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Showing papers on "Fluence published in 1999"


Journal ArticleDOI
TL;DR: In this article, the authors show that high precision machining of all dielectrics (oxides, fluorides, explosives, teeth, glasses, ceramics, SiC, etc.) with no thermal shock or distortion of the remaining material by this mechanism is described.
Abstract: There is a strong deviation from the usual τ1/2 scaling of laser damage fluence for pulses below 10 ps in dielectric materials. This behavior is a result of the transition from a thermally dominated damage mechanism to one dominated by plasma formation on a time scale too short for significant energy transfer to the lattice. This new mechanism of damage (material removal) is accompanied by a qualitative change in the morphology of the interaction site and essentially no collateral damage. High precision machining of all dielectrics (oxides, fluorides, explosives, teeth, glasses, ceramics, SiC, etc.) with no thermal shock or distortion of the remaining material by this mechanism is described.

508 citations


Journal ArticleDOI
TL;DR: In this article, femtosecond laser pulses were applied to study the energy deposition depth and transfer to the lattice for Au, Ni, and Mo films of varying thickness, and the onset of melting, defined here as damage threshold, was detected by measuring changes in the scattering, reflection and transmission of the incident light.
Abstract: Femtosecond laser pulses were applied to study the energy deposition depth and transfer to the lattice for Au, Ni, and Mo films of varying thickness. The onset of melting, defined here as damage threshold, was detected by measuring changes in the scattering, reflection and transmission of the incident light. Experiments were done in multi-shot mode and single-shot threshold fluences were extracted by taking incubation into account. Since melting requires a well-defined energy density, we found the threshold depends on the film thickness whenever this is smaller than the range of electronic energy transport. The dependence of the threshold fluence on the pulse length and film thickness can be well described by the two-temperature model, proving that laser damage in metals is a purely thermal process even for femtosecond pulses. The importance of electron–phonon coupling is reflected by the great difference in electron diffusion depths of noble and transition metals.

262 citations


Journal ArticleDOI
TL;DR: In this article, two different ablation regimes were found in terms of the laser fluence and optical skin depth and thermal diffusion length, respectively, for the femtosecond laser ablation of bulk crystals of Au, Ag and Cu.
Abstract: Femtosecond laser ablation of metallic bulk crystals of Au, Ag and Cu was experimentally studied with laser pulse widths ranging from 120 fs through 800 fs at a center wavelength of 780 nm for micro-machining applications. Two different ablation regimes were found in terms of the laser fluence. The characteristic length of different ablation regimes was explained in terms of the optical skin depth and thermal diffusion length; it was determined by the peak electron temperature in the two-temperature model. The lateral feature of the two ablation regimes is discriminated by the amount of particles accumulated by the evaporation process. Ablated particle was observed less in the lower fluence regime than in the higher fluence regime, but there was no significant difference on the ablated surface. The parameters used in the two-temperature model, are discussed in order to model the ultrashort pulsed laser ablation process theoretically. It is shown that the obtainable range of the lower fluence regime is enhanced with the shorter pulse lasers, because the ablation etch rate is decreased with longer pulse width.

204 citations


Journal ArticleDOI
TL;DR: In this article, the leakage current increase of silicon detectors irradiated with fast neutrons was measured in the fluence range from 10 11 to 10 15 ǫ −2 for a wide range of different starting material.
Abstract: The leakage current increase of silicon detectors irradiated with fast neutrons was measured in the fluence range from 10 11 to 10 15 cm −2 for a wide range of different starting material. The oxygen concentration in the investigated silicon varied from 9×10 17 cm −3 to below 2×10 14 cm −3 and the carbon concentration from 2×10 16 cm −3 to below 5×10 15 cm −3 . Furthermore the resistivity differed from 100 Ω cm to 20 kΩ cm for the used n-type and from 400 Ω cm to 2 kΩ cm for the p-type silicon. It is found that up to the highest fluence the current-related damage parameter alpha is almost independent of the initial resistivity and impurity concentration. After irradiation a universal annealing behavior for all material is observed which unmistakably indicates that the microscopic defects underlying the generation of leakage current are of intrinsic origin. Furthermore it is shown that the parameterization of the annealing behavior at an elevated temperature (here 60°C) provides an excellent tool for comparing the so-called hardness factors of different irradiation sources. As an example the hardness factors for the 24 GeV/ c CERN proton synchrotron and the TRIGA research reactor in Ljubljana were determined to be 0.51 and 0.90, respectively.

