Chiral photonic materials that selectively control circularly polarized light are of growing interest for optical filtering, sensing, and polarization-dependent light management. Cholesteric liquid crystal polymers provide a versatile platform for chiral photonics due to their self-organized helical structure, although their optical response is typically limited to narrow reflective stopbands determined by uniform pitch. Here we show that a dye-based photoinitiator can act as a structure-directing element, guiding the formation of a cholesteric polymer network with chirped helical pitch and dissipative chiral photonic coupling. Optical spectroscopy reveals a broadband low-transmission region far exceeding the bandwidth of uniform-pitch cholesteric, while preserving handedness-dependent attenuation. This behavior originates from the interplay between a depth-dependent helical pitch frozen during photopolymerization and the complex optical anisotropy introduced by aligned dye molecules embedded in the polymer network. The resulting pitch gradient distributes the Bragg condition along the film thickness, while isotropic absorption and linear dichroism render the Bragg interaction intrinsically dissipative. A coupled-wave model incorporating pitch chirping and complex optical parameters consistently describes the observed broadband attenuation and polarization-selective response. These findings demonstrate that photoinitiator dyes can actively shape supramolecular organization during polymerization, enabling programmable solid-state chiral photonic materials with broadband dissipative and polarization-selective functionalities.

Hierarchical surface structuring is a critical aspect of advanced materials design, impacting fields ranging from optics to biomimetics. Among several laser-based methods for complex structuring of photo-responsive surfaces, the broadband vectorial interferometry proposed here offers unique performances. Such a method leverages a polychromatic laser source, an unconventional choice for holographic encoding, to achieve deterministic multiscale surface structuring through interference light patterning. Azopolymer films are used as photosensitive substrates. By exploring the interaction between optomechanical stress modulations at different spatial periodicities induced within the polymer bulk, we demonstrate the emergence of hierarchical Fourier surfaces composed of multiple deterministic levels. These structures range from sub-micrometer to tens of micrometers scale, exhibiting a high degree of control over their morphology. The experimental findings reveal that the optical encoding scheme significantly influences the resulting topographies. The polarization light patterns lead to more regular and symmetric hierarchical structures compared to those obtained with intensity patterns, underscoring the role of vectorial light properties in controlling surface morphologies. The proposed method is fully scalable, compatible with more complex recording schemes (including multi-beam interference), and it is applicable to a wide range of advanced technological fields. These include optics and photonics (diffractive elements, polarimetric devices), biomimetic surfaces, topographical design, information encoding, and anti-counterfeiting, offering a rapid, reliable, and versatile strategy for high-precision surface structuring at a submicrometric scale.

Standing-waves created by counter-propagating light beams can adopt various forms, offering flexible and efficient methods for recording complex periodic structures in polarization-sensitive materials. Compared to conventional holographic/lithographic techniques, this approach simplifies the encoding of intricate and customizable light structures with finely tunable periodicities and highresolution. It also overcomes limitations at submicrometric periodicities, where traditional methods struggle to maintain fidelity to desired designs. This study explores 1D standing-waves with different polarization gradients, such as corkscrew and Sisyphus patterns. Generated by laser beams operating in multiline-mode with decoupled intensity and polarization control, these light structures can encode multiple, independent polarization volume gratings simultaneously in a single-step process. Submicrometric periodicities are achieved by positioning the material layer at a tilting angle within the standing-wave, allowing fine-tuning of the recording periodicities with a few nanometers spatial resolution. The resulting gratings diffract light at notably large angles, preserving polarization properties and avoiding crosstalk. These spatio-spectral structures hold transformative potential for ultra-compact optical systems. Key applications include material structuring, advanced information processing with higher capacity and security, and augmented/virtual reality platforms, where efficient polarization control ensures high-fidelity image projection and interaction. This method opens unexplored opportunities for scalable, high-resolution applications in cutting-edge optical technologies.

