Showing papers on "Fluence published in 2013"
TL;DR: In this article, the authors studied the effect of laser irradiation on graphite oxide (GO) to graphene induced by picosecond pulsed laser irradiations and showed that the reduction of graphite oxide oxide to graphene with successive laser pulses was effective.
158 citations
TL;DR: In this paper, the formation of laser-induced periodic surface structures (LIPSS) on titanium upon irradiation with linearly polarized femtosecond (fs) laser pulses (τ=30,fs, λ=790,nm) in an air environment is studied experimentally and theoretically.
Abstract: The formation of laser-induced periodic surface structures (LIPSS) on titanium upon irradiation with linearly polarized femtosecond (fs) laser pulses (τ=30 fs, λ=790 nm) in an air environment is studied experimentally and theoretically. In the experiments, the dependence on the laser fluence and the number of laser pulses per irradiation spot has been analyzed. For a moderate number of laser pulses (N<1000) and at fluences between ∼0.09 and ∼0.35 J/cm2, predominantly low-spatial-frequency-LIPSS with periods between 400 nm and 800 nm are observed perpendicular to the polarization. In a narrow fluence range between 0.05 and 0.09 J/cm2, high-spatial-frequency-LIPSS with sub-100-nm spatial periods (∼λ/10) can be generated with an orientation parallel to the polarization (N=50). These experimental results are complemented by calculations based on a theoretical LIPSS model and compared to the present literature.
142 citations
TL;DR: In this article, the mechanisms of ripple formation on silicon surface by femtosecond laser pulses are investigated and the experimental conditions required for the excitation of surface plasmon polaritons are revealed.
Abstract: The mechanisms of ripple formation on silicon surface by femtosecond laser pulses are investigated. We demonstrate the transient evolution of the density of the excited free-carriers. As a result, the experimental conditions required for the excitation of surface plasmon polaritons are revealed. The periods of the resulting structures are then investigated as a function of laser parameters, such as the angle of incidence, laser fluence, and polarization. The obtained dependencies provide a way of better control over the properties of the periodic structures induced by femtosecond laser on the surface of a semiconductor material.
122 citations
TL;DR: In this article, the mechanisms of ripple formation on silicon surface by femtosecond laser pulses are investigated and the experimental conditions required for the excitation of surface plasmon polaritons are revealed.
Abstract: The mechanisms of ripple formation on silicon surface by femtosecond laser pulses are investigated. We demonstrate the transient evolution of the density of the excited free-carriers. As a result, the experimental conditions required for the excitation of surface plasmon polaritons are revealed. The periods of the resulting structures are then investigated as a function of laser parameters, such as the angle of incidence, laser fluence, and polarization. The obtained dependencies provide a way of better control over the properties of the periodic structures induced by femtosecond laser on the surface of a semiconductor material.
121 citations
TL;DR: In this paper, the surface modification was studied with scanning electron microscopy, and deuterium retention was measured by thermal desorption spectroscopy (TDS) in the case of high fluence exposures.
Abstract: Samples of tungsten and tungsten-tantalum alloy (with 5 mass per cent of Ta) were exposed to high-flux deuterium plasma at different fluences. The surface modification was studied with scanning electron microscopy, and deuterium retention was measured by thermal desorption spectroscopy (TDS). In the high fluence range of similar to 3.5 x 10(26)-10(27)m(-2), multiple large-size blisters are formed on the W surface, while blisters on the W-Ta surface are considerably smaller in size and number. Deuterium retention in this fluence range was found to be systematically higher in W than in W-Ta. Correlation between the evolution of the blistering patterns and the TDS spectra as a function of fluence suggests that trapping in the sub-surface cavities associated with blisters is the predominant trapping mechanism in tungsten in the case of high fluence exposures. We attribute the lower retention in W-Ta under the investigated conditions to the weaker blistering.
98 citations
TL;DR: In this paper, the authors derived the flux equation of the ion beam of any gas; link to the Lee Model code and hence compute the ionbeam properties of a plasma focus.
