Ablation Plume Research Articles

Comparison of plume expansion in femtosecond laser ablation on oxidized and non-oxidized Sm surfaces

Time development of Sm+ and Sm ablation plume produced by the femtosecond laser irradiation has been investigated. The two-dimensional spatial profiles of Sm and Sm+ emitted from oxidized and non-oxidized Sm surface were visualized using a planar laser-induced fluorescence method. It was observed that the flow velocity of Sm+ is much faster than that of Sm plume in both surfaces. The plumes from the oxidized Sm surface show higher velocity than that from non-oxidized surface, which is originated by the small electric conductivity at the surface. Expansion property observed for Sm+ and Sm plume in the oxidized Sm surface ablation implies the formation of the Knundsen layer nearby the surface. Meanwhile, continuous emission of Sm indicates the large contribution of heating effect to emission process at the non-oxidized surface. We conclude that the fsLA process strongly depends on the electric property of the ablated surface and the heating effect contributes to the particle emission process on the conductive material surface.

Ablative Impulse Characteristics of Polyacetal with Repetitive CO2 Laser Pulses

Impulse characteristics for a polyacetal target repetitively irradiated with pulses from a transversely excited atmospheric CO 2 laser were experimentally investigated. About 10-J laser pulses were repetitively irradiated up to 110 times onto a 6.6- or 8.6-mm-diam spot on the target, which was mounted on a torsion-type impulse balance. In the first several laser pulses, the impulse and ablation rate were strongly influenced by the initial conditions of the target surface. After ten cleaning pulses, 100 pulses were irradiated in various burst modes. Successive laser pulses in a burst were irradiated at a repetition frequency of 50 Hz. The time interval between successive bursts was greater than 3 min. The momentum coupling coefficient C m was almost independent of the burst mode. With a fluence of 18.8 J/cm 2 , C m gradually increased with an increasing total number ofpulses, reaching 220 μN. s/J at an ambient pressure of 10 -2 Pa and 145 μN - ·s/J in the atmosphere. When the fluence was 31.8 J/cm 2 , C m began to decrease after about 50 pulses. C m was smaller for a smaller spot diameter. Those impulse characteristics were closely associated with target surface morphology and fluid dynamics of the ablation plume and the ambient air.

Growth of ZnO nanoparticles and nanorods with ultrafast pulsed laser deposition

In this work, we study the application of ultrafast pulsed laser deposition (PLD) in ZnO nanomaterial synthesis, including nanoparticles and nanorods. PLD using long pulse (nanosecond) lasers has been widely used as a method for growing prototype materials. The recently-emerged ultrafast PLD is expected to be able to overcome the problem of large liquid droplet formation. Using near infrared and femtosecond laser pulses in ablation, we first characterize the ablation plume using a Langmuir probe and plasma optical emission spectroscopy. We then examine the structural properties of the nanoparticles generated during low-fluence ablation. Finally, we demonstrate that using nanoparticle aggregates as templates, assisted by plume-excited nitrogen radicals at a high fluence, high quality ZnO nanorods can be grown free of metal catalysts.

Mass and kinetic energy distribution of the species generated by laser ablation of La0.6Ca0.4MnO3

The mass distributions of the species generated by laser ablation from a La0.6Ca0.4MnO3 target using laser irradiation wavelengths of 193 nm, 266 nm and 308 nm have been investigated with and without a synchronized gas pulse of N2O. The kinetic energies of the species are measured using an electrostatic deflection energy analyzer, while the mass distributions of the species were analyzed with a quadrupole mass filter. In vacuum (pressure 10−7 mbar), the ablation plume consists of metal atoms and ions such as La, Ca, Mn, O, LaO, as well as multiatomic species, e.g. LaMnO+. The LaO+ diatomic species are by far the most intense diatomic species in the plume, while CaO and MnO are only detected in small amounts. The interaction of a reactive N2O gas pulse with the ablation plume leads to an increase in plume reactivity, which is desired when thin manganite films are grown, in order to incorporate the necessary amount of oxygen into the film. The N2O gas pulse appears to have a significant influence on the oxidation of the Mn species in the plume, and on the creation of negative ions, such as LaO−,O− and O 2 − .

