Spin-orbit coupling induced interference in quantum corrals

Lack of inversion symmetry at a metallic surface can lead to an observable spin-orbit interaction. For certain metal surfaces, such as the Au(111) surface, the experimentally observed spin-orbit coupling results in spin rotation lengths on the order of tens of nanometers, which is the typical length scale associated with quantum corral structures formed on metal surfaces. In this work, multiple scattering theory is used to calculate the local density of states (LDOS) of quantum corral structures composed of nonmagnetic adatoms in the presence of spin-orbit coupling. Contrary to previous theoretical predictions, spin-orbit coupling induced modulations are observed in the theoretical LDOS, which should be observable using scanning tunneling microscopy.     

Wide-angle stray-light reduction for a spaceborne optical hemispherical imager

We describe a simple visible-light stray-background-reducing baffle, suitable for use on a stabilized interplanetary platform. The design is a corrallike enclosure with five concentric walls. The baffle reduces direct sunlight and reflections from illuminated portions of the spacecraft by a factor of 10(-12), provided that all these lie beyond at least a hemisphere centered on the viewing aperture. With this condition these bright sources do not directly illuminate within the outermost wall of the corral, and diffraction over the wall tops is the dominant mechanism by which light reaches the corral interior. We present design calculations for such a corral, as well as a laboratory measurement confirming the basic design assumption.     

Quasicrystal Photonic Metasurfaces for Radiation Controlling of Second Harmonic Generation

Photonic metasurfaces, a kind of 2D structured medium, represent a novel platform to manipulate the propagation of light at subwavelength scale. In linear optical regime, many interesting topics such as planar meta‐lenses, metasurface optical holography, and so on have been widely investigated. Recently, metasurfaces have gone into the nonlinear optical regime. While it is recognized that the local symmetry of the meta‐atoms plays a vital role in determining the polarization, phase, and intensity of the nonlinear waves, much less attention has been paid to the global symmetry of the nonlinear metasurfaces. According to the Penrose tiling and the newly proposed hexagonal quasicrystalline tiling, nonlinear optical quasicrystal metasurfaces are designed and fabricated based on the geometric‐phase‐controlled plasmonic meta‐atoms with local rotational symmetry. It is found that the far‐field radiation behavior of second harmonic generation waves are determined by both the tiling schemes of quasicrystal metasurfaces and the local symmetry of meta‐atoms they consist of. The proposed concept may open new avenues for designing nonlinear optical sources with metasurface crystals.     

Experimental confirmation of the transversal symmetry breaking in laser profiles

The Snell phase effects on the propagation of optical beams through dielectric blocks have been matter of recent theoretical studies. The effects of this phase on the laser profiles have been tested in our experiment. The data show an excellent agreement with the theoretical predictions confirming the axial spreading modification and the transversal symmetry breaking. The possibility to set, by rotating the dielectric blocks, different configurations allows to recover the transversal symmetry. Based on this experimental evidence, dielectric blocks can be used as alternative optical tools to control the beam profile.     

A parity-time symmetry single-mode laser based on graphene

The development of advanced optical systems, especially coherent optical systems demands high-performance single-mode lasers. Here, we proposed a parity-time symmetry single-mode laser based on graphene with superior performance over the widely utilized technologies of the index-coupled DFB laser working at telecommunication wavelength. The unique properties of graphene have been used to tune the III-V/Silicon hybrid laser to the PT symmetry broken phase where the lasing mode has a minimum overlap with graphene nanostructures while all other modes have been suppressed by the loss in graphene. Our results suggest a high-performance silicon-based laser source for photonic integrated circuits. Such a compact single-mode laser source can be widely used in some applications, such as on-chip optical interconnects, optical spectrometry, biochemical sensing and imaging.     

Decentred elliptical flat-topped light beams and their coherent and incoherent combinations

A new kind of laser beam called the decentred elliptical flat-topped light beam (DEFTB) is introduced in this paper by using a tensor method. Based on the generalized Collins integral, the propagation formula for a DEFTB passing through an axially nonsymmetrical paraxial optical system is derived through vector integration. The derived formula can be reduced to the formulae for the generalized decentred elliptical Gaussian beam and elliptical flat-topped light beam under certain conditions. As a typical application example of the derived formula, the propagation characteristics of a DEFTB in a thin lens system are calculated and discussed. Furthermore, the generalized laser beam arrays with rectangular symmetry and radial symmetry by using DEFTBs as fundamental modes are constructed and the propagation properties of both a coherent and an incoherent combination of DEFTBs in the thin lens system with numerical examples are investigated.     

