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25 February 2004 Correlation between laser-induced-damage and nanosized absorbing defects
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In the context of high power laser applications like the French "Laser Megajoule" or the "National Ignition Facility" in the United States, laser-induced-damage in fused silica appears to be a limitation. Although it has been established that nano-sized defects are suspected to be responsible of the damage initiation in optical components, the induced-breakdown process is still unknown. The specific apparatus developed at the Institut Fresnel permits to study in real time the laser interaction on an isolated absorbing defect (around 100 nm): Indeed the coupling of a nanosecond focused laser (beam diameter about 10μm) and a high resolution photothermal microscope (beam diameter 1μm) in a unique facility permits to highlight the evolution of the local absorption of the defect versus irradiation energy density. Furthermore, the morphology of this modification is followed thanks to a "refraction mapping" (photothermal deflection measured at frequency 0). An in-situ dark field microscope and an ex-situ AFM complete the observations. In order to simulate the presence of the nano-defects, engineered sub-micronic gold particles (100-600 nm) were embedded in silica samples. The whole observations contribute in the understanding of the different stages of the damage initiation and more particularly, a determination of a "pre-damage" threshold can be performed.
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Bertrand Bertussi, Jean-Yves Natoli, Annelise During, Mireille Commandre, Laurent Gallais, Jean Luc Rullier, Herve Bercegol, and Philippe Bouchut "Correlation between laser-induced-damage and nanosized absorbing defects", Proc. SPIE 5250, Advances in Optical Thin Films, (25 February 2004);

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