The geometric Pancharatnam-Berry (PB) phase not only is of physical interest but also has wide applications ranging from condensed-matter physics to photonics. Space-varying PB phases based on ...inhomogeneously anisotropic media have previously been used effectively for spin photon manipulation. Here we demonstrate a novel wave-vector-varying PB phase that arises naturally in the transmission and reflection processes in homogeneous media for paraxial beams with small incident angles. The eigenpolarization states of the transmission and reflection processes are determined by the local wave vectors of the incident beam. The small incident angle breaks the rotational symmetry and induces a PB phase that varies linearly with the transverse wave vector, resulting in the photonic spin Hall effect (PSHE). This new PSHE can address the contradiction between spin separation and energy efficiency in the conventional PSHE associated with the Rytov-Vladimirskii-Berry phase, allowing spin photons to be separated completely with a spin separation up to 2.2 times beam waist and a highest energy efficiency of 86%. The spin separation dynamics is visualized by wave coupling equations in a uniaxial crystal, where the centroid positions of the spin photons can be doubled due to the conservation of the angular momentum. Our findings can greatly deepen the understanding in the geometric phase and spin-orbit coupling, paving the way for practical applications of the PSHE.
The influence of the charge treatment by ultrahigh dilution (UHD) technology on oxide single crystals grown by the Czochralski technique was studied for monoclinic MgMoOsub.4 crystals doped by 1 at. ...% of Ndsup.3+ ions. The series of 10 Nd:MgMoOsub.4 crystals was grown from the charges that were subjected to UHD treatment, as well as from the charges treated with two types of control or with no special treatment at all. The grown crystals were studied by X-ray powder diffraction analysis, inductively coupled plasma atomic emission spectroscopy, mass-spectrometry, optical absorption, emission spectroscopy and luminescence kinetic analysis. We found that: (i) wetting of MgO + MoOsub.3 mixture by a water-ethanol solution before calcining leads to some enrichment of the mixture with MoOsub.3 , whereas the wetting of the charge after the calcining leads to some enrichment of it with MgO; (ii) congruent melting composition of MgMoOsub.4 crystal is in the field of some MoOsub.3 excess; (iii) the solid-phase solubility of the excess MoOsub.3 in MgMoOsub.4 probably does not depend on temperature, whereas the solid-phase solubility of the excess MgO in MgMoOsub.4 crystal depends on temperature. We suggest that the corresponding solidus line passes through the range of retrograde solubility; (iv) the crystals grown within this range are characterized by the enhanced Ndsup.3+ segregation coefficient between the crystal and the melt (approximately 0.006 versus 0.004); (v) unit cell parameters of MgMoOsub.4 crystal with the excess of MoOsub.3 are larger than those of the crystal of the stoichiometric composition and of the crystal with the excess of MgO; (vi) the shapes of the optical absorption and luminescence spectra of Nd:MgMoOsub.4 crystal do not depend on the charge treatment; (vii) luminescence decay kinetics are single-exponential for all the studied crystals, the luminescence decay time being different for the crystals grown from the charges that underwent different types of treatment; (viii) the luminescence intensity of Nd:MgMoOsub.4 crystal grown from the charge that underwent UHD treatment before calcining (solid-phase synthesis) is reduced by an order of magnitude in comparison with the other studied crystals.
Wilhelm's law of stress optics establishes the relationship between stress and refractive index in elastic birefringence effect, and the relationship between birefringence optical path difference ...(BOPD) and principal stress under uniaxial stress can be given according to it. BOPD can be measured and calculated based on photo-elastic principle and spectrometric method, and now the measurement system of BOPD has been designed and realized for getting quantitative result. In the previous research work of the laboratory, BOPD of single acrylic sample with internal stress was measured and analyzed for evaluating internal stress level, however, there were few studies involving BOPD superimposition issue. BOPD superimposition has been studied by means of the measurement system including quarter wave plate, and it not only can give BOPD result of acrylic sample but also help determine whether internal stress is tensile or compressive after uniaxial stress direction is identified. BOPD superimposition can give more useful information on internal stress. The theoretical analysis of BOPD superimposition is discussed, the verification is illustrated and the application of BOPD superimposition in acrylic sample testing is introduced in this article.
