Polarization-dependent Absorption Research Articles

Ultrafast Laser Manipulation of In-Lattice Plasmonic Nanoparticles.

Plasmonic nanoparticles enable manipulation and enhancement of light fields at deep subwavelength scales, leading to structures and devices for diverse applications in optics. Despite hybrid plasmonic materials display remarkable optical properties due to interactions between components in nanoproximity, scalable production of plasmonic nanostructures within a single-crystalline matrix to achieve an ideal plasmon-crystal interface remains challenging. Here, a novel approach is presented to realize efficient manipulation of in-lattice plasmonic nanoparticles. Employing ultrafast-laser-driven plasmonic nanolithography, metallic nanoparticles with controllable morphology are precisely defined in the crystalline lattice of yttrium aluminum garnet (YAG) crystal. Through direct ion implantation, hybrid plasmonic material composed of nanoparticles embedded in a sub-surface amorphous YAG layer is created. Subsequently, femtosecond laser pulses guide formation and reshaping of plasmonic nanoparticles from the amorphous layer into the single-crystalline matrix along direction of light propagation, facilitated by a plasmon-mediated evolution of laser energy deposition. By tailoring resonance modes and optimizing the coupling between structured particle assemblies, a range of applications including polarization-dependent absorption and nonlinearity, controllable photoluminescence, and structural color generation is demonstrated. This research introduces a new approach for fabricating advanced optical materials featuring in-lattice plasmonic nanostructures, paving the way for the development of diverse functional photonic devices.

Dual-band high quality-factor perfect absorber based on uniaxial/biaxial anisotropic van der Waals polar crystals

Phonon polaritons (PhPs) in two-dimensional van der Waals crystals, such as hexagonal boron nitride (hBN) and α-phase molybdenum trioxide (α-MoO3), exhibit remarkable spatial confinement and extremely low optical losses, offering possibilities for the development of novel micro and nanophotonic devices at mid-infrared wavelengths. Here, we demonstrate the potential of the proposed Tamm structure to achieve dual-band high quality-factor perfect absorption within the mid-infrared range. This structure utilizes upper and lower spacer layers to isolate the anisotropic materials hBN and α-MoO3 from one-dimensional photonic crystals, where the Tamm phonon polaritons (TPhPs) are respectively excited at the interfaces, facilitating strong coupling with incident light and leading to significant dual-band perfect absorption phenomena. The results demonstrate that due to polariton resonances, the absorption peaks exhibit extremely narrow absorption bandwidths, with the maximum quality-factor reaching up to 297. In addition, tunable resonant wavelengths and polarization-dependent absorption properties are also demonstrated in the proposed Tamm structure. This study provides an alternative and straightforward approach for constructing dynamic and multifunctional optical devices such as optical modulators, tunable multi-band filters and biosensors.

Coumarin Derivative and Gold Nanoparticle Conjugate as a Selective Fluorescent Sensor for Mercury Ion in Real Sample.

A biphenyl based coumarin fluorescent molecule, N,N'-bis(7-diethylamino-2-oxo-2H-chromen-3-yl)methylene)biphenyl-2-2'-dicarbohydrazide (molecule 1) has been synthesized and characterised. Photophysical studies of 1 exhibit solvent polarity dependent absorption and emission maxima. Citrate capped gold nanoparticles (AuNPs) have been mixed with molecule 1 for the preparation of AuNPs/1 conjugate. The association constant of the AuNPs/1 conjugate has been calculated to 4.54 × 104 M- 1. The AuNPs/1 conjugate has been found to detect Hg2+ ion selectively by fluorescence enhancement. While addition of molecule 1 into the solution of AuNPs, fluorescence intensity of 1 quenched. On addition of several monovalent, divalent and trivalent metal ion into the solution of AuNPs/1 conjugate separately, there was no change in fluorescence intensity of 1 has been observed. However, upon addition of Hg2+ ion into the solution of AuNPs/1 conjugate, the fluorescence intensity enhancement occurred, indicating released of 1 from the surface of AuNPs and probably aggregation of AuNPs took place in presence of Hg2+ ion. The AuNPs/1 conjugate has been found to have a detection limit of 2.3 × 10- 9 M for Hg2+ ion in aqueous solvent. Meanwhile, the AuNPs/1 conjugate have also been successfully applied for the determination of Hg2+ in real water samples.

