Doppler optomechanics of a photonic crystal

A laser beam directed at a mirror attached onto a flexible mount adds friction to its mechanical motion by the Doppler effect. For a normal mirror the efficiency of this radiative Doppler friction is very weak and practically masked by laser shot noise. We find that it can become very efficient using a photonic crystal mirror near its photonic band gaps. As an example, a Bragg mirror used at the long wavelength edge of its band stop can be efficiently optically cooled using the Doppler friction. The opposite effect opens new routes for optical pumping of mechanical systems: a laser pointing at a Bragg mirror and tuned at its short wavelength edge induces amplification of the vibrational excitation of the mirror leading eventually to its self-oscillation. These new effects rely on the strong dependency of a photonic crystal reflectivity on the wavelength.     

An alternative approach to determine the spot-size of a multi-mode laser beam and its application to diode laser beams

An alternative approach is suggested to determine the spot-size of a multi-mode laser beam. It has been shown by simulations that the suggested approach can give the beam quality factor and characteristic radius with less than 5% error. Unlike the power content method, the proposed method is applicable to the beams even with diameter one tenth of the CCD size. The new approach has been applied to a multi-mode diode laser output and it is shown that the ABCD matrix analysis can be used for beam propagation, with the measured parameters of the laser.     

Etude dans la serie des radicaux heterocycliques—X : Reaction de pseudo-gomberg: Décomposition en milieu protique et aprotique d'amino-2 thiazoles en série pyridinique. Nouvelle voie d'accès aux thiazolylpyridines.

The decomposition of 2-aminothiazoles in the presence of isoamylnitrite has been studied with pyridine substrates. GLC/MS allows the identification of thiazolylpyridines and by-products. An important solvation effect and the electrophilic nature of thiazol-2-yl radicals in strongly basic substrates have been demonstrated. The greater reactivity of di or trimethyl pyridines can be exploited to synthesize new thiazolylpyridines having interesting insecticidal properties. In acidic media, contrary to what is observed with other radical sources, these substrates show a poor reactivity relative to benzene, which may be related to the cage decomposition mechanism of diazoamino compounds.     

Analysis of coupled conduction and radiation heat transfer in presence of participating medium- using a hybrid method

The current study addresses the mathematical modeling aspects of coupled conductive and radiative heat transfer in presence of absorbing, emitting and isotropic scattering gray medium within two-dimensional square enclosure. The walls of the enclosure are considered to be opaque, diffuse and gray. The enclosure comprised of isothermal vertical walls and insulated horizontal walls. A new hybrid method where the concepts of modified differential approximation employed by blending discrete ordinate method and spherical harmonics method, has been developed for modeling the radiative transport equation. The finite volume method has been adopted as the numerical technique. The effect of various influencing parameters i.e., radiation-conduction parameter, surface emissivity, single scattering albedo and optical thickness has been illustrated. The compatibility of the method with regard to solving coupled conduction and radiation has also been addressed.     

Electrical rectification by monolayers of three molecules

Rectification, i.e. asymmetrical electrical conduction by a Langmuir-Blodgett monolayer of dicyano{4-[1-cyano-2-(1-hexadecylquinolin-1-ium-4-yl)vinyl]phenyl} methanide ( 1 ), occurs between both Al and Au electrodes: this rectification arises from the asymmetry of the molecule, and the interplay between the zwitterionic ground state D⁺-π-A⁻ and the less dissociated first electronic excited state D⁰-π-A⁰. Two more monolayer rectifiers have been found: 1-butyl-2,6-bis{2-[4-(dibutylamino)phenyl] vinyl}pyridin-1-ium iodide ( 2 ) is an interionic rectifier with back charge transfer between the iodide ion and the pyridinium ring. 1a-[4-(dimethylamino)phenyl]-1aH-1a-aza-1(2)a-homo(C₆₀-I_h)[5,6]fullerene ( 3 ) is a moderate rectifier, with a rectification ratio of 2.