arXiv subjects

George D. Tsibidis

Publications and source records attributed to George D. Tsibidis.

At least 19 recordsLinked to original sources

arXiv2026

Influence of Inter-Pulse Delay and Geometric Constraints on Damage and Optical Characteristics in thin Metal Targets Irradiated by Double Ultrashort Laser Pulses

Femtosecond pulsed laser systems constitute powerful tools for the high-precision structuring of materials at micro/nano-scale resolutions. A critical parameter influencing the efficacy of ultrafast laser-material interactions is the laser-induced damage threshold (LIDT), which is defined as the minimum laser fluence required to induce irreversible modification to the material surface. While extensive studies have addressed single-pulse damage mechanisms, the response of thin metallic films to double-pulse femtosecond irradiation, particularly when the film thickness is of the order of the optical penetration depth, remains, generally, unexplored. In this work, we present a rigorous theoretical investigation into the spatiotemporal evolution of energy deposition, thermalization processes and optical parameter changes under double-pulse excitation conditions. The analysis considers key parameters including the inter-pulse delay and the film thickness to evaluate their influence on the LIDT for a range of technologically relevant metals: Au, Ag, Cu, Al, Ni, Ti, Cr, Pt, W, Mo and Stainless Steel (100Cr6). ). A comparative analysis highlights the potential of controlled double-pulse irradiation schemes to manipulate energy coupling efficiency, improve the spatial selectivity of laser-induced modifications and compile a comprehensive LIDT database for commonly used industrial materials. The approach is aimed to provide a robust foundation for the design and optimization of advanced laser micromachining and nanofabrication protocols across a broad spectrum of metallic systems.

physics.optics↗

arXiv2025

Highly ordered LIPSS on Au thin film for plasmonic sensing fabricated by double femtosecond pulses

Periodic plasmonic arrays making possible excitations of surface lattice resonances (SLRs) or quasi-resonant features are of great importance for biosensing and other applications. Fabrication of such arrays over a large area is typically very costly and time-consuming when performed using conventional electron beam lithography and other methods, which reduce application prospects. Here, we propose a technique of double femtosecond pulse (~ 170 fs) laser-assisted structuring of thin (~ 32 nm) Au films deposited on a glass substrate and report a single-step fabrication of homogeneous and highly ordered Au-based Laser Induced Periodic Surface Structures (LIPSS) over a large area. Our experimental results unveil the key importance of the interpulse delay as the determining factor rendering possible the homogeneity of laser induced structures and confirm that highly ordered, functional LIPSS occur solely upon double pulse irradiation under a specific interpulse delay range. A theoretical investigation complements experimental results providing remarkable insights on the structure formation mechanism. Ellipsometric measurements show that such LIPSS structures can exhibit highly valuable plasmonic features in light reflection. In particular, we observed ultranarrow resonances associated with diffraction-coupled SLRs, which are of paramount importance for biosensing and other applications. The presented data suggest that femtosecond double pulse structuring of thin metal films can serve as a valuable and low-cost tool for a large-scale fabrication of highly ordered functional elements and structures.

cond-mat.mtrl-sci↗

arXiv2025

Fabrication of highly uniform laser-induced periodic structures on polycarbonate via UV femtosecond pulses

In this work, we focus on the fabrication of highly uniform laser-induced periodic surface structures (LIPSS) on bulk polycarbonate (PC) using 258 nm femtosecond laser pulses. A systematic approach was pursued to investigate the influence of various laser parameters such as fluence, effective number of pulses, energy dose and polarisation on the features of the generated LIPSS. Experimental results showed that linearly polarized beams produce LIPSS with period comparable to the laser wavelength. Moreover, it was observed that the orientation of LIPSS is either parallel or perpendicular to the laser polarization, depending on the excitation level. These features are similar to the LIPSS formed on dielectrics, despite the considerably higher absorption and larger extinction coefficient (~10-2) of polycarbonate at 258 nm. The orientation and features of the patterns at different excitation levels are explained using Sipe's theory, while the excitation and induced carrier densities were quantified through the application of a theoretical physical model that describes ultrafast dynamics in polymers. Furthermore, observations revealed that low excitation levels with linearly polarized enhance the uniformity of LIPSS, whereas irradiating PC targets with circularly polarized beams leads to the formation of microscale topographies decorated with protruding nanosphered-like structures, with their size varying based on the laser conditions. A detailed analysis of the impact of the induced topographies on their wetting and optical properties demonstrated a steady increase in hydrophilicity over time, in contrast to a modest increase in optical absorbance. The results regarding the morphological features and properties of the induced topographies on PC are anticipated to support future efforts in creating patterned surfaces on polymeric materials for potential applications.