Cluster growth in an ablation plume propagating through a buffer gas

A phenomenological mixed-propagation model that describes the expansion of an ablation plume through a buffer gas is introduced. Selected experiments including LaMnO3 and tin ablation in oxygen, as well as tungsten ablation in argon, are analysed. For given ablation conditions the expansion parameters required to model the growth of clusters in the expanding plasma plume are deduced and the average asymptotic size of the clusters is calculated and compared (for tungsten) with the size of clusters measured by transmission electron microscopy.

Pulsed laser deposition of TiO2: diagnostic of the plume and characterization of nanostructured deposits

Promising applications of TiO2 nanostructures include the development of optical devices, sensors, photocatalysts and self-cleaning coatings. In view of their importance, research on the synthesis of nanosized TiO2 is a particularly active field. In this work we report on the investigation of the effect of laser irradiation wavelength (Q-switched Nd:YAG laser at 532, 355 and 266 nm), the temperature of the substrate and the atmosphere of deposition (vacuum, Ar and O2) that are suitable for obtaining nanostructured deposits from TiO2 sintered targets. The ablation plume emission is characterized with spectral and temporal resolution by optical emission spectroscopy (OES), while the surface morphology and chemical states of the material deposited on a Si (100) substrate are examined by environmental scanning electron microscopy (ESEM) and atomic force microscopy (AFM) and by X-ray photoelectron spectroscopy (XPS), respectively. Deposits with nanostructured morphology with grain size down to 40 nm and keeping the stoichiometry of the targets were obtained at high temperature, while the highest concentration of particulates was observed at the longest laser wavelength of 532 nm on a substrate heated up to 650°C. In situ characterization of the ablation plume, carried out by OES, indicated the presence of emissions assigned to Ti I, Ti II and O I.

Modelling the propagation of an ablation plume in a gas

Pulsed laser ablation gives rise to an expanding microplasma that consists of the evaporated species, energised by the photons in the tail of the laser pulse. The values of the process parameters, including laser energy density, wavelength and pulse duration, besides the presence of a specific buffer gas at a given pressure, affect the expansion of the ablation plasma plume. After a discussion of the analytical models available in the literature to describe the propagation of an ablation plume, it is shown that by a combined-propagation model, based on a modification of the diffusion and the drag models, the characteristics of plume expansion can be predicted. Model parameters are directly extracted from the available experimental parameters. By combined-propagation model, the expansion of ablation plumes from elemental targets of silicon, silver, tin and tungsten, vapourised in inert gases and in oxygen at different pressures is analysed.

Influence of the atomic mass of the background gas on laser ablation plume propagation

A combination of time-of-flight ion probe measurements and gas dynamical modeling has been used to investigate the propagation of a laser ablation plume in gases of different atomic/molecular weight. The pressure variation of the ion time-of-flight was found to be well described by the gas dynamical model of Predtechensky and Mayorov (Appl. Supercond. 1:2011, 1993). In particular, the model describes how the pressure required to stop the plume in a given distance depends on the atomic/molecular weight of the gas, which is a feature that cannot be explained by standard point-blast-wave descriptions of laser ablation plume expansion in gas.

Correlation between plasma expansion and damage threshold by femtosecond laser ablation of fused silica

We experimentally investigated the ultrafast ablation of fused silica under 100 fs laser pulses at 800 nm in vacuum. The ablation plume dynamics was monitored by plasma fast imaging and time- and space-resolved optical emission spectroscopy (OES). We used optical microscopy to determine the ablation threshold and rate in multi-shot operation at 100 Hz.We found that, unlike metal ablation, the plasma generated by femtosecond laser pulses from a fused silica target had only one ‘main’ component. This evidence was supported by the results of OES. The characteristic expansion velocity of this unique component was about one order of magnitude higher than the velocity of the fast plume component observed during metal ablation. We identified in optical emission spectra Si and O neutral atoms only, characterized by very different expansion velocities. In contrast to metal ablation, the ‘slow’ plasma component usually assigned in the literature to optical emission from nanoparticles was not detected by either plasma fast imaging or OES even for the highest laser fluence used in our experiments. The influence of laser fluence on both plasma expansion and ablation rate was investigated. We considered that the ablation mechanism in this case was dominated by thermal material removal processes.

