Ablation Products Research Articles

Study of synthesis dynamics of ceramic materials nanopowders at different processing modes by ultrafast laser pulses

The paper presents a developed experimental setup for the synthesis of spherical nanoparticles using different processing modes by exposure of femtosecond laser pulses in an argon atmosphere. Using the combined processing approach leads to both an increase in ablation process efficiency and an increase in the dispersion of particle size of the resulting fraction as a result of coagulation of ablation products due to prolonged stay in the discharge plasma. When processing is carried out in an electrostatic field, there is a close to linear growth in ablation process efficiency in the investigated range of laser pulse energy. In this case, compared to the treatment with only a laser beam without an electrostatic field the dispersion of particle size of the resulting fraction is reduced. The difference in efficiency between these modes is about 70% at pulse energy of 145 μJ.

Investigations on continuous-wave laser and pulsed laser induced controllable ablation of SiCf/SiC composites

To lay a foundation for the feasibility exploration of laser-induced ablation-assisted machining for SiCf/SiC composites, combined with numerical simulation and experiments, the laser-induced ablation mechanism of SiCf/SiC composites was studied, and the relationship between laser parameters and ablation depth was analyzed. The laser-induced ablation products of SiCf/SiC composites mainly consisted of recrystallized 3C-SiC and amorphous SiO2, which were powdery and porous. According to the stratification characteristic, the ablation products were divided into attached smoke dust layer, sublimate recrystallization layer, heat-affected layer, and unaffected layer from the surface to the inside of the material. By adjusting the laser parameters (significant factors were the scanning speed and the scanning spacing), the depth of laser-induced ablation was adjustable and controllable. The ablation depth was greater in continuous-wave (CW) mode due to the continuous energy input. Therefore, CW laser is more suitable for generating larger and various ablation depths to match various cutting allowances.

Four year evaluation of therapeutic hysteroscopy under procedural sedation in an outpatient clinic

ObjectiveDue to the evolution of hysteroscopic instruments, therapeutic hysteroscopic procedures are increasingly performed in an outpatient, office-based setting. The most important limiting factor of performing these hysteroscopic treatments is patient discomfort. Procedural Sedation Analgesia (PSA) decreases patient discomfort and anxiety. The main goal of this study is to determine safety, feasibility and patient satisfaction of therapeutic hysteroscopy performed under procedural sedation in an outpatient clinic. Our second objective was to compare 9 mm scopes with smaller diameter scopes. Study designAll consecutive patients suitable for procedural sedation and scheduled for a therapeutic hysteroscopy in the outpatient clinic were prospectively included from February 2014 to November 2018 in a teaching hospital in the Netherlands. A variety of therapeutic hysteroscopies procedures was performed including myomectomy, removal of retained products of conception and endometrial ablation. Therapeutic hysteroscopes with 3.8 mm, 5 mm and 9 mm diameter were used. In all selected women procedure time, admission time, pain scores, anaesthesiologic and procedural complications were assessed. All women received a questionnaire on patient satisfaction. ResultsIn total 455 patients underwent a therapeutic hysteroscopy. Median procedure time was 11 min (2–63 min) and median admission time was 130 min (30–480 min). Median pain score according to the visual analog scale (VAS) before, during and after procedure were respectively 0 (0–10), 0 (0–4) and 0 (0–9). Anaesthesiologic complication rate was 4.4 %, all minor. Procedural complications consisted of infection postoperatively (0.4 %), excessive blood loss during procedure (0.6 %) and perforation (0.4 %). Procedure was incomplete in 3.3 % of all procedures. Patient satisfaction was high, as 96 % of the women were satisfied. No differences were found in pain scores, VAS 0 versus 1 after the procedure, between 3.8 or 5 mm and 9 mm scopes. ConclusionIt is safe and feasible to perform a therapeutic hysteroscopy under procedural sedation in an outpatient setting, with low pain scores and a high degree of patient satisfaction, also when large diameter instruments are used.

Experimental and quantum-chemical characterization of heavy carbon subchalcogenides: Infrared detection of SeC3Se

High-resolution infrared studies of laser ablation products from carbon-selenium targets have revealed a new vibrational band at 2057 cm−1 that is identified as the ν3 vibrational fundamental of the SeC3Se cluster. Because of the rich isotopic composition of selenium and the heavy nuclear masses involved, the vibrational band shows a relatively compact and complex structure despite the simple linear geometric arrangement. Overall, rotational-vibrational lines of six isotopologues could be assigned and fitted permitting the derivation of an accurate selenium-carbon bond length.Spectroscopic analysis has been greatly supported by high-level quantum-chemical calculations of the molecular structure and the harmonic and anharmonic force fields performed at the CCSD(T) level of theory. Scalar-relativistic effects on the molecular structure were also considered but found of little importance.