Photopolymerizable liquid crystals, also known as reactive mesogens, are leading candidates for additive manufacturing of smart microdevices via two‐photon lithography (TPL). While substantial advancements are made toward innovative applications, precise control of molecular alignment during fabrication, essential for tailoring complex optical and mechanical responses, remains a significant challenge. Current solutions require elaborate multi‐step procedures or customized setups to achieve 2D or 3D alignment patterns. Herein, the deterministic effect of TPL on the orientation of mesogenic moieties is reported, under optimized printing conditions. Specifically, a single‐step simple method is developed for aligning the nematic director in situ, with sub‐diffraction‐limited resolution, during 3D printing. Based on the conventional TPL workflow, the “director‐tuning mode” (DiTuM) relies on the anisotropic photopolymerization reaction occurring along the print path at low laser scan speeds (≈0.1mm s −1 ). A TPL‐induced “easy axis” arises for the mesogenic moieties, programmable in direction and strength, and competes with the initial alignment to create potentially convolute 3D director fields. The method holds considerable promise for 3D/4D printing, enabling advanced functionalities, and offers a robust platform for anti‐counterfeiting applications, leveraging the unique optical signatures generated by complex microstructures.

Under simultaneously tangential and perpendicular alignment, known as hybrid alignment, chiral nematic liquid crystals with specific pitch lengths form a striped pattern with significant potential for applications such as diffraction gratings. This study employs computer simulations to investigate methods for fabricating different striped patterns using substrates with a predesigned organisation of the easy axis on the planar (tangential) surface. The substrate designs include chequerboard, circular, and triangular patterns, with the easy axis oriented perpendicularly in alternating regions. The number of domains with a given pattern varies, and the resulting changes in the stripe pattern, including the system's elastic energies, are analysed. The simulations demonstrate the feasibility of controlling the formation of complex patterns through simple modifications of the planar substrate.

This study aims to test and validate the modern orientation approach of Saphiannikova et al. within the context of viscoplastic photoalignment (VPA) modeling. We focus on the formation of topographical structures under interference patterns featuring spatially varying elliptical polarization. By comparing our VPA modeling results with the asymmetric height profiles reported by Pagliusi et al., we observe a pronounced coupling effect between elliptically polarized light and the anisotropic orientation of azo-chromophores induced by this light. Our findings suggest that the photoinduced birefringent layer deviates the azimuth of elliptically polarized light, which in turn rotates the main axis of the anisotropic orientation in a chiral propagating structure. This self-induced rotation of light polarization influences the spatial dependence of interference profiles as a function of depth within the film. This research not only reinforces the importance of polymer backbone reorientation in azopolymer films but also enhances the predictive capabilities of VPA modeling in designing complex, light-driven topographical structures.

The helicoidal architecture of cholesteric reactive mesogens allows for smart 4D responsive microdevices that reflect selectively the wavelength and polarisation of the incident light. Two-photon lithography is an effective 4D microprinting technology which also enables fine tuning of the Bragg reflection, as a function of the energy delivered during the manufacturing and the polymerisation degree. When CRMs objects undergo temperature variation, thermal expansion causes the elongation of the effective helix pitch and the consequent red-shift of the photonic band gap. A thermal characterisation of the optical response of CRMs microcylinders is presented, showing a tunable red-shift from 2 to 37 nm in the 30-150(degrees)C range. The red-shift is enhanced for tall structures, with high polymerisation degree. This characterisation is exploited to add a security label to a 4D cholesteric QR code. [GRAPHICAL ABSTRACT]

The ever-growing demand for submicrometer-structured surfaces with hierarchical features is guided by efficient applications in augmented/virtual reality, display technologies, and Fourier optics, as well as for the development of multifunctional platforms for biomedicine, sensors, and security. Among all, Fourier surfaces still represent a challenge. Indeed, the current technologies are mainly based on multistep processes which involve lithographic methods and/or thermal/chemical/electrical treatment and often suffer in terms of losses due to their intrinsic binary design. Herein, a broadband laser composed of close and highly correlated lines allows for the simultaneous photoinscription of extremely precise hierarchical Fourier surfaces via vectorial interference. By simply setting the number of lines, their amplitude, and polarization, the polychromatic light enables a high-fidelity encoding of multiple sinusoidal profiles with nanometric spatial resolution. Beat phenomena that arise in the bulk of the recording medium result in the never-observed hierarchical structuring of the topography. Such an approach, unconventional for holographic techniques where monochromaticity of light is a key element, provides promising perspectives for the in situ design of hierarchical Fourier surfaces and the scale-up of customized structured platforms, besides the obvious advantages of the method in terms of scalability, reconfigurability, and tunability.

