Polarization Direction Of Incident Light Research Articles

Investigation of growth and polarized spectra of Ho3+ ions heavily doped BaY2F8 crystal

A BaY2F8 (BYF) single crystal heavily doped with Ho3+ ion was grown successfully using the Czochralski (Cz) method. The infrared fluorescence spectra (2–4 μm) and fluorescence lifetime at 3.9 μm were investigated. The detailed polarization absorption properties of Ho:BYF, especially the absorption spectrum in 850–950 nm range, were reported for the first time. The maximum absorption cross-section was at 888.15 nm, σabs = 1.26✕10−21 cm2 (E//c). In comparison, the peak positions of the absorption cross sections in the other two polarization directions were at 885.80 nm and 890.45 nm, respectively, indicating that incident light's polarization direction greatly influences absorption. The spectroscopic parameters were calculated based on the Judd–Ofelt theory.

Ultrafast spatiotemporal control of orthogonally directional surface plasmon polariton via a compact nanoantenna

Ultrafast spatiotemporal control over the launch direction of surface plasmon polariton (SPP), which is highly desirable for the realization of integrated nanophotonic devices and ultrafast data processing systems within plasmonic nano-circuitry, remains a significant challenge. In particular, ultrafast spatial-temporal switching of SPP directional emissions in orthogonal directions has not yet been reported. Here, we propose a novel compact plasmonic nanoantenna structure design for spatiotemporal control of SPP launch at the nano−femto scale. This device possesses the capacity to launch the SPP directionally into different orthogonal output channels by changing the polarization direction of incident light. More importantly, ultrafast switching of the SPP directional launch at a femtosecond time scale has been proposed via adjusting the instantaneous polarization state of the excitation light. This study can lay the foundation for the development of miniaturized signal processing systems for high-speed data processing, and highly integrated nanophotonic devices, as well as for enhancing the functionality of next-generation optical nanocircuits.

Orientational effects in the polarized absorption spectra of molecular aggregates.

We present a detailed theoretical analysis of polarized absorption spectra and linear dichroism of cyanine dye aggregates whose unit cells contain two molecules. The studied threadlike ordered system with a molecular exciton delocalized along its axis can be treated as two chains of conventional molecular aggregates, rotated relative to each other at a certain angle around the aggregate axis. Our approach is based on the general formulas for the effective cross section of light absorption by a molecular aggregate and key points of the molecular exciton theory. We have developed a self-consistent theory for describing the orientational effects in the absorption and dichroic spectra of such supramolecular structures with nonplanar unit cell. It is shown that the spectral behavior of such systems exhibits considerable distinctions from that of conventional cyanine dye aggregates. They consist in the strong dependence of the relative intensities of the J- and H-type spectral bands of the aggregate with a nonplanar unit cell on the angles determining the mutual orientations of the transition dipole moments of constituting molecules and the aggregate axis as well as on the polarization direction of incident light. The derived formulas are reduced to the well-known analytical expressions in the particular case of aggregates with one molecule in the unit cell. The calculations performed within the framework of our excitonic theory combined with available vibronic theory allow us to quite reasonably explain the experimental data for the pseudoisocyanine bromide dye aggregate.

Infrared plasmonic refractive index sensor utilizing 2D grating of nano-bowtie particles for both gas and liquid

We propose a plasmonic structure that can be used for refractive index sensing with different analytes in the same wavelength-domain. A two-dimensional (2D) grating composed of nano-bowtie particles is used as the optical momentum coupling structure. The double-period feature of the 2D grating makes the structure have two excitation approaches with different polarization directions of incident light. The physical mechanisms of the plasmonic structure are revealed in detail by theoretical analysis and finite-difference time-domain method. The simulation results show that the structure can achieve a gas sensing sensitivity of 1235 nm/RIU and a liquid sensing sensitivity of 950 nm/RIU in the same wavelength-domain from 1200 nm to 1400 nm. This structure can be widely used in the field of gas or liquid biochemistry due to its simple geometry and competitive sensing performance.