200 citations


Journal ArticleDOI
TL;DR: In this article, the ablation rate expressed as the amount of removed material per laser shot was calculated for pure metal samples under different experimental conditions: laser fluence (1.3 −16.7 J cm 2 ), buffer gas (air, He and Ar) and gas pressure (10 3 ‐10 5 mbar).
Abstract: The ablation rate expressed as the amount of removed material per laser shot was calculated for pure metal samples under different experimental conditions: laser fluence (1.3‐16.7 J cm 2 ), buffer gas (air, He and Ar) and gas pressure (10 3 ‐10 5 mbar). Fluence values covered the range between the plasma threshold (~1‐2 J cm 2 for most elements) and 16.7 J cm 2 . The 581 nm output of an excimer-pumped dye laser was used. Results pointed out a strong dependence of ablation rate on experimental parameters. At high fluence, the ablated material efficiently attenuates the incoming laser radiation (plasma shielding) and reduces the ablation rate. The extent of this shielding effect depend also on the experimental variables (buffer gas, pressure) and sample nature. These studies are useful to determine the amount of ablated material as a function of experimental parameters, to understand the extension of the shielding process and to establish the conditions under which it may be avoided. Copyright ” 1999 John Wiley & Sons, Ltd.

110 citations


Journal ArticleDOI
TL;DR: In this article, two distinct regimes of molecular ejection separated by a well-defined threshold fluence are observed in molecular dynamics simulation of pulsed laser irradiation of an organic solid.
Abstract: Two distinct regimes of molecular ejection separated by a well-defined threshold fluence are observed in molecular dynamics simulation of pulsed laser irradiation of an organic solid. At fluences above the threshold a collective multilayer ejection or ablation occurs where large liquid droplets are ejected and the total yield of the ablated material follows a critical volume density of the deposited energy. Below threshold thermal desorption from the surface is observed and the desorption yield has an Arrhenius-type dependence on the laser fluence. The yield of monomers does not have a step increase at the threshold and thus deceptively does not give a straightforward interpretation of the ejection mechanisms.

105 citations


Journal ArticleDOI
TL;DR: In this article, the authors demonstrate the direct deposition of Pt, Cr and In2O3 microstructures on glass using an ultrashort excimer laser pulse ablating the source film at the quartz/film interface and results in the forward-transfer deposition of material onto the nearby glass receiver.

84 citations


Journal ArticleDOI
TL;DR: In this article, the effect of the initial sample temperature and laser pulse duration on the mechanisms of molecular ejection from an irradiated molecular solid is investigated by large-scale molecular dynamics simulations.
Abstract: The effect of the initial sample temperature and laser pulse duration on the mechanisms of molecular ejection from an irradiated molecular solid is investigated by large- scale molecular dynamics simulations. The results of simu- lations performed for two initial temperatures are found to be consistent with the notion of two distinct regimes of mo- lecular ejection separated by a threshold fluence. At low laser fluences, thermal desorption from the surface is observed and the desorption yield is described by an Arrhenius-type depen- dence on the laser fluence. At fluences above the threshold, a collective multilayer ejection or ablation occurs and the ab- lation depth follows a critical density of the deposited energy. The same activation energy for desorption and critical energy density for ablation provide a good description of the fluence dependence of the total yield in simulations with different ini- tial temperatures. Comparison of the simulation results for two pulse durations is performed to elucidate the differences in the ejection mechanisms in the regimes of thermal and stress confinement. We find that in the regime of stress con- finement, high thermoelastic pressure can cause mechanical fracture=cavitation leading to energetically efficient ablation and ejection of large relatively cold chunks of material.

