Pulsed Laser Irradiation Research Articles

Insights Into the Local Heating Effects in Triple-Cation Mixed-Halide Perovskite Cells: Charge Dynamics, Coherent Phonons, Anion Segregation.

The behavior of triple-cation mixed halide perovskite solar cells (PSCs) under ultrashort laser pulse irradiation at varying fluences is investigated, with a focus on local heating effects observed in femtosecond transient absorption (TA) studies. The carrier cooling time constant is found to increase from 230 fs at 2 µJcm⁻2 to 1.3ps at 2 mJcm⁻2 while the charge population decay accelerates from tens of nanoseconds to the picosecond range within the same fluence range. At fluences between 0.5 and 5 mJcm2, distinct oscillations in the TA signal (≈1.1MHz) reveal the presence of coherent longitudinal acoustic phonons (CLAP). These phonons induce lattice strain propagating at the speed of sound through the perovskite layer and exhibit relatively long damping times. TA spectra further reveal a partially reversible segregation of iodide and bromide anions under pulsed excitation. Interestingly, higher local heating at increased pump fluences slows the segregation process, with time constants extending from 40 min at low fluences to 110 min at high fluences. However, the continuous irradiation results in significantly smaller segregation effects compared to ultrashort pulse irradiation.

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

Abstract Using different laser irradiation patterns to modify 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.

Nanosecond Laser Pulses Facilitating Efficient and Specific Cell Killing with Doxorubicin‐Loaded Gold Nanoparticles Targeted to the Folate Receptor

Nanoparticle‐based drug carrier systems with active targeting and a controlled release capacity are of considerable interest to bypass side effects of conventional chemotherapy. One appealing approach involves chemotherapeutic‐loaded photothermal nanoparticles, where laser irradiation can release the loaded anticancer drug while also inducing local cytotoxicity through photothermal effects. This study investigates the potential of using nanosecond‐pulsed laser light for efficient and specific killing of folate receptor (FR)‐overexpressing cancer cells in combination with FR‐targeted doxorubicin‐loaded gold nanoparticles (AuNPs). Nanosecond pulsed laser irradiation allows the induction of mechanical forces alongside thermal effects. The effect of nanoparticle concentrations and laser fluences on cytotoxicity is systematically tested, achieving near‐complete tumor cell killing under the most stringent conditions. FR targeting is confirmed using FR‐positive and ‐negative cell lines, showing that folic acid functionalization of AuNPs results in more favorable nanoparticle–cell interactions and more efficient photothermal effects. Additionally, doxorubicin could be efficiently released from the AuNPs and endosomal compartments upon laser irradiation, adding to the observed cytotoxicity. Cell killing was precisely confined to irradiated cells, leaving surrounding cells unharmed. Overall, the significant reduction of tumor cell viability following the proposed combination demonstrates this approach to be a promising step toward safer, more effective anticancer therapies.

Study of metallic nano-structures formed in liquids by large pulsed laser radiation spots using transmission electron microscopy

Abstract Pulsed Laser Ablation in Liquids (PLAL) represents a prominent method for synthesising metallic nanoparticles and nano-alloys. This technique offers the potential precise control over the process and resulting products. However, a comprehensive description of the underlying mechanisms is still necessary to enhance control. Our investigation involved the utilisation of low fluence 6 ns laser pulses on 35 mm2 areas of thin films comprising layers of Ag, Pt, and Au to investigate the nano-structures and alloys obtained. The large laser spot produced nano-structures with peculiar morphological characteristics. Their analysis by High-Resolution Transmission Electron Microscopy (HRTEM) confirms that the early stages of the ablation plume play an essential role in the nucleation of nano-structures when the ablating metals have a strong interaction with the fluid, which has surpassed its critical temperature and pressure. 

Photocoloring Reaction Behavior in Spironaphthooxazine Nanoparticles under Nanosecond Pulse Laser Irradiation

Photocoloring Reaction Behavior in Spironaphthooxazine Nanoparticles under Nanosecond Pulse Laser Irradiation

Interplay between classical and quantum dissipation in light-matter dynamics.

