Laser Radiation Research Articles

Additive manufacturing between cooled confinements with the LDNA process

Laser-assisted double-wire welding with nontransferred arc (LDNA) is characterized by two converging wires between which an electrical arc burns to melt both wires. The molten material falling onto the substrate is distributed with oscillating laser radiation with a power of 1.5 kW to ensure sufficient bonding with the substrate without delamination and pores. The process is characterized by high deposition rates of more than 7.5 kg/h. Due to the high deposition rate, only high values for waviness in the buildup direction can be achieved in the production of multilayer additive structures. The approach investigated in this publication examines the potential to produce additive structures with a confined melt pool. The use of water-cooled copper jaws and the deposition of ER70S-6 between these confinements using the LDNA process are being investigated to produce additive 10 mm wide and 100 mm long structures with significantly improved waviness in the direction of buildup and improved dimensional accuracy. It can be shown that a wall-like structure can be welded between the confinements without material bonding to the cooling jaws. Additionally, it has been observed that the confinements can easily be removed which is attributed to the thermal contraction of the steel. Metallographic examinations of the produced structures in the longitudinal and transverse sections as well as hardness curves in the transverse section are carried out and evaluated. Multilayer structures with up to five layers are produced and the waviness and surface roughness on the side surfaces defined by the jaws are measured and evaluated.

Ignition of anthracite microparticles by continuous laser radiation with wavelengths of 450 and 808 nm

The energy and spectral-kinetic characteristics of ignition of anthracite microparticle powders with a bulk density of 0.5 g/cm3 were measured when exposed to continuous laser radiation at wavelengths λ = 450 and 808 nm with an exposure time of 1 second. Ignition delay times were measured depending on the radiation power density and critical values of the ignition energy density of anthracite samples were determined. The energy cost of igniting anthracite for radiation with λ = 450 nm is less than for radiation with λ = 808 nm. In the emission spectra of anthracite resulting from the absorption of laser radiation, there is a glow associated with the release and ignition of volatile substances (flame CO, glow of excited molecules CO, C2 and H2O) and thermal glow associated mainly with the heated surface of the samples, as well as the flight of incandescent carbon particles.

Investigation of Changes in the Reflection Spectrum of Human Blood When Exposed to Laser Radiation With Wavelengths of 450 or 980 nm.

This study aimed to determine and explain changes in the reflectance spectrum of human blood in vitro when exposed to laser radiation at wavelengths of 450 or 980 nm. Reflectance spectra of venous blood samples were measured before and after exposure to a single pulse of 450 or 980 nm laser radiation. A numerical optical model based on the Monte Carlo method was applied. Laser irradiation at 450 and 980 nm caused the most significant changes in the reflectance spectrum around 600 nm, associated with alterations in blood oxygen saturation. The maximum efficiency of reducing oxygen saturation was 0.20%/W for 980 nm and 0.72%/W for 450 nm, likely due to differences in blood absorption at these wavelengths. The greatest change in intensity reflectance spectra and oxygen saturation of human venous blood occurs when exposed to laser radiation at 450 nm, not at 980 nm.

Switchable Photovoltaic Effect and Robust Nonlinear Optical Response in a High-Temperature Molecular Ferroelectric [C8N2H22][PbI4

Hybrid organic-inorganic molecular ferroelectrics (HOIMFs) have garnered significant attention for their potential applications in nonvolatile memory and spintronic devices. However, few efforts have been devoted to the photoelectric properties of lead halide molecular ferroelectrics, despite the fact that robust ferroelectricity and flexibility are desirable for thin-film photoelectric devices. Herein, we present a novel lead halide molecular ferroelectric [C8N2H22][PbI4] (1) synthesized hydrothermally. A polar monoclinic structure of 1 was solved by single-crystal X-ray diffraction and second-harmonic generation (SHG) tests. A direct band gap of 2.36 eV was confirmed by UV-vis spectrum and theoretical calculation. Hysteresis measurements demonstrated inherent room-temperature (RT) ferroelectricity in 1 with a spontaneous polarization (Ps) of 3.2 μC/cm2. The 1-based photoelectric device shows a notable photovoltaic (PV) effect with Voc ∼ 0.27 V, Jsc ∼ 38 nA/cm2 under AM 1.5 G illumination, and a rapid response time of ∼1.5 ms. A considerable enhancement in PV performance has been achieved by adjusting the ferroelectric polarization, resulting in a maximum Voc ∼ 0.75 V, Jsc ∼ 2.28 μA/cm2. Notably, 1 exhibits a rather large SHG signal, which is approximately 2.61-fold higher than that of KH2PO4 (KDP) upon a 1064 nm laser radiation. This study offers a bright avenue for lead halide molecular ferroelectrics as promising optoelectronic devices and SHG materials.

