Showing papers on "Fluence published in 2009"
TL;DR: In this paper, the formation of nearly wavelength-sized laser-induced periodic surface structures (LIPSSss) on single-crystalline silicon upon irradiation with single or multiple femtosecond-laser pulses (pulse duration τ=130
Abstract: The formation of nearly wavelength-sized laser-induced periodic surface structures (LIPSSs) on single-crystalline silicon upon irradiation with single or multiple femtosecond-laser pulses (pulse duration τ=130 fs and central wavelength λ=800 nm) in air is studied experimentally and theoretically. In our theoretical approach, we model the LIPSS formation by combining the generally accepted first-principles theory of Sipe and co-workers with a Drude model in order to account for transient intrapulse changes in the optical properties of the material due to the excitation of a dense electron-hole plasma. Our results are capable to explain quantitatively the spatial periods of the LIPSSs being somewhat smaller than the laser wavelength, their orientation perpendicular to the laser beam polarization, and their characteristic fluence dependence. Moreover, evidence is presented that surface plasmon polaritons play a dominant role during the initial stage of near-wavelength-sized periodic surface structures in fem...
555 citations
TL;DR: In this paper, surface and sub-surface morphology and deuterium retention in polycrystalline tungsten, undamaged and pre-damaged with 5.5 MeV W2+ ions to damage levels of 0.04, 0.4, and 1.2
121 citations
TL;DR: It is demonstrated that a photochromic reaction can be driven by irradiation from a weak, near-infrared continuous-wave (NIR-CW) laser light, and an "enhancing effect" that acts on the electromagnetic field of the gold nanoparticles excites it to a state from which the ring-opening Reaction can be initiated.
Abstract: We demonstrate that a photochromic reaction can be driven by irradiation from a weak, near-infrared continuous-wave (NIR-CW) laser light. A two-photon ring-opening photochromic reaction of a diarylethene (DE) derivative can be induced by irradiation with a NIR-CW laser light (lambda = 808 nm). An ultrathin polymer film doped with DE in its closed form was coated onto a gold-nanoparticle-integrated glass substrate. Upon irradiation of the sample with a CW laser at low fluence (0.1-4.0 W/cm(2)), we could clearly observe bleaching of the DE (ring-opening reaction). Following the IR irradiation, the bleached absorption could be reversibly recovered by applying UV irradiation (ring-closing reaction). We verified that the yield of the photochromic ring-opening reaction of the DE was proportional to the square of the irradiation fluence. The origin of this NIR-CW-induced two-photon photochromic reaction is an "enhancing effect" that acts on the electromagnetic field (localized surface plasmon) of the gold nanoparticles. The DE interacts with the surface plasmon and receives energy from two photons, which excites it to a state from which the ring-opening reaction can be initiated.
121 citations
TL;DR: In this research, the formation of laser-induced periodic surface structures on the stainless steel surface using femtosecond laser pulses is studied using a 780 nm wavelength laser focused through a 0.2 mm pinhole aperture.
Abstract: In this research, we studied the formation of laser-induced periodic surface structures on the stainless steel surface using femtosecond laser pulses. A 780 nm wavelength femtosecond laser, through a 0.2 mm pinhole aperture for truncating fluence distribution, was focused onto the stainless steel surface. Under different experimental condition, low-spatial-frequency laser-induced periodic surface structures with a period of 526 nm and high-spatial-frequency laser-induced periodic surface structures with a period of 310 nm were obtained. The mechanism of the formation of laser-induced periodic surface structures on the stainless steel surface is discussed.
114 citations
TL;DR: In this paper, the surface topography of titanium samples irradiated by femtosecond laser pulses is described and ripples with a period of about 700nm are formed when the fluence is about 0.5 and 2.5
106 citations
TL;DR: Highly efficient ablation of healthy tooth enamel using 55 ps infrared laser pulses tuned to the vibrational transition of interstitial water and hydroxyapatite is demonstrated, attributed to an enhanced photomechanical effect due to ultrafast vibrational relaxation into heat and the scattering of powerful ultrafast acoustic transients with random phases off the mesoscopic heterogeneous tissue structures.
