Daniel Lougnot

Fabry-Perot refractometer based on an end-of-fiber polymer tip

A micrometric Fabry-Perot refractometer based on an end-of-fiber polymer tip is proposed. The fiber tip, with a length of 36 mum, was fabricated by self-guiding photopolymerization. The two-wave interferometric operation was achieved by combining the light waves generated at the interface between the single-mode fiber and the polymer tip, and at the fiber tip end (Fresnel reflection). The Fabry-Perot interferometer is coherence addressed and heterodyne interrogated, resulting into a liquid refractive index resolution of approximately 7.5x10(-4).

Spatially controlled synthesis of silver nanoparticles and nanowires by photosensitized reduction

The present paper reports on the spatially controlled synthesis of silver nanoparticles (NPs) and silver nanowires by photosensitized reduction. In a first approach, direct photogeneration of silver NPs at the end of an optical fiber was carried out. Control of both size and density of silver NPs was possible by changing the photonic conditions. In a further development, a photochemically assisted procedure allowing silver to be deposited at the surface of a polymer microtip was implemented. Finally, polymer tips terminated by silver nanowires were fabricated by simultaneous photopolymerization and silver photoreduction. The silver NPs were characterized by UV-visible spectroscopy and scanning electron microscopy.

New insights into photoinduced processes in hybrid sol–gel glasses containing modified titanium alkoxides

Hybrid organic–inorganic sol–gel compounds have been widely used for the design of new optical devices, since they combine the characteristics of both glasses and polymers and improve the properties of the final material. Hybrid precursors in which both phases are chemically grafted are of increasing interest: volume shrinkage is minimized and phase separation can be kept below the level of Rayleigh scattering, thus leading to highly transparent glasses. Polymerizable acrylate or methacrylate functions grafted onto modified silicone alkoxides can react ia a free-radical mechanism initiated either by heating or UV-light. Considerable attention has already been focused on the chemical mechanisms involved in the construction of the inorganic network. However, no extensive study of the organic part of the process has so far been conducted. This paper points out the characteristics of the photopolymerization process taking place in hybrid sol–gel materials. In particular, the influence of inorganic moieties on the photopolymerization kinetics was studied by UV and real time FTIR spectroscopy. Particular interest was focused on the incorporation of alkoxymetals that are usually added to improve the optical and physical properties of the final material. The role of the titanium component in the photopolymerization process is emphasized. The results provide insights into processes leading to simultaneous formation of interpenetrating organic–inorganic networks and are of crucial importance for the generation of optical devices.

Fabrication of polymer waveguides between two optical fibers using spatially controlled light-induced polymerization

A new method for the fabrication of polymer waveguides between two optical fibers using a spatially controlled photopolymerization is reported. By taking advantage of the self-guiding effect of light through a photopolymerizable medium, polymer waveguides perfectly aligned with the fiber cores and strongly anchored to their surfaces are fabricated. The process is characterized by following in situ the coupling efficiency of a nonactinic laser source. Examples of waveguides exhibiting good coupling efficiency and high flexibility are given. By selecting the suitable monomers and adjusting the photonic parameters, the optical and mechanical waveguide properties (diameter, length, refractive index, rigidity, and flexibility) can be controlled in view of optical sensor applications.

Fabrication of microlenses by direct photo-induced crosslinking polymerization

Growing interest in the manufacture of microlenses results from their standard use as optical components with current applications in the telecommunication industry. A number of techniques were developed by using various materials and processes. One approach involved the ability of self-processing photopolymers to generate microlens arrays. Spatially controlled illumination of a photosensitive layer induced an inhomogeneous photopolymerization involving formation of 3-D polymer network, mass-transport process of reactive species and bending of the surface resulting from a gradient of surface free energy. The imaging process that generated as a relief in the photopolymer layer, exhibited a completely self-processing character without any chemical post-treatment. The lens arrays displayed diameters ranging from less than 100 μm to 1 mm and focal lengths from 100 μm to a few millimeters, depending on photonic, optical and physico-chemical parameters.

Fabrication of micro-optical devices by self-guiding photopolymerization in the near IR.

Micropillars and microlenses, integrated at the end of optical fibers, were fabricated by microfabrication by direct photopolymerization in the near-IR (NIR) region (700-950 nm). They were built by self-guiding polymerization using the NIR-light emerging from the optical fiber. The aim is to demonstrate that photopolymer material can be used to fabricate micro-optical devices by a single step process utilizing NIR activation. The material and process described here fulfill the requirements for a simple and fast implementation of micro-optics onto NIR sources.

Quenching effects in flashlamp-excited polymethine dye lasers

Abstract The main action of oxygen dissolved in air-saturated polymethine-dye laser solutions is the quenching of the excited singlet state by enhancing transitions between it and the triplet state. A substantial increase of laser efficiency was observed by outgasing the solutions of five di- and tri-carbocyanine dyes. In one case (DOTC) a specific triplet state quencher (COT) was found.

Flashlamp-excited dye lasers in the near infrared

Abstract The laser emission of flashlamp-excited polymethine dyes is investigated. The spectral shift towards longer wavelengths due to relatively slow pumping is discussed in terms of transient triplet-triplet absorption. First results concerning mode locking and tuning on the 785–805 nm and 872–880 nm ranges of two tricarbocyanine dyes are presented.

The benzophenone-amine photoinitiator in vinyl polymerization

SummaryFast spectroscopy experiments have been performed upon the photoinitiation process of a vinyl polymerization with the benzophenone-amine derivative system. The rate constants of the processes in the excited states have been determined. The results make it possible to discuss the rate constant of the polymerization and to deduce the efficiency of the initiating radicals.

Analysis of photopolymerized acrylic films by AFM in pulsed force mode

This paper highlights the potential of atomic force microscopy in the pulsed force mode to investigate the photopatterning of acrylic‐based films. The pulsed force mode is a nonresonant mode designed to allow approach curves to be recorded along the scanning path. It thereby provides the topography of the sample and a direct and simple local characterization of adhesion and stiffness. This mode can be used either for imaging or for locally probing the mechanical properties of a surface. In particular, a correlation between stiffness and conversion of the monomer was established. The close examination of the pulsed force mode signal brought accurate information on the photoinduced modification of the film. Polymer films with submicron photopatterning generated by interferometric illumination were analyzed by pulsed force mode. It was established that the gradient of mechanical properties throughout the films was strongly dependant on the irradiation conditions.