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1

Femtosecond laser ablation of gallium arsenide investigated with time-of-flight mass spectroscopy  

E-print Network

Femtosecond laser ablation of gallium arsenide investigated with time- of-flight mass spectroscopy laser-induced ablation of gallium arsenide using time-of-flight mass spectroscopy. At the ablation into a collisional expansion process. Above the ablation threshold, the behavior of gallium particles can

von der Linde, D.

2

Laser ablation of copper based alloys by single and double pulse laser induced breakdown spectroscopy  

NASA Astrophysics Data System (ADS)

Single and double pulse laser induced breakdown spectroscopy was applied to the analysis of copper based alloys samples, in order to investigate the material ablation process under two different experimental conditions. An Nd:YAG laser, emitting at the fundamental wavelength (1064 nm) for a fixed value of total energy with the same pulse width, has been used for both set-up configurations. Certified samples of copper based alloys were examined in order to investigate the effect of their different compositions on the ablation process efficiency. The craters produced by the laser on the samples surfaces were measured by a contact profilometer in order to evaluate the mass of ablated material. In this respect the differences in behaviour of the single and the double pulse ablation for Laser Induced Breakdown Spectroscopy (LIBS), respectively, have been considered. The dependence, under the same experimental conditions, of the LIBS background emission of the different ablated masses of the material has also been investigated, by looking for normalization algorithms for quantitative data reduction. The behaviour of some peculiar intensity ratios, suitable for building calibration curves, has been studied in order to evaluate the trend in fractionated evaporation on going from the single pulse to the double pulse technique.

Caneve, L.; Colao, F.; Fantoni, R.; Spizzichino, V.

2006-11-01

3

Laser-ablated active doping technique for visible spectroscopy measurements on Z.  

SciTech Connect

Visible spectroscopy is a powerful diagnostic, allowing plasma parameters ranging from temperature and density to electric and magnetic fields to be measured. Spectroscopic dopants are commonly introduced to make these measurements. On Z, dopants are introduced passively (i.e. a salt deposited on a current-carrying surface); however, in some cases, passive doping can limit the times and locations at which measurements can be made. Active doping utilizes an auxiliary energy source to disperse the dopant independently from the rest of the experiment. The objective of this LDRD project was to explore laser ablation as a method of actively introducing spectroscopic dopants. Ideally, the laser energy would be delivered to the dopant via fiber optic, which would eliminate the need for time-intensive laser alignments in the Z chamber. Experiments conducted in a light lab to assess the feasibility of fibercoupled and open-beam laser-ablated doping are discussed.

Gomez, Matthew Robert

2013-09-01

4

Emission spectroscopy of laser ablation plasma with time gating by acousto-optic modulator  

SciTech Connect

The capability of acousto-optic modulator (AOM) to perform time-gated measurements for laser ablation plasma spectroscopy has been examined. Especially, we focused on the capability of the ''AOM gating'' to exclude the continuum and extremely broadened spectra usually observed immediately after the laser ablation. Final goal of the use of the AOM is to achieve considerable downsizing of the system for in situ and on-site analyses. In the present paper, it is shown that narrow and clear spectral lines can be obtained with the AOM gating even if the target is submerged in water. Also, application of this technique to the targets in air is demonstrated. It has been revealed that the AOM gating is fast enough to exclude the continuum and broadened lines, while effectively acquiring sufficiently narrow atomic lines lasting slightly longer than the continuum.

Sakka, Tetsuo [Institute of Advanced Energy, Kyoto University, Uji, Kyoto 611-0011 (Japan); Institute of Sustainability Science, Kyoto University, Uji, Kyoto 611-0011 (Japan); Irie, Kyohei; Fukami, Kazuhiro; Ogata, Yukio H. [Institute of Advanced Energy, Kyoto University, Uji, Kyoto 611-0011 (Japan)

2011-02-15

5

[Study on characteristics of laser ablation in KTP crystal and its influence on the Raman spectroscopy].  

PubMed

The research and development of the KTP crystal with high threshold is of very importance for its application in high-energy laser systems. Ablation characteristics in KTP crystal as well as their influence on the Raman spectroscopy were studied by UV laser with high repetition frequency. The research results show that the laser plasma effects are the main reasons for the damage in the KTP crystal. The inverse bremsstrahlung absorption effect can increase the deposition of the laser pulse energy greatly; the ionization effect can make the crystal dislocated completely; shock wave effect can push away the mixture of melted, vaporized and ionized materials and cause cracks in the pit. Through investigation and comparison of the Raman spectroscopy before and after the laser ablation, it was found that the distribution characteristics of Raman peaks are almost the same, suggesting that the basic structures of KTP crystal do not change. But almost all the Raman characteristic peaks' R1R values have changed and the widths are broadened, which means that the crystalline degree has been decreased. The Raman peaks of TiO6 and PO4 oxygen polyhedron shift to the lower wave number, which indicates that bonding force becomes weaker and the KTP crystal can be damaged easily. PMID:23016332

Han, Jing-Hua; Duan, Tao; Fan, Wei-Xing; Feng, Guo-Ying; Yang, Li-Ming; Niu, Rui-Hua; Yang, Jie; Zhai, Ling-Ling; Guo, Chao

2012-07-01

6

Progress of laser ablation for accelerator mass spectroscopy at ATLAS utilizing an ECRISa)  

NASA Astrophysics Data System (ADS)

Beams of ions from the laser ablation method of solid materials into an electron cyclotron resonance ion source (ECRIS) plasma have been used for the first time in experiments at ATLAS. Initial accelerator mass spectroscopy experiments using laser ablation for actinides and samarium have been performed. Initial results of coupling the laser system to the ECR source have guided us in making a number of changes to the original design. The point of laser impact has been moved off axis from the center of the ECR injection side. Motor control of the laser positioning mirror has been replaced with a faster and more reliable piezo-electric system, and different raster scan patterns have been tested. The use of the laser system in conjunction with a multi-sample changer has been implemented. Two major problems that are being confronted at this time are beam stability and total beam intensity. The status of the development will be presented and ideas for further improvements will be discussed.

Scott, R.; Palchan, T.; Pardo, R.; Vondrasek, R.; Kondev, F.; Nusair, O.; Peters, C.; Paul, M.; Bauder, W.; Collon, P.

2014-02-01

7

Two-tracer spectroscopy diagnostics of temperature profile in the conduction layer of a laser-ablated plastic foil  

SciTech Connect

A technique that combines the diagnostics of electron temperature history and the measurements of ablation velocity with two-tracer x-ray spectroscopy has been developed for diagnosing the temperature profiles in the thermal conduction layers of laser-ablated plastic foils. The electron temperature in the plastic ablator was diagnosed using the isoelectronic line ratios of Al Ly{alpha} line to Mg Ly{alpha} line, emitted from a tracer layer of Al/Mg mixture buried under the ablator. The ablation velocity was inferred from the time delay between the onset time of x-ray line emissions from Al and Mg tracer layers buried at two depths in the ablator, respectively. From the measured electron temperatures and ablation velocity, the electron temperature profile in the conduction layer was inferred. The measured temperature profile was compared with the simulated one and reasonable agreement was found.

Zhang Jiyan; Yang Guohong; Hu Xin; Yang Jiamin; Ding Yaonan; Ding Yongkun; Zhang Baohan; Zheng Zhijian [Research Center of Laser Fusion, P. O. Box 919-986, Mianyang 621900 (China); Xu Yan; Yan Jun; Pei Wenbin [Institute of Applied Physics and Computational Mathematics, Beijing 100088 (China)

2010-11-15

8

Dynamics of femto-and nanosecond laser ablation plumes investigated using optical emission spectroscopy  

E-print Network

emission lifetime. Though both ns and fs laser-plasmas showed similar temperatures ($1 eV), the fs LPP representation of laser-target and laser-plasma coupling along with emission in the visible region is given density surpasses the ablation threshold of the material. The laser-target interaction involves many

Harilal, S. S.

9

Detection and Classification of Individual Airborne Microparticles using Laser Ablation Mass Spectroscopy and Multivariate Analysis  

SciTech Connect

We are developing a method for the real-time analysis of airborne microparticles based on laser ablation mass spectroscopy. Airborne particles enter an ion trap mass spectrometer through a differentially-pumped inlet, are detected by light scattered from two CW laser beams, and sampled by a 10 ns excimer laser pulse at 308 nm as they pass through the center of the ion trap electrodes. After the laser pulse, the stored ions are separated by conventional ion trap methods. In this work thousands of positive and negative ion spectra were collected for eighteen different species: six bacteria, six pollen, and six particulate samples. The data were then averaged and analyzed using the Multivariate Patch Algorithm (MPA), a variant of traditional multivariate anal ysis. The MPA correctly identified all of the positive ion spectra and 17 of the 18 negative ion spectra. In addition, when the average positive and negative spectra were combined the MPA correctly identified all 18 species. Finally, the MPA is also able to identify the components of computer synthesized mixtures of the samples studied

Gieray, R.A.; Lazar, A.; Parker, E.P.; Ramsey, J. M.; Reilly, P.T.A.; Rosenthal, S.E.; Trahan, M.W.; Wagner, J.S.; Whitten, W.B.

1999-04-27

10

Resonance-enhanced multiphoton ionization spectroscopy of laser-ablated copper atoms  

NASA Astrophysics Data System (ADS)

Resonance-enhanced multiphoton ionization (REMPI) spectra of laser-ablated copper atoms entrained in a supersonic free jet expansion are reported. Depending on the ionization scheme employed, and the conditions under which the copper atoms are produced, very different spectra are produced, which are discussed. In some circumstances, high proportions of metastable atoms survive the ablation and expansion process and are clearly seen in the spectra. The spectroscopic transitions for the observed lines are identified, and it is noted that some caution is merited in the assumption that only ground state copper atoms are present following laser ablation.

Andrejeva, Anna; Harris, Joe P.; Wright, Timothy G.

2014-10-01

11

Characterization of laser ablation of copper in the irradiance regime of laser-induced breakdown spectroscopy analysis  

NASA Astrophysics Data System (ADS)

The LIBS signal depends both on the ablated mass and on the plasma excitation temperature. These fundamental parameters depend in a complex manner on laser ablation and on laser-plasma coupling. As several works in the literature suggest that laser ablation processes play a predominant role compared to plasma heating phenomena in the LIBS signal variations, this paper focuses on the study of laser ablation. The objective was to determine an interaction regime enabling to maximally control the laser ablation. Nanosecond laser ablation of copper at 266 nm was characterized by scanning electron microscopy and optical profilometry analysis, in air at 1 bar and in the vacuum. The laser beam spatial profile at the sample surface was characterized in order to give realistic values of the irradiance. The effect of the number of accumulated laser shots on the crater volume was studied. Then, the ablation crater morphology, volume, depth and diameter were measured as a function of irradiance between 0.35 and 96 GW/cm². Results show that in the vacuum, a regular trend is observed over the whole irradiance range. In air at 1 bar, below a certain irradiance, laser ablation is very similar to the vacuum case, and the ablation efficiency of copper was estimated at 0.15 ± 0.03 atom/photon. Beyond this irradiance, the laser beam propagation is strongly disrupted by the expansion of the dense plasma, and plasma shielding appears. The fraction of laser energy used for laser ablation and for plasma heating is estimated in the different irradiance regimes.