Study on dynamics of ablation plumes produced by fusion products in laser fusion liquid wall chamber

An integrated ablation simulation code DECORE (DEsign COde for REactor) has been developed to analyze characteristics of plumes produced by ablation, and also an integrated code for condensation of a plume DECORE-condensation has been developed to clarify the ability of the chamber clearance. Characteristics of a plume produced by ablation in liquid wall chamber of KOYO-fast have been analyzed. A plume produced by ablation moves with velocities of a few km/s. Formation of clusters in a plume with hydrodynamic motion is carried out. Radius of clusters in a plume in liquid wall chamber of KOYO-fast is mainly from 25 nm to 35 nm.

Langmuir probe investigation of surface contamination effects on metals during femtosecond laser ablation

Characterisation of the plasma plume induced by femtosecond laser–metal interactions has been carried out using a Langmuir probe. A double peak distribution of ablated ions and electrons has been recorded during time of flight (TOF) experiments for three metals studied (Ag, Cu and Ni). The first peak which occurs earliest in time is attributed to a surface layer of contaminants on the metal surface as it is shown to disappear after several laser shots. The re-growth of this peak, thought to be due to a recontamination process on the surface of the metal, is the subject of this paper. Two re-contamination mechanisms were considered; adsorption of contaminants from the ambient gas, and surface diffusion effects from the surrounding contaminants. Re-contamination rates for Ag, Cu and Ni were studied under two distinct gas pressures to investigate the contamination effects from the ambient. Effects arising from surface diffusion were investigated by raising the temperature of the metal sample to increase the surface mobility of the contaminants. The total contribution of contamination species present in the ablation plume was estimated by conducting angular distribution measurements of the plume. Surface diffusion of the surrounding contaminants was found to be the dominant recontamination process.

Correlation between ablation efficiency and nanoparticle generation during the short-pulse laser ablation of metals

The mechanisms of material ablation and nanoparticle generation from metal samples exposed to intense short laser pulses are experimentally investigated. We performed measurements of the ablated volume using optical microscopy and the analysis of the ablation plume by fast imaging. The results confirm the existence of two distinguished ablation regimes as a function of the laser fluence, and give a deeper insight in the involved physical mechanisms. Thus, both regimes are found to be related to the relative amount of atoms and nanoparticles within the plume. Comparing the results obtained for copper and gold, it is possible to determine the influence of electron-lattice coupling on the sample heat regime and the resulting plume properties.

Correlation between ablation efficiency and nanoparticle generation during the short-pulse laser ablation of metals

The mechanisms of material ablation and nanoparticle generation from metal samples exposed to intense short laser pulses are experimentally investigated. We performed measurements of the ablated volume using optical microscopy and the analysis of the ablation plume by fast imaging. The results confirm the existence of two distinguished ablation regimes as a function of the laser fluence, and give a deeper insight in the involved physical mechanisms. Thus, both regimes are found to be related to the relative amount of atoms and nanoparticles within the plume. Comparing the results obtained for copper and gold, it is possible to determine the influence of electron-lattice coupling on the sample heat regime and the resulting plume properties.

Determination of carbon in soil by laser spectral analysis

We have used a combination laser/electrospark method for fast determination of carbon content in soil. Excitation of the spectra is carried out both directly in a laser ablation plume and when a pulsed electric discharge is applied to it. We have plotted a calibration curve that is linear for the major concentration range of practical importance for the analyte element, all the way up to 8.6%. The carbon detection limit for the combination discharge approach is 0.07%. We have analyzed the ratio of the nitrogen and carbon contents, and also the hydrogen and carbon contents as a function of the carbon concentration in the studied soils samples.

Propagation of a femtosecond pulsed laser ablation plume into a background atmosphere

We investigate the effects of ambient gas on the expansion dynamics of laser plume produced during femtosecond laser ablation of a metallic target. We studied experimentally plume propagation for ambient air pressure ranging from 10−6to50mbar, observing that the atomic and nanoparticles plume components experience different effects. We interpret these results with a simplified model of the plume front propagation, which is able to fully reproduce the main experimental features. Our results allow us to estimate quantitatively the nanoparticles plume content (up to about 80%), and can help identifying optimal conditions of nanoparticles deposition for thin films production.

