High-repetition Laser Research Articles

Effect of high-repetition frequency nanosecond laser remelting on microstructure and oxidation properties of low-pressure plasma sprayed NiCoCrAlYTa coating

MCrAlYX coatings are widely utilized as bond coat in thermal barrier coating systems. This study employs high-repetition frequency nanosecond laser remelting (HRF-NLR) to enhance the resistance to high-temperature oxidation of NiCoCrAlYTa coatings prepared via low-pressure plasma spraying (LPPS). The objective of this study is to investigate how laser remelting influences the microstructural evolution of the NiCoCrAlYTa coating and the growth characteristics of the thermally grown oxide (TGO). Various scanning speeds and laser pulse energy densities were employed to investigate the microstates of the molten pool and the polishing mechanisms of the samples after HRF-NLR. Increasing the repetition frequency effectively mitigates the ablation issues typically associated with conventional laser remelting, while also enabling precise control over depth of the remelted coating. Microstructure analysis shows that the original rough surface was remelted and polished, contributing to a significant reduction in surface roughness, noticeable grain refinement, a high density of dislocations, and the redistribution of active elements within the modified coating. Oxidation results at 1150 °C reveal that the HRR-NLR coating can induce the formation of a dense, continuous, and slow-growing single α-Al2O3 film, demonstrating that HRF-NLR is an efficient and feasible method for improving the resistance of MCrAlYX coatings to high-temperature oxidation.

Enhancing durable electrical conductivity in multi‐walled carbon nanotubes‐epoxy composites via laser repetition rate nanojoining for flexible electronics

AbstractWith the development of nanotechnology, laser matter interaction has become intriguing for many applications, including the manufacturing of flexible electronics to improve interface behaviors. Employing high laser repetition rate nanojoining transfer patterning, this study ensures the robust and consistent stability of electrical properties of MWCNTs. This procedure meticulously eliminates contaminants from the interface between flexible PET substrates and carbon nanotube‐containing epoxy, significantly influencing the degree of alteration in composite material and interface behaviors. By increasing the laser repetition rate from the original sample to the sample irradiated by a laser with a repetition rate of 80 kHz, the defect concentration in carbon nanotubes decreases from 0.448 × 106/nm2 to 0.39376 × 106/nm2, respectively. The relationship between defect concentration and electrical conductivity in semiconductor carbon nanotubes under laser irradiation is multifaceted and context‐dependent. Optimizing the laser repetition rate is crucial in defining the kind and density of semiconductor carbon nanotubes. This study found an electrical conductivity of 3.6799 × 10−4 S/m at a laser repetition rate of 80 kHz. Laser ablation nanojoining with a high laser repetition rate is poised to become a key recycling method for plastic materials in future industries. When MWCNTs are used in processing new materials, this method not only enhances the electrical and mechanical properties of recycled plastics but also creates high‐performance composites with added value. Additionally, the quick nature of this process helps minimize toxicity in material processing by reducing exposure time and the need for harmful chemicals. These composites exhibit superior properties suitable for advanced applications such as flexible electronics, sensors, and nanocomposite materials, contributing to both sustainability and economic value in various industrial sectors.

Production of Cu/Zn Nanoparticles by Pulsed Laser Ablation in Liquids and Sintered Cu/Zn Alloy

As a preliminary step to establish technology for fabricating High-Entropy Alloys (HEAs) that can make a large-scale HEA using a pulse laser with high peak intensity and high-repetition in the future, we fabricated alloys in which two types of metal atom are mixed close together in the order of nanometers. For the method to produce the alloy, metal alloy nanoparticles were prepared by irradiating the material in liquid with focused high-repetition Q-switched laser pulses using an in-liquid laser ablation method. When brass powder was used as an original material, analysis results by TEM showed that numerous nanoparticles mixed with copper and zinc atoms could be produced. Furthermore, it was clarified by SEM EDS that copper and zinc atoms in the nanoalloy were maintained at a ratio of 3:1 in sintered alloy, and that the atoms were spatially uniformly distributed over a wide range in sintered metal.

