arXiv subjects

Alexander V. Bulgakov

Publications and source records attributed to Alexander V. Bulgakov.

13 recordsLinked to original sources

arXiv2026

Enhanced LIBS Emission Using Laser Beam Splitting: Interacting Multi-Plume Plasma Dynamics

The optical emission in laser-induced breakdown spectroscopy (LIBS) is governed by the spatial intensity distribution of the incident laser beam, which influences plasma formation and evolution. Beam shaping therefore offers a route to control plasma dynamics and emission yield; however, its effects in LIBS remain insufficiently quantified, particularly under conditions relevant to compact instrumentation. In this work, a diffractive optical element (DOE) is used to transform a Gaussian beam into a 2x2 array, producing simultaneously expanding, co-propagating ablation plumes that interact during expansion. Plasma evolution from Cu and Si targets is investigated in vacuum using a Nd:YAG laser (1064 nm, 5 ns, 10 J/cm2), combining time-resolved imaging with optical emission spectroscopy. The multi-spot configuration results in enhanced emission intensity compared to single-spot irradiation, with increases of ~9 for Si and ~3 for Cu. The observed enhancement is attributed to plume-plume interaction effects that modify plasma density and emission characteristics. These results demonstrate that DOE-based beam shaping provides an effective and technically simple approach to increasing the LIBS signal without additional system complexity.

physics.app-ph↗

arXiv2025

Femtosecond Laser Crystallization of Ultrathin a-Ge Films in Multilayer Stacks with Silicon Layers

Ultrashort pulsed laser annealing is an efficient technique for crystallizing amorphous semiconductors with the possibility to obtain polycrystalline films at low temperatures, below the melting point, through non-thermal processes. Here, a multilayer structure consisting of alternating amorphous silicon and germanium films was annealed by mid-infrared (1500 nm) ultrashort (70 fs) laser pulses under single-shot and multi-shot irradiation conditions. We investigate selective crystallization of ultrathin (3.5 nm) a-Ge film, promising for the generation of highly photostable nanodots. Based on Raman spectroscopy analysis, we demonstrate that, in contrast to thicker (above 10 nm) Ge films, explosive stress-induced crystallization is suppressed in such ultrathin systems and proceeds via thermal melting. This is likely due to the islet structure of ultrathin films which results in the formation of nanopores at the Si-Ge interface and reduces stress confinement during ultrashort laser heating.

physics.optics↗

arXiv2025

The Roadmap of New Capabilities of High-Intensity Lasers in Material Design and Manipulation

One of the current trends of laser applications in material science is using high-intensity lasers to provide fast and efficient surface or volume modifications for achieving controllable material properties, synthesis of novel materials with desired functionalities, and upscaling laser technologies with industry-demanded throughputs. Depending on the parameters, lasers can offer versatile solutions for scientific and industrial applications, starting from exploring the fundamental physics of warm dense matter and molecular chemistry at ultrashort timescales to large-scale fabrication of surfaces with anti-bacterial, tribological, hydrophobic, or hydrophilic properties. The objectives of this Chapter are to provide a review of recent advancements in several laser application fields, which involve high-intensity lasers, both ultrashort (femto- and picosecond) and short (nanosecond). After summarizing general trends in high-intensity laser processing of materials, we will first focus on the new opportunities offered by high-intensity lasers for the controlled synthesis of multielement nanoparticles for catalytic and theranostic applications. Then, the blister-based laser-induced forward transfer (BB-LIFT) technique will be presented, allowing a one-step, high-precision printing of nanomaterials on any substrates. The next section will discuss the selective crystallization of amorphous (as prepared) semiconductor nanoscale materials. The processes enabling high selectivity of crystallization into the desired phase using ultrashort powerful lasers will be analyzed. After that, opportunities for using high-power lasers will be discussed for upscaling surface nanostructuring with high throughput for bio-medical and industrial applications. Finally, an introduction to the Open Access program of the HiLASE Centre, which is targeted at offering users high-intensity beam time, will be given.

physics.optics↗

arXiv2024

Laser-Induced Gas-Phase Transfer and Direct Stamping of Nanomaterials: Comparison of Nanosecond and Femtosecond Pulses

