Two-photon polymerization (2PP) enables the fabrication of complex 3D scaffolds for tissue engineering, yet the lack of biocompatible and bioactive photoinitiators remains a bottleneck for functional bio-manufacturing. Here, a one-step strategy is presented using curcumin (CUR), a naturally derived polyphenol, as a high-efficiency multifunctional photoinitiator for gelatin methacryloyl (GelMA) hydrogels. Nonlinear optical characterization reveals a synergistic interaction between CUR and the GelMA protein backbone, resulting in a significantly enhanced two-photon absorption cross-section (σ ≈ 1500 GM) that outperforms conventional initiators. This synergy facilitates an exceptionally broad processing window and high-speed fabrication (up to 52 mm/s) of high-fidelity, complex triply periodic minimal surface (TPMS) and biomimetic bone-like scaffolds. Beyond its initiation efficiency, CUR imparts intrinsic multifunctionality to the resulting 3D constructs. The scaffolds exhibit exceptional biocompatibility with mesenchymal stem cells while demonstrating a potent dual-action antimicrobial defense: a selective passive antifouling effect against E. coli and active photodynamic eradication (>99.9%) of S. aureus upon blue LED irradiation. This "all-in-one" approach transforms the photoinitiator from an inert processing tool into a source of intrinsic scaffold bioactivity, eliminating the need for complex post-fabrication functionalization.

High-resolution lithographic techniques are often limited by low volumetric throughput, since there is no universal and scalable manufacturing process that can produce 3D metasurfaces. In this work, we demonstrate a high-speed holographic 3D printing platform based on spatiotemporal beam shaping, exceeding the repetition rate while keeping the resolution high. The system integrates a femtosecond laser source with a spectral pulse compressor and a beam shaper to project uniform, axially confined light fields to project patterns directly on the advanced photoresists using a Digital Micromirror Device DMD. We investigate the process window for rapid polymerization, optimizing the photoinitiator choice to eliminate thermal crosstalk at high repetition rates. Using this setup, we achieve a production throughput of more than a million voxels per second with sub-micron resolution below 400 nm. The system's reliability is validated through the fabrication of large-area woodpile-like lattices and uniform micropillar arrays, establishing a workflow for scalable manufacturing of micro-optical components.

Multiphoton 3D lithography (MP3DL) based on ultrafast nonlinear light‐matter interactions to enable micro‐/nano‐structuring with resolution beyond the diffraction limit, yet the physical origin of the nonlinear energy deposition that initiates polymerization in photoresists remains ambiguous. Here, we investigate the optical nonlinearities governing MP3 DL using SZ2080TM, a widely used hybrid organic–inorganic photoresist in micro‐/nano‐fabrication. Both the pure resist and formulations containing the photoinitiators/photosensitizers Irgacure369 and 4,4′‐bis(diethylamino)benzophenone are characterized by Z‐scan technique. The nonlinear absorption and refraction coefficients are experimentally determined at commonly used femtosecond laser wavelengths (515, 800, and 1030 nm) under different focusing configurations. These coefficients reveal energy deposition particularities, indicating that the majority of deposited energy originated from the resist itself and can be further enhanced through strong interaction with the photoinitiator, particularly via charge transfer effects. Additionally, we show that nonlinear energy deposition can be substantially increased by extending the interaction volume through an increased beam Rayleigh length, providing an alternative route for improving MP3DL efficiency. Our findings challenge the conventional assumption that photo‐polymerization is initiated exclusively by photoinitiators and establish the fundamental basis for photo‐initiator‐free 3D laser lithography, offering predictive guidelines of polymerization conditions and accelerating the design and optimization of advanced micro‐/nano‐fabrication.

Ultrafast nonlinear optical (NLO) response, fast carrier recovery, broadband absorption, and resistance to radiation and heat make 2D materials promising for photonic technologies. However, low electronic conductivity and carrier concentration limit the performance of semiconducting or semimetallic materials. This work investigates the ultrafast NLO properties and carrier dynamics of Ta 4 C 3 T x and out‐of‐plane ordered Mo 2 Ti 2 C 3 T x MXenes using Z‐scan and pump‐probe optical Kerr effect techniques under visible and infrared femtosecond laser pulses. Their NLO response surpasses all previously studied MXenes and most other 2D nanomaterials, attaining exceptionally high third‐order susceptibility ( χ (3) ) values on the order of 10 −13 esu. Mo 2 Ti 2 C 3 T x exhibits the strongest NLO response under both excitation regimes, attributed to charge transfer between Mo and Ti layers in the MXene structure. Under visible excitation, the studied MXenes display pronounced saturable absorption, while under infrared excitation, they exhibit strong reverse saturable absorption, resulting in efficient optical limiting. Additionally, pump‐probe experiments identify two distinct relaxation processes: a fast one on the sub‐picosecond timescale and a slower one a few picoseconds after photoexcitation. The results indicate that these MXenes are among the strongest NLO materials. They show their great potential for advanced photonic and optoelectronic applications in laser technologies, optical protection, telecommunications, and optical/quantum computing.

