Normal Reflection Research Articles

Reflectance-based non-destructive assessment of distributed feedback gratings

A new grating assessment technique has been developed based on normal reflectance measurements. The technique is capable of analysing a wide range of grating pitches and experimental results agree closely with a theoretical model. The technique is proposed as a standard tool for high precision production.

Specular optical activity in α-HgS

We report the first positive experimental observation of the optical activity effect on normal reflection. The experiment was performed along the optic axis in a gyrotropic crystal of α-HgS (cinnabar) in a spectral region of strong absorption.

Mechanical studies of the esophageal function.

The discussion centers on the use of mechanical principles, mathematical modeling, and concurrent manometric and videofluoroscopic data to study the esophageal function. Basic principles of mechanics indicate that intrabolus pressure must be distinguished from the direct contractile squeeze of the circular muscle on the manometric assembly. Because these two regions are mechanically distinct, pressure amplitude is not a proper indicator of the forces characterizing esophageal bolus transport. In the application of computer simulations to the transport of a fluid bolus through the aortic arch regions, it was discovered that separate contraction waves must exist in the upper and lower esophageal segments when bolus retention occurs. Through detailed analysis of enhanced concurrent manometric and videofluoroscopic data in human volunteers, we have found that a dual-wave characteristic across the transition zone is a normal reflection of the change in muscle types, each muscle type producing a separate contraction wave. In normal transport, these two contraction waves are properly coordinated spatially and temporally. However, during bolus retention, a mismatch in space and time between these two waves takes place. Analysis suggests that this mismatch is neurological rather than histological in origin, and occurs primarily within the lower smooth-muscle segment.

Domain size modelling in yba2cu307−δ powders and powdered single crystals by means of X-ray diffraction

Abstract YBa2Cu3O7−δ powders prepared from nitrate salts have been analysed by high-resolution powder diffraction at the Daresbury Laboratory Synchrotron Radiation Source. X-ray diffraction patterns were analysed and line profiles could be fitted by an analytical function when a ‘short’-c-axis (c = 11.69 A) tetragonal component was included in addition to the normal orthorhombic reflections. From the line profiles of the orthorhombic phase, the broadening due to strain was shown to be negligible and individual (hkl) reflections gave an indication of the size of coherently diffracting domains in a direction perpendicular to the (hkl) planes. The length of each domain-size vector was corrected for domain size and shape effeets. The domain size and shape could only be modelled successfully when the vectors from (hhl) reflections were treated separately. A rectangular parallelepiped domain of A ≈ 50 nm, B ≈ 60 nm and C ≈ 80 nm was obtained for the powder, and a domain of A ≈ 60nm, B ≈ 70nm and C ≈ 180nm for t...

Excimer laser processing for surface improvement of tin oxide thin films

Results are presented on the processing of tin oxide films using an excimer laser. Commercially available films of SnO2 deposited on glass substrates were treated using a KrF excimer laser (248 nm). The results of these treatments were characterized by normal optical absorption, transmittance, and reflectance measurements in the VIS-NIR region along with x-ray diffraction and electrical conductivity measurements and a scanning electron microscopy (SEM) study. These were compared to the nontreated samples. The results inferred a relation between the amount of photoablated material with laser fluence, up to saturation. The optical spectroscopy results and the SEM study evidence modifications of the treated surface. On the other hand, the x-ray analysis indicates that the crystal structure is not altered by the laser treatment but the film morphology is. Furthermore, an increase of 15% and better in the normalized integrated optical transmittance in the visible region was obtained with this treatment, without changing the film electrical conductivity.

A balance method of measuring birefringence for normal reflection

The measurement of the birefringence when the optic axes of the beam incident on the object and of the beam reflected from the object coincide, is considered. An instrument is described which uses balancing of the fluxes of the mutual orthogonal components of the polarization of the reflected beam. It is shown that this method suitably combined high measurement accuracy and practical simplicity.

Broken symmetry of the kinetic coefficients and specular polarization phenomena

The optical consequences of the violation of thermodynamic equilibrium in a crystal are investigated. If this violation occurs it may lead to breaking of time reversibility. As a result of this the internal symmetry of the optical susceptibility tensors changes and new ``forbidden'' tensor components arise. This gives way to some forbidden specular polarization phenomena in optics, observation of which may be used for diagnostics of the crystal equilibrium. The wave theory of normal reflection from a crystal interface including consideration of the role of the forbidden components is developed. Two mechanisms for forbidden specular polarization effects are identified, one due to the appearance of a contribution to the dielectric tensor which is antisymmetric under interchange of tensor indices, and another associated with the symmetric contribution to the nonlocal optical response. Crystal point group analysis shows that, depending on crystal class, forbidden specular polarization effects may be seen with or without a background of ``conventional'' optical activity. The physical conditions for their observation are discussed and recent polarization-sensitive experiments in optically excited GaAs crystals are explained in terms of the developed theory. It is also shown how this approach may be used for the description of time-reversal-symmetry-breaking specular optical activity in the superconducting phase of high-${\mathit{T}}_{\mathit{c}}$ cuprate materials.