Picard, J.; Sirven, J.-B.; Lacour, J.-L.; Musset, O.; Cardona, D.; Hubinois, J.-C.; Mauchien, P.

2014-11-01

12

Acoustic spectroscopy of Er:YAG laser ablation of skin: first results  

Microsoft Academic Search

We investigated the acoustic signal of Er:YAG laser ablation in a gaseous environment. The high absorption coefficient of water at the laser wavelength of 2.94 micrometer leads to a small penetration depth of the Er:YAG laser pulses into tissue. The deposition of laser energy in a thin layer at the tissue surface causes a rapid evaporization of tissue water. The

Kester Nahen; Alfred Vogel

1998-01-01

13

Multielemental analysis of prehistoric animal teeth by laser-induced breakdown spectroscopy and laser ablation inductively coupled plasma mass spectrometry  

SciTech Connect

Laser-induced breakdown spectroscopy (LIBS) and laser ablation (LA) inductively coupled plasma (ICP) mass spectrometry (MS) were utilized for microspatial analyses of a prehistoric bear (Ursus arctos) tooth dentine. The distribution of selected trace elements (Sr, Ba, Fe) was measured on a 26 mmx15 mm large and 3 mm thick transverse cross section of a canine tooth. The Na and Mg content together with the distribution of matrix elements (Ca, P) was also monitored within this area. The depth of the LIBS craters was measured with an optical profilometer. As shown, both LIBS and LA-ICP-MS can be successfully used for the fast, spatially resolved analysis of prehistoric teeth samples. In addition to microchemical analysis, the sample hardness was calculated using LIBS plasma ionic-to-atomic line intensity ratios of Mg (or Ca). To validate the sample hardness calculations, the hardness was also measured with a Vickers microhardness tester.

Galiova, Michaela; Kaiser, Jozef; Fortes, Francisco J.; Novotny, Karel; Malina, Radomir; Prokes, Lubomir; Hrdlicka, Ales; Vaculovic, Tomas; Nyvltova Fisakova, Miriam; Svoboda, Jiri; Kanicky, Viktor; Laserna, Javier J.

2010-05-01

14

Evolutions in time and space of laser ablated species by dual-laser photoabsorption spectroscopy  

SciTech Connect

An atmospheric aluminum laser induced plasma is investigated by means of absorption and emission spectroscopies in the near ultraviolet range. The absorbed radiation is produced by a second aluminum laser induced plasma, which is generated at adjustable time delay. The measurements of both ground and resonant state number densities are derived from the fitting of the experimental 308.21 nm ({sup 2}P{sub 1/2}{sup 0}-{sup 2}D{sub 3/2}) and 396.15 nm ({sup 2}P{sub 3/2}{sup 0}-{sup 2}S{sub 1/2}) line absorption profiles on the numerical solution of the radiative transfer equation. Owing to the dominant role played by the Stark effect in the line broadening and shifting, the calculation also provides the evolution in time and in space of the free electron density along the line of sight. More classically, the same method is applied to the emission profiles which exhibit strong self-absorbed shapes. The reliability of the results derived from both absorption and emission experiments is analyzed and the origin of the asymmetric shape of the absorption lines is discussed.

Ribiere, M.; Mees, L.; Allano, D.; Cheron, B. G. [Technopole du Madrillet, UMR 6614 CNRS (CORIA), BP 12, 76801 Saint Etienne du Rouvray (France)

2008-08-15

15

Pb distribution in bones from the Franklin expedition: synchrotron X-ray fluorescence and laser ablation/mass spectroscopy  

NASA Astrophysics Data System (ADS)

Synchrotron micro-X-ray Fluorescence has been used to map the metal distribution in selected bone fragments representative of remains associated with the Franklin expedition. In addition, laser ablation mass spectroscopy using a 25 ?m diameter circular spot was employed to compare the Pb isotope distributions in small regions within the bone fragments. The X-ray Fluorescence mapping shows Pb to be widely distributed in the bone while the Pb isotope ratios obtained by laser ablation within small areas representative of bone with different Pb exchange rates do not show statistically significant differences. These results are inconsistent with the hypothesis that faulty solder seals in tinned meat were the principle source of Pb in the remains of the expedition personnel.

Martin, Ronald Richard; Naftel, Steven; Macfie, Sheila; Jones, Keith; Nelson, Andrew

2013-04-01

16

Time-of-flight spectroscopy of the energy distribution of laser-ablated atoms and ions  

SciTech Connect

The growth of ultrathin films, deposited by laser ablation, crucially depends on the energy of the ablated species. Therefore, a time-of-flight (TOF) spectrometer has been constructed and measurements have been carried out in order to determine the energy distribution of laser-ablated Fe and Pt atoms and ions in the plasma created by nanosecond pulses of a frequency-doubled neodymium doped yttrium aluminum garnet laser. The experiments have been performed in ultrahigh vacuum at relatively low laser power. For measuring the spectra of the neutrals, a cross-beam electron source for postionization and electric as well as magnetic fields for repelling the ions are employed. Nevertheless, measurements of neutral particles are restricted to low plasma densities due to electrostatic shielding within the plasma, leading to an inefficient deflection of charged particles by electrostatic and magnetic fields. Test measurements have been performed by utilizing the TOF spectrometer as a pressure gauge and also by chopping the electron beam, running the TOF spectrometer as a residual gas mass spectrometer. The spectra of the laser-ablated plasmas have shown plasma conditions with a Debye length of approximately 10{sup -4} m, densities of 10{sup 15}-10{sup 16} m{sup -3} and ion energies up to 150 eV. Neutral spectra have shown an unexpectedly low fraction of neutrals (10{sup -3}-10{sup -4}) and hyperthermal energies up to several 10 eV, possibly contributed by recombination of ions and electrons in the plasma. Even though gas spectra had demonstrated the expected sensitivity of the TOF spectrometer for low-energy neutrals, no thermally evaporated neutral atoms could be found.

Buchsbaum, A.; Rauchbauer, G.; Varga, P.; Schmid, M. [Institut fuer Allgemeine Physik, TU Wien, Wiedner Hauptstrasse 8-10, A-1040 Wien (Austria)

2008-04-15

17

Nanoparticles by Laser Ablation  

Microsoft Academic Search

This review concerns nanoparticles collected in the form of nanopowder or a colloidal solution by laser ablating a solid target that lies in a gaseous or a liquid environment. The paper discusses the advantages of the method as compared with other methods for nanoparticle synthesis, outlines the factors on which the properties of the produced nanoparticles depend, explains the mechanisms

N. G. Semaltianos

2010-01-01

18

Diagnostics of Carbon Nanotube Formation in a Laser Produced Plume: An Investigation of the Metal Catalyst by Laser Ablation Atomic Fluorescence Spectroscopy  

NASA Technical Reports Server (NTRS)

Carbon nanotubes, elongated molecular tubes with diameters of nanometers and lengths in microns, hold great promise for material science. Hopes for super strong light-weight material to be used in spacecraft design is the driving force behind nanotube work at JSC. The molecular nature of these materials requires the appropriate tools for investigation of their structure, properties, and formation. The mechanism of nanotube formation is of particular interest because it may hold keys to controlling the formation of different types of nanotubes and allow them to be produced in much greater quantities at less cost than is currently available. This summer's work involved the interpretation of data taken last summer and analyzed over the academic year. The work involved diagnostic studies of carbon nanotube formation processes occurring in a laser-produced plume. Laser ablation of metal doped graphite to produce a plasma plume in which carbon nanotubes self assemble is one method of making carbon nanotube. The laser ablation method is amenable to applying the techniques of laser spectroscopy, a powerful tool for probing the energies and dynamics of atomic and molecular species. The experimental work performed last summer involved probing one of the metal catalysts, nickel, by laser induced fluorescence. The nickel atom was studied as a function of oven temperature, probe laser wavelength, time after ablation, and position in the laser produced plume. This data along with previously obtained data on carbon was analyzed over the academic year. Interpretations of the data were developed this summer along with discussions of future work. The temperature of the oven in which the target is ablated greatly influences the amount of material ablated and the propagation of the plume. The ablation conditions and the time scale of atomic and molecular lifetimes suggest that initial ablation of the metal doped carbon target results in atomic and small molecular species. The metal atoms survive for several milliseconds while the gaseous carbon atoms and small molecules nucleate more rapidly. Additional experiments and the development of in situ methods for carbon nanotube detection would allow these results to be interpreted from the perspective of carbon nanotube formation.

deBoer, Gary; Scott, Carl

2003-01-01

19

Fundamental Characteristics of a Laser Ablation Microthruster  

NASA Astrophysics Data System (ADS)

The fundamental characteristics of a laser ablation microthruster were investigated for a 10 kg-class microspacecraft. A single-shot impulse measurement was performed using a thrust stand on which a prototype thruster was installed and the associate ablated mass was estimated from the pressure increase in the space chamber. The best performance of several polymer materials was obtained using polyvinylchloride as the propellant. More heavily carbon doped polyvinylchloride showed higher performance, which means absorption length has a large effect on performance. The intensity of the laser beam on the ablation material was changed using constant laser power, and it was shown that intensity had little effect on the performance. This qualitative behavior agreed with the results of a simple thermal analysis. Mass spectroscopy of the ablation plume showed that the dominant reaction was dehydrochlorination in the range of 470 to 640 K, and the low-temperature reaction resulted in the best performance for polyvinylchloride.

Koizumi, Hiroyuki; Inoue, Takayoshi; Komurasaki, Kimiya; Arakawa, Yoshihiro

20

Comparative investigation of laser ablation plumes in air and argon by analysis of spectral line shapes: Insights on calibration-free laser-induced breakdown spectroscopy  

NASA Astrophysics Data System (ADS)

We investigate the characteristic features of plume expansion in air and argon resulting from ultraviolet laser ablation of solid matter in conditions typically applied in material analysis via laser-induced breakdown spectroscopy (LIBS). Barite crown glass is chosen as a target material for the characteristic emission spectrum suitable for plasma diagnostics. The space-integrated plasma emission spectrum recorded with an echelle spectrometer coupled to a gated detector is compared to the computed spectral radiance of a nonuniform plasma in local thermodynamic equilibrium. In particular, resonance lines of neutral sodium atoms and barium ions are observed to probe gradients of temperature and density within the plume. It is shown that laser ablation in argon leads to an almost uniform plasma whereas gradients of temperature and density are evidenced in ambient air. The discrepancy is attributed to the different physical properties of both gases leading to a stronger vapor-gas energy exchange in the case of air. However, strong gradients occur only in a thin peripheral zone, close to the vapor-gas contact front. The larger plasma core appears almost uniform. The peripheral zone of low temperature mostly contributes to the plasma emission spectrum by absorption and material analysis via calibration-free LIBS in air may ignore the nonuniform character of the plasma if only transitions of small optical thickness are considered.

