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Optical activity (polarization rotation of light) is one of the most desired features of chiral media, as it is important for many polarization related applications. However, in the THz region, chiral media with strong optical activity are not available in nature. Here, we study theoretically, and experimentally a chiral metamaterial structure composed of pairs of vertical U-shape resonators of "twisted" arms, and we reveal that it demonstrates large pure optical activity (i.e. optical activity associated with negligible transmitted wave ellipticity) in the low THz regime. The experimental data show polarization rotation up to 25 (deg) for an unmatched bandwidth of 1 THz (relative bandwidth 80 %), from a 130 um-thickness structure, while theoretical optimizations show that the rotation can reach 45 (deg). The enhanced chiral response of the structure is analyzed through an equivalent RLC circuit model, which provides also simple optimization rules for the enhancement of its chiral response. The proposed chiral structures allow easy fabrication via direct laser writing and electroless metal plating, making them suitable candidates for polarization control applications., Comment: 17 pages, 7 figures

This perspective is an overview of a recent direction in optical 3D printing, where polymerization of crosslinkable materials and nanomaterial fillers can be guided to the final structures and new composites via high temperature annealing (HTA). Defining 3D nano/micro-structures by ultrafast laser direct writing and tailoring their precursor composition with subsequent tunability of the final properties during 750–1500 °C HTA step takes place at the large surface-to-volume ratio conditions favoring efficient pyrolysis and calcination, which are required for exchange of chemical materials/gases between glass/ceramic phase and surrounding. Previously, unexplored inorganic material formation conditions in terms of fast thermal quenching, composition mixing and surface tension guided formation can be harnessed by glass making for creation of new materials endowed with preferable technical properties. An immediate application perspective for a high durability, integrated, and active 3D micro-optics is foreseen.

Multi-photon lithography -a powerful laser nanoscale additive-manufacturing method- is employed for structuring micro-ring traveling-wave resonators onto micrometric diameter, optical fiber tapers. These weakly guided, micro-ring resonating structures achieve light circulation with Q-factors of the order of ∼2.0 × 103, for typical diameters of tens of micrometers, in the spectral band of 1550 nm. The parametrization of the fabrication process, the characterization of these structures in TE and TM polarization, and the numerical simulation of their spectral performance is presented and analyzed. Moreover, these micro-ring resonators are exemplified into the demonstration of an ethanol vapor sensor, readily achieving detectivities of 0.5 ppm, based on reversible physisorption effects. Our demonstration aims at developing a new type of photonic platforms, based on a versatile, laser based prototyping approach onto micrometric size, optical fiber tapers, while exhibiting unique guiding and modal interaction characteristics, for departing the laboratory bench, while being implemented into diverse types of sensing and actuating devices.

Summarization: This study describes the fabrication of ultrafast laser-induced periodic nanostructures on Nickel sheets and their use as cathodes in alkaline electrolysis. For the first time, to the best of our knowledge, laser-nanostructured Ni sheets were used as cathode electrodes in a custom-made electrolysis cell at actual, Hydrogen producing conditions, and their efficiency has been compared to the untreated Nickel sheets. The electrochemical evaluation showed higher Jpeaks, lower overpotential, and enhanced double-layer capacitance for the nanostructured electrode. A decrease in the Tafel slope was also found for the nanostructured electrode. The hydrogen production efficiency was found to be 3.7 times larger for the laser-nanostructured Nickel electrode, which was also confirmed by current-time measurements during electrolysis. Also, a novel approach is proposed to improve the stability of the current density during electrolysis and, therefore, the hydrogen production process by about 10%. Presented on: International Journal of Hydrogen Energy