Charge transfer excitons and directional fluorescence of in-plane lateral MoSe2-WSe2 heterostructures.

In this article, the linear and nonlinear optical properties of in-plane lateral MoSe2-WSe2 heterostructures are theoretically investigated. The polarization-dependent strongest optical absorption in one-photon absorption occurs in charge transfer excited states, where electrons transfer from WSe2 to MoSe2. This phenomenon is supported by the LUMO (lowest unoccupied molecular orbital) and HUMO (highest occupied molecular orbital) imaging obtained through scanning tunneling microscopy. The charge difference density and transition density matrix are used to interpret the electronic transitions, and these interpretations rely on the concept of transition density. The optical properties of two-photon absorption in its nonlinear optical process are significantly different from the excitation in one-photon absorption, where the strongest optical absorption is contributed from direct transition from the ground state to the final state without going through an intermediate excited state, due to the very large difference of permanent dipole moments between the excited and ground states. Our results also reveal directional fluorescence and physical mechanism of in-plane lateral MoSe2-WSe2 heterostructures. Our work can provide insights into the physical mechanism of the optical properties of in-plane lateral MoSe2-WSe2 heterostructures.

Gold Nanorods - An Overview

This article provides an overview of current research in structure, synthesis, properties, application of gold nanorods. Interest in rod- shaped nanoparticles steam of unique optical properties, A gold nanorod is defined as nanometer-sized gold particles that are rod shaped. These solid, cylindrical nanoparticles have uniform diameters ranging from a few nanometers to hundreds of nanometers, with aspect ratios (length/diameter) larger than 1 but typically smaller than 10. The most popular and successful method for creating high-quality gold nanorods is seed-mediated development. optical properties of gold nanorods, absorption spectrum of colloidal dispersion of gold nanorods, local field effect and sensing application, color of colloidal dispersion of gold nanorod, polarization dependent color and absorption in polymer gold. Gold nanorods are utilized in a range of applications including biosensing, photothermal therapy, bioassays, biomedical imaging, and drug delivery. All these properties make gold nanorod a good candidate for future nanoelectronics in this article, we will describe the preparation and characterization of gold nanorods.

Rashba Effect and Spin-Dependent Excitonic Properties in Chiral Two-Dimensional/Three-Dimensional Composite Perovskite Films.

Among various chiral semiconductor materials, chiral two-dimensional (2D)/three-dimensional (3D) composite perovskites (CPs) offer the benefits of strong interface asymmetry and energy transfer between 2D and 3D phases, making the chiral CPs promising for spintronic devices. Therefore, understanding their spintronic properties will be greatly important for expanding their relevant applications. In this work, we synthesized one pair of chiral 2D/3D CP films. Their Rashba effect and spin relaxation process have been investigated by polarization-dependent femtosecond transient absorption spectroscopy. Interestingly, under left- and right-handed circularly polarized light (CPL) excitation, a two-photon emission intensity difference is observed in chiral 2D/3D CP films at 298 K. This work sheds light on the spin-dependent excitonic characteristics of chiral 2D/3D CPs and confirms the feasibility of their application in near-infrared CPL detection.

Dual-channel dynamic modulation for polarization-dependent absorption by gating ultrathin TiN films in the near-infrared region

Ultrathin titanium nitride (TiN) is a novel material flatform for constructing active metasurfaces in the near-infrared region (NIR). In this paper, we numerically achieved the dual-channel dynamic modulation for polarization-dependent absorption by adjusting incident angles and gating ultrathin TiN films. To enhance the active modulation effect of ultrathin TiN film, the “卍” shaped gold resonator is integrated with ultrathin TiN film for constructing a metasurface Salisbury screen (MSS). By electrical reducing TiN carrier concentration by 12%, the absorption peak of TE wave blueshifts 100 nm. The magnitude and the frequency of the polarization-dependent absorption are independently tuned by changing incident angles or the carrier concentration in TiN film. The ultrathin TiN film based polarization-dependent metasurface enabling versatile dual-channel modulation has great potentials in the applications of optical communication, information encryption, real-time imaging etc.