Plasma interactions in ion beam assisted pulsed laser deposition of Al-O-N films

Interactions between plasmas produced by a nitrogen ion beam source and the pulsed laser ablation of an Al2O3 target were studied for the growth of Al-O-N films. Plasma fluxes from both sources were intersected on the substrate surface in a typical arrangement for ion beam assisted pulsed laser deposition (IBPLD). Plasma emission imaging and spectroscopic analyses were performed in real time, using laser pulses for analysis synchronization while varying the N2 background pressure in the range from 0.08 to 4 Pa. This study was focused on the detection of temporal and spatial plasma distributions, excitation states, and chemical reactions during the IBPLD process which were not present when operating each of the plasma sources separately. Two significant plasma interaction effects were discovered. One was the production of atomic N and O in the near-substrate region, resulting in the formation of NO molecules which then reacted with Al to form Al-O-N. Another was the formation of short-lived plasma channels connecting ion beam and laser-ablated plasmas, which was observed in the 2–4 Pa pressure regime. These channels resulted in plasma bending and shifting from the substrate surface and affected film composition. These findings suggest that the interaction of ion beam and laser ablation plumes in IBPLD might considerably affect plasma chemistry, excitation states, and spatial distribution, thus providing opportunities for the control of deposited film properties.

Solid phase formation of silicon nanocrystals by bulk ultrafast laser-matter interaction

Ultrashort pulse laser interaction with silica-silicon interfaces is presented as a means for all-solid-phase formation of high-purity silicon nanoparticles in the absence of ablation plumes or any substrate intermixing with surfaces in ambient air. Transmission electron microscopy and Raman spectroscopy provide definitive evidence for creation of nanocrystals in the silica host, while compressive stress in the silicon substrate corroborates the formation of optical waveguides parallel to the tracks.

High resolution selective multilayer laser processing by nanosecond laser ablation of metal nanoparticle films

Ablation of gold nanoparticle films on polymer was explored using a nanosecond pulsed laser, with the goal to achieve feature size reduction and functionality not amenable with inkjet printing. The ablation threshold fluence for the unsintered nanoparticle deposit was at least ten times lower than the reported threshold for the bulk film. This could be explained by the combined effects of melting temperature depression, lower conductive heat transfer loss, strong absorption of the incident laser beam, and the relatively weak bonding between nanoparticles. The ablation physics were verified by the nanoparticle sintering characterization, ablation threshold measurement, time resolved ablation plume shadowgraphs, analysis of ablation ejecta, and the measurement and calculation of optical properties. High resolution and clean feature fabrication with small energy and selective multilayer processing are demonstrated.

Dynamical Study of Femtosecond-Laser-Ablated Liquid-Aluminum Nanoparticles Using Spatiotemporally Resolved X-Ray-Absorption Fine-Structure Spectroscopy

We study the temperature evolution of aluminum nanoparticles generated by femtosecond laser ablation with spatiotemporally resolved x-ray-absorption fine-structure spectroscopy. We successfully identify the nanoparticles based on the L-edge absorption fine structure of the ablation plume in combination with the dependence of the edge structure on the irradiation intensity and the expansion velocity of the plume. In particular, we show that the lattice temperature of the nanoparticles is estimated from the L-edge slope, and that its spatial dependence reflects the cooling of the nanoparticles during plume expansion. The results reveal that the emitted nanoparticles travel in a vacuum as a condensed liquid phase with a lattice temperature of about 2500 to 4200 K in the early stage of plume expansion.

Solid structure formation during the liquid/solid phase transition

This review examines six different mechanisms of forming solid structures by freezing: solidification driven extrusion (SDE), hydrodynamic sputtering, laser-induced periodic surface structures (LIPSS), capillary waves, the Mullins–Sekerka instability, and laser zone texturing. Particular emphasis is placed on how these mechanisms relate to structures formed after melting of surfaces with laser irradiation, even though several of these mechanisms operate also for more conventional melts. The Bally–Dorsey model of SDE explains a mechanism for making spikes of materials that expand upon melting and that scales from the centimeter regime down the nanoscale. Capillary waves are often said to “cause” or be “responsible for” the formation of structures with periodicities Λ ranging anywhere from the wavelength of the incident light to over 10× the wavelength. Here it is shown that while capillary waves formed in conjunction with femtosecond to nanosecond pulsed laser irradiation above the melting threshold support structures with 150 nm ⩽ Λ ⩽ 5 μm, they do not cause the structures to form and some other stimulus is required to select the dominant capillary wave. Capillarity actually inhibits the formation of the smallest structures. Features with larger periodicities can be formed during laser irradiation but they require mass transport that is achieved by, e.g., thermocapillarity or the pressure of the laser ablation plume.