Pulsed Irradiation Research Articles

Tailor-joining of Ti6Al4V skin with V-shaped assembly error using enhanced PLBW scheme: Keyhole dynamics and metal bridging behavior

Building thin-walled titanium alloy skin using conventional laser beam welding (LBW) frequently suffers from undesirable seam quality due to the V-shaped notch; a typical assembly error occurs after skin rolling with a specific sheet thickness range. This work proposed an improved scheme with metal bridging capacity and liquid film stability to overcome this by executing a pulsed laser beam and spot irradiation in a flat-top mode. Welding was performed on 1.5 mm-thick Ti6Al4V sheets configured in the butt joint with a reserved notch geometry, which is 20 degrees between the groove surface. We also conducted numerical modeling and solutions concerning the heat-flow-phase dynamics using an enhanced ray tracing algorithm. Results show that the as-build weld beads, characterized by middle rippers, slight depression, and edge ridges, present superb continuity and uniformity when applying an average heat input of 40–90 J/mm and a pulse energy of 187.5–750 J. Effective metal bridging across the notch error is achieved at both pulse duration and interval phases due to not only the complete melting of welding side but also the enhanced melt film stability against the surface tension. The cooling of the weld pool starts with a sharp temperature drop at ∼3×105 K/s (on average) during the keyhole collapsing regime, then slows down due to the damped up-down oscillation of the free surface combined with the natural convection-conduction effect. The flow pattern of molten metal changes from squeezing-like to vortexes and finally to a backfilling mode, depending on the evolution of keyhole geometry. Although the keyhole dynamics differs, various process conditions regarding heat input and pulse energy yield effective metal bridging of a single weld spot and sufficient refusion between the adjacent weld spots, ensuring the well-overlapped weld bead formation.

Direct nanosecond laser metallization of AlN ceramics

In this paper, a study of the influence of laser processing parameters with pulsed nanosecond laser radiation on the degree of metallization and the quality of the metallized surface of aluminum nitride ceramics is presented. Experiments were carried out to create conductive structures with the lowest resistance using direct laser metallization. The dependences of resistance on duration, pulse overlap, and laser fluence were obtained and analyzed, and changes in surface roughness were considered. In addition, the composition of the surface of laser-metallized ceramics was studied using energy-dispersive x-ray spectroscopy. As a result, it was shown that the resistance is inversely proportional to the square root of the pulse duration, the thermal diffusion length was estimated as lT = 8.2 μm for 200 ns and lT = 1.2 μm for 4 ns, and the presence of optimal values of pulse overlap Oy (scanning direction) equal to 50% and pulse overlap Ox (step direction) equal to 96% and 99.7% for pulse durations of 200 and 4 ns, respectively, was determined. The choice of optimal pulse overlaps with the highest laser fluence allowed us to obtain the minimum resistance value with maximum performance.

Nanosecond-Laser-Induced Breakdown of Aqueous Colloidal Solutions of Dysprosium Nanoparticles: The Influence of Nanoparticle Concentration on the Breakdown Plasma and the Intensity of Physical and Chemical Processes

This paper studies the dynamics of the development of laser breakdown plasma in aqueous colloids of dysprosium nanoparticles by analyzing the time patterns of plasma images obtained using a high-speed streak camera. In addition, the distribution of plasma flashes in space and their luminosity were studied, and the amplitude of acoustic signals and the rate of generation of new chemical products were studied depending on the concentration of dysprosium nanoparticles in the colloid. Laser breakdown was initiated by pulsed radiation from a nanosecond Nd:YAG laser. It is shown that the size of the plasma flash, the speed of motion of the plasma–liquid interface, and the lifetime of the plasma flash decrease with an increasing concentration of nanoparticles in the colloid. In this case, the time delay between the beginning of the laser pulse and the moment the plasma flash reaches its maximum intensity increases with increasing concentrations of nanoparticles. Varying the laser fluence in the range from 67 J/cm2 to 134 J/cm2 does not lead to noticeable changes in these parameters, due to the transition of the breakdown plasma to the critical regime. For dysprosium nanoparticles during laser breakdown of colloids, a decrease in the yield of hydrogen peroxide and an increase in the rate of formation of hydroxyl radicals per water molecule, characteristic of nanoparticles of rare earth metals, are observed, which may be due to the participation of nanoparticles and hydrogen peroxide in reactions similar to the Fenton and Haber–Weiss reactions.