Anisotropic photocurrent response at MnBi2Te4-metal interface

The magnetic topological insulator MnBi2Te4 has attracted a lot of research interests for its exotic properties due to the interplay between nontrivial topology and magnetism. Here, we report the photocurrent (PC) response of MnBi2Te4 flakes under the excitation wavelengths between 633 nm and 4000 nm measured by scanning PC microscopy. We observe a significant polarization dependent PC response at the interface between metal electrode and MnBi2Te4, while the PC response remains polarization-independent at MnBi2Te4 layer steps. The polarization dependent PC at the MnBi2Te4-metal electrode interface, which is attributed to the polarization dependent light absorption at the interface, preserves in the whole tested wavelength range. The responsivity of the device is 80 μA W−1. This responsivity as well as PC polarity is consistent with the results calculated based on a photo-thermoelectric generation mechanism, thus we infer that photo-thermoelectric effect dominates in the PC generation at MnBi2Te4-metal interface. Our results reveal the photoelectric response mechanism of the emerging material MnBi2Te4 for its potential optoelectronic applications.

Exciton dispersion in two-dimensional organic perylene crystal indicates substantial charge-transfer exciton coupling

Two-dimensional, high-quality perylene single crystals were grown with a space-confined strategy method. The grown films crystallize in the $\ensuremath{\alpha}$ form, as is confirmed by a combination of techniques. Polarization-dependent optical absorption measurements show a strong anisotropy in very good agreement with the literature data, and the anisotropic mobility data in field-effect transistors document the very high crystalline order. Momentum-dependent studies using electron energy-loss spectroscopy reveal a negative dispersion of the first exciton along the crystal $b$ direction with an exciton bandwidth of 72 meV. We argue that this behavior is a result of charge-transfer exciton coupling between the perylene dimers in the unit cell.

Polarization-Dependent Absorption and Transmission Metasurfaces for Linearly and Circularly Polarized Light in Terahertz Band

Polarization detection is an important part of many polarization applications such as polarization imaging, wireless communication, and circular dichroism spectroscopy. In this paper, two polarization-dependent terahertz wave absorption and transmission metasurface for linearly and circularly polarized light are proposed and proved by numerical simulations. Polarization filtering and polarization absorption are integrated on a single cell, and the orthogonal polarization component is transmitted and absorbed, respectively. The linearly polarization-dependent transmission and absorption structure can obtain a transmission extinction ratio of 11.5 dB and an absorption extinction ratio of over 270 dB at 3 THz. Moreover, the circularly polarization-dependent structure can obtain a transmission extinction ratio of 8.1 dB and an absorption extinction ratio of 4.66 dB at 2.8 THz. Our design facilitates the acquisition of full Stokes parameters and the high-resolution imaging.

Atomic optical spatial mode extractor for vector beams based on polarization-dependent absorption

Vector beams with spiral phase and spatially varying polarization profiles have many applications from optical micromanipulation to materials processing. Here, we propose and demonstrate an atomic spatial mode extracting scheme for the vector beam based on polarization-dependent absorption in the atom vapor. By employing the linear polarization pump beam which induces polarization sensitive absorption in the atomic ensemble, a counter-propagated weak probe vector beam is extracted by spatial absorption, and extracted part still maintains the original polarization and the vortex phase. The topological charges of the extracted mode are verified by interfering with the Gaussian beam, and it can be found that the orbital angular momentum is conserved in the extracting process. Our work will have potential applications in non-destructive spatial mode identification, and is also useful for studying higher-dimensional quantum information based on atomic ensembles.

Tunable and anisotropic perfect absorber using graphene-black phosphorus nanoblock.