Hermann, Jörg; Gerhard, Christoph; Axente, Emanuel; Dutouquet, Christophe

2014-10-01

21

Femtosecond laser ablation of bovine cortical bone  

NASA Astrophysics Data System (ADS)

We study the surface topographical, structural, and compositional modifications induced in bovine cortical bone by femtosecond laser ablation. The tests are performed in air, with a Yb:KYW chirped-pulse-regenerative amplification laser system (500 fs, 1030 nm) at fluences ranging from 0.55 to 2.24 J/cm2. The ablation process is monitored by acoustic emission measurements. The topography of the laser-treated surfaces is studied by scanning electron microscopy, and their constitution is characterized by glancing incidence x-ray diffraction, x-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, and micro-Raman spectroscopy. The results show that femtosecond laser ablation allows removing bone without melting, carbonization, or cracking. The structure and composition of the remaining tissue are essentially preserved, the only constitutional changes observed being a reduction of the organic material content and a partial recrystallization of hydroxyapatite in the most superficial region of samples. The results suggest that, within this fluence range, ablation occurs by a combination of thermal and electrostatic mechanisms, with the first type of mechanism predominating at lower fluences. The associated thermal effects explain the constitutional changes observed. We show that femtosecond lasers are a promising tool for delicate orthopaedic surgeries, where small amounts of bone must be cut with negligible damage, thus minimizing surgical trauma.

Cangueiro, Liliana T.; Vilar, Rui; Botelho do Rego, Ana M.; Muralha, Vania S. F.

2012-12-01

22

High spatial resolution mapping of deposition layers on plasma facing materials by laser ablation microprobe time-of-flight mass spectroscopy  

NASA Astrophysics Data System (ADS)

A laser ablation microprobe time-of-flight mass spectroscopy (LAM-TOF-MS) system with high spatial resolution, ˜20 nm in depth and ˜500 ?m or better on the surface, is developed to analyze the composition distributions of deposition layers on the first wall materials or first mirrors in tokamak. The LAM-TOF-MS system consists of a laser ablation microprobe combined with a TOF-MS and a data acquisition system based on a LabVIEW program software package. Laser induced ablation combined with TOF-MS is an attractive method to analyze the depth profile of deposited layer with successive laser shots, therefore, it can provide information for composition reconstruction of the plasma wall interaction process. In this work, we demonstrate that the LAM-TOF-MS system is capable of characterizing the depth profile as well as mapping 2D composition of deposited film on the molybdenum first mirror retrieved from HL-2A tokamak, with particular emphasis on some of the species produced during the ablation process. The presented LAM-TOF-MS system provides not only the 3D characterization of deposition but also the removal efficiency of species of concern.

Xiao, Qingmei; Li, Cong; Hai, Ran; Zhang, Lei; Feng, Chunlei; Zhou, Yan; Yan, Longwen; Duan, Xuru; Ding, Hongbin

2014-05-01

23

Femtosecond laser ablation of solid materials  

NASA Astrophysics Data System (ADS)

In this dissertation, femtosecond laser materials processing is studied. A time-of-flight mass spectrometer has been designed, constructed and utilized to measure the time-of-flight spectra of the ions ablated by femtosecond laser pulses. The velocities and kinetic energies of the ions are determined. Emission spectroscopy and imaging have been carried out to analyze the laser-induced plume. Craters ablated in vacuum and under ambient pressure are measured by a scanning electron microscope (SEM) and a light interferometric microscope. Numerical methods in microscale energy transfer are first reviewed. Subsequently, a numerical model based on the two-temperature concept is utilized to account for the non-equilibrium energy transfer processes dominating the ultrashort laser pulse excitation of materials. Time-of-flight measurements reveal the presence of extremely energetic ions in femtosecond laser-induced plumes, with kinetic energies more than one order of magnitude higher than those of nanosecond laser-induced ions. Two different ablation regimes, exhibiting different laser fluence dependence of the total ion yields, and the corresponding percentage of energetic ions and the crater depths, are discovered for femtosecond laser ablation of titanium. Numerical modeling shows that the laser fluences associated with the second ablation regime can raise the lattice system to the range of the thermodynamic critical point and hence may cause explosive evaporation leading to the observed higher ablation rates. The first regime, however, occurs at lower laser fluences, when the laser energy is mainly deposited in the shallow region defined by the optical penetration depth. The more localized energy deposition is believed to lead to higher percentage of energetic ions, albeit to less total ablation volume. Femtosecond laser-induced plumes have been found to be much smaller in spatial dimensions and weaker in intensity than those induced by nanosecond laser pulses. The ambient pressure is found to restrain the expansion of the plumes. The non-equilibrium microscopic energy transfer between the electron and lattice subsystems needs to be considered to model femtosecond laser materials processing. The two-temperature approach is capable of at least semi-quantitatively modeling real engineering problems. Due to the large temperature range encountered in typical laser ablation applications, the temperature dependence of the materials thermal properties is found to be very important for accurate modeling. (Abstract shortened by UMI.)

Ye, Mengqi

24

Laser Ablation for Medical Applications  

NASA Astrophysics Data System (ADS)

Medical applications of laser are measurement, laser surgery, in-situ monitoring, and processing of medical devices. In this paper, author briefly reviews the trends of medical applications, describes some new applications, and then discuss about the future trends and problems of medical applications. At present, the domestic market of laser equipment for medical applications is nearly 1/10 of that for industrial applications, which has registered significant growth continuously. Laser surgery as a minimum invasive surgery under arthroscope is expected to decrease the pain of patients. Precise processing such as cutting and welding is suitable for manufacturing medical devices. Pulsed laser deposition has been successfully applied to the thin film coating. The corneal refractive surgery by ArF excimer laser has been widely accepted for its highly safe operation. Laser ablation for retinal implant in the visual prosthesis is one of the promising applications of laser ablation in medicine. New applications with femtosecond laser are expected in the near future.

Hayashi, Ken-Ichi

25

Species-resolved imaging and gated photon counting spectroscopy of laser ablation plume dynamics during KrF- and ArF-laser PLD of amorphous diamond films  

SciTech Connect

Gated photon counting spectroscopy and species-resolved ICCD photography were used to study the weak plasma luminescence following the propagation of the initial ablation plume in vacuum and during the rebound of the plume with a substrate during pulsed laser deposition of amorphous diamond. These methods techniques were required in order to investigate notable differences between amorphous diamond-like carbon films formed by pulsed laser deposition from ArF (193 nm) and KrF (248 nm) irradiation of pyrolytic graphite in vacuum. Three principal regions of plume emission were found: (1) a bright luminescent ball (v {approximately}3--5 cm/{mu}s) displaying nearly entirely C{sup +} emission which appears to result from laser interaction with the initial ejecta, (2) a spherical ball of emission (v {approximately} 1 cm/{mu}s) displaying neutral carbon atomic emission lines and, at early times, jets of excited C{sub 2}, and (3) a well-defined region of broadband emission (v {approximately} 0.3 cm/{mu}s) near the target surface first containing emission bands from C{sub 2}, then weak, continuum emission thought to result from C{sub 3} and higher clusters and/or blackbody emission from hot clusters or nanoparticles.

Geohegan, D.B. [Oak Ridge National Lab., TN (United States); Puretzky, A.A. [Russian Academy of Sciences, Troitsk (Russian Federation). Inst. of Spectroscopy

1995-12-01

26

Laser ablation based fuel ignition  

DOEpatents

There is provided a method of fuel/oxidizer ignition comprising: (a) application of laser light to a material surface which is absorptive to the laser radiation; (b) heating of the material surface with the laser light to produce a high temperature ablation plume which emanates from the heated surface as an intensely hot cloud of vaporized surface material; and (c) contacting the fuel/oxidizer mixture with the hot ablation cloud at or near the surface of the material in order to heat the fuel to a temperature sufficient to initiate fuel ignition.

Early, James W. (Los Alamos, NM); Lester, Charles S. (San Juan Pueblo, NM)

1998-01-01

27

Laser Ablation of Biological Tissue Using Pulsed CO2 Laser  

Microsoft Academic Search

Laser scalpels are currently used as a form of laser treatment. However, their ablation mechanism has not been clarified because laser excision of biological tissue occurs over a short time scale. Biological tissue ablation generates sound (laser-induced sound). This study seeks to clarify the ablation mechanism. The state of the gelatin ablation was determined using a high-speed video camera and

Yuichi Hashishin; Shu Sano; Takeyoshi Nakayama

2010-01-01

28

UV laser ablation of parylene films from gold substrates  

SciTech Connect

Parylene films, coating gold substrates, were removed by laser ablation using 248 nm light from an excimer laser. Each sample was processed by a different number of pulses in one of three different environments: air at atmospheric pressure, nitrogen at atmospheric pressure, and vacuum. The laser-induced craters were analyzed by optical microscopy and x-ray photoelectron spectroscopy. Multi-pulse ablation thresholds of gold and parylene were estimated.

O. R. Musaev, P. Scott, J. M. Wrobel, and M. B. Kruger

2009-11-19

29

LASER ABLATION-INDUCTIVELY COUPLED PLASMA-ATOMIC EMISSION SPECTROSCOPY STUDY AT THE 222-S LABORATORY USING HOT-CELL GLOVE BOX PROTOTYPE SYSTEM  

SciTech Connect

This report describes the installation, testing, and acceptance of the Waste Treatment and Immobilization Plant (WTP) procured laser ablation-inductively coupled plasma-atomic emission spectroscopy (LA-ICP-AES) system for remotely analyzing high-level waste (HLW) samples in a hot cell environment. The work was completed by the Analytical Process Development (APD) group in accordance with Task Order 2005-003; ATS MP 1027, Management Plan for Waste Treatment Plant Project Work Performed by Analytical Technical Services. The APD group at the 222-S Laboratory demonstrated acceptable turnaround time (TAT) and provide sufficient data to assess sensitivity, accuracy, and precision of the LA-ICP-AES method.

SEIDEL CM; JAIN J; OWENS JW

2009-02-23

30

LASER ABLATION-INDUCTIVELY COUPLED PLASMA-ATOMIC EMISSION SPECTROSCOPY STUDY AT THE 222-S LABORATORY USING HOT-CELL GLOVE BOX PROTOTYPE SYSTEM  

SciTech Connect

This report describes the installation, testing and acceptance of the Waste Treatment and Immobilization Plant procured laser ablation-inductively coupled plasma-atomic emission spectroscopy (LA-ICP-AES) system for remotely analyzing high-level waste samples in a hot cell environment. The 2005-003; ATS MP 1027, Management Plan for Waste Treatment Plant Project Work Performed by Analytical Technical Services. The APD group at the 222-S laboratory demonstrated acceptable turnaround time (TAT) and provide sufficient data to assess sensitivity, accuracy, and precision of the LA-ICP-AES method.