Antibacterial effect of semiconductor laser radiation against the strains of S. aureus and P. aeruginosa, leading pathogens in osteomyelitis

Introduction The study of the antibacterial effect of photodynamic therapy against the leading pathogens of chronic osteomyelitis is one of the promising directions today.Purpose of the work was to evaluate the antibacterial effect against the strains of Staphylococcus aureus and Pseudomonas aeruginosa with the ALOD-01 laser system in the presence of photodithazine.Materials and methods The object of the study was 24-hour archival cultures of gram-positive and gram-negative microorganisms belonging to two taxa: Staphylococcus aureus (25923), Pseudomonas aeruginosa (27853). The antibacterial effect after the exposure to laser radiation in the presence of photodithazine on the microbial cells of the studied cultures was assessed by the absence of microorganism growth in the area of the light beam.Results Laser exposure in combination with photodithazine (concentration 0.5–1.0 mg/ml) on S. aureus for two minutes at 200–300 J achieved a bactericidal effect in the beam area. A bactericidal effect on the entire surface of the Petri dish was achieved with light exposure of 400 J for 5 minutes and a photodithazine concentration of 1.0 mg/ml. Laser exposure for 2 minutes in the presence of photodithazine at a concentration of 0.5 mg/ml and 1 mg/ml did not have an antibacterial effect on P. aeruginosa strains. Continuous growth of microorganisms was observed on the dish. Increasing the light dose and exposure time contributed to a decrease in the growth of microbial cells. A bactericidal effect was obtained only in the center of the dish in treating the bacterial suspension with photodithazine at a concentration of 5 mg/ml.Discussion The effectiveness of PDT depends on the type of microorganisms, the anatomical location of the infection site, as well as the properties of the photosensitizer and the laser used. Depending on the structure of the cell wall, different susceptibility of bacteria to photodynamic effects is observed.Conclusion S. aureus strains can be successfully photoinactivated using photodithazine. For P. aeruginosa strains, it was not possible to find a regime in which microbial cell growth was absent throughout the dish. The photodynamic reaction occurs only when adequate doses of light energy act on the photosentisizer in the presence of oxygen in the medium, while the photodynamic damage is local and the bactericidal effect is limited by the zone of light exposure.

PHOTOELECTRICAL PROPERTIES OF CdMnSe THIN FILMS

The studied semiconductor structure for photovoltaic cells is composed of SnO2-coated glass and CdMnSe thin film. A study is made by examining the photoluminescence from the surface of the CdMnSe thin film with laser power and sample temperature for an as-grown, then an air-annealed thin film and undergone CdCl2 treatment. Thin films of Cd1-xMnxSe (x=0.02) were grown on a glass substrate. The lifetime of charge carriers under pulsed illumination was determined from the kinetic decay of the photocurrent. The study of relaxation curves of nonequilibrium photoconductivity under the influence of laser radiation confirmed the presence of two recombination channels - intrinsic and impurity. Photocurrent relaxation occurs through fast and slow recombination channels. The fast relaxation time τ = 6 μs associated with the intrinsic transition and the slow relaxation time is due to impurity excitation and τ = 22 μs. The photoluminescence spectra of thin films of Cd1-xMnxSe (x=0.02) were studied. In the photoluminescence study, two maxima are observed due to donor-acceptor recombination and intracenter transition of Mn atom.

Conformational Composition of Ethylene Glycol in Aqueous Solutions and on Metal Substrates

In this work, we studied the Raman spectra of ethylene glycol (EG) and its aqueous solutions, as well as the spectra of ethylene glycol solutions deposited on a metal substrate prepared by laser ablation. Scattering was excited by laser radiation with wavelengths of 532 nm and 785 nm. It was found that the Raman spectra of EG are similar to the spectra of aqueous solutions of EG and to the spectra of EG solutions on a metal substrate, which may indicate the stability of the conformational composition of EG upon dissolution and drying on a structured metal substrate.

Multimode light generation in an injection semiconductor laser based on a chiral AlAs/(Al, Ga)As/GaAs microcavity

Experimental investigations of chiral injection AlAs/(Al, Ga)As/GaAs vertical-cavity surface-emitting lasers in the multimode generation regime are performed. A high circular polarization degree 70% of different generation modes measured with a high spectral resolution, is demonstrated. Detailed maps of spatial and angular distribution of laser radiation intensity were constructed.

Spectroscopic Properties of TmF3-Doped CaF2 Crystals.

