Pulsed Laser Irradiation Research Articles

Optical Binding-Driven Micropatterning and Photosculpting with Silver Nanorods.

Controlling the nano- and micropatterning of metal structures is an important requirement for various technological applications in photonics and biosensing. This work presents a method for controllably creating silver micropatterns by laser-induced photosculpting. Photosculpting is driven by plasmonic interactions between pulsed laser radiation and silver nanorods (AgNRs) in aqueous suspension; this process leads to optical binding forces transporting the AgNRs in the surroundings, while electronic thermalization results in photooxidation, melting, and ripening of the AgNRs into well-defined 3D structures. This work call these structures Airy castles due to their structural similarity with a diffraction-limited Airy disk. The photosculpted Airy castles contain emissive Ag nanoclusters, allowing for the visualization and examination of the aggregation process using luminescence microscopy. This work comprehensively examines the factors that define the photosculpting process, namely, the concentration and shape of the AgNRs, as well as the energy, power, and repetition rate of the laser. Finally, this work investigates the potential applications by measuring the metal-enhanced luminescence of a europium-based luminophore using Airy castles.

Evaluating the effects of space weathering on magnetite on airless planetary bodies

Magnetite is a relevant mineral component of asteroids as it has been identified in carbonaceous chondrites, on the surface of asteroid Bennu through remote sensing observations, and in samples returned from asteroid Ryugu. However, the effects of space weathering processes on magnetite have not yet been explored. To investigate how this mineral phase responds to space weathering, here we simulate micrometeoroid bombardment and solar wind irradiation of magnetite using pulsed laser and ion irradiation experiments. We performed X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), and visible to near-infrared (VNIR) reflectance spectroscopy analyses to characterize the chemical, microstructural, and spectral response of magnetite to simulated space weathering. In addition, we carried out ion impact simulations using the SDTrimSP software to evaluate the calculated response of magnetite to 1 keV H+ and 4 keV He+ ions and compared these results to our XPS and TEM results. Ion irradiation simulated ∼750 years on the surface of asteroid Bennu, with a solar-wind appropriate total H:He fluence ratio (∼24). Within this time, depletion of O was observed with H+ and He+ ion irradiation, with significantly greater change via protons due to the larger fluence, where preferential sputtering promotes the formation of a metallic iron layer at the magnetite surface. This suggests that solar wind ions act as reducing agents on Fe oxides, with a fraction remaining implanted in these phases. Indeed, we observe elongated defects contained in a crystalline rim created by He+ implanted ions in the TEM. Pulsed laser irradiation, analogous to micrometeoroid impacts, generates melts on the surface of the magnetite grains. The impact melts and H+-generated metallic iron rims both result in increased VNIR spectral reflectance, but lower fluence He+ implantation has no significant spectral effect. These results suggest that space weathered magnetite could contribute to bright regions detected in remote sensing analyses of the Ryugu and Bennu surfaces by the Hayabusa2 and OSIRIS-REx missions and will contribute to the identification and interpretation of space weathered magnetite in returned samples retrieved from both asteroids.

Some Initial Results on Modification of aC:H Films by Pulsed Laser Irradiation

It has recently been shown both theoretically and experimentally that a significant modification of the aC:H films is possible using UV irradiation even with a very low irradiation fluence. Some initial results on the modification of aC:H films with thickness of about 40 nm with UV laser irradiation are presented here. The fourth harmonic (λ = 266 nm) of a Nd:YAG laser system (the fundamental wavelength λ = 1064 nm) was used in our experiments. The modified areas of the aC:H films were characterized by optical microscopy, Raman spectroscopy as well as by atomic force microscopy (AFM). A significant modification of aC:H films under certain conditions (laser irradiation fluence and modification modes) to multi-layer graphene accompanied by ablation of a part of the film was established. It was also found that similar aC:H films deposited on 330 nm SiO2/Si substrates did not undergo significant modification under these conditions.