Abstract: A recent paper derived benchmarks for deuteron beam fluence and flux in a plasma focus (PF) [S Lee and S H Saw, Phys Plasmas 19, 112703 (2012)] In the present work we start from first principles, derive the flux equation of the ion beam of any gas; link to the Lee Model code and hence compute the ion beam properties of the PF The results show that, for a given PF, the fluence, flux, ion number and ion current decrease from the lightest to the heaviest gas except for trend-breaking higher values for Ar fluence and flux The energy fluence, energy flux, power flow, and damage factors are relatively constant from H2 to N2 but increase for Ne, Ar, Kr and Xe due to radiative cooling and collapse effects This paper provides much needed benchmark reference values and scaling trends for ion beams of a PF operated in any gas
75 citations
TL;DR: The saturation of pump-induced bleaching of graphene is studied and a quadratic dependence of the saturation fluence on the pump photon energy in the infrared spectral range is revealed.
Abstract: We present the results of pump–probe experiments on multilayer graphene samples performed in a wide spectral range, namely from the near infrared (photon energy 1.5 eV) to the terahertz (photon energy 8 meV) spectral range. In the near infrared, exciting carriers and probing at higher photon energies provides direct evidence for a hot carrier distribution. Furthermore, spectroscopic signatures of the highly doped graphene layers at the interface to SiC are observed in the near-infrared range. In the mid-infrared range, the various relaxation mechanisms, in particular scattering via optical phonons and Auger-type processes, are identified by comparing the experimental results to microscopic modeling. Changes from induced transmission to induced absorption are attributed to probing above or below the Fermi edge of the graphene layers. This effect occurs for certain photon energies in the near-infrared range, where it is related to highly doped graphene layers at the interface to SiC, and in the far-infrared range for the quasi-intrinsic graphene layers. In addition to the relaxation dynamics, the saturation of pump-induced bleaching of graphene is studied. Here a quadratic dependence of the saturation fluence on the pump photon energy in the infrared spectral range is revealed.
72 citations
TL;DR: In this paper, a Q-switched Nd:YAG laser of 1064 and 532 nm wavelengths at 7 ns pulse width and different fluences is employed to irradiate the solid target in acetone.
Abstract: Silver nanoparticles were synthesized using pulsed laser ablation of Ag metal plate in acetone The pulsed of a Q-switched Nd:YAG laser of 1064 and 532 nm wavelengths at 7 ns pulse width and different fluences is employed to irradiate the solid target in acetone The UV–Visible absorption spectra of the Ag nanoparticles exhibit absorptions in the ultraviolet and in visible regions because of interband transition and surface plasmon resonance oscillations in Ag nanoparticles, respectively In the case of nanoparticles produced with laser pulse of 1064 nm, TEM images indicate that with increasing the laser fluence, the average size of the spherical nanoparticles increases It is found that Ag nanoparticles exhibit photoluminescence emission, at room temperature, in the UV–Visible region due to electron–hole recombination
69 citations
15 May 2013-Nuclear Instruments & Methods in Physics Research Section B-beam Interactions With Materials and Atoms
TL;DR: In this article, the effect of high fluence, the temperature and the impurities on the onset of the structure formation of a tungsten-based divertor was investigated. And the authors concluded that MD reproduces the experimentally found square root of time dependence of the surface growth.
Abstract: When helium (He) escapes a fusion reactor plasma, a tungsten (W)-based divertor may, under some conditions, form a fuzz-like nano-morphology. This is a highly undesired phenomenon for the divertor, and is not well understood. We performed molecular dynamics simulations of high fluence He and also C-seeded He (He+C) irradiation on W, focusing on the effect of the high fluence, the temperature and the impurities on the onset of the structure formation. We concluded that MD reproduces the experimentally found square root of time dependence of the surface growth. The He atomic density decreases when increasing the number of He atoms in the cell. A higher temperature causes a larger bubble growth and desorption activity, specially for the pure He irradiation cases. It also it leads to W recrystallization for the He+C irradiation cases. Carbon acts as a local He trap for small clusters or single atoms and causes a larger loss of crystallinity of the W surface.
