Laser Ablation Of Solids Research Articles

Visualization of surface transformations during laser ablation of solids by femtosecond pump–probe time-resolved microscopy

A femtosecond time-resolved microscope (fs-TRM) based on pump–probe excitation has been used to follow the dynamic of the processes occurring during laser–matter interaction, from initial surface alterations to final solidification through transient melting. The time-resolved microscope described in the manuscript has been designed to allow a precise control of the excitation beam to cover ranges below and above the plasma formation energy, and a large temporal variation in the pump–probe delay to include the different timescales of the different processes occurring up to the plasma formation. The microscope has been demonstrated to be robust and allows the subpicosecond monitoring of laser ablation single-shot events, of importance in the analysis of ultra thin layers, or biological tissues.The fs-TRM excites (pump) the sample with 35-fs laser pulses at 800nm and follows the processes by a second (probe) beam at 400nm. The relative delay between both beams allows the acquisition of pictures with a temporal resolution of 200fs up to 3ns after the reaching of the pump pulse. In the ablative regime near the ablation threshold, transient surface reflectivity patterns (dynamic Newton fringes) are observed from a ps to ns time-scale. The timescale and number of such rings are affected by the fluence value. Significant differences between metals (Al, Cu and Sn), semiconductors (Si) and polymers (polytetrafluoroethylene and polyurethane) have been also observed in the transformation patterns.

Influence of the per pulse laser fluence on the optical properties of carbon nanoparticles synthesized by laser ablation of solids in liquids

In this work we present experimental results on the optical characterization of carbon-nanoparticles (CNPs) synthesized by the laser ablation of solids in liquids technique (LASL). A pulsed Nd-YAG laser, a graphite disk and acetone were used in the laser ablation experiments. The per pulse laser fluence was varied, while all the other irradiation parameters (irradiation time, repetition rate, etc.) were kept constant. Both the graphite target and the obtained CNPs were characterized by Raman micro-spectroscopy. The colloidal solutions were characterized by UV–vis and photoluminescence (PL) spectroscopies. Additionally, the CNPs were also characterized by TEM and HRTEM. Our results show that spherical nanoparticles in the range of 4–20 nm in diameter were obtained. UV–vis and PL results for the obtained CNPs colloidal solutions showed that the optical absorption and PL intensity are dependent on the per pulse laser fluence. We also found that the PL spectral emission of the CNPs can be tuned from blue to yellow by varying the excitation wavelength.

Production of silver nanoparticles by laser ablation in open air

Silver nanoparticles have attracted much attention as a subject of investigation due to their well-known properties, such as good conductivity, antibacterial and catalytic effects, etc. They are used in many different areas, such as medicine, industrial applications, scientific investigation, etc. There are different techniques for producing Ag nanoparticles, chemical, electrochemical, sonochemical, etc. These methods often lead to impurities together with nanoparticles or colloidal solutions. In this work, laser ablation of solids in open air conditions (LASOA) is used to produce silver nanoparticles and collect them on glass substrates. Production and deposition of silver nanoparticles are integrated in the same step to reduce the process. The obtained particles are analysed and the nanoparticles formation mechanism is discussed. The obtained nanoparticles were characterized by means of transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM) and UV/VIS absorption spectroscopy. The obtained nanoparticles consisted of Ag nanoparticles showing rounded shape with diameters ranging from few to 50nm

Formation of ring-patterned nanoclusters by laser–plume interaction

This article reports for the first time a unique study performed to regulate the ring diameter of nanoclusters fabricated during femtosecond laser ablation of solids and a mechanism is proposed for the formation of those ring clusters. The ring nanoclusters are made out of nanoparticles with a range of 10–30 nm. Our experimental studies showed the synthesis of ring nanoclusters with random diameter distribution on metals, nonmetals, and semiconductors, such as titanium, aluminum, glasses, ceramics, graphite, and silicon. To regulate the ring size, the effects of laser parameters, such as wavelength, pulse duration, pulse energy, and repetition rate on the ring diameter are analyzed. The influence of ablated materials and the background gas on ring size is also elaborated in this article. The motion of plume species under the influence of ponderomotive force on free electrons possibly played a key role in the formation of the ring-patterned nanoclusters. This study could help to understand the fundamentals in laser ablative nanosynthesis as well as to produce nanostructures with organized ring diameter that controls the density and porosity of those 3D nanostructures.

Pure colloidal metal and ceramic nanoparticles from high-power picosecond laser ablationin water and acetone

The generation of colloids by laser ablation of solids in a liquid offers a nearlyunlimited material variety and a high purity as no chemical precursors are required.The use of novel high-power ultra-short-pulsed laser systems significantlyincreases the production rates even in inflammable organic solvents. By applyingan average laser power of 50 W and pulse durations below 10 ps, up to 5 mg min−1 of nanoparticles have been generated directly in acetone, marking a breakthrough inproductivity of ultra-short-pulsed laser ablation in liquids. The produced colloids remainstable for more than six months. In the case of yttria-stabilized zirconia ceramic, thenanoparticles retain the tetragonal crystal structure of the ablated target. Laser beamself-focusing plays an important role, as a beam radius change of 2% on the liquid surfacecan lead to a decrease of nanoparticle production rates of 90% if the target position is notre-adjusted.

