Critical Angle For Total Reflection Research Articles

The effect of total reflection in PLIF imaging of annular thin films

Planar laser-induced fluorescence (PLIF) imaging techniques are increasingly used to study wavy annular flows in vertical and horizontal pipes. We present a ray-tracing study that analyzes the imaging properties of the PLIF technique for uniform and wavy annular films. Part of the emitted fluorescence will hit the water–air interface at angles greater than the critical angle of total reflection. As a consequence, PLIF imaging probes the film twice: From bottom to top and then again from top to bottom. Deflected fluorescence widens PLIF images of uniform films by about 30%. Surface waves further increase the contribution of deflected rays to the overall signal. At the steep slopes of large amplitude axial waves, total reflection might widen PLIF signals by up to a factor of two.

New fabrication method for an ellipsoidal neutron focusing mirror with a metal substrate.

We propose an ellipsoidal neutron focusing mirror using a metal substrate made with electroless nickel-phosphorus (NiP) plated material for the first time. Electroless NiP has great advantages for realizing an ellipsoidal neutron mirror because of its amorphous structure, good machinability and relatively large critical angle of total reflection for neutrons. We manufactured the mirror by combining ultrahigh precision cutting and fine polishing to generate high form accuracy and low surface roughness. The form accuracy of the mirror was estimated to be 5.3 μm P-V and 0.8 μm P-V for the minor-axis and major-axis direction respectively, while the surface roughness was reduced to 0.2 nm rms. The effect of form error on focusing spot size was evaluated by using a laser beam and the focusing performance of the mirror was verified by neutron experiments.

Polymer encapsulation of flexible top-emitting organic light-emitting devices with improved light extraction by integrating a microstructure

An improved efficiency from an encapsulated flexible top-emitting organic light-emitting device (FTOLED) has been demonstrated by integrating a microstructure onto the polymer encapsulation film. Soft-nanoimprint lithography is employed to integrate the microstructure onto the polymer surface, which enables large area fabrication with high quality, low cost, and repeatable use of the poly(dimethylsiloxane) mold. The light extraction of the FTOLEDs has been improved by integrating the microstructure with two-dimensional tapered micropillars array on the polymer encapsulation film, which can suppress the reflection by enhancing the critical angle of total reflection owing to its gradually changed refractive index. Moreover, the microstructured surface exhibits a hydrophobic property owing to its high contact angle, which results in a self-cleaning ability to protect the FTOLEDs from being polluted by water droplets and dust particles in practical applications.

Studying the surface reaction between NiO and Al2O3viatotal reflection EXAFS (ReflEXAFS)

The reaction between NiO and (0001)- and (1102)-oriented Al2O3 single crystals has been investigated on model experimental systems by using the ReflEXAFS technique. Depth-sensitive information is obtained by collecting data above and below the critical angle for total reflection. A systematic protocol for data analysis, based on the recently developed CARD code, was implemented, and a detailed description of the reactive systems was obtained. In particular, for (1102)-oriented Al2O3, the reaction with NiO is almost complete after heating for 6 h at 1273 K, and an almost uniform layer of spinel is found below a mixed (NiO + spinel) layer at the very upmost part of the sample. In the case of the (0001)-oriented Al2O3, for the same temperature and heating time, the reaction shows a lower advancement degree and a residual fraction of at least 30% NiO is detected in the ReflEXAFS spectra.

Design of transverse magnetic-reflected polarizing film

We propose a wideband transverse magnetic-reflected polarizing film composed of Cr and SiO2. Based on the polarization characteristics of reflected light from Cr/SiO2 film, the film can serves as a polarizer to severely attenuate the transverse electric (TE)-polarized light and reflect the transverse magnetic (TM)-polarized light in a wavelength range from 600 to 900 nm. By suitably choosing the film thicknesses, the operation angles of such polarizers can be adjusted over a wide angle range greater than the critical angle of total reflection. Cr/SiO2 film has potential use in surface plasmon resonance (SPR) sensors based on Kretchmann configuration to form integrated structures.

