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°. 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.

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We designed, fabricated and tested a Vector Diffractive Optical Element (VDOE) to simultaneously determine the Stokes vector of light. It comprises several sectors. Each one is a vector Fresnel zone plate which focuses the light on separate foci and has different polarization properties. The polarization state is calculated from their intensities. From simulations, we could identify the error sources that were analytically removed. The residual uncertainty after applying our corrections was as low as 6x10^(-5). The uncertainty obtained for our fabricated VDOE, 3.33 %, is competitive with the results from state-of-the-art techniques.

The real-time monitoring of physical and chemical parameters in running fluids is of importance for biomedical, biochemical, and environmental applications, such as the presence of biomarkers or chemomarkers, or the departure from some preset values of critical parameters. In this contribution we present a new generation of Permeable Diffractive Optical Elements (PDOE) based on photon sieves. In brief, the PDOE is made of passing holes properly placed on specific locations on a rigid surface. This arrangement makes PDOEs ideal to work with running fluids. Our PDOE is optimized maximizing the irradiance at is focal plane, maintaining an appropriate permeability ratio. The starting point is the classical Fresnel zone distribution. We have used two different optimization strategies to design a working PDOE: i) Particle Swarm Optimization has been applied to modify the distribution of holes on the PDOE simultaneously considering all of them; ii) an iterative minimization algorithm adding one hole at the time until filling the PDOE aperture. Both optimization algorithms generate focal spots that are compared to choose the design better suited for the proposed application. Once the PDOE is optimized and fabricated, the surface of the remaining rigid structure is nanostructured (for example using Laser Induced Periodic Surface Structures), or functionalized, to provide specific sensing capabilities. In addition, the PDOE is integrated within a pipe where the fluid under analysis circulates through. A proposal for the optoelectronic assembly of the device-including auxiliary optical elements, light sources, and detectors - is also presented in this contribution.

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