Abstract: Mechanical and thermodynamic responses of biomaterials after impulsive heat deposition through vibrational excitations (IHDVE) are investigated and discussed. Specifically, we demonstrate highly efficient ablation of healthy tooth enamel using 55 ps infrared laser pulses tuned to the vibrational transition of interstitial water and hydroxyapatite around 2.95 µm. The peak intensity at 13 GW/cm2 was well below the plasma generation threshold and the applied fluence 0.75 J/cm2 was significantly smaller than the typical ablation thresholds observed with nanosecond and microsecond pulses from Er:YAG lasers operating at the same wavelength. The ablation was performed without adding any superficial water layer at the enamel surface. The total energy deposited per ablated volume was several times smaller than previously reported for non-resonant ultrafast plasma driven ablation with similar pulse durations. No micro-cracking of the ablated surface was observed with a scanning electron microscope. The highly efficient ablation is attributed to an enhanced photomechanical effect due to ultrafast vibrational relaxation into heat and the scattering of powerful ultrafast acoustic transients with random phases off the mesoscopic heterogeneous tissue structures.
82 citations
TL;DR: In this paper, the diameters, depths and morphologies of the drilled craters were studied and two novel phenomena were found: as hole diameters decreased with fluence, a change of slope of the trend line indicated a change in ablation mechanism for Al and Ti alloy.
Abstract: Picosecond laser single pulse ablation of Au, Al and Ti alloy (Ti6Al4V) was experimentally investigated with a laser pulse width of 10 ps at a wavelength of 1064 nm for potential industrial micromachining applications. The diameters, depths and morphologies of the drilled craters were studied. Two novel phenomena were found: as hole diameters decreased with fluence, a change of slope of the trend line indicated a change in ablation mechanism for Al and Ti alloy, metallic materials with short electron-phonon coupling times (<10 ps), while Au showed no such transition: an isolated island structure was also observed on Au due to significant melt expulsion. A one-dimensional two-temperature model has been used to discriminate different ablation phenomena. It is shown that metallic materials with different electron–phonon coupling constant have different ablation characteristics in the ps regime. This study could be very helpful for metallic material micromachining with high repetition rate ps lasers pulses which indicates that high throughput may be achieved as well as good machining quality.
81 citations
TL;DR: In this article, the effects of laser energy on the structural, morphological and optical transmission properties of the films were studied, and it was conjectured that the observed low band gap values obtained in this study may be attributable to tungsten incorporation in the films as well as the increase in laser fluence.
80 citations
TL;DR: In this paper, single-shot femtosecond laser ablation of graphite was studied by combining a variety of experimental techniques including Raman spectroscopy, atomic force microscopy as well as time of flight spectrometry.
Abstract: We have studied single-shot femtosecond laser ablation of graphite by combining a variety of experimental techniques including Raman spectroscopy, atomic force microscopy as well as time of flight spectrometry. The comprehensive analysis reveals insights into the ablation process by exploring the surface structure, the fluence dependence, and the structural dynamics of the detachment. The results show formation and detachment of charged carbon products (such as graphene nanoflakes) from the surface. Time-resolved measurements of ion yields and velocities reveal strong quenching and revival of Coulomb explosion as a function of delay time in the range of 100--200 fs, suggesting a displacive motion between the topmost surface layers which regulates the optical properties of the system.
74 citations
TL;DR: In this paper, a femtosecond laser (180 fs, 775 nm, 1 kHz) ablation characteristics of the nickel-based superalloy C263 were investigated and the single pulse ablation threshold was measured to be 0.26±0.03.