Experimental observation of specular optical activity.

We report the first positive experimental observation of the optical activity effect on normal reflection. The experiment was performed along the optic axis in a gyrotropic semiconductor crystal of \ensuremath{\alpha}-HgS, cinnabar, in a spectral region of strong absorption. Reflected light polarization azimuth rotation resulting from the reflection is in the order of ${10}^{\mathrm{\ensuremath{-}}4}$ rad and has pronounced dependence on \ensuremath{\Elzxh}\ensuremath{\omega}-${\mathit{E}}_{\mathit{g}}$.

Enhanced optical detection of hydrogen using the excitation of surface plasmons in palladium

The generation of a surface plasmon wave at a palladium interface is used in the design of an all optical hydrogen sensor. Large (>90%) changes in reflected light intensity from the sensor element are observed when the sensor is exposed to hydrogen concentrations corresponding to percentage levels. This is a ten-fold enhancement of the reflectivity change observed in sensors using normal reflection from palladium.

Quasiparticle interferometer controlled by quantum-correlated Andreev reflection.

We propose a quasiparticle interferometer and give a theoretical analysis for it. It consists of a Josephson junction (JJ) and a Y junction composed of normal-electron waveguides. The interferometer should enable us to confirm experimentally the phase interaction between a quasiparticle and a superconducting state at the superconductor--normal-metal (SN) interface. This interaction is caused by Andreev reflection. The supercurrent through the JJ modifies, by Andreev reflection, the interference of a quasiparticle in the waveguide and affects the normal resistance of the waveguide. The dependence of the resistance on the phase difference of JJ is determined by the characteristics of the Y junction and the normal reflection at the SN interface.

Orientation development in injection moulded plaque of liquid crystal copolyesteramide using normal incidence specular reflection

The orientation development that takes place during injection moulding of liquid crystalline polymer (LCP) is analysed by FTi.r. specular reflection. The LCP used is the commercial Hoechst-Celanese product Vectra B900 based on terephthalic acid, p-aminophenol and 6-hydroxy 2-naphthoic acid. Dichroic ratios were measured from the 1016 cm −1 absorption band which is associated with a vibration of the 1,4-disubstituted benzene rings. The results, which are in good agreement with previous photoacoustic measurements, show that orientation is maximum along the principal axis of the mould with two significant minima of orientation located approximately at 2 and 3.2 cm from the injection gate. Furthermore, as the sample position shifts along the transverse direction towards the mould edge, there is a marked fall-off in orientation and the orientation minima occur at positions closer to the gate.

Specular optical activity in GaAs

We report the first experimental observation of light polarization plane rotation, of approximately 10 -3 rad, on normal reflection from a [001] GaAs surface. The rotation is attributed to both surface anisotropy and bulk crystal nonlocality due to violation of time-reversibility, appearing from the importance of the electron spin-orbit interaction.

Comparative Mapping of Pluto's Sub-Charon Hemisphere: Three Least Squares Models Based on Mutual Event Lightcurves

Photometric observations of Pluto-Charon transit events obtained at the University of Texas McDonald Observatory from 1985 through 1990 enable us to construct a normal reflectance map for the Charon-facing hemisphere of Pluto. We apply a least squares procedure within three separate models (spherical harmonic, polynomial, and finite element) to solve for Pluto's surface brightness distribution. A singular valve decomposition (SVD) algorithm is used to implement all of the least squares fits. The SVD method robustly indicates when pairs of fitted parameters are nearly linearly dependent. Through the computation of singular values and the covariance matrix we can thus demonstrate the linear independence of all solutions and rigorously propagate the formal uncertainties associated with the brightness value for each surface element. All three models produce similar mapping solutions showing a large, very bright region over the south pole, a dark band over the mid-southern latitudes, and a bright band over the mid-northern latitudes. Values for the normal reflectances range from 0.2 to 1.0. As the reflectance value of the higher northern latitudes is about the same as Pluto's average, we do not find evidence of a bright cap over the north polar region. We find excellent agreement with the independent map produced by M. W. Buie, D. J. Tholen, and K. Horne (1992, Icarus 97, 211-227), giving us confidence that the deconvolution of mutual event lightcurves yields a reliable resolved view of Pluto. This view allows us to begin making a physical interpretation of the evolution of Pluto's surface.