Accurate knowledge of nonlinear optical parameters is essential for optimizing energy deposition in ultrafast laser 3D printing, yet these values remain undetermined for many commonly used materials. In this study, we address this gap by experimentally determining the two-photon absorption (TPA) and non-linear refraction coefficients ( β and n 2 ) of the widely used SZ2080 TM resist with the photo-initiators (PI) IRG369 and BIS (Irgacure 369 and 4,4′ bis(diethylamino)-benzophenone or Michler’s ketone). Using the Z-scan method at 515 nm with a low repetition rate (1 kHz) to avoid thermal accumulation, we found that the nonlinear response of the host polymer has a considerable contribution to energy deposition despite the addition of the PI, as the host polymer makes up the majority of 99 % in the solution. The TPA cross section σ were 5.7 ± 0.4 GM (1 GM = 10 −50 cm 4 s photon −1 ) for pure SZ2080 TM , ∼ 40 $\sim 40$ GM for IRG and ∼ 87 $\sim 87$ GM for BIS at 515 nm. The nonlinear refractive index n 2 for pure polymer was (85.3 ± 6) × 10 −5 cm 2 /TW, favoring a self-focusing, and was larger than that for PIs: ∼ 16 × 1 0 − 5 $\sim 16{\times}1{0}^{-5}$ cm 2 /TW (IRG369) and ∼ 2.8 × 1 0 − 5 $\sim 2.8{\times}1{0}^{-5}$ cm 2 /TW (BIS). Hence, the properties of the host material govern non-linear light propagation, although, in high numerical aperture focusing, self-focusing has a minor contribution to the variation of refractive index. Crucially, the determined TPA coefficients for pure SZ2080 TM provide experimental evidence that it can initiate polymerization without PIs, enabling a more sustainable and environmentally friendly fabrication route by avoiding the use of toxic additive compounds. These findings will allow for the estimation of exact energy deposition in 3D laser printing using ultrashort laser pulses and support the development of an initiator-free additive manufacturing approach.

Multiphoton lithography (MPL), an additive manufacturing method, enables the fabrication of intricate three-dimensional micro- and nanostructures with high spatial resolution, crucial for applications in photonics, micro-optics, and biomedicine. Central to the performance of the MPL is the choice of photoinitiator (PI), which governs polymerization efficiency, resolution, and application-specific functionality. However, conventional PIs often suffer from drawbacks such as high autofluorescence and poor spectral selectivity, limiting their utility in fluorescence-sensitive applications. This work presents a systematic study on the nonlinear optical (NLO) properties of lab-made low-fluorescence PIs (LF, indane-1,3-dione-based push-pull compounds), comparing them to high-fluorescence PIs (HF, triphenylamine-based aldehydes), and examines their effectiveness for MPL. The NLO properties of the PIs were investigated employing the two-beam initiation threshold (2-BIT) method and Z-scan technique both in solution and integrated into the hybrid photoresist SZ2080. The characterization of NLO properties and manufacturing tests were performed within a single optical setup, under similar spectrotemporal laser radiation conditions (pulse width, 150 fs; wavelength, 780 nm). This proposed approach allows for a straightforward and efficient evaluation of the suitability of aPI for MPL. LF-PIs were found to be up to 2 orders of magnitude less fluorescent than HF-PIs, as determined by photoluminescence analysis, and exhibited up to 10-fold higher NLO absorption-related parameters. This indicates that high fluorescence may compete with the NLO performance by interfering with absorption processes essential for effective polymerization. Most importantly, LF-PIs enabled structuring performance comparable to that of SBB (a benchmark material for low-fluorescent MPL-fabricated structures) when embedded in SZ2080, and the resulting printed structures exhibited an improved selective fluorescence response, indicating their strong potential for printing scaffolds in biorelated applications, where a high fluorescent signal usually hinders signal detection and analysis.