•Study the possible forms of birefringence optical path difference (BOPD) superimposition from a theoretical perspective.•Design and realize the measurement system for verification and application of BOPD superimposition.•Provide a good solution for uni-axial stress direction identification by the measurement system.•Besides BOPD result, it can also help determine the tensile and compressive properties of uni-axial stress.•Suitable for various transparent materials, such as PMMA, PVC and PE.
Following many years of evolutionary development, first at the National Synchrotron Light Source, Brookhaven National Laboratory, and then at the Advanced Photon Source (APS), Argonne National ...Laboratory, the APS ultra‐small‐angle X‐ray scattering (USAXS) facility has been transformed by several new developments. These comprise a conversion to higher‐order crystal optics and higher X‐ray energies as the standard operating mode, rapid fly scan measurements also as a standard operational mode, automated contiguous pinhole small‐angle X‐ray scattering (SAXS) measurements at intermediate scattering vectors, and associated rapid wide‐angle X‐ray scattering (WAXS) measurements for X‐ray diffraction without disturbing the sample geometry. With each mode using the USAXS incident beam optics upstream of the sample, USAXS/SAXS/WAXS measurements can now be made within 5 min, allowing in situ and operando measurement capabilities with great flexibility under a wide range of sample conditions. These developments are described, together with examples of their application to investigate materials phenomena of technological importance. Developments of two novel USAXS applications, USAXS‐based X‐ray photon correlation spectroscopy and USAXS imaging, are also briefly reviewed.
The ultra‐small‐angle X‐ray scattering (USAXS) facility at the Advanced Photon Source has been significantly upgraded to provide rapid USAXS scanning at high X‐ray energies together with associated pinhole small‐angle X‐ray scattering (SAXS) and wide‐angle X‐ray scattering (WAXS) measurements. Complete USAXS/SAXS/WAXS data can be obtained within 5 min, allowing flexible in situ and operando measurement capabilities under a wide range of conditions.
This paper considers diffeomorphism invariant theories of gravity coupled to matter, with second order equations of motion. This includes Einstein-Maxwell and Einstein-scalar field theory with (after ...field redefinitions) the most general parity-symmetric four-derivative effective field theory corrections. A gauge-invariant approach is used to study the characteristics associated to the physical degrees of freedom in an arbitrary background solution. The symmetries of the principal symbol arising from diffeomorphism invariance and the action principle are determined. For gravity coupled to a single scalar field (i.e., a Horndeski theory) it is shown that causality is governed by a characteristic polynomial of degree 6 which factorizes into a product of quadratic and quartic polynomials. The former is defined in terms of an "effective metric" and is associated with a "purely gravitational" polarization, whereas the latter generically involves a mixture of gravitational and scalar field polarizations. The "fastest" degrees of freedom are associated with the quartic polynomial, which defines a surface analogous to the Fresnel surface in crystal optics. In contrast with optics, this surface is generically nonsingular except on certain surfaces in spacetime. It is shown that a Killing horizon is an example of such a surface. It is also shown that a Killing horizon satisfies the zeroth law of black hole mechanics. The characteristic polynomial defines a cone in the cotangent space and a dual cone in the tangent space. The latter is used to define basic notions of causality and to provide a definition of a dynamical black hole in these theories.
Spherical geometry, adaptive optics, and highly dense network of neurons bridging the eye with the visual cortex, are the primary features of human eyes which enable wide field-of-view (FoV), low ...aberration, excellent adaptivity, and preprocessing of perceived visual information. Therefore, fabricating spherical artificial eyes has garnered enormous scientific interest. However, fusing color vision, in-device preprocessing and optical adaptivity into spherical artificial eyes has always been a tremendous challenge. Herein, we demonstrate a bionic eye comprising tunable liquid crystal optics, and a hemispherical neuromorphic retina with filter-free color vision, enabled by wavelength dependent bidirectional synaptic photo-response in a metal-oxide nanotube/perovskite nanowire hybrid structure. Moreover, by tuning the color selectivity with bias, the device can reconstruct full color images. This work demonstrates a unique approach to address the color vision and optical adaptivity issues associated with artificial eyes that can bring them to a new level approaching their biological counterparts.
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