Patterned dielectric mirrors for uniformly high reflection in polarized light

Two types of multilayered dielectric mirrors with high reflection in the visible range are fabricated on line-patterned substrates using a suitable combination of cost-effective soft lithography and RF magnetron sputtering. They are characterized at different visible wavelengths lying outside and inside their stopband range. Their response to linearly polarized incident light depends on the wavelength, angle of incidence, and the direction of orientation of the patterned lines on the substrate with respect to the direction of polarization. A comparison of these broadband high reflectors on patterned substrates with that of equivalent high reflectors on planar substrates confirmed that the patterned high reflectors have a much higher uniformity in their reflectance value when the polarization direction of incident light is changed, both within and outside their stopband range, even at oblique angles of incidence. These broadband high reflectors are useful in applications that require uniformly high reflection even while there are changes in wavelength, polarization and the angle of incidence.

Energy spectrum and light absorption of arsenene quantum dots

As a close relative of phosphorene, puckered arsenene is stable and has been demonstrated experimentally as a promising two-dimensional semiconductor material. By means of a multi-orbital tight-binding model, we investigate theoretically the energy spectrum and magneto-optical properties of circular and rectangular arsenene quantum dots (AQDs). The tight-binding parameters are obtained by reproducing accurately the electron energy bands of puckered arsenene from the first-principle calculation. For both AQDs, the density of states (DOS), probability distribution and inverse participation ratio (IPR) of eigenstates, and optical absorption spectrum are calculated numerically. It is found that edge states of AQDs fill up the bulk band gap of puckered arsenene and are only localized near the armchair edges of AQDs. These features differ greatly from those in quantum dots made of graphene or phosphorene. The band edges of arsenene monolayer can be located roughly from the IPR and DOS spectrum. The light absorptivity of both AQDs under zero magnetic field depends strongly on the polarization direction of incident light. The position and intensity of absorption peaks can be tuned by the shape of quantum dots and the applied magnetic field. The anisotropy ratio of light absorption can be reduced by one order of magnitude under a magnetic field of tens of Tesla.

LCP /TLC based composite multi-dimensional polarization-dependent anti-counterfeiting device

Modern anti-counterfeiting technology can effectively suppress and combat forgery and counterfeiting behaviors, which is of great significance in information security, national defense and economy. However, the realization of multi-dimensional, integrated, difficult-to-copy and easy-to-detect optical anti-counterfeiting devices is still a challenge. In this paper, a multi-dimensional and polarization-dependent anti-counterfeiting device with structure color is designed, which is composed of patterned liquid crystal polymer (LCP) nematic layer and thermotropic cholesteric liquid crystal (TLC) layer. It has the advantages of displaying and hiding polarization states, wide color tuning range, convenient operation, high integration and security. For incident light with a specific polarization state, the patterned nematic phase LCP layer can carry out regionalized phase editing and polarization state modulation, while the TLC layer can selectively reflect the incident light. Therefore, a patterned structural color security label is subtly realized. The anti-counterfeiting device can realize the display, hiding, color adjustment and image/background conversion of patterns by adjusting the polarization direction of incident light. In addition, the TLC layer in the device can meet the application requirements of the anti-counterfeit device at different environmental temperatures through the flexible design of the system weight ratio. Furthermore, the device can be easily heated by body temperature, realize dynamic real-time wide-spectrum color modulation and reversible pattern erasure, and further enhance its security dimension and security. The multi-polarization-type anti-counterfeiting device has three-dimensional anti-counterfeiting efficacy. The first dimensional anti-counterfeiting efficacy is achieved by the thermochromic liquid crystal layer. The thermochromic liquid crystal layer has no reflection color outside the operating temperature range of TLC material, and the entire device displays black background. The second and the third dimensional anti-counterfeiting efficacy are related to the polarization state of the incident light and the linear polarization direction, respectively. Only when the incident light is linearly polarized light and its polarization direction makes an angle of 45° or –45° with respect to the optical axis of the liquid crystal, will the device show the designed pattern. Consequently, our proposed anti-counterfeiting device is expected to provide a new idea for developing the anti-counterfeiting field.