The two-dimensional nanomaterial, hexagonal boron nitride (hBN) was cleanly transferred via a blister-based laser-induced forward-transfer method. The transfer was performed utilizing femtosecond and nanosecond laser pulses for separation distances of ~16 and ~200 micrometers between a titanium donor film deposited on a glass substrate and a silicon/silicon dioxide receiver. Transfer efficiency was examined for isolated laser pulses as well as for series of overlapping pulses and single layer transfer was confirmed. It was found that hBN is transferable for all tested combinations of pulse duration and transfer distances. The results indicate that transfer proceeds via direct stamping for short donor-to-receiver distances while, for the larger distance, the material is ejected from the donor and lands on the receiver. Furthermore, with overlapping pulses, nanosecond laser pulses enable a successful printing of hBN lines while, for fs laser pulses, the Ti film can be locally disrupted by multiple pulses and molten titanium may be transferred along with the hBN flakes. For reproducibility, and to avoid contamination with metal deposits, low laser fluence transfer with ns pulses and transfer distances smaller than the blister height provide the most favourable and reproducible condition.

physics.optics↗

arXiv2024

Coherence effects in LIPSS formation on silicon wafers upon picosecond laser pulse irradiations

Using different laser irradiation patterns to modify of silicon surface, it has been demonstrated that, at rather small overlapping between irradiation spots, highly regular laser-induced periodic surface structures (LIPSS) can be produced already starting from the second laser pulse, provided that polarization direction coincides with the scanning direction. If the laser irradiation spot is shifted from the previous one perpendicular to light polarization, LIPSS are not formed even after many pulses. This coherence effect is explained by a three-wave interference, - surface electromagnetic waves (SEWs) generated within the irradiated spot, SEWs scattered from the crater edge formed by the previous laser pulse, and the incoming laser pulse, - providing conditions for amplification of the periodic light-absorption pattern. To study possible consequences of SEW scattering from the laser-modified regions, where the refractive index can change due to material melting, amorphization, and the residual stress formed by previous laser pulses, hydrodynamic modelling and simulations have been performed within the melting regime. The simulations show that stress and vertical displacement could be amplified upon laser scanning. Both mechanisms, three-wave interference and stress accumulation, could enable an additional degree of controlling surface structuring.

physics.optics↗

arXiv2024

Dual-wavelength femtosecond laser-induced low-fluence single-shot damage and ablation of silicon

A study of damage and ablation of silicon induced by two individual femtosecond laser pulses of different wavelengths, 1030 and 515 nm, is performed to address the physical mechanisms of dual-wavelength ablation and reveal possibilities for increasing the ablation efficiency. The produced ablation craters and damaged areas are analyzed as a function of time separation between the pulses and are compared with monochromatic pulses of the same total energy. Particular attention is given to low-fluence irradiation regimes when the energy densities in each pulse are below the ablation threshold and thus no shielding of the subsequent pulse by the ablation products occurs. The sequence order of pulses is demonstrated to be essential in bi-color ablation with higher material removal rates when a shorter-wavelength pulse arrives first at the surface. At long delays of 30-100 ps, the dual-wavelength ablation is found to be particularly strong with the formation of deep smooth craters. This is explained by the expansion of a hot liquid layer produced by the first pulse with a drastic decrease in the surface reflectivity at this timescale. The results provide insight into the processes of dual-wavelength laser ablation offering a better control of the energy deposition into material.

physics.optics↗

arXiv2022

Melting of gold by ultrashort laser pulses: Advanced two-temperature modeling and comparison with surface damage experiments

The ultrafast laser-induced solid-liquid phase transition in metals is still not clearly understood and its accurate quantitative description remains a challenge. Here we systematically investigated, both experimentally and theoretically, the melting of gold by single femto- and picosecond near-infrared laser pulses. Two laser systems with wavelengths of 800 and 1030 nm and pulse durations ranging from 124 fs to 7 ps were used and the damage and ablation thresholds were determined for each irradiation condition. The theoretical analysis was based on two-temperature modeling. Different expressions for the electron-lattice coupling rate and contribution of ballistic electrons were examined. In addition, the number of free electrons involved in the optical response is suggested to be dependent on the laser intensity and the influence of the fraction of involved electrons on the damage threshold was investigated. Only one combination of modelling parameters was able to describe consistently all the measured damage thresholds. Physical arguments are presented to explain the modeling results.