Laser-assisted synthesis of metallic composite nanostructures in aqueous solutions

The method of pulsed laser ablation in liquids (PLAL) is applied for synthesis of composite nanostructures on the basis of TiOx and ZnO combined with noble metals like Au, Pt and Pd. The metallic plate immersed in water is laser ablated by nanosecond Nd:YAG pulsed laser irradiation. Its fundamental wavelength and the fourth harmonic are used, respectively, to produce and to modify the morphology and structure of the nano-objects. The synthesis procedure consists of two consecutive steps: laser ablation of the selected metal targets followed by unfocused laser beam irradiation of the initial colloids of nanostructures. The phase composition, structural and the shape and size morphological features were assessed by analytical method – transmission electron microscopy (TEM) in its main modes – Bright Field TEM (BF TEM), High Resolution TEM (HRTEM) and Selected Area Electron Diffraction (SAED). Formation of bimetallic polycrystalline alloys and Pt/Ti(TixOy) and Pd/Ti(TixOy) core-shell nanoparticles was founded.

Boosting the high gas sensing performance via laser embedding Schottky heterointerfaces at particle boundaries in SnO2 nanofibers

Metal oxide semiconductor-based gas sensors often require noble metals for modification to enhance the carrier mobility of the material. However, current noble metal modifications are almost always performed at the material surface, making it difficult to apply them to the particle boundaries (PBs) of the material, which can greatly reduce the utilization of noble metals. We herein synthesized Pt nanocrystals (NCs) with average size of 1 nm by the technology of pulsed laser irradiation, followed by in situ embedded at the PBs of SnO2 nanofibers to address the unwanted carrier loss at PBs for substantially improved gas sensing. The Pt NCs/SnO2 exhibited 2.23-fold enhancement of response values, and 2.86-fold improvement on selectivity for NO2 at 50 °C, comparing to these samples without PBs engineering. Further analysis showed that the enhancement of the gas-sensitive performance is mainly due to the electronic and chemical sensitization of Pt NCs at the SnO2 PBs and the high utilization of Pt NCs leading to a significant increase in the carrier mobility of the material. We thus believe present work provides an efficient alternative for developing high performance gas sensing based on materials with intrinsic particle boundaries.

Binder-free NiO/CuO hybrid structure via ULPING (Ultra-short Laser Pulse for In-situ Nanostructure Generation) technique for supercapacitor electrode

Developing a cost-effective pseudocapacitor electrode manufacturing process incorporating binder-free, green synthesis methods and single-step fabrication is crucial in advancing supercapacitor research. This study aims to address this pressing issue and contribute to the ongoing efforts in the field by introducing ULPING (Ultra-short Laser Pulse for In-situ Nanostructure Generation) technique for effective design. Laser irradiation was conducted in ambient conditions to form a CuO/NiO hybrid structure providing a synergistic contribution to the electrical behavior of the electrode. Mainly, the effects of surface morphology and electrochemical surface because of tuning laser intensity were analyzed. The samples demonstrated high oxide formation, fiber generation, excellent porosity, and ease of ion accessibility. Owing to a less than 10-min binder-free fabrication method, the electrochemical performance of the as-fabricated electrode was 25.8 mC cm−2 at a current density of 1 mA cm−2 proved to be excellent. These excellent surface properties were possible by the simple working principle of pulsed laser irradiation in ambient conditions and smart tuning of the important laser parameters. The CuO/NiO electrode demonstrates excellent conductivity and rewarding cyclic stability of 83.33% after 8000 cycles. This study demonstrates the potential of the ULPING technique as a green and simple method for fabricating high-performance pseudocapacitor electrodes.

Automated geometry characterization of laser-structured battery electrodes

Micro structuring of battery electrodes with pulsed laser radiation substantially increases the performance of lithium-ion batteries. For process design and monitoring, determining the resulting hole diameters and depths is essential. This study presents an automated, model-based approach for the geometry characterization of laser-drilled structures in battery electrodes. An iteratively re-weighted least squares algorithm is used for fitting of a reference plane to confocal laser scanning microscopy images of laser-structured electrodes. Using a threshold-based segregation of the generated weights, the holes are segmented from the pristine electrode surfaces. The results from the automated geometry determination were found to coincide well with manual measurements. By reducing the image resolution, the runtime of the code could be decreased, which yet lowered the accuracy of the hole depth prediction. In a sensitivity analysis, the algorithm performed stably under changes in the recording conditions, such as altered image brightness, frame rate, or vertical resolution. In conclusion, the presented method reduces the effort and increases the reproducibility for analyzing large experimental data sets in laser electrode structuring. Furthermore, the approach can be successfully transferred to other applications, which is demonstrated by indentations in battery current collector foils stemming from electrode calendering.

