Showing papers on "Fluence published in 2007"
TL;DR: The observed transient behavior displays a notable “structural isosbestic” point and a threshold effect for the dependence of c-axis expansion on fluence (F), with Δc/F = 0.02 angstrom/(millijoule per square centimeter).
Abstract: Nonequilibrium phase transitions, which are defined by the formation of macroscopic transient domains, are optically dark and cannot be observed through conventional temperature- or pressure-change studies. We have directly determined the structural dynamics of such a nonequilibrium phase transition in a cuprate superconductor. Ultrafast electron crystallography with the use of a tilted optical geometry technique afforded the necessary atomic-scale spatial and temporal resolutions. The observed transient behavior displays a notable “structural isosbestic” point and a threshold effect for the dependence of c-axis expansion (Δc) on fluence (F), with Δc/F = 0.02 angstrom/(millijoule per square centimeter). This threshold for photon doping occurs at ∼0.12 photons per copper site, which is unexpectedly close to the density (per site) of chemically doped carriers needed to induce superconductivity.
206 citations
TL;DR: In this paper, an experimental characterization and a theoretical analysis of ultrashort laser ablation of a nickel target is presented, which highlights the more general and peculiar features of femtosecond (fs) laser ablations of metals.
Abstract: We present an experimental characterization and a theoretical analysis of ultrashort laser ablation of a nickel target, which highlights the more general and peculiar features of femtosecond (fs) laser ablation of metals. The study has been carried out by using visible (527 nm) laser pulses of ≈ 300 fs duration. The vacuum expansion dynamics of the ablated species has been investigated by using fast photography and optical emission spectroscopy, while the fs laser pulse–metal interaction has been studied theoretically by means of molecular dynamics simulations. Special attention has been given to the study of the dependence of ablation depth on laser fluence, which has been carried out by comparing the SEM analysis of micro-holes drilled into the nickel samples with the predictions of the theoretical model. The main outcomes of our investigation, which are very satisfactorily reproduced and accounted for by the theoretical model, are (i) the nonlinear dependence of the ablation yield on the laser fluence, and its reliance to the electron heat diffusion, in the process of redistribution of the absorbed energy, (ii) the splitting of the material blow-off into two main classes of species, atoms and nanoparticles, characterized by different expansion dynamics, and (iii) the different degrees of heating induced by the laser pulse at different depths into the material, which causes the simultaneous occurrence of various ablation mechanisms, eventually leading to atoms and nanoparticles ejection.
144 citations
TL;DR: In this paper, a numerical simulation of the two-temperature model has been performed for Au, Ag, Cu and Al, and an analytical model for the ablation rates in the high fluence regime is proposed.
119 citations
TL;DR: In this paper, the process of particle generation during ultrafast pulsed laser ablation of nickel is investigated, and two types of particles with different sizes depending on the laser fluence are found, indicating different particle generation mechanisms.
Abstract: The process of particle generation during ultrafast pulsed laser ablation of nickel is investigated. Two types of particles with different sizes depending on the laser fluence are found, indicating different particle generation mechanisms. By limiting the laser fluence below a threshold of strong plasma formation, the large dropletlike particles can be eliminated. In addition, by supplying different background gases, various crystalline structures are obtained for the particles, including Ni∕NiO core/shell spheres and NiO cubes. This study provides evidence that ultrafast laser ablation can be a room temperature physical method for generating nanocrystals with a narrow particle size distribution.
101 citations
01 Feb 2007-Nuclear Instruments & Methods in Physics Research Section B-beam Interactions With Materials and Atoms
TL;DR: In this article, the effects induced by pulsed laser ablation on different materials as a function of the laser wavelength were investigated experimentally on different metals, semiconductors and polymers.