Near-Wall Flow Features In ZPG-TBL At Various Reynolds Numbers Using Dense 3D Lagrangian Particle Tracking

The 3D Lagrangian particle tracking method Shake-The-Box (STB) and, subsequently, the data assimilation method FlowFit3 have been applied to measure the flow field in a narrow wall-parallel volume inside the nearwall region of a zero-pressure-gradient (ZPG) turbulent boundary layer (TBL) flow at various Reynolds numbers. The STB experiments have been conducted in the 1m- wind tunnel facility of DLR in Göttingen at relatively high particle image densities (~0.07 ppp) using µm-sized DEHS particles and high-repetition pulse laser at up to 38.1 kHz. The results show that the chosen methodology is able to volumetrically resolve almost all features of the flow inside the viscous sub-, buffer- and lower logarithmic- layer in space and time at Reynolds numbers up to Re θ = 5,455. The gained data consists of time-series of spatially well resolved 3D velocity, acceleration and pressure fields, as well as a huge amount of long Lagrangian particle trajectories. Selecting the viscous sublayer part of the measurement volume provides time-series of the 2D distribution of both components of the instantaneous wall-shear stresses w,x/z . The resulting data are used for conditional and time-resolved 3D analyses of coherent structures, rare (e.g. back flow) events and two-point space-timecorrelations.

Femtosecond laser synthesis of YAG:Ce3+ nanoparticles in liquid

YAG:Ce3+ nanocrystals are promising bio-labeling materials due to their low toxicity and high photostability. It is in demand to efficiently synthesize YAG:Ce3+ nanocrystals of a small size. Pulse laser ablation is an approach to produce nanoparticles directly from bulk materials with the advantages of smaller particle sizes and lower production costs. Here, we present the synthesis of YAG:Ce3+ nanocrystals from bulk crystal using the femtosecond laser ablation method in liquid. Comparing the liquid environment, we demonstrated that the lauryl dimethylaminoacetic acid betain (LDA) aqueous solution is preferred for the formation of smaller-sized YAG:Ce3+ nanoparticles than deionized water due to the attractiveness between the LDA molecules and the YAG:Ce3+ nanoparticles. We also verified that the high laser repetition rate had no effect on the average size of YAG:Ce3+ nanocrystals, where the fragmentation process is saturated under a high laser repetition rate. This study provides a simple and effective method to synthesize small size YAG:Ce3+ nanoparticles by femtosecond laser ablation in liquid.

Development of liquid metal targets for high-repetition intense laser and pulsed-power discharge applications

In this study, we investigate the response of linear liquid metal flow to a magnetic field when used as a load for high-repetition pulsed-power discharges and as a sheet for a laser target. When a magnetic field was applied perpendicular to the liquid metal flow, the flow deformed while maintaining its thickness. This approach may reduce current and enhance light sources in Z-pinch and alternative X-pinch discharges. However, low-frequency fluctuations were more prominent when the magnetic field was applied parallel to the liquid metal flow in sheet form. These findings suggest that combining liquid metal flow with a magnetic field could effectively facilitate high-repetition pulsed-power discharges and laser operations.

Radioisotope production using lasers: From basic science to applications

The discovery of chirped pulse amplification has led to great improvements in laser technology, enabling energetic laser beams to be compressed to pulse durations of tens of femtoseconds and focused to a few micrometers. Protons with energies of tens of MeV can be accelerated using, for instance, target normal sheath acceleration and focused on secondary targets. Under such conditions, nuclear reactions can occur, with the production of radioisotopes suitable for medical application. The use of high-repetition lasers to produce such isotopes is competitive with conventional methods mostly based on accelerators. In this paper, we study the production of 67Cu, 63Zn, 18F, and 11C, which are currently used in positron emission tomography and other applications. At the same time, we study the reactions 10B(p,α)7Be and 70Zn(p,4n)67Ga to put further constraints on the proton distributions at different angles, as well as the reaction 11B(p,α)8Be relevant for energy production. The experiment was performed at the 1 PW laser facility at Vega III in Salamanca, Spain. Angular distributions of radioisotopes in the forward (with respect to the laser direction) and backward directions were measured using a high purity germanium detector. Our results are in reasonable agreement with numerical estimates obtained following the approach of Kimura and Bonasera [Nucl. Instrum. Methods Phys. Res., Sect. A 637, 164–170 (2011)].

Atmospheric Thermodynamic Profiling through the Use of a Micro-Pulse Raman Lidar System: Introducing the Compact Raman Lidar MARCO.

