Showing papers on "Total internal reflection published in 2016"
20 Feb 2016
TL;DR: In this paper, it was shown that the direction of momentum fundamentally locks the polarization of evanescent electromagnetic waves, which is called spin-momentum locking, and the authors trace the origin of this phenomenon to complex dispersion and causality requirements on evanescence waves.
Abstract: We show the existence of an inherent property of evanescent electromagnetic waves: spin-momentum locking, where the direction of momentum fundamentally locks the polarization of the wave. We trace the ultimate origin of this phenomenon to complex dispersion and causality requirements on evanescent waves. We demonstrate that every case of evanescent waves in total internal reflection (TIR), surface states, and optical fibers/waveguides possesses this intrinsic spin-momentum locking. We also introduce a universal right-handed triplet consisting of momentum, decay, and spin for evanescent waves. We derive the Stokes parameters for evanescent waves, which reveal an intriguing result—every fast decaying evanescent wave is inherently circularly polarized with its handedness tied to the direction of propagation. We also show the existence of a fundamental angle associated with TIR such that propagating waves locally inherit perfect circular polarized characteristics from the evanescent wave. This circular TIR condition occurs if and only if the ratio of permittivities of the two dielectric media exceeds the golden ratio. Our work leads to a unified understanding of this spin-momentum locking in various nanophotonic experiments and sheds light on the electromagnetic analogy with the quantum spin-Hall state for electrons.
269 citations
TL;DR: Here it is discovered that not only does the beam contain orbital angular momentum but can trivially be converted to a radially polarized beam, and the Fresnel coefficients are reasonably stable across the visible spectrum, which is demonstrated by measuring white light polarization profiles.
Abstract: The reflection of light is governed by the laws first described by Augustin-Jean Fresnel: on internal reflection, light acquires a phase shift, which depends on its polarization direction with respect to the plane of incidence. For a conical reflector, the cylindrical symmetry is echoed in an angular variation of this phase shift, allowing us to create light modes with phase and polarization singularities. Here we observe the phase and polarization profiles of light that is back reflected from a solid glass cone and, in the case of circular input light, discover that not only does the beam contain orbital angular momentum but can trivially be converted to a radially polarized beam. Importantly, the Fresnel coefficients are reasonably stable across the visible spectrum, which we demonstrate by measuring white light polarization profiles. This discovery provides a highly cost-effective technique for the generation of broadband orbital angular momentum and radially polarized beams.
108 citations
TL;DR: In this article, a unified view on spin-momentum locking and how it affects optical forces on chiral and achiral particles was presented, and it was shown that the fundamental origin of optical chiral forces is spinmomental locking, where the direction of propagation is locked to the inherent polarization of the wave.
Abstract: Evanescent electromagnetic waves possess spin-momentum locking, where the direction of propagation (momentum) is locked to the inherent polarization of the wave (transverse spin). We study the optical forces arising from this universal phenomenon and show that the fundamental origin of recently reported non-trivial optical chiral forces is spin-momentum locking. For evanescent waves, we show that the direction of energy flow, the direction of decay, and the direction of spin follow a right hand rule for three different cases of total internal reflection, surface plasmon polaritons, and HE11 mode of an optical fiber. Furthermore, we explain how the recently reported phenomena of lateral optical force on chiral and achiral particles are caused by the transverse spin of the evanescent field and the spin-momentum locking phenomenon. Finally, we propose an experiment to identify the unique lateral forces arising from the transverse spin in the optical fiber and point to fundamental differences of the spin density from the well-known orbital angular momentum of light. Our work presents a unified view on spin-momentum locking and how it affects optical forces on chiral and achiral particles.
89 citations
TL;DR: In this article, the authors theoretically and experimentally investigate visco-thermal effects on the acoustic propagation through metamaterials consisting of rigid slabs with subwavelength slits embedded in air.
