Pastor-Villarubia, V. (Verónica)

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    Gold-coated split laser-induced periodic surface structures as refractometric sensors
    (2023) Soria-García, A. (Angela); Pastor-Villarubia, V. (Verónica); Olaizola, S.M. (Santiago Miguel); San-Blas, A. (Alejandro); Elshorbagy, M.H. (Mahmoud); Rodríguez-González, A. (Ainara); Alda, J. (Javier); Granados, E. (Eduardo); Del-Hoyo, J. (Jesús); Sanchez-Brea, L.M. (Luis M.)
    The generation of surface plasmon resonances (SPR) in laser-induced periodic surface structures (LIPSS) allows their application in the field of optical sensing, such as the detection of refractive index variations in gases and liquids. We have fabricated gold-coated LIPSS nanostructures on stainless steel substrates by using femtosecond laser nano-ablation. This technique is a low-cost and high-throughput fabrication method applicable to fast and large-scale manufacturing. The depth profile of the fabricated LIPSS shows a central dip at the top of each ripple that split the geometry. The actual topography is modeled and included in a computational electromagnetism package to obtain the expected optical response under the experimental conditions. The measured and simulated spectral reflectances are compared, and the differences are explained by the departure of the fabricated LIPSS from the ideal topography. The experiments and simulations showed excellent agreement for the main spectral characteristics, like the Fano-like lineshapes of the spectral reflectance. This fitting provides the values used to determine the refractometric performance of the fabricated device, that shows a sensitivity of 518 nm/RIU and a figure of merit of 32 RIU-1 for an aqueous analyte. Our experimental results show that the fabricated devices are competitive in terms of cost and simplicity when compared to existing devices with similar performance.
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    Polarization conversion using customized subwavelength laser-induced periodic surface structures on stainless steel.
    (2022) Elshorbagy, M.H. (Mahmoud); Sanchez-Brea, L.M. (Luis M.); Buencuerpo, J. (Jerónimo); Del-Hoyo, J. (Jesús); Soria-García, A. (Angela); Pastor-Villarubia, V. (Verónica); San-Blas, A. (Alejandro); Rodríguez-González, A. (Ainara); Olaizola-Izquierdo, S.M. (Santiago Miguel); Alda, J. (Javier)
    Stainless steel is a basic raw material used in many industries. It can be customized by generating laser-induced periodic surface structure (LIPSS) as subwavelength gratings. Here, we present the capabilities of an LIPSS on stainless steel to modify the polarization state of the reflected radiation at the IR band. These structures have been modeled using the finite element method and fabricated by femtosecond laser processing. The Stokes parameters have been obtained experimentally and a model for the shape has been used to fit the simulated Stokes values to the experimental data. The birefringence of the LIPSS is analyzed to explain how they modify the polarization state of the incoming light. We find the geometry of the subwavelength grating that makes it work as an optical retarder that transforms a linearly polarized light into a circularly polarized wave. In addition, the geometrical parameters of the LIPSS are tuned to selectively absorb one of the components of the incoming light, becoming a linear axial polarizer. Appropriately selecting the geometrical parameters and orientation of the fabricated LIPSS makes it possible to obtain an arbitrary pure polarization state when illuminated by a pure linearly polarized state oriented at an azimuth of 45 degrees. The overall reflectance of these transformations reaches values close to 60% with respect to the incident intensity, which is the same reflectivity obtained for non-nanostructured stainless steel flat surfaces.