Predominant reaction products and dielectric breakdown properties of gas mixtures consisting of SF6 and ablation products of C2F4/BN in the temperature range of 300–3000 K

For a high voltage SF6 circuit breaker equipped with a boron nitride (BN)-filled polytetrafluoroethylene ((C2F4)) nozzle, the predominant reaction products in a high-temperature SF6 mixture with vapor decomposition of C2F4 and BN at temperatures of 300–3000 K are determined based on calculations of equilibrium composition. The calculation is performed by considering the molecular products obtained by chemical reactions with boron atoms (e.g. BN, BS, BC, BF, BF2 and BF3), nitrogen atoms (e.g. N2, N3, CN, NS, NF, NF2 and NF3) and carbon atoms (e.g. CS, CS2, C2F4, CF2, CF3 and CF4). The results obtained for the C2F4–BN molar fraction of 20%–80% reveal that BF3, N2 and CF4, the molecules originating from the nozzle material, are produced at high molar fractions over a range of 300–3000 K. Such an evaluation of the gas composition allows the derivation of a reduced collision ionization coefficient α/N and a reduced electron attachment coefficient η/N of the gas, considering various electron impact processes such as BF3 + e BF2 + F− and CF4 + e CF3 + F−. The evaluation subsequently enables us to determine a critical reduced electric field strength causing . The results suggest that the decomposed C2F4–BN mixture at of 80% causes the reduction of to 110 Td in the range of 1000–2000 K at a gas pressure of 1.0 MPa. This strength is 20 Td lower than that determined separately for the SF6 gas mixture with only 80% C2F4 vapor decomposition, because of the CF4 molar fraction reduction in the SF6/C2F4–BN mixture.

Femtosecond laser micromachining of thin-film coatings in a high-voltage electrostatic field

The work is devoted to the problem of forming micro- and nanoscale elements topologies of high-resolution by means of controlled treatment of material surface with ultrashort laser pulses. The technology of processing thin-film coatings by the method of selective laser ablation is described. The possibility of using a high-voltage electrostatic field for collecting ablation products and preventing their deposition on the surface of formed microstructures is shown.

Optimizing pulsed-laser ablation production of AlCl molecules for laser cooling.

Aluminum monochloride (AlCl) has been proposed as a promising candidate for laser cooling to ultracold temperatures, and recent spectroscopy results support this prediction. It is challenging to produce large numbers of AlCl molecules because it is a highly reactive open-shell molecule and must be generated in situ. Here we show that pulsed-laser ablation of stable, non-toxic mixtures of Al with alkali or alkaline earth chlorides, denoted XCln, can provide a robust and reliable source of cold AlCl molecules. Both the chemical identity of XCln and the Al : XCln molar ratio are varied, and the yield of AlCl is monitored using absorption spectroscopy in a cryogenic gas. For KCl, the production of Al and K atoms was also monitored. We model the AlCl production in the limits of nonequilibrium recombination dominated by first-encounter events. The non-equilibrium model is in agreement with the data and also reproduces the observed trend with different XCln precursors. We find that AlCl production is limited by the solid-state densities of Al and Cl atoms and the recondensation of Al atoms in the ablation plume. We suggest future directions for optimizing the production of cold AlCl molecules using laser ablation.

Динамика теплового излучения, сопровождающего конденсацию паров вольфрама в газообразном и сверхтекучем гелии

In this work the cooling of the products of pulsed laser ablation of a tungsten target in vacuum, helium gas and in liquid superfluid helium was investigated by pyrometric measurements. It was shown that quantitative measurements of the characteristics of thermal emission make it possible to clarify the features of the mechanisms of the condensation processes of nanostructures in these media. The obtained data were used to calculate the cross sections of the emitting particles. It was shown that in vacuum mainly submicron particles emit, while in superfluid helium - nanoparticles. The results obtained are confirmed by the data of electron microscopy.

Pyrometric investigation of nanoparticles condensation process in gaseous and superfluid helium

The work is devoted to the study of thermal radiation accompanying the condensation of products of pulsed laser ablation of a tungsten target in vacuum, superfluid and gaseous helium. Pyrometric measurements have shown that the radiation characteristics depend on the medium. The obtained data imply that the sources of radiation in vacuum and gas are predominantly submicron particles, while in superfluid helium (He II) they are nanometer particles. These conclusions have been confirmed by electron microscopy data.