Abstract: A study of the effects induced by pulsed laser ablation on different materials as a function of the laser wavelength is presented. In particular the ablation at low laser fluence, of the order of 10 8 –10 10 W/cm 2 with ns pulse width, is investigated experimentally on different metals, semiconductors and polymers. Two theoretical models, explain the experimental results about the fluence threshold value measurements, as depending on the laser wavelength are discussed. The photothermal process is valid for the estimation of the threshold fluence for IR and visible radiation, both inducing thermal heating in metals and semiconductors through the photon-free electron energy transfer. This model is not valid for polymers. The photochemical process is valid for the estimation of the threshold fluence for UV radiation, which photon energy is higher with respect to the chemical binding energy. This radiation induces chemical bond breaking in insulators and scission and cross linking effects can be produced. This last model is not valid for metals and semiconductors.
93 citations
TL;DR: In this paper, the authors investigated the transition of the height and diameter as functions of fluence and pulse width, and concluded that the decrease of size is due to the diffusion of electron to notexcited region, and due to heat conduction to not heated region or substrate, or change of absorbance of laser.
91 citations
TL;DR: In this article, the authors showed that the threshold for surface-damage is on the order of the fluence required for thermal melting for larger fluences, suggesting that the craters are formed by two-phase vaporization.
Abstract: We exposed samples of B4C, amorphous C, chemical-vapor-deposition (CVD)-diamond C, Si, and SiC to single 25 fs-long pulses of 325 nm free-electron-laser radiation at fluences of up to 22 J/cm{sup 2} The samples were chosen as candidate materials for x-ray free electron laser (XFEL) optics We found that the threshold for surface-damage is on the order of the fluence required for thermal melting For larger fluences, the crater depths correspond to temperatures on the order of the critical temperature, suggesting that the craters are formed by two-phase vaporization [1] XFELs have the promise of producing extremely high-intensity ultrashort pulses of coherent, monochromatic radiation in the 1 to 10 keV regime The expected high output fluence and short pulse duration pose significant challenges to the optical components, including radiation damage It has not been possible to obtain direct experimental verification of the expected damage thresholds since appropriate x-ray sources are not yet available FLASH has allowed us to study the interaction of high-fluence short-duration photon pulses with materials at the shortest wavelength possible to date With these experiments, we have come closer to the extreme conditions expected in XFEL-matter interaction scenarios than previously possible
81 citations
TL;DR: In this paper, the results of patterning of the indium-tin oxide (ITO) film on the glass substrate with high repetition rate picosecond lasers at various wavelengths are presented.
76 citations
TL;DR: In this article, the distribution and nature of 3He implantation-induced defects in polycrystalline tungsten samples were studied by Positron Annihilation Spectroscopy as a function of implantation fluence.
76 citations
TL;DR: For fluences typical of high energy short pulse laser experiments, saturation occurs, inducing the appearance of artifact ringlike structures, which can be distinguished from the genuine rings occurring below saturation and characteristic of low energy laser accelerated proton beams.
Abstract: The occurrence of saturation in CR39 solid state nuclear track detectors has been systematically studied as a function of the incident ion (alpha particles and laser-accelerated protons) fluence and the etching time. When overexposed (i.e., for fluences above approximately 10(8) particles/cm(2)) and/or overetched, the CR39 detectors enter a saturated regime where direct track counting is not possible anymore. In this regime, optical measurements of saturated CR39 detectors become unreliable as well, since the optical response of the saturated detectors with respect to the ion fluence is highly nonlinear. This nonlinear optical response is likely due to scattering from the surface of irregular clumping patterns which have a diameter approximately 20 microm, i.e., ten times larger than the diameter of individual tracks. These patterns, which aggregate many individual tracks, are observed to develop in highly saturated regimes. For fluences typical of high energy short pulse laser experiments, saturation occurs, inducing the appearance of artifact ringlike structures. By careful microscopic analysis, these artifact ring patterns can be distinguished from the genuine rings occurring below saturation and characteristic of low energy laser accelerated proton beams.