The two-photon absorption (TPA) and non-linear refraction coefficients β and n2 of SZ2080TM resist with the photo-initiators (PI) IRG369 and BIS (Irgacure 369 and 4,4' bis(diethylamino)-benzophenone or Michler’s ketone) are determined using the Z-scan method at a wavelength of 515 nm. The nonlinear response of the host polymer is shown to have a considerable contribution to energy deposition despite the addition of the PI, as the host polymer makes up the majority of 99% in the solution. TPA cross section σ = 5.7 ± 0.4 GM (1GM = 10-50 cm4sphoton-1) for pure SZ2080ΤΜ, 40 GM for IRG and 87 GM for BIS at 515 nm. The positive n2 = (85.3 ± 6) × 10-5 cm2/TW for pure polymer favors self-focusing and is larger than that for PIs: 16 × 10-5 cm2/TW (IRG369) and 2.8 × 10-5 cm2/TW (BIS). Hence, the properties of the host material govern non-linear light propagation, although, in high numerical aperture focusing, the self-focusing has a negligible effect. Z-scan experiments were carried out at a low 1 kHz laser repetition rate to exclude thermal accumulation at the focal region. These findings will allow for the estimation of exact energy deposition in 3D laser printing using ultrashort laser pulses.

Materials exhibiting strong nonlinear optical (NLO) properties along with fast carrier recovery have fostered significant advancements in photonic devices, enabling the development of ultrafast lasers, optical limiters, optical switches, modulators, photodetectors, and more. Among these materials, transition metal carbides, nitrides, and carbonitrides (MXenes), characterized by the general formula $\mathrm{M}_{\mathrm{n}+1}\mathrm{X}_{\mathrm{n}}\mathrm{T}_{x}$ (where M is a transition metal, X is C or N, and $\mathrm{T}_{x}$ represents surface terminated groups such as -OH, -O, or -F), are particularly attractive for such applications due to their exceptional NLO response, broadband absorption, ultrafast carrier relaxation, and resistance to radiation and heat.

Ultrafast nonlinear optical (NLO) response, fast carrier recovery, broadband absorption, and resistance to radiation and heat make 2D materials promising for photonic technologies. However, low electronic conductivity and carrier concentration limit the performance of semiconducting or semimetallic materials. This work investigates the ultrafast NLO properties and carrier dynamics of Ta_4C_3T_x and out-of-plane ordered Mo_2Ti_2C_3T_x MXenes using Z-scan and pump-probe optical Kerr effect techniques under visible and infrared femtosecond laser pulses. Their NLO response surpasses all previously studied MXenes and most other 2D nanomaterials, attaining exceptionally high third-order susceptibility (ḩi̧(3)) values on the order of 10^-13 esu. Mo_2Ti_2C_3T_x exhibits the strongest NLO response under both excitation regimes, attributed to charge transfer between Mo and Ti layers in the MXene structure. Under visible excitation, the studied MXenes display pronounced saturable absorption, while under infrared excitation, they exhibit strong reverse saturable absorption, resulting in efficient optical limiting. Additionally, pump-probe experiments identify two distinct relaxation processes: a fast one on the sub-picosecond timescale and a slower one a few picoseconds after photoexcitation. Our results indicate that these MXenes are among the strongest NLO materials. They show their great potential for advanced photonic and optoelectronic applications in laser technologies, optical protection, telecommunications, and optical/quantum computing.

The present work reports on the ultrafast nonlinear optical (NLO) properties of a series of D-pi-Alpha and D-A push-pull carbazole-based dyes and establishes a correlation between these properties and their efficiency for potential photonic and optoelectronic applications such as multiphoton lithography (MPL). The ultrafast NLO properties of the studied dyes are determined by two distinct experimental techniques, Z-scan and pump-probe optical Kerr effect (OKE), employing 246 fs laser pulses at 515 nm. The results indicate that chemical functionalization of the carbazole moiety with various strong electron-donating and/or electron-withdrawing groups, such as benzene, styrene, 4-bromostyrene, nitrobenzene, trimethyl isocyanurate, methyl, and indane-1,3-dione, can result in a controlled and significant enhancement of the NLO absorptive and refractive responses. In the context of potential applications, the efficiency of carbazole-based organic materials as photoinitiators (PIs) for MPL applications is demonstrated. The fabricated woodpile microstructure using chemically functionalized carbazole as a PI demonstrates improvements in both feature size and MPL efficiency compared to that using unfunctionalized carbazole as a PI. This is attributed to the efficient charge transfer resulting from chemical functionalization, which leads to a substantial increase (approximately 1 order of magnitude) in the values of the imaginary part of the second-order hyperpolarizability (Im gamma) and the two-photon absorption cross section (sigma). The achieved feature size of 280 nm is comparable to that obtained with other widely used PIs in MPL applications. Additionally, owing to the strong NLO properties of the studied functionalized carbazole, they could also be promising candidates for further applications in photonics and optoelectronics.