Charge-order melting in the one-dimensional Edwards model

We use infinite matrix-product-state techniques to study the time evolution of the charge-density-wave (CDW) order after a quench or a light pulse in a fundamental fermion-boson model. The motion of fermions in the model is linked to the creation of bosonic excitations, which counteracts the melting of the CDW order. For low-energy quenches corresponding to a change of the boson relaxation rate, we find behavior similar to that in an effective t−V model. When the boson energy is quenched instead or a light pulse is applied to the system, the transient dynamics are more complex, with the CDW order first quickly decreasing to an intermediate value while the density-wave-like order of the bosons rises. In the case of pulse irradiation, the subsequent time evolution of the CDW order depends strongly on the photon frequency. For frequencies slightly below the boson energy, we observe a temporary increase of the CDW order parameter. Our results reveal the complex physics of driven Mott insulators in low-dimensional systems with strong correlations. Published by the American Physical Society 2024

Uneven response of phytoplankton-bacteria coupling under Saharan dust pulse and ultraviolet radiation in the south-western Mediterranean Sea

The microbial carbon (C) flux in the ocean is a key functional process governed by the excretion of organic carbon by phytoplankton (EOC) and heterotrophic bacterial carbon demand (BCD). Ultraviolet radiation (UVR) levels in upper mixed layers and increasing atmospheric dust deposition from arid regions may alter the degree of coupling in the phytoplankton-bacteria relationship (measured as BCD:EOC ratio) with consequences for the C-flux through these compartments in marine oligotrophic ecosystem. Firstly, we performed a field study across the south-western (SW) Mediterranean Sea to assess the degree of coupling (BCD:EOC) and how it may be related to metabolic balance (total primary production: community respiration; PPT:CR). Secondly, we conducted a microcosm experiment in two contrasting areas (heterotrophic nearshore and autotrophic open sea) to test the impact of UVR and dust interaction on microbial C flux. In the field study, we found that BCD was not satisfied by EOC (i.e., BCD:EOC >1; uncoupled phytoplankton-bacteria relationship). BCD:EOC ratio was negatively related to PPT:CR ratio across the SW Mediterranean Sea. A spatial pattern emerged, i.e. in autotrophic open sea stations uncoupling was less severe (BCD:EOC ranged 1–2), whereas heterotrophic nearshore stations uncoupling was more severe (BCD:EOC > 2). In the experimental study, in the seawater both enriched with dust and under UVR, BCD:EOC ratio decreased by stimulating autotrophic processes (particulate primary production (PPP) and EOC) in the heterotrophic nearshore area, whereas BCD:EOC increased by stimulating heterotrophic processes [heterotrophic bacterial production (HBP), bacterial growth efficiency (BGE), bacterial respiration (BR)] in the autotrophic open sea. Our results show that this spatial pattern could be reversed under future UVR × Dust scenario. Overall, the impact of greater dust deposition and higher UVR levels will alter the phytoplankton-bacteria C-flux with consequences for the productivity of both communities, their standing stocks, and ultimately, the ecosystem's metabolic balance at the sea surface.