The ever‐growing demand for ultracompact micro‐ and nano‐optics is guided by efficient applications in augmented/virtual reality, displays, and Fourier optics. The current technologies, mainly based on meta‐solutions, suffer in terms of efficiency and tunability, as well as complex and multi‐step fabrication methods that may limit their full‐scale potential. Herein, a broadband laser composed of close and highly correlated lines allows, via interference patterning, for simultaneous encoding of multiplexed, independent, and cross‐talk free holograms with nanometric separation. The reported findings show that such light, unusual for holographic recording, unlocks new features of organized collective phenomena, overcoming the usual spatial resolution limitations of the optical techniques. This approach gives promising perspectives for in situ design of reconfigurable structured optics, besides the obvious advantages of full‐scalability, easiness, cost effectiveness, and time and energy consumption.

The development of efficient and cost-effective micromachines is a challenge for applied and fundamental science, given their wide fields of usage. Light is a suitable tool to move small objects in a noncontact way, given its capabilities in exerting forces and torques. However, when complex manipulation is required, micro-objects with proper architecture could play a specific role. Here we report on the rotational dynamics of core-shell particles, with a polymeric nematic core of ellipsoidal shape capped by Au nanoparticles. They undergo a peculiar synchronous spinning and orbital motion when irradiated by a simple Gaussian beam, which originates from the coupling of the metallic nanoparticles’ optical response and the core anisotropies. The rotation capabilities are strongly enhanced when the trapping wavelength lies in the plasmonic resonance region: indeed, the spin kinetic energy reaches values two orders of magnitude larger than the one of bare microparticles. The proposed strategy brings important insights into optimizing the design of light controlled micro-objects and might benefit applications in microfluidics, microrheology, and micromachining involving rotational dynamics.

Gold nanoparticles (GNPs) can be patterned on specific positions and substrates by Multi-Photon Direct Laser Writing (MP-DLW) in wet polymeric matrices doped with tetrachloroauric acid (HAuCl 4 ) as gold precursor. The Hamaker constants describing the GNP-GNP interaction and the interaction between the GNPs and the surrounding materials is described, defining the role of the polymeric matrix; thus, its limits and the advantages are thoroughly analysed. The Multi-Photon Photo-Reduction (MPPR) process, leading to the GNPs creation, triggers a local temperature rising, which can ablate the polymer and influences the particle distribution, size and density. The GNPs polydispersity also depends on the water content in the film, variable because of the vaporization. A protocol to perform MP-DLW of GNPs, without the use of the polymer is illustrated: by treating the surface with a surfactant, it is possible to make the particles stick to the substrate, control their size and reduce the diffusive and convective effects generated by the MPPR.

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.

Laser interferometry is a consolidated technique for materials structuring, enabling single step and large area patterning. Here we report the investigation of the morphological modification encoded on a thin film of a photosensitive material by the light interference pattern obtained from a laser operating in multiline mode. Four lines with equal intensity are retained, with the same p linear polarization. An azopolymer is exploited as medium for the holographic recording. Optical microscopy and profilometer measurements analyze the modification induced in the bulk and on the surface of the irradiated area. We show that the intensity profile of the interference patterns of two laser beams is the one obtained assuming each line of the laser as an independent oscillator of given intensity and wavelength, and how these light structures are faithfully replicated in the material bulk and on the topography of the free surface. Patterns at different length scales are achievable in a single step, that can be traced back to both interference fringes and wave envelopes. The proposed multi-wavelength holographic patterning provides a simple tool to generate complex light structures, able to perform multiscale modifications of photoresponsive materials

Multi-photon direct laser writing (MP-DLW) in polymeric matrices doped with a tetrachloroauric acid (HAuCl4) water solution allows creating clusters of gold nanoparticles (GNPs) inside the focus figure of a tightly focused ultrafast laser beam. The key physical phenomena involved in the process are analyzed, with the aim to assess the limits and potential of this promising technology. Multi Photon Absorption (MPA) triggers the photo-reduction of AuCl4– ions and the consequent creation of GNPs in the spotted volume. Thermal electronic decays lead to a local abrupt increase of the temperature, which influences the morphology of the created structures. At the same time, two different effects take place, related to the dehydration of the polymeric matrix, and the concentration gradient of the gold precursor upon localized photoreduction. Given their different timescales, these phenomena allow for controlling the GNPs density and size dispersity when a given energy dose is delivered in multiple exposures, tuning the delay between consecutive laser exposures. A simple yet effective experiment to estimate the temperature distribution at the micron-scale is also proposed.