cond-mat.mtrl-sci↗

arXiv2004

Production of Gas Phase Zinc Oxide Nanoclusters by Pulsed Laser Ablation

We present experimental results on the photoluminescence (PL) of gas-suspended zinc oxide nanoclusters prepared during ablation of sintered ZnO targets by a pulsed ArF laser in the presence of oxygen ambient gas. The PL spectra in the UV spectral region correspond to the exciton recombination in the nanoclusters which are crystallized and cooled down to the temperature of the ambient gas in the ablation chamber. The time evolution of the spectra as well as their dependence on the ambient gas pressure are discussed.

cond-mat.mtrl-sci↗

arXiv2004

Silicon clusters produced by femtosecond laser ablation: Non-thermal emission and gas-phase condensation

Neutral silicon clusters Si_n (up to n = 7) and their cations Si_n+ (up to n = 10) have been produced by femtosecond laser ablation of bulk silicon in vacuum and investigated using time-of-flight mass spectrometry. Two populations of the Si_n+ clusters with different velocity and abundance distributions in the ablation plume have been clearly distinguished. Possible mechanisms of cluster formation (Coulomb explosion, gas-phase condensation, phase explosion) are discussed.

physics.atm-clus↗

arXiv2004

Cluster emission under femtosecond laser ablation of silicon

Rich populations of clusters have been observed after femtosecond laser ablation of bulk silicon in vacuum. Size and velocity distributions of the clusters as well as their charge states have been analyzed by reflectron time-of-flight mass spectrometry. An efficient emission of both neutral silicon clusters Sin (up to n = 6) and their cations Sin+ (up to n = 10) has been observed. The clusters are formed even at very low laser fluences, below ablation threshold, and their relative yield increases with fluence. We show the dependencies of the cluster yield as well as the expansion dynamics on both laser wavelength and laser fluence. The mechanisms of the cluster formation are discussed.

physics.atm-clus↗

arXiv2003

Laser ablation synthesis of zinc oxide clusters: a new family of fullerenes?

Positively charged zinc oxide clusters ZnnOm (up to n = 16, m <= n) of various stoichiometry were synthesized in the gas phase by excimer ArF laser ablation of a ZnO target and investigated using time-of-flight mass spectrometry. Depending on ablation conditions, either metal rich or stoichiometric clusters dominate in the mass spectrum. When the irradiated target surface is fairly fresh, the most abundant clusters are metal rich with Zn(n+1)On and Zn(n+3)On being the major series. The stoichiometric clusters are observed with an etched ablated surface. The magic numbers at n = 9, 11 and 15 in mass spectra of (ZnO)n clusters indicate that the clusters have hollow spheroid structures related to fullerenes. A local abundance minimum at n = 13 provides an additional evidence for the presence in the ablation plume of fullerene-like (ZnO)n clusters.

physics.atm-clus↗

arXiv2003

Synthesis and Laser Processing of ZnO Nanocrystalline Thin Films

We present the results of experiments on synthesis of ZnO nanoclusters by reactive pulsed laser deposition (PLD). The nanoclusters were formed and crystallized in the gas phase and deposited on SiO2 substrates. The nanostructured films were characterized by conventional photoluminescence (PL). The PL spectra consist of a narrow UV excitonic band and a broad visible band related to defects in the film. The film preparation conditions such as the substrate temperature, ambient gas nature and pressure, were optimized in order to increase the intensity of excitonic emission and prevent the formation of defects. A post-growth annealing by UV laser radiation improved the optical quality of the deposited films. The photoluminescence intensity was found to be dependent significantly on the laser fluence and on the number of shots per site. The nature of the defects responsible for the observed luminescence in a visible range is discussed.

cond-mat.mtrl-sci↗

arXiv2003

Ablation de ZnO par laser UV (193 nm) : Nano-agregats en phase gazeuse

The condensation of zinc oxide nano clusters produced in gas phase has been evidenced in the ablation of a ZnO solid target by a pulsed ArF laser. We compare the spatio-temporal evolution of the shape of ZnO ablated plasma plume, both in vacuum and in controlled gas environments (Helium and/or Oxygen) from monitoring with CCD camera and from spectroscopic studies. The expansion of the plasma plume and the growth of the nanoclusters depend strongly upon the collisions between the ablated particles and surrounding gas molecules, as well as on the chemical reactions in the case of oxygen. The spectra of the observed plasma emittion are mainly due to atomic transitions in the neutral Zn. We have also observed the photoluminescence of the nanoclusters suspended in the gas and their decomposition in the beam of ArF laser.

physics.atm-clus↗