In this study, we report the growth and comprehensive spectroscopic analysis of TmF3-doped CaF2 crystals, grown using the vertical Bridgman method. The optical absorption and photoluminescence properties of both trivalent (Tm3+) and divalent (Tm2+) thulium ions were investigated. Optical absorption spectra in the UV-VIS-NIR range reveal characteristic transitions of Tm3+ ions, as well as weaker absorption bands corresponding to Tm2+ ions. The Judd-Ofelt (JO) formalism was applied to determine the intensity parameters Ω2, Ω4, and Ω6, which were used to calculate radiative transition probabilities, branching ratios, and radiative lifetimes for the Tm3+ ions. The emission spectra showed concentration-dependent quenching effects, with significant emissions observed for the concentration of 0.1 mol% TmF3 under excitation at 260 nm and 353 nm for Tm3+ ions and at 305 nm for Tm2+ ions. A new UV emission associated with divalent Thulium is reported. The results indicate that higher TmF3 concentrations lead to increased non-radiative energy transfer, which reduces luminescence efficiency. These findings contribute to the understanding of the optical behavior of Tm-doped fluoride crystals, with implications for their application in laser technologies and radiation dosimetry.

Mathematical Modelling of the Impact of IR Laser Radiation on an Oncoming Flow of Nanoparticles with Methane

Introduction. The study is devoted to the numerical investigation of laser radiation’s effect on an oncoming two-phase flow of nanoparticles and multicomponent hydrocarbon gases. Under such exposure, the hydrogen content in the products increases, and methane is bound into more complex hydrocarbons on the surface of catalytic nanoparticles and in the gas phase. The hot walls of the tube serve as the primary source of heat for the reactive two-phase medium containing catalytic nanoparticles. Materials and Methods. The main method used is mathematical modelling, which includes the numerical solution of a system of equations for a viscous gas-dust two-phase medium, taking into account chemical reactions and laser radiation. The model accounts for the two-phase gas-dust medium’s multicomponent and multi-temperature nature, ordinary differential equations (ODEs) for the temperature of catalytic nanoparticles, ODEs of chemical kinetics, endothermic effects of radical chain reactions, diffusion of light methyl radicals CH3 and hydrogen atoms H, which initiate methaneconversion, as well as absorption of laser radiation by ethylene and particles. Results. The distributions of parameters characterizing laminar subsonic flows of the gas-dust medium in an axisymmetric tube with chemical reactions have been obtained. It is shown that the absorption of laser radiation by ethylene in the oncoming flow leads to a sharp increase in methane conversion and a predominance of aromatic compounds in the product output. Discussion and Conclusion. Numerical modelling of the dynamics of reactive two-phase media is of interest for the development of theoretical foundations for the processing of methane into valuable products. The results obtained confirm the need for joint use of mathematical modelling and laboratory experiments in the development of new resource-saving and economically viable technologies for natural gas processing.

Nonlinear Excitation of Color Centers in a LiF Crystal by Femtosecond Laser Radiation

Experiments were carried out in which the luminescence of color centers in lithium fluoride crystals was excited by two different femtosecond lasers with significantly different energies, durations and pulse repetition rates. It was established that in all experiments the main center, the luminescence of which was excited nonlinearly, was the F3+ color center. Unusual experimental data were obtained; a laser with low pulse energy (4 nJ) excited triplet luminescence of these centers (570 nm) but did not excite singlet luminescence (540 nm). Another laser with a higher pulse energy (0.3 mJ), on the other hand, excited singlet luminescence and did not excite triplet luminescence. A proposed diagram of energy levels and quantum transitions is presented, explaining the possible mechanisms of nonlinear excitation of luminescence in these experiments.

Impact of photobiomodulation therapy on pro-inflammation functionality of human peripheral blood mononuclear cells – a preliminary study

Research into the efficacy of photobiomodulation therapy (PBMT) in reducing inflammation has been ongoing for years, but standards for irradiation methodology still need to be developed. This study aimed to test whether PBMT stimulates in vitro human peripheral blood mononuclear cells (PBMCs) to synthesize pro-inflammatory cytokines, including chemokines. PBMCs were irradiated with laser radiation at two wavelengths simultaneously (λ = 808 nm in continuous emission and λ = 905 nm in pulsed emission). The laser radiation energy was dosed in one dose as a whole (5 J, 15 J, 20 J) or in a fractionated way (5 J + 15 J and 15 J + 5 J) with a frequency of 500, 1,500 and 2,000 Hz. The surface power densities were 177, 214 and 230 mW/cm2, respectively. A pro-inflammatory effect was observed at both the transcript and protein levels for IL-1β after PBMT at the energy doses 5 J and 20 J (ƒ=500 Hz) and only at the transcript level after application of PBMT at energy doses of 20 J (ƒ= 1,500; ƒ=2,000 Hz) and 5 + 15 J (ƒ=500 Hz). An increase in CCL2 and CCL3 mRNA expression was observed after PBMT at 5 + 15 J (ƒ=1,500 Hz) and 15 + 5 J (ƒ=2,000 Hz) and CCL3 concentration after application of an energy dose of 15 J (frequency of 500 Hz). Even though PBMT can induce mRNA synthesis and stimulate PBMCs to produce selected pro-inflammatory cytokines and chemokines, it is necessary to elucidate the impact of the simultaneous emission of two wavelengths on the inflammatory response mechanisms.

