This study presents a comprehensive theoretical and experimental investigation of vat photopolymerization using ultraviolet pulsed laser irradiation (VPP-UV-PL). A process model is developed by extending Jacob’s working curve, originally formulated for CW sources, to pulsed Gaussian beam regimes. The model incorporates both spatial and temporal pulse overlap, enabling prediction of cured geometries by accounting for cumulative exposure from successive laser pulses along and between scan lines. Closed-form expressions are derived for the full 2D curing profile as well as the curing depth (Cd) and width (Cw) of individual scan lines. Simulations and experiments, performed with identical parameters demonstrate excellent agreement at low average exposure, with minor deviations at higher exposures attributed to scattering and unmodeled chemical effects. Numerical simulations reveal a clear morphological transition from isolated hillocks to sawtooth-like strings and ultimately to ribbon-like structures as the average power increases at a fixed scanning speed, or equivalently, as the scanning speed decreases at a fixed average power. These simulation results were experimentally validated by fabricating surface structures over a wide range of scanning speeds and average powers using a custom-built three-dimensional stereolithography (SLA) printer. Ribbon-like structures were formed at a high scanning speed of 100 mm/s for exposure doses exceeding 60 mJ/cm2, whereas isolated hillocks were obtained for exposure doses below 7 mJ/cm2. Increasing the scanning speed reduces pulse overlap, leading to the formation of discrete features. At very high scanning speeds of 200 mm/s, the morphology reverted to isolated hillocks even for exposure doses as high as 90 mJ/cm2. Beyond achieving uniform structures, the method enables controlled fabrication of periodic surface textures (< 100 µm features) with potential applications in cell growth guidance, wettability control, and optical surface functionalization. This model offers a predictive tool for optimizing high-resolution, high-speed additive manufacturing with pulsed UV lasers.

This work demonstrates the capability of pulsed UV laser stereolithography (SLA) for surface texturing with controllable micro-topographies. Rather than emphasizing analytical modeling, this study focuses on numerical calculations and experimental validation to reveal how pulse repetition rate (PRR), scanning speed, and pulse energy collectively determine the morphology of polymerized structures on a transparent substrate. A modified dynamic exposure model, extending existing static intermittent-exposure formulations, was developed to numerically predict curing profiles under pulsed-laser scanning. The numerical calculations show that increasing PRR enhances pulse overlap, promoting the coalescence of isolated hillocks, while higher pulse energy deepens the cured regions. Experiments conducted using a custom-built pulsed SLA setup confirmed these predictions. The textures were created on the rear side of a glass plate placed onto the resin surface; therefore, oxygen inhibition is effectively suppressed, eliminating the need to incorporate this effect into the model. The observed morphological evolution from discrete micro-hillocks to merged, saw-tooth, and ribbon-like structures matched numerically calculated profiles, with good quantitative agreement between predicted and measured feature dimensions. The control of PRR, scanning speed, and pulse energy directly governs the lateral and vertical curing dimensions, as confirmed by numerical calculations and experiment results. Consequently, this combined numerical–experimental approach establishes pulsed SLA as a promising tool for creation of tailored surface topographies and functional microtextures for optical, and biomedical applications.

This study investigates the asymmetry in the closed-aperture (CA) Z-scan transmittance curve. CA Z-scan, a technique used to determine nonlinear refractive indices, produces a symmetric curve under small-aperture and low nonlinear phase change assumptions. However, numerical evaluations based on far-field diffraction reveal an inherent asymmetry. We quantify this asymmetry for both third- and fifth-order nonlinearities as a function of peak, valley, and null point positions (z(p), z(v), and z(null)), as well as peak height (P-h) and valley depth (V-d). Results show that as the nonlinear phase change increases, the closed-aperture (CA) Z-scan transmittance shifts toward +z for positive nonlinearity, increasing the peak-to-valley position ratio (z(p)/z(v)), while it shifts toward -z for negative nonlinearity, decreasing the ratio. However, the peak-to-valley distance (z(p)-z(v)) remains nearly constant for a given aperture size. The peak-to-valley transmittance difference (T-p-T-v) increases with the nonlinear phase change. However, the valley depth and peak height grow at different rates, leading to an increasing disparity between them (V-d-P-h) . However, this holds true only for nonlinear phase changes below pi , where the beam profile exiting the sample remains nearly similar to that of the input beam. Aperture size significantly affects curve shape and magnitude, with larger apertures reducing both peak-to-valley transmittance differences and distance. While the nonlinearity sign is discernible from the curve shape, the order of nonlinearity is not immediately evident. These findings could provide evidence for determining the order of nonlinearity and detecting nonlinear absorption, thereby enhancing our understanding of nonlinear optical phenomena.

