Laser Shot Research Articles

Study of the isomeric yield ratio in the photoneutron reaction of natural holmium induced by laser-accelerated electron beams

Introduction: An accurate knowledge of the isomeric yield ratio (IR) induced by the photonuclear reaction is crucial to study the nuclear structure and reaction mechanisms. 165Ho is a good candidate for the investigation of the IR since the Ho target has a natural abundance of 100% and the residual nuclide has a good decay property.Methods: In this study, the photoneutron production of 164m, gHo induced by laser-accelerated electron beams is investigated experimentally. The γ-ray spectra of activated Ho foils are off-line detected. Since the direct transitions from the 164mHo are not successfully observed, we propose to extract the IRs of the 164m, gHo using only the photopeak counts from the ground-state decay.Results: The production yields of 164m, gHo are extracted to be (0.45 ± 0.10) × 106 and (1.48 ± 0.14) × 106 per laser shot, respectively. The resulting IR is obtained to be 0.30 ± 0.08 at the effective γ-ray energy of 12.65 MeV.Discussion: The present data, available experimental data, and TALYS calculations are then compared to examine the role of the excitation energy. It is found that besides the giant dipole resonance, the excitation energy effect also plays a key role in the determination of the IRs.

Fatigue life prediction of AA2524 thin plate strengthened using compound laser heating and laser shot peening method

AA2524 is a aluminum alloy based on damage tolerance design, and it is mainly used for the manufacturing of aircraft skins. Aircraft skins often occur fatigue failure due to harsh working conditions. To improve the fatigue resistance of aircraft skins and to accurately predict the fatigue life of AA2524 compact tension (CT) samples. The compound strengthening method of lsear heating (LH) and lsear shot peening (LSP) is proposed to improve the fatigue life of AA2524 in this paper. Considering the effect of stress ratio (R), residual stress (RS), stress intensity factor range (ΔK), and maximum stress intensity factor (Kmax) on the fatigue crack growth rate (FCGR), the fatigue life of CT samples was predicted applying artificial neural networks, support vector regression models. The results show that laser heating and laser shot peening can obviously improve the fatigue life by 30.703% at R = 0.1 and 4.701% at R = 0.5, compared with base materials. The neural networks have better fatigue life prediction ability, and the fit coefficients for the neural networks predicting fatigue life reach 0.97, which is better than that of Walker model (0.91). The prediction value for ANN model is 75,462 cycles, the magnitude for SVR model is 78,234 cycles, and the experimental value is 74,204 cycles. The deviation are 1.7% and 5.43%, respectively. Meanwhile, the effect of R on the FCGR of AA2524 is closely associated with the crack closure effect.

Quantifying Platinum and Palladium in Solid Ore Using Laser-Induced Breakdown Spectroscopy Assisted by the Laser-Induced Fluorescence (LIBS-LIF) Technique.

The laser-induced breakdown spectroscopy assisted by laser-induced fluorescence (LIBS-LIF) in a two-step process was used to measure the concentration of platinum (Pt) and palladium (Pd) by surface analysis of a solid ore core from the Lac des Iles mine followed by analysis of the same core that was pulverized and compacted. This work focuses mainly on the measurement of Pt since the case of Pd has been extensively discussed in previous work. The excitation of Pt is performed at 235.71 nm with fluorescence emission observed near 269.84 nm. Calibration was performed with synthetic samples prepared from the same ore as the samples studied and the calibration curve shows good linearity in Pt content over several orders of magnitude. A limit of detection (LOD) of approximately 0.15 parts per million (ppm) over an average of 200 laser shots was demonstrated. In contrast, conventional LIBS provides a LOD of about 21 ppm over an average of 200 laser shots due to low signal-to-noise ratio and spectral interference from other elements and does not meet the requirements for estimating the average Pt concentration in the ore. The Pt concentrations obtained using LIBS-LIF on solid ore are generally in good agreement with those obtained in its pulverized and compacted form, as well as with laboratory measurements made by conventional chemical methods. However, the comparison of the results obtained for Pd using LIBS-LIF with the laboratory showed a less satisfactory agreement, probably due to its more inhomogeneous distribution in the ore.