Fast Delivery of Multifunctional NIR-II Theranostic Nanoaggregates Enabled by the Photoinduced Thermoacoustic Process.

Multifunctional nanoaggregates are widely used in cancer phototheranostics. However, it is challenging to construct their multifunctionality with a single component, and deliver them rapidly and efficiently without complex modifications. Herein, a NIR-absorbing small molecule named TBT-2(TP-DPA) is designed and certify its theranostic potentials. Then, their nanoaggregates, which are simply encapsulated by DSPE-PEG, demonstrate a photothermal efficiency of 51% while keeping a high photoluminescence quantum yield in the NIR region. Moreover, the nanoaggregates can be excited and delivered by an 808nm pulse laser to solid tumors within only 40 min. The delivery efficiency and theranostic efficacy are better than that of the traditional enhanced permeability and retention (EPR) effect (generally longer than 24 hours). This platform is first termed as the photoinduced thermoacoustic (PTA) process, and confirm its application requires both NIR-responsive materials and pulse laser irradiation. This study not only inspires the design of multifunctional nanoaggregates, but also offers a feasible approach to their fast delivery. The platform reported here provides a promising prospect to boost the development of multifunctional theranostic drugs and maximize the efficacy of used medicines for their clinical applications.

Modeling of inhomogeneous heating behavior in ultrafast laser interaction with dielectric–dielectric nanocomposite with band gap contrast

Inspired by the optical data storage and photothermal therapy applications of metal–dielectric nanocomposite materials relying on the difference in laser absorption mechanism between metal and dielectric, the ultrashort single pulse laser irradiation of zirconia–alumina nanocomposite, a dielectric–dielectric nanocomposite with band gap contrast, was investigated. A femtosecond (fs) laser of 250 fs pulse duration and 10 W maximum average power was used for the experiment. A seemingly unusual phase melting phenomenon - whereby the higher melting point zirconia phase (2715 °C) was melted, while the lower melting point alumina phase (2072 °C) remained intact - was observed, thereby suggesting a huge temperature heterogeneity in the composite under ultrashort single pulse laser irradiation. Theoretical modeling indicates that the material band gap plays a significant role in laser energy absorption under an intense laser field. A sharp increase in the total absorbed laser energy and concomitant temperature increase around the laser ablation threshold was revealed. Under appropriate laser fluence, the smaller band gap zirconia phase (5.8 eV) can absorb much more laser energy than the alumina phase (8.8 eV), resulting in a remarkable temperature difference between these two phases. This research demonstrates the capability of generating huge phase specific temperature differences in composite nanostructures composed of phases with band gap contrast by using ultrashort pulsed laser irradiation.

Terahertz sound generation at the effect of a femtosecond pulse of laser radiation on a metal.

Sound generation by a femtosecond laser pulse in a metal layer on a dielectric substrate is studied. The excitation of sound caused by the effect of the ponderomotive force, temperature gradients of electrons, and lattice is considered. A comparison is made of these generation mechanisms for various excitation conditions and frequencies of generated sound. It is shown that in the case when effective collision frequencies in the metal are low, sound generation dominates in the terahertz frequency range due to the ponderomotive effect of the laser pulse.

GHz bursts in MHz burst (BiBurst) enabling high-speed femtosecond laser ablation of silicon due to prevention of air ionization

For the practical use of femtosecond laser ablation, inputs of higher laser intensity are preferred to attain high-throughput material removal. However, the use of higher laser intensities for increasing ablation rates can have detrimental effects on ablation quality due to excess heat generation and air ionization. This paper employs ablation using BiBurst femtosecond laser pulses, which consist of multiple bursts (2 and 5 bursts) at a repetition rate of 64 MHz, each containing multiple intra-pulses (2–20 pulses) at an ultrafast repetition rate of 4.88 GHz, to overcome these conflicting conditions. Ablation of silicon substrates using the BiBurst mode with 5 burst pulses and 20 intra-pulses successfully prevents air breakdown at packet energies higher than the pulse energy inducing the air ionization by the conventional femtosecond laser pulse irradiation (single-pulse mode). As a result, ablation speed can be enhanced by a factor of 23 without deteriorating the ablation quality compared to that by the single-pulse mode ablation under the conditions where the air ionization is avoided.

