scispace - formally typeset
Search or ask a question

Showing papers on "Fluence published in 2005"


Journal ArticleDOI
TL;DR: In this article, the ablation laser fluence was found to have a very strong effect on the lattice constant and defect structure of the thin oxide films, and nonstoichiometric transfer of material from a target to a non-ablation target was observed when either the fluence or beam spot area was inadequate.
Abstract: Pulsed laser deposition (PLD) is a good method for growing high-quality functional oxide thin films because of the technical simplicity and the ease with which deposition can be switched from one material to another. However, the repeatability of film quality is often hard to achieve, especially when using several different PLD systems. Here we report the steps that we have taken to grow nearly bulk-equivalent defect-free thin films, with SrTiO3 as an example, by using PLD in a reproducible fashion. The ablation laser fluence was found to have a very strong effect on the lattice constant and defect structure of the films. Nonstoichiometric transfer of material from the ablation target was observed when either the laser fluence or the beam spot area was inadequate.

226 citations


Journal ArticleDOI
TL;DR: In this article, the authors studied the effect of laser pulse durations on thermal ablation thresholds and penetration depths for steel, Cu and Al in micromachining of laser pulses.

184 citations


Journal ArticleDOI
Ronan Le Harzic1, H. Schuck1, D. Sauer1, Tiemo Anhut1, Iris Riemann1, K. König1 
TL;DR: Techniques based on laser scanning microscopes for nanoprocessing of periodic structures on silicon with ultra-short laser pulses have been developed and smaller features of 70-100nm spacing were achieved in oil by using a high numerical focusing objective.
Abstract: Techniques based on laser scanning microscopes for nanoprocessing of periodic structures on silicon with ultra-short laser pulses have been developed. Ripples of 800-900 nm spacing were obtained after laser irradiation at a wavelength of 1040 nm, a repetition rate of 10 kHz and a fluence of 2 J/cm2 in air. Smaller features of 70-100nm spacing were achieved in oil at a wavelength of 800 nm, a repetition rate of 90 MHz and a fluence of 200-300 mJ/cm2 by using a high numerical focusing objective.

155 citations


Journal ArticleDOI
TL;DR: In this paper, a drift-diffusion-based model is proposed to describe the dynamics of electronic excitation, heating, and charge-carrier transport in different materials (metals, semiconductors, and dielectrics) under femtosecond and nanosecond pulsed laser irradiation.
Abstract: We present a continuum model, based on a drift-diffusion approach, aimed at describing the dynamics of electronic excitation, heating, and charge-carrier transport in different materials (metals, semiconductors, and dielectrics) under femtosecond and nanosecond pulsed laser irradiation. The laser-induced charging of the targets is investigated at laser intensities above the material removal threshold. It is demonstrated that, for near-infrared femtosecond irradiation, charging of dielectric surfaces causes a sub-picosecond electrostatic rupture of the superficial layers, alternatively called Coulomb explosion (CE), while this effect is strongly inhibited for metals and semiconductors as a consequence of superior carrier transport properties. On the other hand, application of the model to UV nanosecond pulsed laser interaction with bulk silicon has pointed out the possibility of Coulomb explosion in semiconductors. For such regimes a simple analytical theory for the threshold laser fluence of CE has been developed, showing results in agreement with the experimental observations. Various related aspects concerning the possibility of CE depending on different irradiation parameters (fluence, wavelength and pulse duration) and material properties are discussed. This includes the temporal and spatial dynamics of charge-carrier generation in non-metallic targets and evolution of the reflection and absorption characteristics.