Damage in the Peripheral Nervous System (PNS) is related to numerous neurodegenerative diseases and has consequently drawn the attention of Tissue Engineering (TE), which is considered a promising alternative to already established methods such as surgery and autografts. TE focuses on the design, optimization, and use of scaffolds in vitro and in vivo. In this work, the authors used a novel scaffold geometry fabricated via Multiphoton Lithography (MPL), a commonly used fabrication method, for the mono- and co-cultures of glial Schwann (SW10) and neuronal Neuro-2a (N2a) cells. Both cell types have already been used for the study of various neurodegenerative diseases. However, their focus has been on only one of the cell types at a time, with studies regarding their co-culture only recently documented. Here, the suitability of the fabricated scaffolds has been explored and the effects of topography on SW10 and N2a behavior have been investigated. Our findings demonstrate that scaffold co-culture systems favor the presence of neurites compared to mono-cultures at 21 days (31.4 ± 5.5% and 15.4 ± 5.4%, respectively), while there is also a significant decrease in long neurites in the mono-culture over time (45.3 ± 15.9% at 7 days versus 15.4 ± 5.4% at 21 days). It has been shown that the scaffolds can successfully manipulate cell growth, elongation, and morphology, and these results can form a basis for the development of an experimental model for the study of PNS-related diseases and understanding of key cell functions such as myelination.

The rapid development of additive manufacturing has fueled a revolution in various research fields and industrial applications. Among the myriad of advanced 3D printing techniques, two-photon polymerization lithography (TPL) uniquely offers a significant advantage in nanoscale print resolution, and has been widely employed in diverse fields, for example, life sciences, materials sciences, mechanics, and microfluidics. More recently, by virtue of the optical transparency of most of the resins used, TPL is finding new applications in optics and photonics, with nanometer to millimeter feature dimensions. It enables the minimization of optical elements and systems, and exploration of light-matter interactions with new degrees of freedom, never possible before. To review the recent progress in the TPL related optical research, it starts with the fundamentals of TPL and material formulation, then discusses novel fabrication methods, and a wide range of optical applications. These applications notably include diffractive, topological, quantum, and color optics. With a panoramic view of the development, it is concluded with insights and perspectives of the future development of TPL and related potential optical applications.

The current protocols for biocompatibility assessment of biomaterials, based on histopathology, require the sacrifice of a huge number of laboratory animals with an unsustainable ethical burden and remarkable cost. Intravital microscopy techniques can be used to study implantation outcomes in real time though with limited capabilities of quantification in longitudinal studies, mainly restricted by the light penetration and the spatial resolution in deep tissues. We present the outline and first tests of a novel chip which aims to enable longitudinal studies of the reaction to the biomaterial implant. The chip is composed of a regular reference microstructure fabricated via two-photon polymerization in the SZ2080 resist. The geometrical design and the planar raster spacing largely determine the mechanical and spectroscopic features of the microstructures. The development, in-vitro characterization and in vivo validation of the Microatlas is performed in living chicken embryos by fluorescence microscopy 3 and 4 days after the implant; the quantification of cell infiltration inside the Microatlas demonstrates its potential as novel scaffold for tissue regeneration.

Description, A substantial improvement in the strength of a material is made with a new optimization method applicable to many science problems., We use a previously unexplored Bayesian optimization framework, “evolutionary Monte Carlo sampling,” to systematically design the arrangement of defects in an architected microlattice to maximize its strain energy density before undergoing catastrophic failure. Our algorithm searches a design space with billions of 4 × 4 × 5 3D lattices, yet it finds the global optimum with only 250 cost function evaluations. Our optimum has a normalized strain energy density 12,464 times greater than its commonly studied defect-free counterpart. Traditional optimization is inefficient for this microlattice because (i) the design space has discrete, qualitative parameter states as input variables, (ii) the cost function is computationally expensive, and (iii) the design space is large. Our proposed framework is useful for architected materials and for many optimization problems in science and elucidates how defects can enhance the mechanical performance of architected materials.

Optics manufacturing technology is predicted to play a major role in the future production of integrated photonic circuits. One of the major drawbacks in the realization of photonic circuits is the damage of optical materials by intense laser pulses. Here, we report on the preparation of a series of organic–inorganic hybrid photoresists that exhibit enhanced laser-induced damage threshold. These photoresists showed to be candidates for the fabrication of micro-optical elements (MOEs) using three-dimensional multiphoton lithography. Moreover, they demonstrate pattern ability by nanoimprint lithography, making them suitable for future mass production of MOEs.