LOCKREM LL; OWENS JW; SEIDEL CM

2009-03-26

31

Wavelength effects in the ultraviolet-laser ablation of polycarbonate and poly(?-methylstyrene) examined by time-of-flight mass spectroscopy  

NASA Astrophysics Data System (ADS)

Slow moving material (velocity ?3×104 cm/s) ejected from polycarbonate and poly(?-methylstyrene) targets by ultraviolet laser photoablation is probed using time-of-flight mass spectroscopy. The product distribution seen from polycarbonate, using resonant-two-photon ionization with 248- or 266-nm light, consists of aromatic species smaller than the monomer. Mass spectra are similar for 355-, 266-, and 193-nm ablation, and the products differ structurally from the starting material; both observations suggest that slow moving species are ejected by a thermal mechanism at all three wavelengths. 248-nm ablation of polycarbonate near the ablation threshold, gives a different product distribution and it is argued that a cooler thermal regime is being sampled or, that photochemical effects are important. The dominant product seen in 266-, 248-, and 193-nm ablation of poly(?-methylstyrene) is the monomer in each case. Subtle differences present in the resulting mass spectra may be due to photochemical effects, but major similarities suggest that slow movers are ejected by a photothermal mechanism.

Hansen, S. G.

1990-08-01

32

Size dependent Cu dielectric function for plasmon spectroscopy: Characterization of colloidal suspension generated by fs laser ablation  

NASA Astrophysics Data System (ADS)

Copper metal nanoparticles (Nps) have received increasing interest during the last years due to their potential applications in several fields of science and technology. Their optical properties depend on the characteristics of the dielectric function of the metal, their size, and the type of environment. The contribution of free and bound electrons on the dielectric function of copper Nps is analyzed as well as their influence on its plasmonic properties. The contribution of free electrons is corrected for particle size under 10 nm, introducing a term inversely proportional to the particle's radius in the damping constant. For bound electron contribution, interband transitions from the d-band to the conduction band are considered. For particles with sizes below 2 nm, the larger spacing between electronic energy levels must be taken into account by making the electronic density of states in the conduction band size-dependent. Considering these specific modifications, optical parameters and band energy values could be determined by fitting the bulk complex dielectric function. The obtained values were coefficient for bound electron contribution Kbulk = 2 × 1024, gap energy Eg = 1.95 eV, Fermi energy EF = 2.15 eV, and bound electrons damping constant ?b = 1.15 × 1014 Hz. Based on the dielectric function determined in this way, experimental extinction spectra of colloid suspensions generated by ultrafast laser ablation of a solid copper target in liquids was fitted using the Drude-interband model and Mie's theory. Depending on the experimental conditions and liquid medium, the particles in the suspension may have nanometric or subnanometric core size and may be capped with a shell of oxide. From the fitting, it was possible to determine the structure and size distribution of spherical bare core and core-shell copper Nps in the nanometer-subnanometer size range. These results were compared with those obtained by standard microscopy techniques such as AFM and HRTEM. There is a very good agreement between the three techniques, showing that optical extinction spectroscopy (OES) is a good complementary technique to standard high resolution electron microscopy and AFM for sizing spherical nanometric-subnanometric Nps. OES has also the advantage of a very good measurement statistics, due to the large number of probed particles across the sample cell. Besides, it avoids coalescence effects since the measurement is made directly on the colloidal suspension.

Santillán, J. M. J.; Videla, F. A.; Fernández van Raap, M. B.; Schinca, D. C.; Scaffardi, L. B.

2012-09-01

33

Laser ablation of silicone composites  

NASA Astrophysics Data System (ADS)

Silicone rubber based composites are widely used to produce outdoor insulators. In adverse weather conditions these can be damaged by surface discharge activity resulting in deterioration of their dielectric properties and an eventual need for replacement. Inclined plane tracking tests are frequently used to determine the relative performance of different material formulations used in their construction. An alternative approach to characterisation is to use an infra-red laser to deposit known amounts of energy at a known rate to the sample's surface allowing comparative ranking of different materials. In this paper several silicone based composites have been ranked using a laser ablation technique and the results were then compared to those obtained from tracking tests on the same materials. The comparison indicates that laser ablation ranks the materials in the same order as the tracking tests and may therefore constitute a quick and cost effective method for the routine characterisation of outdoor insulation components.

Hosier, I. L.; Abd Rahman, M. S.; Vaughan, A. S.; Krivda, A.; Kornmann, X.; Schmidt, L. E.

2011-08-01

34

[Characteristic study of plasma plume produced by nanosecond pulsed laser ablation of silicon using optical emission spectroscopy].  

PubMed

The 355 nm laser pulse from THG (Third Harmonic Generation) of a Qswitched Nd3+ : YAG laser was used to ablate silicon mounted in air. The time-and space-resolved optical emission spectra were measured for different pulse energy in the wavelength range of 380-420 nm, the emission spectra of N+ was found for impact ionization of air near target surface on the early stage of plasma plume expansion. Under the model of local thermodynamic equilibrium, the electronic temperature of plasma was deduced to be in the range of 18 000-40 000 K using the Saha equation by the relative line intensities, and the electron density was deduced to be in the 10(17) cm(-3) scale by FWHM (the full width at half maximum) of Si spectral lines, the temporal and spatial evolution of the electronic temperature and electron density was given, showing that the electronic temperature and electron density exhibited second order exponential decreasing with laser delay time and a Lorentz distribution in space. The reason for the spatial position deviation of the maximum electron density from the maximum spectral intensity was analyzed. The relationship between the plasma plume parameters and laser pulse energy was discussed. PMID:20707170

Gao, Xun; Jin, Ming-Xing; Ding, Da-Jun; Lin, Jing-Quan

2010-06-01

35

Laser Ablation Propulsion A Study  

NASA Astrophysics Data System (ADS)

Laser Ablation Propulsion (LAP) will serve as an alternative propulsion system for development of microthrusters. The principle of LAP is that when a laser (pulsed or continuous wave) with sufficient energy (more than the vaporization threshold energy of material) is incident on material, ablation or vaporization takes place which leads to the generation of plasma. The generated plasma has the property to move away from the material hence pressure is generated which leads to the generation of thrust. Nowadays nano satellites are very common in different space and defence applications. It is important to build micro thruster which are useful for orienting and re-positioning small aircraft (like nano satellites) above the atmosphere. modelling of LAP using MATLAB and Mathematica. Schematic is made for the suitable optical configuration of LAP. Practical experiments with shadowgraphy and self emission techniques and the results obtained are analysed taking poly (vinyl-chloride) (PVC) as propellant to study the

Irfan, Sayed A.; Ugalatad, Akshata C.

36

Experimental investigation of the laser ablation process on wood surfaces  

NASA Astrophysics Data System (ADS)

Processing of wood by conventional mechanical tools like saws or planes leaves behind a layer of squeezed wood only slightly adhering to the solid wood surface. Laser ablation of this layer could improve the durability of coatings and glued joints. For technical applications, thorough knowledge about the laser ablation process is necessary. Results of ablation experiments by excimer lasers, Nd:YAG lasers, and TEA-CO 2 lasers on surfaces of different wood types and cut orientations are shown. The process of ablation was observed by a high-speed camera system and optical spectroscopy. The influence of the experimental parameters are demonstrated by SEM images and measurement of the ablation rate depending on energy density. Thermal effects like melting and also carbonizing of cellulose were found for IR- and also UV-laser wavelengths. Damage of the wood surface after laser ablation was weaker for excimer lasers and CO 2-TEA lasers. This can be explained by the high absorption of wood in the ultraviolet and middle infrared spectral range. As an additional result, this technique provides an easy way for preparing wood surfaces with excellently conserved cellular structure.

Panzner, M.; Wiedemann, G.; Henneberg, K.; Fischer, R.; Wittke, Th.; Dietsch, R.

1998-05-01

37

ablation laser spectrometer  

E-print Network

to detect pyrolysis products from plant materi- als using poplar, a potentially high-impact bioenergy:YAG laser (355 nm). The resulting vapors are entrained in a free jet expansion of helium, then skimmed gasification. Potential Impact This combined platform used for the measurement and analysis of biomass cell

38

Laser Spectroscopy  

NASA Astrophysics Data System (ADS)

Anderson localization of matter-waves in a controlled disorder: a quantum simulator? / A. Aspect ... [et al.] -- Squeezing and entanglement in a Bose-Einstein condensate / C. Gross ... [et al.] -- New physics in dipolar Bose-Einstein condensates / Y. Kawaguchi, H. Saito, and M. Ueda -- Observation of vacuum fluctuations in a spinor Bose-Einstein condensate / C. Klempt ... [et al.] -- Negative-index media for matter waves / F. Perales ... [et al.] -- Entanglement of two individual atoms using the Rydberg blockade / A. Browaeys ... [et al.] -- Array of mesoscopic ensembles on a magnetic atom chip / A. F. Tauschinsky ... [et al.] -- Stability of the proton-to-electron mass ratio tested with molecules using an optical link to primary clock / A. Amy-Klein ... [et al.] -- Metastable helium: lifetime measurements using cold atoms as a test of QED / K. G. H. Baldwin ... [et al.] -- Optical lattice clocks with single occupancy bosons and spin-polarized fermions toward 10[symbol] accuracy / M. Takamoto ... [et al.] -- Frequency measurements of Al[symbol] and Hg[symbol] optical standards / W. M. Itano ... [et al.] -- Switching of light with light using cold atoms inside a hollow optical fiber / M. Bajcsy ... [et al.] -- Room-temperature atomic ensembles for quantum memory and magnetometry / K. Jensen ... [et al.] -- Components for multi-photon non-classical state preparation and measurement / G. Puentes ... [et al.] -- Quantum field state measurement and reconstruction in a cavity by quantum nondemolition photon counting / M. Brune ... [et al.] -- XUV frequency comb spectroscopy / C. Gohle ... [et al.] -- Ultrahigh-repetition-rate pulse train with absolute-phase control produced by an adiabatic raman process / M. Katsuragawa ... [et al.] -- Strongly correlated bosons and fermions in optical lattices / S. Will ... [et al.] -- Bragg spectroscopy of ultracold bose gases in optical lattices / L. Fallani ... [et al.] -- Synthetic quantum many-body systems / C. Guerlin ... [et al.] -- Ultracold Ytterbium atoms in optical lattices / S. Sugawa ... [et al.] -- Ultracold polar molecules in the rovibrational ground state / J. Deiglmayr ... [et al.] -- Polar molecules near quantum degeneracy / J. Ye and D. S. Jin -- Production of a quantum gas of rovibronic ground-state molecules in an optical lattice / J. G. Danzl ... [et al.] -- Recent progress in x-ray nonlinear optics / K. Tamasaku, K. Sawada, and T. Ishikawa -- Gas in scattering media absorption spectroscopy - laser spectroscopy in unconventional environments / S. Svanberg -- Laser spectroscopy on relativistic ion beams / S. Reinhardt ... [et al.] -- Single frequency microcavity lasers and applications / L. Xu ... [et al.].