physics.optics↗

arXiv2025

Deciphering Carrier Dynamics in Polycarbonate Following Excitation with Ultrashort Laser Pulses

Polymers exposed to ultrashort pulsed lasers (UPL) experience a range of physical and chemical changes that play a key role in applications ranging from material processing to advanced photonics, and biomedicine. To elucidate the interaction of UPL with polymeric materials, ultrafast phenomena such as carrier dynamics, recombination and relaxation are investigated assuming polycarbonate (PC) as a test material exposed to laser pulses of moderate energies. A theoretical model developed for dielectric materials is extended to describe the, previously, unexplored excitation and carrier dynamics for PC while femtosecond Transient Absorption Spectroscopy is used to elucidate the evolution of the materials response and ultrafast dynamics. Interpreting the experimental measurements using the theoretical model suggests the existence of an energy level that facilitates the formation of self-trapped exciton metastates between the conduction and valence bands (approximately 2.4-2.8 eV below the conduction band). It also predicts the electron-plasma lifetime (around 110-150 fs), the recombination time (about 34 ps), and the non-linear part of the refractive index due to Kerr effect (with n_2 values ranging from (1.1-1.5)x10^{-16} cm2/W). Furthermore, the dominant character of multi-photon assisted ionisation is emphasised while the optical breakdown threshold is also calculated and found to be equal to 2.55 x10^12 W/cm2. The results are expected to support future efforts aimed at elucidating how intense ultrashort laser pulses interact with polymeric materials which is crucial for optimizing the manufacturing processes of these materials for potential applications.

physics.optics↗

arXiv2024

Formation of Highly Tunable Periodic Plasmonic Structures on Gold Films Using Direct Laser Writing

Direct laser writing method is a promising technique for the large-scale and cost-effective fabrication of periodic nanostructure arrays exciting hybrid lattice plasmons. This type of electromagnetic mode manifests a narrow and deep resonance peak with a high dispersion whose precise controllability is crucial for practical applications in photonic devices. Here, the formation of differently shaped gold nanostructures using the direct laser writing method on Au layers of different thicknesses is presented. The resonance peak is demonstrated to be highly dependent on the shape of the structures in the array, thus its position in the spectra, as well as the quality, can be additionally modulated by changing the morphology. The shape of the structure and the resonance itself pertain not only on the laser pulse energy but also on the grating period. This overlapping effect occurring at distances smaller than the diameter of the focused laser beam is studied in detail. By taking advantage of the highly controllable plasmonic resonance, the fabricated gratings open up new opportunities for applications in sensing.

cond-mat.mtrl-sci↗

arXiv2024

Control of the damage threshold of Si via a SiO2 coating upon irradiation with Mid-IR femtosecond laser pulses

A key issue in the use of high-power mid-infrared (Mid-IR) laser sources for a plethora of applications is the investigation of the exciting laser driven physical phenomena taking place in materials coated with dielectric films. Here, we present a theoretical investigation of the ultrafast processes and thermal response upon excitation of two-layered complexes consisting of fused silica thin films placed on silicon substrates with ultrashort pulsed lasers in the Mid-IR spectral regime. Through the development of a theoretical model, we demonstrate that the control of the underlying ultrafast phenomena and the damage threshold (DT) of the substrate are achieved via an appropriate modulation of the thickness of the SiO2 film. It is shown that a decrease of DT by up to 27% compared to the absence of coating is feasible emphasising the impact of coatings of a lower refractive index than the substrate. Besides this, it is demonstrated that no absorption of energy occurs within the SiO2 layer, therefore the dynamics of the reflectivity of the two-layered complex is directly associated with the electron excitation in the substrate. These remarkable predictions can be employed for the development of new optical coatings and components for nonlinear optics and photonics for a large range of Mid-IR laser-based applications.

physics.optics↗

arXiv2023

Influence of Antireflection Si coatings on the Damage Threshold of fused silica upon irradiation with Mid-IR femtosecond laser pulses