Ultrahigh-level enhancement on nonlinear optical susceptibility of cubic quantum dots achieved by THz laser and electric field.

Multi-physics coupling, composed of an intense THz laser and electric field, serves as a new approach to realize the ultrahigh-level enhancement on third-harmonic generation (THG) of cubic quantum dots (CQDs). The exchange of quantum states caused by anticrossing of intersubbands is demonstrated by the Floquet method and finite difference method with the increasing laser-dressed parameter and electric field. The results show that the rearrangement of the quantum states excites the THG coefficient of CQDs four orders of magnitude higher than that achieved with a single physical field. The optimal polarization direction of incident light that maximizes the THG exhibits strong stability along the z axis at high laser-dressed parameter and electric field.

Polarized Raman spectroscopy on topological semimetal Co3Sn2S2

AbstractWe present polarized Raman spectroscopy of the topological semimetal Co3Sn2S2, which was recently shown to host a Weyl semimetal phase. Stokes Raman spectra were obtained with the incident light parallel to the c‐axis of Co3Sn2S2. Two major phonon Raman peaks were observed at 289 and 386 cm−1 over continuous background emission signals. The intensity of the low‐wavenumber (289 cm−1) peak showed no polarization dependence. The high‐wavenumber (386 cm−1) peak and the continuous background signal were strongly polarized in the incident light polarization direction. These responses were almost independent of the in‐plane crystal orientation to the incident polarization, as is the manifestation of the point group symmetry of the unit cell of Co3Sn2S2. According to the group theory and Raman tensor analyses, the low‐ and high‐wavenumber Raman signals are attributed to Γ point phonon modes with and symmetries, respectively. Furthermore, line shape analyses revealed that the high‐wavenumber mode exhibited asymmetric peak feature well described by the Breit–Wigner–Fano function. These results suggest the Fano resonance between the phonon scattering with the continuous electronic background associated with low energy excitations near the Fermi energy. The clarified phonon energies and symmetries, as well as the electronic contribution to the Raman scattering, will not only be useful as a fingerprint to readily verify the experimentally grown or theoretically calculated crystal structure but also suggest importance of Raman spectroscopy as an effective tool to study low energy excitations and their interactions in Co3Sn2S2.

Electric field- and polarisation-dependent two-photon absorption in bilayer black phosphorus

We use an analytical method based on the five-hopping parameter continuous approximate Hamiltonian to theoretically investigate two-photon absorption (TPA) in bilayer black phosphorus (BP) and its dependence on an applied electric field and the polarisation direction of incident light. The results show that there is a threshold value of the energy difference between layers caused by an external electric field, Δ = 1.4625 eV, at which the bandgap of bilayer BP closes. When the electric field intensity is enhanced, but keeping Δ < 1.4625 eV, the absorption peak of TPA increases with a redshift; when Δ > 1.4625 eV, the absorption peak of TPA decreases with a blueshift, and the bandgap reopens around the Γ point. Moreover, the TPA coefficient changes periodically with the polarisation angle of the incident light as a cosine function, making BP a potentially viable linear polariser for applications.

Field Enhancement for the Composite MXene/Black Phosphorus-Based Metasurface.

Both MXene and black phosphorus (BP), which actg as hot two-dimensional (2D) materials, have unique optical properties and important applications for nano-micro optical devices. Here, a composite MXene/BP-based metasurface, consisting of Ti3C2Tx and BP layers, is proposed for investigating the optical responses and electric field by using the finite-difference time-domain numerical simulation method in the microwave band. The research results show that the Fano resonance-like spectra can be observed when the coupling of surface plasmons (SPs) on the BP and MXene layers appears. Furthermore, the field enhancement, based on the Fano resonance-like optical responses, can be improved by an order of magnitude through adjusting the structural parameters and the polarization direction of incident light for the proposed metasurface. The findings may provide important theoretical insights into the design and realization of high-performance plasmonic devices.