Quantitative Determination of Lateral Concentration and Depth Profile of Histidine-Tagged Recombinant Proteins Probed by Grazing Incidence X-ray Fluorescence

We have demonstrated that the complementary combination of grazing incidence X-ray fluorescence (GIXF) with specular X-ray reflectivity (XRR) can be used to quantitatively determine the density profiles of Ni(2)(+) ions complexed with chelator headgroups as well as S atoms in recombinant proteins anchored to lipid monolayers at the air/water interface. First, we prepared phospholipid monolayers incorporating chelator lipid anchors at different molar fractions at the air/water interface. The fine-structures perpendicular to the global plane of monolayers were characterized by XRR in the presence of Ni(2)(+) ions, yielding the thickness, roughness, and electron density of the stratified lipid monolayers. X-ray fluorescence intensities from Ni Kα core levels recorded at the incidence angles below and above the critical angle of total reflection allow for the determination of the position and lateral density of Ni(2)(+) ions associated with chelator headgroups with a high spatial accuracy (±5 Å). The coupling of histidine-tagged Xenopus cadherin 11 (Xcad-11) can also be identified by changes in the fines-structures using XRR. Although fluorescence intensities from S Kα level were much weaker than Ni Kα signals, we could detect the location of S atoms in recombinant Xcad-11 proteins.

Comparative Research on Different Solutions of a High-Performance Thin-Film Polarizing Beam Splitter

In the process of fabricating an ultra-high precision thin-film polarizing beam splitter (PBS), which is the key element in a new kind of Y-shaped cavity dual-frequency laser, low production yield is a serious problem. Based on the robust design method by controlling sensitivity of optical films to production errors, response characteristics to production errors of different kinds of PBSs are comparatively studied. By experimental study of robust design, essential determinant of sensitivity of PBSs to production errors is found to be the physical requirement that the propagation angle should be larger than the critical angle of total reflection of the interface between the substrate and outer space. By fulfilling the physical requirement, optimum incidence angle has been found by repeated robust design on different incidence angles, and a high-performance thin-film PBS with low sensitivity to production errors has been designed. The coating structure of the obtained PBS is simple and it is easy to be batch manufactured, which will make a positive impact on fabrication, engineering and application of the new Y-shaped cavity dual-frequency laser.

Grazing incidence X-ray diffraction for the study of polycrystalline layers

Different diffraction patterns measured above and below the critical angle for total reflection were recorded on a Gd doped ceria layer deposited on a Si(100) substrate in asymmetric coplanar diffraction conditions. From the analysis of diffraction patterns, it was possible to point out peculiar optical aberrations responsible for the shifts and the broadenings of Bragg peaks induced by this setup. Corrections for all these aberrations were implanted in a Rietveld programme. Using these corrections, it becomes possible to follow the evolution of the structure (chemical composition, phases) and the micro structure (strain field, micro strain due to heterogeneities between grains, size of coherent diffracting domains) versus the depth on thin films.

Laser profile reshaping in a Fabry–Perot thin film

We report the observation of non-Gaussian reflected and transmitted laser spatial profiles resulting from the excitation of resonant modes below the critical angle for total reflection in a Fabry-Perot cavity formed by a thin ~7 um air film between two glass prisms. The observations of an interference minimum in the reflected profile and exponential decay in the transmitted profile are new and in excellent agreement with a complex pole theory. Extension of the theory to a larger ~0.7 m cavity at normal incidence predicts similar reshaped profiles.

Nanoscale structures and dynamics of a boundary liquid layer

Our long term scientific interest is the understanding of the interface properties of flowingliquids on a microscopic level. Various mechanisms have been introduced to explain theorigin of slip at a solid–liquid interface like the formation of a thin depletion layeror a molecular ordering of the liquid near the interface. Reflectometry (usingx-rays or neutrons) is a powerful technique to probe structures in this surfaceregion. However, to date much less attention has been paid to the dynamicalproperties. In the first part of this paper we show that a different ordering of waterexists next to a hydrophobic substrate in comparison to a hydrophilic interface.Furthermore, we find that shear has no effect on the depletion layer on hydrophobicsubstrates, while no depletion layer exists for hydrophilic surfaces. The second partof the paper addresses the dynamical properties of the boundary layer, and wepresent a new method which enables the observation of the diffusion dynamicsof polymers next to a solid substrate. As a proof of concept, the dynamics ofmicelles next to the interface has been explored using grazing incidence neutronspin-echo spectroscopy. We were able to verify that investigation of the dynamicsof the sample is feasible with this grazing incidence technique and we presentdata taken near the critical angle of total reflection. It appears that the diffusivemotion of micelles at the hydrophobic (repulsive) interface is faster than at ahydrophilic interface or in the bulk. Furthermore, neutron spin-echo spectroscopywas extended to a first evaluation of the Doppler shift which occurs under flow.