Two-dimensional (2D) materials, which have attracted attention due to intriguing optical properties, form a promising building block in optical and photonic devices. This paper numerically investigates a tunable and anisotropic perfect absorber in a graphene-black phosphorus (BP) nanoblock array structure. The suggested structure exhibits polarization-dependent anisotropic absorption in the mid-infrared, with maximum absorption of 99.73% for x-polarization and 53.47% for y-polarization, as determined by finite-difference time-domain FDTD analysis. Moreover, geometrical parameters and graphene and BP doping amounts are possibly employed to tailor the absorption spectra of the structures. Hence, our results have the potential in the design of polarization-selective and tunable high-performance devices in the mid-infrared, such as polarizers, modulators, and photodetectors.

Optical Anisotropy and Momentum-Dependent Excitons in Dibenzopentacene Single Crystals

High-quality single crystals of the organic semiconductor (1,2;8,9)-dibenzopentacene were grown via physical vapor transport. The crystal structure—unknown before—was determined by single-crystal X-ray diffraction; polarization-dependent optical absorption measurements display a large anisotropy in the ac plane of the crystals. The overall Davydov splitting is ∼110 meV, which is slightly lower than that in the close relative pentacene (120 meV). Momentum-dependent electron energy-loss spectroscopy measurements show a clear exciton dispersion of the Davydov components. An analysis of the dispersion using a simple 1D model indicates smaller electron- and hole-transfer integrals in dibenzopentacene as compared to pentacene. The spectral weight distribution of the excitation spectra is strongly momentum-dependent and demonstrates a strong momentum-dependent admixture of Frenkel excitons, charge-transfer excitons, and vibrational modes.

Method for the definitive detection of orbital angular momentum states in neutrons by spin-polarized 3He.

A standard method to detect thermal neutrons is the nuclear interaction 3He(n,p)3H. The spin dependence of this interaction is also the basis of a neutron spin-polarization filter using nuclear polarized 3He. We consider the corresponding interaction for neutrons placed in an intrinsic orbital angular momentum (OAM) state. We derive the relative polarization-dependent absorption cross sections for neutrons in an OAM state. The absorption of those neutrons results in compound states , , and . Varying the three available polarizations tests that an OAM neutron has been absorbed and probes which decay states are physically possible. We describe the energetically likely excited states of 4He after absorption, taking account of the odd parity of the compound state. This provides a definitive method for detecting neutron OAM states and suggests that intrinsic OAM states offer the possibility to observe new physics, including anomalous cross sections and new channels of radioactive decay.

Van der Waals forces enhanced light–graphene interaction in optical microfiber polarizer

A facile and efficient approach to manufacturing optical devices with a plane graphene-coupled microfiber structure is proposed—attaching the optical microfiber onto a monolayer graphene-coated polydimethylsiloxane substrate. Such devices exhibit strong light–graphene interaction via the evanescent fields of the guided light in microfibers and show evident optical polarization and polarization-dependent saturable absorption effect. When the monolayer graphene with propagation distance is 2.5 mm, and the microfiber diameter is 3.9 μm, the polarization extinction ratio can reach up to 31.0 dB with the light wavelength at 1550 nm. The transmission in TM modes could be increased continuously by increasing the input power of light at 980 nm. The transmission with 3 and 10 dB modulation depths in TM modes could be achieved via 980 nm pump power of 15.1 and 66.1 mW, respectively, which is advantageous over unpolarized graphene-coupled microfiber devices. The proposed microfiber on graphene structure could efficiently integrate optical waveguides with two-dimensional materials, with great potential applications in optical polarizers, all-optical modulators, mode-locked fiber lasers, and sensors, especially for all-fiber systems.

Polarization-dependent conversion efficiency of carbon nanotube-Si heterojunction solar cells based on aligned carbon nanotube films

We have fabricated solar cells that implement heterojunctions of Si and aligned carbon nanotube (CNT) films. Polarization-dependent optical absorption of highly aligned CNTs led to polarization-dependent conversion efficiencies, which in turn provided insight into the role of the CNT layer in the power generation mechanism in these heterojunction solar cells. When the incident light polarization was parallel to the CNT alignment direction so that the light absorption in the CNT layer was maximized, the short circuit photocurrent decreased by ∼25%. This indicates that electron–hole pair generation in the CNT layer does not directly lead to power generation and that the CNT-Si heterojunctions in our devices are Schottky junctions rather than p–n junctions.