Template‐Assisted Self‐Assembly of Colloidal Silicon Nanoparticles for All‐Dielectric Nanoantenna

AbstractA solution‐based bottom‐up process to produce one‐ and two‐dimensional arrays of densely packed spherical nanoparticles (NPs) of crystalline silicon (Si), having the lowest order Mie resonance in the visible range, is developed. First, an agglomeration‐free solution of Si NPs with a narrow size distribution is prepared. By using grooves fabricated on the surface of a polymer as a template, arrays of Si NPs with different shapes are formed by a template‐assisted self‐assembly method, and then they are transferred to an arbitrary substrate. To demonstrate proper formation of Si NP arrays, polarization‐resolved scattering spectra are measured for different size linear arrays, i.e., a monomer to a pentamer, of Si NPs placed on a silica substrate. The observed spectra are well‐reproduced by the numerical simulations. When the polarization direction of incident light is parallel to the array axis, the scattering spectra are strongly modified from that of a Si NP monomer due to near‐field coupling of the electric dipole (ED) modes. In a Si NP tetramer, the peak of the ED mode overlaps with that of the magnetic dipole (MD) mode and strong forward scattering is observed at the MD peak wavelength due to the Kerker effect.

Study on the characteristics of a photonic crystal sensor with rectangular lattice based on bound states in the continuum

In this paper, a sensor model of a photonic crystal with a rectangular lattice is proposed and its sensing characteristics based on bound states in the continuum are studied using the finite element method. Using the different resonances of the rectangular lattice in two axes, the resonance line-width can be adjusted by the polarization direction of incident light. This structure can achieve a sensitivity of 148 nm RIU−1 and the figure of merit above 821 RIU−1, which shows a great potential in high-quality sensors, filter, laser line-width modulation as well as measurement of angle and angular velocity.

Quadruple plasmon-induced transparency of polarization desensitization caused by the Boltzmann function.

This study proposes a graphene metamaterial desensitized to the polarized angle to produce tunable quadruple plasmon-induced transparency (PIT). As a tool employed to explain the PIT, n-order coupled mode theory (CMT) is deduced for the first time and closely agrees with finite-difference time-domain (FDTD) simulations according to the quadruple PIT results in the case of n = 5. Additionally, the response of the proposed structure to the angle of polarized light is investigated. As a result, the Boltzmann function satisfied by the response of graphene strips to the polarization direction of incident light is proposed for the first time. Its property of polarization desensitization can be attributed to structural centrosymmetry, and conjugated variety which the Boltzmann functions result in. Therefore, a quintuple-mode modulation based on simultaneous electro-optical switch is realized by tuning Fermi levels within graphene. Its modulation degrees of amplitude and dephasing times are obtained. Given that the slow-light property is an important application of PIT, the n-order group index is thereby obtained. Hence, not only do the insights gained into polarization-desensitization structure provide new ideas for the design of novel optoelectronic devices, but also the results from the n-order CMT offer new research progress and references in theory.

Conditions for surface lattice resonances and enhancement of second harmonic generation based on split-ring resonators