58 citations
TL;DR: In this paper, a comparison between femtosecond and picosecond (ps) laser ablation of electrolytic iron was carried out in ambient air, and it was shown that the quality of the craters produced by femto-cond laser arborization at low fluence is better than those created at high fluence or using femtocond laser pulses.
Abstract: In this study, a comparison between femtosecond (fs) and picosecond (ps) laser ablation of electrolytic iron was carried out in ambient air. Experiments were conducted using a Ti:sapphire laser that emits radiation at 785 nm and at pulse widths of 110 ps and 130 fs, before and after pulse compression, respectively. Ablation rates were calculated from the depth of craters produced by multiple laser pulses incident normally to the target surface. Optical and scanning electron microscopy showed that picosecond laser pulses create craters that are deeper than those created by the same number of femtosecond laser pulses at the same fluence. Most of the ablated material was ejected from the ablation site in the form of large particles (few microns in size) in the case of picosecond laser ablation, while small particles (few hundred nanometers) were produced in femtosecond laser ablation. Thermal effects were apparent at high fluence in both femtosecond and picosecond laser ablation, but were less prevalent at low fluence, closer to the ablation threshold of the material. The quality of craters produced by femtosecond laser ablation at low fluence is better than those created at high fluence or using picosecond laser pulses.
55 citations
TL;DR: In this paper, an experimental approach is presented for the determination of irradiation parameters of extended surface areas homogenously covered with LIPSS, based on accumulated fluence and consists of two steps, first the empirical determination of accumulatedfluence domain boundaries and second the approximation of irradiated parameters.
TL;DR: In this article, the authors performed relativistic ultrafast electron diffraction (UED) measurements of the structural dynamics of photoexcited gold nanofilms and developed an atomistic model, based on the two-temperature molecular dynamics (2T-MD) method, which allows them to make a direct comparison of the time evolutions of measured and calculated Bragg peaks.
Abstract: We performed relativistic ultrafast electron diffraction (UED) measurements of the structural dynamics of photoexcited gold nanofilms and developed an atomistic model, based on the two-temperature molecular dynamics (2T-MD) method, which allows us to make a direct comparison of the time evolutions of measured and calculated Bragg peaks. The quantitative agreement between the temporal evolutions of the experimental and theoretical Bragg peaks at all fluences suggests that the 2T-MD method provides a faithful atomistic representation of the structural evolution of photoexcited gold films. The results reveal the transition between slow heterogeneous melting at low absorbed photon fluence to rapid homogeneous melting at higher fluence and nonthermally driven melting at very high fluence. At high laser fluence, the time evolution of Bragg peaks calculated using the conventional 2T-MD model disagrees with experiment. We show that using an interatomic potential that directly depends on the electron temperature delivers a much better agreement with UED data. Finally, our ab initio calculations of phonon spectra suggest electronic bond softening, if the nanofilms can expand freely under electronic pressure, and bond hardening, if they are constrained in all three dimensions.
TL;DR: This work shows that the metal-adsorbate coordination is initially increased due to hot-electron-driven vibrational excitations in the first picosecond after laser excitation, which is faster than, but occurs in parallel with, the transition into the precursor state.
Abstract: We have studied the femtosecond dynamics following optical laser excitation of CO adsorbed on a Ru surface by monitoring changes in the occupied and unoccupied electronic structure using ultrafast soft x-ray absorption and emission. We recently reported [M. Dell'Angela et al. Science 339, 1302 (2013)] a phonon-mediated transition into a weakly adsorbed precursor state occurring on a time scale of >2 ps prior to desorption. Here we focus on processes within the first picosecond after laser excitation and show that the metal-adsorbate coordination is initially increased due to hot-electron-driven vibrational excitations. This process is faster than, but occurs in parallel with, the transition into the precursor state. With resonant x-ray emission spectroscopy, we probe each of these states selectively and determine the respective transient populations depending on optical laser fluence. Ab initio molecular dynamics simulations of CO adsorbed on Ru(0001) were performed at 1500 and 3000 K providing insight into the desorption process.