Ablation properties of Cf/SiCp-Al self-transpiration cooling composites

The high-temperature application of Cf/SiCp-Al composites requires the evaluation of the self-transpiration cooling behaviour and ablation property during high temperature erosion. The 3D needle-punched Cf/SiCp-Al composites were prepared through a powder slurry injection technique and a vacuum pressure infiltration method. An erosion test was conducted by oxy-acetylene flame. The microstructure evolution was studied by SEM and EDS. The anti-ablation performance and transpiration cooling behavior underlying the 3D needle-punched Cf/SiCp-Al composites at different ablation times were studied. The obtained results showed that the self-transpiration Cf/SiCp-Al composites significantly reduced the ablation surface temperature. The ablation products Al2O3 and SiO2 provided good self-sealing protection for Cf/SiCp skeleton during the ablation process. The Cf/SiCp-Al composites exhibited a better anti-ablation performance compared with the widely used C/C composite.

On the anthropogenic and natural injection of matter into Earth’s atmosphere

Every year, more and more objects are sent to space. The increasing number of countries with space programs, advancing commercialization, and ambitious satellite constellation projects raise concerns about space debris and the increase of mass flux into the atmosphere due to deorbiting of satellites and rocket bodies. A comparison of this anthropogenic influx to the natural influx due to meteoroids is presented giving detailed information about the mass, composition and ablation of the entering matter. Currently, anthropogenic material does make up about 2.8% compared to the annual injected mass of natural origin. For two different future scenarios considering planned and already partially installed large satellite constellations this fraction increases to nearly 13%, respectively 40%. For these cases, the anthropogenic injection of several metals prevails the injection by natural sources by far. Considering different ablation products, we find that the anthropogenic injection of aerosols into the atmosphere increases disproportionately. Today, they make up about 1% compared to the injected aerosol mass of natural origin, increasing to 30% and 94% for the two future scenarios, respectively. Considering the injection of atoms, the natural injection is dominant by far. For the two future scenarios, the anthropogenic injection is only at 5%, respectively 15% compared to the annual natural atom injection. The predicted strong increase in anthropogenic injection will make it significant in comparison to the natural injection which can have yet unknown effects on Earth’s atmosphere and the terrestrial habitat.

Ablative Laser Processing of Metals and Dielectrics in an Electrostatic Field

The work considers the task of synthesis of highly dispersed spherical powder granules by laser ablation method. To improve the geometry of synthesized particles and increase the process productivity, an electrostatic system for collecting ablation products was used, which allows the formed particles to leave the area of laser irradiation without being subjected to excessive exposure to a heat source. Using an external field makes particle motion predetermined, ensuring their adhesion to the electrodes. The paper shows the experimental results on the removal of ablated particles, as well as an assessment of the effectiveness of electrostatic field for accelerating particle motion.

Association Between Meteor Radio Afterglows and Optical Persistent Trains

AbstractThis paper presents the first observed association between meteor radio afterglows (MRAs) and persistent trains (PTs) and provides the first evidence of a link between these two phenomena. Coobservations of four meteor trails (trains) from the Long Wavelength Array (LWA) telescopes in New Mexico and the Widefield Persistent Train (WiPT) camera associate the long‐lasting (tens of seconds), self‐generated radio emission known as MRAs with the long‐lasting (tens of minutes) optical emissions known as PTs. Each of the four MRAs presented in this paper were spatially and temporally coincident with a PT. In one case, the MRA follows a relatively small (≤400 m × 400 m) noticeably bright region (knot) of emission within the PT, whereas the other three cases were associated with broader regions of PT activity. As PTs are thought to be driven by exothermic chemical reactions between atmospheric oxygen and ablation products, we show that the same reactions, specifically those involving anions, may produce the necessary suprathermal electrons to power MRAs. We show that only one part in ∼1010 of the available power needs to be converted to radio emission in order to produce a typical MRA.