A quantum-electrodynamics approach is presented to describe the dynamics of electrons that exchange energy with both photon and phonon baths. Our ansatz is a dissipative quantum Liouville equation, cast in the Redfield form, with two driving terms associated with radiative and vibrational relaxation mechanisms, respectively. Remarkably, within the radiative contribution, there is a term that exactly replicates the expression derived from a semiclassical treatment where the power dissipated by the electronic density is treated as the emission from a classical dipole [Bustamante et al., Phys. Rev. Lett. 126, 087401 (2021)]. Analysis of the distinct contributions to the total radiation shows that the semiclassical emission depends on the coherences, with the remainder of the quantum-electrodynamics driving term determined by the excited populations, thus accounting for the relaxation of eigenstates or incoherent mixed states. This approach is used to investigate the response of the Su-Schrieffer-Heeger model for trans-polyacetylene to both pulsed and continuous laser irradiation. Upon excitation with a short pulse and in the absence of the vibrational mechanism, the conducting band population exhibits a stepwise relaxation, characterized by cycles of exponential decay followed by a transient subradiant state. The latter arises from the collective coupling between Bloch states featuring a quasi-continuum energy spectrum in reciprocal space. The separate examination of the semiclassical dynamics reveals that it is this contribution that is responsible for the collective behavior. If vibrational dissipation is active, following the laser pulse, the excited electrons rapidly populate the minimum of the conduction band, and the emission spectrum shifts to lower frequencies with respect to absorption. Meanwhile, continuous irradiation drives the system to a stationary state with a broad emission spectrum.

Multiscale modeling of short pulse laser induced amorphization of silicon

Silicon surface amorphization by short pulse laser irradiation is a phenomenon of high importance for device manufacturing and surface functionalization. To provide insights into the processes responsible for laser-induced amorphization, a multiscale computational study combining atomistic molecular dynamics simulations of nonequilibrium phase transformations with continuum-level modeling of laser-induced melting and resolidification is performed. Atomistic modeling provides the temperature dependence of the melting/solidification front velocity, predicts the conditions for the transformation of the undercooled liquid to the amorphous state, and enables the parametrization of the continuum model. Continuum modeling, performed for laser pulse durations from 30 ps to 1.5 ns, beam diameters from 5 to 70 μm, and wavelengths of 532, 355, and 1064 nm, reveals the existence of two threshold fluences for the generation and disappearance of an amorphous surface region, with the kinetically stable amorphous phase generated at fluences between the lower and upper thresholds. The existence of the two threshold fluences defines the spatial distribution of the amorphous phase within the laser spot irradiated by a pulse with a Gaussian spatial profile. Depending on the irradiation conditions, the formation of a central amorphous spot, an amorphous ring pattern, and the complete recovery of the crystalline structure are predicted in the simulations. The decrease in the pulse duration or spot diameter leads to an accelerated cooling at the crystal–liquid interface and contributes to the broadening of the range of fluences that produce the amorphous region at the center of the laser spot. The dependence of the amorphization conditions on laser fluence, pulse duration, wavelength, and spot diameter, revealed in the simulations, provides guidance for the development of new applications based on controlled, spatially resolved amorphization of the silicon surface.

Enhancing the sub-bandgap photo-response of silicon by inert element co-hyperdoping.

The introduction of intermediate bands by hyperdoping is an efficient way to realize infrared light absorption of silicon. In this Letter, inert element (helium and argon for specific)-doped black silicon is obtained by helium ion-implantation followed by femtosecond pulse laser irradiation in an argon atmosphere based on near-intrinsic silicon substrates. Within the 200 nm of the silicon surface, the concentrations of helium and argon are both above the order of 1019 cm-3. The defect states related to impurities and structural defects contribute to the absorption in sub-bandgap (1100-2500 nm). Vertically structured devices based on the inert element-doped black silicon exhibit the responsivity of 350 mA/W for 1550 nm and 165 mA/W for 1310 nm at 12 V operating bias, respectively, proving its potential application in infrared detection.

Pulsed laser irradiation effects and experimental study of glass ceramics during synchronized laser-enhanced servo-cutting process

Pulsed laser irradiation effects and experimental study of glass ceramics during synchronized laser-enhanced servo-cutting process