Calculation of Parameters of Prism Deflector for Laser Scanner

The prism deflector which is a multifaceted prism with reflective facets is the most common scanning element that allows to quickly fill a wide scanning area with laser radiation pulses along one coordinate. The parameters of a prismatic deflector are related to the characteristics of the laser radiation of the scanned area parameters and of the deflector position, and are also limited by various factors, such as safety requirements or scanning time. The aim of this work was to analyze the relationship between the external operating conditions of a laser scanning system and the internal design parameters of a prism deflector.A variant of calculating of laser pulses frequency by the number of spots and their overlap coefficient is considered. A method for calculating of a prism deflector characteristics based on external parameters, such as the angle of incidence of radiation to the facet and the width of the Gaussian beam with dimensions that are safe for а human eye is proposed. Рrismatic deflectors parameters are proposed depending on the number of reflecting facets. Dependence of a deflector size on the angle of radiation incidence to the reflecting face is shown.When designing a prismatic deflector of a laser scanner used to fill a certain scanning area with the required angular size σ by varying such parameters as the number of faces m and the feed angle α it is possible to achieve optimal deflector characteristics and scanning mode for the task.

Preparation and application of novel thermo-sensitive molecularly imprinted polymer for selective extraction of omeprazole from pharmaceutical formulation and biological fluids

ABSTRACT Omeprazole selective molecularly imprinted polymer was synthesized by polymerization using 2-hydroxyethyl methacrylate as a monomer, N-vinylcaprolactam as a thermo-sensitive polymer, and N, N′-methylenebisacrylamide as cross-linker, respectively. This study aimed to develop a novel polymer as a nanoadsorbent for the extraction of omeprazole in biological and pharmaceutical samples. To achieve maximum extraction recovery of the drug, the Nd:YAG pulsed laser irradiation was used to convert adsorbent particles into smaller sizes using water solvent at different irradiation times. Properties of prepared thermo-sensitive molecularly imprinted polymer were characterized by different analyses. The optimal extraction conditions were thermo-sensitive molecularly imprinted polymer dosage of 0.01 g, a cross-linking agent of 0.15 g, contact time of 15 min, eluent of methanol, the temperature of 25°C, initial drug concentration of 20 mg L−1, and solution pH of 4. The sorption isotherms and selective recognition of thermo-sensitive molecularly imprinted polymer were investigated in detail. Sorption results fitted well into the linearized Langmuir equation. The selectivity experiment has shown that the sorption capacity and selectivity of thermo-sensitive molecularly imprinted polymer to omeprazole were higher than those of bicalutamide and prednisolone. A high-performance liquid chromatography-ultra-violet detector method was validated and utilized for analysis of drug extracted from biological and pharmaceutical samples. The method was linear in the range of 0.5–80 mg L−1 with a relative standard deviation value of 0.094 and a limit of detection and a limit of quantification of 0.9 and 30 µg L−1, respectively. The recovery of omeprazole drug ranged from 94.3%, 99.2%, and 98.1%, respectively, in human plasma, human urine, and pharmaceutical samples.

Feasibility and equivalence analysis of transient dose rate effect simulation by pulsed laser in level-shifting transceiver and TCAD simulation on its ESD circuits

Compared to linear accelerators, pulsed lasers have the characteristics of high efficiency, low cost, stable pulse output, and low environment interference for researching the transient dose rate effect (TDRE) on semiconductor devices. In this paper, pulsed laser radiation experiments are performed on a level-shifting transceiver. The experimental results are consistent with the results of the transient γ-ray radiation experiment, demonstrating the feasibility of using the pulsed laser in TDRE research on the level-shifting transceiver. This paper obtains theoretical and experimental conversion factors (CFs) through theoretical analysis and equivalency of the peak photocurrents, which are measured in pulsed laser and transient γ-ray radiation experiments. The CF results from the two approaches are within 7% of each other. In pulsed laser radiation experiments, an uncommon phenomenon is found. At the I/O (Input/Output) ports of the level-shifting transceiver, a trend of a positive photocurrent followed by a negative pulse is observed. A hypothesis is proposed that this photocurrent is produced by the turn-on and turn-off of the parasitic PNP (Positive-Negative-Positive) transistors in electrostatic discharge circuits at the level-shifting transceiver I/O ports. In addition, this hypothesis is verified by TCAD (Technology Computer Aided Design) simulations.