It was for a long time believed that lidar systems based on the use of high-repetition micro-pulse lasers could be effectively used to only stimulate atmospheric elastic backscatter echoes, and thus were only exploited in elastic backscatter lidar systems. Their application to stimulate rotational and roto-vibrational Raman echoes, and consequently, their exploitation in atmospheric thermodynamic profiling, was considered not feasible based on the technical specifications possessed by these laser sources until a few years ago. However, recent technological advances in the design and development of micro-pulse lasers, presently achieving high UV average powers (1-5 W) and small divergences (0.3-0.5 mrad), in combination with the use of large aperture telescopes (0.3-0.4 m diameter primary mirrors), allow one to presently develop micro-pulse laser-based Raman lidars capable of measuring the vertical profiles of atmospheric thermodynamic parameters, namely water vapor and temperature, both in the daytime and night-time. This paper is aimed at demonstrating the feasibility of these measurements and at illustrating and discussing the high achievable performance level, with a specific focus on water vapor profile measurements. The technical solutions identified in the design of the lidar system and their technological implementation within the experimental setup of the lidar prototype are also carefully illustrated and discussed.

Development of spinning-disk solid sample delivery system for high-repetition rate x-ray free electron laser experiments.

X-ray free-electron lasers (XFELs) deliver intense x-ray pulses that destroy the sample in a single shot by a Coulomb explosion. Experiments using XFEL pulse trains or the new generation of high-repetition rate XFELs require rapid sample replacement beyond those provided by the systems now used at low repletion-rate XFELs. We describe the development and characterization of a system based on a spinning disk to continuously deliver a solid sample into an XFEL interaction point at very high speeds. We tested our system at the Linac Coherent Light Source and European XFEL hard x-ray nano-focus instruments, employing it to deliver a 25 μm copper foil sample, which can be used as a gain medium for stimulated x-ray emission for the proposed x-ray laser oscillator.

Developing system arrays for new experimental approach in nuclear astrophysics

The advent of facilities providing high-intensity and high-resolution gamma ray beams and/or ultra-short and high-repetition laser pulses can potentially open a new path of astrophysical research. Indeed, a pencil size gamma beams with tunable energies from few keV up to tens MeV will offer distinctive chances to conduct precise measurements of small cross sections (on the scale of μb or even smaller) pertaining to nuclear reactions in the field of astrophysics. Consequently, it provides essential data for modeling astrophysical S-factors crucial to stellar evolution. On the other hand, the possibility to mimic the stellar conditions by laser-matter interaction generating a controlled laboratory plasma with thermodynamical status not too different from stellar conditions will open the way for the study of nuclear reactions of utmost importance for nuclear astrophysics.For photonuclear reactions with astrophysical significance, as photodissociations occur at photon energies slightly above particle emission thresholds due to typical stellar temperatures, the resulting fragments possess low energies spanning from a few hundred keV to a few MeV. Consequently, detectors with low thresholds become imperative in such cases. Also, in the case of laser-induced reactions, in order to detect the fusion products and to measure the laser-accelerated ion distribution a proper system of detection is needed. Depending on the available exit channels of the nuclear reaction of interest, both charged particles and neutrons are foreseen.Here, we present the Asfin’s efforts on developing new detectors arrays suitable for the experimental requirements in these challenging measurements. Indeed, an experimental campaign is ongoing in order to test the feasibility of excitation functions and angular distributions determinations using versatile silicon strip arrays (namely LHASA and/or ELISSA). Moreover, extensive studies and simulations will be presented regarding the developing of a dedicated detection system comprising a cryogenically cooled supersonic nozzle, an appropriate interaction chamber, an array of neutron and charged particle detectors and two compact ion spectrometers for performing systematic study of laser-induced nuclear fusion reactions.

Performance improvement of iron chalcogenide films grown at high laser repetition rates by pulsed laser deposition

AbstractFor mass production, a high deposition rate is necessary. A powerful approach is to deposit Fe(Se, Te) (FST) superconducting films at a high laser repetition rate by pulsed laser deposition. Hence, the FST films were grown on flexible metallic tapes using pulsed laser deposition at different laser repetition rates to explore the effect of laser repetition rate on the properties. It was found that as the laser repetition rate increases, the crystallinity and stoichiometry of FST films deteriorate, resulting in a degeneration in superconductivity. The critical temperature of the FST film deposited at a high repetition rate of 120 Hz dropped to 12.89 K. Furthermore, high‐performance FST film was successfully deposited at 120 Hz by increasing the substrate temperature with = 16.96 K and = 18.32 K. The self‐field critical current density can reach 1.3 MA/cm2 at 4.2 K. The analysis of the pinning mechanism reveals that normal surface pinning centers play a dominant part in the FST film and are independent of the temperature. The collective pinning theory states that the FST film exhibits δl pinning. The results may offer valuable information for rapid deposition of FST‐coated conductors for industrial production.