High-Entropy Electrocatalysts for Seawater Splitting

Due to the consumption of primary energy, the demand for renewable energy is increasing. Because of its high energy density and zero carbon emissions, water electrolysis to produce hydrogen is an ideal and clean energy choice. However, fresh water is a high demand resource for people's livelihood which only takes less 3 percent in the full water resource. Therefore, exploring the use of seawater, which accounts for over 70% of the earth, as a source for seawater splitting is worthwhile. We need to find a more efficient and long-last catalyst to avoid the chorine evolution, a competition reaction during oxygen evolution (OER), causing the corrosion process to suppress the life span of catalyst for usage of the seawater to produce hydrogen. High entropy materials, a potential promising catalyst candidate, due to their tunable electronic structures leading to a much lower OER overpotential and corrosion resistance. In this work. we use a pulsed laser irradiation scanning on mixed salt solutions (PLMS) method to produce a six elements high entropy ceramic nanoparticles as OER catalyst for efficient and stable work in seawater environments. The (AlCoCrFeMnNi)O high-entropy ceramic (HEC) we proposed demonstrate a great performance in the seawater environment. The onset voltage of oxygen-evolution can low down to 1.47V vs. RHE, and in terms of stability our catalyst is capable to operate for 1000 hours under 100mA/cm2. Furthermore, to understand the mechanism behind our (AlCoCrFeMnNi)O HEC, the in-situ XAS (X-ray absorption spectroscopy) measurement and In-situ EXAFS are carried out in this work under different OER voltage applied. Co, Mn, and Ni identified as the active sites of OER and these three elements work intimately together with each different reaction routes, including the adsorbate evolution mechanism (AEM) and lattice oxygen-participated mechanism (LOM). While Al, Cr, and Fe are not directly contributed to the catalytic activity but they play important roles to stabilize the high entropy structure during the whole reaction. Figure 1

Effect of CuO nanoparticle size distribution on Cu-based patterns fabricated via femtosecond laser-pulse-induced thermochemical reduction

Copper-direct writing using laser reductive sintering of CuO nanoparticles has received significant interest for printing technology. We investigated the effect of the particle size distribution in CuO nanoparticle inks on patterns fabricated using femtosecond laser-pulse-induced thermochemical reduction. First, Gaussian- and bimodal-type inks were prepared using commercially available and chemically synthesized nanoparticles, respectively. Both types of inks on glass substrates with a thickness of approximately 10 µm were estimated to be absorbed 80% of the irradiated near-infrared femtosecond laser pulses, as indicated by both absorption coefficients. The bimodal-type ink increased the density of the patterns, as expected using the packing theory. However, the patterns comprised non-reduced CuO and Cu2O, as well as residual polyvinylpyrrolidone. In contrast, the patterns fabricated using the Gaussian-type ink were well-reduced to Cu and exhibited a low density and high surface area. In addition, the patterns were advantageous for electrochemical applications, which exhibited intense peaks corresponding to the reduction of CuO and Cu2O surface oxides back to metallic copper in comparison of the patterns fabricated using the bimodal-type ink, regardless of laser irradiation conditions.

Self-focusing and stimulated Brillouin scattering effect of low-temporal coherence light and corresponding damage characteristics in fused silica

Laser-induced damage thresholds (LIDTs) of input/exit surfaces and filamentation of fused silica under low-temporal coherence light (LTCL) and a corresponding damage mechanism are investigated. By comparing self-focusing effects of fused silica for each incident laser, the lower LIDT of filamentation damage under LTCL irradiation is mainly attributed to stronger self-focusing than traditional single longitudinal mode (SLM) pulse lasers. Meanwhile, differences in LIDTs for input/exit surfaces by LTCL and SLM pulse laser irradiation are attributed to self-focusing effects and backward stimulated Brillouin scattering. Finally, influences of fused silica thickness and incident laser polarization on LIDT are demonstrated. The research contributes to exploring safe boundaries for fused silica application in high-power LTCL devices.

Au@hydroxyapatite nanocomposite as a novel apoptosis Inducer and NF-κB translocation Inhibitor in prostate cancer cell line

In the current study, we used an environmentally friendly method called pulsed laser irradiation for the preparation of AuNPs and hydroxyapatite NPs alone and as a composite nanomaterials. The optical, morphology, and chemical bonding possessions of prepared AuNPs, hydroxyapatite NPs, and Au-hydroxyapatite composites were studied using different techniques like Transmission Electron Microscopy (TEM), Ultraviolet–visible Spectram (UV–VIS), and Fourier transform infrared spectroscopy (FTIR). The anticancer activity of prepared Au NPs, hydroxyapatite NPs, and Au-hydroxyapatite composites against prostate cancer cell line (PC-3 cells) was evaluated by MTT assay as well the possible mechanisms underlying the induction of apoptosis. The consequences suggest that the nanoparticles can act against an antiproliferative agent against PC-3 cells-induced apoptosis by activating caspase-8 and reducing the NF-κB translocation pathway. The current study demonstrates the potential role of an Au-hydroxyapatite composite for anticancer applications via the activation of the apoptosis pathway through extrinsic and intrinsic pathways.

Supercontinuum saturation of a femtosecond laser filament in pressurized gases.