Crystallization of Germanium-SiO2 composite films via nanosecond laser pulse irradiation

Germanium (Ge)-SiO2 composite films fabricated by using radio frequency magnetron co-sputtering were subjected to nanosecond (ns) laser pulse irradiation. The intense laser irradiation effects on as deposited composite films lead to the modification and the formation of Ge nanocrystals (NCs) embedded in SiO2. The as-deposited and laser treated samples have been characterized with X-ray diffraction (XRD) and micro-Raman spectroscopy to understand the formation of Ge NCs due to laser irradiation. The respective Ge NCs related peaks in XRD pattern as well as the Ge-Ge related optical phonon vibrational peaks in micro-Raman spectra confirm the formation of Ge NCs. Transmission electron microscopy images indicate the formation of Ge NCs after the laser irradiation. The effects of laser pulse energy and the irradiation time play a vital role in the crystallization of the as-deposited films. The changes in the Ge NCs size related shifts in the peak position of Ge optical phonons from the Raman spectra of the respective samples are explained with Ge-Ge optical phonon vibrational model. The observed photoluminescence emission in the green and red region of the visible spectrum from the laser treated samples are explained using the phenomenon of creation of Ge NCs in the Ge+SiO2 composite films and the oxygen defects created in SiO2 during the ns laser treatment.

Time-domain electric field analysis of few-cycle pulse damage behavior in ultra-broadband chirped mirrors

The laser-induced damage resistance performance of ultra-broadband chirped mirrors (UBCM) is a critical factor influencing the generation of petawatt or exawatt laser pulses in thin film compression techniques. In this study, a few-cycle pulse damage testing platform was set up, and two UBCMs with different designs were fabricated for a comparative study of their laser-induced damage. Because light of varying wavelengths forms an electric field at different times within UBCMs under few-cycle pulse irradiation, a time-domain electric field model was developed to obtain transient electric field variations and explain the damage behavior. The model successfully elucidated the origin of the damage and discrepancy between the two UBCMs in terms of damage thresholds, showcasing its potential applications in designing high-threshold UBCMs for high-power laser systems.

Keldysh crossover in one-dimensional Mott insulators

Recent advancements in pulse laser technology have facilitated the exploration of nonequilibrium spectroscopy of electronic states in the presence of strong electric fields across a broad range of photon energies. The Keldysh crossover serves as an indicator that distinguishes between excitations resulting from photon absorption triggered by near-infrared multicycle pulses and those arising from quantum tunneling induced by terahertz pulses. Using a time-dependent density-matrix renormalization group, we investigate the emergence of the Keldysh crossover in a one-dimensional (1D) Mott insulator. We find that the Drude weight is proportional to photo-doped doublon density when a pump pulse induces photon absorption. In contrast, the Drude weight is suppressed when a terahertz pulse introduces doublons and holons via quantum tunneling. The suppressed Drude weight accompanies glassy dynamics with suppressed diffusion, which is a consequence of strong correlations and exhibits finite polarization decaying slowly after pulse irradiation. In the quantum tunneling region, entanglement entropy slowly grows logarithmically. These contrasting behaviors between the photon-absorption and quantum tunneling regions are a manifestation of the Keldysh crossover in 1D Mott insulators and provide a novel methodology for designing the localization and symmetry of electronic states called subcycle-pulse engineering.

Time-resolved spectral investigation of low-temperature plasma induced in gas mixtures by laser-produced plasma or nanosecond pulses of extreme ultraviolet radiation

Time-resolved spectral investigation of low-temperature plasma induced in gas mixtures by laser-produced plasma or nanosecond pulses of extreme ultraviolet radiation

Large-amplitude density waves produced in ozone-mixed gas by ultraviolet laser irradiation

A remarkable large-amplitude density modulation has been observed in ozone-mixed oxygen gas at atmospheric density and temperature conditions following irradiation with a nanosecond pulse of ultraviolet laser radiation. This paper outlines the experimental findings and describes a hydrodynamic simulation that reproduces several quantitative aspects of this phenomenon. It is important to note that these density waves are not simple sound waves; instead, they are combined with another type of density modulation wave. These density modulation wave profiles are expected to have applications for new optical components using a gas medium.