153 citations


Journal ArticleDOI
TL;DR: In this article, a fast ion-beam irradiation procedure based on electronic (not nuclear) excitation was used to generate a large index jump step-like optical waveguide (Δn0≈0.2,Δne≈ 0.1) in LiNbO3.
Abstract: We demonstrate a swift ion-beam irradiation procedure based on electronic (not nuclear) excitation to generate a large index jump step-like optical waveguide (Δn0≈0.2,Δne≈0.1) in LiNbO3. The method uses medium-mass ions with a kinetic energy high enough to assure that their electronic stopping power Se(z) reaches a maximum value close to the amorphous (latent) track threshold inside the crystal. Fluorine ions of 20 and 22MeV and fluences in the range (1–30)×1014 are used for this work. A buried amorphous layer having a low refractive index (2.10 at a wavelength of 633nm) is then generated at a controlled depth in LiNbO3, whose thickness is also tuned by irradiation fluence. The layer left at the surface remains crystalline and constitutes the core of the optical waveguide which, moreover, is several microns far from the end of the ion range. The waveguides show, after annealing at 300°C, low propagation losses (≈1dB∕cm) and a high second-harmonic generation coefficient (50%–80% of that for bulk unirradiat...

142 citations


Journal ArticleDOI
TL;DR: In this article, the authors compared the results of micromachining a single crystal silicon wafer using a 150-femtosecond and a 30-nanosecond laser.

141 citations


Journal ArticleDOI
TL;DR: In this paper, the physical effects reducing the damage threshold of dielectric films when exposed to multiple femtosecond pulses are investigated, and the measured temperature increase of a Ta2O5 film scales exponentially with the pulse fluence.
Abstract: The physical effects reducing the damage threshold of dielectric films when exposed to multiple femtosecond pulses are investigated. The measured temperature increase of a Ta2O5 film scales exponentially with the pulse fluence. A polarized luminescence signal is observed that depends quadratically on the pulse fluence and is attributed to two-photon excitation of self-trapped excitons that form after band-to-band excitation. The damage fluence decreases with increasing pulse number, but is independent of the repetition rate from 1 Hz to 1 kHz at a constant pulse number. The repetition rate dependence of the breakdown threshold is also measured for TiO2, HfO2, Al2O3, and SiO2 films. A theoretical model is presented that explains these findings.

126 citations


Journal ArticleDOI
TL;DR: In this article, a new model is proposed which greatly improves the accuracy in predicting the ablation depth and, for the first time, can predict the flat bottom crater shape for wide bandgap materials ablated by a femtosecond laser pulse.

101 citations


Journal ArticleDOI
TL;DR: In this article, the experimental and molecular dynamics simulation study of crystalline copper (Cu) ablation using femtosecond lasers is described, focusing on the heat-affected zone after femto-conditional laser ablation.
Abstract: We describe the experimental and molecular dynamics simulation study of crystalline copper (Cu) ablation using femtosecond lasers. This study is focused on the heat-affected zone after femtosecond laser ablation and the laser ablation rate. As a result of the x-ray diffraction measurement on the ablated surface, the crystallinity of the surface is partially changed from a crystal structure into an amorphous one. At the laser fluences below the ablation threshold, the entire laser energy coupled to the Cu target is absorbed, while during the fluence regime over the threshold fluence, the ablation rate depends on the absorption coefficient, and the residual energy which is not used for the ablation, is left in the Cu substrate. The heat-affected zone at the fluences below the threshold is estimated to be greater than that over the threshold fluence. In addition, the laser ablation of Cu is theoretically investigated by a two-temperature model and molecular dynamics (MD) simulation to explain the heat-affect...

97 citations


Journal ArticleDOI
TL;DR: In this paper, the authors investigated terahertz (THz) emission from heavy ion-irradiated In0.53Ga0.47As photoconductive antennas excited at 1550 nm.
Abstract: We investigate terahertz (THz) emission from heavy-ion-irradiated In0.53Ga0.47As photoconductive antennas excited at 1550 nm. The carrier lifetime in the highly irradiated In0.53Ga0.47As layer is less than 200 fs, the steady-state mobility is 490cm2V−1s−1, and the dark resistivity is 3Ωcm. The spectrum of the electric field radiating from the Br+-irradiated In0.53Ga0.47As antenna extends beyond 2 THz. The THz electric field magnitude is shown to saturate at high optical pump fluence, and the saturation fluence level increases with the irradiation dose, indicating that defect center scattering has a significant contribution to the transient mobility.