84 citations


Journal ArticleDOI
TL;DR: In this paper, the authors performed neutron response calibrations for miniature SiC semiconductor detectors based on a Schottky diode design in neutron fields maintained at the National Institute of Standards and Technology (NIST).
Abstract: Neutron response calibrations have been performed for miniature SiC semiconductor detectors based on a Schottky diode design in neutron fields maintained at the National Institute of Standards and Technology (NIST). The SiC diodes detect neutrons via neutron-induced charged particles (tritons) produced by the 6 Li(n,α) 3 H reaction. The neutron response was calibrated at fluence rates from 1.76×10 4 to 3.59×10 10 cm −2 s −1 in NIST neutron fields. The maximum deviation from linearity of the fit of the neutron response of the SiC detectors to the NIST-measured fluence rates is much less than 5%, which is the estimated uncertainty in the measured fluence rates. A direct comparison of the SiC count rates to count rates obtained with a NIST double fission chamber over limited ranges where the detector positions and configurations remain unchanged shows a relative precision of ±0.6%. In a separate set of calibrations, a SiC neutron detector that had been previously irradiated with a fast ( E >1 MeV) neutron fluence of 1.3×10 16 cm −2 was found to have an absolute neutron fluence rate response that was indistinguishable from that of a previously unirradiated detector.

76 citations


Journal ArticleDOI
25 Jun 1999-Langmuir
TL;DR: In this article, the surface roughness of photoablated poly(ethylene terephthalate) (PET) has been characterized by atomic force microscopy (AFM), micro-confocal Raman spectroscopy, and wettability measurements.
Abstract: Surface topography, crystallinity, and wettability of photoablated poly(ethylene terephthalate) (PET) resulting from various ablation conditions have been characterized by atomic force microscopy (AFM), microconfocal Raman spectroscopy, and wettability measurements. Two ablation modes have been considered here: (i) static ablation, where the samples are immobilized in front of the pulsed laser beam and (ii) dynamic ablation, where the samples are moved in order to write three-dimensional structures in the polymer. Laser fluence, repetition rate, and speed of the substrate motion during the ablation process have been varied. The laser fluence has been observed to strongly affect the resulting surface roughness, which increased to a maximum value at fluences between 70 and 600 mJ·cm-2. For all fluences in the range of 1000−3000 mJ·cm-2, the roughness was found to be similar. No remarkable effects could be attributed to the pulse frequency of the 23 ns laser pulses. Raman spectroscopy studies demonstrated t...

72 citations


Journal ArticleDOI
TL;DR: In this article, the structural characteristics, optical and electrical properties of the laser-irradiated films were investigated and compared with those of heat-treated films, and the differences in crystallinity and orientation were explained in terms of the thermal effect caused by laser irradiation.

Journal ArticleDOI
TL;DR: In this article, micro-lenses with well-defined optical parameters are generated on polymethylmethacrylate (PMMA) substrates doped with diphenyltriazene (DPT) by controlled use of a swelling effect generated under conditions of subablative excimer laser illumination.
Abstract: Micro-lenses with well-defined optical parameters are generated on polymethylmethacrylate (PMMA) substrates doped with diphenyltriazene (DPT) by controlled use of a swelling effect generated under conditions of subablative excimer laser illumination. The surface profiles depend on the laser spot size and energy density. A sensitively balanced combination of matrix softening, substrate volume expansion due to photochemical nitrogen release, and surface tension is responsible for the final shape of the lenses. Complete arrays of identical lenses with 15 μm diameters and a focal length of 30 μm are produced by irradiation of (0.25 wt. %) DPT-PMMA with a single laser pulse at a wavelength of 308 nm and a fluence of 3 J/cm2. It is shown experimentally and theoretically that appropriate volume expansion is possible without introducing internal light scattering due to the formation of small bubbles.