In Vivo Microwave-Induced Thermoacoustic Endoscopy for Colorectal Tumor Detection in Deep Tissue.

Optical endoscopy, as one of the common clinical diagnostic modalities, provides irreplaceable advantages in the diagnosis and treatment of internal organs. However, the approach is limited to the characterization of superficial tissues due to the strong optical scattering properties of tissue. In this work, a microwave-induced thermoacoustic (TA) endoscope (MTAE) was developed and evaluated. The MTAE system integrated a homemade monopole sleeve antenna (diameter = 7 mm) for providing homogenized pulsed microwave irradiation to induce a TA signal in the colorectal cavity and a side-viewing focus ultrasonic transducer (diameter = 3 mm) for detecting the TA signal in the ultrasonic spectrum to construct the image. Our MTAE, system combined microwave excitation and acoustic detection; produced images with dielectric contrast and high spatial resolution at several centimeters deep in soft tissues, overcome the current limitations of the imaging depth of optical endoscopy and mechanical wave-based imaging contrast of ultrasound endoscopy, and had the ability to extract complete features for deep location tumors that could be infiltrating and invading adjacent structures. The practical feasibility of the MTAE system was evaluated i n vivo with rabbits having colorectal tumors. The results demonstrated that colorectal tumor progression could be visualized from the changes in electromagnetic parameters of the tissue via MTAE, showing its potential clinical application.

Boosting electron and x-ray emission from laser produced plasmas by doping liquid droplets

In recent studies, it has been shown that under optimal dual pulse irradiation, it is possible to generate anomalous relativistic temperature (>500 keV) electron emission even with mJ/pulse lasers at 1/100th of the relativistic intensity when micrometer droplets of methanol are used as a high repetition rate target. In this paper, we present the results of doping these droplets with CH3I to bring out a 30-fold enhancement in electron emission. Experiments and simulations presented here find a route to enhance electron emission driven by two plasmon decay instability. Improving compact laser plasma based sources of MeV electrons, x-ray emission schemes that use a high repetition rate, and mJ/pulse laser systems is important not only for basic science but also applications of imaging and radiography.

Spatial Selection-Based Intelligent N-OFDM Signal Processing in Wireless Communication Systems

The method of joint processing of pulses and OFDM (N-OFDM) signals is proposed. The corresponding analytical relations for the lower Cramer-Rao boundary on the dispersion of OFDM (N-OFDM) signals amplitude ratings in the presence of sources of pulsed radiation are obtained. Using mathematical modeling properties and limitations of the demodulation method of OFDM (N-OFDM) signals in the background of impulse signals in the integrated radar and telecommunication systems are established. It is determined that the use of the angular distance between the pulsed and OFDM signals sources at a value that is not less than 0.75 widths of the secondary beam of the digital antenna array pattern does not affect the accuracy of the OFDM signal amplitudes. The same applies to the active interferences.

NEW APPROACHES TO THE SYNTHESIS OF FUNCTIONAL MATERIALS WITH SPECIFIED PROPERTIES UNDER THE INFLUENCE OF CONCENTRATED RADIATION AND PULSE TUNNEL EFFECT

This article explores the prospects of synthesizing materials with a complex of specified properties using the pulsed tunneling effect (PTE) and concentrated solar radiation. The mechanisms of formation of metastable phases and the emergence of unique electrical and magnetic properties due to numerous structural distortions are described. The concept of using such materials as “artificial dopants” is proposed. Promising application areas are considered, ranging from the creation of extremely strong materials to the achievement of non-standard superconducting and magnetic effects.