74 citations
TL;DR: In this article, conditions defining melting fluence thresholds for silicon under pulsed laser irradiation are introduced, and a definition of the non-thermal melting threshold is given as the laser fluence above which the nonthermal contribution dominates over the thermal contribution.
Abstract: Conditions defining melting fluence thresholds for silicon under pulsed laser irradiation are introduced in this paper. The melting conditions include both thermal and non-thermal contributions. Furthermore, a definition of the non-thermal melting threshold is given as the laser fluence above which the non-thermal contribution dominates over the thermal one and a short-lived non-thermal liquid phase appears in the femtosecond time scale. Numerical values of thresholds obtained through a two-temperature model are in good agreement with experimental data. The dependence of fluence thresholds on both wavelength and pulse width is explored and discussed in detail.
TL;DR: In this article, the formation of ultrathin amorphized Si layer by femtosecond laser irradiation is reported and the thickness of amorphous Si layer was found to be quite uniform and did not depend on the number of irradiated laser pulses and fluence.
Abstract: Formation of ultrathin amorphized Si layer by femtosecond laser irradiation is reported in this letter. Below the fluence of ablation threshold, femtosecond laser irradiation induced an amorphization of crystalline Si. The authors confirmed the thickness of amorphous Si layer by transmission electron microscope. The thickness of the amorphized layer was found to be quite uniform and did not depend on the number of irradiated laser pulses and fluence, which was related to the effective light penetration depth.
TL;DR: In this paper, the authors describe the characteristics features of the plasma plume dynamics and material removal efficiency during ultrashort, visible (527 nm, ≈300 fs) laser ablation of nickel in high vacuum.
Abstract: We present an experimental characterization describing the characteristics features of the plasma plume dynamics and material removal efficiency during ultrashort, visible (527 nm, ≈300 fs) laser ablation of nickel in high vacuum. The spatio-temporal structure and expansion dynamics of the laser ablation plasma plume are investigated by using both time-gated fast imaging and optical emission spectroscopy. The spatio-temporal evolution of the ablation plume exhibits a layered structure which changes with the laser pulse fluence F. At low laser fluences (F 0.5 J/cm2), a third component of much faster atoms is observed to precede the main atomic plume component. These atoms can be ascribed to the recombination of faster ions with electrons in the early stages of the plume evolution. A particularly interesting feature of our analysis is that the study of the ablation efficiency as a function of the laser fluence indicates the existence of an optimal fluence range (a maximum) for nanoparticles generation, and an increase of atomization at larger fluences.
TL;DR: In this article, the ablation-induced plasma physics at reduced ablation crater dimensions is experimentally investigated, where laser pulses are tightly focused through objective lenses onto a thin film coated on quartz wafer in order to obtain ablation craters of submicron lateral dimensions.
Abstract: The ablation-induced plasma physics at reduced ablation crater dimensions is experimentally investigated. Frequency doubled femtosecond laser pulses are tightly focused through objective lenses onto a Cr thin film coated on quartz wafer in order to obtain ablation craters of submicron lateral dimensions. Side-view time-resolved emission images and the corresponding spectra depict the detailed plasma evolution at the fluence range near the ablation threshold. Collected emission spectra at the laser fluence level of around two to three times of ablation threshold display characteristic atomic transition peaks of the ablated Cr material from submicron ablation craters. This finding confirms that improved spatial resolution for laser-induced breakdown spectroscopy can be achieved.
TL;DR: In this article, a-Si:H films of thickness in the range of 1.5 μm to 2 μm were applied to soda lime glass after exposure to femtosecond laser pulses and X-ray diffraction results indicated the formation of a nano-crystalline structure with (111 and (311) crystal orientation after the laser treatment.
