Search results for "reflectivity"
showing 10 items of 130 documents
Dependence of polytetrafluoroethylene reflectance on thickness at visible and ultraviolet wavelengths in air
2020
[EN] Polytetrafluoroethylene (PTFE) is an excellent diffuse reflector widely used in light collection systems for particle physics experiments. However, the reflectance of PTFE is a function of its thickness. In this work, we investigate this dependence in air for light of wavelengths 260 nm and 450 nm using two complementary methods. We find that PTFE reflectance for thicknesses from 5 mm to 10 mm ranges from 92.5% to 94.5% at 450 nm, and from 90.0% to 92.0% at 260 nm We also see that the reflectance of PIFE of a given thickness can vary by as much as 2.7% within the same piece of material. Finally, we show that placing a specular reflector behind the PTFE can recover the loss of reflectan…
Effect ofA-site andB-site substitution on the infrared reflectivity spectra ofLa1−yAyMn1−xBxO3(A=Ba,Sr;B=Cu,Zn,Sc;0<y<~0.3;0<~x<~0.1)mang…
2003
We have measured the infrared reflectivity spectra of ${\mathrm{La}}_{1\ensuremath{-}y}[\mathrm{Sr}(\mathrm{Ba}){]}_{y}{\mathrm{Mn}}_{1\ensuremath{-}x}[\mathrm{Cu}(\mathrm{Zn},\mathrm{Sc}){]}_{x}{\mathrm{O}}_{3}$ $(0lyl~0.3,0l~xl~0.10)$ manganites, in a wide frequency $(100\char21{}4000{\mathrm{cm}}^{\ensuremath{-}1})$ and temperature (80 K\char21{}300 K) range. The reflectivity spectra were analyzed by a fitting procedure based on a model that includes Drude, midinfrared electronic, and phonon oscillator contributions to the dielectric constant. Six infrared active ${(3A}_{u}$ and ${3E}_{u})$ modes of rhombohedral symmetry are clearly observed. We assigned all observed modes according to e…
Unraveling exciton dynamics in amorphous silicon dioxide: Interpretation of the optical features from 8 to 11 eV.
2011
Physical review / B 83, 174201 (2011). doi:10.1103/PhysRevB.83.174201
Risken–Nummedal–Graham–Haken instability in class-B lasers
1999
We determine analytical expressions for the Risken-Nummedal-Graham-Haken multimode laser instability outside the uniform field limit in the case of very fast polarization decay (class-B laser). A new condition for the observability of that instability, concerning the value of the cavity mirrors reflectivity, is predicted.
Echographic patterns of an orbital myxoma and schwannoma
1988
A case of intramuscular orbital myxoma and of a schwannoma of the orbit were studied with B-scan and standardized A-scan echography as described by Ossoinig. The myxoma appeared as a well outlined process with medium internal reflectivity and areas of low internal reflectivity. Postoperatively the incompletely excised tumour was followed with echography as well as CT and MRI. The second tumour, a schwannoma had a very sharply defined shape, with a thick low to medium reflective outer wall and low internal reflectivity. This corresponds to the Antoni A and Antoni B patterns of the excised tumour.
Simulation of skin reflectance images using 3D tissue modeling and multispectral Monte Carlo light propagation.
2008
In this work we propose a method to simulate the expected, i.e. seen by a camera, multispectral reflectance images of a large skin surface area by combining Monte Carlo light propagation model and realistic tissue modeling based on three dimensional data acquisition of human body areas. In particular, we aim to simulate more accurately light transport in biological tissue by taking into account the geometrical topography of the skin surface, the structure and optical properties of the skin layers, and the subcutaneous veins in presence. We describe our computation method in detail and present simulated reflectance images results.
Carbon coatings for soft-x-ray reflectivity enhancement
2007
In X-ray astronomical telescopes, the focalization of the radiation is achieved by means of grazing incidence Wolter I (parabola + hyperbola) optics in total reflection regime. In general, high density materials (e.g. Au, Pt, Ir, W) are used as reflecting coatings, in order to increase as much as possible the cut-off angles and energies for total reflection. However these materials present an important reduction of the reflectivity between 0.2 and 5 keV, due to the photoabsorption, and this phenomenon is particularly enhanced in correspondence of the M absorption edges (between 2 and 3.5 keV). In general, this determines a strong decrease of the telescope effective area. To overcome the pro…
Semilinear photorefractive oscillator with reflection gratings
2003
We present results of calculation of the steady-state output characteristics for a semilinear photorefractive oscillator pumped with two independent counterpropagating waves when the reflection grating is operative and compare them with measurements made with a BaTiO3:Co.
Lorenz–Haken instability in a laser with arbitrary mirrors reflectivity
2000
Abstract We study the Lorenz–Haken instability in a laser with arbitrary mirrors reflectivity R . In the limit of slow population difference we demonstrate that in order to observe the instability the reflectivity must exceed the critical value R c ≃0.5379, which coincides with that found recently for the multimode (Risken–Nummedal–Graham–Haken) instability. Several other differences with respect to the uniform field limit R →1 are presented.
How neutron scattering experiments can target the structure and dynamics of milk proteins?
2016
International audience; The powerful of neutron scattering techniques to characterize structure and dynamics of milk proteins is illustrated. Small angle neutron scattering and reflectivity are used to determine the structure and the interactions between milk proteins in solution, during gelation processes, or the protein structure at different interfaces. Experiments performed by inelastic and quasielastic neutron scattering allow one to observe the dynamics of water and proteins showing the major role of hydration on the dynamics of milk proteins.