Abstract: Femtosecond laser (180 fs, 775 nm, 1 kHz) ablation characteristics of the nickel-based superalloy C263 are investigated. The single pulse ablation threshold is measured to be 0.26±0.03 J/cm2 and the incubation parameter ξ=0.72±0.03 by also measuring the dependence of ablation threshold on the number of laser pulses. The ablation rate exhibits two logarithmic dependencies on fluence corresponding to ablation determined by the optical penetration depth at fluences below ∼5 J/cm2 (for single pulse) and by the electron thermal diffusion length above that fluence. The central surface morphology of ablated craters (dimples) with laser fluence and number of laser pulses shows the development of several kinds of periodic structures (ripples) with different periodicities as well as the formation of resolidified material and holes at the centre of the ablated crater at high fluences. The debris produced during ablation consists of crystalline C263 oxidized nanoparticles with diameters of ∼2–20 nm (for F=9.6 J/cm2). The mechanisms involved in femtosecond laser microprocessing of the superalloy C263 as well as in the synthesis of C263 nanoparticles are elucidated and discussed in terms of the properties of the material.
73 citations
TL;DR: The same fluence in different fluence rates showed dissimilar levels of inactivation on yeast cells as well as in ROS formation, and the increase of the fluence rate showed an improvement on cell photoinactivation.
Abstract: The aim of this study was to investigate the influence of light parameters on yeast cells. It has been proposed for many years that photodynamic therapy (PDT) can inactivate microbial cells. A number of photosensitizer and light sources were reported in different light parameters and in a range of dye concentrations. However, much more knowledge concerning the importance of fluence, fluence rate and exposure time are required for a better understanding of the photodynamic efficiency. Suspensions (106 CFU/mL) of Candida albicans, Candida krusei, and Cryptococcus neoformans var. grubii were used. Two fluence rates, 100 and 300 mW/cm2 were compared at 3, 6, and 9 min of irradiation, resulting fluences from 18 to 162 J/cm2. The light source was a laser emitting at λ = 660 nm with output power adjusted at 30 and 90 mW. As photosensitizer, one hundred-μM methylene blue was used. Temperature was monitored to verify possible heat effect and reactive oxygen species (ROS) formation was evaluated. The same fluence in different fluence rates showed dissimilar levels of inactivation on yeast cells as well as in ROS formation. In addition, the increase of the fluence rate showed an improvement on cell photoinactivation. PDT was efficient against yeast cells (6 log reduction), and no significant temperature increase was observed. Fluence per se should not be used as an isolate parameter to compare photoinactivation effects on yeast cells. The higher fluence rate was more effective than the lower one. Furthermore, an adequate duration of light exposure cannot be discarded.
TL;DR: In this paper, a 1064 nm Nd:YAG laser with 300 ns pulses was used to experimentally investigate pulsed laser polishing on microfabricated nickel samples with microscale line features.
Abstract: The precision of parts created by microfabrication processes is limited by surface roughness. Therefore, as a means of improving surface roughness, pulsed laser micropolishing on nickel was examined numerically and experimentally. A one-dimensional finite element method model was used to estimate the melt depth and duration for single 50-300 ns laser pulses. The critical frequency was introduced to predict the effectiveness of polishing in the spatial frequency domain. A 1064 nm Nd:YAG laser with 300 ns pulses was used to experimentally investigate pulsed laser polishing on microfabricated nickel samples with microscale line features. A microfabricated sample with 2.5 μm wide and 0.2 μm high lines spaced 5 μm apart and one with 5 μm wide and 0.38 μm high lines spaced 10 μm apart were polished with 300 ns long pulses of 47.2 J/cm 2 and 44.1 J/cm 2 fluences, respectively. The critical frequency for these experimental conditions was predicted and compared with the reduction in the average surface roughness measured for samples with two different spatial frequency contents. The average surface roughness of 5 μm and 10 μm wavelength line features were reduced from 0.112 μm to 0.015 μm and from 0.112 μm to 0.059 μm, respectively. Four regimes of pulsed laser micropolishing are identified as a function of laser fluence for a given pulse width: (1) at low fluences no polishing occurs due to insufficient melting, (2) moderate fluences allow sufficient melt time for surface wave damping and significant smoothing occurs, (3) increasing fluence reduces smoothing, and (4) high fluences cause roughening due to large recoil pressure and ablation. Significant improvements in average surface roughness can be achieved by pulsed laser micropolishing if the dominant frequency content of the original surface features is above the critical spatial frequency for polishing.