Journal ArticleDOI
TL;DR: In this article, several fundamental aspects of defect cluster accumulation in irradiated ceramics and face centered cubic metals are reviewed, with particular emphasis on radiation hardening and the microstructural evolution in Cu observed by transmission electron microscopy (TEM).
Abstract: Several fundamental aspects of defect cluster accumulation in irradiated ceramics and face centered cubic metals are reviewed, with particular emphasis on radiation hardening and the microstructural evolution in Cu observed by transmission electron microscopy (TEM). At temperatures where interstitials are mobile (> 50 K in Cu), the defect cluster density in pure Cu is initially proportional to the dose and exhibits a square root dose dependence above ∼ 10−4 displacements per atom. This fluence dependence (determined from electrical resistivity and TEM studies) helps to resolve a long-standing controversy on the fluence dependence of radiation hardening. The fraction of freely migrating interstitials in copper irradiated with 14 MeV neutrons at room temperature is ∼ 11%. The activation energy for annealing stage V (stacking fault tetrahedra evaporation) in neutron-irradiated copper has been measured to be 0.84eV. Some features of the point defect accumulation behavior in ceramics are found to be v...

Journal ArticleDOI
TL;DR: This method has application for those situations in which GUVR from more than one direction or source impinges on a three‐dimensional object, and when it is of interest to determine the radiant fluence experienced by the object.
Abstract: A method is demonstrated for measuring germicidal (254 nm) ultraviolet radiation (GUVR) in an omnidirectional manner. This method has application for those situations in which GUVR from more than one direction or source impinges on a three-dimensional object, and when it is of interest to determine the radiant fluence experienced by the object. For this purpose spherical quartz vessels were constructed varying from 0.8 to 1.25 cm in outside diameter. The vessels were filled with an actinometric solution consisting of KI and KIO3. This solution is optically opaque at 254 nm and is insensitive to room light. Upon exposure to GUVR this solution, which counts all of the 254 nm photons, forms triiodide. Following radiation, the contents of the vessel are removed, the absorbance of triiodide measured and the fluence rate determined based on a relationship that takes the volume to cross-sectional area of the actinometer into account. It is demonstrated that, in accordance with theory, the area of the sphere that intercepts the radiant energy is equal to the cross-sectional area of the sphere. A demonstration of the utility of this method was carried out in a test facility 90 m3 equipped with five GUVR lamps, one in each corner and one in the center of the room, arranged so as to irradiate the air in the upper portion of the room. Twenty spherical actinometers were evenly distributed around the room and exposed for either 30 or 90 min. The fluence rate varied from one part of the room to another, peaking near the GUVR lamps at 65-85 microW per cm2. By averaging over all 20 points, a pseudoaverage fluence rate for the room was found to be 42 and 44 microW per cm2 for the 30 and 90 min exposures, respectively. The similarities in the values for this metric demonstrates that the actinometric response is linear over this exposure range.

Journal ArticleDOI
TL;DR: In this paper, the effective sputter yield during pulsed-laser deposition was measured by measuring the deposition rate on tilted substrates, and the sputter yields of up to 0.17 and 0.55 were found at a laser fluence of 4.5 J/cm2 for Fe and Ag, respectively.
Abstract: To determine the effective sputter yield during pulsed-laser deposition a method by measuring the deposition rate on tilted substrates is proposed. Under vacuum conditions, sputter yields of up to 0.17 and 0.55 were found at a laser fluence of 4.5 J/cm2 for Fe and Ag, respectively. These strong resputtering effects are induced by the large fraction of energetic ions occurring during deposition. With decreasing laser fluence or increasing Ar gas pressure, the sputter yields are reduced due to a decrease of the kinetic energy of the ions. For the deposition of stoichiometric films, an optimum Ar partial pressure of about 0.04 mbar exists, where the deposition rate is highest and the sputter yield is reduced.