Abstract: We report the observation of crystallization and simultaneous formation of surface microstructures in hydrogenated amorphous silicon (a-Si:H) thin films as one step laser processing. Light trapping microstructures of around 300 nm in height were formed on a-Si:H films of thickness in the range of 1.5 μm to 2 μm deposited on soda lime glass after exposure to femtosecond laser pulses. Scanning electron microscope (SEM) images show the formation of spikes that are around 1 μm part and their heights could be controlled by the laser fluences. Atomic force microscope (AFM) images were taken to study the roughness created on the surface. The mean roughness of the textured surface increases with laser fluence at smaller power densities, and for power densities beyond 0.5 J/cm2 the film removal deteriorates the texturing. X-ray diffraction results indicate the formation of a nano-crystalline structure with (111) and (311) crystal orientation after the laser treatment. The observed black color and enhanced optical absorption in the near infrared region in laser treated films may be due to a combined effect of light trapping in the micro-structured silicon surface because of multiple total internal reflections, phase change in the film, possible defect sites induced after laser treatment and formation of SiOx. Demonstration of light trapping microstructures in thin a-Si:H films and simultaneous crystallization could provide new opportunities for optoelectronic devices.
TL;DR: In this paper, the authors used a 355-nm DPSS Nd:YVO4 laser to carry out a laser ablation of polyimide (PI) and copper (Cu) films.
01 Apr 2007
TL;DR: In this paper, the formation of cone-like protrusions (CLP) on titanium (Ti) plate by the femtosecond laser ablation was reported, and the formation process of the CLP was found to depend on the laser produced periodic microstructures oriented parallel to the direction of the laser polarization vector.
Abstract: Microstructure formation of cone-like protrusions (CLP) on titanium (Ti) plate by the femtosecond laser ablation is reported. The number of the laser pulses to irradiate the Ti plate was varied from 10 to 230 at average laser fluence of 0.75 J/cm2 per pulse on the plate. The onset of CLP creation was observed with exposure of 70 pulses, and yielding CLP with a height from the bottom of the irradiation area of about 9 m after 230 pulses. The formation process of the CLP was found to depend on the laser produced periodic microstructures oriented parallel to the direction of the laser polarization vector.
TL;DR: In this paper, a modified version of the laser induced backside wet etching (LIBWE) was proposed, where the absorbing liquid was replaced by an absorbing solid thin film.
TL;DR: In this article, the effect of ion irradiation on the order in the atomic arrangement of Li 2 TiO 3 crystal was examined by X-ray diffraction (XRD) and Raman spectroscopy.
TL;DR: In this paper, a Schwarzschild mirror objective coated with Mo/Si multilayers was adapted to a compact laser-based extreme ultraviolet (EUV) plasma source (pulse energy 3mJ at 14.5nm, plasma diameter ∼300 μm).
Abstract: In order to perform material interaction studies with intense extreme ultraviolet (EUV) radiation, a Schwarzschild mirror objective coated with Mo/Si multilayers was adapted to a compact laser-based EUV plasma source (pulse energy 3 mJ at λ=13.5 nm, plasma diameter ∼300 μm). By 10× demagnified imaging of the plasma a pulse energy density of ∼75 mJ∕cm2 at a pulse length of 6 ns can be achieved in the image plane of the objective. As demonstrated for poly(methyl methacrylate) (PMMA), photoetching of polymer surfaces is possible at this EUV fluence level. This paper presents first results, including a systematic determination of PMMA etching rates under EUV irradiation. Furthermore, the contribution of out-of-band radiation to the surface etching of PMMA was investigated by conducting a diffraction experiment for spectral discrimination from higher wavelength radiation. Imaging of a pinhole positioned behind the plasma accomplished the generation of an EUV spot of 1 μm diameter, which was employed for direct...
TL;DR: In this article, the influence of low energy helium and hydrogen/deuterium plasma irradiation to tungsten or Tungsten-coated graphite samples was investigated and experimental conditions of helium hole/bubble formation and hydrogen blister formation were summarized.
TL;DR: In this paper, the authors proposed a physical mechanism of laser-induced bursting of holes/bubbles for achieving a significant reduction in ablation power threshold for tungsten (W) using optical emission spectroscopy.