Abstract: We theoretically and experimentally investigate visco–thermal effects on the acoustic propagation through metamaterials consisting of rigid slabs with subwavelength slits embedded in air. We demonstrate that this unavoidable loss mechanism is not merely a refinement, but that it plays a dominant role in the actual acoustic response of the structure. Specifically, in the case of very narrow slits, the visco–thermal losses avoid completely the excitation of Fabry–Perot resonances, leading to 100% reflection. This is exactly opposite to the perfect transmission predicted in the idealised lossless case. Moreover, for a wide range of geometrical parameters, there exists an optimum slit width at which the energy dissipated in the structure can be as high as 50%. This work provides a clear evidence that visco–thermal effects are necessary to describe realistically the acoustic response of locally resonant metamaterials.
78 citations
TL;DR: In this paper, a spin-wave fiber using a magnetic domain structure with two domain walls was designed and demonstrated that such a spinwave fiber can transmit spin waves over long distances by total internal reflections, in analogy to an optical fiber.
Abstract: Spin waves are collective excitations propagating in the magnetic medium with ordered magnetizations. Magnonics, utilizing the spin wave (magnon) as an information carrier, is a promising candidate for low-dissipation computation and communication technologies. We discover that, due to the Dzyaloshinskii-Moriya interaction, the scattering behavior of the spin wave at a magnetic domain wall follows a generalized Snell's law, where two magnetic domains work as two different mediums. Similar to optical total reflection that occurs at water-air interfaces, spin waves may experience total reflection at the magnetic domain walls when their incident angle is larger than a critical value. We design a spin-wave fiber using a magnetic domain structure with two domain walls, and demonstrate that such a spin-wave fiber can transmit spin waves over long distances by total internal reflections, in analogy to an optical fiber.
64 citations
TL;DR: A simple method to achieve ∼20-nm axial resolution based on total internal reflection fluorescence (TIRF) microscopy is described and two-color imaging of epidermal growth factor ligand andClathrin revealed the dynamics of EGF-activated clathrin-mediated endocytosis during internalization.
Abstract: We report superresolution optical sectioning using a multiangle total internal reflection fluorescence (TIRF) microscope. TIRF images were constructed from several layers within a normal TIRF excitation zone by sequentially imaging and photobleaching the fluorescent molecules. The depth of the evanescent wave at different layers was altered by tuning the excitation light incident angle. The angle was tuned from the highest (the smallest TIRF depth) toward the critical angle (the largest TIRF depth) to preferentially photobleach fluorescence from the lower layers and allow straightforward observation of deeper structures without masking by the brighter signals closer to the coverglass. Reconstruction of the TIRF images enabled 3D imaging of biological samples with 20-nm axial resolution. Two-color imaging of epidermal growth factor (EGF) ligand and clathrin revealed the dynamics of EGF-activated clathrin-mediated endocytosis during internalization. Furthermore, Bayesian analysis of images collected during the photobleaching step of each plane enabled lateral superresolution (<100 nm) within each of the sections.
58 citations
Patent•
23 Feb 2016
TL;DR: In this article, an optical device including a light waves-transmitting substrate has two major surfaces and edges, optical means for coupling light into the substrate by total internal reflection, and a plurality of partially reflecting surfaces (22 a, 22 b ) carried by the substrate.
Abstract: An optical device, including a light waves-transmitting substrate has two major surfaces and edges, optical means for coupling light into the substrate by total internal reflection, and a plurality of partially reflecting surfaces ( 22 a, 22 b ) carried by the substrate. The partially reflecting surfaces ( 22 a, 22 b ) are parallel to each other and are not parallel to any of the edges of the substrate, one or more of the partially reflecting surfaces ( 22 a, 22 b ) being an anisotropic surface. The optical device has dual operational modes in see-through configuration. In a first mode, light waves are projected from a display source through the substrate to an eye of a viewer. In a second mode, the display source is shut off and only an external scene is viewable through the substrate.
55 citations
TL;DR: The use of liquid-crystal droplets as optical microcavities and lasers is reviewed and possible applications are discussed in this article, where a simple method that enable scalable production since their internal structure is formed by self-assembly is presented.