Recent progress in the development of high-power mid-IR laser sources and the exciting laser driven physical phenomena associated with the irradiation of solids via ultrashort laser pulses in that spectral region are aimed to potentially create novel capabilities for material processing. In particularly, the investigation of the underlying physical processes and the evaluation of the optical breakdown threshold (OBT) following irradiation of bulk dielectric materials with Mid-IR femtosecond (fs) pulses has been recently presented. In this report, we will explore the conditions that generate sufficient carrier excitation levels which leads to damage upon irradiated a dielectric material (SiO2) coated with antireflection (AR) semiconducting films (Si) of variable thickness with fs pulses. Simulation results demonstrate that the reflectivity and transmissivity of the Si/SiO2 are thickness-dependent which can be employed to modulate the damage threshold of the substrate. The study is to provide innovative routes for selecting material sizes that can be used for antireflection coatings and applications in the Mid-IR region.

physics.optics↗

arXiv2023

Impact of plasmonic modes on the formation of self-organised nano-patterns in thin films

Formation of nanoscale laser-induced periodic surface structures on thin metal films (of the size of the optical penetration depth) is a yet unexplored area that is expected to open new routes for laser patterning and a wealth of exciting applications in optics, photonics, and sensing. In contrast to the common belief that excitation of Surface Plasmon Polaritons (SPPs) on the air/metal interface plays the dominant role in the features of the induced topographies, in this work, we demonstrate that the excitation of coupled SPPs in both air/metal and metal/substrate interfaces, along with other parameters such as the thickness of the material, the photon energy, and the substrate refractive index, dictate the spatial modulation of the absorbed energy. A detailed theoretical analysis of the excited plasmonic waves and a multiscale modelling of laser-induced physical phenomena manifests that depending on the laser conditions and thickness of the irradiated solid, topographies with periodic features of diverse sizes (ranging from $λ_L/3$ to $λ_L$, where $λ_L$ stands for the laser wavelength) and different orientation can be realized. The capability to control and tune the characteristics of the produced structures on thin films is expected to enable novel surface patterning approaches.

physics.optics↗

arXiv2022

Damage threshold evaluation of thin metallic films exposed to femtosecond laser pulses: the role of material thickness

The employment of femtosecond pulsed lasers has received significant attention due to its capability to facilitate fabrication of precise patterns at the micro- and nano- lengths scales. A key issue for efficient material processing is the accurate determination of the damage threshold that is associated with the laser peak fluence at which minimal damage occurs on the surface of the irradiated solid. Despite a wealth of previous reports that focused on the evaluation of the laser conditions that lead to the onset of damage, the investigation of both the optical and thermal response of thin films of sizes comparable to the optical penetration depth is still an unexplored area. In this report, a detailed theoretical analysis of the impact of various parameters such as the photon energies and material thickness on the damage threshold for various metals (Au, Ag, Cu, Al, Ni, Ti, Cr, Stainless Steel) is investigated. A multiscale physical model is used that correlates the energy absorption, electron excitation, relaxation processes and minimal surface modification which leads to the onset of material damage. The satisfactory agreement of the theoretical model with some experimental results indicates that the damage threshold evaluation method could represent a systematic approach towards designing efficient laser-based fabrication systems and optimizing the processing outcome for various applications.

cond-mat.mtrl-sci↗

arXiv2022

The impact of the substrate on the opto-thermal response of thin metallic targets following irradiation with femtosecond laser pulses

Femtosecond pulsed lasers have been widely used over the past decades due to their capability to fabricate precise patterns at the micro- and nano- lengths scales. A key issue for efficient material processing is the determination of the laser parameters used in the experimental set ups. Despite a systematic investigation that has been performed to highlight the impact of every parameter independently, little attention has been drawn on the role of the substrate material on which the irradiated solid is placed. In this work, the influence of the substrate is emphasised for films of various thicknesses which demonstrates that both the optical and thermophysical properties of the substrate affect the thermal fingerprint on the irradiated film while the impact is manifested to be higher at smaller film sizes. Two representative materials, silicon and fused silica have been selected as typical substrates for thin films of different optical and thermophysical behaviour (gold and nickel) and the thermal response and damage thresholds are evaluated for the irradiated solids. The pronounced influence of the substrate is aimed to pave the way for new and more optimised designs of laser-based fabrication set ups and processing schemes.

physics.optics↗

arXiv2022

The synergy of electromagnetic effects and thermophysical properties of metals in the formation of laser induced periodic surface structures