TL;DR: Ablation of expanded polytetrafluoroethylene without disruption of the fine porous structure is demonstrated using an intense femtosecond-pulse laser and contributions from the Coulomb explosions of the ions rather than those of thermal expansion to generate high-energy ions are shown.
Abstract: Ablation of expanded polytetrafluoroethylene without disruption of the fine porous structure is demonstrated using an intense femtosecond-pulse laser. As a result of laser-matter interactions near ablation threshold fluence, high-energy ions are emitted, which cannot be produced by thermal dissociation of the molecules. The ion energy is produced by Coulomb explosion of the elements of (-CF2-CF2-)n, and the energy spectra of the ions show contributions from the Coulomb explosions of the ions rather than those of thermal expansion to generate high-energy ions. The dependence of ion energy on the laser fluence of a 180-fs pulse, compared with that of a 400-ps pulse, also suggests that the high-energy ions are accelerated by Coulomb explosion.
TL;DR: In this paper, the authors found that the energy absorption depends on the crystal orientation and that pre-ripples are only formed at very low fluence, while at higher energy, regular ripples initiate on secondary carbides or on grain boundaries.
Abstract: Laser induced self-organizing rippled nanostructures on steel are formed by femtosecond laser pulses. They are applied as hydrophobic surfaces. A low fluence results in ‘regular ripples’ with a spatial repetition of 300–500 nm, orientated perpendicular to the laser polarization direction. In twinned areas ‘pre-ripples’ with much smaller wavelength (about 150 nm) are observed, with a different orientation. We found indications that the energy absorption depends on the crystal orientation and that pre-ripples are only formed at very low fluence. Pre-ripples initiate on secondary carbides or on grain boundaries. At higher energy, regular ripples initiate in areas with pre-ripples; at even increasing fluence disordered structures are obtained.
Abstract: We use ultrafast electron diffraction to study lattice heating of 20nm noble metal films after femtosecond optical excitation with moderate excitation fluences. Using the Debye–Waller effect, the rise times of the lattice temperature were measured to be 1.1ps in copper (5.9mJ∕cm2 incident fluence) and 4.7ps in gold (0.9mJ∕cm2).
TL;DR: A highly accurate photoacoustic measurement of the subsurface tissue optical absorption spectrum has been achieved for the first time by introducing an extrinsic optical contrast agent with known optical properties.
Abstract: In photoacoustic imaging, the intensity of photoacoustic signal induced by optical absorption in biological tissue is proportional to light energy deposition, which is the product of the absorption coefficient and the local light fluence. Because tissue optical properties are highly dependent on the wavelength, the spectrum of the local light fluence at a target tissue beneath the sample surface is different than the spectrum of the incident light fluence. Therefore, quantifying the tissue optical absorption spectrum by using a photoacoustic technique is not feasible without the knowledge of the local light fluence. In this work, a highly accurate photoacoustic measurement of the subsurface tissue optical absorption spectrum has been achieved for the first time by introducing an extrinsic optical contrast agent with known optical properties. From the photoacoustic measurements with and without the contrast agent, a quantified measurement of the chromophore absorption spectrum can be realized in a strongly scattering medium. Experiments on micro-flow vessels containing fresh canine blood buried in phantoms and chicken breast tissues were carried out in a wavelength range from 680 nm to 950 nm. Spectroscopic photoacoustic measurements of both oxygenated and deoxygenated blood specimens presented an improved match with the references when employing this technique.
TL;DR: In this article, a study of the damage production in yttria-stabilized cubic zirconia single crystals irradiated with swift heavy ions was presented, where a combination of techniques which probe the material at different spatial scales (Rutherford backscattering spectrometry in channeling geometry, x-ray diffraction, transmission electron microscopy, and atomic force microscopy) was used in order to gain information about the damage depth distribution, the disordering buildup, the nature of radiation defects, and the occurrence of microstructural modifications.