Journal ArticleDOI
TL;DR: In this paper, the photoluminescence of Si implanted and annealed SiO2 films on Si have been performed to determine the depth distribution of luminescent Si nanocrystals.
Abstract: Depth-resolved measurements of the photoluminescence of Si implanted and annealed SiO2 films on Si have been performed to determine the depth distribution of luminescent Si nanocrystals. Si nanocrystals with diameters ranging from ~ 2 to 5 nm were formed by implantation of 35 keV Si ions into a 110-nm-thick thermally grown SiO2 film on Si(100) at a fluence of 6 × 1016 Si/cm2, followed by a thermal anneal at 1100 °C for 10 min. The photoluminescence spectrum is broad, peaks at lambda =790 nm, and contains contributions from both recombination of quantum confined excitons in the nanocrystals and ion-implantation-induced defects. By chemical etching through the SiO2 film in steps and analyzing the changes in the photoluminescence spectrum after each etch step, the depth from which each of the two luminescence features originate is determined. The etch rate of the oxide, as derived from Rutherford backscattering spectrometry data, varies from 1.3 nm/s in the regions of small excess Si to 0.6 nm/s at the peak of the concentration profile (15 at. % excess Si). It is found that the defect luminescence originates from an ~ 15-nm-thick near-surface region. Large nanocrystals luminescing at long wavelengths (lambda =900 nm) are mainly located in the center of the film, where the Si concentration is highest (48 at. %). This is corroborated by transmission electron microscopy that shows a high density of Si nanocrystals in the size range of 2–5 nm in the center of the film. The largest density of small luminescent nanocrystals (lambda =700 nm), not detectable by electron microscopy is found near the SiO2 surface and the SiO2/Si interface. This is attributed to either the fact that the surface and the SiO2/Si interface affect the Si nanocrystal nucleation kinetics in such a way that small nanocrystals are preferentially formed in these regions, or an optical interaction between nanocrystals of different sizes that quenches the luminescence of small nanocrystals in the center of the film.

Journal ArticleDOI
TL;DR: In this article, a study of laser-induced back ablation of aluminum thin film targets with picosecond laser pulses is reported, where the authors studied ablated plume edge velocities as a function of film thickness, laser pulse width, and incident laser fluence.
Abstract: A study of laser-induced back ablation of aluminum thin film targets with picosecond laser pulses is reported. Ablated plume edge velocities are studied as a function of film thickness, laser pulse width, and incident laser fluence. Edge velocity results are compared to a model of total transmitted fluence incident at the substrate/film interface. A model including laser-induced avalanche ionization and multiphoton ionization mechanisms in the substrate shows a transmitted fluence limit which is consistent with observed edge velocity limits.

Journal ArticleDOI
TL;DR: In this article, the authors investigated heat transfer and phase change phenomena during excimer laser interaction with nickel specimens, and found that surface evaporation occurs when the laser fluence is below 5.2 J cm −2.

Journal ArticleDOI
TL;DR: In this article, an accurate radiation degradation model, based on measured radiation damage to devices and physical principles on radiation-induced defects in Si, has been established to improve the radiation-resistance of the Czochralski (CZ)-grown and floating-zone (FZ) grown single-crystal Si space solar cells.
Abstract: An accurate radiation degradation model, based on measured radiation damage to devices and physical principles on radiation-induced defects in Si, has been established to improve the radiation-resistance of the Czochralski (CZ)-grown and floating-zone (FZ)-grown single-crystal Si space solar cells. We have successfully carried out the optimization of radiation-resistant Si space solar cells by taking into account the effective base carrier concentration dependence of the most important analytical parameters, damage coefficient K/sub L/, for the minority-carrier diffusion length and carrier removal rate R/sub c/ for majority-carriers. The model can be used to adequately predict the radiation degradation of the Si solar cells irradiated with a complete spectrum of electron fluence. It has been established that the radiation-resistance of the silicon solar cell is very dependent on effective carrier concentration in the high fluence range and irradiation tolerance can be improved further by varying the base carrier concentration upon irradiation.