Molecular-frame photoelectron angular distributions during double core-hole generation in and molecules

Angular distributions of photoelectrons emitted upon double core-hole (DCH) generation in nitrogen and oxygen molecules are studied theoretically in the frame of a molecular reference. The respective electronic structure calculations are performed by the single center method for photoelectron kinetic energies up to 40 eV in the relaxed-core Hartree–Fock approximation. The molecular frame photoelectron angular distributions are computed for single-site and two-site DCH creation processes and further analyzed for different orientations of the molecular axis with respect to the electric field vector of linearly polarized incident light and for localized or delocalized emitting atomic site scenarios. The present theoretical results provide reliable predictions for future experiments with high-repetition free-electron lasers.

Design and construction of a compact, high-repetition-rate ultrafast electron diffraction instrument.

We present the design and performance of a compact ultrafast electron diffraction instrument. The diffractometer provides a means of examining time-resolved ultrafast dynamical properties of solids. The system's utilization is discussed in terms of instrument parameters and diffraction data from selected condensed matter samples. The difractometer's performance is highlighted in terms of detection sensitivity, instrumental temporal resolution, and the electron beam transverse coherence length. Following specific details of the construction, we present a practical discussion of parameters such as repetition rate and provide advice on general construction approaches for laboratory-based, keV ultrafast electron diffractometers. In addition, design guidance for constructing a compact electron gun source that is well-suited for studying diffraction from hard condensed matter is given. A unique data acquisition scheme, utilizing high laser repetition rates, is presented.

Experimental study of medical isotopes 62,64Cu and 68Ga production using intense picosecond laser pulse

Radioisotopes are indispensable agents in medical diagnosis and treatment, among which copper-62, 64 (62,64Cu) and gallium-68 (68Ga) are medical isotopes widely used in positron emission tomography (PET) imaging. Experiments that generate these radioisotopes via laser-induced photonuclear reactions were performed on the XingGuangIII laser facility of the Laser Fusion Research Center in Mianyang. High-charge ( ∼ 40 nC) MeV electron (e− ) beams were generated with 100 terawatts, picosecond laser pulses. The e− beams were then impinged on a metal stack composed of Ta foil and activation plates (natural Cu and Ga2O3), producing high-energy bremsstrahlung x-rays and medical isotopes 62,64Cu and 68Ga, respectively. The characteristic emissions of the produced 62,64Cu and 68Ga were detected off-line , and the production yields of 62,64Cu and 68Ga were obtained to be of the order of 106 per laser shot. For electrons with energy higher than 8 MeV, the dependence of isotope production efficiency (per e− ) on electron temperature () is investigated through Geant4 simulations. It is found that the production efficiency increases with the . At ∼ 10 MeV, the values are 10−4 for 62Cu and 2 × 10 − 5 for 68Ga, respectively. The prospect of producing the medical isotopes 62,64Cu and 68Ga are further evaluated using a table-top femtosecond laser system of high repetition. With a repetition rate of 100 Hz, their activity is expected to reach 0.2 GBq for 62Cu, 0.1 GBq for 64Cu and 0.05 GBq for 68Ga, respectively. Such activity would meet the required dose for clinical PET imaging, indicating the great potential to produce medical isotopes with an all-optical, high-repetition laser system.

Thermal-induced effects on ultrafast laser filamentation in ethanol

Fs laser filamentation in ethanol is studied for bottom-up nanomaterials synthesis at different laser repetition rate. Measurements of energy loss, visible conical images, transmitted beam profile and the optical emission spectra show that laser repetition rate affects ultrafast laser filamentation in ethanol significantly because of the induced thermal processes. Firstly, near the threshold laser energy for self-focusing, high laser repetition rate could interfere with the process, via thermal defocusing that inhibits the onset of filamentation. An enlarged, near flat-top laser beam is produced for the conditions that favor thermal lensing. Secondly, at high laser energy, thermal defocusing effect is saturated as convective heat dissipation occurs. Thus, self-focusing prevailed and led to filamentation at all repetition rates. The strong convection at high laser repetition rate increases the rate of reactions for nanodiamonds synthesis, as the flow of fresh ethanol precursor to the localized filamentation zone is enhanced.