96 citations


Journal ArticleDOI
TL;DR: In this paper, the authors measured the thermal energy remaining in the bulk of Cu, Mg, Au, and Si samples following multi-pulse femtosecond laser ablation and showed that with a sufficiently large number of pulses at high fluence, virtually all the incident laser energy can be retained in the sample.
Abstract: We perform direct measurement of the thermal energy remaining in the bulk of Cu, Mg, Au, and Si samples following multi-pulse femtosecond laser ablation. In contrast to the previous belief that the thermal energy remaining in the ablated sample is negligible using femtosecond pulses, we show a significant amount of residual thermal energy deposited in various materials. In fact, with a sufficiently large number of pulses at high fluence, virtually all the incident laser energy can be retained in the sample. Several possible mechanisms are investigated for their role in residual heating, including laser-induced surface modification, exothermic chemical processes, and pressure effects.

Journal ArticleDOI
TL;DR: In this article, an aluminum laser plasma produced in ambient air at atmospheric pressure by laser pulses at a fluence of 10 J/cm 2 is characterized by time and space-resolved measurements of electron density and temperature.

Journal ArticleDOI
TL;DR: In this paper, polycrystalline tungsten samples have been irradiated at near room temperature by high flux deuterium plasma beams with incident ion energies ranging 7-98 eV/D.

Journal ArticleDOI
TL;DR: In this paper, the fluence dependence of the nanostructure formation, which has been observed in recent experiments on femtosecond (fs)-laser ablation, was examined in detail for hard thin films of TiN and CrN.
Abstract: The fluence dependence of the nanostructure formation, which has been observed in our recent experiments on femtosecond (fs)-laser ablation, was examined in detail for hard thin films of TiN and CrN. The size D of the periodic fine structure formed with fs-laser pulses can be divided into two regions that depend on the laser fluence F, i.e. the region I where D increases rapidly with increasing F near the ablation threshold, and the region II where D increases slowly with an increase in F and almost saturates. The nanostructure has been observed only in the region I with a narrow width of F. The region II produces a periodic ripple structure whose size is 1/2–4/5 of the wavelength used. The effects of the thermal process and material composition on the nanostructure formation are discussed.

Journal ArticleDOI
TL;DR: These laser pulses interacting with fused silica are shown to produce above-critical plasma densities and electron energy densities sufficient to attain experimentally measured damage thresholds, consistent with recent experimental results.
Abstract: The interaction of intense, femtosecond laser pulses with a dielectric medium is examined using a numerical simulation. The simulation uses the one-dimensional electromagnetic wave equation to model laser pulse propagation. In addition, it includes multiphoton ionization, electron attachment, Ohmic heating of free electrons, and temperature-dependent collisional ionization. Laser pulses considered in this study are characterized by peak intensities approximately 10(12) -10(14) W/cm(2) and pulse durations approximately 10-100 fsec . These laser pulses interacting with fused silica are shown to produce above-critical plasma densities and electron energy densities sufficient to attain experimentally measured damage thresholds. Significant transmission of laser energy is observed even in cases where the peak plasma density is above the critical density for reflection. A damage fluence based on absorbed laser energy is calculated for various pulse durations. The calculated damage fluence threshold is found to be consistent with recent experimental results.

Journal ArticleDOI
TL;DR: In this paper, the radiated terahertz field from (100) InAs surfaces under excitation at fluences of millijoules per centimeter squared has been studied in detail in order to identify the main generation mechanism.
Abstract: The radiated terahertz field from (100) InAs surfaces under excitation at fluences of millijoules per centimeter squared has been studied in detail in order to identify the main generation mechanism. We find that the terahertz emission depends strongly on pump polarization, and that the predominant emission mechanism appears to be the surface nonlinear optical response of the InAs crystal. A saturation fluence of 29±4μJ∕cm2 is found for the emission.

Journal ArticleDOI
TL;DR: In this article, the synthesis of chromium (III, IV) oxides films by KrF laser-assisted CVD was described, which were deposited onto sapphire substrates at room temperature by the photodissociation of Cr(CO) 6 in dynamic atmospheres containing oxygen and argon.