Journal ArticleDOI
TL;DR: In this article, an optical multichannel analyzer (OMA) was used to analyze the spectrum of Al plasma induced by a KrF excimer laser (248 nm) in a vacuum chamber.
Abstract: Optical emission spectrum of Al plasma induced by a KrF excimer laser (248 nm) in a vacuum chamber is investigated using an optical multichannel analyzer (OMA). It is observed that different air pressures and delay times after the laser pulse play important roles in the characterization of emission spectrum from Al surface. The optimal conditions for spectroscopic study of Al plasma are estimated. A spectrum self-absorption effect can be observed clearly from the calibrated spectral line profiles at the initial stage of plasma expansion and high fluence. Assuming local thermodynamic equilibrium (LTE) conditions, the plasma temperature and density are estimated from two spectral lines (Al I, 309.2 and 396.1 nm) as a function of air pressure, delay time and laser fluence. The plasma temperature is derived to be in the range of 5500 to 10000 K using the relative intensities of the spectral lines. The electron density is estimated from Stark broadening profiles of the spectral lines, and found to range from 0.7×1018 to 3.5×1018 cm-3. The behaviors of the plasma temperature and density reveal a 1-D plasma expansion at a delay time shorter than 200 ns and the plasma shielding effect at high fluence.

Journal ArticleDOI
TL;DR: An initial characterization of the spectral and temporal signature of the laser-induced incandescence as a function of the excitation laser fluence and wavelength is presented.
Abstract: Laser-induced incandescence is both characterized and demonstrated for the measurement of metal nanoparticle concentration. Reported are the results of an initial characterization of the spectral and temporal signature of the laser-induced incandescence as a function of the excitation laser fluence and wavelength. Validation of the incandescence as a measure of the concentration is demonstrated by absorption measurements. Fluence dependence measurements are also presented. Double-pulse measurements determine the fluence for the onset of vaporization-induced mass loss. Comparisons between the present observations and those for carbon nanostructures are also made. Metals tested include (in order of increasing vaporization temperature) Fe, Ti, Mo, and W.

Journal ArticleDOI
TL;DR: In this article, a single ultraviolet pulse from a frequency doubled copper vapor laser (255.3 nm) was used to remove particles as small as 0.3 µm in diameter from a glass surface.
Abstract: Particles as small as 0.3 μm in diameter have been successfully removed from a glass surface using a single ultraviolet pulse from a frequency doubled copper vapor laser (255.3 nm). Quantitative analysis of the particle density before and after laser irradiation shows that laser cleaning occurs after a fluence threshold is reached. The cleaning efficiency after threshold follows a nonlinear trend with respect to fluence. A model is presented which reveals that the cleaning efficiency is a function of the irradiance distribution of the beam used. Results of modeling thermal expansion of the substrate and particles, and particle adhesion do not confirm a thermal expansion mechanism for laser cleaning in this study, in contrast with other recent reports.

Journal ArticleDOI
TL;DR: In this article, the role of target material and state, solid or liquid, laser photon energy and fluence has been investigated and compared in comparison to the findings of previous investigations, and an estimate of the electrostatic plasma potential in PLA, based on electron loss rate arguments, is presented to account for the high ion energies observed.
Abstract: . The measurements reveal components with different charge-to-mass ratio and distinct components with the same charge/mass ratio. The most probable kinetic energy has values of several tens of eV for singly charged ions, and is larger by a factor exceeding 2 for doubly charged ions. The role of target material and state, solid or liquid, laser photon energy and fluence has been investigated and is discussed in comparison to the findings of previous investigations. An estimate of the electrostatic plasma potential in PLA, based on electron loss rate arguments, is presented to account for the high ion energies observed.