Model Predictive Thermal Dose Control of a Robotic Laser System to Automate Skin Photorejuvenation

In this article, we present a new method to control the thermal stimulation of skin during a photorejuvenation procedure. The proposed method can precisely administer the thermal dose while controlling the tissue's temperature under a safe limit. For that, a model-based treatment controller is developed and evaluated on a 3-D biophysics-based numerical model of skin. A hardware implementation is experimentally tested on a gelatin-based phantom tissue subjected to pulsed laser irradiation. A key component of our method is the use of a new thermal dose metric that enables quantifying and controlling the skin photorejuvenation process. This metric represents a suitable alternative to the lack of consensus on the metrics used by the photodermatology community. The reported experiments demonstrate that the developed controller endowed with the proposed dose unit can automatically deliver a prescribed laser irradiation and thermal dose over the tissue surface. The significance of our result is that it provides a control-theoretic framework to automate skin photorejuvenation treatments with thermal-guided robots. This approach has the potential to introduce standards in the automation of these types of phototreatments.

Space weathering effects and potential spectral alteration on Phobos and the Moon: Clues from the Fe content of olivine

Context. Olivine responds to space weathering in the fastest and most profound way, which results in significant space weathering spectral alteration effects (SWSAEs) on airless silicate bodies. Although Mg-rich olivine (Fa10) has been subjected to extensive studies, SWSAEs of Fe-rich (Fa# > 20) or Fa-dominant (Fa# ⩾ 50) olivine are still poorly understood. Aims. We aim to systematically characterize the space weathering effects and the associated spectral alterations of Fe-rich olivine on the surface of Phobos and the Moon. Methods. We conducted nanosecond pulsed laser irradiation experiments on a set of synthetic Fe-rich olivine (Fa29, Fa50, Fa71, and Fa100) with energy levels simulated for Phobos and the Moon and analyzed the irradiated olivine for microscopic characteristics and near-infrared (NIR) and Raman spectroscopy. Results. Micron-level thick alteration layers are found in Fa100 compared to those hundreds of nanometers thick in Fa29, Fa50, and Fa71. With increasing irradiation energy levels and Fa# values, nanophase iron (np-Fe0) particles increase in size but decrease in quantity. The np-Fe0 formed via in situ decomposition are ubiquitously present, while those formed via vapor deposition are primarily found in Fa29 but rarely in Fa# ⩾ 50. The size fraction of intermediate (10–40 nm) and large (40–60 nm) np-Fe0 proportionally increases with Fa# values. The NIR spectra of weathered olivine show darkening over reddening in most cases, but Fa100 under the most irradiated condition shows brightening-reddening spectral effects. The Raman spectra of weathered olivine show a reduction in intensity without peak shifts. Conclusions. The Fa# values of olivine are a more critical factor in controlling the SWSAEs on Phobos than those on the Moon. If Phobos and Deimos contain substantial Fe-rich or Fa-dominant olivine, similar to Mars, thick alteration rims and large np-Fe0 formed via space weathering may cause darkening-reddening and potentially brightening-reddening spectral effects on the Martian moons.

Laser Generation of Colloidal Nanoparticles in Liquids: Key Processes of Laser Dispersion and Main Characteristics of Nanoparticles

The processes of laser dispersion of materials for high-performance generation of colloidal nanoparticles in liquids have been considered. Various laser and material parameters affecting this process have been studied. Efficiencies and ergonomics of the generation of colloidal nanoparticles with the help of laser systems having nano-, pico-, and femtosecond pulse durations have been compared using optical and mass criteria by the example of laser ablation of a chemically inert model material (gold) in distilled water without the use of chemical stabilizers. The main characteristics of gold and silver nanoparticles obtained by ablation in water using pulsed laser radiation of different durations have been comprehensively compared. The types of colloidal interactions between nanoparticles in aqueous media have been discussed, and the contributions of structural and ion-electrostatic interactions to the long-term stability of gold and silver nanoparticle dispersions have been analyzed.