Abstract: The use of liquid-crystal droplets as optical microcavities and lasers is reviewed and possible applications are discussed. Liquid-crystal droplets are prepared by simple methods that enable scalable production since their internal structure is formed by self-assembly. Light is trapped in droplets due to total internal reflection on the surface due to refractive index mismatch or because of a photonic bandgap structure in cholesteric liquid crystals (CLCs). Light confinement gives rise to a variety of optical modes and by employing a fluorescent dye end external optical pumping, lasing can be achieved. Liquid-crystal-droplet cavities are largely tunable by applying an electric field or a temperature change. Such cavities can be used as temperature and chemical sensors, and tunable light sources and filters in future integrated soft photonic circuits.
55 citations
TL;DR: The maximum transverse shift of tunneling light through a FTIR structure with identical HMM can be significantly enlarged by more than three times which reaches −38 μm without any amplification method.
Abstract: Giant enhancement of spin Hall effect of tunneling light (SHETL) is theoretically proposed in a frustrated total internal reflection (FTIR) structure with hyperbolic metamaterial (HMM). We calculate the transverse shift of right-circularly polarized light in a SiO2-air-HMM-air-SiO2 waveguide and analyze the physical mechanism of the enhanced SHETL. The HMM anisotropy can greatly increase the transverse shift of polarized light even though HMM loss might reduce it. Compared with transverse shift of transmitted light through a single HMM slab with ZnAlO/ZnO multilayer, the maximum transverse shift of tunneling light through a FTIR structure with identical HMM can be significantly enlarged by more than three times which reaches −38 μm without any amplification method.
55 citations
TL;DR: The optimization of the length of a D-shaped plastic optical fiber sensor for refractive index (RI) sensing from a numerical and experimental point of view enables the application of this optical platform for chemical and biochemical evanescent field sensing.
Abstract: We report the optimization of the length of a D-shaped plastic optical fiber (POF) sensor for refractive index (RI) sensing from a numerical and experimental point of view. The sensing principle is based on total internal reflection (TIR). POFs with 1 mm in diameter were embedded in grooves, realized in planar supports with different lengths, and polished to remove the cladding and part of the core. All D-shaped POF sensors were tested using aqueous medium with different refractive indices (from 1.332 to 1.471) through intensity-based configuration. Results showed two different responses. Considering the refractive index (RI) range (1.33–1.39), the sensitivity and the resolution of the sensor were strongly dependent on the sensing region length. The highest sensitivity (resolution of 6.48 × 10−3 refractive index units, RIU) was obtained with 6 cm sensing length. In the RI range (1.41–1.47), the length of the sensing region was not a critical aspect to obtain the best resolution. These results enable the application of this optical platform for chemical and biochemical evanescent field sensing. The sensor production procedure is very simple, fast, and low-cost.
54 citations
TL;DR: To formulate the transmission and reflection coefficients for SV- and P-waves, an analytical model is established using thin plate theory that couples the waveguide modes with the waves in the exterior body.
Abstract: Gradient index (GRIN), refractive, and asymmetric transmission devices for elastic waves are designed using a solid with aligned parallel gaps. The gaps are assumed to be thin so that they can be considered as parallel cracks separating elastic plate waveguides. The plates do not interact with one another directly, only at their ends where they connect to the exterior solid. To formulate the transmission and reflection coefficients for SV- and P-waves, an analytical model is established using thin plate theory that couples the waveguide modes with the waves in the exterior body. The GRIN lens is designed by varying the thickness of the plates to achieve different flexural wave speeds. The refractive effect of SV-waves is achieved by designing the slope of the edge of the plate array, and keeping the ratio between plate length and flexural wavelength fixed. The asymmetric transmission of P-waves is achieved by sending an incident P-wave at a critical angle, at which total conversion to SV-wave occurs. An array of parallel gaps perpendicular to the propagation direction of the reflected waves stop the SV-wave but let P-waves travel through. Examples of focusing, steering, and asymmetric transmission devices are discussed.