Ultrafast nonlinear optical (NLO) response, fast carrier recovery, broadband absorption, and resistance to radiation and heat make 2D materials promising for photonic technologies. However, low electronic conductivity and carrier concentration limit the performance of semiconducting or semimetallic materials. This work investigates the ultrafast NLO properties and carrier dynamics of Ta$_{4}$C$_{3}$T$_{x}$ and out-of-plane ordered Mo$_{2}$Ti$_{2}$C$_{3}$T$_{x}$ MXenes using Z-scan and pump-probe optical Kerr effect techniques under visible and infrared femtosecond laser pulses. Their NLO response surpasses all previously studied MXenes and most other 2D nanomaterials, attaining exceptionally high third-order susceptibility (\c{hi}(3)) values on the order of 10^{-13} esu. Mo$_{2}$Ti$_{2}$C$_{3}$T$_{x}$ exhibits the strongest NLO response under both excitation regimes, attributed to charge transfer between Mo and Ti layers in the MXene structure. Under visible excitation, the studied MXenes display pronounced saturable absorption, while under infrared excitation, they exhibit strong reverse saturable absorption, resulting in efficient optical limiting. Additionally, pump-probe experiments identify two distinct relaxation processes: a fast one on the sub-picosecond timescale and a slower one a few picoseconds after photoexcitation. Our results indicate that these MXenes are among the strongest NLO materials. They show their great potential for advanced photonic and optoelectronic applications in laser technologies, optical protection, telecommunications, and optical/quantum computing.

In the area of optoelectronics, Epsilon Near Zero (ENZ) materials possess a special place, as due to them, high nonlinearities can be achieved. Our interest is focused at the telecommunication wavelengths, as a lot of nanophotonic phenomena are taking place. Transparent Conductive Oxides (TCOs) is a group of materials that are used in the ENZ regime. Aluminum Zinc Oxide (AZO) is a TCO that has been proved that is preferred for telecom applications. In order to achieve higher nonlinearities in ENZ regime, we fabricate 3D photonic nanostructures, via Multiphoton lithography and we cover them with AZO via Pulsed Laser Deposition.

A novel dual cure photopolymerizable system was developed by combining two plant-derived acrylic monomers, acrylated epoxidized soybean oil and vanillin dimethacrylate, as well as the thiol monomer pentaerythritol tetrakis (3-mercaptopropionate). Carefully selected resin composition allowed the researchers to overcome earlier stability/premature polymerization problems and to obtain stable (up to six months at 4 °C) and selectively-polymerizable resin. The resin demonstrated rapid photocuring without an induction period and reached a rigidity of 317.66 MPa, which was more than 20 times higher than that of the other vanillin-based polymers. Improved mechanical properties and thermal stability of the resulting cross-linked photopolymer were obtained compared to similar homo- and copolymers: Young's modulus reached 4753 MPa, the compression modulus reached 1634 MPa, and the temperature of 10% weight loss was 373 °C. The developed photocurable system was successfully applied in stereolithography and characterized with femtosecond pulsed two-beam initiation threshold measurement for the first time. The polymerization threshold of the investigated polymer was determined to be controlled by the sample temperature, making the footprint of the workstations cheaper, faster, and more reliable.

Three new triphenylamine derivatives bearing formyl groups were synthesized and tested for their suitability as photo-initiators for multi-photon lithography. The efficiency of the photo-polymerization was tested by two different setups and for a variety of applications. Based on their broad fabrication window, the well-defined 3D prints in the sub-micron range (resolution and aspect ratio), the solubility, we demonstrate these photo-initiators are a viable alternative to standard photo-initiators.

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

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.