Filamented plasmas in laser ablation of solids

We report results from laser-solid experiments at PALS using an x-ray laser probe with a pulse length of 0.1 ns and a wavelength of 21.2 nm. A laser with a pulse length of 0.3 ns, a peak intensity of up to 5 × 1013 W cm−2 and a wavelength of 1.3 µm was focused to a 0.15 mm wide line on 3 mm long zinc and 1 mm long iron targets and the probe was passed along the length of the plasma formed. The results show plasma ‘hairs’, or filaments, appearing only below the critical density, 0.1 ns before the peak of the laser pulse. The plasma around the critical density was clearly imaged and remained uniform. Magneto-hydrodynamic modelling indicates that this is caused by a magnetic field that diffuses from the critical surface, where it is generated, leading to a magnetic pressure comparable to the plasma pressure below the critical density. A dispersion relation is derived for density perturbations perpendicular to a temperature gradient in the presence of an existing magnetic field, which shows that such perturbations always grow, with the growth rate being the greatest for small wavelength perturbations and at low densities. These results indicate that the hair-like structures should be a typical feature of laser ablated plasmas below the critical density following significant plasma expansion, in agreement with numerous experimental results. The implications for x-ray lasers and fast ignition inertial confinement fusion are discussed.

Nanoparticle formation during laser ablation of solids in liquids

The experimental data on the generation of metal and semiconductor nanoparticles during their laser ablation in liquids is reviewed. The dependence of the morphology of noble metal nanoparticles on the liquid type and laser parameters is discussed. The data on the kinetics of the formation of alloyed Au-Ag nanoparticles under laser irradiation of a mixture of colloid solutions of individual nanoparticles are presented. The effect of femtosecond laser beam self-action during metal ablation in liquids via the second harmonic generation at Ag nanoclusters is discussed. The data on the generation of core-shell nanoparticles during laser ablation of alloys and in the presence of the chemical interaction of formed nanoparticles with surrounding liquid are presented. It was shown that laser ablation of CdS and ZnSe crystals leads to the formation of quantum dots of these semiconductors in solution. The parameters controlling the properties of nanoparticles during ablation in liquids and possible applications of the method are discussed.

Ion Mobility Spectrometry of Gas-Phase Ions from Laser Ablation of Solids in Air at Ambient Pressure

A mobility spectrometer was used to characterize gas-phase ions produced from laser ablation of solids in air at 100 degrees C and at ambient pressure with a beam focused to a diameter of <or=0.2 mm at energy of 6 mJ/pulse and wavelength of 266 nm. Metals, organic polymers, glass, graphite, and boron nitride exhibited characteristic mobility spectra with peaks at drift times between 8.75 and 12.5 ms (reduced mobility values of 2.19 to 1.53 cm(2)/Vs). Ion intensities increased initially and then decreased with repeated laser shots through drilling of the solid, and persistence of signal was proportional to hardness. A single comparatively narrow peak for negative ions was observed in mobility spectra for all materials and this was mass-identified as O(2)(-). These ions were formed in air from reactions of oxygen with electrons emitted from the ablation step. Positive ions ablated directly from the solid were masked in ion mobility spectrometry/mass spectrometry (IMS/MS) studies by ionization of moisture and impurities. Positive ions from solids were seen only in the IMS analyzer at elevated temperature and low moisture. Under such conditions, materials were classified from mobility spectra alone with principal component analysis.

Nickel and cobalt nanoparticles produced by laser ablation of solids in organic solution

Nanoparticles of nickel (Ni) and cobalt (Co) have been produced through laser ablation in organic solution. Pure Ni, Ni 50Co 50 alloy, and Co metal plates as the targets, respectively, have been irradiated under 532 nm Nd:YAG laser in ethylene glycol (EG). The produced metal nanoparticles are stabilized with poly ( N-vinyl-2-pyrrollidone) (PVP) in EG. Under the same laser fluence and irradiation time, the average particle size of Ni nanoparticles is 8 nm in diameter, smaller than 22 nm of Co nanoparticles. The laser-induced structural transition at interface of bulk metal and liquid has been investigated. It has been found that laser-generated Co nanoparticles show fcc structure, while the target of laser ablation is hexagonal Co bulk. In addition, the surface plasmon resonance (SPR) absorptions of Ni and Co nanoparticles stabled by PVP in EG are 355 nm and 510 nm, respectively. This research demonstrates that laser ablation in liquid, a one-step, non-catalyst process, can produce stable Ni and Co nanoparticles.