05 Jun 2016
TL;DR: In this paper, the authors show the existence of an inherent handedness (spin) of evanescent-electromagnetic-waves which is fundamentally locked to the direction of propagation (momentum).
Abstract: We show the existence of an inherent handedness (spin) of evanescent-electromagnetic-waves which is fundamentally locked to the direction of propagation (momentum). It is universal and accompanies evanescent waves in total internal reflection, waveguides/fibers and surface-states.
TL;DR: A label-free microscopy technique, which can generate thousands of super-resolved, high contrast images at a frame rate of 100 Hertz and without any post-processing and is applied to living mouse macrophages and helical bacteria revealing unexpected dynamic processes.
Abstract: Living cells are highly dynamic systems with cellular structures being often below the optical resolution limit. Super-resolution microscopes, usually based on fluorescence cell labelling, are usually too slow to resolve small, dynamic structures. We present a label-free microscopy technique, which can generate thousands of super-resolved, high contrast images at a frame rate of 100 Hertz and without any post-processing. The technique is based on oblique sample illumination with coherent light, an approach believed to be not applicable in life sciences because of too many interference artefacts. However, by circulating an incident laser beam by 360° during one image acquisition, relevant image information is amplified. By combining total internal reflection illumination with dark-field detection, structures as small as 150 nm become separable through local destructive interferences. The technique images local changes in refractive index through scattered laser light and is applied to living mouse macrophages and helical bacteria revealing unexpected dynamic processes.
TL;DR: A reflection-type phase-sensitive weak measurement for biosensing and chemical label-free sensing is presented and the applicability is demonstrated by real-time monitoring biomolecular interaction of IgG and protein A.
Abstract: A reflection-type phase-sensitive weak measurement for biosensing and chemical label-free sensing is presented. The phase difference between p and s polarizations in total internal reflection caused by biomolecular recognition is measured by weak value amplification. The system with p and s polarizations in a common path is stable and robust. The sensing process occurring on the silicon dioxide surface is achieved with a resolution of 3.6×10−6 refractive index units. The applicability is demonstrated by real-time monitoring biomolecular interaction of IgG and protein A.
TL;DR: In this paper, the effect of random incidence in a diffuse field on sound transmission through double-shell composite structures with poroelastic cores is studied analytically with the focus on the effects of external mean flow.
TL;DR: This study improves the understanding of the optical mechanisms responsible for the silver color of C. bombycina and the remarkable thermoregulatory properties of the hair coat covering the ant’s body.
Abstract: The Saharan silver ant Cataglyphis bombycina is one of the terrestrial living organisms best adapted to tolerate high temperatures. It has recently been shown that the hairs covering the ant's dorsal body part are responsible for its silvery appearance. The hairs have a triangular cross-section with two corrugated surfaces allowing a high optical reflection in the visible and near-infrared (NIR) range of the spectrum while maximizing heat emissivity in the mid-infrared (MIR). Those two effects account for remarkable thermoregulatory properties, enabling the ant to maintain a lower thermal steady state and to cope with the high temperature of its natural habitat. In this paper, we further investigate how geometrical optical and high reflection properties account for the bright silver color of C. bombycina. Using optical ray-tracing models and attenuated total reflection (ATR) experiments, we show that, for a large range of incidence angles, total internal reflection (TIR) conditions are satisfied on the basal face of each hair for light entering and exiting through its upper faces. The reflection properties of the hairs are further enhanced by the presence of the corrugated surface, giving them an almost total specular reflectance for most incidence angles. We also show that hairs provide an almost 10-fold increase in light reflection, and we confirm experimentally that they are responsible for a lower internal body temperature under incident sunlight. Overall, this study improves our understanding of the optical mechanisms responsible for the silver color of C. bombycina and the remarkable thermoregulatory properties of the hair coat covering the ant's body.