Effect of initial γ-irradiation on infrared laser ablation of poly(vinyl alcohol) studied by infrared spectroscopy

The effect of initial γ-irradiation of poly(vinyl alcohol) (PVA) on the kinetics of polymer ablation under CO2 laser irradiation was studied using infra-red spectroscopy. The rate of laser ablation rapidly decreases with increasing time of laser ablation up to 10 s. Initial γ-irradiation of a dose up to 100 kGy reduces the rate of the laser ablation, just like the effect of laser exposure. The number of OH and CH groups decrease in PVA both with laser irradiation and with γ-irradiation. The number of OH groups decreases more under laser irradiation. Unsaturated bonds are formed in γ–irradiated PVA on the surface of the crater formed by laser ablation of the polymer that has undergone radiolysis. Increasing the dose of initial γ-irradiation from 100 to 2300 kGy leads to an increase in the intensity of the IR bands of the unsaturated bonds. The number of IR bands in the spectra of the laser ablation crater of PVA does not change with the dose of initial γ-irradiation. A dose of radiolysis of 3500 kGy significantly changes the IR spectra of both the ablation crater and the coating formed from the ablation products. Many bands characteristic for PVA are no longer present and the intensities of bands corresponding to unsaturated bonds are increased. A computational model for loss of water and ketone formation was developed for PVA and PVA including a diol using G3(MP2). The highest activation energy barrier step in the decomposition reaction was formation of the enol species and water was shown to catalyze all decomposition steps.

Nanosecond laser ablation of a metallic glass in water: a high time-resolved imaging study

ABSTRACT We use a state-of-the-art, ultrafast camera to probe the nanosecond pulse laser ablation of a metallic glass target in water. The laser-induced plasma of metallic glass is captured for the first time. We further observe a series of shock waves in water and the cavitation bubble on the target surface. The shock waves inherit the rapid expansion of the plasma, satisfying the momentum conservation. But the cavitation bubble stems from the nucleation of the surrounding water due to the heating of the plasma. We find that the bubble growth deviates from the Rayleigh-Plesset theory. The primary reason for this deviation is the effect of ablation products due to the temporal overlap between the explosive boiling and the bubble dynamics. Our findings provide a fundamental understanding of underwater laser ablation of metallic glasses, which is an important step to forward such ablation-related applications.

Mechanism of Nickel Phyllosilicate Formation by Laser Ablation in Liquid

One-step synthesis of nickel-phyllosilicate (Ni-PS) nanocomposites was achieved using a femtosecond-reactive laser ablation in liquid (fs-RLAL) technique. The focusing of intense femtosecond laser pulses onto a silicon wafer immersed in aqueous nickel nitrate generated Ni-PS with high Ni loading in excess of 20 wt % under alkaline pH conditions. Analysis of the dissolved species in solution present after laser processing revealed that silicic acid was the key dissolved ablation product that reacted with the nickel nitrate to form the Ni-PS under alkaline conditions. When the solution was below pH 7, no silicic acid was generated from ablation, and consequently, no Ni-PS was formed in the dried product. The mechanism of Ni-PS formation from fs-RLAL of a silicon wafer immersed in aqueous nickel nitrate solutions is discussed. On the basis of this mechanism, it is expected that the fs-RLAL method will be capable of generating a variety of metal-phyllosilicates from different metal salt precursors.

Ultrafast laser ablation of silver targets in miscible and immiscible liquid mixtures

• Effect of polar-polar miscible liquids on ablation. • Effect of polar-nonpolar immiscible liquids on ablation. • Influence of liquid parameters on silver nanoparticles and nanostructures. In this article we report the results obtained from ultrafast laser ablation of silver targets immersed in polar/polar miscible and polar/non-polar immiscible combinations of liquids with laser pulses of ∼2 ps duration. Former combination included acetone and water while the latter combination was toluene and water. The prepared silver nanoparticles in pure acetone, pure water (double distilled) were compared with the silver nanoparticles fabricated in acetone–water (double distilled) mixture. Similarly, synthesized silver nanoparticles in pure toluene, pure water were compared with the silver nanoparticles fabricated in toluene-water mixture. The TEM images of Ag NPs generated in acetone demonstrated that average size of Ag nanoparticles fabricated in acetone, water, and double distilled water–acetone mixture were ∼4.5 ± 1.8 nm, ∼16 ± 4 nm, and 5 ± 1.7 nm, respectively. In the case of double distilled water-toluene combination, formed silver nanoparticles were trapped inside the graphitic matrix. Obtained morphologies and average sizes of silver nanoparticles in polar/polar miscible and polar/non-polar immiscible combinations demonstrated the effect of the difference in the formatted cavitation bubble (CB). In general, products of ablation are determined by the dynamics of CB and its oscillations those depend on the intrinsic behaviour of aqueous medium of interest.