Journal ArticleDOI
TL;DR: In this paper, the effect of nitrogen partial pressure on amorphous carbon nitride (a-CNx) (0.0⩽x⵽0.17) films prepared by ultrafast high repetition rate pulsed laser deposition has been studied.
Abstract: The effect of nitrogen partial pressure on amorphous carbon nitride (a-CNx) (0.0⩽x⩽0.17) and laser fluence on amorphous carbon (a-C) films prepared by ultrafast high repetition rate pulsed laser deposition has been studied. The chemical bonding structure of the films was investigated by x-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and Fourier transform infrared (FTIR) analysis. XPS studies of films revealed an increase in the CN sites at the expense of CC bonded carbon sites as nitrogen content in the films increased. Films (a-C) prepared as a function of laser fluence showed an increase in sp3-bonded carbon as laser fluence was increased from 0.36 to 1.7J∕cm2. The ID∕IG ratio and G peak position increased as a function of nitrogen whereas the full width at half maximum (FWHM) of the G peak decreased. This is indicative of either an increase in the size or number of the sp2 sites. Films prepared as a function of laser fluence revealed a decrease of the ID∕IG ratio and an increase in the FWH...

Journal ArticleDOI
TL;DR: In this paper, atomic force microscopy was employed to investigate the morphology of ultraviolet nanosecond-pulsed-laser damage in SiO2 thin films, and the results indicated that, at laser fluences close to the crater-formation threshold, the dominating regime of material removal is melting and evaporation.
Abstract: Atomic force microscopy was employed to investigate the morphology of ultraviolet nanosecond-pulsed-laser damage in SiO2 thin films. Gold nanoparticles, 18.5‐nm diameter, embedded in the film were used as calibrated absorbing defects. Damage-crater diameter, depth, and cross-sectional profiles were measured as a function of laser fluence and the lodging depth of gold nanoparticles. The results indicate that, at laser fluences close to the crater-formation threshold and for lodging depths of a few particle diameters, the dominating regime of the material removal is melting and evaporation. The morphology of craters initiated by deep absorbing defects, with a lodging depth larger than ∼10 particle diameters, clearly points to a two-stage material-removal mechanism. The process starts with the material melting within the narrow channel volume and, upon temperature and pressure buildup, film fracture takes place. Crater-diameter variation with lodging depth and laser fluence is compared with theoretical predi...

Journal ArticleDOI
TL;DR: In this article, water ice was used as a matrix for the biotechnologically important guest material, polyethylene glycol (PEG), for concentrations from 0.5 to 4.5 wt.%.

Journal ArticleDOI
TL;DR: In this article, the effects of heat dissipation on the annealing duration and on the graphitized layer thickness of amorphous hydrogenated carbon (a-C:H) films were investigated for the case of laser processing with short pulses.

Journal ArticleDOI
TL;DR: In this article, the irradiation induced structural and optical modifications were studied using glancing angle x-ray diffraction (GAXRD), optical absorption and photoluminescence (PL) spectroscopy.
Abstract: Thermally deposited 200 nm polycrystalline films of lithium fluoride (LiF) grown on glass substrates were irradiated with 150 MeV Ag ions at various fluences between 1 × 1011 and 2 × 1013 ions cm−2. The irradiation induced structural and optical modifications were studied using glancing angle x-ray diffraction (GAXRD), optical absorption and photoluminescence (PL) spectroscopy. The GAXRD results show that the films are polycrystalline and the average grain size (estimated from the widths of the GAXRD peak using the Scherrer formula) decreases systematically from 46.3 nm for the pristine sample to 18.3 nm for the sample irradiated at a fluence of 3 × 1012 ions cm−2. Thereafter, it remains constant. This reduction is attributed to strain induced fragmentation of grains. The optical absorption studies show dominant absorption bands of F3 (385 nm) and F2 (445 nm) colour centres. It is observed that the concentration of the colour centres increases with ion fluence and gets saturated at higher fluences. This can be correlated with GAXRD results in the sense that as the density of grain boundaries increases the concentration of colour centres also increases. The variation with fluence in PL intensities of the F2 and colour centres is studied. The intensity of both bands (F2 and ) increases up to a fluence of 1 × 1012 ions cm−2, followed by an exponential decrease, which is due to the increase in the non-radiative transition rate in the presence of defect-rich material.