Retracted: Clinical Observation of Laser Peripheral Iridoplasty with Number of Laser Shots in the Treatment of Acute Angle-Closure Glaucoma.

[This retracts the article DOI: 10.1155/2022/7968999.].

Properties and performance of nitrogen laser systems for calibration of LHAASO-WFCTA

The Wide Field of view Cherenkov Telescope Array (WFCTA) of the Large High Altitude Air Shower Observatory (LHAASO), located in Haizishan National Natural Reserve, Sichuan Province, China, is designed to perform nearly calorimetric measurements of extensive air showers induced by cosmic rays with energies between 1013eV–1018eV. The end-to-end calibration method will be employed in the WFCTA and nitrogen lasers have been proven to work properly in our application at the altitude of 4410 m a.s.l. for the first time.Due to extremely harsh environment, especially outdoor temperature as low as about −30 °C during operation of WFCTA, a high-stability thermotank for lasers was designed to stabilize temperature and humidity, with a thermal stability of 1 °C. In order to precisely control the beam pointing, a high-precision 3D Lifting Rotating Platform (HiRoP) with a home-made standard zero monitoring system is developed. To eliminate the error of the beam pointing by manual controls, an automatic scanning program was adopted to control the beam pointing when scanning the full field-of-view (FOV) of WFCTA. Both the on-site and remote controls are applied for the nitrogen laser systems and ∼13 million laser shots have been recorded by WFCTA from Sept. 2020 to May 2022. In this paper, the design, properties, operation and the on-site performance of the nitrogen laser systems at LHAASO are reported.

Laser-produced craters in minerals of a palladium ore sample

Laser-induced breakdown spectroscopy (LIBS) is an emerging technique in geochemistry that allows rapid in-situ analysis of the elemental composition and concentration of minerals by laser ablation of the material surface and measurement of the light emitted by the resulting plasma. However, this type of application is still under development for geochemical analyses. Indeed, it is still difficult to know how minerals are ablated under laser pulses in the context of LIBS geochemical analysis using a high-power Q-switched Nd:YAG laser operating at 1064 nm with pulse durations on the order of nanoseconds. Important questions remain unanswered regarding the volume sampled by the laser beam on the minerals to be analyzed, as well as the plasmas induced by the laser on the minerals in air at atmospheric pressure. The objective of this work is to provide insight into laser-mineral interactions within the framework of LIBS geochemical analysis of ore samples with emphasis on the characterization of plasmas and laser ablation craters under ambient air at atmospheric pressure. We study the crater morphology in the three main phases of a palladium ore fragment (Lac des Iles mine, Canada), namely plagioclase feldspar, amphibole and sulfides [Mohamed et al., Geostand Geoanal Res 45:539, (2021)] We performed four series of laser shots (50, 250, 500 and 1000 shots) in the three mineral phases and characterized the morphology of the craters obtained by scanning electron microscopy and optical coherence tomography. It turns out that laser ablation is most effective in plagioclase, presumably due to its lower thermal conductivity. In addition, the temperature and electron density of the plasma were determined for each phase from the iron and nickel lines of LIBS spectra taken 4 µs after the laser shots. They are between 6300 and 8600 °C and about 2 × 1017 cm−3, respectively.

Impact of nanosecond laser annealing on vacancies in electroplated Cu films studied by monoenergetic positron beams

Positron annihilation was used to probe vacancy-type defects in electrodeposited Cu films after nanosecond pulse laser annealing. For the as-deposited Cu film, we identified the coexistence of two different vacancy-type defects, vacancy clusters (such as V16) and monovacancy-type defects, coupled with impurities. An enlargement in the vacancy size was observed after the laser annealing process. The size of these defects was estimated to be close to V30, and such defects could not be formed by conventional furnace annealing. After furnace annealing at 400 °C, the size of the larger vacancy clusters decreased, but that of the smaller vacancies increased. The observed change in the sizes of vacancies is considered to be related to interactions between vacancies and impurities. The depth profile of the defects varied by changing the laser energy density and the number of laser shots. The impact of laser annealing on the vacancy-type defects was observed even after furnace annealing at 800 °C. Because the presence of point defects in electroplated Cu directly correlates with electromigration and grain growth, the ability of laser annealing to introduce large vacancy clusters in the localized region shows the potential of nanosecond laser annealing as a low-thermal budget process tool for back-end-of-line materials.

