Jean-Claude Pommier

Radially polarized 3 kW beam from a CO2 laser with an intracavity resonant grating mirror.

A 3 kW radially polarized beam is generated from a CO(2) laser by means of a resonant grating mirror. The design results and spectral characterization of a broadband polarizing mirror are presented as well as the mirrors operation in a CO(2) laser resonator. In a long-term experiment a radially polarized beam with a power of 2.7 kW was observed for several hours, proving the high stability of this polarizing scheme.

Synthèse et structure des stannaoxacycloalcanes

Abstract The reactions of diols with dimethoxydibutyltin lead to the formation of monomeric or dimeric heterocycles without linear polycondensation products. In some cases, dimeric products can give upon heating the monomeric corresponding heterocycle. IR and NMR data of these compounds show that, in spit of the apparent slight strength of the bonding in the dimer, a large cycle exists rather than a coordination complex between two monomeric species.

Reactions d'halogeno-2, -3 et -4 alcoxysilanes avec le magnesium: resultants experimentaux et etude du mecanisme

Abstract The Grignard reaction with 2-, 3- or 4-halogenoalkoxysilanes does not lead to stable organomagnesium derivatives. Besides, or sometimes instead of, the normally expected elimination, a coupling or a disproportionation reaction takes place. It is shown that this unexpected behaviour occurs via free radical species at the surface of the magnesium, the process involving quite a long life time for the free radical intermediate Me 3 SiO( . The exact nature of the elimination is less obvious, but the results lead to us believe that it stems from the intermediate formation of an unstable organomagnesium derivative.

High-efficiency diffraction grating coupler for multimode optical interconnect

The device presented in this paper is designed for coupling a free space optical wave under quasi-normal incidence in and out of a highly multimode waveguide with high efficiency. It uses two resonant diffraction gratings at the substrate-waveguide interface that are made of a shallow metal grating, covered with a high refractive index layer. It is shown that the resonant structure can theoretically diffract up to 90% of the incident energy in and out of the waveguiding layer. The geometrical parameters of the structure and the tolerances can easily be achieved by conventional technology means.

Etude comparative de l'alkylation des tetraphenylporphyrines de l'etain et de leurs formes reduites par les reactifs de grignard

Abstract A comparative study of alkylation by Grignard reagents of PSn(OH) 2 (P = tetraphenylporphyrin (TPP), tetraphenylchlorine (TPC), tetraphenylisobacteriochlorine (TPiBC)) shows that dialkylstannylisobacteriochlorines are the most easily obtained. The presence of transition metals in the magnesium crystals directs the reaction towards reduction of the macrocycle instead of alkylation on tin. This is supplementary proof for the intervention of a single electron transfer mechanism (SET) in alkylation of a macrocycle by Grignard reagents. These results fit very well with earlier electrochemical experiments and the measurements of the reduction potentials of the Group IVB metalloporphyrins and their reduced forms.

Microchip-laser polarization control by destructive-interference resonant-grating mirror

An output coupler comprising a resonant grating submirror monolithically associated with a standard multilayer submirror polarizes the emission of a Nd:YAG microchip laser linearly over its full emission bandwidth by intra-mirror destructive interference for the undesired polarization. A polarization extinction ratio of more than 25 dB is obtained up to 6.1microJ pulse energy. This passively Q-switched laser performance is almost identical to that of a gratingless non-polarized microchip laser. The design and fabrication of the resonant grating mirror are described.

A new wireless and miniaturized high-resolution optical displacement sensor

A wireless displacement sensor is proposed which is composed of a fixed active head and a passive head which moves relatively to a grating scale. The passive head comprises a grating and two mirrors. It can be so small as to be inserted non-obtrusively where the displacement must be measured without spoiling the system optimum by undesirable size and structural compromises. It is insensitive to electromagnetic perturbations. The key characteristics of the sensor are high resolution and a very small size. The encoder uses a fixed grating scale as in standard designs, a passive-optical read head on the moving element and a stationary, opto-electronic source/detector module. Communication between the moving head and the detector module is done without cables using a free-space optical interconnection.

Preparation, characterisation, and some properties of secondary enamines

Partial methanolysis of organo-tin or -magnesium salts of imines leads to secondary enamines which are stable in aprotic media allowing the study of their physical and chemical properties.

Polarization control of a Yb:YAG ceramic microchip laser by constructive-interference resonant grating mirror

A laser output coupler comprising a resonant grating submirror monolithically associated with a multilayer submirror according to a constructive interference scheme polarizes the emission of a rare-earth-doped YAG-ceramic microchip laser over its full bandwidth. The design and fabrication of the resonant grating mirror are described. A polarization contrast ratio of more than 1000 was obtained with single transverse mode operation.

Continuous writing technique of long gratings for metrological applications

The method presented here is an optical technique allowing the high productivity printing of long submicron period gratings by means of a phase mask illuminated by an intensity modulated laser beam. The continuous writing of the grating permits to avoid stitching errors and the fabrication of very long gratings. The main applications concern the fabrication of long optical scales for high resolution optical encoders. The experimental results presented here show 100 mm long resist gratings with 500 nm period.