TL;DR: In this article, the capacity of Cu/V interfaces to absorb helium ion radiation-induced defects spanning a peak damage range of 0.6-18 displacements per atom (dpa) was explored.
Abstract: We have explored the capacity of Cu/V interfaces to absorb helium ion radiation-induced defects spanning a peak damage range of 0.6–18 displacements per atom (dpa). The study provides evidence of alleviated nucleation of He bubbles in the multilayer films from Cu/V 50 nm to Cu/V 2.5 nm. Layer interfaces are retained in all irradiated specimens. Peak bubble density increases monotonically with fluence, and is lower in multilayers with smaller individual layer thickness. Radiation hardening decreases with decreasing layer thickness and appears to reach saturation upon peak radiation damage of 6 dpa. Size- and fluence-dependent radiation damage in multilayers is discussed.
TL;DR: The first femtosecond MIXSEL emitting pulses with a duration as short as 620 fs at 4.8 GHz repetition rate and 101 mW average output power are presented.
Abstract: Novel surface-emitting optically pumped semiconductor lasers have demonstrated >1 W modelocked and >100 W continuous wave (cw) average output power. The modelocked integrated external-cavity surface emitting laser (MIXSEL) combines the gain of vertical-external-cavity surface-emitting lasers (VECSELs) with the saturable absorber of a semiconductor saturable absorber mirror (SESAM) in one single semiconductor structure. This unique concept allows for stable and self-starting passive modelocking in a simple straight cavity. With quantum-dot based absorbers, record-high average output power was demonstrated previously, however the pulse duration was limited to 17 ps so far. Here, we present the first femtosecond MIXSEL emitting pulses with a duration as short as 620 fs at 4.8 GHz repetition rate and 101 mW average output power. The novel MIXSEL structure relies on a single low temperature grown quantum-well saturable absorber with a low saturation fluence and fast recovery dynamics. A detailed characterization of the key modelocking parameters of the absorber and the challenges for absorber integration into the MIXSEL structure are discussed.
TL;DR: In this paper, the authors investigated thermal ablations of metal films by a single femtosecond laser pulse and by a laser burst using a comprehensive computational model including a two-temperature model with dynamic optical properties, two phase change models for melting and evaporation under superheating, and a phase explosion criterion for ejection of the mixture of metastable liquid droplets and vapor.
TL;DR: In this article, the influence of laser parameters such as laser fluence, laser wavelength as well as focusing condition of laser beam on the size and morphology of the gold nanoparticles prepared in de-ionized water by pulsed laser ablation was studied.
Abstract: The generation of nanoparticles using pulsed laser ablation has inherent advantages compared to conventional methods, like the purity and stability of the fabricated nanoparticles, aerosols and colloids. This study addresses the influence of laser parameters such as laser fluence, laser wavelength as well as focusing condition of laser beam on the size and morphology of the gold nanoparticles prepared in de-ionized water by pulsed laser ablation. The optimum conditions at which gold nanoparticles are obtained with controllable average size have been reported as these parameters affected the size, distribution and absorbance spectrum. The effect of laser fluence was studied. The laser fluences were divided into three regions (low, middle and high). A noteworthy change was observed at each region. At low fluences, the size of the nanoparticles decreases as the fluence increases to a certain critical value after which the size of the nanoparticles increases as the fluence increases. Also a significant change in the size distribution of the gold nanoparticles was noticed during the variation of the focusing conditions at gold–water interface.
TL;DR: In this article, the influence of laser fluence and pulse duration on the morphology and the internal structure of plasma induced by infrared nanosecond laser pulse on an aluminum target placed in an argon ambient gas of one atmosphere pressure was experimentally studied.
TL;DR: The structural changes of carbon-containing Au nanoparticles embedded in amorphous carbon matrix were investigated using X-ray diffraction and transmission electron microscopy in this article, where the surface plasmon resonance (SPR) band was observed to be blue shifted (∼50 nm) in both cases, with increasing fluence and temperature.