Correlation between 1064 nm laser attack and thermal behavior in STT-MRAM

In this paper, the impact of a 1064 nm laser attack on an STT-MRAM cell is experimentally studied in real-time, for the first time, during reading and writing operations, in order to understand the behavior of a sensing circuit under a temperature variation from 25 °C to 105 °C. This must be considered for the implementation of a hybrid CMOS/MRAM Light-Weight Cryptography circuit, to overcome a laser attack. We highlight a reading current variation during the laser shots, that can impact the sensing circuits. The switching probability between the two states has been measured as well as the impact of the irradiation time, laser power, and cell size. We correlate the results with electrical characterizations in a wide range of temperatures, demonstrating the 1064 nm laser attack thermally affects the STT-MRAM behavior. In conclusion, suitable countermeasures can be adopted.

Stable high repetition-rate laser-driven proton beam production for multidisciplinary applications on the advanced laser light source ion beamline.

Laser-driven proton accelerators are relevant candidates for many applications such as material science or medicine. Today, there are multi-hundred-TW table-top laser systems that can generate relativistic peak intensities >1018 W/cm2 and routinely reach proton energies in the MeV range. However, for most desired applications, there is still a need to optimize the quality and stability of the laser-generated proton beam. In this work, we developed a 0.625Hz high repetition-rate setup in which a laser with 2.5% RMS energy stability is irradiating a solid target with an intensity of 1019 to 1020 W/cm2 to explore proton energy and yield variations, both with high shot statistics (up to about 400 laser shots) and using different interaction targets. Investigating the above-mentioned parameters is important for applications that rely on specific parts of the proton spectrum or a high ion flux produced over quick multi-shot irradiation. We demonstrate that the use of a stable "multi-shot mode" allows improving applications, e.g., in the detection of trace elements using laser-driven particle-induced x-ray emission.

Connecting Obsidian Artifacts with Their Sources Using Multivariate Statistical Analysis of LIBS Spectral Signatures

With the recent introduction of handheld instruments for field use, laser-induced breakdown spectroscopy (LIBS) is emerging as a practical technology for real-time in situ geochemical analysis in the field. LIBS is a form of optical emission spectroscopy that is simultaneously sensitive to all elements with a single laser shot so that a broadband LIBS spectrum can be considered a diagnostic geochemical fingerprint. Sets of LIBS spectra were collected for seven obsidian centers across north-central California, with data processed using multivariate statistical analysis and pattern recognition techniques. Although all obsidians exhibit similar bulk compositions, different regional obsidian sources were effectively discriminated via partial least squares discriminant analysis. Obsidian artifacts from seven archaeological sites were matched to their putative sources with a high degree of confidence.

Microstructural and mechanical characterization of pearlitic steel after high intensity laser peening and shot peening

This study investigated the microstructural/mechanical properties of annealed 4340 pearlitic steel after shot peening (SP) and high intensity laser peening (LP). SP at 0.012–0.016 A resulted in fragmentation of the pearlite colonies ∼1–2 µm from the treated surface and sub-surface cracking as well as significant distortion of pearlite colonies ∼30 µm from the treated surface. LP at a pulse energy of 19 J with a pulse full-width half height of 27 ns and a square spot size of 3x3 mm2 resulted in an intense irradiance on the metal surface of 8 GW/cm2. During this process a thin, micrometer-range layer of surface material is ablated which generates and heats a plasma plume in less than 1 ns to a temperature in the range of 15,000 K. A recast layer ∼5–10 µm in thickness from the treated surface with significant porosity was observed in the LPed specimen. The highest average microhardness (266 ± 9 HV) was observed in the SPed specimen ∼63 µm from the treated surface, however the hardness quickly returned to the baseline hardness (218 HV) ∼250–500 µm from the treated surface. In the LPed specimen, the averaged microhardness values exceeded the baseline hardness up to a depth of ∼1500–2000 µm with an average microhardness of 237 ± 4 HV from ∼60–2500 µm from the treated surface. It is shown that LP not only improves the sub-surface microhardness of the 4340 pearlitic steel up to greater depths than SP, but that it also preserves the pearlitic microstructure near the treated surface.