Patent•
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09 Mar 2016
TL;DR: In this article, a lamp for a vehicle, comprising a light source and an optical waveguide formed on a front side of the light source so as to increase an efficiency of a total reflection of light.
Abstract: The present invention relates to a lamp for a vehicle, comprising a light source, and an optical waveguide formed on a front side of the light source so as to increase an efficiency of a total reflection of light. The optical waveguide comprises: a light incident surface wherein light of the light source is penetrated; a refracting surface to change a light path which penetrates through the light incident surface; a total reflection surface wherein the light incident surface-penetrated light is totally reflected; and a light distribution surface formed on an end unit of the total reflection surface. The vehicle identification is able to easily be delivered to a pedestrian and a driver by increasing optical efficiency.
TL;DR: It is shown that the fabricated sensor has strong interference visibility exceeding 15 dB over a wide measurement range of RI, and the sensor sensitivity is higher than 1160 nm/RIU, and RI resolution is better than 1.0 × 10−6 RIU.
Abstract: In this study, a new type of highly sensitive fiber-optic Fabry–Perot interferometer (FFPI) is proposed with a high sensitivity on a wide refractive index (RI) measurement range based on internal reflection mirrors of micro-cavity. The sensor head consists of a single-mode fiber (SMF) with an open micro-cavity. Since light reflections of gold thin films are not affected by the RI of different measuring mediums, the sensor is designed to improve the fringe visibility of optical interference through sputtering the gold films of various thicknesses on the inner surfaces of the micro-cavity, as a semi-transparent mirror (STM) and a total-reflection mirror (TRM). Experiments have been carried out to verify the feasibility of the sensor’s design. It is shown that the fabricated sensor has strong interference visibility exceeding 15 dB over a wide measurement range of RI, and the sensor sensitivity is higher than 1160 nm/RIU, and RI resolution is better than 1.0 × 10−6 RIU.
TL;DR: A rigorous coupled wave analysis of black silicon is presented, where the black silicon needle shaped structure is approximated by a randomized cone structure, and the simulated absorptance agrees well with measurement data.
Abstract: Due to their low reflectivity and effective light trapping properties black silicon nanostructured surfaces are promising front side structures for thin crystalline silicon solar cells. For further optimization of the light trapping effect, particularly in combination with rear side structures, it is necessary to simulate the optical properties of black silicon. Especially, the angular distribution of light in the silicon bulk after passage through the front side structure is relevant. In this paper, a rigorous coupled wave analysis of black silicon is presented, where the black silicon needle shaped structure is approximated by a randomized cone structure. The simulated absorptance agrees well with measurement data. Furthermore, the simulated angular light distribution within the silicon bulk shows that about 70% of the light can be subjected to internal reflection, highlighting the good light trapping properties.
TL;DR: In this article, the authors examined the sudden drop in properties of aluminum, titanium and chromium thin films prepared by the glancing angle deposition method and found that the critical point is around 60° for all metallic materials and a critical angle of 60° is also found for the residual stress.
TL;DR: In this paper, the reflection coefficients of plane qP waves are derived in terms of the angle of incidence, the elastic, electric and thermal parameters of the medium, as well as the thermal relaxation times.
Abstract: In this paper, the well-established two-dimensional mathematical model for linear pyroelectric materials is employed to investigate the reflection of waves at the boundary between a vacuum and an elastic, transversely isotropic, pyroelectric material. A comparative study between the solutions of (a) classical thermoelasticity, (b) Cattaneo–Lord–Shulman theory and (c) Green–Lindsay theory equations, characterised by none, one and two relaxation times, respectively, is presented. Suitable boundary conditions are considered in order to determine the reflection coefficients when incident elasto–electro–thermal waves impinge the free interface. It is established that, in the quasi-electrostatic approximation, three different classes of waves: (1) two principally elastic waves, namely a quasi-longitudinal Primary (qP) wave and a quasi-transverse Secondary (qS) wave; and (2) a mainly thermal (qT) wave. The observed electrical effects are, on the other hand, a direct consequence of mechanical and thermal phenomena due to pyroelectric coupling. The computed reflection coefficients of plane qP waves are found to depend upon the angle of incidence, the elastic, electric and thermal parameters of the medium, as well as the thermal relaxation times. The special cases of normal and grazing incidence are also derived and discussed. Finally, the reflection coefficients are computed for cadmium selenide observing the influence of (1) the anisotropy of the material, (2) the electrical potential and (3) temperature variations and (4) the thermal relaxation times on the reflection coefficients.
