24 November 2010 Ripple-patterned substrates for light enhancement applications
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Proceedings Volume 7376, Laser Applications in Life Sciences; 737602 (2010) https://doi.org/10.1117/12.871049
Event: Laser Applications in Life Sciences 2010, 2010, Oulu, Finland
We report on surface structuring of sapphire, silicon carbide, and silicon by femtosecond laser pulses in multipulse irradiation mode. The formed ripples on the flat surface or on the vertical walls with hierarchical structures whose feature sizes are ranging from the irradiation wavelength down to ~ 50 nm are prospective templates for surface enhanced Raman scattering after coating with plasmonic metals. We study complex patterns of fine ripples with periods Λr, as small as λ/Rp, where Rp (see manuscript) 3 - 5. The mechanisms suggested for such Rp values are discussed: temperature and density of breakdown plasma, angle of incidence, mechanism of second harmonic generation (SHG) and absorption. Predictions of the surface and bulk models of ripple formation are compared with experimental values of Rp-factor. We propose a model of ripple formation on the surface, which is based on the known in-bulk sphere-to-plane formation of breakdown plasma in the surface proximity. In semiconductor 4H:SiC normal ripples with periods 190 and 230 nm were recorded with 800 nm and 1030 nm fs-laser pulses respectively. We show that the period of ripples is defined by the dielectric properties of crystalline (solid) phase rather than the molten phase in the case of silicon. Generation of SHG on the surface of sample and plasma nano-bubbles are discussed: surface-SHG is found not important in ripples' formation as revealed by comparative study of periods on Al2O3 and TiO2 at 800 nm wavelength of irradiation. We propose that ripple periodicity is pinned to the smallest possible standing wave cavity (λ/n)/2 inside material of refractive index n.
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Ricardas Buividas, Ricardas Buividas, Tadas Kudrius, Tadas Kudrius, Remigijus Sliupas, Remigijus Sliupas, Lorenzo Rosa, Lorenzo Rosa, Gintas Slekys, Gintas Slekys, Saulius Bagdonas, Saulius Bagdonas, Ricardas Rotomskis, Ricardas Rotomskis, Saulius Juodkazis, Saulius Juodkazis, } "Ripple-patterned substrates for light enhancement applications", Proc. SPIE 7376, Laser Applications in Life Sciences, 737602 (24 November 2010); doi: 10.1117/12.871049; https://doi.org/10.1117/12.871049

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