Journal ArticleDOI
TL;DR: In this paper, the nonlinear optical response (intensity-dependent refractive index) of Ge nanocrystallites embedded in a silica matrix was measured at a wavelength of 800 nm and found to increase linearly with increasing Ge fluence.
Abstract: Time-resolved degenerate-four-wave-mixing measurements were used to study the nonlinear optical response (intensity-dependent refractive index) of Ge nanocrystallites embedded in a silica matrix. Nanocrystals were fabricated by ion-implanting silica with 1.0 MeV Ge ions to fluences in the range from 0.6 to 3×1017 Ge cm−2, followed by annealing at 1100 °C for 60 min. For the highest fluence, this resulted in nanocrystals with a log-normal size distribution, having a geometric mean diameter of 3.0 nm and a dimensionless geometric standard deviation of 0.25. The intensity-dependent refractive index |n2| was measured at a wavelength of 800 nm and found to increase linearly with increasing Ge fluence. For the highest fluence, |n2| was determined to be in the range 2.7–6.9×10−13 cm−2 W−1, depending on the duration of the excitation pulse; values were consistently smaller for shorter pulse lengths. Relaxation of the nonlinear response was found to have two characteristic time constants, one <100 fs and the other ∼1 ps.

Journal ArticleDOI
TL;DR: By making an array of nanoholes on an alumina target, X-ray emission from laser-produced plasma can be greatly enhanced even in soft x-ray energy regions as discussed by the authors.
Abstract: By making an array of nanoholes on an alumina target, x-ray emission from laser-produced plasma can be greatly enhanced even in soft x-ray energy regions (<0.25 keV). X-ray fluence enhancement around 30 times was achieved in the 5–25 nm wavelength range. The enhancement increases as the ionization level of Al becomes higher and the x-ray wavelength becomes shorter. Over 50-fold enhancement was obtained at a soft x-ray wavelength around 6 nm, which corresponds to the emission from Al8+,9+ ions. X-ray pulse duration was 17 ps, which is much shorter than that obtained by using the prepulse technique.

Journal ArticleDOI
TL;DR: In this paper, the morphology of the ablated areas generated by laser pulses at a fluence slightly above the ablation threshold was characterized in dependence on the pulse number by scanning electron microscopy and atomic force microscopy.
Abstract: Ti:sapphire laser pulses of 130 fs and 800 nm were focused on 3.2-μm-thick TiN films by a 60-mm focal length lens in air. The morphology of the ablated areas generated by laser pulses at a fluence slightly above the ablation threshold was characterized in dependence on the pulse number by scanning electron microscopy (SEM) and atomic force microscopy (AFM). The cavity profiles, depths, diameters, and volumes were quantitatively evaluated by AFM. The polarization state of the laser light is discussed as a further parameter, in addition to fluence and pulse number, that influences and controls the ablation precision of these materials. It was observed that circularly polarized radiation enhances the average ablation rates and reduces the roughness in the cavities by a factor of 2–3 as compared to linearly polarized radiation of the same incident laser fluence. Special attention was paid to the interfacial region between the coating and substrate. Ultrashort-pulse laser drilling into the Si substrate revealed the generation of columnar features which even may surmount the original coating under laser conditions.

Journal ArticleDOI
TL;DR: In this article, the ion beam-induced modification of the electrical conductivity and the related structural features have been studied for thin films of poly-iso-quinazolindione (PIQ).
Abstract: The ion beam-induced modification of the electrical conductivity and the related structural features have been studied for thin films of poly-iso-quinazolindione (PIQ). The films, deposited onto specially designed test patterns, were irradiated by using 600 keV Ar+ ions in the fluence range between 1 × 1014 to 1 × 1015 ions/cm2. The beam-induced chemical and structural modifications have been investigated by using X-ray Photoelectron Spectroscopy (XPS) and Raman Spectroscopy, while the modification of the electrical properties was followed by performing a complete set of I/V measurements. In particular, we obtained the evidence of the occurrence of a true semiconducting state for samples irradiated at fluence around 6 × 1014 ions/cm2, which exhibited the characteristic I/V features of a Schottky diode. Samples irradiated at higher fluence showed a good conductivity, with a saturation value of 4 × 102 Ω cm. The XPS data demonstrate that the modification of the electrical properties is due to the progressive formation with increasing ion fluence of a dense amorphous carbon network, while Raman data suggest the existence of different structural features, respectively for the semiconducting and the conducting phases.