Abstract: Nanosecond laser ablation of tungsten (W) exposed to helium plasma is investigated using optical emission spectroscopy. Submicrometer-sized holes/bubbles are formed on the surface of W when it was exposed to the helium plasma at a sufficiently high temperature (≳1500–1600K). The emissions from a virgin W (before the helium plasma irradiation) cannot be detected when the fluence is <1J∕cm2; however, the threshold fluence for the detection of neutral W emission after it was exposed to the helium plasma is ∼0.2J∕cm2. The physical mechanism of laser-induced bursting of holes/bubbles is proposed for achieving a significant reduction in ablation power threshold.
TL;DR: In this article, the changes in the morphology, structure and chemical composition of the layers were studied by SEM, EDS, XPS, SIMS and Raman spectroscopy as a function of the laser fluence in the 4-60 cm −2.
TL;DR: Displacement damage (DD) caused by fast neutrons in unbiased Gallium Arsenide (GaAs) light emitting diodes (LED) resulted in a reduction of the light output, but a similar type of LED irradiated with gamma rays from a (60)Co source up to a dose level in excess of 1.0 kGy (1.0 x 10(5) rad) was found to show no significant drop in the light emission.
Abstract: Displacement damage (DD) caused by fast neutrons in unbiased Gallium Arsenide (GaAs) light emitting diodes (LED) resulted in a reduction of the light output. On the other hand, a similar type of LED irradiated with gamma rays from a (60)Co source up to a dose level in excess of 1.0 kGy (1.0 x 10(5) rad) was found to show no significant drop of the light emission. This phenomenon was used to develop a low cost passive fluence monitor and kinetic energy released per unit mass dosemeter for accelerator-produced neutrons. These LED-dosemeters were used to assess the integrated fluence of photoneutrons, which were contaminated with a strong bremsstrahlung gamma-background generated by the 730 MeV superconducting electron linac driving the free electron laser in Hamburg (FLASH) at Deutsches Elektronen-Synchrotron. The applications of GaAs LED as a routine neutron fluence monitor and DD precursor for the electronic components located in high-energy accelerator environment are highlighted.
TL;DR: The refractive index profile as a function of the applied electron fluence has been determined by a reflection scan method in the nonlinear optical organic crystal 4-N, N-dimethylamino-4'-N-N'-methyl-stilbazolium tosylate (DAST).
Abstract: We report on optical channel waveguiding in an organic crystalline waveguide produced by direct electron beam patterning. The refractive index profile as a function of the applied electron fluence has been determined by a reflection scan method in the nonlinear optical organic crystal 4-N, N-dimethylamino-4’-N’-methyl-stilbazolium tosylate (DAST). A maximal refractive index reduction of Δn1=-0.3 at a probing wavelength of 633 nm has been measured for an electron fluence of 2.6mC/cm2. Furthermore, a new concept of direct channel waveguide patterning in bulk crystals is presented and waveguiding has been demonstrated in the produced structures by end-fire coupling. Mach-Zehnder modulators have been successfully realized and a first electro-optic modulation at a wavelength of λ=1.55 µm has been demonstrated therein.
TL;DR: In this paper, laser ablation was applied for surface cleaning and spectroscopic diagnostics of historical paper documents and model samples in the framework of the conservation projects in the literature.
TL;DR: In this article, Yttria-stabilized zirconia single crystals were irradiated with a variety of different swift heavy ions (from 145MeV C to 2.6GeV U) in a broad fluence range (between 1011 and 1015cm−2).