High-frequency dynamics in the near-surface region studied by inelastic x-ray scattering: the case of liquid indium

Inelastic x-ray scattering in grazing angle geometry provides a novel tool for studying the surface and bulk lattice dynamics in a single experiment by varying the incidence angle around the critical angle of total reflection. At very small incidence angles (below the critical angle), it is possible to study the collective dynamics in a subsurface region of a few nanometres at interatomic length and time scales. An experimental study on liquid indium in the near-surface region is presented here and the results are analysed within a theoretical framework, based on classical hydrodynamics for the height–height fluctuations (capillary waves and non-propagating fluctuations) and generalized hydrodynamics for the bulk density fluctuations. The investigation reveals the presence of capillary waves in the inelastic x-ray spectra as an additional contribution at zero-energy transfer and a modification of the bulk density fluctuation contribution. A longer structural relaxation time and a larger longitudinal viscosity with respect to bulk indium are observed, similarly to related studies in confined liquids.

Goos-Hänchen-like shifts for Dirac fermions in monolayer graphene barrier

We investigate the Goos-H\"{a}nchen-like shifts for Dirac fermions in transmission through a monolayer graphene barrier. The lateral shifts, as the functions of the barrier's width and the incidence angle, can be negative and positive in Klein tunneling and classical motion, respectively. Due to their relations to the transmission gap, the lateral shifts can be enhanced by the transmission resonances when the incidence angle is less than the critical angle for total reflection, while their magnitudes become only the order of Fermi wavelength when the incidence angle is larger than the critical angle. These tunable beam shifts can also be modulated by the height of potential barrier and the induced gap, which gives rise to the applications in graphene-based devices.

Study of copper surface oxidation by grazing angle X-ray excitation

This work reports measurements of copper surface oxidation by XRF analysis under grazing angle excitation. The mathematical model for analyzing data is based on the usual equation for XRF intensity, corrected by the stratified model for the layer excitation. The final expressions are fitted to the data by using the Simplex algorithm. Three samples of silicon wafers with surface layers of copper were made by using the controlled-evaporation technique under vacuum. The final layer thicknesses were 190 Å, 400 Å, and 800 Å. For each sample, several measurements were carried out by performing an angular scan in the region of the critical angle for total reflection. Different measurements were taken immediately after evaporation, after 30 min, after 1 h, after 4 h, and after 30 min in oven at 65°. The results show small variations among the different spectra measured for each sample. The most significant variations are observed for the first measurement (after evaporation) and the last one (after the heating in oven). The mathematical model works correctly for a two-layer scheme but shows inconsistencies for more complex schemes. This indicates that the stratified model is not appropriate for continuous media due to the nature of the theoretical assumptions in which the stratified model is based. Our results show also that the surface oxidation process takes place in the first moments of exposition to air and does not progress afterwards except if the sample is heated.

Visualization of Negative Refraction in Chiral Nihility Media

Chiral nihility media are known to produce a backward wave as one of their two polarizations, yielding negative refraction at the interface of the chiral nihility medium and free space. In this paper, the analysis of chiral nihility effects is illustrated by showing the propagation of a Gaussian beam, both reflected and refracted from an air-chiral interface, and through layered chiral nihility media that are matched to free space. The critical angle for total reflection, and the index-matched total transmission in a matched chiral half-space, are demonstrated. Also demonstrated are the wave splitting, wave widening, and a wave of “standing phase” in matched chiral nihility slabs.

