Search

International audience; We propose a method for producing a conical beam based on the lateral refraction of the TM01 mode from a two-mode fiber after chemical etching of the cladding, and for controlling its radial polarization. The whole power of the guided mode is transferred to the refracted beam with low diffraction. Polarization control by a series of azimuthal detectors and a stress controller affords the transmission of a stabilized radial polarization through an optical fiber. A solid component usable for many applications has been obtained.

International audience; Acoustic field distribution was determined in HIFU sonoreactors as well as localization of cavitation activity by crossing different techniques: modeling, hydrophone measurements, laser tomography and SCL measurements. Particular care was taken with quantification of this last technique by pixels or photon counting. Cavitation bubbles generated by HIFU are mainly located on the outer layer of the propagation cone in the post-focal zone. Greatest acoustic activity is not located at the geometrical focal, but corresponds to a high concentration of bubbles zone. On the contrary, the main sonochemical activity shifts slightly toward the transducer, whereas quenching of inertial cavitation is observed directly at the focal. Finally, SCL thresholds have been determined.

We report on a heterodyne interferometric scanning near-field optical microscope developed for characterizing, at the nanometric scale, refractive index variations in thin films. An optical lateral resolution of 80 nm (lambda/19) and a precision smaller than 10(-4) on the refractive index difference have been achieved. This setup is suitable for a wide set of thin films, ranging from periodic to heterogeneous samples, and turns out to be a very promising tool for determining the optical homogeneity of thin films developed for nanophotonics applications. (C) 2009 American Institute of Physics. [doi:10.1063/1.3226660]

International audience; This work addresses the use of fixed-angle laser reflectometry to follow in situ the deposition of self-assembled polyelectrolyte films in a large domain of thickness. It is shown theoretically and illustrated experimentally that the reflectometric output can be interpreted in terms of refractive index and thickness way above the usual range which covers the earlier deposition steps of the polymers (i.e., 30-50 layers, depending on the film composition). Thick films containing up to 320 deposition steps (160 bilayers) were made in the reflectometric cell with the polymer pair poly(allylamine, hydrochloride) and poly(styrene sulfonate) on a silica substrate. They were imaged with AFM, and their thickness was measured using the focused ion beam (FIB) technique. In the course of construction, the reflectometric data started to alternate more or less regularly between positive and negative values, exhibiting absolute values at the extrema which decreased progressively. This phenomenon was coherent with simulated data, once the diffusion of the incident beam and the change of refractive index were taken into account. The phenomenon gives an opportunity to evaluate the composition and the mean thickness of the film during the growth, which is confirmed by comparison with the FIB measurements.

The thickness evolution of multilayer film is investigated by focused ion beam (FIB) in the domain of polymer multilayers. This method, currently used in the modification and the characterization of integrated circuits, proves it is possible to determine the polymer film thickness. Sample cutting and its observation of the cross-section are performed in the FIB without leaving the vacuum chamber. Two main conclusions can be drawn: (1) the roughness of the film increases with the number of layer deposit, (2) the film growth changes from nonlinear (called exponential) to linear beyond 300 nm (70 layers).

International audience

International audience

International audience

A new type of electrochemical cell has been developed for use in electrochemical, chemical and biological applications. Using a platinum microelectrode as working electrode, this cell incorporates a silver microelectrode as reference electrode. These microelectrodes, whose area is equal to 1 μm 2 , were fabricated using photolithography, sputtering, and focused ion beam (FIB) technologies since these micro-fabrication techniques allow us to develop miniaturized electrochemical cells useful either for nanoelectrochemistry or biosensors applications. In this study, we show it is possible to coat a surface by chemical or biological compounds by immersing the microelectrodes in a solution, then setting a difference of potential between the two microelectrodes of the cell. For example, we used this miniaturized cell to realize the electrochemical polymerization of aniline into polyaniline to show that this electrochemical cell is efficient to coat a surface with a thin film of polymer.

Micromachining technology has potential for fabrication of precision-defined integrated optic (IO) circuits and offers easy alignment procedures for optical fibers, reducing packaging costs. The main difficulties in fiber sensing technologies are optical fiber alignment requirements, high temperature and vibration effects sensitivity, and phase noise. An alternative is the use of MEMS/MOEMS to approach these problems, combining fiber-optic technology and silicon micromachining. Integrated sensors, when linked by optical fibers, can provide EMI immunity and isolation from high voltage circuits. Detection of displacements of cantilever beams, microbridges, or membranes is used to sense the physical parameter, converting mechanical displacement to a change in optical intensity, and serves as the basis for sensors, since many physical parameters (temperature, pressure, force, acceleration) can be converted to a displacement or strain. The interest in silicon micromachining is also demonstrated in coupling of optical fibers to optoelectronic devices by passive alignment of fiber on a V-groove shaped silicon microbench. Finally, highly reproducible processes such as focused ion beam (FIB) may fabricate near-field optical sensors with nanometer apertures at the apex of tapered fibers. In this paper, a number of sensors are discussed in order to analyse how silicon micromachining contributes to fiber optic sensor technology.

The present paper deals with the experimental measurement of temperature along various shapes of fiber tips used as near-field optical microscope probes. An ultra-small thermoelectric couple makes it possible to detect the tip temperature as far as the junction dimension remains smaller than the local investigated area. The couple is a 0.5 μ m Pt and Pt–Rh 10 % welded wires, whose dynamic and dimensional characteristics allow the investigation of the thermal behaviors of tapers under steady-state and periodic excitation modes (bandwidth near 1 kHz). Temperature profiles along these fiber tips (up to 400 μ m from the apex) are shown and discussed. Confirming some authors' results, dramatic temperature increases due to an internal heating can occur for some configurations. Such temperatures can play a key role in the imaging process, because of the resulting behaviors of the apex, mainly due to its thermal expansion. Indeed, variation of the aperture diameter and thermoelastic interaction with the sample surface could explain some artefacts in the resulting images.