Nonlinear (NL) absorption and refraction are crucial optical phenomena in the development and application of optical materials. The Z-scan technique, first proposed by Bahae, is widely used to accurately measure the coefficients of NL absorption and refraction. This review presents a comprehensive overview of the most established versions of the Z-scan technique, including the transmittance closed aperture (CA) and open aperture (OA) Z-scan, reflecting CA and OA Z-scan, eclipsing Z-scan, and white light Z-scan. In each version, different sources with varying spatial and temporal intensity distributions are usually utilized. Numerical and analytical calculation results are provided for each version considering both continuous wave (CW) and pulsed laser sources. Unlike conventional reviews, which often summarize previously published results, this review primarily focuses on reproducing the findings from the literature. The analytical results, which are typically derived under specific approximations, are compared with numerical calculations to highlight the limitations of analytically derived relations. Furthermore, the necessary criteria and conditions for applying each Z-scan version are discussed.

The synthesis of two dye-labeled azides via de-symmetrization of 2,6-bis(4-azidobenzylidene)-4-methylcyclohexanone (BAC-M) with a copper(I)-catalyzed alkyne-azide cycloaddition (CuAAC) using fluorescent dyes is reported. An alkyne functionalized dansyl derivative and an alkyne functionalized perylene diimide derivative were used as the dyes. The photo-physical properties of these dye dyads are described, and their performance in multi-photon grafting onto polyethylene glycol-based hydrogels is investigated. While the dansyl-conjugated BAC derivate is well suited for multi-photon grafting with lasers operating at 800 nm, the perylene diimide-bearing dye does not give the desired result.

Development of materials with highly nonlinear optical activity represents an intensively studied discipline due to potentially unique applications of such materials in photonics and information technologies. In this work the creation of ordered nanostructured arrays of c-shaped metals (Ag, Au, Al, and Pd) and characterization of their nonlinear optical properties are described. Large scale ordered arrays were created by the excimer laser pattering of a polymer surface and subsequent coating with Ag, Au, Al, and Pd. The successful creation of required structures was confirmed by the conductive AFM and FIB-SEM techniques. Linear optical response of the structures was examined using the UV–Vis technique and strong excitation of surface plasmon polariton resulting in appearance of strong absorption band was confirmed. The Z-scan technique with femtosecond laser pulses was used to determine the nonlinear optical response of the prepared metal arrays. It was found that the strong two-photon absorption appears under the illumination at the wavelength corresponding to the surface plasmon excitation. Extensive comparison with available literature data shows that the present structures exhibit markedly higher two-photon absorption activity.

This paper reports on the effect of both the pulse duration and environments on the surface morphology, ablated area, ablation rate, and mechanical properties of a femtosecond laser irradiated zinc (Zn) in air and ethanol. The targets were exposed to 1000 succeeding pulses of Ti:sapphire laser (800 nm) at a fluence of 2.5Jcm−2 with various pulse durations ranging from 30 to 550 fs. The surface structures have been characterized by a field emission scanning electron microscope, whereas the ablation rate has been measured using confocal and optical microscopy. The mechanical behavior of irradiated targets has been explored by using a microhardness tester. It is observed that in the case of Zn ablation in air, a crater with nonuniform surface morphology along with formation of both micro- and nanoscale droplets rims, organized laser-induced periodic surfaces are observed, whereas in the case of ablation in ethanol, nano- and microscale scale droplets, pores, cones, agglomerates, and channels are formed. The growth and the shape of these structures are strongly dependent on the pulse durations and environments. The hardness of laser-treated samples is found to be higher as compared to untreated ones and is also found higher for liquid-assisted ablated Zn as compared to air-assisted ablated targets due to an increased chemical reactivity in an ethanol-confined environment. The decreasing trend of hardness with increasing pulse duration for both environments is observed, which is attributed to decreasing trend in both shock pressure and ablation pressure with increasing pulse duration.

