29 research outputs found

    Low loss coatings for the VIRGO large mirrors

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    présentée par L. PinardThe goal of the VIRGO program is to build a giant Michelson type interferometer (3 kilometer long arms) to detect gravitational waves. Large optical components (350 mm in diameter), having extremely low loss at 1064 nm, are needed. Today, the Ion beam Sputtering is the only deposition technique able to produce optical components with such performances. Consequently, a large ion beam sputtering deposition system was built to coat large optics up to 700 mm in diameter. The performances of this coater are described in term of layer uniformity on large scale and optical losses (absorption and scattering characterization). The VIRGO interferometer needs six main mirrors. The first set was ready in June 2002 and its installation is in progress on the VIRGO site (Italy). The optical performances of this first set are discussed. The requirements at 1064 nm are all satisfied. Indeed, the absorption level is close to 1 ppm (part per million), the scattering is lower than 5 ppm and the R.M.S. wavefront of these optics is lower than 8 nm on 150 mm in diameter. Finally, some solutions are proposed to further improve these performances, especially the absorption level (lower than 0.1 ppm) and the mechanical quality factor Q of the mirrors (thermal noise reduction)

    La cohérence de la lumière et l’imagerie des tissus du corps humain

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    L’optique s’impose comme un outil de choix dans le monde biomédical. En particulier le laser, par ses propriétés uniques, se révèle irremplaçable pour la thérapie, mais aussi pour l’imagerie. Nous avons cherché ici à illustrer deux notions qui sont souvent évoquées quand on parle de laser : la cohérence spatiale et la cohérence temporelle. Nous montrons sur deux exemples (la microscopie confocale et la tomographie de cohérence ou OCT), qui ont leur place dans les laboratoires et les hôpitaux, comment on peut réaliser des images qui sont de véritables coupes virtuelles, non invasives et non destructives, dans des cellules ou des tissus du corps humain

    A resolution insensitive to geometrical aberrations by using incoherent illumination and interference imaging

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    This contribution is another opportunity to acknowledge the influence of Roger Maynard on our research work when he pushed one of us (ACB) to explore the field of waves propagating in complex media rather than limiting ourselves to the wavelength scale of thermal waves or near field phenomena. Optical tomography is used for imaging in-depth scattering media such as biological tissues. Optical coherence tomography (OCT) plays an important role in imaging biological samples. Coupling OCT with adaptive optics (AO) in order to correct eye aberrations has led to cellular imaging of the retina. By using our approach called Full-Field OCT (FFOCT) we show that, with spatially incoherent illumination, the width of the point-spread function (PSF) that governs the resolution is not affected by aberrations that induce only a reduction of the signal level. We will describe our approach by starting with the PSF experimental data followed by a simple theoretical analysis, and numerical calculations. Finally full images obtained through or inside scattering and aberrating media will be shown

    En face coherence microscopy [Invited]

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    Massachusetts Institute of Technology. Twenty-fourth Annual Catalogue of the Officers and Students, with a Statement of Instruction, and a List of the Alumni. 1888-1889. Includes a list of professors and students; the objectives and regulations of the Institute; conditions for admission and graduation; description of courses for each year; and Lowell courses. This edition also includes a list of graduates and their occupations; the titles of theses of successful candidates for the degree of bachelor of science, June 1888; and a description of the Association of the Alumni. Digitized from microfiche copies. Digital version may contain microfiche headers and targets