Normal Reflection Research Articles

Pyroreflectometry to Determine the True Temperature and Optical Properties of Surfaces

In this paper, we present a theoretical analysis and experimental results of a pyrometric temperature measurement method based on a two-color pyroreflectometer (working wavelengths of 1.3μm and 1.55μm) equipped with an optical fiber probe. By measuring simultaneously the radiance temperature and the normal reflectivity, the true temperature of the measurement target can be determined without the previous knowledge of the optical properties of the sample. The method is based on the introduction and the definition of the diffusivity factor ηd and the assumption that it is equal for the two wavelengths. Besides the experimental results, the sources of errors and their impact on the method accuracy and the performance of the setup are discussed. The quality of the measurement results demonstrates the utility of the pyroreflectometry in a domain where fundamental parameters, such as the temperature and radiative properties, present the major measurement difficulties. The diffusivity factor appears not only a step to determine the true temperature but also as a parameter very useful to evaluate the diffusing behavior of opaque materials.

Quantum transport of injected electrons in an asymmetric FM/I1/SC/I2/FM junction: Directional dependence

We have studied the directional dependence of the spin dependent coherent quantum transport in an asymmetric nano layer FM/I1/SC/I2/FM junction. We have used the Bogoliubov-de Gennes equations to describe the quasiparticles in the different layers in the junction. The two ferromagnetic layers are taken to be the same material, while the SC is taken to be a s-wave superconductor, I1 and I2 are taken to be thin insulating layers made with different materials. Both the effects of parallel (P) and anti parallel (AP) alignments of the magnetizations in the different FM layers are studied. We find that the probabilities for the Andreev and normal reflections and for the transmission of the particles into the ferromagnetic layers are dependent on the spins. We also find that the transports of the particles injected from the left side into the FM/I1/SC/I2/FM and into the FM/I2/SC/I1/FM junctions are different. When the I1 and I2 are removed (resulting in the formation of a trilayer FM/SC/FM junction) and the thickness of the SC layer is made small, the probability for the Andreev reflection is seen to depend on the spins of the particles in contradiction to the results obtained by Bozovic and Radovic [M. Bozovic, Z. Radovic, Phys. Rev. B 66 (2002) 134524].

High frequency propagation in and scattering from water‐saturated granular sediments: Laboratory study

Acoustic properties of water‐saturated granular sediments at frequencies from 150 kHz to 8 MHz were studied in controlled laboratory conditions using broadband transducers. Two samples of medium sand sediments, with the same mean grain size, but with different width of the size distribution, were taken for the study, degassed, and their surface was flattened. Another sample of sediments was composed of glass beads of the same grain size. The main difference of glass beads from sand grains was their shape. Backscattering strength at normal and oblique incidence and reflection coefficient at normal incidence were measured for the three samples. The reflection experiments were made for different thicknesses of the samples, so that reflections from both first and second interfaces of the sediment layer were measured. This allowed also estimating sound speed and attenuation in the sediments. The results obtained for the three chosen types of the sediments were compared to demonstrate effects of the grain size distribution width and the grain shape on acoustic properties of the sediment. [Work supported by ONR and CNRS].

Experimental study of lamb mode conversions at the junction of two joined plates

In this study we are interested in a welded junction of two plates. Plates have the same thickness and are joined along their edges. Some previous theoretical studies have shown that guided Lamb waves are suitable for the characterisation of the interface between two plates [C. Scandrett and N. Vasudevan & M.V Predoi and M. Rousseau]. In a first time a junction perpendicular to the plates is experimentally investigated. Aluminum, copper and steel plates are used. Incident S0 Lamb wave is excited by a contact piezocomposite transducer and the surface displacements of the plate are detected by use of a laser vibrometer on both side of the junction. Converted waves are observed. From the measured normal surface displacements, reflection and transmission energy coefficients of the incident S0 wave through the junction are calculated. These coefficients are in a good agreement with the theoretically predicted ones. In a second time, the studied junction is not perpendicular to the plate. Experimental results are presented and compare to numerical ones obtained with the Comsol® Finite Element code.

