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Microwave ablation (MWA) is based on localized heating of biological tissues, enabled by an electric field. Antennas for ablation are commonly designed in a forward approach to generate a temperature profile specific to the design. The concept of an inversely-designed MWA antenna, consisting of printed dipoles, is presented herein. This design can be configured to synthesize a desired target temperature profile by controlling and optimizing its current distribution, as demonstrated by simulations. This concept provides the functionality of a phased array on the tip of an interstitial device. [ABSTRACT FROM AUTHOR]

The influence of different background gases and substrate heating on the plasma plume dynamics from silver ablation is investigated by species selected time and space resolved imaging. The results provide a time-resolved understanding on how those process parameters affect the expansion: from a free expansion in vacuum with velocities exceeding 20 000 m/s to a very slow expansion in Ar at 1×10-1 mbar with arrival velocities of 280 m/s. In addition, we observe a rebound of the ablated material on the substrate holder leading to a re-coating of the ablated target. At 1×10-1 mbar, it seems that the expansion of the plasma plume displaces a considerable portion of the background gas and traps it against the frontal area of the substrate holder. This leads to a transient high local pressure just above the substrate. In the case of Ar, the rebound is enhanced due to inelastic scattering, whereas for an O2 background, an area of high reactivity/emission in addition to the rebound is created. Imaging of selected species shows that the light emission in this area is mainly due to excited Ag and metal oxygen species. There is a clear influence of substrate heating on the plasma expansion due to the background gas density gradients, reducing the stopping ability of the background gas and already detectable 2 cm away from the substrate. Both rebound and excitation effects are reduced in intensity due to the substrate heating. [ABSTRACT FROM AUTHOR]

The plume expansion dynamics strongly affects the growth and the chemistry of pulsed laser deposited thin films. The interaction with the background gas determines the kinetic energy of the species impinging on the substrate, their angular broadening, the plasma chemistry, and eventually the cations stoichiometric ratio in oxide films. Here, we exploit two-dimensional, spectrally resolved plume imaging to characterize the diverse effects of the oxygen background pressure on the expansion dynamics of La, Ga, and LaO species during pulsed laser deposition of LaGaO3. The propagation of the ablated species towards the substrate is studied for background oxygen pressures ranging from high vacuum up to ≈10-1 mbar. Our experimental results show specie-dependent effects of the background gas on the angular distribution of the precursors within the plume. These findings suggest that even in the presence of a stoichiometric ablation and of a globally stoichiometric plume, cations off-stoichiometry can take place in the forefront portion of the plume impinging on the substrate. We show that such effect can be compensated by a proper choice of process parameters. [ABSTRACT FROM AUTHOR]

The presented study addresses the characterization of nanometer sized defects acting as damage precursors in nanosecond laser pulse duration regime. Two approaches are used to extract distributions of localized damage precursors, namely, damage probability and damage density measurements. Testing is performed on uncoated and SiO2 monolayer film deposited fused silica substrate exposed with pulsed UV irradiation (355 nm, 4.8 ns). Then, a direct comparison of damage precursor ensembles obtained from both methods is carried out. Our analysis indicates apparent differences between both methods that are discussed in detail. Contamination by ablation products is identified as one of the key factors that influence damage density measurements. [ABSTRACT FROM AUTHOR]

In this work, chemical properties, surface modification, and micro structures formation on ablated polyallyl di-glycol carbonate (CR-39) polymer by ArF laser irradiation (k=193 nm) at various fluences and pulse number were investigated. CR-39 samples have been irradiated with an ArF laser (λ=193 nm) at a repetition rate of 1 Hz. Threshold fluence of ablation and effective absorption coefficient of CR-39 were determined. Conical microstructures (Taylor cone) formed on laser-ablated CR-39 exhibit: smooth, Taylor cone shape walls and sharp tips together with interference and well defined fringe-structure with a period of 230 nm, around cone base. Mechanism of cone formation and cone evolution of CR-39 ablated surface were investigated by change of fluences (at a given pulse number) and pulse number (at a given fluence). Cone height, cone base, and region of interface were increased in micrometer steps by increasing the total fluence. Depression on the base of the cone and the circular fringe were simulated. FTIR spectra were measured and energy dispersive x-ray analysis of irradiated and un-irradiated samples was performed. [ABSTRACT FROM AUTHOR]

In multi-pulse laser damage and ablation experiments, the laser-induced damage threshold (LIDT) usually changes with the number of pulses in the train, a phenomenon known as incubation. We introduce a general incubation model based on two physical mechanisms-pulse induced change of (i) absorption and (ii) critical energy that must be deposited to cause ablation. The model is applicable to a broad class of materials and we apply it to fit data for dielectrics and metals. It also explains observed changes of the LIDT as a function of the laser repetition rate. We discuss under which conditions the crater-size method to determine LIDTs can be applied in multi-pulse experiments. [ABSTRACT FROM AUTHOR]

We present the studies of the high-order harmonic generation of 802-nm, 64-fs pulses in the extended plasmas contained the carbon-based clusters (fullerenes, nanofibers, nanoparticles, and nanotubes). Our studies show that the 11th-19th harmonics in the 15-33 eV range may originate from the low-sized nanoparticles produced during ablation of large clusters and agglomerates. The conversion efficiency of the 11th harmonic generated from the 5-mm-long fullerene plasma was estimated to be 2 x 10-5. [ABSTRACT FROM AUTHOR]