Temporal coupled-mode theory for the Fano resonance in optical resonators

We present a theory of the Fano resonance for optical resonators, based on a temporal coupled-mode formalism. This theory is applicable to the general scheme of a single optical resonance coupled with multiple input and output ports. We show that the coupling constants in such a theory are strongly constrained by energy-conservation and time-reversal symmetry considerations. In particular, for a two-port symmetric structure, Fano-resonant line shape can be derived by using only these symmetry considerations. We validate the analysis by comparing the theoretical predictions with three-dimensional finite-difference time-domain simulations of guided resonance in photonic crystal slabs. Such a theory may prove to be useful for response-function synthesis in filter and sensor applications.     

Quantum manipulation via atomic-scale magnetoelectric effects

Magnetoelectric effects at the atomic scale are demonstrated to afford unique functionality. This is shown explicitly for a quantum corral defined by a wall of magnetic atoms on a metal surface where spin-orbit coupling is observable. We show these magnetoelectric effects allow one to control the properties of systems placed inside the corral as well as their electronic signatures; they provide powerful alternative tools for probing electronic properties at the atomic scale.     

The electronic structure of capped and uncapped CdS nanoparticles

The electronic structure of spherical Cd(m),S(n) nanoparticles having zinc-blende symmetry and the diameters of up to around 3 nm has been studied by Hartree-Fock theory to find out the effect of the cluster size on the optical energy gap between HOMO and LUMO. The effect of encapsulation on the electronic structure has been also investigated for CdS4 and Cd13S4 clusters embedded in SiO2 matrix and sodalite cage by Hartree-Fock theory. It was found that the energy gap of CdS nanoparticles can be regulated by both the cluster size and the interface provided by the SiO2 matrix and sodalite cage. The energy gap between HOMO and LUMO has been found to be increased to upper boundary of the visible spectra when CdS4 and Cd13S4 clusters have been embedded in either SiO2 matrix or sodalite cage.     

Excited-state absorption of meso-tetrasulfonatophenyl porphyrin: Effects of pH and micelles

The influence of the environment on the excited state transitions of meso-tetrakis(p-sulfonatophenyl) porphyrin (TPPS) is reported. TPPS was investigated in protonated and non-protonated forms, and in the presence of the cationic cetyltrimethylammonium bromide (CTAB) micelles. The singlet excited-state absorption spectra were measured by using the white-light continuum Z-scan technique and the triplet–triplet absorption spectra were acquired employing an association of laser flash photolysis and Z-scan techniques. Our results show that the perseveration of the molecular symmetry, upon excitation, depends on the state of multiplicity of the molecules, as well as on the environment and structural characteristics of the porphyrin. Additionally, it was observed that for excited molecules, the ring distortion caused by the protonation of porphyrin ring has great influence on the changes observed for the symmetry and vibronic structure. The results clearly show that the porphyrin investigated is a promising candidate for optical limiting applications for all investigated environments.     

Correlation between optical and topographical images from an external reflection near-field microscope with shear force feedback

An external reflection scanning near-field optical microscope with shear force regulation of the tip-surface distance is described. Near-field optical and shear force topographical images are compared for various samples. It is shown that the most important correlative relationships between these images can be deduced from symmetry considerations. The possibility of extracting additional information from the optical images is demonstrated on images of human blood cells.     

Preparation of TiO2 nanoparticles by using tripodal tetraamine ligands as complexing agent via two-step sol–gel method and their application in dye-sensitized solar cells

The effect of different tripodal tetraamine ligands was investigated on the particle size, agglomeration level, optical and photovoltaic properties of TiO₂ nanoparticle prepared via a two-step sol–gel method. The products were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), transmission electron spectroscopy (TEM), scanning electron microscopy (SEM), and UV–vis spectroscopy. The results showed that the symmetry of ligands has a crucial effect on the size and agglomeration level of the products. The optical and photovoltaic properties of the products were studied, as well. The reflectivity property of the samples due to different agglomeration sizes is shown to be very important factor in increasing conversion efficiency of DSSC.     

Thermoelastic Fields in Sapphire

The temperature and thermoelastic fields in growth systems are considered theoretically in order to assess their effect on the optical symmetry of the growing crystal. The process is modeled using three-dimensional curvilinear coordinates to describe a closed, low-strain thermoelastic system, with allowance made for the temperature variations of the thermal properties of the multilayer growth system and nonlinear and unsteady-state processes with arbitrary boundary conditions. The results, presented as plots of the strain, stress, displacement, and temperature fields, demonstrate the potential of the method for designing new growth units and improving the existing ones and suggest that crystals without frustration of optical symmetry can, in principle, be grown.     