Nanoparticles produced by laser ablation of solids in liquid environment

Nanoparticles produced by laser ablation of solids in liquid environment

Nanoparticles produced by laser ablation of solids in liquid environment

The formation of Ti, Si, Ag and Au nanoparticles under laser ablation of metal targets in liquid environment (H 2O, C 2H 5OH, C 2H 4Cl 2) is reported. The use of a high-repetition-rate Cu vapor laser (wavelength 510.5 nm, pulse duration 20 ns, repetition rate 15 kHz) allows high rate of nanoparticles formation as a sol. The nanoparticles are characterized by X-ray diffraction (XRD), UV–visible transmission spectrometry, high resolution transmission electron microscopy (HRTEM) and atomic force microscopy (AFM). The nanoparticle size dependence on both the laser fluence and the nature of the liquid is studied. In some cases, nanoparticles of compounds are formed via reaction of the metal with the liquid.

Erratum: Rarefaction shock wave: Formation under short-pulse laser ablation of solids [Phys. Rev. E63,046311 (2001)

Erratum: Rarefaction shock wave: Formation under short-pulse laser ablation of solids [Phys. Rev. E<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mn>63</mml:mn><mml:mo>,</mml:mo></mml:math>046311 (2001)

Possibility of rarefaction shock wave under short pulse laser ablation of solids.

Attention is drawn to a phenomenon that may give a radically different explanation for the recent observations of the system of dark rings above a solid surface vaporized by a short laser pulse. If a substance is heated to near-critical temperature, the existence of the compression shock wave becomes impossible, whereas the rarefaction wave takes a form of shock. The rarefaction shock can be considered as an interface in the expanding near-critical substance to form Newton rings in time-resolved optical microscopy experiments. The qualitative picture of the laser-ablated material expansion in vacuum with the generation of the rarefaction shock is discussed.

Computational modeling of physical processes during laser ablation

A combined theoretical and experimental effort to model various physical processes during laser ablation of solids using a variety of computational techniques is described. Currently the focus of the modeling is on the following areas: (a) rapid transformations through the liquid and vapor phases under possibly nonequilibrium thermodynamic conditions induced by laser-solid interactions; (b) breakdown of the vapor into a plasma in the early stages of ablation through both electronic and photoionization processes; (c) hydrodynamic behavior of the vapor/plasma during and after ablation; and (d) the effects of initial conditions in the vapor, in particular, the nature of the initial velocity distribution, on the characteristics of subsequent vapor expansion. The results from the modeling will be compared with experimental observations where possible.

Gas-phase metal sulfide cluster anions

The formation of metal sulfide cluster anions by laser ablation of solids has been examined for most of the first-row transition metals. Maps of the compositions of the clusters [MxSy]– show well defined continuous distributions of x vs. y for each metal, and the slope of each distribution is related to the position of the metal in the transition series. The 290 new molecular forms of metal sulfides range in size up to [Cu45S23]–. Fourier-transform ion cyclotron resonance mass spectrometry revealed that the cluster anions have lifetimes of up to 100 s in vacuo. Experiments concentrating on the copper–sulfur anions showed their resistance to dissociation on energised collision with argon, and their general lack of reactivity, except with sulfur-containing reactants. In experiments designed to produce mixed-metal anions, cobalt has been shown to substitute for copper in many of the smaller anions. Geometrical structures and structural principles for the copper sulfide clusters are revealed by non-local density functional calculations.

Laser-induced stresses versus mechanical stress power measurements during laser ablation of solids

Laser-induced stresses resulting from high-power laser-material interactions have been studied extensively. However, the rate of change in mechanical energy, or stress power, due to laser-induced stresses has only recently been investigated. An unanswered question for monitoring laser-material interactions in the far-field is whether stress power differs from stresses measured, particularly with respect to laser-energy coupling to a solid target. This letter shows experimental acoustic data which demonstrate that stress power measured in the far field of the target shows changes in laser-energy coupling, whereas the stresses measured do not. For the ambient medium above the target, stress power and stress together reflect changes in laser-energy coupling.

Particle size distributions of aerosols formed by laser ablation of solids at 760 Torr

The size distributions of aerosol particles generated in N2 and O2 at ambient atmospheric pressure by repetitive excimer laser ablation of solids have been measured in quasi-steady-state from 10 nm to 1 μm diameter with a differential mobility analyzer (DMA). A light scattering technique extended the range of measurable sizes up to 20 μm, beyond the upper limit of sizes observed in the aerosol. Irradiation near focus was required to observe metal particles above 0.1 μm diameter. YBCO ceramic (YBa2Cu3O7) produced copious smaller particles with mild focusing. For an ablated polymer, PMMA, particulate production increased and the size distribution altered shape with continued energy deposition.

Spatial distributions of electron density in microplasmas produced by laser ablation of solids

The spatial distribution of electron density in argon microplasmas produced by laser ablation of solids has been investigated by time-resolved emission spectroscopy. The electron density was derived from Stark broadening and shift of spectral lines. It was found that the radial gradient of the electron density is much smaller than the gradient of the atomic number density of atoms ablated by the laser into the plasma. The almost homogeneous plasma conditions in the centre of the microplasmas are essential for quantitative element analysis of solid samples by laser ablation. On the other hand, because of the homogeneous conditions microplasmas are excellent sources for measurements of reliable Stark broadening and shift parameters of atomic and ionic spectral lines of all elements which can be ablated by lasers from solid samples.