The effect of ablation crater on geomaterials caused by laser shot accumulation on the laser-induced plasma and shock wave

The stability of laser-induced breakdown spectroscopy (LIBS) signal is vital for its application in geomaterials, which is challenged by spectral fluctuations caused by variable ablation craters. To investigate the influence of the ablation crater caused by laser shot accumulation, the shot-to-shot variation of plasma was analyzed from the aspects of shock wave propagation, ablation crater morphology, plasma morphology, and spectral evolution, which was conducted based on a fiber-optic LIBS (FO-LIBS) system. A pressure sensor was applied to monitor the shock wave signal due to the shock wave propagation characteristics related to the number of shots and types of binding materials. The evolution of the ablation crater profile and depth was tracked, and a linear correlation model between crater depth and shock wave energy was established. It was found that the spectral intensity increases first rapidly and gradually decreases, which can be attributed to the competition between the enhancement of spatial confinement and the plasma cooling phase. Strong self-reversal was observed due to the laser pulse accumulation, with an increase in the plasma expanding distance. This study illustrates the interaction of laser pulses, ablation, and plasma from different aspects, and provides a simple method to track the ablation process.

The role of potassium in depth profiling of the tumor border in bone-invasive oral cancer using laser-induced breakdown spectroscopy (LIBS): a pilot study

PurposeMicroscopic tumor spread beyond the macroscopically visible tumor mass in bone represents a major risk in surgical oncology, where the spatial complexity of bony resection margins cannot be countered with rapid bone analysis techniques. Laser-induced breakdown spectroscopy (LIBS) has recently been introduced as a promising option for rapid bone analysis. The present study aimed to use LIBS-based depth profiling based on electrolyte disturbance tracking to evaluate the detection of microscopic tumor spread in bone.MethodsAfter en bloc resection, the tumor-infiltrated mandible section of a patient’s segmental mandibulectomy specimen was natively investigated using LIBS. Spectral and electrolytic depth profiles were analyzed across 30 laser shots per laser spot position in healthy bone and at the tumor border. For the histological validation of the lasered positions, the mandibular section was marked with a thin separating disc.ResultsSolid calcium (Ca) from hydroxyapatite and soluble Ca from dissolved Ca can be reliably differentiated using LIBS and reflect the natural heterogeneity of healthy bone. Increased potassium (K) emission values in otherwise typically healthy bone spectra are the first spectral signs of tumorous bone invasion. LIBS-based depth profiles at the tumor border region can be used to track tumor-associated changes within the bone with shot accuracy based on the distribution of K.ConclusionDepth profiling using LIBS might enable the detection of microscopic tumor spread in bone. In the future, direct electrolyte tracking using LIBS should be applied to other intraoperative challenges in surgical oncology to advance rapid bone analysis by spectroscopic–optical techniques.

UV femtosecond single-pulse and collinear double-pulse laser-induced breakdown spectroscopy (LIBS) for depth-resolved characterization of nano-scaled films