We report on the synthesis, characterization, and application of biomimetic, spherical Au nanoparticles (AuNPs) coated with keratin (Ker-AuNPs). They are characterized in terms of morphological, spectral, and thermo-optical properties. Besides their excellent colloidal stability, Ker-AuNPs exhibit excellent biocompatibility. The latter is verified by performing viability assay experiments of a strain of Escherichia coli (E. coli) in the presence of Ker-AuNPs as a function of the incubation time. Ker-AuNPs do not affect the E. coli viability and proliferation, even at the highest concentration tested (C = 5.83*10(-5) M). Photo-thermal assisted viability experiments are performed by setting the starting temperature at 37 degrees C, mimicking the normal human body temperature condition. They evidence the capability of the Ker-AuNPs to generate a temperature up to about 73 degrees C (an increase of 36 degrees C), thus reducing the viability of bacterial cells 3 order of magnitudes. We also conducted a theoretical analysis with an ad-hoc model that evidences an excellent agreement between theory and experiments. Ker-AuNPs represent a new generation of multifunctional nanotherapeutics, and they constitute a new opportunity in drug-free and minimally invasive biomedical applications.

Core-shell architecture enables to impart unique customized properties to microparticles, through the proper selection of composition and aggregation state of the inner and outer materials. Here, the synthe-sis of microparticles with a chiral dielectric core and a metallic shell of gold nanoparticles is demon-strated. The chiral core is obtained by UV induced polymerization of the self-organized droplets of a cholesteric reactive mesogen in a chloroauric acid aqueous solution. Gold nanoparticles precipitation contemporarily occurs upon UV irradiation, covering the microparticles surface. Electron microscopy and optical spectroscopy investigations give evidence that the degree of coverage of the core by gold nanoparticles, with size less than 100 nm, depends on the chloroauric acid concentration, while their aggregation is influenced by the polymeric surface morphology. The optical properties of the chiral microparticles are modified by the gold shell. Specifically, gold coating of dye doped chiral microparticles, working as Bragg onion resonators, clearly improves the stability of omnidirectional microlasers. The pro-posed strategy, due to the flexibility of the chiral material and of the method, opens a route toward fab-rication of microdevices with wide control over light manipulation, in term of intensity, polarization, generation. (c) 2021 Elsevier Inc. All rights reserved.

Correction for ‘Collective motion of chiral Brownian particles controlled by a circularly-polarized laser beam’ by Raúl Josué Hernández et al., Soft Matter, 2020, 16, 7704–7714, DOI: 10.1039/C9SM02404B.

Core-shell architecture enables to impart unique customized properties to microparticles, through the proper selection of composition and aggregation state of the inner and outer materials. Here, the synthesis of microparticles with a chiral dielectric core and a metallic shell of gold nanoparticles is demonstrated. The chiral core is obtained by UV induced polymerization of the self-organized droplets of a cholesteric reactive mesogen in a chloroauric acid aqueous solution. Gold nanoparticles precipitation contemporarily occurs upon UV irradiation, covering the microparticles surface. Electron microscopy and optical spectroscopy investigations give evidence that the degree of coverage of the core by gold nanoparticles, with size less than 100 nm, depends on the chloroauric acid concentration, while their aggregation is influenced by the polymeric surface morphology. The optical properties of the chiral microparticles are modified by the gold shell. Specifically, gold coating of dye doped chiral microparticles, working as Bragg onion resonators, clearly improves the stability of omnidirectional microlasers. The proposed strategy, due to the flexibility of the chiral material and of the method, opens a route toward fabrication of microdevices with wide control over light manipulation, in term of intensity, polarization, generation.

Photochromic liquid crystalline block copolymers (PLCBCs) are currently playing a significant role as light-responsive materials because of their light controllable features over multiple length scales. Herein, a study of the photoinduced optical anisotropy derived by the combination of orientation phenomena at molecular and supramolecular levels in a novel kind of side-chain PLCBCs with mesogenic phenyl benzoate groups and pyridine units that is hydrogen bonded with azobenzene-containing phenol is reported. Based on the polymeric architectures and composition, the supramolecular configuration self-organizes in different microphases that affect the material response to the external stimuli. Simple, 1D, polarization holograms are recorded to evaluate the photoinduced birefringence. The first step, light patterning, involves the orientation of the azobenzene units and precedes a thermal treatment that amplifies the induced anisotropy through the cooperative orientation of the mesogenic units. By selective extraction, the azobenzene units can be removed, making the material transparent to the visible light. Excellent photostability of the material birefringence is obtained, whose final value is strongly affected by the block copolymer's architecture. The versatility in the molecular design, the fine control of the photoinduced features by external parameters, and, finally, the possibility to achieve photostability make these materials of great potential for developing optical and photonic devices.