Filamentation of high-power femtosecond optical pulses in high-pressure gases has gained increasing academic and practical interest from the viewpoint of studying large-scale spectral and temporal transformations occurring with pulsed laser radiation and obtaining super-broadened spectra and extremely short (attosecond) wave packets. Experimentally and theoretically, for the first time to the best of our knowledge, we show that as a result of a 45 fs Ti:sapphire laser pulse filamentation in an optical cell filled with pressurized up to 50 bar nitrogen or argon, the pulse spectrum can reach maximally about eightfold broadening. This limiting pulse spectral width is reached at a gas pressure of about 20 bar and with further pressure increase exhibits saturation and even a slight decrease relative to the limiting value. As a possible reason for this finding, we suppose the increase of pulse energy depletion in the self-created plasma at high gas pressure.

Toward tailored light absorption manipulation by Kerr nonlinear nanoslits within a grating Fabry-Perot cavity coupled with reconfigurable GST225 material

In this paper, we investigate the absorption tunability of a silver plasmonic grating incorporating Kerr-type nonlinear graphene-oxide (GO) nanoslits and Ge2Sb2Te5 (GST225) phase-change material at telecom wavelengths. The linear absorption spectra reveal that the amorphous GST225 grating exhibits two distinct absorption peaks, while half-crystallization leads to a single pronounced peak, and full crystallization results in a redshifted peak with a slightly decreased value. These findings confirm that the crystalline degree of GST225 significantly modulates the absorption characteristics. Upon exposure to a nanosecond Gaussian pulse laser irradiation with appropriate fluences, the electric field confinement within the nanoslits intensifies, particularly at the center of the pulse, leading to a pronounced absorption adjustment due to Kerr nonlinearity. Temporal examination at the L-band wavelength of 1591.5 nm reveals a U-shaped absorption response for both amorphous and crystalline GST225, with a pronounced dip at the pulse’s peak. In the half-crystallized state, the weak linear absorption can be substantially enhanced at both the leading and trailing edges of the pulse, with a dip at the center, illustrating the Kerr nonlinearity within the GO nanoslits. The dynamic behavior of absorption under different laser fluences underscores the potential of this system for high-contrast optical switching. Our results offer insights into the development of reconfigurable optical switches utilizing nonlinear Kerr effects, paving the way for advancements in tunable optical communication technologies.

Influence of defocusing of UV pulse laser radiation on LIG synthesis on Polyetheretherketone

Laser-induced graphene (LIG) technology, a technique for preparing three-dimensional porous graphene by laser direct writing on carbon precursors under ambient condition, has been widely used due to its low cost and high efficiency. However, there is still a lack of research on the influence of the defocusing on LIG synthesis. In this paper, LIG is prepared by UV laser on Polyetheretherketone (PEEK) film, and a finite element simulation of this process is established to infer the temperature field. The influence of the defocusing on the structure, morphology, specific surface area SSA, and electrical properties of PEEK-LIG is investigated while maintaining the same energy radiated per unit area. The results show that the defocusing changes the structure and morphology of PEEK-LIG by affecting the temperature field distribution in both the surface and thickness directions, which affects the properties of LIG, where the surface area ratio Sdr does not depend on the defocusing amount monotonically. As the UV laser nears the beam waist at the threshold of LIG formation, Sdr has its maximum value and improves its electrical conductivity.

A Biotechnical System for Increasing the Effectiveness of the Pre-Sowing Pulsed Laser Irradiation of Seeds to Increase Sunflower Yield

In this study, we investigated the use of the pre-sowing electrophysical stimulation of seeds, particularly focusing on optimizing technological regimes for enhancing seed quality. The aim of this study was to improve sunflower seed germination utilizing laser optical radiation. The methods explored involved the pre-sowing stimulation of oilseeds and analyzing the key mechanisms affecting germination. Through our experimental research, we sought to identify the most effective laser irradiation parameters, ensuring the maximum seed quality improvement with minimal energy use. Using seeds of the first reproduction, we employed artificial aging to simulate a reduced seed quality and determined optimal irradiation regimes. Standard methods were followed to assess seed quality before and after irradiation, with 6–7 days of further exposure. Seed germination was carried out under controlled light and temperature conditions using the “on paper” method with paper napkins. A full factorial experiment was performed and key parameters for laser irradiation were determined, confirming that the pre-sowing laser pulse treatment significantly improved seed quality. In this research, we developed a biotechnical system for processing seeds and propose a method to adjust irradiation parameters based on the initial seed quality. The system effectively enhanced germination and crop yield, offering a reliable solution for improving sunflower seed productivity through laser treatment.