Journal ArticleDOI
TL;DR: In this paper, the authors measured the surface plasmon resonance (SPR) spectra of polymethyl methacrylate (PMMA) implanted with Ag− and Cu− at 3 μA/cm2 up to 3×1017 ions/cm 2.
Abstract: Negative ion implantation has been applied to polymers in order to modify the surface and to fabricate nanoparticles. Metal nanoparticles in the vicinity of a polymeric surface are promising for biomedical applications as well as nonlinear optical applications. Substrates of polymethyl methacrylate (PMMA) were implanted with Ag− and Cu− of 60 keV at 3 μA/cm2 up to 3×1017 ions/cm2. Optical absorption spectra of the implanted PMMA were measured in a photon range from 0.5 to 4.5 eV. A peak of surface plasmon resonance (SPR) emerges in the absorption spectra above about 1×1017 ions/cm2, both for the Ag− and Cu− cases. A coexisting absorption slope, due mostly to defects, increases but tends to saturate with ion fluence. The SPR peak of Ag-implanted PMMA is much broader than that of the Cu-implanted one. Corresponding to the SPR spectra, metal nanoparticles are observed by cross-sectional TEM. With increasing ion fluence, the Ag nanoparticles spread out towards the surface, in contrast to the localized Cu nanoparticles. The results demonstrate that metal nanoparticle fabrication in polymers is capable by using appropriate low-energy ions and provides a variety of spatial distributions dependent on ion species and fluence. In particular, Ag− ion implantation fabricates surface-exposed/gradient nanoparticles, which are suitable for biomedical applications such as anti-microbial effects.

Journal ArticleDOI
TL;DR: In this article, the wear-life of MoS2 film was evaluated by in situ tribological testing under 5 eV atomic oxygen exposures which simulated atomic oxygen environment in low Earth orbit.
Abstract: Wear-life of the MoS2 film was evaluated by in situ tribological testing under 5 eV atomic oxygen exposures which simulated atomic oxygen environment in low Earth orbit. A combination of a laser-detonation atomic oxygen source and a conventional pin-on-disk friction tester was used to perform tribological tests. It was confirmed that the friction coefficient was not affected by atomic oxygen exposure when atomic oxygen fluence was low; however, the friction coefficient increased with increasing atomic oxygen fluence and it reached as high as 0.05 at the atomic oxygen fluence of 3.4 × 1016 atoms/cm2/cycle (nine times larger than the normal value). Effect of atomic oxygen on the wear-life of the film has much more drastic. With atomic oxygen fluence of 1.7 × 1016 atoms/cm2/cycle, wear-life of the film was reduced less than one-tenth of that during ex situ testing result of the same film. It was also observed that the wear-life of the film was inversely proportional to the atomic oxygen fluence between sliding passes.

Journal ArticleDOI
TL;DR: In this paper, three sets of metallic and dielectric standards (brass, aluminium, silicate glass) have been analyzed for Zn and Cu using He as buffer gas, and it has been found that the measured Zn/Cu ratio of these standards remains nearly unchanged in the fluence range considered (0.8 J cm−2).
Abstract: The facilities of near-IR (NIR) femtosecond laser ablation (fs LA) inductively-coupled plasma optical emission spectrometry (ICP-OES) for the analysis of solid materials applying non-matrix matched standards have been examined. Three sets of metallic and dielectric standards (brass, aluminium, silicate glass) have been analyzed for Zn and Cu using He as buffer gas. It has been found that the measured Zn/Cu ratio of these standards remains nearly unchanged in the fluence range considered (0.8 J cm−2 ≤ F ≤ 11.0 J cm−2). At fluences close to the threshold, however, the Zn/Cu ratio for brass and aluminium tends to slightly increase, suggesting preferential evaporation of Zn during the ablation process. Furthermore, LA above a fluence of 5 J cm−2 resulted in linear, matrix-independent calibration graphs. According to the results achieved, NIR fs LA-ICP-OES carried out in the medium and high fluence regime permits efficient suppression of fractionation and performance of accurate analyses even if non-matrix matched standard materials have to be used.