Abstract: Yttria-stabilized zirconia single crystals were irradiated with a variety of different swift heavy ions (from 145MeV C to 2.6GeV U) in a broad fluence range (between 1011 and 1015cm−2). Surface profilometry measurements show that the out-of-plane expansion of the samples increases versus ion fluence up to an asymptotic value of about 0.2%; the larger the ion mass, the smaller the fluence needed to reach saturation. Rutherford backscattering spectrometry data on irradiated crystals under channeling conditions give clear evidence of lattice damage creation for ions heavier than Br corresponding to a threshold electronic stopping power about 20keVnm−1. In contrast, no threshold is found for the swelling data which scale fairly well with the number of displacements per atom (except for the irradiation with U ions). In all cases we find a linear increase of the out-of-plane expansion versus the concentration of F+-type centers (singly ionized oxygen vacancies) measured by electron paramagnetic resonance spectr...
TL;DR: In this article, the formation of buried heavily damaged and amorphous layers by a variety of swift-ion irradiations (F at 22MeV, O at 20MeV and Mg at 28MeV) on congruent LiNbO3 has been investigated.
Abstract: The formation of buried heavily damaged and amorphous layers by a variety of swift-ion irradiations (F at 22MeV, O at 20MeV, and Mg at 28MeV) on congruent LiNbO3 has been investigated. These irradiations assure that the electronic stopping power Se(z) is dominant over the nuclear stopping Sn(z) and reaches a maximum value inside the crystal. The structural profile of the irradiated layers has been characterized in detail by a variety of spectroscopic techniques including dark-mode propagation, micro-Raman scattering, second-harmonic generation, and Rutherford backscattering spectroscopy∕channeling. The growth of the damage on increasing irradiation fluence presents two differentiated stages with an abrupt structural transition between them. The heavily damaged layer reached as a final stage is optically isotropic (refractive index n=2.10, independent of bombarding ion) and has an amorphous structure. Moreover, it has sharp profiles and its thickness progressively increases with irradiation fluence. The dy...
TL;DR: The feasibility of depositing a porous calcium phosphate (CaP) bio-ceramic coating using a continuous wave Nd:YAG laser on a Ti-6Al-4V substrate has been demonstrated and microhardness measurements in the cross section of samples showed a maximum hardness within the coating.
Abstract: In the present paper the feasibility of depositing a porous calcium phosphate (CaP) bio-ceramic coating using a continuous wave Nd:YAG laser on a Ti-6Al-4V substrate has been demonstrated. The advantages offered by such porous bio-ceramic coating are its inertness combined with the mechanical stability of the highly convoluted interface that develops when bone grows into the pores of ceramic. The formation of different phases with varying laser fluences is studied using x-ray diffraction (XRD). A quantitative estimation of the crystallite size and relative amounts of Ti and other predominant phases such as TiO(2) and alpha-tricalcium phosphate (alpha-TCP) were obtained. An increase in the crystallite size with increasing laser fluence is observed for all the above three phases. It is observed that TiO(2) is the predominant phase for all laser fluences and there is an increase in the alpha-TCP phase with increasing laser fluence. Surface porosity measurements indicated a decreasing trend with increasing laser fluence. Microhardness measurements in the cross section of samples showed a maximum hardness within the coating. The bioactivity of the coatings was further demonstrated by the formation of an apatite-like layer on the surface of the sample after being immersed in a simulated biofluid.
01 Apr 2007-Nuclear Instruments & Methods in Physics Research Section B-beam Interactions With Materials and Atoms
TL;DR: In this article, the morphology of gold nanoclusters deposited on the SiO 2 surface and irradiated by 200 keV-Ar + ion beam at room temperature was investigated by atomic force microscopy and transmission electron microscopy.
Abstract: The morphology of gold nanoclusters deposited on the SiO 2 surface and irradiated by 200 keV-Ar + ion beam at room temperature was investigated by atomic force microscopy and transmission electron microscopy. The possibility of controlling the Au clusters size and size distribution by an appropriate choice of the process parameters was demonstrated and, in particular, the effects of ion flux and fluence was studied. The experimental data were modelled by clusters ripening and inverse ripening theory taking into account the sputtering process of the gold atoms from the surface by ion irradiation.