Katori, H.; Yoneda, H.; Nakagawa, K.; Shimizu, F.

2010-02-01

39

Analysis of geological samples by atomic emission spectroscopy of plasmas induced by laser ablation at low pressures  

NASA Astrophysics Data System (ADS)

Elemental analysis of geologic samples based on atomic emission spectroscopy is currently considered for several future space lander missions to planets, moons and asteroids in solar system. The spectroscopic techniques, called laser-induced plasma (breakdown) spectroscopy (LIBS), provides quantitatively the microscopic in-situ abundances of all major and many trace elements of surfaces of solar system bodies. Excitation and evolution of the plasmas induced by lasers depend on the properties of the investigated material and on environmental conditions. This study focuses on the feasibility of spectroscopy of plasmas induced by low-energy laser (below 1 mJ per pulse) for the exploration of solar system bodies with thin atmospheres (pressures below 1 mPa). At such low pressures the excited plasmas have small plumes and expand very rapidly, which limits both the LIBS signal intensity and the available acquisition time. This, in turn, requires usually relatively powerful laser sources to create a detectable LIBS plasma. The low pressure conditions are simulated in a dedicated chamber at the DLR-Berlin Institute of Planetary Research, that can hold the Martian-like atmosphere or high vacuum conditions. Two infrared Q-switched lasers are used for comparative investigation of atomic emission spectra: Firstly, a Nd:YAG laser (Inlite, Continuum) operating at 1064 nm and at 10 Hz, pulse energy up to 230 mJ at 8-10 ns pulse duration and, secondly, developed for future planetary missions Nd:YLF laser (NeoLASE) operating at 1053 nm and at 10-50 Hz, pulse energy up to 3 mJ at 3-5 ns pulse duration. The emitted light of the laser-induced plasma is analysed by an echelle spectrometer (LTB Aryelle Butterfly) covering the wavelength range of 280-900 nm with a spectral resolution of around 104. Identification of atomic transitions is performed using the LTB built-in spectrometer software by comparison with the NIST spectral database. Several basaltic rock and sediment standards were crushed to powder and pressed into pellets. Reduction of both pressure and laser excitation energy results in a significant decrease of the signal-to-noise ratio for most atomic lines (an exception are the widely broadened lines of H). However, the detection of atomic emission lines of elements with relative abundances above 10-3 (0.1 wt%) - Al, Ca, Cr, H, K, Mg, Mn, Na, Ni, O, Si, Ti, - is possible down to a laser excitation energy of 0.9 mJ (laser irradiance on the sample surface 46 MW/mm2). Additionally, the detection of carbon and sulphur, having strong atomic transitions in ultraviolet range, can be expected by extension of the spectral range of the LIBS spectrometer to 190 nm. Atomic doublet and triplet transitions, broadened by atomic collisions at ambient pressures (100 kPa), become spectrally resolved and are identified below 1 mPa. This demonstrates the feasibility of miniaturized laser-induced breakdown spectrometry for space missions to solar bodies with absent or thin atmospheres.

Pavlov, S.; Schröder, S.; Jessberger, E.; Hübers, H.

2011-12-01

40

Observation of femtosecond-laser-induced ablation plumes of aluminum using space- and time-resolved soft x-ray absorption spectroscopy  

SciTech Connect

The dynamics of the laser ablation plume expansion of aluminum was investigated by using space- and time-resolved soft x-ray absorption spectroscopy. Blueshifts of the Al L-shell photoabsorption edge indicating the state of aluminum were observed in the plumes, which were generated by irradiating an aluminum target with 120 fs near-infrared pulses at an intensity of 10{sup 14} W/cm{sup 2}. The spatiotemporal evolution of the plumes exhibited a multilayer structure consisting of vaporized aluminum and condensed aluminum particles, following the expansion of plasma, with expansion velocities of 10{sup 4} m/s for the atomic state and 10{sup 3} m/s for the condensed state.

Okano, Yasuaki; Oguri, Katsuya; Nishikawa, Tadashi; Nakano, Hidetoshi [NTT Basic Research Laboratories, Nippon Telegraph and Telephone Corporation, 3-1 Morinosato Wakamiya, Atsugi, Kanagawa 243-0198 (Japan)

2006-11-27

41

Characterization of the laser ablation plasma used for the deposition of amorphous carbon  

Microsoft Academic Search

The plasma produced by laser ablation of a graphite target was studied by means of optical emission spectroscopy and a Langmuir planar probe. Laser ablation was performed using a Nd:YAG laser with emission at the fundamental line with pulse length of 28ns. In this work, we report the behavior of the mean kinetic energy of plasma ions and the plasma

Enrique Camps; L. Escobar-Alarcón; V. H. Castrejón-Sánchez; M. A. Camacho-López; Stephen Muhl

2007-01-01

42

Fractal Character of Titania Nanoparticles Formed by Laser Ablation  

SciTech Connect

Titania nanoparticles were fabricated by laser ablation of polycrystalline rutile in water at room temperature. The resulting nanoparticles were analyzed with x-ray diffraction, Raman spectroscopy, and transmission electron microscopy. The electron micrograph image of deposited nanoparticles demonstrates fractal properties.

Musaev, O.; Midgley, A; Wrobel, J; Yan, J; Kruger, M

2009-01-01

43

Characterization of toners and inkjets by laser ablation spectrochemical methods and Scanning Electron Microscopy-Energy Dispersive X-ray Spectroscopy  

NASA Astrophysics Data System (ADS)

Detection and sourcing of counterfeit currency, examination of counterfeit security documents and determination of authenticity of medical records are examples of common forensic document investigations. In these cases, the physical and chemical composition of the ink entries can provide important information for the assessment of the authenticity of the document or for making inferences about common source. Previous results reported by our group have demonstrated that elemental analysis, using either Laser Ablation-Inductively Coupled Plasma-Mass Spectrometry (LA-ICP-MS) or Laser Ablation Induced Breakdown Spectroscopy (LIBS), provides an effective, practical and robust technique for the discrimination of document substrates and writing inks with minimal damage to the document. In this study, laser-based methods and Scanning Electron Microscopy-Energy Dispersive X-Ray Spectroscopy (SEM-EDS) methods were developed, optimized and validated for the forensic analysis of more complex inks such as toners and inkjets, to determine if their elemental composition can differentiate documents printed from different sources and to associate documents that originated from the same printing source. Comparison of the performance of each of these methods is presented, including the analytical figures of merit, discrimination capability and error rates. Different calibration strategies resulting in semi-quantitative and qualitative analysis, comparison methods (match criteria) and data analysis and interpretation tools were also developed. A total of 27 black laser toners originating from different manufacturing sources and/or batches were examined to evaluate the discrimination capability of each method. The results suggest that SEM-EDS offers relatively poor discrimination capability for this set (~ 70.7% discrimination of all the possible comparison pairs or a 29.3% type II error rate). Nonetheless, SEM-EDS can still be used as a complementary method of analysis since it has the advantage of being non-destructive to the sample in addition to providing imaging capabilities to further characterize toner samples by their particle morphology. Laser sampling methods resulted in an improvement of the discrimination between different sources with LIBS producing 89% discrimination and LA-ICP-MS resulting in 100% discrimination. In addition, a set of 21 black inkjet samples was examined by each method. The results show that SEM-EDS is not appropriate for inkjet examinations since their elemental composition is typically below the detection capabilities with only sulfur detected in this set, providing only 47.4% discrimination between possible comparison pairs. Laser sampling methods were shown to provide discrimination greater than 94% for this same inkjet set with false exclusion and false inclusion rates lower than 4.1% and 5.7%, for LA-ICP-MS and LIBS respectively. Overall these results confirmed the utility of the examination of printed documents by laser-based micro-spectrochemical methods. SEM-EDS analysis of toners produced a limited utility for discrimination within sources but was not an effective tool for inkjet ink discrimination. Both LA-ICP-MS and LIBS can be used in forensic laboratories to chemically characterize inks on documents and to complement the information obtained by conventional methods and enhance their evidential value.

Trejos, Tatiana; Corzo, Ruthmara; Subedi, Kiran; Almirall, José

2014-02-01

44

Laser ablation in analytical chemistry - A review  

SciTech Connect

Laser ablation is becoming a dominant technology for direct solid sampling in analytical chemistry. Laser ablation refers to the process in which an intense burst of energy delivered by a short laser pulse is used to sample (remove a portion of) a material. The advantages of laser ablation chemical analysis include direct characterization of solids, no chemical procedures for dissolution, reduced risk of contamination or sample loss, analysis of very small samples not separable for solution analysis, and determination of spatial distributions of elemental composition. This review describes recent research to understand and utilize laser ablation for direct solid sampling, with emphasis on sample introduction to an inductively coupled plasma (ICP). Current research related to contemporary experimental systems, calibration and optimization, and fractionation is discussed, with a summary of applications in several areas.

Russo, Richard E.; Mao, Xianglei; Liu, Haichen; Gonzalez, Jhanis; Mao, Samuel S.

2001-10-10

45

Dynamics of laser driven, ablatively accelerated targets  

Microsoft Academic Search

The characteristics of ablation plasma from planar targets, driven by long Nd:glass laser pulses (4 nsec, - 10 to the 14th power w\\/sq cm), and the velocity of the ablatively accelerated targets are experimentally studied. Ablation plasma diagnostics include arrays of time-of-flight ion collectors, plasma calorimeters, and ballistic pendula which directly measure the plasma velocity, energy, and momentum. The ballistic

J. Grun

1981-01-01

46

Fundamental Characteristics of a Laser Ablation Microthruster  

Microsoft Academic Search

The fundamental characteristics of a laser ablation microthruster were investigated for a 10 kg-class microspacecraft. A single-shot impulse measurement was performed using a thrust stand on which a prototype thruster was installed and the associate ablated mass was estimated from the pressure increase in the space chamber. The best performance of several polymer materials was obtained using polyvinylchloride as the

Hiroyuki Koizumi; Takayoshi Inoue; Kimiya Komurasaki; Yoshihiro Arakawa

2007-01-01

47

Femtosecond laser ablation of the stapes  

NASA Astrophysics Data System (ADS)

A femtosecond laser, normally used for LASIK eye surgery, is used to perforate cadaveric human stapes. The thermal side effects of bone ablation are measured with a thermocouple in an inner ear model and are found to be within acceptable limits for inner ear surgery. Stress and acoustic events, recorded with piezoelectric film and a microphone, respectively, are found to be negligible. Optical microscopy, scanning electron microscopy, and optical coherence tomography are used to confirm the precision of the ablation craters and lack of damage to the surrounding tissue. Ablation is compared to that from an Er:YAG laser, the current laser of choice for stapedotomy, and is found to be superior. Ultra-short-pulsed lasers offer a precise and efficient ablation of the stapes, with minimal thermal and negligible mechanical and acoustic damage. They are, therefore, ideal for stapedotomy operations.