Femtosecond pulsed lasers have been widely used over the past decades for precise materials structuring at the micro- and nano- scales. In order, though, to realize efficient material processing and account for the formation of laser induced periodic surfaces structures (LIPSS), it is very important to understand the fundamental laser-matter interaction processes. A significant contribution to the LIPSS profile appears to originate from the electromagnetic fingerprint of the laser source. In this work, we follow a systematic approach to predict the pulse-by-pulse formation of LIPSS on metals due to the development of a spatially periodic energy deposition that results from the interference of electromagnetic far fields on a non-flat surface profile. On the other hand, we demonstrate that the induced electromagnetic effects, alone, are not sufficient to allow the LIPSS formation, therefore, we emphasize on the crucial role of electron diffusion and electron-phonon coupling on the formation of stable periodic structures. Gold and stainless Steel are considered as two materials to test the theoretical model while simulation results appear to confirm the experimental results that, unlike gold, fabrication of pronounced LIPSS on stainless Steel is feasible.

physics.optics↗

arXiv2021

Impact of pre-patterned structures on features of Laser Induced Periodic Surface structures

The efficiency of light coupling to surface plasmon polariton (SPP) represents a very important issue in plasmonics and laser fabrication of topographies in various solids. To illustrate the role of pre-patterrned surfaces and impact of laser polsarisation in the excitation of electromagnetic modes and periodic pattern formation, Nickel surfaces are irradiated with femtosecond laser pulses of polarisation perpendicular or parallel to the orientation of the pre-pattern ridges. Experimental results indicate that for polarisation parallel to the ridges, laser induced periodic surface structures (LIPSS) are formed perpendicularly to the pre-pattern with a frequency that is independent of the distance between the ridges and periodicities close to the wavelength of the excited SPP. By contrast, for polarisation perpendicular to the pre-pattern, the periodicities of the LIPSS are closely correlated to the distance between the ridges for pre-pattern distance larger than the laser wavelength. The experimental observations are interpreted through a multi-scale physical model in which the impact of the interference of the electromagnetic modes is revealed.

cond-mat.mtrl-sci↗

arXiv2021

Tailoring Sub-micrometer Periodic Surface Structures via Ultrashort Pulsed Direct Laser Interference Patterning

Direct laser Interference Patterning (DLIP) with ultrashort laser pulses (ULP) represents a precise and fast technique to produce tailored periodic sub-micrometer structures on various materials. In this work, an experimental and theoretical approach is presented to investigate the previously unexplored fundamental mechanisms for the formation of unprecedented laser-induced topographies on stainless steel following proper combinations of DLIP with ULP. DLIP is aimed to determine the initial conditions of the laser-matter interaction by defining an ablated region while double ULP are used to control the reorganisation of the self-assembled laser induced sub-micrometer sized structures by exploiting the interplay of different absorption and excitation levels coupled with the melt hydrodynamics induced by the first of the double pulses. A multiscale physical model is presented to correlate the interference period, polarization orientation and number of incident pulses with the induced morphologies. Special emphasis is given to electron excitation, relaxation processes and hydrodynamical effects that are crucial to the production of complex morphologies. Results are expected to derive new knowledge of laser-matter interaction in combined DLIP and ULP conditions and enable enhanced fabrication capabilities of complex hierarchical sub-micrometer sized structures for a variety of applications.

physics.app-ph↗

arXiv2020

Polarization dependent spike formation on black silicon via ultrafast laser structuring

A comparative experimental and theoretical investigation is presented that centres on the effects of structuring black silicon surfaces with linearly, circularly and azimuthally polarized laser pulses under SF6 ambient atmosphere. It is shown that the asymmetric elliptical micro-cone formations induced by linearly polarized beams result in variable light absorption due to their spatial asymmetry. By contrast, the use of azimuthally polarized beams leads to an omni-directionality of the elliptical cone orientation which is dependent on the local electric field during laser scanning. The locally variant electric field state that is azimuthally polarized leads to a selective conical orientation for the induced structures. The omni-directional conical distribution induced by azimuthal polarization produces similar, angle-independent absorption in the visible spectrum with the symmetrical conical structures that could only be realized with circularly polarized beams.

cond-mat.mtrl-sci↗

arXiv2020

Biomimetic Omnidirectional Anti-reflective Glass via Direct Ultrafast Laser Nanostructuring

