eigenmodes shows significant changes, especially with different magneto-optical activity parameters.

High-Efficiency Long-Wave Infrared Quantum Well Photodetector Based on Cascaded Dielectric Metasurfaces with Almost 100% Absorption

Quantum well infrared photodetectors (QWIPs) are popular due to their following advantages: low cost, maturity of manufacturing, high uniformity, ease of wavelength adjustment, resistance to heat, and resistance to ionizing radiation. However, their low absorption efficiency due to their unique anisotropic absorption properties and ohmic loss of the metal grating severely limit their further adoption. We cleverly used cascaded dielectric metasurfaces to replace the traditional single-layer metal grating, which increased the absorption efficiency to near the upper limit of 100%. By analyzing the near-field profile of the electric field of the miniaturized device, we found that the upper grating, QWIP, and lower grating formed a high-efficiency FP cavity with a strong photon localization capability, allowing the microdevice to effectively achieve 99.3% absorption. In addition, QWIPs with cascade gratings can be incorporated into a polarimeter, allowing for the comprehensive detection of linear polarization information at a wavelength of 14 μm through rational rotations. Our proposed double-layer grating coupling method can be considered a technology that can effectively address the low-absorption problem associated with QWIPs.

Theoretical study on the prediction of optical properties and thermal stability of fullerene nanoribbons

In this work, we predicted two different configurations of fullerene nanoribbons (quasi-hexagonal phase (qHP) and quasi-tetragonal phase (qTP)) based on two-dimensional fullerenes, with widths of 1, 2, and 3 fullerene units, respectively. Based on first-principles calculations and ab-initio molecular dynamics (AIMD), the thermal stability and optical properties of six fullerene nanoribbons were predicted. AIMD studies indicate that wider qHP nanoribbons (qHPs) exhibit better thermal stability, while increased temperatures lead to greater instability. In contrast, qHP-3 shows the best thermal stability among the six structures. Then, the optical gap between the calculated and experimental quasi-hexagonal two-dimensional fullerenes is compared to illustrate the accuracy of the calculation. The absorption spectra of six fullerene nanoribbons were calculated and the anisotropy of light absorption was analyzed. Finally, the charge transfer modes of each excited state were visualized through electron-hole density plots. This work provides an essential theoretical foundation for understanding new all-carbon materials, specifically fullerenes.

Multi-scale analysis of solute transport in hydrodynamic fluid flows through a porous channel with anisotropic permeability and boundary absorption

Multi-scale analysis of solute transport in hydrodynamic fluid flows through a porous channel with anisotropic permeability and boundary absorption

Metallic Ca Aggregates Formed Along Ion Tracks and Optical Anisotropy in CaF2 Crystals Irradiated with Swift Heavy Ions

It is known that swift heavy ion (SHI) irradiation induces the shape elongation of metal nanoparticles (NPs) embedded in transparent insulators, which results in anisotropic optical absorption. Here, we report another type of the optical anisotropy induced in CaF2 crystals without including intentionally embedded metal NPs. The CaF2 samples were irradiated with 200 MeV Xe14+ ions with an incident angle of 45° from the surface normal. With the increasing fluence, an absorption band at ~550 nm, which is ascribed to Ca aggregates, increases both the intensity and the anisotropy. XTEM observation clarified the formation of the continuous line structures and the discontinuous NP chains parallel to the SHI beam. Numerical simulations of the optical absorption spectra suggested the NP chains but not the continuous line structures as the origin of the anisotropy. The optical anisotropy in CaF2 irradiated with SHIs is different from the shape elongation of NPs.

Van der Waals GeSe with Strain- and Gate-Tunable Linear Dichroism for Wearable Electronics.

The direct detection of light polarization poses a crucial challenge in the field of optoelectronics and photonics. Herein, the tunable linear dichroism (LD) in GeSe-based polarized photodetectors is presented through electronic and structural asymmetry modulation, and demonstrate their application prospects in wearable electronics. An improvement in the dichroic ratio up to 34% is achieved under a gate voltage of 20V, and the improvement reaches 44% by applying a tensile strain along the zigzag direction. Theoretical calculations reveal that the gate regulation of barrier height between GeSe and Au electrodes is responsible for the electrical-tunable LD, while the anisotropic optical absorption in response to strains leads to the strain-tunable LD. Moreover, flexible GeSe transistors are developed for wearable applications including motion sensors and glucose monitors. This study offers viable approaches for modulating the optical anisotropy of low-dimensional materials and emphasizes the versatility of van der Waals materials for practical applications in wearable electronic devices.