We show spectacular and different effect of the sequential and simultaneous writing of two perpendicularly polarized ultrashort laser pulse trains on profile and magnitude of induced optical retardation inside fused silica glass. Clear birefringence was observed in the region exposed to linearly polarized pulse train radiation. It found out that the induced birefringence is erasable. It means that, when the sample is irradiated again with pulse train having perpendicular polarization, the induced birefringence is vanished and can be totally erased by optimizing the pulse energy. However, in a simultaneous writing approach, a contradictory result was observed. When the glass substrates were simultaneously (i.e. with an accuracy better than the pulse duration) exposed to two beams with perpendicular polarization the induced birefringence not only remained but also enhanced. Discussion and study on the results of interaction of polarized single ultrashort laser pulse and sequential laser beams (which spatially overlapped) having different polarizations and also change of energy ratio of simultaneously writing pulse trains helps us to analyze different results of the simultaneous interaction of two orthogonally polarized ultrashort laser pulse trains with transparent material. Our results provide pieces of evidence for further understanding the physical mechanism of creation of the birefringence using ultrashort laser pulses. Additionally, they provide the ability to manipulate the transient electron dynamics to control the profile and tailor of the induced birefringence.

Femtosecond laser pulses have high peak intensity due to their very short duration thus permanent changes can be appeared in materials as a consequence of interaction with femtosecond pulses. We have used femtosecond pulses in order to create polymeric 3D micro-structure with nonomerter resolution. This technique is based on two-photon absorption (2PA) which provides structuring with resolution beyond the diffraction limit. In this work we used a titanium-sapphire (Ti-sapp) laser producing 70 fs, 25 nJ pulses at 80 MHz repetition rate which can be tuned from 700 nm to 900 nm. A mixture of a monomer with a two-photon initiator (2PI), called resin, turns to polymer after absorbing femtosecond laser pulses. In this process the laser beam is focused inside the resin using a high numerical objective. Different 2PIs were examined for 2PP. The 2PA cross section of examined 2PIs was measured using Z-scan technique. For each 2PI the pulse energy and scanning speed were optimized in order to achieve the best quality and highest resolution. Using this unique technique it is feasible to create micro scale 3D structures with resolution better than 100 nm thus our products can be indeed considered as micro/nano structures.

In this work, the creation of ordered nanostructure arrays of metals (Ag, Au, Al, and Pd) and characterization of their nonlinear optical properties are described. Large scale ordered metal nanostructure arrays were created by the excimer laser patterning of a polymer surface and subsequent coating with Ag, Au, Al, and Pd. The successful creation of accepted structures was confirmed by the conductive AFM and FIB-SEM techniques. The open-aperture Z-scan technique with femtosecond laser pulses was performed to determine the two-photon absorption (2PA) coefficient of the prepared metal nanostructure arrays. It was found that the strong 2PA appears under the illumination at the wavelength of 800 nm with the polarization direction perpendicular to the long scale metal nano-wires whereas no 2PA was observed when irradiated with laser beam polarized parallel to the metal nano-wires. This reveals that the observed high 2PA activity is a plasmonic-based property due to the confinement effect. An extensive comparison with available literature data shows that the present structures exhibit markedly higher 2PA activity. Obtained results confirmed that the examined approach could be used for the preparation of plasmon-active nanostructures for many applications for a wide range of optical components and devices.

we report on the ability of the Multi-photon absorption (MPA) to build 3D polymeric structures with nano resolution and arbitrary dimension. 100 fs laser pulses were utilized for structuring. Different parameters such as laser power (laser pulse energy) and scanning speed were optimized to build qualitative structures. Using a medium numerical aperture (NA=0.85) microscope objective resolution of 300 nm was achieved.