TL;DR: In this article, the authors studied the propagation of optical pulses inside temporal waveguides, both analytically and numerically, and showed that the waveguide supports a finite number of temporal modes.
Abstract: Temporal total internal reflection (TIR), in analogy to the conventional TIR of an optical beam at a dielectric interface, is the total reflection of an optical pulse inside a dispersive medium at a temporal boundary across which the refractive index changes. A pair of such boundaries separated in time acts as the temporal analog of planar dielectric waveguides. We study the propagation of optical pulses inside such temporal waveguides, both analytically and numerically, and show that the waveguide supports a finite number of temporal modes. We also discuss how a single-mode temporal waveguide can be created in practice. In contrast with the spatial case, the confinement can occur even when the central region has a lower refractive index.
TL;DR: In this paper, the interplay between angular and lateral Goos-Haenchen shift of a focused He-Ne laser beam for incidence near the critical angle was investigated.
Abstract: By using a weak measurement technique, we investigated the interplay between the angular and lateral Goos-Haenchen shift of a focused He-Ne laser beam for incidence near the critical angle. We verified that this interplay dramatically affects the composite Goos-Haenchen shift of the propagated beam. The experimental results confirm theoretical predictions that recently appeared in the literature.
TL;DR: In this paper, the divergence problem at critical angle is overcome and a closed Artmann formula in terms of modified Bessel functions of the first kind is presented. But the results obtained in this study clearly show the Goos-H\"anchen lateral displacement dependence on the angular distribution shape of the incoming beam.
Abstract: The Artmann formula provides an accurate determination of the Goos-H\"anchen lateral displacement in terms of the light wavelength, refractive index, and incidence angle. In the total reflection region, this formula is widely used in the literature and confirmed by experiments. Nevertheless, for incidence at critical angle, it tends to infinity and numerical calculations are needed to reproduce the experimental data. In this paper, we overcome the divergence problem at critical angle and find, for Gaussian beams, a closed formula in terms of modified Bessel functions of the first kind. The formula is in excellent agreement with numerical calculations and reproduces, for incidence angles greater than critical ones, the Artmann formula. The closed form also allows one to understand how the breaking of symmetry in the angular distribution is responsible for the difference between measurements done by considering the maximum and the mean value of the beam intensity. The results obtained in this study clearly show the Goos-H\"anchen lateral displacement dependence on the angular distribution shape of the incoming beam. Finally, we also present a brief comparison with experimental data and other analytical formulas found in the literature.
TL;DR: In this article, the effect of an internal air gap flow on acoustic transmission across double-wall sandwich shells with poroelastic materials is analyzed in terms of the random incidence transmission loss in a diffuse field and the limiting angle of incidence due to total internal reflection.
TL;DR: An in-fiber interferometer based on a gas-filled hollow-core photonic crystal fiber and refractive index resolution is described, and values are experimentally measured and theoretically validated using mode field calculations.
Abstract: We describe an in-fiber interferometer based on a gas-filled hollow-core photonic crystal fiber. Expressions for the sensitivity, figure of merit and refractive index resolution are derived, and values are experimentally measured and theoretically validated using mode field calculations. The refractive indices of nine monoatomic and molecular gases are measured with a resolution of δns < 10−6.
27 Sep 2016
TL;DR: In this article, the evanescent wave in a total internal reflection setup coupled with a conductive interface was used to enhance the attenuation efficiency of terahertz (THz) light.