Abstract: This article presents a study of the damage production in yttria-stabilized cubic zirconia single crystals irradiated with swift heavy ions The combination of techniques which probe the material at different spatial scales (Rutherford backscattering spectrometry in channeling geometry, x-ray diffraction, transmission electron microscopy, and atomic force microscopy) was used in order to gain information about the damage depth distribution, the disordering buildup, the nature of radiation defects, and the occurrence of microstructural modifications The damage results from the formation of tracks, due to the huge electronic excitations induced in the wake of incident ions The melting of the material in the core of tracks, via a thermal spike mechanism, leads to the creation of large hillocks at the surface of the crystals The overlapping of ion tracks at high fluence (above similar to 10(12) cm(-2)) induces a severe transformation of the microstructure of the material Nanodomains slightly disoriented from the main crystallographic direction are formed, with a size decreasing with increasing irradiation fluence These results may be used to predict the damage evolution in other nonamorphizable ceramics irradiated with swift heavy ions
TL;DR: In this article, an electronic excitation induced controlled tuning of the surface plasmon resonance (SPR) wavelength of Ag nanoparticles (NPs) in fullerene C70 matrix was reported.
Abstract: We report the electronic excitation induced controlled tuning of the surface plasmon resonance (SPR) wavelength of Ag nanoparticles (NPs) in fullerene C70 matrix. The transformation of fullerene C70 into amorphous carbon (a:C) under ion irradiation is used to tune the SPR wavelength of C70–Ag nanocomposite thin films. A 100 nm blue shift was recorded for irradiation at a fluence of 3 × 1013 ions cm−2 by 120 MeV Ag ions. A growth of Ag NPs from 7.0 ± 0.8 to 11.0 ± 0.4 nm with increasing fluence was observed by transmission electron microscopy and it is explained in the framework of thermal spike model. The transformation of fullerene C70 into amorphous carbon with ion irradiation was confirmed by Raman spectroscopy. This work demonstrates the possibility to locally excite the SPR at a desired wavelength and therefore, acquiring multiple SPR bands at a single substrate which could be useful in developing more efficient optical sensors.
TL;DR: In this article, the size characteristics of core-shell Ag-Ag2O colloid nanostructures (smaller than 10 nm) obtained by femtosecond laser ablation of solid silver targets in different liquid media (water or ethanol) through the study of their optical extinction spectra.
Abstract: The generation of small silver metal nanoparticles (Nps) by ultrashort pulsed laser ablation has been an active area of research in recent years due to their interest in several fields of applied research such as biotechnology and material research, in particular those with sizes smaller than 10 nm. In general, laser ablation tends to produce environmentally clean metal Nps compared with wet chemical methods. However, since silver may be oxidized in the presence of water or ethanol, core–shell silver–silver oxide (Ag–Ag2O) Nps can be formed, whose size and thickness must be determined and characterized for functionalization related to future applications. This work analyses the size characteristics of core–shell Ag–Ag2O colloid nanostructures (smaller than 10 nm) obtained by femtosecond laser ablation of solid silver targets in different liquid media (water or ethanol) through the study of their optical extinction spectra. A fit of full experimental spectrum using Mie theory allows the determination of core size and shell thickness distributions as a function of fluence. The red-shift of the plasmon peak wavelength with respect to the bare-core peak wavelength at 400 nm, produced by the oxide shell, may be easily measured even for very small thicknesses. It was found that the dominant Ag2O effective thickness is inversely proportional to the fluence, reaching a maximum of 0.2 nm for a fluence of 60 J cm−2 and a minimum of 0.04 nm for a fluence of 1000 J cm−2.
TL;DR: In this article, a combination of the laser-induced breakdown spectroscopy (LIBS) and laser induced fluorescence (LIF) techniques was investigated to improve the limit of detection (LoD) of trace elements in solid matrices.
TL;DR: In this paper, deuterium retention and local melting at tungsten exposed to high-fluence (up to 1027 D/m2) of highflux (1022 D+/m 2/s) and low-energy (38 eV) deutrium plasma at varying temperature were examined with scanning electron microscopy (SEM), focused ion beam (FIB), thermal desorption spectroscopy (TDS), and electron probe microanalysis (EPMA).