Abstract: Thin films of carbon-containing Au nanoparticles (NPs), prepared by the co-sputtering using a neutral Ar atom beam, were irradiated by 120 MeV Ag ions and also annealed, separately, at increasing temperatures in inert atmosphere. The surface plasmon resonance (SPR) band of the nanocomposite film was observed to be blue shifted (∼50 nm) in both cases, with increasing fluence and temperature. The structural changes of Au NPs embedded in amorphous carbon matrix were investigated using X-ray diffraction and transmission electron microscopy. A growth of Au NPs was observed with increasing fluence and also with increasing temperature. A percolation of Au NPs was observed at 500 °C. A growth of Au NPs with ion irradiation is explained in the framework of a thermal spike model. Raman spectroscopy revealed the ordering of a-C thin films with increasing fluence and temperature, which is ascribed to a change of refractive index and the blue shift of the SPR band.
TL;DR: In this paper, a systematic ablation study with 10 ps pulses at 1064nm wavelength on copper and iron under different gases atmospheres and pressures was done, and the results showed that the change of the energy penetration depth is the main cause of the incubation and that an adapted model better fits the trend of the threshold fluence and the penetration depth as a function of the number of pulses applied.
Abstract: For laser micro processing with short and ultra-short pulses the threshold fluence is affected by the incubation and changes with the number of pulses applied. In general the incubation effect is described by a power function including the incubation coefficient S. Beside the threshold fluence also the energy penetration depth is subject to the incubation effect; moreover it is a main cause for the change of the threshold fluence with increasing pulse number. The behavior of the threshold fluence can be explained by varying absorption (due to changes in the surface reflectivity), chemical changes of the surface (e.g. due to oxidation) or changes in the microstructure of the material whereas the behavior of the energy penetration depth could be explained by the latter two effects but should not be affected by a change in the absorption. To try to distinguish between these three effects a systematic ablation study with 10 ps pulses at 1064nm wavelength on copper and iron under different gases atmospheres and pressures was done. The results show on the one hand the change of the energy penetration depth is the main cause of the incubation and that on the other hand an adapted model better fits the trend of the threshold fluence and the penetration depth as a function of the number of pulses applied. The influence of the gas (air, oxygen, nitrogen and argon) is only marginal whereas a reduction of the pressure from normal atmosphere down to 50 mbar results in a 25% increase of the maximum removal rate. Induced changes in the microstructure were detected by a high resolution X-ray diffraction analysis on single crystal (111-orientation) copper and iron samples.
TL;DR: In this paper, the surface characterization of PLLA and its ablation due to excimer laser treatment is introduced, where the main focus is to determine surface wettability and morphology changes in combination with changes of surface chemistry.
TL;DR: In this paper, the surface topography progression using the swift heavy ion irradiation was studied, which shows creation of unique surface morphologies and regular structures on the surface of the SnO 2 thin film at particular fluences.
TL;DR: In this paper, it was shown that the duration of graphitization depends on the incoming photon energy: the higher the photon energy is, the longer the secondary electron cascading which promotes the electrons into the conduction band will take.
Abstract: Diamond irradiated with an ultrashort intense laser pulse in the regime of photon energies from soft up to hard x rays can undergo a phase transition to graphite. This transition is induced by an excitation of electrons from the valence band or from atomic deep shells of the material into its conduction band, which is followed by a transient rapid change of the interatomic potential. Such a nonthermal phase transition occurs on a femtosecond time scale, shortly after or even during the laser pulse. In this work we show that the duration of the graphitization depends on the incoming photon energy: the higher the photon energy is, the longer the secondary electron cascading which promotes the electrons into the conduction band will take. The transient kinetics of the electronic and atomic processes during the graphitization is analyzed in detail. The damage threshold fluence is calculated in the broad photon energy range and is found to be always $\ensuremath{\sim}$0.7 eV/atom in terms of the average dose absorbed per atom. It is confirmed that the temporal characteristics of a femtosecond laser pulse (at a fixed pulse duration and fluence) do not significantly influence the transient damage kinetics. Finally, the influence of an additional surface layer of high-$Z$ material on the damage within diamond is discussed.