Journal ArticleDOI
TL;DR: In this paper, the refractive index profiles induced by high-energy (5 MeV, 7.5 MEV) silicon irradiation in LiNbO3 have been systematically determined as a function of ion fluence in the range 1013-1015 cm-2.
Abstract: The refractive-index profiles induced by high-energy (5 MeV, 7.5 MeV) silicon irradiation in LiNbO3 have been systematically determined as a function of ion fluence in the range 1013–1015 cm-2. At variance with irradiations at lower energies, an optically isotropic (‘amorphous’) homogeneous surface layer is generated whose thickness increases with fluence. These results have been associated with an electronic excitation mechanism. They are discussed in relation to the well-documented phenomenon of latent (amorphous) track generation under ion irradiation, requiring a threshold value Se,th for the electronic stopping power Se. Our optical data have yielded a value of ≈5 keV/nm for such a threshold, within the range reported by independent single-track measurements. The propagation of the amorphous boundary into the crystal during irradiation indicates that the threshold value decreases on increasing the fluence. Complementary Rutherford backscattering–channeling and micro-Raman (on samples irradiated at 30 MeV) experiments have been performed to monitor the induced structural changes.

Journal ArticleDOI
TL;DR: In this paper, a theoretical model is developed and a molecular dynamics simulation technique is applied for the description of ultrashort laser ablation of metals using 0.1, 0.5 and 5-ps laser pulses at wavelengths of 248 and 800nm.

Journal ArticleDOI
TL;DR: In this paper, the authors measured the terahertz (THz) emission from samples as a function of excitation fluence in the reflection geometry, and found that the THz emission from both bulk and porous InP (111) saturates at high excitationfluence, emitting comparable levels of far-infrared radiation.
Abstract: Bulk n-InP wafers and porous membrances with (111) crystallographic orientation have been illuminated with 120 fs pulses of 800 nm radiation from a Ti:Sapphire amplified laser system. Terahertz (THz) emission from samples was measured as a function of excitation fluence in the reflection geometry. It was established that the THz emission from both bulk and porous InP (111) saturates at high excitation fluence, emitting comparable levels of far-infrared radiation. Below saturation, however, the emission from the porous InP (111) membrane was found to be approximately an order of magnitude greater in radiated electric field or approximately two orders of magnitude in power relative to the bulk sample. The observed increase in efficiency from the porous, relative to the bulk samples, can be attributed either to the local field enhancement in the porous network for the nonlinear contribution to the radiated THz fields, or to modifications of the transient currents resulting in enhanced THz radiation.

Journal ArticleDOI
A.M.P. Hussain1, Ashok Kumar1, D. Saikia1, Fouran Singh, D.K. Avasthi 
TL;DR: In this article, polypyrrole thin films doped with LiCF3SO3, [CH3(CH2)3]4NBF4 and [CH 3(CH 2)3]-4NPF6 have been electrodeposited potentiodynamically on ITO coated glass substrate.
Abstract: Conducting polymer polypyrrole thin films doped with LiCF3SO3, [CH3(CH2)3]4NBF4 and [CH3(CH2)3]4NPF6 have been electrodeposited potentiodynamically on ITO coated glass substrate. The polymer films are irradiated with 160 MeV Ni12+ ions at three different fluences of 5 × 1010, 5 × 1011 and 3 × 1012 ions cm−2. An increase in dc conductivity of polypyrrole films from ∼100 S/cm to ∼170 S/cm after irradiation with highest fluence is observed in four-probe measurement. X-ray diffractogram shows increase in the crystallinity of the polypyrrole films upon SHI irradiation, which goes on increasing with the increase in fluence. Absorption intensity increase in the higher wavelength region is observed in the UV–Vis spectra. The SEM studies show that the cauliflower like flaky microstructure of the surface of polypyrrole films turns globular upon SHI irradiation at fluence 5 × 1011 ions cm−2 and becomes smooth and dense at the highest fluence used. The cyclic voltammetry studies exhibit that the redox properties of the polypyrrole films do not change much on SHI irradiation.

Journal ArticleDOI
TL;DR: In this article, the influence of laser ablation of a Zn target in oxygen reactive atmosphere, the oxygen being supplied either by a standard gas inlet valve or from a radiofrequency (rf) oxygen plasma, was studied.