McCaughey, Ryan G.; Sun, Hui; Rothholtz, Vanessa S.; Juhasz, Tibor; Wong, Brian J. F.

2009-03-01

48

Femtosecond Laser Ablation: Fundamentals and Applications  

E-print Network

, laser plasma interactions, and plume hydrodynam- ics. Analytical figures of merit will be discussed. The physics involved in laser-plasma generation and subsequent evolution is very complex and contains manyChapter 6 Femtosecond Laser Ablation: Fundamentals and Applications Sivanandan S. Harilal, Justin R

Harilal, S. S.

49

Laser Ablation of Alumina in Water  

SciTech Connect

Bulk {alpha}-alumina immersed in distilled water was ablated by pulsed UV laser radiation. The resulting colloidal solution contained micron and submicron size particles. X-ray diffraction and Raman spectra of the ablated and original material are similar. Hence, most of the ablated material is {alpha}-alumina. From transmission electron microscope images, most of the submicron and all of the micron-sized particles have sharp edges and do not have spherical shapes, indicating that the dominant ablation mechanism is due to crack propagation. Some spherical particles of diameter less than 100 nm are observed, indicating that they were formed from the liquid state.

Musaev, O.; Midgley, A; Wrobel, J; Kruger, M

2010-01-01

50

Analytical procedure for characterization of medieval wall-paintings by X-ray fluorescence spectrometry, laser ablation inductively coupled plasma mass spectrometry and Raman spectroscopy  

NASA Astrophysics Data System (ADS)

Analytical procedure for the comprehensive chemical characterization of samples from medieval Nubian wall-paintings by means of portable X-ray fluorescence (pXRF), laser ablation inductively coupled plasma mass spectrometry (LA-ICPMS) and Raman spectroscopy (RS) was proposed in this work. The procedure was used for elemental and molecular investigations of samples from archeological excavations in Nubia (modern southern Egypt and northern Sudan). Numerous remains of churches with painted decorations dated back to the 7th-14th century were excavated in the region of medieval kingdoms of Nubia but many aspects of this art and its technology are still unknown. Samples from the selected archeological sites (Faras, Old Dongola and Banganarti) were analyzed in the form of transfers (n = 26), small fragments collected during the excavations (n = 35) and cross sections (n = 15). XRF was used to collect data about elemental composition, LA-ICPMS allowed mapping of selected elements, while RS was used to get the molecular information about the samples. The preliminary results indicated the usefulness of the proposed analytical procedure for distinguishing the substances, from both the surface and sub-surface domains of the wall-paintings. The possibility to identify raw materials from the wall-paintings will be used in the further systematic, archeometric studies devoted to the detailed comparison of various historic Nubian centers.

Syta, Olga; Rozum, Karol; Choi?ska, Marta; Zieli?ska, Dobrochna; ?ukowska, Gra?yna Zofia; Kijowska, Agnieszka; Wagner, Barbara

2014-11-01

51

Dynamics of mid-infrared femtosecond laser resonant ablation  

NASA Astrophysics Data System (ADS)

Resonant ablation is beneficial to avoiding uncontrollable subsurface damages in the laser ablation of polymers. In this paper the dynamics of mid-infrared laser resonant ablation of polylactic acid and toluene was calculated by using fluid dynamic equations. The merits and drawbacks of mid-infrared femtosecond laser resonant ablation of high molecular weight polymers have been discussed.

Pang, Dongqing; Li, Yunxuan; Wang, Qingyue

2014-06-01

52

Novel Laser Ablation Technology for Surface Decontamination  

SciTech Connect

Laser ablation for surface cleaning has been pursued for the removal of paint on airplanes. It has also been pursued for the cleaning of semiconductor surfaces. However, all these approaches have been pursued by laser ablation in air. For highly contaminated surface, laser ablation in air can easily cause secondary contamination. Thus it is not suitable to apply to achieve surface decontamination for DOE facilities since many of these facilities have radioactive contaminants on the surface. Any secondary contamination will be a grave concern. The objective of this project is to develop a novel technology for laser ablation in liquid for surface decontamination. It aims to achieve more efficient surface decontamination without secondary contamination and to evaluate the economic feasibility for large scale surface decontamination with laser ablation in liquid. When laser ablation is pursued in the solution, all the desorbed contaminants will be confined in liquid. The contaminants can be precipitated and subsequently contained in a small volume for disposal. It can reduce the risk of the decontamination workers. It can also reduce the volume of contaminants dramatically.

Cheng, Chung H.

2004-06-01

53

Laser Ablation of Biological Tissue Using Pulsed CO2 Laser  

NASA Astrophysics Data System (ADS)

Laser scalpels are currently used as a form of laser treatment. However, their ablation mechanism has not been clarified because laser excision of biological tissue occurs over a short time scale. Biological tissue ablation generates sound (laser-induced sound). This study seeks to clarify the ablation mechanism. The state of the gelatin ablation was determined using a high-speed video camera and the power reduction of a He-Ne laser beam. The aim of this study was to clarify the laser ablation mechanism by observing laser excision using the high-speed video camera and monitoring the power reduction of the He-Ne laser beam. We simulated laser excision of a biological tissue by irradiating gelatin (10 wt%) with radiation from a pulsed CO2 laser (wavelength: 10.6 ?m; pulse width: 80 ns). In addition, a microphone was used to measure the laser-induced sound. The first pulse caused ablation particles to be emitted in all directions; these particles were subsequently damped so that they formed a mushroom cloud. Furthermore, water was initially evaporated by laser irradiation and then tissue was ejected.

Hashishin, Yuichi; Sano, Shu; Nakayama, Takeyoshi

2010-10-01

54

Basic ablation phenomena during laser thrombolysis  

NASA Astrophysics Data System (ADS)

This paper presents studies of microsecond ablation phenomena that take place during laser thrombolysis. The main goals were to optimize laser parameters for efficient ablation, and to investigate the ablation mechanism. Gelatin containing an absorbing dye was used as the clot model. A parametric study was performed to identify the optimal wavelength, spot size, pulse energies, and repetition rate for maximum material removal. The minimum radiant exposures to achieve ablation at any wavelength were measured. The results suggest that most visible wavelengths were equally efficient at removing material at radiant exposures above threshold. Ablation was initiated at surface temperatures just above 100 degrees Celsius. A vapor bubble was formed during ablation. Less than 5% of the total pulse energy is coupled into the bubble energy. A large part of the delivered energy is unaccounted for and is likely released partly as acoustic transients from the vapor expansion and partly wasted as heat. The current laser and delivery systems may not be able to completely remove large clot burden that is sometimes encountered in heart attacks. However, laser thrombolysis may emerge as a favored treatment for strokes where the occlusion is generally smaller and rapid recanalization is of paramount importance. A final hypothesis is that laser thrombolysis should be done at radiant exposures close to threshold to minimize any damaging effects of the bubble dynamics on the vessel wall.

Sathyam, Ujwal S.; Shearin, Alan; Prahl, Scott A.

1997-05-01

55

Computer Simulations of Laser Ablation of Molecular Substrates Leonid V. Zhigilei* and Elodie Leveugle  

E-print Network

of laser plasma thrusters for micro- satellites.10 Further optimization of experimental parameters picture of the ablation process. Time-resolved spectroscopy and imaging methods have been also employed

56

Improved laser ablation model for asteroid deflection  

NASA Astrophysics Data System (ADS)

This paper presents an improved laser ablation model and compares the performance - momentum coupling and deflection system mass - of laser ablation against contactless deflection methods based on ion-propulsion. The deflection of an asteroid through laser ablation is achieved by illuminating the surface of the asteroid with high intensity laser light. The absorbed energy induces the sublimation of the surface material and the generation of a plume of gas and ejecta. Similar to a rocket engine, the flow of expelled material produces a continuous and controllable thrust that could be used to modify the trajectory and tumbling motion of the asteroid. Recent results gained from a series of laser ablation experiments were used to improve the sublimation and deflection models. In each experiment a terrestrial olivine sample was ablated, under vacuum, with a 90 W continuous wave laser. The paper presents a model that better fits the outcomes of the experimental campaign, in particular in terms of mass flow rate and spot temperature.

Vasile, Massimiliano; Gibbings, Alison; Watson, Ian; Hopkins, John-Mark

2014-10-01

57

Optical modeling of laser ablated microstructures  

NASA Astrophysics Data System (ADS)

From only an a priori knowledge of the optical parameters of a laser beam, the delivery system together with a substrate's material properties, a ray-tracing model capable of predicting the 3-D topology of micro/nanostructures machined by pulsed laser ablation has been developed. The model includes secondary illumination effects produced by the microstructure created by successive pulses (wall reflections, refraction, wave guiding, shadowing, etc.) as well as the complete optical properties of the beam delivery system. We have used material ablation by pulsed excimer lasers and associated beam delivery systems to demonstrate some of the capabilities of the model. Good agreement is obtained between computations and experimental results in terms of the predicted ablation depth per pulse and the wall taper angle of channels and holes. The model can predict ablated profiles of holes and indicate the most efficient drilling strategy in terms of material removal rates. The model also shows diffraction effects are not required to explain the tapering vertical walls observed when ablating microstructures. Finally, the model has been used to demonstrate aberrations in an optical imaging system limiting the creation of submicron features in an ablated microstructure. Provided photons are absorbed linearly in a substrate according to Beer's law with negligible thermal diffusion effects, the model is equally applicable to using other types of pulsed laser sources and systems with imaged or focused beams.

Gower, M. C.; Davies, E.; Holmes, A. S.

2012-11-01

58

XeCl laser ablation of polyetheretherketone  

NASA Astrophysics Data System (ADS)

Ablation of polyetheretherketone (PEEK), a high temperature thermoplastic, by XeCl laser radiation occurs at fluences in excess of 0.07±0.01 J cm-2. The volatile products of ablation are CO and C2H2 with smaller quantities of CH4, C4H2, C6H6 and other C3 and C4 hydrocarbons. At fluences close to the threshold ablation produces involatile material of relatively high molecular weight but at high fluences extensive disruption of the PEEK structure occurs with conversion of all of the oxygen in the polymer to carbon monoxide.

Dyer, P. E.; Oldershaw, G. A.; Schudel, D.