UV and pulsed electron beam radiation for effective bisphenol A degradation

The paper presents the results of studying the efficiency of the bisphenol A transformation in water exposed to ultraviolet radiation and a high-energy-pulse-electron beam (e-beam). It has been shown that in both cases, degradation of dissolved bisphenol A occurs, accompanied by an increase in the absorption coefficient in the wavelength region of more than 300 nm. After exposure, products were recorded that fluoresced in the region of more than λ = 400 nm. The fluorescent transformation product of bisphenol A in water (λ = 425 nm) was maximum formatted after an KrCl excilamp irradiated, and under the action of an e-beam, the accumulation of this product was minimal. Under e-beam radiation (170 keV) the efficiency of bisphenol A (1 mM) removal reached 97%. The data obtained allow us to develop ideas about photolysis and radiolysis in natural water systems when knowledge about targeted and optimal conditions for the degradation of bisphenol A is needed.

Magnetic-field oscillation model of pulsar radio emission: prediction of an observable effect

Abstract Since the discovery of pulsars, the rotating-lighthouse model has been the choice of model to explain the radiation pulsation of pulsars. After discovering that some main sequence stars (e.g. CU Virginis) and ultracool dwarfs (e.g. TVLM 513-46546) also behave like pulsars, the lighthouse model was again adopted to explain their pulse signals. Our research found that if we use the magnetic-field oscillation (MO) model, we can explain the pulse radiation results better regardless of whether its source is a neutron star, a main-sequence star or an ultracool dwarf. We propose a verifiable prediction that can be used to evaluate the MO model. Our prediction is that there is a 90○ phase lag between the magnetic field and radio signal of TVLM 513-46546, and the zero-crossing point of the magnetic field is the moment when the direction of the light’s circular polarization is reversed. No new observations are needed to check this prediction, but certain existing data needs to be re-mined.

DERIVATION OF EXPRESSION FOR PHOTOCURRENT DENSITY FOR NON-DESTRUCTIVE TESTING OF 3D PRINTING FILAMENT BY MEANS OF TERAHERTZ SPECTROSCOPY

This report presents a revised expression for the photocurrent density in terahertz spectroscopy, which is a non-destructive testing technique of particular interest to the authors in the context of 3D printed parts. 3D printing, also known as additive manufacturing, involves creating three-dimensional objects based on computer-aided design (CAD) models. The process entails depositing, joining, or solidifying material under computer control, layer by layer.
 
 Defects in 3D printing, such as weak infill, gaps in thin walls, inconsistent extrusion, layer separation, and bed drop, can lead to low printing quality and render some printed parts unfit and unsafe for use. Moreover, the ability to tamper with internal layers without altering the exterior could result in the production of maliciously defective parts without detection. Therefore, it is crucial to test 3D printed details and filaments at each stage of processing using non-destructive methods.
 
 A comprehensive review of the relevant literature indicates the potential for enhancing measurement accuracy through various improvements in terahertz spectrometer models. The mathematical model for the photocurrent involves a convolution integral of the current density and the laser radiation pulse that irradiates the surface of the material under study. The expression within the integral incorporates parameters such as the duration of the optical pulse, carrier lifetime, and momentum relaxation time. By evaluating the integral, the result can be obtained as two terms, each being a product of an exponent and a complementary error function with the same parameters mentioned earlier.
 
 The calculation involves several steps, including a change of variables during integration. Verification using Maple software demonstrates agreement with analytical calculations and suggests a pathway for further refinement of the expression for the photocurrent density. The Maple program influenced the results by means of repeating same calculation with aid of computer and allowing to compare if analytical results are same and true, also it could be use for simulation and example calculation, for results graphical representation. 
 
 The connection between the obtained mathematical expression and its relation to 3D printing (additive manufacturing) exists. The explanation is in that the 3D printer uses filament, filament has defects, defectoscopy of filament in the terahertz domain have models and methods. The research of defectoscopy models and methods is helpful to increase accuracy of measurement of filament defect parameters and account on it and improve the quality of 3D printed details.