TL;DR: Three cinnamic acid matrices were investigated andimal peptide ion intensities were obtained if the laser wavelength fell within the peak of the absorption profile of the compound and for fluences two to three times the corresponding ion detection threshold.
Abstract: A high analytical sensitivity in ultraviolet matrix-assisted laser desorption ionization mass spectrometry (MALDI-MS) is only achieved if the laser wavelength corresponds to a high optical absorption of the matrix. Laser fluence and the physicochemical properties of the compounds, e.g., the proton affinity, also influence analytical sensitivity significantly. In combination, these parameters determine the amount of material ejected per laser pulse and the ion yield, i.e., the fraction of ionized biomolecules. Here, we recorded peptide ion signal intensities as a function of these parameters. Three cinnamic acid matrices were investigated: α-cyano-4-hydroxycinnamic acid, α-cyano-4-chlorocinnamic acid, and α-cyano-2,4-difluorocinnamic acid. In addition, 2,5-dihydroxybenzoic acid was used in comparison experiments. Ion signal intensities “per laser shot” and integrated ion signal intensities were acquired over 900 consecutive laser pulses applied on distinct positions on the dried-droplet sample preparations. With respect to laser wavelength, the two standard MALDI wavelengths of 337/355 nm were investigated. Also, 305 or 320 nm was selected to account for the blue-shifted absorption profiles of the halogenated derivatives. Maximal peptide ion intensities were obtained if the laser wavelength fell within the peak of the absorption profile of the compound and for fluences two to three times the corresponding ion detection threshold. The results indicate ways for improving the analytical sensitivity in MALDI-MS, and in particular for MALDI-MS imaging applications where a limited amount of material is available per irradiated pixel.
TL;DR: In this article, the effect of energy loss of ions on the ion irradiation-induced tuning of surface plasmon resonance (SPR) wavelength of Au nanoparticles (NPs) in fullerene C70 matrix was investigated.
Abstract: We investigated the effect of energy loss of ions on the ion irradiation-induced tuning of surface plasmon resonance (SPR) wavelength of Au nanoparticles (NPs) in fullerene C70 matrix. The transformation of fullerene C70 into amorphous carbon (a-C) under ion irradiation was used to tune the SPR wavelength of Au–C70 nanocomposite thin films. It is found that the range of tuning of SPR wavelength increases with increase in electronic energy loss of the incoming beam. The growth of Au NPs with increasing fluence was observed in all the cases and total growth is proportional to the electronic energy loss. The average diameter of Au NPs in pristine film is ~4.8 nm and a maximum growth of ~3 nm was observed at a fluence of 3 × 1013 ions/cm2, when the film was irradiated with 120 MeV Ag ions. It was also observed that nuclear energy loss via collision cascades has lower efficiency for SPR tuning in comparison with the electronic excitations.
TL;DR: In this paper, a large array of sub-micrometre blind holes and with a filling ratio up to 60% on areas of millimetre square are realized on silicon.
Abstract: Large arrays of sub-micrometre blind holes and with a filling ratio up to 60% on areas of millimetre square are realized on silicon. The structuration ensues from combining both Langmuir–Blodgett deposition technique and ultraviolet nanosecond laser-assisted photonic nanojet ablation through C18 functionalized silica microspheres. Different laser fluence ranges and numbers of laser shots are studied to understand the tradeoff between size, quality of the craters and surface morphology after laser irradiation. In particular, tuning the irradiation fluence yields selectivity of the characteristic lateral dimension of the imprinted craters on the substrate and laser operation in multishot mode allows obtaining high quality and regularity of the surface morphology of the resulting millimetre square arrays of holes. This simple, fast, long-range and low-cost near-field nanolithography technique is of interest for fabricating devices with new functionalities and finds applications in many fields in nanoscience and nanoengineering.