1990-11-01

59

The rotational spectrum of CuCCH(X~ 1?+): A Fourier transform microwave discharge assisted laser ablation spectroscopy and millimeter/submillimeter study  

NASA Astrophysics Data System (ADS)

The pure rotational spectrum of CuCCH in its ground electronic state (X~ 1?+) has been measured in the frequency range of 7-305 GHz using Fourier transform microwave (FTMW) and direct absorption millimeter/submillimeter methods. This work is the first spectroscopic study of CuCCH, a model system for copper acetylides. The molecule was synthesized using a new technique, discharge assisted laser ablation spectroscopy (DALAS). Four to five rotational transitions were measured for this species in six isotopologues (63CuCCH, 65CuCCH, 63Cu13CCH, 63CuC13CH, 63Cu13C13CH, and 63CuCCD); hyperfine interactions arising from the copper nucleus were resolved, as well as smaller splittings in CuCCD due to deuterium quadrupole coupling. Five rotational transitions were also recorded in the millimeter region for 63CuCCH and 65CuCCH, using a Broida oven source. The combined FTMW and millimeter spectra were analyzed with an effective Hamiltonian, and rotational, electric quadrupole (Cu and D) and copper nuclear spin-rotation constants were determined. From the rotational constants, an rm(2) structure for CuCCH was established, with rCu-C=1.8177(6) A?, rC-C=1.2174(6) A?, and rC-H=1.046(2) A?. The geometry suggests that CuCCH is primarily a covalent species with the copper atom singly bonded to the CtrpbndC-H moiety. The copper quadrupole constant indicates that the bonding orbital of this atom may be sp hybridized. The DALAS technique promises to be fruitful in the study of other small, metal-containing molecules of chemical interest.

Sun, M.; Halfen, D. T.; Min, J.; Harris, B.; Clouthier, D. J.; Ziurys, L. M.

2010-11-01

60

[The deposition of elements in the process of laser ablation of silicon].  

PubMed

Laser processing in the semiconductor industry (especially silicon material) has broad application prospects. The interaction between the laser and silicon is complex, and the present paper mainly studied the silicon morphology in UV laser ablation and the influence law of ambient gas. Studies have shown that the laser plasma ionization effect of silicon in the UV laser ablation has a decisive impact: the removal of the material becomes possible because of generating gasification and ionization, laser plasma shock wave can make phase transition material discharge effectively, and laser plasma spectroscopy ionization effect can make the oxygen elements in the air ionize and deposit effectively. PMID:23697147

Wang, Shao-Peng; Feng, Guo-Ying; Duan, Tao; Han, Jing-Hua

2013-02-01

61

Quantifying the quality of femtosecond laser ablation of graphene  

NASA Astrophysics Data System (ADS)

The influence of beam intensity on laser ablation quality and ablation size is experimentally studied on graphene-coated silicon/silicon dioxide substrates. With an amplified femtosecond-pulsed laser system, by systematically decreasing the average power, periodic stripes with decreasing widths are ablated. Histogram analyses of the untouched and ablated regions of scanning electron microscope images of the fabricated structures make it possible to quantify the ablation quality. These analyses reveal that submicron ablation can be achieved while maintaining 75 % ablation accuracy by adjusting the beam intensity around the ablation threshold.

Sahin, Ramazan; Akturk, Selcuk; Simsek, Ergun

2014-08-01

62

Deposition of fibrous nanostructure by ultrafast laser ablation  

NASA Astrophysics Data System (ADS)

This research work demonstrated that laser-induced reverse transfer (LIRT) can be used for controllable site-specific deposition of fibrous nanostructure. The LIRT method makes it possible to generate and deposit the fibrous nanostructure of a wide variety of materials on a transparent acceptor in a single-step process at an ambient condition. The deposition of fibrous nanostructures was conducted using ultrafast laser ablation of silicon and aluminum targets placed behind a glass acceptor. Femtosecond laser pulses pass through the transparent acceptor and hit the bulk donor. Consequently a mass quantity of nanoparticles ablates from the donor and then aggregates and forms a porous fibrous nanostructure on the transparent acceptor. Our experiments demonstrated that the gap between the target and the glass acceptor was critical in the formation and accumulation of nanofibers and it determines the density of the formed nanostructure. The formation mechanism of the nanostructures can be explained by the well-established theory of vapor condensation within the plume induced by ultrafast laser ablation. Experimental results also show that the length of the nanostructure can be controlled by the gap between the target and glass acceptor. Lastly, energy-dispersive x-ray spectroscopy (EDS) analysis shows the oxygen concentration in the nanofibrous structure which is associated with oxidation of ablated material at ambient atmosphere.

Tavangar, Amirhossein; Tan, Bo; Venkatakrishnan, K.

2010-05-01

63

Generation of Core/shell Nanoparticles with Laser Ablation  

E-print Network

Two types of core/shell nanoparticles (CS-NPs) generation based on laser ablation are developed in this study, namely, double pulse laser ablation and laser ablation in colloidal solutions. In addition to the study of the generation mechanism of CS...

Jo, Young Kyong

2012-10-19

64

Ultrashort Pulse Laser Ablation for Depth Profiling of Bacterial Biofilms  

PubMed Central

Sample ablation by pulsed lasers is one option for removing material from a sample surface for in situ depth profiling during imaging mass spectrometry, but ablation is often limited by laser-induced damage of the remaining material. A preliminary evaluation was performed of sub-100 fs, 800 nm pulsed laser ablation for depth profiling of bacterial biofilms grown on glass by the drip flow method. Electron and optical microscopy were combined with laser desorption vacuum ultraviolet postionization mass spectrometry to analyze biofilms before and after ablation. Ultrashort laser pulses can ablate 10 – 100 µm thick sections of bacterial biofilms, leaving behind a layer of lysed cells. However, mass spectra from intact and ablated biofilms doped with antibiotic are almost identical, indicating little chemical degradation by ablation. These results are consistent with prior observations from laser surgery and support the use of ultrashort pulse laser ablation for minimally disruptive depth profiling of bacterial biofilms and intact biological samples. PMID:21031139

Milasinovic, Slobodan; Liu, Yaoming; Gasper, Gerald L.; Zhao, Youbo; Johnston, Joanna L.; Gordon, Robert J.; Hanley, Luke

2010-01-01

65

Laser Ablation for Small Hepatocellular Carcinoma  

PubMed Central

Hepatocellular carcinoma (HCC) is one of the most common malignancies worldwide and is increasingly detected at small size (<5?cm) owing to surveillance programmes in high-risk patients. For these cases, curative therapies such as resection, liver transplantation, or percutaneous ablation have been proposed. When surgical options are precluded, image-guided tumor ablation is recommended as the most appropriate therapeutic choice in terms of tumor local control, safety, and improvement in survival. Laser ablation (LA) represents one of currently available loco-ablative techniques: light is delivered via flexible quartz fibers of diameter from 300 to 600??m inserted into tumor lesion through either fine needles (21g Chiba needles) or large-bore catheters. The thermal destruction of tissue is achieved through conversion of absorbed light (usually infrared) into heat. A range of different imaging modalities have been used to guide percutaneous laser ablation, but ultrasound and magnetic resonance imaging are most widely employed, according to local experience and resource availability. Available clinical data suggest that LA is highly effective in terms of tumoricidal capability with an excellent safety profile; the best results in terms of long-term survival are obtained in early HCC so that LA can be proposed not only in unresectable cases but, not differently from radiofrequency ablation, also as the first-line treatment. PMID:22191028

Pacella, Claudio Maurizio; Francica, Giampiero; Di Costanzo, Giovanni Giuseppe

2011-01-01

66

Plume dynamics and shielding by the ablation plume during Er:YAG laser ablation  

Microsoft Academic Search

Free-running Er:YAG lasers are used for precise tissue abla- tion in various clinical applications. The ablated material is ejected into the direction perpendicular to the tissue surface. We investigated the influence of shielding by the ablation plume on the energy depo- sition into an irradiated sample because it influences the ablation dy- namics and the amount of material ablated. The

Kester Nahen; Alfred Vogel

2002-01-01

67

Optical analysis of the ablation processes in pulsed laser deposition  

E-print Network

in the laser-target and laser-plasma interactions. As laser light strikes the target, it is absorbed via material that is ablated from a target by interaction with a high fluence, pulsed laser. One disadvantage is ablated from a target by interaction with a high fluence, pulsed laser beam and deposited onto a substrate

Reilly, Anne

68

What can We Learn about Atmospheric Meteor Ablation and Light Production from Laser Ablation?  

Microsoft Academic Search

Laboratory based laser ablation techniques can be used to study the size of the luminous region, predict spectral features, estimate the luminous efficiency factor, and assess the role of chemically differentiated thermal ablation. A pulsed Nd:YAG laser was used to ablate regions from ordinary and carbonaceous chondrite meteorites. CCD cameras and a digital spectroscope were used to measure the size

R. L. Hawkes; E. P. Milley; J. M. Ehrman; R. M. Woods; J. D. Hoyland; C. L. Pettipas; D. W. Tokaryk

2008-01-01

69

Analysis of metallic fuels by laser ablation  

Microsoft Academic Search

A hot cell-based solid sampling system has been developed for application to the analyses of irradiated materials such as metallic reactor fuel from a nuclear reactor, and radioactive waste forms. This system employs one of two sampling techniques, glow discharge or laser ablation, for introduction of material into one of two instruments for analysis, either a time of flight mass

Stephen G. Johnson; Phillip S. Goodall; Sandra M. Kimbrell; Elon L. Wood

1995-01-01

70

Time-resolved diagnostics of excimer laser-generated ablation plasmas used for pulsed laser deposition  

SciTech Connect

Characteristics of laser plasmas used for pulsed laser deposition (PLD) of thin films are examined with four in situ diagnostic techniques: Optical emission spectroscopy, optical absorption spectroscopy, ion probe studies, and gated ICCD (intensified charge-coupled-device array) fast photography. These four techniques are complementary and permit simultaneous views of the transport of ions, excited states, ground state neutrals and ions, and hot particulates following KrF laser ablation of YBCO, BN, graphite and Si in vacuum and background gases. The implementation and advantages of the four techniques are first described in order to introduce the key features of laser plasmas for pulsed laser deposition. Aspects of the interaction of the ablation plume with background gases (i.e., thermalization, attenuation, shock formation) and the collision of the plasma plume with the substrate heater are then summarized. The techniques of fast ICCD photography and gated photon counting are then applied to investigate the temperature, velocity, and spatial distribution of hot particles generated during KrF ablation of YBCO, BN, Si and graphite. Finally, key features of fast imaging of the laser ablation of graphite into high pressure rare gases are presented in order to elucidate internal reflected shocks within the plume, redeposition of material on a surface, and formation of hot nanoparticles within the plume.

Geohegan, D.B.