We present an experimental technique to determine the degenerate two-photon absorption (2PA) spectra by performing a single Z-scan using a high-spectral-irradiance white light continuum (WLC) generated by a hollow core fiber. The hollow fiber was filled with Argon (Ar) gas at a pressure of 0.6 bar and was pumped with 500 mJ, 30 fs, and 800 nm pulses. The broadband WLC pulses with 350 nm bandwidth in the range of 600–950 nm were compressed to sub-8 fs pulses. To characterize and interpret the data obtained from this method, the spectral, temporal and spatial characteristics of the WLC were first analyzed. The WLC emerging from the compressor was dispersed using a prism pair and then focused into the sample by a cylindrical lens. Since different spectral components are spatially separated, any part of the sample in the beam cross section is irradiated with almost single wavelength pulses leading to only a degenerate 2PA process. The nonlinear transmittance was then measured by a charge-coupled-device (CCD) line camera as a function of the sample position while the sample was moved along the beam direction by a motorized translation stage. In this way the Z-scans at different wavelengths in the WLC spectral range can be measured and thus the wavelength-resolved degenerate 2PA spectra can be obtained by performing a single scan using dispersive WLC. This method was verified on a well-characterized dye Rhodamine B and yield a reasonable agreement with the data found in the literature. We used this method to determine the 2PA spectra of some two-photon initiators (2PIs) developed for two-photon polymerization (2PP) based 3D micro-structuring.

In order to generate high-spectral-irradiance white light continuum (WLC) a hollow fiber with 250 μm inner diameter was used. The hollow fiber was mounted on a V-groove holder inside a chamber filled with Argon gas. The output beam of a Ti:sapphire laser producing 30 fs pulses was focused at the entrance of the hollow fiber using a plano-convex lens. The high intensity of the incident laser beam inside the hollow fiber causes self-phase modulation leading to broadening the spectral of the input light. The broadening strength depends on many parameters such as the energy of the incident pulses, duration of incident pulses, length of hollow fiber, gas pressure inside the hollow fiber and the ratio of the beam waist diameter to inner diameter of the hollow fiber. At optimal conditions of 175 cm length hollow fiber, 500 μJ pulse energy, 150 cm focal length lens and 0,6 bar gas pressure the white light exiting the fiber possesses a spectrum ranging from 600 nm950 nm which results in generation of sub-8 fs pulses via compressing by a compressor consisting of 8 chirp mirrors.

A cleavable, biocompatible diazosulfonate two-photon initiator (2PI) was developed overcoming limitations caused by the toxicity of state-of-the-art bimolecular 2PIs.

We have succeeded in realizing a method to control the spatial distribution of optical retardation as a result of nanogratings in bulk-fused silica induced by ultrashort laser pulses. A colorimetry-based retardation measurement (CBRM) based on the Michel-Levy interference color chart using a polarization microscope is used to determine the profiles of the optical retardation. Effects of the spatial overlap of written regions as well as the energy and polarization of the writing pulses on the induced retardations are studied. It has been found that the spatial overlap of lines written by pulse trains with different energies and polarizations can result in an adjustment of the induced birefringence in the overlap region. This approach offers the possibility of designing polarization-sensitive components with a desired birefringence profile.

This study reports on the evaluation of laser processed natural polymer-chitosan, which is under consideration as a biointerface used for temporary applications as skin and cartilage substitutes. It is employed for tissue engineering purposes, since it possesses a significant degree of biocompatibility and biodegradability. Chitosan-based thin films were processed by femtosecond laser radiation to enhance the surface properties of the material. Various geometry patterns were produced on polymer surfaces and employed to examine cellular adhesion and orientation. The topography of the modified zones was observed using scanning electron microscopy and confocal microscopy. Test of the material cytotoxicity was performed by evaluating the life/dead cell correlation. The obtained results showed that texturing with femtosecond laser pulses is appropriate method to initiate a predefined cellular response. Formation of surface modifications in the form of foams with an expansion of the material was created under laser irradiation with a number of applied laser pulses from N = 1–5. It is shown that irradiation with N > 5 results in disturbance of microfoam. Material characterization reveals a decrease in water contact angle values after laser irradiation of chitosan films. Consequently, changes in surface roughness of chitosan thin-film surface result in its functionalization. Cultivation of MC3T3 and ATMSC cells show cell orientational migration concerning different surface patterning. The influence of various pulse durations (varying from τ = 30–500 fs) over biofilms surface was examined regarding the evolution of surface morphology. The goal of this study was to define the optimal laser conditions (laser energy, number of applied pulses, and pulse duration) to alter surface wettability properties and porosity to improve material performance. The acquired set of results indicate the way to tune the surface properties to optimize cell–interface interaction.