Nanosecond pulsed laser coloring of the CrMnFeCoNi high entropy alloy

High-entropy alloys (HEAs) possess great potential for applications in the aerospace and military fields due to their excellent performance. Surface coloring can endow HEAs diverse functions. However, achieving a multi-color surface with minimal surface damage and cost remains a significant challenge. In this study, surface coloring of the CrMnFeCoNi HEA was attempted by nanosecond pulsed laser irradiation in air, and the multi-color surface was achieved. The evolution of surface color and morphology with laser parameters was analyzed. Then, five typical colors were selected, and the corresponding morphologies and chemical compositions were characterized by various techniques. The results showed that the change in oxide layer thickness as well as the formation of chromium-rich β-spinel and Cr (VI) compounds induced noticeable changes in surface color. Accordingly, complex surface patterns with various stable colors were prepared on the HEA surface, demonstrating the potential application of nanosecond pulsed laser coloring of HEAs.

Deciphering the Electronic Coupling Dynamics of Laser-induced Ru/Cu Electrocatalyst for Dual-Side Hydrogen Production and Formic Acid Co-synthesis via DFT Analysis.

Herein, a straightforward approach using pulsed laser technology to synthesize selective hexagonal-close-packed (hcp) Ru nanoparticles attached to Cu nanospheres (Ru/Cu) as bifunctional electrocatalyst for catalyzing the hydrogen evolution reaction (HER) and formaldehyde oxidation reaction (FOR) are reported. Initially, Ru-doped CuO flakes are synthesized using a coprecipitation method followed by transformation into Ru/Cu composites through a strategy involving pulsed laser irradiation in liquid. Specifically, the optimized Ru/Cu-4 composite not only demonstrates a low overpotential of 182mV at 10 mA·cm-2 for the HER but also an ultralow working potential of 0.078V (versusreversible hydrogen electrode) for the FOR at the same current density. Remarkably, the FOR∥HER-coupled electrolyzer employing the Ru/Cu-4∥Ru/Cu-4 system achieves H2 production at both electrodes with a cell voltage of 0.42 V at 10 mA·cm-2 while co-synthesizing formic acid. Furthermore, density functional theory analyses elucidate that the superior activity of the Ru/Cu composite originates from optimized adsorption energies of reactive species on the catalyst surfaces during the HER and FOR, facilitated by the synergistic coupling between Ru and Cu. This study presents an alternative strategy for synthesizing highly effective electrocatalytic materials for use in energy-efficient H2 production with the cosynthesis of value-added chemicals suitable for practical applications.

Dynamic tunability of NIR absorption in a plasmonic grating through nonlinear kerr-effect of graphene-oxide and photothermal phase transition of GSST

In this paper, we present an in-depth examination of the absorption dynamics of a silver plasmonic grating incorporating Kerr-type nonlinear graphene-oxide (GO) nanoslits and a Ge2Sb2Se4Te1 (GSST) phase-change material, both in linear and nonlinear regimes. Linear absorption approaches unity at the resonant wavelength when GSST is amorphous. Upon exposure to a nanosecond Gaussian pulse laser irradiation with appropriate fluences, the amorphous GSST partially crystallizes through a thermoplasmonic-induced process, resulting in a significant reduction of the linear on-resonance absorption in the form of a step-like curve. Additionally, the weak off-resonance linear absorption of the system can be enhanced owing to the non-uniform phase-transition within the GSST. Transitioning to a nonlinear regime, considering the third-order nonlinearity of GO nanoslits, reveals distinct absorption behaviors. Temporal analysis reveals that at the on-resonance wavelength, the unit absorption decreases with increasing laser intensity, reaching a minimum at the pulse peak due to the Kerr nonlinearity in the GO. Intriguingly, the absorption exhibits a U-shaped curve at lower fluences, while at higher fluences, it stabilizes at a lower value post-pulse peak where the amorphous GSST undergoes a thermally driven partially crystallization phase transformation. In the off-resonance mode, the weak absorption enhances dramatically by increasing the fluence, tracing an imperfect parabolic trajectory that reaches nearly unit at the trailing edge of the pulse, attributed to the Kerr nonlinearity within the GO nanoslits. By further increasing the laser fluence, the photothermal response of the GSST emerges as the dominant factor, diminishing the unity absorption observed at the trailing edge of the pulse. These findings underscore the dynamic responsiveness of the proposed grating to pulsed laser illumination, driven by the nonlinear Kerr effect and GSST reconfigurability, offering promising opportunities for developing active optical switching devices.