TL;DR: In this paper, a two-dimensional hydrodynamic model is presented to investigate the femtosecond laser ablation of silicon in air, and the ion expansion speed, electric field distribution, and velocity distribution of different ions are investigated.
Abstract: In this paper, a two-dimensional hydrodynamic model is presented to investigate the femtosecond laser ablation of silicon in air. Fast electron/ion ejection and the resultant early stage plasma dynamics are studied at laser fluence much higher than the ablation threshold (above 10 J cm−2). It is revealed that the early plasma splits into two portions during its expansion, comprised of fast and slow particles, respectively. During the ablation process, ultra-fast ion ejection (before 0.2 ps) from the silicon surface appears to occur before thermal ejection starts. By investigating the ion expansion speed, electric field distribution, and velocity distribution of different ions, the occurrence of Coulomb explosion (CE) is demonstrated in the ablation of silicon at high laser fluence, due to the intense electron emission at the early stage. It leads to a fast ion ejection from the target surface, increasing the material removal rate at the early stage. In contrast, CE is absent in the ablation of copper, although a double-layer effect exists.
TL;DR: In this article, the effects of nanosecond laser processing parameters on the depth and width of microchannels fabricated from polymethylmethacrylate (PMMA) polymer are investigated.
Abstract: This paper presents investigations on the effects of nanosecond laser processing parameters on depth and width of microchannels fabricated from polymethylmethacrylate (PMMA) polymer. A neodymium-doped yttrium aluminium garnet pulsed laser with a fundamental wavelength of 1,064 nm and a third harmonic wavelength of 355 nm with pulse duration of 5 ns is utilized. Hence, experiments are conducted at near-infrared (NIR) and ultraviolet (UV) wavelengths. The laser processing parameters of pulse energy (402–415 mJ at NIR and 35–73 mJ at UV wavelengths), pulse frequency (8–11 Hz), focal spot size (140–190 μm at NIR and 75 μm at UV wavelengths) and scanning rate (400–800 pulse/mm at NIR and 101–263 pulse/mm at UV wavelengths) are varied to obtain a wide range of fluence and processing rate. Microchannel width and depth profile are measured, and main effects plots are obtained to identify the effects of process parameters on channel geometry (width and depth) and material removal rate. The relationship between process variables (width and depth of laser-ablated microchannels) and process parameters is investigated. It is observed that channel width (140–430 μm at NIR and 100–150 μm at UV wavelengths) and depth (30–120 μm at NIR and 35–75 μm at UV wavelengths) decreased linearly with increasing fluence and increased non-linearly with increasing scanning rate. It is also observed that laser processing at UV wavelength provided more consistent channel profiles at lower fluences due to higher laser absorption of PMMA at this wavelength. Mathematical modeling for predicting microchannel profile was developed and validated with experimental results obtained with pulsed laser micromachining at NIR and UV wavelengths.
TL;DR: In this paper, an approach to use Al2O3:C,Mg-based fluorescent nuclear track detectors and confocal laser scanning microscopy as a semiautomatic tool for fluence measurements in clinical ion beams is presented.
TL;DR: Helium ion microscopy was used to investigate the interaction of a focused He+ ion beam with energies of several tens of kiloelectronvolts with metals and shows a power-law dependence on the ion fluence.
Abstract: Helium ion microscopy (HIM) was used to investigate the interaction of a focused He+ ion beam with energies of several tens of kiloelectronvolts with metals. HIM is usually applied for the visualization of materials with extreme surface sensitivity and resolution. However, the use of high ion fluences can lead to significant sample modifications. We have characterized the changes caused by a focused He+ ion beam at normal incidence to the Au{111} surface as a function of ion fluence and energy. Under the influence of the beam a periodic surface nanopattern develops. The periodicity of the pattern shows a power-law dependence on the ion fluence. Simultaneously, helium implantation occurs. Depending on the fluence and primary energy, porous nanostructures or large blisters form on the sample surface. The growth of the helium bubbles responsible for this effect is discussed