Multi-functional materials are of paramount importance in biomedical engineering. In this work, we present the synthesis of a hybrid, organic–inorganic material functionalized with covalently-attached natural antimicrobial moeties based on thymol, an essential oil found in thyme. The hybrid material is a double organic–inorganic network formed by sol–gel chemistry followed by photopolymerizaton of the organic moeities, and allows the fabrication of highly accurate 3D scaffolds by means of multi-photon polymerization. The cytocompatibility of the materials and scaffolds was proved by the excellent cell adhesion and proliferation of dental pulp stem cells, whereas their osteogenic potential was evidenced by the significant production of calcium in the matrix, following functionalization with bone morphogenetic protein-2. The antimicrobial activity of the thymol-functionalized 3D scaffolds against E. coli and B. cereus was demonstrated by the inhibition of bacterial growth after 1 and 4 days in culture. These dual-functional, hybrid materials, exhibiting simultaneously biocompatibility and osteogenic potential, as well as an effective antimicrobial activity are excellent candidates for bone tisue engineering.

Multiphoton lithography, based on multiphoton polymerization, is a powerful technique for the fabrication of complex three-dimensional (3D) structures. Herein, we report on the photostructuring of novel biopolymer-based hybrid hydrogels, comprising gelatin methacrylamide and a water-soluble chitosan derivative, via multiphoton polymerization. The nontoxic, Food and Drug Administration-approved, biocompatible photosensitizer eosin Y was exploited as the sole photoinitiator, without the coinitiators and/or comonomer that are commonly used, allowing for further expansion of the available wavelengths up to 800 nm. Importantly, the obtained hybrid material exhibits excellent biocompatibility, evidenced by the increased proliferation of dental pulp stem cells, compared with the individual components and the polystyrene control, after 7 days in culture. Additionally, the 3D hybrid scaffolds promote the matrix mineralization, following their functionalization with bone morphogenetic protein 2. These tailor-made synthetic, biocompatible materials pave the way for further opportunities in 3D scaffold fabrication, including in situ and in vivo biofabrication.

Mechanical metamaterials demonstrate augmented properties derived from their engineered structure. Advances in three-dimensional (3D) printing technologies have enabled the fabrication of complex metamaterial structures even at the microscale, contributing to the development of light-weight materials with superior mechanical properties. However, understanding of metamaterial strain hardening that is intrinsic to both the structure and arrangement of novel unit cells is sparse and fairly empirical. The main objective of this study was to introduce a new design approach for 3D mechanical metamaterials with enhanced strain hardening and energy absorption, fabricated at the microscale by multiphoton lithography, which is the only fabrication technique that can produce micrometer length scales and high structural complexity. This was accomplished by intertwining simple polyhedra to create more complex geometries in 3D space, using penetration twins as a point of reference, a mechanism of crystal in-growth wherein distinct crystals appear to penetrate each other. This structural principle was used to intertwine the lattice members of the structure and tailor their buckling behavior. The present design is inspired by the first stellation of the rhombic dodecahedron. With this concept, plastic deformation can be controlled through localized buckling of select lattice members. Finite element simulations and nanoindentation experiments demonstrate remarkably improved performance with respect to both strain hardening and energy dissipation of the structure compared to both the bulk material and one of the most thoroughly studied ultralight, ultrastiff mechanical metamaterials, the octet truss.

International audience; In this paper, we reveal that the mathematical discrete model of Hencky type, introduced in [1], is appropriate for describing the mechanical behavior of micro-metric pantographic elementary modules. This behavior does not differ remarkably from what has been observed for milli-metric modules, as we prove with suitably designed experiments. Therefore, we conclude that the concept of pantographic microstructure seems feasible for micro-metrically architected microstructured (meta)materials as well. These results are particularly indicative of the possibility of fabricating materials that can have an underlying pantographic microstructure at micrometric scale, so that its unique behavior can be exploited in a larger range of technological applications.