Graphene-coupled silica microsphere polarizer

Polarization-selective devices can control the polarization of the optical system. We develop a compact hybrid structure based on silica microsphere and monolayer graphene to tune the polarization of the optical system, which the working principle is polarization-dependent absorption of graphene combined with silica microsphere through whispering-gallery (WG) TE mode and TM mode. Because of different field distributions and polarization states of resonant modes in microsphere, the gap distance between microsphere and graphene can modify the quality factor and resonant wavelength of microsphere to realize the different variations for TE and TM WG modes, respectively. As gap distance is reduced from 2.2 µm to 0.3 µm, 11 dB polarization extinction ratio is realized between resonance polarized mode in the 90° polarization direction and that in the 0° polarization direction. Furthermore, for different original gap distance between microsphere and graphene, corresponding to different preconditions of quality factors of microsphere, one can obtain a polarization-selective device with the adjustable bandwidth. This results offer an attractive and effective photonic platform to achieve high-performance polarization-selective devices.

Polarization-dependent ultrafast carrier dynamics in GaAs with anisotropic response

The transient dynamics of anisotropic properties of GaAs was systematically studied by polarization-dependent ultrafast time-resolved transient absorption. Our findings revealed that the anisotropy of reflectivity was enhanced in both pump-induced and probe-induced processes, suggesting an extraordinary resonance absorption of photon–phonon coupling (PPC) with intrinsic anisotropic characteristic in carrier relaxation, regardless of the concrete crystallinity and orientation of GaAs sample. The results, delivering in-depth cognition about the polarization-dependent ultrafast carrier dynamics, also proved the paramount importance of interaction between polarized laser and semiconductor.

Polarization-dependent broadband absorber based on composite metamaterials in the long-wavelength infrared range.

Capturing polarization information has long been an important topic in the field of detection. In this study, two polarization-dependent broadband absorbers based on a composite metamaterial structure were designed and numerically investigated. Unlike in conventional metamaterial absorbers, the bottom metallic film is functionalized to achieve a polarization response or broadband absorption. The simulation results show that the type I absorber exhibits TM polarization-dependent broadband absorption (absorptivity>80%) from 8.37 µm to 12.12µm. In contrast, the type II absorber presents TE polarization-dependent broadband absorption (absorptivity>80%) from 8.23 µm to 11.93 µm. These devices are extremely sensitive to the change of polarization angle. The absorptivity changes monotonically with an increase of the polarization angle, but it is insensitive to oblique incidence. This design paves the way for realizing broadband polarization-dependent absorption via a simple configuration. It has bright prospects in thermal detection applications and imaging fields.

Graphene-coupled silica microtoroid for optical polarization controlling and electro-optic modulation

Whispering gallery (WG) microcavities have been applied for a variety of optoelectronic devices due to their extraordinary characteristics of high quality factor ( Q ) and small mode volume, crucial to accurately tune the quality factor for realizing the high-speed optical modulation and short pulse laser. In this paper, we propose and theoretically analyze a hybrid, graphene-coupled silica microtoroid device and realize optical polarization control and electro-optic modulation due to the polarization-dependent absorption of graphene on the different cavity WG modes. By changing the gap distance between graphene and the microtoroid, the influence of graphene absorption on the different polarization modes is diverse due to the different electric field distributions of modes in the microtoroid, therefore demonstrating the different resonant wavelength shifts and quality factor variations. The transmission depth variation of the second-order transverse electric mode upon changing the gap distance between graphene and microtoroid is 4.5 dB more than that of the second-order transverse magnetic mode, verifying that the polarization control is because of the polarization-dependent absorption of graphene. Furthermore, by applying the voltage on the graphene flakes, electro-optic modulation with a high contrast of 21.7 dB is demonstrated based on this hybrid graphene-coupled silica microtoroid.