Two-band parallel conductivity at terahertz frequencies in the superconducting state ofMgB2

The optical response of the two-band superconductor $\mathrm{Mg}{\mathrm{B}}_{2}$ has been studied in the $0.7--4\phantom{\rule{0.3em}{0ex}}\mathrm{THz}$ range on films with very low impurity level. The effect of the high-energy $\ensuremath{\sigma}$ gap is observed in the ratio ${R}_{S}∕{R}_{N}$ between the normal and superconducting state reflectance, while in a neutron irradiated film with a slightly higher impurity level, mainly the effect of the $\ensuremath{\pi}$ gap is evident, as reported in previous experiments. At terahertz frequencies, the electrodynamics of $\mathrm{Mg}{\mathrm{B}}_{2}$ can be well described by the two-band parallel conductivity model and is dominated by the $\ensuremath{\pi}$ bands when the impurity level is only slightly higher than that of an ultraclean sample.

Optical Reflectance Spectroscopy to Differentiate Renal Tumor From Normal Parenchyma

Optical spectroscopy has been evaluated as an innovative technique for the ex vivo study of renal and prostate tumors. In this pilot study we assessed the ability of optical reflectance spectroscopy to reliably differentiate tumor and normal tissue in renal specimens. From January to April 2007 we completed optical reflectance spectroscopy measurements at several standardized tumor and normal parenchymal locations immediately after kidney tumor removal. The slopes of the optical reflectance spectroscopy curves were compared, and the correlation between tumor and normal parenchyma reflectance was assessed. Reliable measurements were obtained from 13 radical and 8 partial nephrectomy specimens. Histology was malignant in 15 cases (clear cell in 14 and papillary in 1) and benign in 6 cases of oncocytoma. Overall we found a significant difference between the average optical reflectance spectroscopy slopes of tumor and normal parenchyma (p = 0.03). In individual radical nephrectomy specimens optical reflectance spectroscopy measurements at different locations in the tumor showed an excellent correlation (r = 0.968). Normal parenchymal measurements also correlated well (r = 0.88), although there was poor correlation between tumor and nontumor tissue in the specimen (r = 0.07). In the partial nephrectomy subset we also found a close correlation among measurements made on the normal parenchymal margin of the tumor (r = 0.94) except in 1 case of a positive margin (oncocytoma), in which the measurement from the positive margin site did not correlate with that of the adjacent parenchymal margin (r = 0.48). Optical reflectance spectroscopy can help distinguish tumor from normal renal tissue in specimens immediately removed at surgery. Optical reflectance spectroscopy may allow real-time assessment of positive margins during partial nephrectomy.

High-accuracy measurements of the normal specular reflectance

The French Laser Megajoule (LMJ) is designed and constructed by the French Commissariat à l'Energie Atomique (CEA). Its amplifying section needs highly reflective multilayer mirrors for the flash lamps. To monitor and improve the coating process, the reflectors have to be characterized to high accuracy. The described spectrophotometer is designed to measure normal specular reflectance with high repeatability by using a small spot size of 100 mum. Results are compared with ellipsometric measurements. The instrument can also perform spatial characterization to detect coating nonuniformity.

Stochastic anticipating boundary value problems

In this paper, we derive and study stochastic differ- ential equations with anticipating integral for function- als of diffusion processes obtained by applying second- ary quantization operators. In a special case, the sec- ondary quantization operators are conditional mathematical expectations. Suppose that { w ( t ); t ≥ 0 } is the standard Wiener process ond , G is a domain with smooth (of class C 2 ) boundary ind , and ( a ij and ( b i are, respectively, a matrix-valued and a vector-valued function three- times continuously differentiable on ; suppose also that a takes values in the set of positive definite matri- ces. Consider diffusion processes x 1 and x 2 on G which are solutions of stochastic differential equations for the process w with diffusion coefficient a and drift b under various boundary conditions, x 1 under the normal reflection conditions and x 2 under the vanishing condi- tions. For x 0 ∈ G , f ∈ C 2 ( ), g ∈ C ( ∂ G ) , and a bounded operator C in L 2 ((0; T ), � d ) with norm at most 1, con- sider the functionals