We report on a single-step, biomimetic approach for the realization of omnidirectional transparent antireflective glass. In particular, it is shown that circularly polarized ultrashort laser pulses produce self-organized nanopillar structures on fused silica (SiO2). The laser induced nanostructures are selectively textured on the glass surface in order to mimic the spatial randomness, pillar-like morphology, as well as the remarkable anti-reflection properties found on the wings of the glasswing butterfly, Greta oto[1] and various Cicada species[2]. The artificial structures exhibit impressive anti-reflective properties, both in the visible and infrared frequency range. Accordingly, the laser-processed glass surfaces show reflectivity smaller than 1% for various angles of incidence in the visible spectrum for S-P linearly polarized configurations. While, in the near infrared spectrum, the laser-textured glass shows higher transmittance compared to the pristine. It is envisaged that our current results will revolutionize the technology of anti-reflective transparent surfaces and impact numerous applications from glass displays to optoelectronic devices.

physics.optics↗

arXiv2020

Tuning the period of femtosecond laser induced surface structures in steel: from angled incidence to quill writing

Exposure of metal surfaces to multiple ultrashort laser pulses under certain conditions leads to the formation of well-defined periodic surface structures. We show how the period of such structures in steel can be tuned over a wide range by controlling the complex interaction mechanisms triggered in the material. Amongst the different irradiation parameters that influence the properties of the induced structures, the angle of incidence of the laser beam occupies a prominent role. We present an experimental and theoretical investigation of this angle dependence in steel upon irradiation with laser pulses of 120 fs duration and 800 nm wavelength, while moving the sample at constant speed. Our findings can be grouped into two blocks. First, we observe the spatial coexistence of two different ripple periods at the steel surface, both featuring inverse scaling upon angle increase, which are related to forward and backward propagation of surface plasmon polaritons. To understand the underlying physical phenomena, we extend a recently developed model that takes into account quantitative properties of the surface roughness to the case of absorbing metals (large imaginary part of the dielectric function), and obtain an excellent match with the experimentally observed angle dependence. As second important finding, we observe a quill writing effect, also termed non-reciprocal writing, in form of a significant change of the ripple period upon reversing the sample movement direction. This remarkable phenomenon has been observed so far only inside dielectric materials and our work underlines its importance also in laser surface processing. We attribute the origin of symmetry breaking to the non-symmetric micro- and nanoscale roughness induced upon static multiple pulse irradiation, leading to non-symmetric modification of the wavevector of the coupled surface plasmon polariton.

physics.app-ph↗

arXiv2020

Predictive modeling approaches in laser-based material processing

Predictive modelling represents an emerging field that combines existing and novel methodologies aimed to rapidly understand physical mechanisms and concurrently develop new materials, processes and structures. In the current study, previously-unexplored predictive modelling in a key-enabled technology, the laser-based manufacturing, aims to automate and forecast the effect of laser processing on material structures. The focus is centred on the performance of representative statistical and machine learning algorithms in predicting the outcome of laser processing on a range of materials. Results on experimental data showed that predictive models were able to satisfactorily learn the mapping between the laser input variables and the observed material structure. These results are further integrated with simulation data aiming to elucidate the multiscale physical processes upon laser-material interaction. As a consequence, we augmented the adjusted simulated data to the experimental and substantially improved the predictive performance, due to the availability of increased number of sampling points. In parallel, a metric to identify and quantify the regions with high predictive uncertainty, is presented, revealing that high uncertainty occurs around the transition boundaries. Our results can set the basis for a systematic methodology towards reducing material design, testing and production cost via the replacement of expensive trial-and-error based manufacturing procedure with a precise pre-fabrication predictive tool.

physics.comp-ph↗

arXiv2020

Ionisation processes and laser induced periodic surface structures in dielectrics with mid-infrared femtosecond laser pulses

Irradiation of solids with ultrashort pulses and laser processing in the mid-Infrared (mid-IR) spectral region is a yet predominantly unexplored field with a large potential for a wide range of applications. In this work, laser driven physical phenomena associated with processes following irradiation of fused silica (SiO2) with ultrashort laser pulses in the mid-IR region are investigated in detail. A multiscale modelling approach is performed that correlates conditions for formation of perpendicular or parallel to the laser polarisation low spatial frequency periodic surface structures for low and high intensity mid-IR pulses (not previously explored in dielectrics at those wavelengths), respectively. Results demonstrate a remarkable domination of tunneling effects in the photoionisation rate and a strong influence of impact ionisation for long laser wavelengths. The methodology presented in this work is aimed to shed light on the fundamental mechanisms in a previously unexplored spectral area and allow a systematic novel surface engineering with strong mid-IR fields for advanced industrial laser applications.

cond-mat.mtrl-sci↗