Since the global energy demand increases annually, a great need is arising in energy-related technologies. Photocatalysis plays a major role in these technologies, as it exploits one of the renewable types of energy, solar energy. For this reason, there is a plethora of scientific investigations in the research field of photocatalysis. In particular, the variety of materials that could be employed to efficiently enhance the procedure, is extensively studied. One of the most widely used materials is titania (TiO 2 ) due to its efficiency in photocatalysis [1] , while maintaining and other notable properties such as non-toxicity, chemo-stability, enhanced electronic and optical characteristics.

The detection of vapours of organic solvents at low concentrations impacts significant market sectors such those of chemical processing, safety, and security. The interaction of organic molecules in the gas phase with optical surfaces mostly refers to physisorption processes, with typical adhesion monolayers in the scale few nm’s or lower; the transduction mechanism for tracing those vapours using evanescent field interactions is a significant challenge. Few gas sensing probes have been realised using planar micro-ring resonators (MRRs), while being used for detecting inert gas pressure changes or vapours of organic molecules using oxide layers.

In this work, we report a one-step sputtering method for direct preparation of Cu2O and CuO coatings on different substrates, i.e. glass, thin polymer films and titanium alloy. Interestingly, these coatings possessing micro- and nanostructures exhibiting controlled dual-scale roughness and the wettability investigation reveals that we can tune the wetting properties.

Photopolymerization of (meth)acrylate-based formulations has become a widespread method for industry due to the high energy efficiency and low curing times of this technology. Various products from simple coatings to more complex applications such as additive manufacturing technologies are based on this versatile method. Common industrial radical photoinitiators are generally based on aromatic ketones. Benzaldehyde is an organic compound consisting of a benzene ring with a formyl substituent. It is the simplest aromatic aldehyde and one of the most industrially useful; for instance in the preparation of various aniline dyes, perfumes, flavorings, and pharmaceutics. Parallel to this, triphenylamines are extensively used for the design of dyes used for solar energy conversion. In this work, three triphenylamine derivatives bearing formyl groups are as a new substance class of multi-photon lithography photoinitiators. The photophysical properties of the PIs were investigated by UV−Vis abs

Welcome and Introduction to SPIE Photonics West LASE conference 11675: Synthesis and Photonics of Nanoscale Materials XVIII

The need for control of the elastic properties of architected materials has been accentuated due to the advances in modelling and characterization. Among the plethora of unconventional mechanical responses, controlled anisotropy and auxeticity have been promulgated as a new avenue in bioengineering applications. This paper aims to delineate the mechanical performance of characteristic auxetic and anisotropic designs fabricated by multiphoton lithography. Through finite element analysis the distinct responses of representative topologies are conveyed. In addition, nanoindentation experiments observed in-situ through scanning electron microscopy enable the validation of the modeling and the observation of the anisotropic or auxetic phenomena. Our results herald how these categories of architected materials can be investigated at the microscale.

Multiphoton lithography allows the high resolution, free-form 3D printing of structures such as micro-optical elements and 3D scaffolds for Tissue Engineering. A major obstacle in its application in these fields is material and structure autofluorescence. Existing photoresists promise near zero fluorescence at the expense of poor mechanical properties, and low printing efficiency. Sudan Black B is a molecular quencher used as a dye for biological studies and as means of decreasing the autofluorescence of polymers. In our study, we report the use of Sudan Black B both as a photoinitiator and as a post-fabrication treatment step, using the zirconium silicate SZ2080 for the development of a non-fluorescent composite. We use this material for the 3D printing of micro-optical elements, and meso-scale scaffolds for mesenchymal stem cell cultures. Our results show that the Sudan Black B photosensitive hybrid can be used for the fabrication of high resolution, highly transparent, autofluorescence-free microstructures.

A ring resonator device developed onto an optical fiber taper, using multi-photon laser lithography, while operating as ethanol vapor sensor is presented. This sensor readily measures ethanol vapor concentrations of 0.5ppm, with Q-factor of 1.9x103.