Collective response of silver islands on a dielectric substrate when normally illuminated with electromagnetic radiation

Normal reflectance measurements of silver island films, for wavelengths between 250 and 1050 nm, are inverted to obtain the effective dielectric function of the inhomogeneous films. An effective medium model is applied to evaluate the dielectric function of the metallic islands, which are modelled in terms of oblate spheroidal particles whose average values for the semiaxes have been estimated from atomic force microscopy images. Effective depolarization factors, which account for substrate effects and dipolar interactions between islands, are used in the context of the effective medium model. The dielectric function of the system of dipoles assigned to the silver island film is also obtained from an approach based on evaluating renormalized polarizabilities of the metallic islands also taking into account dipolar interparticle interactions and substrate effects.

Apparatus designed for very accurate measurement of the optical reflection

The described instrument is a new reflectometer designed to check the normal specular reflectance of 40,000 reflectors necessary for the Laser Megajoule (LMJ). This new reflectometer has a high accuracy over the 400-950 nm wavelength range and allows the delicate measurement of shaped parts. The measurements are relative and several reference mirrors, which are low loss dielectric mirrors [R(lambda)>99.9%], are used for the standardization. The apparatus gives an excellent repeatability (< 0.06% at 2sigma) thanks to its design and automatic focalization imaging system. After a brief review that is related to performance evolution of the spectrophotometers, our facility and its components are described. The methodology of focusing and calibration are explained. The capabilities of our device are illustrated through some measurements realized on flat or shaped samples.

Infrared (0.83–5.1 μm) photometry of Phoebe from the Cassini Visual Infrared Mapping Spectrometer

Three weeks prior to the commencement of Cassini's 4 year tour of the saturnian system, the spacecraft executed a close flyby of the outer satellite Phoebe. The infrared channel of the Visual Infrared Mapping Spectrometer (VIMS) obtained images of reflected light over the 0.83–5.1 μm spectral range with an average spectral resolution of 16.5 nm, spatial resolution up to 2 km, and over a range of solar phase angles not observed before. These images have been analyzed to derive fundamental photometric parameters including the phase curve and phase integral, spectral geometric albedo, bolometric Bond albedo, and the single scattering albedo. Physical properties of the surface, including macroscopic roughness and the single particle phase function, have also been characterized. Maps of normal reflectance show the existence of two major albedo regimes in the infrared, with gradations between the two regimes and much terrain with substantially higher albedos. The phase integral of Phoebe is 0.29 ± 0.03 , with no significant wavelength dependence. The bolometric Bond albedo is 0.023 ± 007 . We find that the surface of Phoebe is rough, with a mean slope angle of 33°. The satellite's surface has a substantial forward scattering component, suggesting that its surface is dusty, perhaps from a history of outgassing. The spectrum of Phoebe is best matched by a composition including water ice, amorphous carbon, iron-bearing minerals, carbon dioxide, and Triton tholin. The characteristics of Phoebe suggest that it originated outside the saturnian system, perhaps in the Kuiper Belt, and was captured on its journey inward, as suggested by Johnson and Lunine (2005).

Threading dislocations in domain-matching epitaxial films of ZnO

The structures of high-quality ZnO epitaxial films grown by pulsed-laser deposition on sapphire (0001) without an oxygen gas flow were investigated by X-ray diffraction and transmission electron microscopy. The great disparity of X-ray diffraction line widths between the normal and in-plane reflections reveals the specific threading dislocation geometry of ZnO. Most threading dislocations are pure edge dislocations. From a combination of scattering and microscopic results, it is found that threading dislocations are not uniformly distributed in the ZnO films, but the films consist of columnar epitaxial cores surrounded by annular regions of edge threading dislocations in large density. The local surface morphology and capacitance signal obtained from atomic force and scanning capacitance microscopes indicate that the aggregation of threading dislocations leads to high interface traps at the annular regions.

