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.

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).

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.

Integration of micrometer-sized polymer elements at the end of optical fibers by free-radical photopolymerization.

A simple method of manufacturing micrometer-sized polymer elements at the extremity of both single-mode and multimode optical fibers is reported. The procedure consists of depositing a drop of a liquid photopolymerizable formulation on a cleaved fiber and using the light that emerges from the fiber to induce the polymerization process. After exposure and rinsing a polymer tip is firmly attached to the fiber as an extension of the fiber core. It is shown that the tip geometry can be adjusted by the variation of basic parameters such as the geometry of the deposited drop and the conditions of drop illumination. When this process is applied to a multimode fiber three-dimensional molds of the fiber's linearly polarized modes can be obtained. The process of polymer-tip formation was simulated by a numerical calculation that consisted of an iterative beam-propagation method in a medium whose refractive index is time varying. It is shown that this process is based on the gradual growth, just above the fiber core, of an optical waveguide in the liquid formulation. Experimental data concerning two potential uses of the tipped fibers are presented.

Dry photopolymer films for computer-generated infrared radiation focusing elements.

A new technological approach makes fabrication of relief computer-generated focusing elements for IR radiation by use of a dry photopolymer recording material possible. The formation of a relief structure by self-development takes place in the dark, subsequent to the holographic illumination, without wet processing. Consequently these diffractive elements exhibit low surface scattering. The formation of a surface wave of the monomer along the light-darkness boundary is observed for the first time to our knowledge and confirms the previously proposed thermodynamic model of the mechanism of the hologram formation in photopolymerizable layers. Dye-sensitized polymerization of acrylamide is found to produce nonlinearity of the relief recording. At least partial compensation of this nonlinearity is attained by the introduction of appropriate corrections into the computer-generated amplitude function. A diffraction efficiency of ~ 55% is obtained for CO(2) laser radiation (λ = 10.6 µm).

Methylene blue sensitized gelatin: evidence of photodemethylation.

The dependence of diffraction efficiency of methylene blue sensitized gelatin gratings vs dye concentration is explained in terms of the aggregations tate of the dye.

Biphotonic process for recording holograms with continuous-wave lasers in the near infrared.

A new process that permits the recording of holograms produced by laser sources emitting in the near infrared is presented. The recording process involves the sensitization of singlet oxygen and the oxidation of an adapted trap. Finally, a second photon initiates a photopolymerization, which induces changes in refractive index and creates the hologram.