Ultrafast laser 3D lithography based on non-linear light–matter interactions, widely known as multi-photon lithography (MPL), offers unrivaled precision rapid prototyping and flexible additive manufacturing options. 3D printing equipment based on MPL is already commercially available, yet there is still no comprehensive understanding of factors determining spatial resolution, accuracy, fabrication throughput, repeatability, and standardized metrology methods for the accurate characterization of the produced 3D objects and their functionalities. The photoexcitation mechanisms, spatial-control or photo-modified volumes, and the variety of processable materials are topics actively investigated. The complexity of the research field is underlined by a limited understanding and fragmented knowledge of light-excitation and material response. Research to date has only provided case-specific findings on photoexcitation, chemical modification, and material characterization of the experimental data. In this review, we aim to provide a consistent and comprehensive summary of the existing literature on photopolymerization mechanisms under highly confined spatial and temporal conditions, where, besides the excitation and cross-linking, parameters such as diffusion, temperature accumulation, and the finite amount of monomer molecules start to become of critical importance. Key parameters such as photoexcitation, polymerization kinetics, and the properties of the additively manufactured materials at the nanoscale in 3D are examined, whereas, the perspectives for future research and as well as emerging applications are outlined.

Multiphoton lithography allows the high resolution, free-form 3D printing of structures such as micro-optical elements and 3D scaffolds for Tissue Engineering. A major obstacle in its application in these fields is material and structure autofluorescence. Existing photoresists promise near zero fluorescent in expense of poor mechanical properties, and low printing efficiency. Sudan Black B is a molecular quencher used as a dye for biological studies and as means of decreasing the autofluorescence of polymers. In our study we report the use of Sudan Black B as both a photoinitiator and as a post-fabrication treatment step, using the zirconium silicate SZ2080™ for the development of a non-fluorescent composite. We use this material for the 3D printing of micro-optical elements, and meso-scale scaffolds for Mesenchymal Stem Cell cultures. Our results show the hybrid, made photosensitive with Sudan Black B, can be used for the fabrication of high resolution, highly transparent, autofluorescence-free microstructures.

Ultrafast laser 3D lithography based on non-linear light-matter interactions, widely known as multi-photon lithography (MPL), offers unrivaled precision rapid prototyping and flexible additive manufacturing options. 3D printing equipment based on MPL are already commercially available, yet there is still no comprehensive understanding of factors determining spatial resolution, accuracy, fabrication throughput, repeatability, and standardized metrology methods for the accurate characterization of the produced 3D objects and their functionalities. The photoexcitation mechanisms, spatial-control or photo-modified volumes, and the variety of processable materials are topics actively investigated. The complexity of the research field is underlined by limited understanding and fragmented knowledge of light-excitation and material response. Research to date has only provided case-specific findings on photoexcitation, chemical modification, and material characterization of the experimental data. In this review, we aim to provide a consistent and comprehensive summary of the existing literature on photopolymerization mechanisms under highly confined spatial and temporal conditions, where, besides the excitation and cross-linking, parameters such as diffusion, temperature accumulation, and the finite amount of monomer molecules start to become of critical importance. Key parameters such as, photoexcitation, polymerization kinetics, and the properties of the additively manufactured materials at the nanoscale in 3D are examined, whereas, the perspectives for future research and as well as emerging applications are outlined.

Author(s): Flamourakis, George; Spanos, Ioannis; Vangelatos, Zacharias; Manganas, Phanee; Papadimitriou, Lina; Grigoropoulos, Costas; Ranella, Anthi; Farsari, Maria

Architected metamaterials exhibit unique properties bestowed by their engineered structure rather than their chemical composition. Extrinsic material properties have been achieved as a result of advances in additive manufacturing. Contemporary fabrication techniques, such as multiphoton lithography and digital light processing, have enabled the fabrication of complex structures with inherent hierarchies at length scales ranging from nanometers to micrometers. However, despite significant insight into the role of buckling in the mechanical behavior of materials reported in earlier studies, particularly strength and energy dissipation, the structural and design principles responsible for the improved mechanical performance were not fully elucidated, thus limiting the design space of these structures. The principal objective of this study was to investigate how controlled three-dimensional assembly and orientation of intertwined lattice members influence localized buckling and the overall mechanical response of such metamaterial structures. The novelty of the present design approach stems from a mechanical metamaterial inspired by the three-compound octahedron and the symmetry variance observed during phase change of crystalline solids. For a specific orientation and tactical joining of the unit cells, this geometry demonstrates unprecedented resilience to large deformations and high energy dissipation capacity. The selective shape modification of specific lattice members is shown to greatly improve the structural integrity of ultralight structures undergoing large deformation. Results from finite element simulations and in situ scanning electron microscopy-microindentation experiments reveal the actual deformation of metamaterial structures with straight and curved lattice members and elucidate the effects of anisotropy and orientation characteristics on the dominant mechanisms affecting the mechanical performance of intertwined lattice structures.