The application of temporally shaped femtosecond laser pulses in the micro/nano-structuring of semiconductor surfaces is demonstrated. As an initial step towards full pulse shaping, sequences of double pulses with variable temporal spacing in the picosecond time domain with equal intensity have been used. Craters decorated with nm-sized ripples are formed following the laser-surface interaction depending on the irradiation conditions. The area, depth and strikingly the ripple periodicity show a dependence on the temporal delay between the double pulses. Our analysis and explanation for the dependence of the micro and nano-morphological features on the pulse delay is based on a combination of mechanisms including laser-triggered ultrafast excitation and relaxation on a semiconductor surface such as carrier excitation, ultrafast carrier-lattice energy exchanges and energy transport along with the slower phenomena of melting, the corresponding hydrodynamics and re-solidification that follow until the final surface morphology is established. Our investigations on laser-irradiated Si and ZnO surfaces are discussed. Correspondence Author – P. A. Loukakos (loukakos@iesl.forth.gr). KeywordsFS Laser Pulses; Nano-Structures.

Summary form only given. We present our latest work on the investigation of new photo-initiator materials using two beam initiation threshold (2-BIT) [1] for Direct Laser Writing (DLW). The technique used for fabricating, often complex, 3D structures is multiphoton polymerisation (MPP) of photopolymers [2]. These have found uses in such diverse fields as optical sensors, metamaterials, and biomedical scaffolding. At the heart of this technique is the localised polymerization/cross linking of photosensitive materials through nonlinear optical absorption of ultrafast femtosecond laser pulses. This photosensitive system is mediated through a photo-initiator (PI) in order to start the polymerisation/cross linking of the multi-photon absorption. The criteria for a successful PI are high multi-photon absorption cross section, good solubility in the solvent medium, and high radical generation yield. 2-BIT is a useful addition to screen promising PIs for their suitability, unambiguously gives the order of the nonlinear absorption and can used with equipment readily available in a nonlinear lithography lab. This technique was used to determine the order of the effective nonlinear absorption of three new PIs [3]. This was further compared with the usual technique of z-scan where the order of the nonlinear absorption is often ambiguous. To ensure the overall viability for biocompatible DLW, the UV-Viz absorption and emission spectra were taken, along with test structures written using different laser intensities and velocities. Further biocompatibility was checked through adhesion, viability, and proliferation of dental Stem Cells.

The development of dynamically responsive 3D photonic elements, which is crucial for the design of active integrated photonic circuits, requires the incorporation of material systems with fast and tunable response. To this end, semiconductor quantum dots have been widely used to perform as the active material system to be integrated; nonetheless, multiple-step processing is usually required for the active functions to be preserved, thereby restricting functionality of integrated 3D quantum photonic elements mostly to the infrared. Here, we report a simple scheme for the realization of visible light active 3D photonic devices by combining direct laser writing with two-photon absorption and in situ synthesis of cadmium sulfide (CdS) nanoparticles. The novel active 3D printable hybrid material is synthesized by crosslinking precursors of CdS quantum dots into a photo-structurable organic-inorganic zirconium-silicon hybrid composite integrating functional properties of both high spatial resolution and high third-order nonlinearity into the photonic matrix. As a proof-of-demonstration for 3D printed active photonic devices, woodpile photonic crystals with an inlayer periodicity down to 500 nm are successfully fabricated showing clear photonic stop bands in the visible spectral region, while for the first time, evidence of an ultrafast dynamic response in the visible is also demonstrated.

A three-step synthetic route to a structurally unique π-expanded pyrrolo[3,2-b]pyrrole derived bis-ketone has been developed. In contrast to all previous ladder-type pyrrolopyrroles, the new dye exhibits a low-energy absorption band in the visible region which is responsible for its red-purple color. Interestingly, even though the compound is centrosymmetric, this band coincides with the lowest energy two-photon absorption (TPA) transition. This non-typical behaviour has been computationally rationalized by finding two close lying excited states, one of which (S1) is active for OPA and the other (S2) for TPA processes, which arise from the mixing of two symmetric partial charge-transfer states. The ultrafast excited-state dynamics was characterized by means of transient absorption analysis. A relaxation process involving S1 symmetry breaking occurs in a few ps, leading to the formation of the lowest energy charge-transfer state. This is weakly emitting, with a measured lifetime in the order of tens of picoseconds. Interestingly, two-photon polymerization has been achieved using this new ketone. The high yield of radical photo-initiation upon two-photon excitation was demonstrated by the fabrication of woodpile photonic crystal templates by direct laser writing using a zirconium-silicon hybrid composite.