Novel materials for radiation sensing in radiotherapy treatments: Development of luminescent YVO4:Eu3+ polymer-based nanocomposites

This scientific work explores the development of luminescent nanocomposite materials for radiation sensors in Fiber Optic Dosimetry (FOD). The study emphasizes the use of YVO4:Eu3+ as a scintillator material due to its high luminescent efficiency. However, the challenge arises from its higher effective atomic number compared to soft tissue. To address this issue, the work explores the dispersion of YVO4:Eu3+ as nanoparticles (NPs) in a biocompatible polymeric matrix, specifically considering poly(methyl methacrylate) (PMMA) and poly(ethylene glycol) dimethacrylate (PEGDMA). Both PMMA/YVO4:Eu3+@TMSPM and PEGDMA/YVO4:Eu3+@TMSPM formulations were synthesized with minimal impact on the glass transition temperatures of the polymers. Under UV and beta particle excitation, these formulations exhibit emission spectra characteristic of Eu3+ f-f transitions. The decay times of the main emission peak at 620 nm were 615 μs, 584 μs, and 567 μs for the NPs, PEGDMA- and PMMA-based polymeric nanocomposites (PNCs), respectively. These decay times fall within the range suitable for scintillators in LINAC pulsed radiation facilities. Also, PEGDMA- and PMMA-based PNCs with varying contents of YVO4:Eu3+ NPs showed radioluminescence spectra under beta particle irradiation. This work demonstrates the feasibility of developing PEGDMA- and PMMA-based PNCs containing dispersed YVO4:Eu3+ NPs for their application as scintillators in radiotherapy dosimetry.

Magnetization reversal of ferromagnetic nanosample by circularly polarized radiation pulse under resonance condition

We consider the problem of the magnetization dynamics of a nanosized ferromagnetic sample caused by the spin–orbit interaction of electrons arising in the field of an incident electromagnetic wave. We discuss the case when the frequency of the incident electromagnetic radiation is close to the frequency of the interband transitions. We show that with the use of high-power lasers, this mechanism causes the appearance of a magnetization component perpendicular to the initial magnetization of the sample. This component shows oscillations with a frequency lower than that of incident electromagnetic waves. These dynamics make possible the magnetization reversal of the sample.

Comparing resistance of bacterial spores and fungal conidia to pulsed light and UVC radiation at a wavelength of 254 nm

Pulsed light (PL) inactivates microorganisms by UV-rich, high-irradiance and short time pulses (250 μs) of white light with wavelengths from 200 nm to 1100 nm. PL is applied for disinfection of food packaging material and food-contact equipment. Spores of seven Bacillus ssp. strains and one Geobacillus stearothermophilus strain and conidia of filamentous fungi (One strain of Aspergillus brasiliensis, A. carbonarius and Penicillium rubens) were submitted to PL (fluence from 0.23 J/cm2 to 4.0 J/cm2) and UVC (at λ = 254 nm; fluence from 0.01 J/cm2 to 3.0 J/cm2). One PL flash at 3 J/cm2 allowed at least 3 log-reduction of all tested microorganisms. The emetic B. cereus strain F4810/72 was the most resistant of the tested spore-forming bacteria. The PL fluence to 3 log-reduction (F3 PL) of its spores suspended in water was 2.9 J/cm2 and F3 UVC was 0.21 J/cm2, higher than F3 PL and F3 UVC of spores of B. pumilus SAFR-032 2.0 J/cm2 and 0.15 J/cm2, respectively), yet reported as a highly UV-resistant spore-forming bacterium. PL and UVC sensitivity of bacterial spores was correlated. Aspergillus spp. conidia suspended in water were poorly sensitive to PL. In contrast, PL inactivated Aspergillus spp. conidia spread on a dry surface more efficiently than UVC. The F2 PL of A. brasiliensis DSM1988 was 0.39 J/cm2 and F2 UVC was 0.83 J/cm2. The resistance of spore-forming bacteria to PL could be reasonably predicted from the knowledge of their UVC resistance. In contrast, the sensitivity of fungal conidia to PL must be specifically explored.