Review of Angular-Selective Windows with Guest–Host Liquid Crystals for Static Window Applications

This review focuses on the development and advancements in angular-selective smart windows, with particular emphasis on static windows utilizing guest–host liquid crystal (GHLC) systems. Angular-selective windows are designed to adjust their transmittance based on the angle of incident light, offering enhanced energy efficiency and visual comfort in both architectural and automotive applications. By leveraging the anisotropic absorption properties of dichroic dyes, GHLC-based windows can selectively block oblique sunlight while preserving clear visibility from normal viewing angles. Various liquid crystal (LC) alignment configurations, including vertically aligned, homogeneously aligned, hybrid aligned, uniformly lying helix, and twisted aligned LC cells, have been investigated to optimize light control for different installation angles, such as for automotive windshields and building windows. These advancements have demonstrated significant improvements in energy conservation and occupant comfort by reducing cooling demands and regulating sunlight penetration. This review summarizes key findings from recent studies, addresses the limitations of current technologies, and outlines potential future directions for further advancements in smart window technology.

Anisotropic nonlinear optical responses of Ta2NiS5 flake towards ultrafast logic gates and secure all-optical information transmission.

Optical logic gates based on nonlinear optical property of material with ultrafast response speed and excellent computational processing power can break the performance bottleneck of electronic transistors. As one of the layered 2D materials, Ta2NiS5 exhibits high anisotropic mobility, exotic electrical response, and intriguing optical properties. Due to the low-symmetrical crystal structures, it possesses in-plane anisotropic physical properties. The optical absorption information of Ta2NiS5 is investigated by anisotropic linear absorption spectra, femtosecond laser intensity scanning (I-scan), and non-degenerate pump-probe technology. The I-scan results show a distinct maximum of ∼4.9 % saturable absorption (SA) and ∼4 % reverse saturable absorption (RSA) at different polarization directions of the incident laser. And, these unique nonlinear optical (NLO) properties originate from the anisotropic optical transition probability. Furthermore, the novel Ta2NiS5-based all-optical logic gates are proposed by manipulating the NLO absorption processes. And, the all-optical OR and NOR logic gates possess an ultrafast response speed approaching 1.7 THz. Meanwhile, an all-optical information transmission method with higher security and accuracy is achieved, which has promising potential to avoid the disclosure of information. This work provides a new path for designing versatile and novel optical applications based on Ta2NiS5 materials.

High performance self-driven broadband photodetector for polarized imaging based on novel ZrS3/ReSe2 van der Waals heterojunction

The distinctive characteristics of anisotropic two-dimensional (2D) materials, including in-plane anisotropy of optical absorption and carrier mobility, render them exceptionally suitable for application in the field of polarization detection and as a novel platform for the polarization imaging. Meanwhile, the consolidation of diverse functionalities within a single photodetector is highly anticipated to meet the demands of some special scenarios. Herein, a novel ZrS3/ReSe2 van der Waals (vdWs) heterostructure device was successfully constructed to realize polarization-sensitive, self-powered, and broadband photodetection and imaging. Owing to the built-in electric field of the type-II band alignment within the heterojunction, the device achieves a self-powered photoresponse ranging from 300 to 980 nm, an ultralow dark currentt ∼1 pA, and a commendable rise/decay time of 0.35/0.28 ms. Additionally, it has been demonstrated that the self-driven photodetector possesses a polarization-sensitivity with a notable anisotropic ratio about 2.02 (1.98) under 490 nm (980 nm) light illumination with zero bias, coupled with an excellent repeatability and stability. Furthermore, we also demonstrate the polarization imaging capabilities of the device in visible and near-infrared spectrum, realizing a contrast-enhanced degree of linear polarization imaging. This work paves a new platform to develop heterojunction photodetectors for high performance polarization-sensitive photodetection and next-generation polarized imaging.