In the current work, we demonstrate the UV femtosecond (248 nm, 450 fs) single-pulse and double-pulse laser-induced breakdown spectroscopy (LIBS) as an effective method for depth profiling of nanometer-thick multi-layered structures, including photovoltaic thin films. Femtosecond LIBS enabled selective detection of both organic and inorganic materials at different depths within nanometer-scale (10–250 nm) multi-layered samples having thicknesses comparable to the etching depth produced by a single laser shot ablation. To enhance the analytical capabilities of the method, we applied the collinear double-pulse LIBS technique, using a Michelson interferometer to split the laser pulse into two equal-energy pulses. Results obtained with Indium Tin Oxide (ITO) nanofilms (115 nm layer thickness) present a clear increase of the intensity emission by a factor of 3 to 10, depending on laser fluence, when the double-pulse approach is used. Single-pulse LIBS achieved an ablation rate of around 60 nm, while the double-pulse configuration achieved 40 nm/pulse, in a sequence of seven laser shots. Furthermore, via double-pulse LIBS spectra were recorded even at fluences as low as 150 mJ/cm2, compared to 250 mJ/cm2 required for capturing spectra, when the same total energy per pulse was maintained.

Formation mechanisms of silicon surface structuring using single-multiple nanosecond laser pulses in ambient air and cold plasma

The formation mechanisms of the surface structures of silicon using single-multiple nanosecond laser pulses at the focus, and below the focus in ambient air and cold plasma was investigated for ablation at 2–5 J cm−2. Ablation in cold plasma, excited by a dielectric-barrier-discharge source in flowing air by applying sinusoidal voltage of 3–5 kV/30 kHz led to regular and consistent low-spatial-frequency and high-spatial-frequency grating-type structures. For plasma, structures were formed inside the crater and suggest that plasma hindered effective coupling of the laser energy to the surface, which resulted in a controlled ablation. Contrary to the ablation in plasma, for ambient air, due to excessive ablation, overlapped-ripples were formed outside the ablation crater. For the increased laser shots fired below the focus, the surface pattern spatially expands and sustains a far-range order. The localized interrupted and broken features were also observed due to the incubation effect of statically fired laser shots. This study finds that ablation in clod plasma seems a promising new concept to use for shaping and structuring surfaces of industry-accepted materials for electronic and photonic devices, such as solar-cells, detectors, large-area grating, and optical waveguides.

Prediction of the superimposed laser shot number for copper using a deep convolutional neural network.

Image-based deep learning (IBDL) is an advanced technique for predicting the surface irradiation conditions of laser surface processing technology. In pulsed-laser surface processing techniques, the number of superimposed laser shots is one of the fundamental and essential parameters that should be optimized for each material. Our primary research aims to build an adequate dataset using laser-irradiated surface images and to successfully predict the number of superimposed shots using the pre-trained deep convolutional neural network (CNN) models. First, the laser shot experiments were performed on copper targets using a nanosecond YAG laser with a wavelength of 532 nm. Then, the training data were obtained with the different superimposed shots of 1 to 1024 in powers of 2. After that, we used several pre-trained deep CNN models to predict the number of superimposed laser shots. Based on the dataset with 1936 images, VGG16 shows a high validation accuracy, higher sensitivity, and more than 99% precision than other deep CNN models. Utilizing the VGG16 model with high sensitivity could positively impact the industries' time, efficiency, and overall production.

Laser Removal of Cosmetic Eyebrow Tattoos with a Picosecond Laser

This current retrospective study, including 98 patients aged 21 to 71 years, aims to assess the safety and the efficiency of a picosecond 755 nm/532 nm laser in the removal of complex eyebrows tattoos. Patients were treated with a picosecond laser at 755 nm with fluences ranging from 0.69 to 6.37 J/cm2 and at 532 nm with a fluence of 0.64 or 1.12 J/cm2. Analyses of Variance (ANOVA, single factor) and comparison tests (F-test) were conducted. A total of 70 subjects finished the full treatment. An average of three laser sessions were necessary to achieve the patients’ objective (total removal, attenuation for redo, or correction). The number of sessions was significantly higher if cosmetic tattoos contained visible warm pigments (red, orange, yellow). A total of 18 patients experienced immediate grey discoloration, although this was not found to significantly influence the number of laser sessions. The main side effects were redness, swelling, and bleeding points. One patient experienced a bruise immediately after laser shots. This retrospective study has shown the picosecond laser to be safe and efficient in removing complex cosmetic tattoos. Further investigation is ongoing to assess optimal parameters for treating red and white pigments.