Formation of CrxCyOz Coatings under Laser Treatment of Chromium Carbide Ceramics

The effect of the pulsed laser irradiation in air on Cr23C6 ceramic with Cr3C2 and Cr7C3 additives has been studied. It is established that the main process occurring in the zone of laser radiation is the melting of the ceramic surface of chromium carbide and the formation of a crater. This process is accompanied by the ejection of melt droplets from the crater zone and the dissociation of chromium carbides. As a result, the crater area is enriched in such ablation products as Cr, C, CO, and CO2. Reduction of hydrogen in the crater zone and neighboring areas leads to slowing down of the rate of oxidation processes, and the presence of ablation products such as Cr and C atoms promotes the process of synthesis of oxycarbides CrxCyOz (x ≈ 0.3–0.8, y ≈ 0.03–0.3, z ≈ 0.61–0.26) in the gas phase. Emission of the newly formed products of ablation from the crater and their distribution to the neighboring areas is accompanied by coagulation of nanoparticles into clusters. Depending on the length of flight of nanoclusters through different temperature zones and temperature of the deposition surface, oxycarbides with different morphology are formed: from islets (like fractal clusters) to film ones. The deposited ablation products are characterized by the signs of particle size “separation.” This makes it possible to create films of a given type and purpose. The passage of particles of different sizes through a gaseous medium containing oxygen is accompanied by the oxidation of oxycarbides to Cr2O3.

Detecting Laser-Volatilized Salts with a Miniature 100-GHz Spectrometer.

Rotational transitions are unique identifiers of molecular species, including isotopologues. This article describes the rotational detections of two laser-volatilized salts, NaCl and KCl, made with a miniature Fourier transform millimeter-wave (FTmmW) cavity spectrometer that could one day be used to measure solid composition in the field or in space. The two salts are relevant targets for icy moons in the outer solar system, and in principle, other molecular solids could be analyzed with the FTmmW instrument. By coupling the spectrometer to a collisionally cooling laser ablation source, (a) we demonstrate that the FTmmW instrument is sensitive enough to detect ablation products, and (b) we use the small size of the FTmmW cavity to measure ablation product signal along the carrier gas beam. We find that for 532 nm nanosecond pulses, ablated molecules are widely dispersed in the carrier-gas jet. In addition to the miniature spectrometer results, we present several complementary measurements intended to characterize the laser ablation process. For pulse energies between 10 and 30 mJ, the ablation product yield increases linearly, reaching approximately 1012 salt molecules per 30 mJ pulse. Using mass spectrometry, we observe Li+, Na+, and K+ in the plumes of ablated NaCl, KCl, and LiCl, which implies dissociation of the volatilized material. We do not observe salt ions (e.g., NaCl+). However, with 800 nm femtosecond laser pulses, the triatomic ion clusters Li2Cl+, Na2Cl+, and K2Cl+ are produced. Finally, we observe incomplete volatilization with the nanosecond pulses: some of the ejecta are liquid droplets. The insights about ablation plume physics gleaned from these experiments should guide future implementations of the laser-volatilization technique.

Investigating the Effects of Different Liquid Environments on the Characteristics of Multilayer Graphene and Graphene Oxide Nanosheets Synthesized by Green Laser Ablation Method

The present study is dedicated to investigate the effects of ablation environment on the characteristics of carbon nanostructures synthesized by pulsed laser ablation method; particularly for graphene and Graphene Oxide (GO) nanosheets. The beam of a Q-switched Nd:YAG laser of 532 nm wavelength at 7 ns pulse width and 0.5 J/cm2 fluence is employed to irradiate the similar graphite targets as the constant experimental conditions while liquid nitrogen and 0.04 M Cetyltrimethylammonium bromide (CTAB) solution are applied as the variable liquid environments. Also, characteristics of the final ablation products are investigated in detail via UV–Vis-NIR spectroscopy, X-ray diffraction pattern, Raman scattering spectrum, and Transmission electron microscopy (TEM). XRD and UV–Vis-NIR analysis exhibit the oxidation of graphene nanosheets in CTAB solution owing to the presence of oxygen molecules in ablation environment. Raman results indicate that the produced graphene nanosheets in liquid nitrogen medium have represented many layers, low level of defects and large SP2 domains size, while the GO nanosheets which are produced in CTAB solution have represented higher level of defects and smaller SP2 domains size. Furthermore, the characteristic features in Raman spectra also propose that there are two different graphene materials: AB stacked multilayer graphene and disoriented or randomly stacked multilayer GO nanosheets. The experimental results suggest that the characteristics of liquid environment such as nonpolar or cationic properties are the most effective parameters in the mass rate of carbon nanoparticles production. Our results provide useful guidance towards the production of carbon nanostructures with the desired attributes.