Journal ArticleDOI
TL;DR: In this article, the influence of swift heavy ion (SHI) irradiation on transport properties of epitaxial thin films of La0.75Ca0.25MnO3 (LCMO) is studied.
Abstract: The influence of swift heavy ion (SHI) irradiation on transport properties of epitaxial thin films of La0.75Ca0.25MnO3 (LCMO) is studied. The films were irradiated with 90 MeV16O beams and 250 MeV107 Ag beams at different fluence values. In the case of 90 MeV16O ions LCMO specimens were irradiated to 1011-1014 ions/cm2 and for 250 MeV107Ag ions with 1010–1013 ions/cm2. A systematic variation in Curie temperature (T c) or resistivity peak temperature (T p) has been observed. It has been noted that for both types of ions the T p increased for the specimen irradiated at 1011 ions/cm2 fluence. Further increase of fluence decreased the T p value and at higher fluence (1014 ions/cm2 for 90 MeV16O and 1013 ions/cm2 for 250 MeV107 Ag ions) the specimens showed no metal-to-insulator transition even at low temperature down to 77K. They show completely semiconducting behavior with high resistance values. These results are discussed in terms of SHI irradiation-induced structural distrotion and strain on thin...

Journal Article
TL;DR: It is confirmed that the corneal ablation properties at 213 nm are comparable with those at the 193-nm excimer laser wavelength, and a solid state laser is feasible to replace the excimer gas laser for performing refractive surgery procedures.
Abstract: PURPOSE. To determine the threshold and efficiency of corneal ablation for various values of laser fluence at the ultraviolet wavelength of 213 nm. METHODS. A commercial Q-switched Nd:YAG laser was used to produce the fifth harmonic wavelength of 213 nm. Ablation trials were carried out on porcine corneas. Slit ablations of dimensions 0.5 × 2.5 mm were performed using seven values of laser fluence to obtain the most efficient fluence for ablation. The morphology of each ablation was obtained using a computer-automated confocal profiling system. These profiles were then analyzed to determine the ablation depth for the range of fluence values used. RESULTS. A fluence in the region of 200 mJ/cm 2 was found to be the most efficient for ablation. The efficiency in this region was approximately 0.35 mm 3 /J, and the ablation rate was found to be 0.6 μm/pulse. The ablation threshold was found to occur at a fluence of 50 mJ/cm 2 . In the region of highest efficiency, the peak varied slightly in the fluence range between 150 and 250 mJ/cm 2 . CONCLUSIONS. This study confirms that the corneal ablation properties at 213 nm are comparable with those at the 193-nm excimer laser wavelength. Increased pulse energy was obtained for the fifth harmonic of Nd:YAG lasers at 213 nm through the use of new nonlinear optical crystals to perform the frequency conversion. A solid state laser is feasible to replace the excimer gas laser for performing refractive surgery procedures. For the first time, the increased energy at 213 nm allows large-beam ablations to be performed at this wavelength.

Journal ArticleDOI
TL;DR: In this paper, the authors present results of the study of 193 nm laser-induced densification of fused silica as a function of incident laser fluence and pulse count, and establish the existence of a dose-rate dependence of the densification phenomenon.
Abstract: We present results of the study of 193 nm laser-induced densification of fused silica as a function of incident laser fluence and pulse count. We describe an internally self-consistent experiment involving the simultaneous irradiation of 12 samples of two different grades, at fluences varying by two orders of magnitude and pulse counts exceeding 1.5 × 109. We are able to establish the existence of a dose-rate dependence of the densification phenomenon and to characterize the empirical rate constants as a function of fluence for two different grades of fused silica.