Quantification of pharmaceutical compounds in tissue and plasma samples using selective ion accumulation with multiple mass isolation windows.

Quantification of pharmaceutical compounds using matrix-assisted laser desorption/ionization (MALDI) mass spectrometry (MS) is an alternative to traditional liquid chromatography (LC)-MS techniques. Benefits of MALDI-based approaches include rapid analysis times for liquid samples and imaging mass spectrometry capabilities for tissue samples. As in most quantification experiments, the use of internal standards can compensate for spot-to-spot and shot-to-shot variability associated with MALDI sampling. However, the lack of chromatographic separation in traditional MALDI analyses results in diminished peak capacity due to the chemical noise background, which can be detrimental to the dynamic range and limit of detection of these approaches. These issues can be mitigated by using a hybrid mass spectrometer equipped with a quadrupole mass filter (QMF) that can be used to fractionate ions based on their mass-to-charge ratios. When the masses of the analytes and internal standards are sufficiently disparate in mass, it can be beneficial to effect multiple narrow mass isolation windows using the QMF, as opposed to a single wide mass isolation window, to minimize chemical noise while allowing for internal standard normalization. Herein, we demonstrate a MALDI MS quantification workflow incorporating multiple sequential mass isolation windows enabled on a QMF, which divides the total number of MALDI laser shots into multiple segments (i.e., one segment for each mass isolation window). This approach is illustrated through the quantitative analysis of the pharmaceutical compound enalapril in human plasma samples as well as the simultaneous quantification of three pharmaceutical compounds (enalapril, ramipril, and verapamil). Results show a decrease in the limit of detection, relative standard deviations below 10%, and accuracy above 85% for drug quantification using multiple mass isolation windows. This approach has also been applied to the quantification of enalapril in brain tissue from a rat dosed in vitro. The average concentration of enalapril determined by imaging mass spectrometry is in agreement with the concentration determined by LC-MS, giving an accuracy of 104%.

Single-shot detection of bacterial spores with Yb-laser-based CARS spectroscopy.

We present a system based on a high-energy femtosecond ytterbium laser seeding an optical parametric amplifier and a photonic crystal hollow core fiber (PCHCF) compressor for coherent anti-Stokes Raman scattering (CARS) spectroscopy. The PCHCF provides spectral broadening of the Stokes pulse which is then compressed to a duration matched to that of the pump pulse. In these conditions, the excitation efficiency of vibrational levels in the target molecules is largely improved, as the time gating effect due to the mismatch between the durations of the pump and Stokes pulses is avoided. Experiments are presented along with a theoretical model to quantify expected improvement of sensitivity. The system is used to detect bacterial spores deposited on a surface with a single laser shot at unprecedented signal-to-noise ratio.

Pulsed laser annealed rare earth doped TiO2 thin films for luminescence and sensing applications

Many research activities target functional luminescent materials based on metal oxides activated with trivalent rare earth ions. Specific applications necessitate optimization of material preparation, annealing and excitation-detection techniques. Hereby we utilized pulsed laser deposition to obtain thin (150 nm) TiO2 films containing 1at% of samarium (Sm) or neodymium (Nd) impurity ions. The effect of pulsed laser annealing (ArF excimer laser, wavelength 193 nm, pulse duration 20 ns) on their structural and luminescent properties was investigated. It was found that, compared to conventional thermal annealing at 700 °C, proper laser annealing (fluence 50 mJ/cm2, 5–15 shots) induced much better crystallization (nearly phase-pure anatase) along with respective improvement of host-sensitized trivalent rare earth fluorescence. The outcome significantly depends on the applied fluence and number of laser shots. Effects of under- and overannealing were witnessed (poor or mixed phase crystallization, weak luminescence and melting/dewetting of the film). A strong luminescence from optimally annealed samples was detected under excitation of 365 nm light emitting diode, which is favorable for potential applications of such thin films. As an example, trace oxygen sensing is demonstrated with the laser annealed TiO2:Sm film.