Probing the Closed Association of Oligoquinoline Foldamers by Time-Resolved Fluorescence Anisotropy.

The metal-mediated dimerization of oligoquinoline foldamers terminated at one end with an oligo(phenylenevinylene) and at the other with a carboxylic acid (OPV-QnA, where n = 4, 8, 17, and 33), and the complexation of OPV-Q8A and Q16A was promoted in chloroform by the addition of a concentrated 16 M aqueous sodium hydroxide solution. UV-vis absorption and time-resolved fluorescence anisotropy (TRFA) experiments were conducted to determine, respectively, the concentration and the average rotational time ⟨ϕ⟩ of the mixture of unassociated and associated foldamers across a range of foldamer concentrations spanning 5 orders of magnitude. Plots of ⟨ϕ⟩ as a function of acid group concentration revealed that ⟨ϕ⟩ increased with increasing foldamer concentration only when the foldamer solution in chloroform was vigorously mixed with the 16 M sodium hydroxide aqueous solution. Furthermore, all plots showed that ⟨ϕ⟩ reached a plateau at high foldamer concentration. The increase in ⟨ϕ⟩ reflected the association of foldamers into larger objects through metal ion coordination with the carboxylate anions generated by deprotonation of the carboxylic acid of OPV-QnA with NaOH, while the plateau obtained at high foldamer concentration indicated that these interactions led to the dimerization of the foldamers via a closed association mechanism. Analysis of the ⟨ϕ⟩ trends yielded the equilibrium constants (K) describing the foldamer dimerization, whose value equaled 1.0 (±0.2) × 106 M-1 for the three longer OPV-QnA foldamers, but was about 10 times smaller for the shortest one (n = 4). Association of OPV-Q8A and Q16A yielded a complex with a ⟨ϕ⟩ matching that of OPV-Q24A, and K for this complexation was similar to that for dimerization. These experiments illustrate the robust nature of TRFA as an experimental method to probe the size of rigid, self-assembled foldamers in solution.

Self – assembled aligned single – walled carbon nanotubes as an anisotropic polarizer and saturable absorber in erbium-doped femtosecond fiber laser

We report the production of a saturable absorber (SA) based on aligned single-walled carbon nanotubes SWCNTs by the self-assembly method. The ultrafast saturation behavior of prepared aligned and random nanostructures shows an increase of modulation depth by 6 % due to the alignment method. We also observed the dependence of aligned SWCNTs loss on the polarization direction of laser radiation. All-fiber Er-doped hybrid mode-locked fiber laser was demonstrated based on the aligned/random SWCNTs-based SAs. We achieved the generation of stable stretched pulses with a pulse duration of 490/569 fs and an average output power of 20.7/18.25 mW. We also investigated the advantages of using aligned SWCNTs compared to the typical structure with random tube distribution. We show that the use of aligned SWCNTs film increased the SNR by 24.5, decreased the mode-locking threshold power by 42 mW, and decreased the RIN level by (20–25) dB in the frequency range [∼0 Hz- 100 kHz] and ∼8 dB in the range [100 kHz–1 MHz].

Thin-film fabrication of polythiophene block copolymer via friction transfer

Abstract A thin film of thiophene block copolymer composed of 3-dodecylthiophene and 3-benzenesulfonato–thiophene was fabricated by using the friction-transfer method. The benzenesulfonato moiety was transformed by heating to the corresponding sulfonic acid, which induced self-doping. The obtained friction-transfer film showed different morphology from the related cast film. It was also revealed that the film indicated anisotropy parallel/perpendicular toward the drawing direction, which induced absorption dichroism and anisotropy of electric conductivity.