In this paper, we theoretically study the condition for the strong coupling between magnetic resonance mode of the two-dimensional periodically arranged gold split-ring resonators and the diffraction mode of the periodic array and its influence on the second harmonic generation efficiency. By controlling the size of the period of the array structure in the &lt;i&gt;x&lt;/i&gt;-axis and &lt;i&gt;y&lt;/i&gt;-axis, the diffraction mode is excited near the magnetic resonance provided by the gold split-ring resonator, solely in one of the directions. In both cases, the diffraction mode and the magnetic resonance coincide in the linear resonance spectrum, but by analyzing the electric field distribution at the position of the diffraction mode, it can be found that when &lt;inline-formula&gt;&lt;tex-math id="M152"&gt;\begin{document}${a_x}$\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="5-20201424_M152.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="5-20201424_M152.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt; is much larger than &lt;inline-formula&gt;&lt;tex-math id="M153"&gt;\begin{document}${a_y}$\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="5-20201424_M153.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="5-20201424_M153.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt;, the electric field direction of the diffraction mode is perpendicular to the polarization direction of the incident light, and no strong coupling occurs. Therefore, the dilution effect is dominant, and the second harmonic intensity gradually decreases with the increase of the period. When &lt;inline-formula&gt;&lt;tex-math id="M154"&gt;\begin{document}${a_y}$\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="5-20201424_M154.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="5-20201424_M154.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt; is much larger than&lt;inline-formula&gt;&lt;tex-math id="M155"&gt;\begin{document}${a_x}$\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="5-20201424_M155.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="5-20201424_M155.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt;, the electric field direction of the diffraction mode is the same as the polarization direction of the incident light. At this time, the diffraction mode and the magnetic resonance mode are strongly coupled. As the period increases, the second harmonic intensity first increases and then decreases. The increase is due to the dominant mode coupling and the decrease is due to the dominant dilution effect. When the number density of split-ring resonators is reduced to about 1/4 of the original one, the second harmonic intensity can be increased by more than twice. From this, we find that the strong coupling between diffraction mode and magnetic resonance can occur when the electric field direction of the diffraction mode is consistent with the polarization direction of incident light, thus generating the surface lattice resonance to achieve near-field enhancement. In short, the rectangular periodic structure is used to distinguish the field enhancement effects in different directions, and the second harmonic enhancement can still be achieved when the number density of split-ring resonators is reduced, which relaxes the requirements for processing technology. This research provides a new possible way to improve the second harmonic generation efficiency based on metal metasurfaces.

Exploring performance of THz metamaterial biosensor based on flexible thin-film.

To extend the application of flexible metamaterial in the biosensor field, a metamaterial biosensor, which consisted of metal elliptical split-ring resonator array with a subwavelength structure based on flexible thin-film (parylene-c), was presented. The structure parameters (ring width, period ratio of structure, gap width, axial ratio) of the elliptical split-ring resonator and polarization direction of incident light were investigated as to how to affect the performances of the flexible metamaterial biosensor. Meanwhile, the permittivity (ε) of the tested sample on the surface of metamaterials biosensor also affected the shift of transmission spectra. The results showed that the sensitivity, quality (Q) factor, and figure of merit (FOM) of the flexible metamaterial biosensor could reach 243 GHz/RIU, 14.2, and 3.3, respectively. Moreover, the full-width-half-maximum (FWHM) was only 82 GHz. Therefore, these results provided an improved direction to design metamaterial biosensors with high Q-factor, low FOM, and high sensitivity, which could meet the need for sample detection in the terahertz regime.

Light‐Assisted Charge Propagation in Networks of Organic Semiconductor Crystallites on Hexagonal Boron Nitride

AbstractIntroducing organic semiconductors as additional building blocks into heterostructures of 2D materials widens the horizon of their applications. Organic molecules can form self‐assembled and self‐aligned crystalline nanostructures on 2D materials, resulting in well‐defined interfaces that preserve the intrinsic properties of both constituents. Thus, organic molecules add unique capabilities to van der Waals heterostructures that have no analogues in inorganic matter. This study explores light‐assisted charge propagation in organic semiconductor networks of quasi‐1D needle‐like crystallites, epitaxially grown on insulating hexagonal boron nitride. Electrostatic force microscopy is employed to demonstrate that upon external illumination it is possible to change the conductivity of organic crystallites by more than two orders of magnitude. Furthermore, by exploiting the highly anisotropic optical properties of the organic nanoneedles, a selective charge propagation along the crystallites is triggered that matches the orientation of the molecular backbones with the incident light's polarization direction. These results demonstrate the possibility to use a “light‐gate” to switch on the conductivity of organic nanostructures and even to guide the charge propagation along desired directions in self‐assembled crystallite networks.