Normal ultrasonic myocardial reflectivity in hypertensive patients. A tissue characterization study.

Ultrasonic backscatter of myocardial walls is directly related to the morphometrically evaluated collagen content in humans. The integrated backscatter is also increased in hypertrophic cardiomyopathy, whereas it gives normal values in the physiological hypertrophy of elite athletes. We assessed the quantitatively evaluated myocardial reflectivity in 46 mild to moderate, clinically uncomplicated essential hypertensive patients, with echocardiographically assessed normal regional and global left ventricular function, and 22 age- and sex-matched normotensive control subjects. With an echo prototype implemented in our institute, we performed an on-line radiofrequency analysis to obtain quantitative operator-independent measurements of the integrated backscatter signal of the ventricular septum and posterior wall. The integrated values of the radiofrequency signal of myocardial walls were normalized for those of the pericardial interface and expressed as a percent (integrated backscatter index). Hypertensive patients and control subjects differed in mean blood pressure (119 +/- 11 versus 95 +/- 5 mm Hg, p < 0.001) and left ventricular mass index (134 +/- 31 versus 105 +/- 21 g/m2, p < 0.001). However, integrated backscatter index overlapped for both the septum (28 +/- 17% versus 25 +/- 6%, p = NS) and the posterior wall (13 +/- 7% versus 13 +/- 4%, p = NS). In the hypertensive group, there was no detectable correlation between septal integrated backscatter index and either septal thickness (r = -0.26, p = NS) or mean arterial pressure (r = -0.14, p = NS). Hypertensive patients showed a normal pattern of quantitatively assessed ultrasonic backscatter, even in the presence of left ventricular hypertrophy.(ABSTRACT TRUNCATED AT 250 WORDS)

A method for the measurement of reflectances of spherical surfaces

A simple procedure for the measurement of normal reflectances of curved (spherical) surfaces using a conventional double-beam spectrophotometer is developed. It requires the attachment of a suitable sample holder to the spectrophotometer and using a surface having the same radius of curvature as the sample as a reflectance reference. The procedure is especially useful for measurement of single-face reflectance of lenses, at either the convex or the concave side.

Characterization of multilayer-interfaces by X-ray diffraction, TEM, SNMS and AES

Prototypes of Ni-C multilayers (up to 40 periods of typically 5 nm thickness) have been prepared by laser pulse vapour deposition (LPVD) and analyzed by a variety of methods. The work showed near normal X-ray reflectivities of typically 5%; an interface roughness ranging from <1 A (determined by image processing of TEM micrographs) to 5 A (determined by simulation of X-ray diffraction); a compensation for the roughness component that is caused by the substrate surface and impurity concentrations <1 at.−% in layers and in interfacial regions. X-ray diffraction, transmission electron microscopy and image processing have been successfully used for the investigation of the interfacial regions, whereas depth profiling methods that involve sputtering (SNMS and AES) can not provide resolution below 10 A.

Anomalous Andreev conductance in InAs-AlSb quantum well structures with Nb electrodes.

The differential conductance of InAs-AlSb quantum wells with superconducting Nb electrodes exhibits a sharp single peak at zero bias, followed by a drop below the normal conductance at voltages an order of magnitude higher than the gap voltage, before returning to the normal value at yet higher bias. The behavior is interpreted in terms of Andreev reflections, modified by multiple normal reflections of both electrons and Andreev holes between the Nb electrodes and the bottom barrier of the quantum well, in the presence of a nonuniform potential along the well.

Experimental examination of growing and newly submerged sea ice including acoustic probing of the skeletal layer

