49 research outputs found
Composition law for polarizers
The polarization process when polarizers act on an optical field is studied.
We give examples for two kinds of polarizers. The first kind presents an
anisotropic absorption - as in a polaroid film - and the second one is based on
total reflection at the interface with a birefringent medium. Using the Stokes
vector representation, we determine explicitly the trajectories of the wave
light polarization during the polarization process. We find that such
trajectories are not always geodesics of the Poincar\'e sphere as it is usually
thought. Using the analogy between light polarization and special relativity,
we find that the action of successive polarizers on the light wave polarization
is equivalent to the action of a single resulting polarizer followed by a
rotation achieved for example by a device with optical activity. We find a
composition law for polarizers similar to the composition law for noncollinear
velocities in special relativity. We define an angle equivalent to the
relativistic Wigner angle which can be used to quantify the quality of two
composed polarizers.Comment: 23 pages, 9 figures, accepted for publication in Physical Review
Thermo-hydraulic characterization of semi-transparent Flat-Plate Pulsating Heat Pipes in variable gravity regimes
Constructing Fresnel reflection coefficients by ruler and compass
A simple and intuitive geometical method to analyze Fresnel formulas is
presented. It applies to transparent media and is valid for perpendicular and
parallel polarizations. The approach gives a graphical characterization
particularly simple of the critical and Brewster angles. It also provides an
interpretation of the relation between the reflection coefficients for both
basic polarizations as a symmetry in the plane
Van der walls induced polarization of physisorbed atoms and molecules: A discrete solid theory
Mesure de lâĂ©paisseur et analyse de la composition des revĂȘtements dâalliage dâor et des Ă©ventuelles sous-couches par microfluorescence X
Aujourdâhui, les applicateurs de traitements de surface et les donneurs dâordres sâĂ©quipent de spectromĂštres de microfluorescence X afin de mesurer les Ă©paisseurs des revĂȘtements notamment pour valider leur conformitĂ© Ă la rĂ©glementation sur les revĂȘtements de mĂ©taux prĂ©cieux ou au cahier des charges. Les spectromĂštres de microfluorescence X de nouvelle gĂ©nĂ©ration, Ă©quipĂ©s de logiciels proposant la dĂ©termination des Ă©paisseurs et de la composition des revĂȘtements, favorisent la diffusion de cette technologie. Cette utilisation complique les relations clients â fournisseurs Ă cause des divergences sur lâutilisation des Ă©quipements et lâinterprĂ©tation des rĂ©sultats obtenus. LâĂ©tude prĂ©sente porte sur la comparaison des valeurs obtenues par spectromĂ©trie de microfluorescence X avec des mesures rĂ©alisĂ©es sur coupe micrographique, considĂ©rĂ©e comme la mĂ©thode de rĂ©fĂ©rence. Plusieurs gammes de traitements, habituelles sur les produits dĂ©coratifs, sont Ă©tudiĂ©es. LâĂ©tude montre la rĂ©elle difficultĂ© et les limites dans la dĂ©termination de lâĂ©paisseur des revĂȘtements d'or par microfluorescence X
Radiative and non-radiative decay of a single molecule close to a metallic nanoparticle
We study the spontaneous emission of a single emitter close to a metallic nanoparticle, with the aim to clarify the distance dependence of the radiative and non-radiative decay rates. We derive analytical formulas based on a dipole-dipole model, and show that the nonradiative decay rate follows a R-6 dependence at short distance, where R is the distance between the emitter and the center of the nanoparticle, as in Forster's energy transfer. The distance dependence of the radiative decay rate is more subtle. It is chiefly dominated by a R-3 dependence, a R-6 dependence being visible at plasmon resonance. The latter is a consequence of radiative damping in the effective dipole polarizability of the nanoparticle. The different distance behavior of the radiative and non-radiative decay rates implies that the apparent quantum yield always vanishes at short distance. Moreover, non-radiative decay is strongly enhanced when the emitter radiates at the plasmon-resonance frequency of the nanoparticle