Hybrid micro and nanostructured silicon surfaces fabricated by laser ablation and electrochemistry

This work reports on laser-processed silicon surfaces' morphological and wetting characteristics. The silicon surfaces were initially exposed to pulsed laser radiation in the femtosecond regime. The laser emitted in its fundamental wavelength (λ = 1030 nm), and the processing was carried out in air at atmospheric pressure. The surfaces were then subjected to electrochemical modification to create micro and nano porosity. The experimental conditions allowed the creation of various hybrid systems based on laser radiation and subsequent electrochemical treatment (using HF-DMSO). This procedure altered the surface wetting behavior from hydrophilic to hydrophobic due to the distinct surface morphology without needing a specific coating.

Gas flows generated by pulse-periodic optical breakdown and quiet optical discharge

Quiet optical discharge in high-pressure xenon is visually stable pre-breakdown stage of optical discharge supported by pulse-periodic short-wavelength infrared laser radiation with intensity of the order of 109 W/cm2. Increasing the laser intensity leads to the transition of the quiet discharge into a pulse-periodic optical breakdown. In this study, quasi-stationary directional flows generated by both the quiet discharge and the optical breakdown are observed. The flows and their initial stages under limited number of discharge pulses are visualized by shadow imaging method using a point-like laser-plasma radiation source. It is shown that the gas streams outflow points in a quiet discharge correspond to the positions of the laser radiation intensity local maxima in the focal beam waist with astigmatism complicated by defocusing effect of thermal lens arising in the discharge zone. The pulse-periodic optical breakdown emits a turbulent gas flow toward the laser beam. The beam refraction on density gradients in the turbulent flow causes the breakdown instability from pulse to pulse. It was found that time-average absorption of laser radiation in a quiet discharge is about 3% (also in a pulse), while that in optical breakdown is 15% and higher (from 70% to 100% in a pulse). Laser beam intensity for quiet discharge at pulse repetition rate νp = 20 kHz ranges from 1.3 × 109 to 1.5 × 109 W/cm2. At intensities above 4 × 109 W/cm2 and repetition rates νp > 50–55 kHz, laser breakdowns are observed in each laser pulse with the focal ratio f/d ≤ 7. At f/d = 10.6 and νp > 28 kHz, the quiet discharge does not transit to laser breakdown due to defocusing by the thermal lens induced.

Time delay of reflected and transmitted laser pulse at laser action on a dense plasma slab

The time delay phenomenon of reflected and transmitted laser pulse under the action of s-polarized laser radiation on a supercritical plasma slab is considered. The dependence of the time delay and peak intensity of reflected and transmitted signals on the slab thickness, plasma density, and angle of laser radiation incidence is investigated. It is shown that with increasing thickness of the plasma slab, the saturation of the transmitted signal delay time (Hartman effect) does not occur due to the exponential decrease in its intensity. The tunneling speed of the laser pulse energy through the slab of supercritical plasma is calculated, and it is shown that at large angles of laser radiation incidence, it can exceed the speed of light in vacuum.

Spectral analysis of high-order harmonic generation in carbon plasma using linearly, radially, and azimuthally polarized femtosecond pulses

We demonstrate high-order harmonic generation in carbon plasma using linearly, radially, and azimuthally polarized beams from a femtosecond laser (1030nm, 40 fs, 50kHz). The conditions for carbon plasma formation during laser ablation were optimized by adjusting the heating pulse energy in the cases of the single-color (1030nm) and two-color (1030nm + 515nm) pump schemes to generate harmonics up to the 39th order. The application of radial and azimuthally polarized annular single-color (1030nm) beams at optimal conditions of plasma formation allowed the demonstration of the spectral division and inclination of the vector harmonics. An asymmetric distribution of harmonics was obtained using the vortex beam generated during the propagation of laser radiation through the quarter-wave plate and S-waveplate.