Vibration absorption of as-built and post-heat-treated Ti-6Al-4V alloy fabricated by laser powder bed fusion additive manufacturing

Vibration absorption of the Ti-6Al-4V alloy fabricated by laser powder bed fusion additive manufacturing (LPBF-AM) was evaluated following as-built and post-heat treatment (i.e., solution treatment followed by water quenching). The base plate was heated at 50°C or 200°C during building. Results showed that the vibration absorption of the as-built Ti-6Al-4V alloy was higher when the base plate was heated at 50°C than at 200°C. Further, the vibration absorption indicated strong anisotropy, with the highest vibration absorption in the direction perpendicular to the building direction and transverse to the laser scanning direction. However, after solution treatment followed by water quenching, the anisotropy in the vibration absorption of the LPBF-AMed Ti-6Al-4V alloy practically disappeared, and relatively high values were obtained parallel to each direction.

Magnetically induced tunable exceptional and Dirac points

The photonic properties of cholesteric liquid crystals (CLCs) in an external magnetic field parallel to the helix axis are theoretically investigated for the first time in the short-wavelength band of the spectrum, where exceptional points (EPs) are found. It was shown that at the EP the real parts of two of four wave numbers touch each other or intersect at the absence of the dielectric anisotropy, and their imaginary parts intersect. At the EP the reflection, transmission and absorption show the same magnitudes for two eigenmodes of CLC layer. At anisotropic absorption near the EP there appear points where the magnetically induced transmittance/absorption are observed. The tunability of the EP was shown, i.e. we can change its wavelength by changing the magnitude of the external magnetic field. It was demonstrated the resonant enhancement of the chirality near the EP. Then it was shown that near the EP the two eigenmodes of CLC layer become strongly non-orthogonal.

Two-dimensional ferroelastic semiconductors InXY (X = S, Se; Y = Cl, Br, I): Promising candidates for photocatalytic water splitting with tunable electronic anisotropy

We have identified a class of two-dimensional ferroelastic monolayers, denoted as InXY (where X = S, Se; Y = Cl, Br, I), through first-principles calculations. The dynamic, thermal, and mechanical stabilities of these InXY monolayers are validated by phonon dispersion spectra, AIMD calculations, and elastic constants, respectively. These monolayers exhibit semiconducting behavior with bandgaps ranging from 1.94 to 2.85 eV and possess excellent ferroelasticity with strong ferroelastic signals and moderate ferroelastic switching barriers. Notably, the band edge positions of InSBr and InSI monolayers are observed to stride the water redox potentials at pH = 0, indicating their potential as photocatalysts for water splitting in acidic environments. We also explored the effects of biaxial strain on the band edge alignments and photocatalytic performance of these monolayers. Moreover, the InXY monolayers exhibit excellent anisotropic optical absorption across the visible to ultraviolet regions, along with high anisotropic carrier transport. The coupling of ferroelastic and anisotropic properties in these monolayers offers promising opportunities for designing controllable electronic devices, thereby expanding their potential applications in multifunctional materials. Our findings reveal that the InXY monolayers are promising candidates for efficient photocatalytic water splitting and controllable optoelectronic applications.

Chiral π-Conjugated Double Helical Aminyl Diradical with the Triplet Ground State

AbstractWe describe effective development of the highly diastereoselective synthesis of double helical tetraamine 2-H2-C2 and propose a mechanism for its formation. The resolution of 2-H2-C2 is facilitated by a high racemization barrier of 43 kcal mol–1 and it is implemented via either a chiral auxiliary or preparative supercritical fluid chromatography. This enables preparation of the first high-spin neutral diradical, with spin density delocalized within an enantiomeric double helical π-system. The presence of two effective 3-electron C–N bonds in the diradical leads to: (1) the triplet (S = 1) high-spin ground state with a singlet-triplet energy gap of 0.4 kcal mol–1 and (2) the long half-life of up to 6 days in 2-MeTHF at room temperature. The diradical possesses a racemization barrier of at least 26 kcal mol–1 in 2-MeTHF at 293 K and chiroptical properties, with an absorption anisotropy factor |g| ≈ 0.005 at 548 nm. These unique magnetic and optical properties of our diradical form the basis for the development of next-generation spintronic devices.1 Introduction2 Synthesis and Resolution of the C 2-Symmetric Double Helical Tetraamine 2-H2-C 2 3 Synthesis and Characterization of Neutral High-Spin Aminyl Diradical 22• -C 2 4 Conclusion