Direct calculation of the optical constants for a thin film using a midpoint envelope

An algebraic method to calculate the optical constants for a weakly absorbing thin film from the spectrum of normal reflectance is described. The calculation of the refractive index of the thin film is simplified by constructing a midpoint envelope through the reflection spectrum. If a portion of the spectrum includes a region where the film is nonabsorbing, the results can be used to calculate an algebraic solution for the refractive index and the absorption coefficient of the thin film throughout the entire spectrum. The method is used to determine the constants for a coating of alumina on a glass substrate. The results are compared to the calculation from the extrema of the spectrum.

In-situ optical reflectance and synchrotron X-ray topography study of defects in epitaxial dilute GaAsN on GaAs

In order to investigate the possibilities of in-situ monitoring of GaAsN bulk layer growth and the crystal quality concerning the formation of misfit dislocations, GaAsN bulk samples with different layer thicknesses were grown using a metal-organic vapor phase epitaxy system equipped with a normal incidence optical reflectance setup. High-resolution X-ray diffractometry and synchrotron radiation X-ray topography were used to characterize the samples after growth. Combining the results from topography images and in-situ reflectance data, the formation of the misfit dislocations can be roughly identified from the reflectance curves and thus observed during growth.

Simulation of applied principles of envelope functions for Fabry-Perot spectroscopy of plane wave for single-layer structures

The method to obtain analytical expressions for envelope functions in spectra of normal incidence light reflection and transmission by single-layer structures is proposed.

Use of a High-Temperature Integrating Sphere Reflectometer for Surface-Temperature Measurements

The National Institute of Standards and Technology (NIST) has developed a new facility for the characterization of the infrared spectral emissivity of samples between 150 and 1,000°C. For accurate measurement of the sample surface temperatures above 150°C, the system employs a high-temperature reflectometer to obtain the surface temperature of the sample. This technique is especially useful for samples that have significant temperature gradients due to the thermal conductivity of the sample and the heating mechanism used. The sample temperature is obtained through two measurements: (a) an indirect sample emissivity measurement with an integrating sphere reflectometer and (b) a relative radiance measurement (at the same wavelengths as in (a)) of the sample as compared to a blackbody source. The results are combined with a knowledge of the blackbody temperature and Planck’s law to obtain the sample temperature. The reflectometer’s integrating sphere is a custom design that accommodates the sample and heater to allow reflectance measurements at temperature. The sphere measures the hemispherical-near- normal (8°) reflectance factor of the sample compared relative to a previously calibrated room-temperature reference sample. The reflectometer technique of sample temperature measurement is evaluated with several samples of varying reflectance. Temperature results are compared with values simultaneously obtained from embedded thermocouples and temperature-drop calculations using a knowledge of the sample’s thermal conductivity.

Suivi d’un cas de maculopathie solaire par OCT

Solar maculopathy is caused by sun-gazing without protection and in most cases appears to be reversible. Retinal damage may be caused by photochemical changes combined with a rise in temperature at the time of sun observation. We report a case of bilateral solar retinopathy following direct sun gazing after observation of the partial eclipse on 3 October 2005. A 25-year-old Caucasian man presented 24 h after watching the eclipse with symptoms of blurred vision and a bright positive central scotoma. Total direct viewing time was approximately 5 min. While observing the eclipse, the patient kept both eyes open. On presentation, his visual acuity was 20/25 in his right eye and 20/32 in his left eye. Ophthalmoscopic examination revealed a bilateral yellowish-white spot in the center of the foveal region. Static visual field examination did not disclose any absolute scotoma but a decrease in the foveal threshold was noted in both eyes. Optical coherence tomography (OCT) examination revealed a bilateral increased reflectivity of the inner foveal retina that was greater in the left eye. This finding was associated with a hyporeflective area of the underlying retinal pigment epithelium: choriocapillaris complex and an increase in retinal thickness. Eight days later, visual acuity was 20/20 in each eye. Funduscopy showed the yellow lesion had vanished. Four months after exposure, funduscopy was normal and OCT scan showed normal reflectivity of all retinal layers in the fovea. However, static visual field examination disclosed a decreased foveal threshold on the left eye. We compare the OCT findings in this patient with the data reported in the literature. Indeed, various OCT findings have been reported depending on the intensity and frequency of sun exposure. This observation demonstrates that OCT appears to be potentially useful in the evolutive follow-up of solar maculopathy, and emphasizes the importance of eye safety during solar eclipse observation.