Tribological analysis of ultra-high molecular weight polyethylene composites with boron carbide micro and nanoparticles

The goal of this study is to investigate the tribological and morphological changes obtained by addition of boron carbide (B4C) micro and nanoparticles into Ultra High Molecular Weight Polyethylene (UHMWPE/B4C). In this work, UHMWPE was reinforced with B4C micro, nano (powder) and nanoparticles prepared using pulsed laser irradiation in liquid by solvent mixing (SM). Subsequently, the mixtures were compression molded at 180 °C and 15 MPa for 15 min, then cooled for 5 min at different concentrations (0, 0.1, 0.3, and 0.5 wt%) to evaluate the thermal, mechanical, and tribological behavior of these composites. Studies on changes in the structural and morphological characteristics of the composite samples were carried out by means of Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), and differential scanning calorimetry (DSC). The microhardness and scratch hardness of the composites were measured using a diamond indenter revealing nanoparticles outperformed micro-particles in both properties. In addition, the tribological behavior of the hot-pressed composite structures was analyzed via a scratch test machine using a normal load of 10 N and a ball-on-disk tribometer with a normal load of 30 N. As a result, the wear resistance of the composite revealed significant improvement up to a certain amount of particles. The coefficient of friction was also reduced. Worn surface analyses were done on the composite using the confocal and scanning electron microscopy (SEM), indicating various wear mechanisms such as delamination, micro-cutting, micro-plowing, and groove-formation. The composites showed low wear rates and were correlated with scratch hardness.

Direct photogeneration of singlet oxygen in biological medium for cancer therapy

Advances in cancer treatment require continuous improvement and the search for new therapies. Methods for direct photogeneration of singlet oxygen in tissue using IR lasers may be an effective alternative to photodynamic tumor therapy. The physical limitation for the direct photogeneration of singlet oxygen in a biological medium is the low absorption cross section of molecular oxygen. To overcome this limitation, it is necessary to use infrared radiation with a high power density, which in a living system is limited by thermal effects. A promising direction in the development of this approach could be the use of pulsed laser irradiation. By solving the problem of direct photogeneration of cytotoxic concentrations of singlet oxygen in a biological environment, including tumor tissue, without simultaneous heating to biocritical temperatures, it is possible to develop new effective and safe methods for the treatment of malignant neoplasms. Key words: single oxygen, direct photogeneration, reactive oxygen species, cancer therapy, photobiomodulation.

Pulsed thulium laser blood vessel haemostasis as an alternative to bipolar forceps during neurosurgical tumour resection

Due to wavelength-specific water absorption, infrared lasers like the thulium laser emitting at 1940 nm wavelength proved to be suitable for coagulation in neurosurgery. Commonly bipolar forceps used for intraoperative haemostasis can cause mechanical and thermal tissue damage, whilst thulium laser can provide a tissue-gentle haemostasis through non-contact coagulation. The aim of this work is a less-damaging blood vessel coagulation by pulsed thulium laser radiation in comparison to standard bipolar forceps haemostasis. Ex vivo porcine blood vessels in brain tissue (0.34 ± 0.20 mm diameter) were irradiated in non-contact with a thulium laser in pulsed mode (1940 nm wavelength, 15 W power, 100–500 ms pulse duration), with a CO2 gas flow provided simultaneously at the distal fibre tip (5 L/min). In comparison, a bipolar forceps was used at various power levels (20–60 W). Tissue coagulation and ablation were evaluated by white light images and vessel occlusion was visualised by optical coherence tomography (OCT) B-scans at a wavelength of 1060 nm. Coagulation efficiency was calculated by means of the quotient of the difference between the coagulation and ablation radius to the coagulation radius. Pulsed laser application achieved blood vessel occlusion rate of 92% at low pulse duration of 200 ms with no occurrence of ablation (coagulation efficiency 100%). Bipolar forceps showed an occlusion rate of 100%, however resulted in tissue ablation. Tissue ablation depth with laser application is limited to 40 μm and by a factor of 10 less traumatising than with bipolar forceps. Pulsed thulium laser radiation achieved blood vessel haemostasis up to 0.3 mm in diameter without tissue ablation and has proven to be a tissue-gentle method compared to bipolar forceps.