Polarization splitter of surface polaritons

We investigate surface polaritons (SPs) at the interface associated with anisotropic metamaterials. The existence conditions and handednesses of $s$- and $p$-polarized SPs are discussed in detail, which reveal that anisotropy is necessary for coexistence of $s$- and $p$-polarized SPs. We explore the reflection and transmission properties of SPs across the boundary separating two interfaces and then find the scaling relations that ensure the elimination of the parasite out-of-plane scattering of SPs. The reflection and transmission coefficients, the Brewster's angle, and the critical angle of total reflection are developed. We propose a compact kind of polarization SP splitter, and its functional characters can be tuned by artificially designed constitutive parameters.

Optimization of a glancing angle for simultaneous trace elemental analysis by using a portable total reflection X-ray fluorescence spectrometer

By using a portable total reflection X-ray fluorescence spectrometer with a 1 W X-ray tube, a specimen containing nanograms of Ca, Sc, Ti, V, Cr, Mn, Fe, and Ni is measured at several glancing angles of incident X-rays. Continuum X-rays are used as the excitation source. The intensities of the spectral background which degrades sensitivity to trace elements are decreased with a decrease of the glancing angle, and all these elements are detected at the glancing angle of 0.13° smaller than the critical angle for total reflection of the incident X-rays (0.20°). An optimum glancing angle for simultaneously detecting these trace elements is around 0.13°, and detection limits at 0.13° are sub-nanograms to ten nanograms.

Enhancement of Light Extraction from Organic Light-Emitting Diodes with Two-Dimensional Hexagonally Nanoimprinted Periodic Structures Using Sequential Surface Relief Grating

Electric characteristics of organic light-emitting diodes (OLEDs) with two-dimensional hexagonally nanoimprinted periodic structures were investigated, and enhanced light extraction from this device was confirmed. A master mold was fabricated from an azobenzene polymer thin film patterned by sequential surface relief grating formation into a three-directional structure. The device shows a higher current density and a higher current efficiency, although leakage current is also higher than that of a device without periodic structures. These results are caused by the extraction of diffracted light from waveguided and substrate-guided light even when incident light has larger angles than the critical angle for total reflection.

ナノシリコン層の歪み解析

A thin silicon nanooverlayer (SNOL) fabricated by oxidation and etch-back in a Separation by IMplantation of OXygen wafer was investigated by grazing incident X-ray diffraction at incident angles between 0.01° and 0.1° below the critical angle of total reflection (0.18°). We measured {220} reflections by probing the sample with respect to surface normal and found that the SNOL has finite domains under strain close to the surface. We also found that annealing the sample up to 1000°C significantly reduced inhomogeneous strain and increased the size of the domains in the surface region of the SNOL.

Combining non-specular X-ray scattering and X-ray absorption spectroscopy for the investigation of buried layers

We will present a new approach for the structural investigation of buried layers and interfaces by non-specular grazing incidence X-ray scattering. By measuring and evaluating the distinct off-specularly scattered intensities which appear for grazing angles in the vicinity of the critical angle of total reflection as a function of the X-ray photon energy in the vicinity of an X-ray absorption edge, the atomic short-range order around the X-ray absorbing atom within the surface or interface region is accessible. We will apply this new technique for the investigation of metallic bilayers consisting of about 25 nm Cu on top of 175 nm Au on a glass substrate, and show that the Cu-atoms at the Cu–air (vacuum)-interface can be separated from those at the inner Cu–Au interface in an unambiguous way.

Giant Goos-Hänchen displacement enhanced by dielectric film in frustrated total internal reflection configuration

It is predicted that the Goos-Hänchen displacement in the usual frustrated total internal reflection configuration can be resonantly enhanced greatly by coating a dielectric thin film onto the surface of the first prism when the angle of incidence is larger than the critical angle for total reflection at the prism-vacuum interface and is smaller than but close to the critical angle for total reflection at the prism-film interface. Theoretical analysis shows that the displacement of transmitted beam is about half the displacement of reflected beam in the thick limit of the vacuum gap between the two prisms. This is to be compared with the relation in the usual symmetric double-prism configuration that the displacement of transmitted beam is equal to the displacement of reflected beam. Numerical simulations for a Gaussian incident beam of waist width of 100 wavelengths reveal that when the dielectric thin film is of the order of wavelength in thickness, both the reflected and transmitted beams maintain well the shape of the incident beam in the thick limit of the vacuum gap. So largely enhanced displacements would lead to applications in optical devices and integrated optics.