Statistical ray method for deriving reflection models of rough surfaces

A statistical ray method is developed for deriving reflection models of rough surfaces. Using this method, we derive generic equations of reflection due to single scattering. We have studied an isotropic surface with Gaussian statistics, and the derived bidirectional reflectance distribution function is found with four distinct regimes, namely, mirror reflection, grazing reflection, retroreflection, and normal reflection. An explicit form of self-shadowing for a surface with Gaussian statistics is also derived, and the result agrees well with computer simulation. Our solution is useful to describe the entire reflection of a highly or moderately smooth surface and offers a basis for studying multiple scattering. While focusing on optical reflection, the approach also applies to other waves if the assumptions are satisfied.

Enhanced vortex heat conductance in mesoscopic superconductors

Electronic heat transport along the flux lines in a long ballistic mesoscopic superconductor cylinder with a radius of the order of several coherence lengths is investigated theoretically using both semiclassical approach and the full quantum-mechanical analysis of the Bogoliubov--de Gennes equations. The semiclassical approach is constructed analogously to the Landauer transport theory in mesoscopic conductors employing the idea that heat is carried by the quasiparticle modes propagating along the vortex core. We show that the vortex heat conductance in a mesoscopic sample is strongly enhanced as compared to its value for a bulk superconductor; it grows as the cylinder radius decreases. This unusual behavior results from a strongly increased number of single-particle transport modes due to giant mesoscopic oscillations of energy levels, which originate from the interplay between the Andreev reflection at the vortex core boundary and the normal reflection at the sample edge. We derive the exact quantum-mechanical expression for the heat conductance and solve the Bogoliubov--de Gennes equations numerically. The results of numerical computations confirm the qualitative Landauer-type picture and allow us to take into account the partial reflections of excitations. We analyze the effect of surface imperfections on the spectrum of core excitations. We show that the giant oscillations of core levels and thus the essential features of the heat transport characteristic to ideal mesoscopic samples hold for a broad class of surface imperfections as well.

Paroxysmal positional vertigo after cochlear implantation

Conclusions. We observed 4 cases of paroxysmal positional vertigo (PPV) among 62 cochlear implant (CI) recipients. They occurred in the implanted ear without chronological relation with the surgical procedure or the implant's activation. All of them relapsed within 3 months after an initially successful repositioning maneuver, and finally recovered after the second one. None of the patients showed labyrinthine weakness in the implanted ear. The outbreak of PPV did not affect the patients’ speech perception performances. Objectives. To report and discuss the occurrence of PPV after cochlear implantation Patients and methods. Among 32 adult patients who received a Nucleus® CI, 4 suffered from PPV on the basis of Dix-Hallpike's maneuvers. After a Semont's repositioning maneuver, recurrences were similarly addressed. An electro-nystagmography (ENG) recording of caloric irrigation tests was obtained once the symptoms subsided Results. The observed incidence of 12.5% exceeds the figures reported in the literature. No anatomic abnormalities were identified in these patients, nor were any intraoperative or postoperative complications reported. PPV developed 1–12 months after CI surgery in the posterior canal and relapsed within 3 months. ENG showed a normal reflectivity in two patients, while the other two had a significant prevalence of the implanted side. The outcomes of the speech perception tests after CI in all the four patients matched those of their corresponding categories.