Effective optical elements with tailored properties often rely on the capability to tune the material's structure at the nanoscale. Thanks to their self‐organized 1D helical arrangement, cholesteric liquid crystals represent a beautiful example of optical materials whose properties are governed by their supramolecular structure. According to the Bragg's law, selective reflection of circular polarized light occurs for wavelengths within the photonic band gap, which, beside the refractive indices, depends on the helix pitch. Here, polymeric microstructures with tailored PBG are demonstrated by two‐photon polymerization direct laser writing in cholesteric reactive mesogens. Turning a renowned disadvantage into an opportunity, the shrinkage upon the layer‐by‐layer photopolymerization is exploited to control the effective helix pitch. Starting from a PBG of the precursor in the near infra‐red, micro‐cylinders which exhibit Bragg selective reflection at lower wavelength ranges, down to the opposite end of the visible spectrum, are fabricated in a single‐step process by tuning the laser exposure parameters. As a proof‐of‐concept, a 4D quick response (QR) micro‐tag, which adds the polarization‐selective structural color and the height of the blocks to the usual 2D black/white QR codes, is demonstrated as a novel paradigm of optical anti‐counterfeiting microdevice.

This work investigates the heat delivered by a mono-layer 1D grating of gold nanoparticles (GNPs) created by photo-reduction through two-photon direct laser writing (2P-DLW) in a poly-vinyl alcohol (PVA) matrix doped with HAuCl₄, under resonant laser radiation. We drop cast a film of a PVA + HAuCl₄ mixture onto a glass substrate, in which we create gratings of 1 mm² made by stripes of GNPs characterized by high polydispersivity. We demonstrate that, by controlling the pitch of the GNP stripes, we obtain different values of the photo-induced temperature variations. In the framework of thermo-plasmonics, the experimental investigation of the heat generation from a monolayer of gold nanoparticles represents a key element as a starting point to design thermo-smart platforms for sensing, solar energy harvesting and thermo-catalysis.

We observe with an atomic force microscope (AFM) the surface of a rough substrate that gives bistable anchoring for typical nematic liquid crystals. This surface is obtained by oblique evaporation of a thin film of SiO (average thickness approximately 150 AA) on a smooth glass plate. It appears highly disordered and exhibits very small structures with a typical horizontal size of 500 AA and a typical vertical size of 200 AA. The fractal properties of the AFM data acquired indicate that the growth process of the substrate SiO structures is governed by a diffusion law. It is reasonable to expect a decrease of the surface order parameter for the interface layer of a liquid crystal close to this kind of substrate.

We report about the study on the physical features of gold nano-particles (GNPs) created by 2-photons photo-reduction Direct Laser Writing in a Poly-Vinyl Alcohol (PVA) matrix doped with HAuCl₄. We drop cast a film of the PVA+ HAuCl₄ onto a glass substrate, in which we create 1D gratings made by stripes of GNPs with a single laser sweep. We show that the stripe width increases with the laser power and the exposure time. We also analyse the influence of the exposure time over the created nano-particles size distribution and density and we show that by suitably adjusting the exposure time it is possible to maximize the frequency of a given diameter. By comparing the experimental results with a polymerization “voxel” model, we are able to evaluate the effective cross section for 2-photons absorption of our material.