Two-photon induced polymerization (2PP) based 3D printing is a powerful microfabrication tool. Specialized two-photon initiators (2PIs) are critical components of the employed photosensitive polymerizable formulations. This work investigates the cooperative enhancement of two-photon absorption cross sections (σ2PA) in a series of 1,3,5-triazine-derivatives bearing 1-3 aminostyryl-donor arms, creating dipolar, quadrupolar and octupolar push-pull systems. The multipolar 2PIs were successfully prepared and characterized, σ2PA were determined using z-scan at 800 nm as well as spectrally resolved two-photon excited fluorescence measurements, and the results were compared to high-level ab initio computations. Modern tunable femtosecond lasers allow 2PP-processing at optimum wavelengths tailored to the absorption behavior of the 2PI. 2PP structuring tests revealed that while performance at 800 nm is similar, at their respective σ2PA-maxima the octupolar triazine-derivative outperforms a well-established ketone-based quadrupolar reference 2PI, with significantly lower fabrication threshold at exceedingly high writing speeds up to 200 mm/s and a broader window for ideal processing parameters.

The effect of femtosecond laser fluence on nanostructuring of Tungsten (W) and Molybdenum (Mo) has been investigated after ablation in ethanol environment. A Ti: Sapphire laser (800nm, 30fs) at fluences ranging from 0.6 to 5.7Jcm−2 was employed to ablate targets. The growth of structures on the surface of irradiated targets is investigated by Field Emission Scanning Electron Microscope (FESEM) analysis. The SEM was performed for both central as well as the peripheral ablated regions. It is observed that both the development and shape of nanoscale features is dependent upon deposited energies to the target surface as well as nature of material. Nanostructures grown on Mo are more distinct and well defined as compared to W. At central ablated areas of W, unorganized Laser Induced Periodic Surface Structures (LIPSS) are grown at low fluences, whereas, nonuniform melting along with cracking is observed at higher fluences. In case of Mo, well-defined and organized LIPSS are observed for low fluences. With increasing fluence, LIPSS become unorganized and broken with an appearance of cracks and are completely vanished with the formation of nanoscale cavities and conical structures. In case of peripheral ablated areas broken and bifurcated LIPSS are grown for all fluences for both materials. The, ablated diameter, ablation depth, ablation rate and the dependence of periodicity of LIPSS on the laser fluence are also estimated for both W and Mo. Parametric instabilities of laser-induced plasma along with generation and scattering of surface plasmons is considered as a possible cause for the formation of LIPSS. For ethanol assisted ablation, the role of bubble cavitation, precipitation, confinement and the convective flow is considered to be responsible for inducing increased hydrodynamic instabilities at the liquid-solid interface.

In this paper, a comprehensive theoretical model is presented to investigate the whole chain of processes occurring in the interaction of a focused ultrashort laser pulse with fused silica glass. The equations describing the nonlinear propagation of an ultrashort pulse inside transparent material, electron density evolution, heat conduction, and thermo-elasto plastic displacement are respectively solved, and lastly, it is calculated induced refractive index changes inside the material and qualitatively compared with experimental results. The results show that the major induced refractive index changes is negative and located in the center of the profile. In the following, the performed experiments show that increasing the number of incident pulses causes inducing periodic nano-structures in focal region that orientation of the induced birefringence axes depends on the polarization of the incident pulses.

The possibility to control surface properties of materials and to tailor behaviour of cells and biomolecules are the basic requirements in the development of a new generation biomaterials for applications in tissue engineering. Surface patterning on micro and nano-scale is critical to distinguish the effects of cell shape, focal adhesion, and ligand input for cell functions. Recently, much attention has been paid to laser-assisted micro and nanofabrication technologies to pattern surfaces with different topographies for providing valuable inside on cell-substrate junction [1]. Laser modification by pulses in the femtosecond time domain, provide a quality of modification of thin films of biopolymers that is unobtainable with longer pulses in the range of nanoseconds [2].