Nanoimprint lithography (NIL) is a technique suitable for the mass production of micro-optical elements using a mould. One drawback, however, is that the materials used in NIL have low laser-induced damage threshold (LIDT). Here, we present our results in the development of a series of high-LIDT organic-inorganic hybrid materials, and their application in NIL using moulds made by multiphoton lithography.

Arrays of hierarchical microstructures are considered nowadays as an effective method to create hydrophobic surfaces. Herein, we use femtosecond 3D printing to manufacture microstructures in different geometric patterns. Direct laser writing and, in particular, multiphoton polymerization lithography (MPL) with ultrafast laser pulses has taken additive manufacturing all the way down to the sub-micrometer scale. MPL is a 3D nanoscale manufacturing tool offering great potential for rapid prototyping and the manufacture of photonic devices, tissue scaffolds and biomechanical parts. In this study, we demonstrate the tuning of the wetting performance of surfaces via trichomes designs of 3D microstructures.

We are presenting a model for a quantitative description of the polymerization process in 3D-laser microfabrication. With aim to assist in estimating the necessary power threshold to obtain certain feature size, particularly the line characteristics, depending on the laser power and writing speed. The focal distribution as well as the photoresist is taken into account. We do not try to gain any chemical insight into the processes involved, and restrict us to a quantitative study of a multi-photon process. Machine learning is used to classify the input SEM images providing a look-up table as a custom field for optimized parameter selection.

Three-dimensional (3D) nanofabrication using the directed self-assembly of block copolymers (BCPs) holds great promise for the nanoscale device fabrication and integration into 3D architectures over large areas with high element densities. In this work, a robust platform is developed for building 3D BCP architectures with tailored functionality using 3D micron-scale woodpile structures (WPSs), fabricated by a multiphoton polymerization technique. By completely filling the spaces of the WPSs and using the interactions of the blocks of the BCPs with the struts of the WPS, well-developed 3D nanoscopic morphologies are produced. Metal ion complexation with one block of the copolymer affords a convenient stain to highlight one of the microdomains of the copolymer for electron microscopy studies but also, with the reduction of the complexing salt to the corresponding metal, a simple strategy is shown to produce 3D constructs with nanoscopic domain resolution.

EUR was partially supported by Grant of Russian Ministry of Science and Education (Grant No. 18-15-00172). Multimode high-power laser diodes suffer from inefficient beam focusing, leading to a focal spot 10-100 times greater than the diffraction limit. This inevitably restricts their wider use in 'direct-diode' applications in materials processing and biomedical photonics. We report here a 'super-focusing' characteristic for laser diodes, where the exploitation of self-interference of modes enables a significant reduction of the focal spot size. This is achieved by employing a conical microlens fabricated on the tip of a multimode optical fibre using 3D laser nano-printing (also known as multi-photon lithography). When refracted by the conical surface, the modes of the fibre-coupled laser beam self-interfere and form an elongated narrow focus, usually referred to as a 'needle' beam. The multiphoton lithography technique allows the realisation of almost any optical element on a fibre tip, thus providing the most suitable interface for free-space applications of multimode fibre-delivered laser beams. In addition, we demonstrate the optical trapping of microscopic objects with a super-focused multimode laser diode beam thus rising new opportunities within the applications sector where lab-on-chip configurations can be exploited. Most importantly, the demonstrated super-focusing approach opens up new avenues for the 'direct-diode' applications in material processing and 3D printing, where both high power and tight focusing is required. Publisher PDF