Kazansky, P.G., Beresna, M., Corbari, C., Shimotsuma, Y., Sakakura, M., Miura, K. and Qiu, J.
Extraordinary modifications and structures in glass produced by ultrafast laser writing.
In, 3rd International Congress on Ceramics , Osaka, Japan,
14 - 18 Nov 2010.
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Femtosecond laser direct writing offers unique potential for realizing photonic devices in the bulk of variety transparent materials including glasses and crystals. Investigation of extraordinary anisotropic modifications produced by femtosecond laser irradiation in glass and related phenomena is important for elucidating the mechanisms of light-matter interaction and device fabrication with unique features, such as space variant birefringence. Polarization grating is one example of such devices with can act as a beam splitter for circular polarized light. Moreover circularly polarized photons carry spin-angular momentum, and an encounter with a gradient of refractive index leads to spin-orbital momentum coupling. We demonstrate theoretically and experimentally that due to this effect the circularly polarized light impinging on the sphere will produce beam with orbital angular momentum ±2. The method is applied to generate array of optical vortexes on a small scale using micro-spheres produced by femtosecond laser in silica glass. Furthermore a new phenomenon of ultrafast light blade, representing itself the first evidence of anisotropic sensitivity of glass due to hidden asymmetry of ultrafast laser beam has been recently discovered. This phenomenon enables polarization control of ultrafast laser writing using pulses with tilted intensity front. We anticipate that the observed extraordinary anisotropic modifications in glass and related phenomena will open new opportunities in laser material processing, fabrication of unique photonic structures and controlling of intense light propagation.
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