Biomedical subjects

Laurent Gallais

Publications and source records attributed to Laurent Gallais.

4 recordsLinked to original sources

PubMed2006

Simultaneous absorption, scattering, and luminescence mappings for the characterization of optical coatings and surfaces.

An experimental setup, based on the laser-induced deflection technique, is developed to measure simultaneously the 244 nm laser absorption, scattering, and luminescence on optical components. The different techniques and methods that have been specifically developed to obtain both high resolution (micronic) and sensitivity (a few 10(-7) of the incident power for the absorption, 10(-8) for scattering and fluorescence) are presented. Different applications are then explored: the study of losses in deep UV multilayer coatings (HfO2/SiO2 mirrors) and the analysis of contamination defects on bare substrate and structural defects in optical coatings.

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PubMed2005

Photothermal deflection in multilayer coatings: modeling and experiment.

A model of the photothermal deflection signal in multilayer coatings is presented that takes into account optical interference effects and heat flow within the stack. Measurements are then taken of high-reflectivity HfO2/SiO2 ultraviolet mirrors made by plasma ion assisted deposition and compared to calculations. Good agreement is found between the experimental results and the model. Using this model for the calibration and the setup described, one can measure absorption in multilayer coatings accurately down to 10(-7) of the incident power.

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PubMed2003

Optimized metrology for laser-damage measurement: application to multiparameter study.

An automatic test apparatus for refined testing of laser damage is presented that permits an in situ analysis of the tested area before, during, and after pulsed irradiation. Spatial and temporal beam profiling are performed in real time and give access to the localized fluence for each shot. Furthermore, an optimization of the initiation of damage detection is undertaken by use of image processing and yields a resolution better than 1 microm. Through several examples, these conditions are demonstrated to be useful for reaching an understanding of the laser-damage process. A complete study is undertaken of different kinds of glass that permits the main influence of test parameters (shot frequency, shot number, beam profile variation, temporal and spatial meshing, ...) on the damage procees to be shown. The study was made for different test procedures (1:1, S:1, R:1) and completed by atomic-force microscope analysis. Evidence indicates that the upgrading of metrology associated with an automatic process offers new opportunities for understanding laser-induced damage mechanisms and for emphasizing specific effects such as damage initiation, damage growth, and conditioning for repetitive shots.

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PubMed2002

Laser-induced damage of materials in bulk, thin-film, and liquid forms.

Accurate threshold curves of laser-induced damage (7-ns single shot at 1.064 microm) are measured in bulk and at the surfaces of optical components such as substrates, thin films, multilayers, and liquids. The shapes and the slopes of the curves are related to the spot size and to the densities of the nanodefects that are responsible for damage. First, these densities are reported for bulk substrates. In surfaces and films the recorded extrinsic and intrinsic threshold curves permit the discrimination of the effects of microdefects and nanodefects. In all cases the density of nanocenters is extracted by means of a phenomenological approach. Then we test liquids and mixtures of liquids with controlled defect densities. The results emphasize the agreement between measurement and prediction and demonstrate the validity of the presence of different kinds of nanocenter as the precursors of laser damage.

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