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.

Features of the defect structure of a lithium-gradient nonlinear optical single crystal LiNbO3 and their manifestation in the Raman spectra

LiNbO3 crystal with a lithium composition gradient of Li/Nb = 0.8 wt%/cm (Li0.97..1.01Nb1.03..0.99O3) were obtained. A monotonic change in the edge of the UV absorption edge is observed when scanning the surface of the gradient crystal along the growth direction. Raman spectra from different areas of studied crystal were analyzed in a wide frequency range, which includes the region of fundamental vibrations of the crystal lattice (100–900 cm−1) and the region of overtone processes (900–3000 cm−1). A compositionally homogeneous, congruent LiNbO3 crystal was used as a comparison sample. It was found that in the spectra obtained from different parts of the gradient crystal, there is a significant scatter in the frequency values of the lines corresponding to the fundamental vibrations of the crystal lattice, but at the same time, the number of lines corresponding to the fundamental vibrations of the lattice for the gradient and compositionally homogeneous LiNbO3 crystals is the same. Moreover, in the spectrum of a gradient crystal in the region of overtone processes of fundamental vibrations, significantly more lines (35 lines) are observed than in the spectrum of compositionally homogeneous crystals (15 lines). The data obtained show that the state of the defect structure of compositionally homogeneous crystals and gradient LiNbO3 crystal is significantly different. The discovered differences between the defective structure of a gradient crystal and the defective structure of a compositionally homogeneous crystal may be the reason for compensation (damping) of distortions during nonlinear optical conversion of laser radiation by a gradient crystal due to the uneven temperature distribution along the length of the crystal. In compositionally homogeneous crystals, such temperature distortions significantly limit the efficiency of nonlinear optical conversion.

Photopolymerization of Chlorpromazine-Loaded Gelatin Methacryloyl Hydrogels: Characterization and Antimicrobial Applications.

This study investigates the synthesis, characterization, and antimicrobial properties of hydrogels synthesized through the UV-pulsed laser photopolymerization of a polymer-photoinitiator-chlorpromazine mixture. Chlorpromazine was used for its known enhanced antimicrobial properties when exposed to UV laser radiation. The hydrogel was formed from a mixture containing 0.05% Irgacure 2959, 10% gelatin methacryloyl, and various concentrations of chlorpromazine (1, 2, and 4 mg/mL). Laser-induced fluorescence spectroscopy was employed to monitor the photoinduced changes of chlorpromazine and Irgacure 2959 during hydrogel formation, providing insight into the photodegradation dynamics. FTIR spectroscopy confirmed the incorporation of irradiated chlorpromazine within the hydrogel matrix, while the release profiles of chlorpromazine showed sustained release only in hydrogels containing 1 mg/mL of CPZ. The hydrogel showed significant antimicrobial activity against MRSA bacteria when compared to that of penicillin. These findings highlight the potential of CPZ loaded during the photopolymerization process into hydrogels as effective antimicrobial agents with sustained release properties, making them suitable for combating resistant bacterial strains.

The effect of a diode-pumped solid-state laser with a wavelength of 589 nm on T-lymphocyte proliferation.

To assess how low-level laser irradiation affects T cells. The case-control interventional study was conducted from November 2021 to April 2022 after approval by the ethics review committee of the College of Medicine, Mustansiriyah University, Baghdad, Iraq, and comprised healthy individuals. Phlebotomy was used to collect 4ml of blood. A portion of each sample was exposed to 589nm laser radiation, while the other portion was used as a control. The irradiated sample was divided into whole blood and in-plate subgroups. Phytohemagglutinin was used for mitotic stimulation of T-lymphocytes, and cell proliferation assay was used to stimulate T lymphocytes measured using MTS assay (3-(4,5-dimethylthiazol-2-yl)-5- (3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium). Optical density was measured using enzyme-linked immunosorbent assay. Data was analysed using GraphPad prism software. There were 35 subjects, 17(49%) males and 18 (51%) females, with an age range between 19-25 years, all without any disease or medication. Laser irradiation stimulated T-lymphocyte proliferation to levels that depended on the dose of laser used. At energy 30J/cm2 there was a significant increase in the in-plate subgroup of irradiated samples compared to controls and between the two irradiated subgroups (p<0.05). At 50J/cm2 dose, there was a significant increase in the whole blood subgroup compared to the controls (p<0.05). At 70J/cm2 dose, there was a significant difference in the whole blood subgroup compared to the controls, and between the two irradiated subgroups (p<0.05). The stimulation of T lymphocyte proliferation by the application of a 589nm laser could have medical applications in the field of immune system enhancement.