TL;DR: In this paper, the fast phase transition process on Ge2Sb2Te5 film induced by picosecond laser pulses was studied using time-resolved reflectivity measurements.
Abstract: Fast phase transition processes on Ge2Sb2Te5 film induced by picosecond laser pulses were studied using time-resolved reflectivity measurements. It was found that after picosecond laser pulse priming, reversible switching could be occurred upon picosecond laser pulse irradiation with the same well-chosen fluence. This is very different from general knowledge that reversible phase change process will be induced by laser pulses with different powers; that is, amorphization process needs much higher fluence than crystallization process. The possible mechanism was discussed qualitatively by a melting-cooling model.
01 Feb 2009-Nuclear Instruments & Methods in Physics Research Section A-accelerators Spectrometers Detectors and Associated Equipment
TL;DR: In this paper, high resistivity standard, oxygenated and magnetic Czochralski p-type materials were irradiated with reactor neutrons and 24 GeV/c protons up to an equivalent fluence of Φ eq =3×10 14 ǫ −2.
Abstract: Diodes fabricated on high resistivity standard, oxygenated and magnetic Czochralski p-type materials were irradiated with reactor neutrons and 24 GeV/ c protons up to an equivalent fluence of Φ eq =3×10 14 cm −2 . Radiation effects on effective trapping times, effective dopant concentration and leakage current were measured at 20 °C. Annealing of defects was performed at 20 and 60 °C.
TL;DR: In this article, high-spatial frequency, quasiperiodic structures (HSFL, Nanoripples) of 170 nm feature size were induced in rutile-type titanium dioxide surfaces by focused 150 fs Ti:sapphire laser pulses at wavelengths around 800 nm.
Abstract: High-spatial frequency, quasiperiodic structures (HSFL, Nanoripples) of 170 nm feature size were induced in rutile-type titanium dioxide surfaces by focused 150 fs Ti:sapphire laser pulses at wavelengths around 800 nm. The ripple formation is distinctly visible for numbers of pulses of N=100–1000. At lower number of pulses (N=10), a significant surface roughening appears instead of ripples which is characterized by randomly meandering nanostructures. These observations confirm an essential contribution of early stage irregular material modifications to the dynamics of quasiperiodic ripple formation. The threshold fluence for ripple generation is estimated on the basis of the conventional theory of laser-induced surface structuring. The decrease in the threshold fluence from 0.34 to 0.24 J/cm2, as it was found for an increase in the number of pulses from N=100 to N=1000, is attributed to a damage accumulation effect. Nanostructuring of spatially extended regions was enabled by utilizing a controlled sample...
TL;DR: Positron annihilation lifetime spectroscopy has been performed with a pulsed positron beam to investigate the nature and evolution of implantation-induced defects created in the track region (TR) of 800 keV 3He ions at different fluences as mentioned in this paper.
Abstract: Positron Annihilation Lifetime Spectroscopy has been performed with a pulsed positron beam to investigate the nature and evolution of implantation-induced defects created in the track region (TR) of 800 keV 3He ions at different fluences. At high fluence - 5×1016 cm–2 - lifetime decomposition exhibits a predominant (98%) positron lifetime of 200 ps which is attributed to irradiation induced monovacancy. The increasing average lifetime as a function of the post-implantation annealing temperature has allowed to identify vacancy clustering due to vacancy migration (that occurs from 473 K). (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
TL;DR: In this article, the laser-induced ablation of silicon in liquids of the dimethyl sulfoxide (DMSO) and the water at different applied laser fluence levels and laser shot numbers was investigated.