Abstract: Efficient methods to modulate terahertz (THz) light are essential for realizing rapid THz imaging and communication applications. Here we report a novel THz modulator which utilizes the evanescent wave in a total internal reflection setup coupled with a conductive interface to enhance the attenuation efficiency of THz light. This approach makes it possible to achieve close to 100% modulation with a small interface conductivity of 12 mS. The frequency dependence of this technique is linked to the optical properties of the materials: a material with close to frequency independent conductivity that is also controllable will result in an achromatic modulation response, and the device performance can be optimized further by tuning the internal reflection angle. In this work, we focus on applying the technique in the terahertz frequency range. Using an LED array with a pump intensity of 475 mW/cm2 to produce carriers in a silicon wafer, we have achieved a modulation depth of up to 99.9% in a broad frequency ran...
TL;DR: The increase of resolution by theUse of microspheres is related to the use of evanescent waves satisfying complex Snell's law with complex trigonometric functions related toThe incident and refracted angles, while the refractive indices are real.
Abstract: The increase of resolution by the use of microspheres is related to the use of evanescent waves satisfying complex Snell’s law with complex trigonometric functions related to the incident and refracted angles, while the refractive indices are real. The evanescent waves are obtained in addition to initial propagating waves satisfying the ordinary Snell’s law. The lateral spatial wave vectors of the evanescent waves, which include information on the object fine structures, are converted at the microsphere surface to smaller wave vectors. Due to the reduction in the magnitudes of the spatial wave vectors of the evanescent waves, they become propagating waves including the fine structures which are recovered in the image plane.
TL;DR: A distinct optical manipulation scheme using the attenuated modes in subwavelength optical channels, where both the trapping and transportation forces are along the channel direction, and can overcome the Brownian motion within a critical length.
Abstract: Optical evanescent wave in total internal reflection has been widely used in efficient optical manipulation, where the object is trapped by the intrinsic intensity gradient of the evanescent wave while transported by the scattering force along the orthogonal direction. Here, we propose a distinct optical manipulation scheme using the attenuated modes in subwavelength optical channels, where both the trapping and transportation forces are along the channel direction. We create such a mode in a sub-wavelength photonic crystal waveguide and quantitatively obtain the net pushing and pulling forces, which can overcome the Brownian motion within a critical length. Due to the presence of the physical channel, subwavelength trapping on the transverse direction is natural, and manipulation along bend trajectories is also possible without the assistance of the self-acceleration beams provided a channel is adopted. This optical manipulation method can be extended to any other channels that support attenuation mode, and may provide an alternate way for flexible optical manipulation.
TL;DR: The use of grazing-incidence X-ray diffraction to determine the crystal structure from thin films requires accurate positions of Bragg peaks to correct refraction effects and multiple scattering events.
Abstract: Dynamical scattering effects are observed in grazing-incidence X-ray diffraction experiments using an organic thin film of 2,2′:6′,2′′-ternaphthalene grown on oxidized silicon as substrate. Here, a splitting of all Bragg peaks in the out-of-plane direction (z-direction) has been observed, the magnitude of which depends both on the incidence angle of the primary beam and the out-of-plane angle of the scattered beam. The incident angle was varied between 0.09° and 0.25° for synchrotron radiation of 10.5 keV. This study reveals comparable intensities of the split peaks with a maximum for incidence angles close to the critical angle of total external reflection of the substrate. This observation is rationalized by two different scattering pathways resulting in diffraction peaks at different positions at the detector. In order to minimize the splitting, the data suggest either using incident angles well below the critical angle of total reflection or angles well above, which sufficiently attenuates the contributions from the second scattering path. This study highlights that the refraction of X-rays in (organic) thin films has to be corrected accordingly to allow for the determination of peak positions with sufficient accuracy. Based thereon, a reliable determination of the lattice constants becomes feasible, which is required for crystallographic structure solutions from thin films.