Nonlinear Optical Properties of Correlated Chromophores in Organic Mesoscopic Superstructures

A new design strategy for enhanced nonlinear optical properties, based on a simple vector model and situated at the mesoscopic level, between the microscopic molecular level and the macroscopic bulk, is explained and exemplified by a number of organic superstructures. The second-order nonlinear optical properties of the structures are analyzed in terms of the corresponding properties of the individual monomeric chromophores that constitute the structure. The chromophores can be considered as electronically independent with a high symmetry. A simple vector model can then account for the large secondorder nonlinear optical polarizability of the mesoscopic superstructure. Another important advantage that is clear from the vector analysis is the improved chromophore alignment, owing to the enlarged mesoscopic dipole moment.     

Experimental evaluation of the isotropy of large masses of continuous media and gauges for such measurement

The structure of the optical pattern in holes of photoelastic ring gauges is discussed briefly. The two symmetry axes of this pattern in rigid stress gauges coincide with the directions of the quasiprincipal stresses in the plane of measurements while in soft gauges the deformations of the symmetry axis of the optical pattern coincide with the directions of the quasiprincipal strains. According to the general propositions of the theory of elasticity in Isotropic media the stress tensors and the strain tensors are coaxial, whereby photoelastic ring gauges can be used to evaluate the isotropy of solid media.Translated from Izmeritel'naya Tekhnika, No. 6, pp. 30–32, June, 1994.     

IR determination of the orientation of molecules in polycrystalline monolayers

A theoretical treatment of the absorption of linearly polarized IR radiation by organic monolayers is given. The present approach applies to polycrystalline monolayers and enables the determination of the microcrystalline orientation and the molecular orientation inside the microcrystals.This model is quite general and can be used to calculate the optical absorption of polycrystalline thin films, irrespective of the symmetry of the microcrystals.     

Transversal symmetry breaking and axial spreading modification for gaussian optical beams

For a long time, it was believed there was no reason to include the geometrical phase in studying the propagation of gaussian optical beams through dielectric blocks. This can be justified by the fact that the first-order term in the Taylor expansion of this phase is responsible for the lateral shift of the optical beam which is also predicted by ray optics. From this point of view, the geometrical phase can be seen as a purely auxiliary concept. In this paper, we show how the second-order term in the Taylor expansion accounts for the symmetry breaking of the transversal spatial distribution and acts as an axial spreading modifier. These new effects clearly show the importance of the geometrical phase in describing the correct behavior of light. To test our theoretical predictions, we briefly discuss a possible experimental implementation.     

Symmetry considerations in CdSe nanocrystals

Semiconductor nanocrystals or quantum dots show a wide range of physical properties depending on their size or shape. In this paper, we show that symmetry is also an important characteristic that can lead to different electronic and optical properties. We use pseudopotential density-functional theory, within a real space approach, and address the sensitivity of electronic and optical properties with respect to the symmetry point groups associated to CdSe nanocrystals.     

Two-beam interferometer for measuring aberrations of optical components with axial symmetry

We present a concept of interferometric testing, believed to be novel, that can be applied to measuring aberrations of optical components that have rotational symmetry. The optical configuration uses two coherent, collimated wave fronts that are tilted to impinge upon the optical component being tested such that one beam is on axis and the other is off axis. For small tilt angles the two aberrated wave fronts can be considered to be carrying the same aberrations. Furthermore, the off-axis beam is displaced along a direction orthogonal to the optical axis of the component. Interference between the two aberrated wave fronts produces a fringe pattern that is similar to a lateral shear interference pattern. Moiré fringes are obtained by spatial beating of the interference pattern with a CCD TV camera array. Under such conditions it is possible to subtract most of the linear carrier that is intrinsically present in the resultant fringe pattern owing to the large defocus aberration and tilt.     

Chiral Assemblies of Laser-Printed Micropillars Directed by Asymmetrical Capillary Force

Artificial microstructures composed of chiral building blocks are of great significance in the fields of optics and mechanics. Here, it is shown that highly ordered chiral structures can be spontaneously assembled by a meniscus-directed capillary force arising in an evaporating liquid. The chirality is facilitated by rationally breaking the intrinsic symmetry in the unit cells through cooperative control of the geometry and spatial topology of the micropillars. The interfacial dynamics of the assembly process are studied to show that the sequential self-organization of the micropillars is influenced by the geometries, stiffness, and spatial arrangements. A diversity of chiral assemblies with controlled handedness is yielded by varying the pillar number, height, cross-section, laser power, and spatial topology. Lastly, the differential reflectance of light carrying opposite orbital angular momentums on the assembled chiral architectures are investigated, showcasing their potential in the field of chiral photonics concerning enantioselective response and exceptional optical functions.