In this paper, we study the ablation phenomena associated with the operation of a capillary discharge for an electrothermal gun. Electrothermal-chemical (ETC) guns are used for enhancement of ignition and combustion of an energetic propellant. One of the major components of the ETC system is a plasma source based on a capillary discharge. In this paper, a model of the capillary discharge is developed. In this model, primary attention is paid to the ablation phenomenon. Different characteristic subregions near the ablated surface, namely, a space-charge sheath, a Knudsen layer, and a hydrodynamic layer, are considered. In this formulation, the ablation rate is determined by the parameters at the edge of the Knudsen layer. The kinetic approach is used to determine the parameters at the interface between the kinetic Knudsen layer and the hydrodynamic layer. Coupling the solution of the nonequilibrium Knudsen layer with the hydrodynamic layer provides a self-consistent solution for the ablation rate. According to the model predictions, the peak electron temperature is about 1.4 eV, the polyethylene surface temperature is about 700 K, and the pressure is about 10 MPa. It is found that the ablation rate increases with the capillary length. The ablated mass and the predicted total pressure agree with previous experimental observations. [ABSTRACT FROM AUTHOR]

We discuss the ablation of aluminum plasma using picosecond pulsed laser in vacuum and in ambient atmosphere of nitrogen. The plume dynamics of picosecond and nanosecond laser-ablated plumes in ambient atmosphere is discussed. The degree of polarization is measured using optical emission spectroscopy for the Al III transition 4s 2S1/2-4p 2P3/2o at 569.6 nm. Strong anisotropy is observed using picosecond laser pulse as compared to nanosecond laser pulse. [ABSTRACT FROM AUTHOR]

Several interrelated phenomena near the surface ablated into a discharge plasma, such as ablation and ionization in accelerated plasma are studied. Two characteristic ablation modes are identified, namely, ablation mode with a velocity at the Knudsen layer edge smaller than the local sound speed and a velocity at the Knudsen layer edge close to the sound speed. The existence of these two ablation modes is determined by the current density in the acceleration region. The nonequilibrium ionization region in the presence of strong electromagnetic plasma acceleration is studied. In the subsonic regime, the ionization region thickness is proportional to the ionization rate and inversely proportional to the magnetic field. Conditions for ionization equilibrium in the accelerating plasma are determined. The specific example of a micropulsed plasma thruster is considered. It is concluded that both the equilibrium and nonequilibrium ionization regimes occur in this device. [ABSTRACT FROM AUTHOR]

We have calculated the concentration of ions in the plasma produced upon ablation of LiNbO[sub 3] with a low fluence ArF excimer laser in vacuum and different gas environments (Ar and O[sub 2]). The model shows that Li and Nb ions (with the amount of Li ions being greater than that of Nb ions) are the most abundant in the plasma with their concentrations being always above their corresponding neutral densities. In addition, we show that the concentration of excited Nb ions is relatively important while no excited Li ions are predicted. We found that the concentration of both Li and Nb ions in O[sub 2] is slightly higher than in Ar and vacuum. Moreover, the calculated spatial evolution of the ionic species suggests that a significant fraction of the predicted ion concentration is not produced by electron–atom ionization events within the plasma; on the contrary, they might have been produced in the LiNbO[sub 3] crystal through a nonthermal mechanism and then ejected from the target after the laser pulse. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Investigates the properties of the ablation products from intense-pulsed ion beam impact on solid targets. Discussion on intense ion beams; Experimental configurations; Characterization of beam and plume; Description of the beam-target interaction model; Results.

Presents information on a study which analyzed laser-interaction experiments performed on a fine-grained, nearly isotropic synthetic graphite grade known as GraphNOL. Factors of the effective heat of ablation; Experimental procedure; Theoretical considerations; Discussion on the energy-balance relation at the surface of an ablating sublimator.

Presents a study that examined thermal transport, mass ablation rates and preheat in six-beam ultraviolet irradiation of spherical targets. Functionality of the thermal transport in laser-target interaction; Discussion of mass ablation and ablation pressure; Possible sources of the discrepancy between spectral and charge-collector measurements.

Investigates the interaction and energy transfer of a laser ablation plasma of Ti with a pulsed N2 supersonic expansion using time-of-flight quadrupole mass spectroscopy and Langmuir probe techniques. Coupling of the nascent plasma with the gas pulse; Timing between the gas pulse and ablation plume; Ion signal quenching by the N2 number density.

Investigates the ablation of free-standing thin aluminum films by a nanosecond laser pulse through time-resolved transmission electron microscopy and numerical simulation. Details of the experimental techniques used; Applications for thin film geometry; Response of the thin films to lower pulse energies.

Presents information on a study which proposed a thermal model for pulsewidth-dependent ablation of polyimide. Plume generation and associated screening of the laser pulse; Heat transfer and material removal model; Estimation of chromophore density.

Presents a study which characterized the pulsed carbon dioxide laser-induced ablation of solid lithium target via laser-induced fluorescence and absorption spectroscopy of emitted atoms. Time of flight and density of lithium atoms in the beam; Velocity and temperature of the emitted atoms; Number of ablated atoms.

Examines ablation event and plume development in thin-film production. Details on the experiment; Information on the time-of-flight velocity distributions of ablated neutrals; Excitation spectrum of barium oxide.

Focuses on a study which investigated thermochemical heat of ablation of solid carbon. Details of analytical evaluation; Description of experimental evaluation; Results and discussion.

Presents a study which calculated the turbulent energy generated at a surface which is accelerating by ablation. Explanation for the phenomenon of mixing of heavy and light fluids in a constant gravitational field; Discussion on classical and strongly inhibited limits.

Comments on an article on the thermochemical heat of ablation of solid carbon. Results of JANAF and Livermore thermochemical ablation models; Argument on the differences between JANAF and Livermore data for carbon; Summary of the heat content, enthalpy of vaporization and heat ablation for solid carbon.