Demonstration of efficient relativistic electron acceleration by surface plasmonics with sequential target processing using high repetition lasers

For high repetition ultrahigh-intensity laser system, automatic alignment of structured target is key to achieving consistent particle acceleration and plasma heating. In this work, we demonstrate efficient electron acceleration with two sequential steps of laser processing using a high repetition rate, 30-fs ultrahigh-intensity laser. The first pulse does laser machining and creates a steep cylindrical crater on the surface of a flat stainless-steel target. The crater is formed by the hydrodynamic expansion of the heated surface and by spallation of the inner, deeper material by nonthermal relativistic electrons. The crater shape is well controlled and reproducible with 200 \ensuremath{\mu}m width and 350 \ensuremath{\mu}m depth. The second pulse irradiates deeply inside the crater and interacts with the crater wall, efficiently accelerating electrons via surface plasmonic, without need for target realignment. The laser absorption efficiency increases from 32.5 to 97.5% by the process.

Towards high-repetition rate petawatt laser experiments with cryogenic jets using a mechanical chopper system

Laser-plasma based ion accelerators require suitable high-repetition rate target systems that enable systematic studies at controlled plasma conditions and application-relevant particle flux. Self-refreshing, micrometer-sized cryogenic jets have proven to be an ideal target platform. Yet, operation of such systems in the harsh environmental conditions of high power laser induced plasma experiments have turned out to be challenging. Here we report on recent experiments deploying a cryogenic hydrogen jet as a source of pure proton beams generated with the PW-class ultrashort pulse laser DRACO. Damage to the jet target system during application of full energy laser shots was prevented by implementation of a mechanical chopper system interrupting the direct line of sight between the laser plasma interaction zone and the jet source.

A Compact Upconversion Single-Photon Imager for Full-Range and Accurate 3-D Imaging

The rapid development of single photon detection technology offers the possibility for an imaging system to go beyond the traditional limits. Recently, single-photon imagers based on upconversion technique have achieved unprecedentedly high resolution and noise tolerance in 3D imaging. Nevertheless, the limited imaging range, complicated optical path and long data acquisition time impose remaining challenges to practical applications. In this work, we build an upconversion single-photon imager for full-range and accurate 3D imaging. A compact all-fiber design allows our system to work robustly in an open environment. Compared to the previous imagers, the imaging speed is increased by three orders of magnitude due to the high upconversion efficiency and photon-efficient algorithm. With the application of a high-repetition laser and a nanosecond optical delay line, we achieve full-range imaging under the upconversion scheme against high solar background noise. For close-up scenes, our imager achieves ultrahigh axial resolution up to 20 μm, which is not affected by the time jitter or pileup effect of the single photon detector. Our proposal can stimulate practical applications in sophisticated scenarios.

Commissioning results from the high-repetition rate nanosecond-kilojoule laser beamline at the extreme light infrastructure

High-power laser–matter interaction and the related high-energy density physics (HEDP) are two important topics in modern physics. However, for decades, a very restrictive limitation prevents researchers from studying these topics efficiently: nanosecond-kilojoule class lasers are typically characterized by a low repetition rate (1 shot h−1) that restricts the data acquisition and limits the available statistics for analysis. Here, we describe the first results obtained using the high-repetition rate nanosecond-kilojoule (L4n laser beamline) experimental platform commissioned at the Extreme Light Infrastructure—Beamlines. We proved the capability to deliver hundreds of joules shots every three min with a very good repeatability. Using high-resolution x-ray spectroscopy, we studied highly resolved spectra of H-like and He-like Cl lines emitted from polyvinyl chloride targets and demonstrated that the plasma parameters (electron temperature and density) derived from the measured spectra are consistent with hydro-simulations. These results demonstrate the fulfillment of the designed platform performance which should become one of the most important assets for the HEDP community in the following decades.

Effect of laser repetition rate on the fluorescence characteristic of a long-distance femtosecond laser filament.

In this paper, the effect of the laser repetition rate on the long-distance femtosecond laser filament in air is investigated by measuring the fluorescence characteristic of the filament. A femtosecond laser filament emits fluorescence due to the thermodynamical relaxation of the plasma channel. Experimental results show that as the repetition rate of femtosecond laser increases, the fluorescence of the filament induced by a single laser pulse weakens, and the position of the filament moves away from the focusing lens. These phenomena may be attributed to the slow hydrodynamical recovery process of air after being excited by a femtosecond laser filament, whose characteristic time is on the millisecond time scale and comparable to the inter-pulse duration of the femtosecond laser pulse train. This finding suggests that at a high laser repetition rate, to generate an intense laser filament, the femtosecond laser beam should scan across the air to eliminate the adverse effect of slow air relaxation, which is beneficial to laser filament remote sensing.