Results of an in-situ experiment to examine acoustic parameters and scattering properties of growing and newly submerged arctic sea ice are presented. The primary emphasis is on the acoustic properties of highly porous sea ice. High-resolution (to about 1 cm) vertical profiles of the longitudinal wave speed in growing and submerged sea ice are derived from the experimental data. The results indicate a skeletal layer about 3 cm thick at the bottom of the growing ice. The time dependence of vertical sound-speed profiles in a submerged ice block reveals a long time scale process of up to 80 h and a short process of a few hours. The former process is the warming of the block; the latter is thought to be due to the disturbance of hydrostatic equilibrium as the ice is submerged. Concurrently with the wave-speed measurements, scattering from the undersurface of the ice was measured at several frequencies. A comparison with predictions based on the sound-speed data demonstrates the ability to predict normal incidence ice reflectivity from sound-speed profiles as well as the viability of using scattering data in inversions to obtain sound-speed profiles. Absorption of a longitudinal wave propagating vertically in ice was also measured. The peak absorption rate found in the skeletal layer was between 2 and 5 dB/cm at 92 kHz. The temperature dependence of absorption seen in the submerged ice suggests that the McCammon–McDaniel equation (∼T−2/3) is useful away from the skeletal layer. The measurements of ice temperature as a function of time and depth allow a calculation of the thermal diffusivity of the upper region of growing sea ice (0.0080 cm2/s) and an ‘‘effective’’ thermal diffusivity of the submerged ice block (about 0.0015 cm2/s ). Measurements of salinity profiles in the ice, along with the temperature profiles, are used to calculate porosity, which is then used in models of the longitudinal wave speed as a function of porosity. A comparison between models and experiment is employed that suggests a possible mechanism for the increased speed seen experimentally in the bottom portion of the ice after submergence.

Mimas: Photometric roughness and albedo map

Voyager imaging observations of Mimas between 6° and 132° in phase angle provide sufficient data to model such surface characteristics as large-scale roughness and directional scattering properties. We have analyzed disk-integrated and disk-resolved Voyager clear filter (0.48 μm) photometric data using a modified version of Hapke's (1986, Icarus 67, 264–280) equation which accommodates anisotropic multiple scattering. Since near-opposition observations are limited, we assume Mimas has a Rhea-like opposition surge, with angular width h = 0.066 and amplitude B o = 0.55. We find a single scattering albedo ω o = 0.951 ± 0.002 , a Henyey-Greenstein asymmetry parameter g = −0.213 ± 0.005, and a macroscopic roughness parameter θ = 30° ± 1° . The photometric roughness θ is greater than those derived in a similar manner from other bright icy satellite surfaces, though comparable to the 30° determined for Mimas by Buratti (1985, Icarus 61, 208–217) who applied the Hapke theory and the 30° ± 25° found by McEwen (1987, personal communication) who used fits to the Minnaert k parameter to evaluate θ . We find a geometric albedo p V = 0.69 ±0.05 and phase integral q = 0.78 ± 0.05, corresponding to a spherical albedo A = p V q = 0.54 ± 0.1 and a mean opposition magnitude V o = +12.62 ± 0.07. Our photometric analysis is summarized in terms of an albedo map which reproduces the satellite's observed lightcurve and indicates that normal reflectance range from 0.64 on the leading hemisphere to 0.74 on the trailing one. Reflectances at extreme southern latitudes are a few percent higher than those at corresponding northern latitudes, though in general the equatorial latitudes are brighter than the polar regions. The photometric properties show no variation across the surface or relation to any particular terrain type.

Surface modification of Venus as inferred from Magellan observations of plains

In Sedna Planitia, clear stratigraphic relations can be discerned among volcanic flow units. Young flows exhibit SAR specific cross section values similar to fresh terrestrial basalt flows, whereas older flows exhibit backscatter signatures similar to degraded terrestrial basalt flows. Total degradation of ∼1 m depth over ∼0.6 b.y. is inferred for the Sedna area from radar signatures, impact crater abundances, and ejecta superposition relations with respect to volcanic flow units. Analyses of parabolic ejecta deposits associated with the crater Stuart imply that the material is typically centimeters in thickness. A relatively small fraction (∼10%) of Venusian impact craters exhibit prominent parabolic ejecta deposits. These craters are interpreted to be relatively young and parabolic deposits are interpreted to be dispersed by aeolian activity over at least tens of millions of years. The inferred dispersal rate (&lt;10−3 μm/yr) is too low to produce the degradation of flows at Sedna Planitia, and it is concluded that the dominant flow modification process is in situ weathering. In addition, elevation dependent weathering is inferred in western Ovda Regio, where plains above 6054 km radius have enhanced reflection coefficients as compared to adjacent plains at lower elevations. The inferred rate of generation of high reflection coefficient materials is no more than ∼10−2μm/yr, based on the inability of aeolian activity to cover high‐reflectivity surfaces with normal reflection coefficient materials and the ubiquitous nature of high‐reflectivity surfaces at high elevations. Surface modification rates on Venus are orders of magnitude lower than on Earth. Venusian rates are also much lower than the inferred rate of aeolian dispersal of friable materials on Mars but are comparable to the estimated rate of weathering and erosion of Martian bedrock. Low surface modification rates imply that it will be possible to determine regional‐scale age variations on Venus based on the degree of preservation of volcanic landforms and microwave signatures.