Study of optical rotation generated by the twisted nematic liquid crystal film: based on circular birefringence effect.

The optical behavior of twisted nematic liquid crystals (TNLCs) is revealed through an angular scanning technique. Experimental results show that the optical rotation and degree of polarization of transmitted light are dependent on the polarization direction of incident light. The optical rotation is reciprocal, i.e., the polarization direction of incident and transmitted light can reciprocate when optical rotation is π/2. In some cases, the optical rotation is zero. The orientation of alignment layers in the TN cell can be determined from the behavior of optical rotation, which agrees with the measurement by an atomic force microscope. The experimental results are explained with the model of circularly polarized light based on the circular birefringence effect. Linearly polarized incident light is the superposition of right- and left-handed circularly polarized light. The propagation velocity of circularly polarized light in the LC is relevant to the polarization direction of incident light, so that the refractive indices of left- and right-handed circularly polarized light, n- and n+, or circular birefringence Δn(=n--n+) are not constants. As a result, when a linearly polarized light with the wavelength λ propagates through a TN cell with the cell gap l, the polarization direction of transmitted light is rotated to an angle Δθ. The optical rotation Δθ(=π(n--n+)l/λ) is dependent on the polarization direction of incident light, whereas the averaged refractive index ⟨n⟩(=(n-+n+)/2) can be independent of that. The incident light is partially linearly polarized light in our experiments, so that the degree of polarization of transmitted light varies with the polarization direction of incident light because the optical rotatory rates for the primary and secondary light beams are different.

Shear strain tunable exciton dynamics in two-dimensional semiconductors

Inhomogeneous strain effects on exciton dynamics have become particularly attractive with the emergence of two-dimensional flexible semiconductors. However, a solid understanding of the shear strain effect is lacking. Here, we study tunable exciton dynamics in two-dimensional semiconductors that have inhomogeneous shear strain. The state-of-the-art first-principles calculations based on the GW plus Bethe-Salpeter equation formalism show that in monolayer molybdenum disulfide, an isotropic semiconductor, the exciton excitation energy can be dramatically tuned as an even function of shear strain with a deformation potential of $\ensuremath{-}50$ meV/1%, despite the induced anisotropy of optical absorption with respect to the polarization direction of incident light. For an anisotropic semiconductor such as phosphorene, the modulation of exciton excitation energy is found to be shear-direction dependent. The finite-element simulations further reveal a shear-induced funnel effect of excitons in a micrometer scale ${\mathrm{MoS}}_{2}$ disk. The enhanced understanding of inhomogeneous strain engineering presented in this study has the potential to be instrumental in the design of novel optoelectronic devices.

Optical polarization response at gold nanosheet edges probed by scanning near-field optical microscopy**Project supported by the National Key Basic Research Program of China (Grant No. 2013CB934004) and the Fundamental Research Funds for the Central Universities, China (Grant No. YWF-13-D2-XX-14).

Optical properties of metallic edge-like structures known as knife-edges are a topic of interest and possess potential applications in enhanced Raman scattering, optical trapping, etc. In this work, we investigate the near-field optical polarization response at the edge of a triangular gold nanosheet, which is synthesized by a wet chemical method. A homemade scanning near-field optical microscope (SNOM) in collection mode is adopted, which is able to accurately locate its probe at the edge during experiments. An uncoated straight fiber probe is used in the SNOM, because it still preserves the property of light polarization though it has the depolarization to some extent. By comparing near-field intensities at the edge and glass substrate, detected in different polarization directions of incident light, the edge-induced depolarization is found, which is supported by the finite differential time domain (FDTD) simulated results. The depolarized phenomenon in the near-field is similar to that in the far-field.