Abstract: Laser fluence and laser shot number are important parameters for pulse laser based micromachining of silicon in liquids. This paper presents laser-induced ablation of silicon in liquids of the dimethyl sulfoxide (DMSO) and the water at different applied laser fluence levels and laser shot numbers. The experimental results are conducted using 15 ns pulsed laser irradiation at 532 nm. The silicon surface morphology of the irradiated spots has an appearance as one can see in porous formation. The surface morphology exhibits a large number of cavities which indicates as bubble nucleation sites. The observed surface morphology shows that the explosive melt expulsion could be a dominant process for the laser ablation of silicon in liquids using nanosecond pulsed laser irradiation at 532 nm. Silicon surface’s ablated diameter growth was measured at different applied laser fluences and shot numbers in both liquid interfaces. A theoretical analysis suggested investigating silicon surface etching in liquid by intense multiple nanosecond laser pulses. It has been assumed that the nanosecond pulsed laser-induced silicon surface modification is due to the process of explosive melt expulsion under the action of the confined plasma-induced pressure or shock wave trapped between the silicon target and the overlying liquid. This analysis allows us to determine the effective lateral interaction zone of ablated solid target related to nanosecond pulsed laser illumination. The theoretical analysis is found in excellent agreement with the experimental measurements of silicon ablated diameter growth in the DMSO and the water interfaces. Multiple-shot laser ablation threshold of silicon is determined. Pulsed energy accumulation model is used to obtain the single-shot ablation threshold of silicon. The smaller ablation threshold value is found in the DMSO, and the incubation effect is also found to be absent.
TL;DR: In this article, the authors presented a theoretical work on short pulse laser interaction with metal targets, where they considered the interplay of two competitive mechanisms of the laser energy dissipation: the fast electron heat conduction and the electron-phonon interaction processes.
TL;DR: In this article, the authors showed that the surface-damage of the bulk SiC samples exceeds the fluence required for thermal melting at all wavelengths, and that the damage threshold of the film sample shows a strong wavelength dependence.
Abstract: We exposed bulk SiC and films of SiC and B4C to single 25 fs long free-electron-laser pulses with wavelengths between 13.5 and 32 nm. The materials are candidates for x-ray free-electron laser optics. We found that the threshold for surface-damage of the bulk SiC samples exceeds the fluence required for thermal melting at all wavelengths. The damage threshold of the film sample shows a strong wavelength dependence. For wavelengths of 13.5 and 21.7 nm, the damage threshold is equal to or exceeds the melting threshold, whereas at 32 nm the damage threshold falls below the melting threshold.
12 Feb 2009
TL;DR: In this paper, the dependence of the film removal fluence threshold on the laser pulse duration was investigated systematically for two different laser wavelengths of 532 nm and 1064 nm for thin-film solar cell production.
Abstract: The removal of thin films widely used in photovoltaics as (transparent) electrodes (e.g. SnO2, molybdenum) or solar absorber (e.g. amorphous silicon) materials is studied experimentally using multi-kHz diode-pumped solid state lasers in the visible and infrared spectral region. The film processing (or what is commonly known as P1, P2, or P3 laser scribing) is performed through the film-supporting glass plate of several millimeter thickness by using a galvo laser scanner setup equipped with f-theta optics. The dependence of the film removal fluence threshold on the laser pulse duration (~8 ns to ~40 ns) is investigated systematically for two different laser wavelengths of 532 nm and 1064 nm. The laser-scribing of continuous lines suitable for thin-film solar cell production is demonstrated successfully at scribe speeds on the order of meters per second. The experimental results are discussed on the basis of laser ablation models considering optical, geometrical, and thermal material properties and are additionally supported by numerical simulations.
TL;DR: In this article, the melting, vaporization and resolidification processes of thin gold film irradiated by a femtosecond pulse laser are studied numerically, and the nonequilibrium heat transfer in electrons and lattice is described using a two-temperature model.
Abstract: Melting, vaporization and resolidification processes of thin gold film irradiated by a femtosecond pulse laser are studied numerically. The nonequilibrium heat transfer in electrons and lattice is described using a two-temperature model. The solid–liquid interfacial velocity, as well as elevated melting temperature and depressed solidification temperature, is obtained by considering the interfacial energy balance and nucleation dynamics. An iterative procedure based on energy balance and gas kinetics law to track the location of liquid–vapor interface is utilized to obtain the material removal by vaporization. The effect of surface heat loss by thermal radiation was discussed. The influences of laser fluence and duration on the evaporation process are studied. Results show that higher laser fluence and shorter laser pulse width lead to higher interfacial temperature, deeper melting and ablation depths.