1994-09-01

71

Laser ablation mechanism of transparent dielectrics with picosecond laser pulses  

NASA Astrophysics Data System (ADS)

Thin glass sheets (thickness <1 mm) have a great potential in OLED and LCD displays. While the conventional manufacturing methods, such as mechanical scribing and breaking, result in poor edge strength, ultra-short-pulsed laser processing could be a promising solution, offering high-quality cutting edges. However laser precision glass cutting suffers from unwanted material modification and even severe damage (e.g. cracks and chipping). Therefore it is essential to have a deep understanding of the ultra-short-pulsed laser ablation mechanism of transparent dielectrics in order to remedy those drawbacks. In this work, the ablation mechanism of transparent dielectrics irradiated by picosecond laser pulses has been studied. Ultrafast dynamics of free-electrons is analyzed using a rate equation for free-electron density including multi-photon ionization, avalanche ionization and loss terms. Two maps of free-electron density in parameter space are given to discuss the dependence of ablation threshold intensity/fluence on pulse duration. The laser ablation model describing laser beam propagation and energy deposition in transparent dielectrics is presented. Based on our model, simulations and experiments have been performed to study the ablation dynamics. Both simulation and experimental results show good agreement, offering great potential for optimization of laser processing in transparent dielectrics. The effects of recombination coefficient and electron-collision time on our model are investigated.

Sun, Mingying; Eppelt, Urs; Russ, Simone; Hartmann, Claudia; Siebert, Christof; Zhu, Jianqiang; Schulz, Wolfgang

2012-11-01

72

117Sn and 119Sn hyperfine structure in the rotational spectrum of tin monosulfide recorded using laser ablation-source equipped, chirped-pulse Fourier transform microwave spectroscopy  

NASA Astrophysics Data System (ADS)

Tin metal has been ablated with pulsed radiation from a Nd:YAG laser ( ?=1064 nm). Carbonyl sulfide, diluted in high pressure argon, has been pulsed into the resultant Sn plasma. One of the results of this experiment has been the production of SnS. These events have allowed a rotational spectrum of tin monosulfide to be studied using a chirped-pulse Fourier transform microwave spectrometer. The resolution of the spectrum obtained was sufficient to observe hyperfine structure from the 117Sn and 119Sn-containing SnS molecules. Tin nuclear spin-rotation hyperfine constants are reported for the first time.

Grubbs, G. S.; Cooke, S. A.

2010-02-01

73

Picosecond laser ablation of porcine sclera  

NASA Astrophysics Data System (ADS)

Lasers have been shown to be successful in certain medical procedures and they have been identified as potentially making a major contribution to the development of minimally invasive procedures. However, the uptake is not as widespread and there is scope for many other applications where laser devices may offer a significant advantage in comparison to the traditional surgical tools. The purpose of this research is to assess the potential of using a picosecond laser for minimally invasive laser sclerostomy. Experiments were carried out on porcine scleral samples due to the comparable properties to human tissue. Samples were prepared with a 5mm diameter trephine and were stored in lactated Ringer's solution. After laser machining, the samples were fixed in 3% glutaraldehyde, then dried and investigated under SEM. The laser used in the experiments is an industrial picosecond TRUMPF TruMicro laser operating at a wavelength of 1030nm, pulse length of 6ps, repetition rate of 1 kHz and a focused spot diameter of 30?m. The laser beam was scanned across the samples with the use of a galvanometer scan head and various ablation patterns were investigated. Processing parameters (pulse energy, spot and line separation) which allow for the most efficient laser ablation of scleral tissue without introducing any collateral damage were investigated. The potential to create various shapes, such as linear incisions, square cavities and circular cavities was demonstrated.

Góra, Wojciech S.; Harvey, Eleanor M.; Dhillon, Baljean; Parson, Simon H.; Maier, Robert R. J.; Hand, Duncan P.; Shephard, Jonathan D.

2013-03-01

74

A Review of Laser Ablation Propulsion  

NASA Astrophysics Data System (ADS)

Laser Ablation Propulsion is a broad field with a wide range of applications. We review the 30-year history of laser ablation propulsion from the transition from earlier pure photon propulsion concepts of Oberth and Sänger through Kantrowitz's original laser ablation propulsion idea to the development of air-breathing ``Lightcraft'' and advanced spacecraft propulsion engines. The polymers POM and GAP have played an important rôle in experiments and liquid ablation fuels show great promise. Some applications use a laser system which is distant from the propelled object, for example, on another spacecraft, the Earth or a planet. Others use a laser that is part of the spacecraft propulsion system on the spacecraft. Propulsion is produced when an intense laser beam strikes a condensed matter surface and produces a vapor or plasma jet. The advantages of this idea are that exhaust velocity of the propulsion engine covers a broader range than is available from chemistry, that it can be varied to meet the instantaneous demands of the particular mission, and that practical realizations give lower mass and greater simplicity for a payload delivery system. We review the underlying theory, buttressed by extensive experimental data. The primary problem in laser space propulsion theory has been the absence of a way to predict thrust and specific impulse over the transition from the vapor to the plasma regimes. We briefly discuss a method for combining two new vapor regime treatments with plasma regime theory, giving a smooth transition from one regime to the other. We conclude with a section on future directions.

Phipps, Claude; Bohn, Willy; Lippert, Thomas; Sasoh, Akihiro; Schall, Wolfgang; Sinko, John

2010-10-01

75

Simulation of femtosecond laser ablation of silicon  

NASA Astrophysics Data System (ADS)

Femtosecond laser ablation is an important process in micromachining and nanomachining of microelectronic, optoelectronic, biophotonic and MEMS components. The process of laser ablation of silicon is being studied on an atomic level using molecular dynamics simulations. We investigate ablation thresholds for Gaussian laser pulses of 800 nm wavelength, in the range of a few hundred femtoseconds in duration. Absorption is modelled via linear and 2-photon absorption processes into a hot electron bath which then transfers energy into the crystal lattice. The simulation box is a narrow column approximately 5.4 nm x 5.4 nm x 81 nm with periodic boundaries in the x and y transverse directions and a 1-D heat flow model at the bottom coupled to a heat bath to simulate an infinite bulk medium corresponding to the solid bulk material. A modified Stillinger-Weber potential is used to model the silicon atoms. The calculated thresholds are compared to various reported experimental values for the ablation threshold of silicon. We provide an overview of the code and discuss the simulation techniques used.

Holenstein, Roman; Kirkwood, Sean E.; Fedosejevs, Robert; Tsui, Ying Y.

2004-11-01

76

Mechanism study of skin tissue ablation by nanosecond laser pulses  

Microsoft Academic Search

Understanding the fundamental mechanisms in laser tissue ablation is essential to improve clinical laser applications by reducing collateral damage and laser pulse energy requirement. The motive of this dissertation is to study skin tissue ablation by nanosecond laser pulses in a wide spectral region from near-infrared to ultraviolet for a clear understanding of the mechanism that can be used to

Qiyin Fang

2002-01-01

77

Specific Impulse Definition for Ablative Laser Propulsion  

NASA Technical Reports Server (NTRS)

The term "specific impulse" is so ingrained in the field of rocket propulsion that it is unlikely that any fundamental argument would be taken seriously for its removal. It is not an ideal measure but it does give an indication of the amount of mass flow (mass loss/time), as in fuel rate, required to produce a measured thrust over some time period This investigation explores the implications of being able to accurately measure the ablation rate and how the language used to describe the specific impulse results may have to change slightly, and recasts the specific impulse as something that is not a time average. It is not currently possible to measure the ablation rate accurately in real time so it is generally just assumed that a constant amount of material will be removed for each laser pulse delivered The specific impulse dependence on the ablation rate is determined here as a correction to the classical textbook definition.

Herren, Kenneth A.; Gregory, Don A.

2004-01-01

78

Plume dynamics and shielding by the ablation plume during Er:YAG laser ablation.  

PubMed

Free-running Er:YAG lasers are used for precise tissue ablation in various clinical applications. The ablated material is ejected into the direction perpendicular to the tissue surface. We investigated the influence of shielding by the ablation plume on the energy deposition into an irradiated sample because it influences the ablation dynamics and the amount of material ablated. The investigations were performed using an Er:YAG laser with a pulse duration of 200 micros for the ablation of gelatin with different water contents, skin, and water. Laser flash photography combined with a dark field Schlieren technique was used to visualize gaseous and particulate ablation products, and to measure the distance traveled by the ablating laser beam through the ablation plume at various times after the beginning of the laser pulse. The temporal evolution of the transmission through the ablation plume was probed using a second free running Er:YAG laser beam directed parallel to the sample's surface. The ablation dynamics was found to consist of a vaporization phase followed by material ejection. The observation of droplet ejection during water ablation provided evidence that a phase explosion is the driving mechanism for material ejection. The laser light transmission was only slightly reduced by the vapor plume, but decreased by 25%-50% when the ejected material passed the probe beam. At radiant exposures approximately 10 times above the ablation threshold, the laser energy deposited into the sample amounted to only 61% of the incident energy for gelatin samples with 90% water content and to 86% for skin samples. For free-running Er:YAG laser pulses shielding must therefore be considered in modeling the ablation dynamics and determining the dosage for clinical applications. PMID:11966301

Nahen, Kester; Vogel, Alfred

2002-04-01

79

Status of the Ablative Laser Propulsion Studies  

NASA Technical Reports Server (NTRS)

We present a short review of our laser-propulsion research as well as some of the current results of the Ablative Laser Propulsion (ALP) studies currently underway at the University of Alabama in Huntsville. It has been shown that direct surface ablation of a solid material produces high specific impulse (Isp) at relatively high energy conversion efficiency (20 - 40%). We detail measurements of specific impulse, thrust and coupling coefficients for elemental target materials both with single and with double pulse laser shots. We also present measurements taken using three independent methods for determination of Isp. The three methods produce consistent values from ion time-of-flight technique, impulse measurements and imaging of the expansion front of plasma plume. We present a demonstration of our ALP lightcraft, a small free-flying micro-vehicle that is propelled by ablation. For ALP lightcraft we use a subscale thin shell of nickel replicated over a diamond turned mandrel that produces a highly polished self-focusing, truncated at the focus parabolic mirror. The mass of the lightcraft is 54 mg and it is driven by 100-ps wide, 35-mJ laser pulses at 532 nm wavelength. This is an ongoing research. We also present the latest work on laserdriven micro-thrusters and detail some the near term goals of our program.

Herren, Kenneth A.; Lin, Jun; Cohen, Tinothy; Pakhomov, Andrew V.; Thompson, M. Shane

2004-01-01

80

A novel method for the identification of inorganic and organic gunshot residue particles of lead-free ammunitions from the hands of shooters using scanning laser ablation-ICPMS and Raman micro-spectroscopy.  

PubMed

A method based on scanning laser ablation and inductively coupled plasma-mass spectrometry (SLA-ICPMS) and Raman micro-spectroscopy for the detection and identification of compounds consistent with gunshot residue particles (GSR) has been developed. The method has been applied to the characterization of particles resulting from the discharge of firearms using lead-free ammunition. Modified tape lifts were used to collect the inorganic and organic residues from skin surfaces in a single sample. Using SLA-ICPMS, aggregates related to the composition of the ammunition, such as Cu-Zn-Sn, Zr-Sr, Cu-Zn, Al-Ti, or Al-Sr-Zr were detected, but this composition is only consistent with GSR from lead-free ammunitions. Additional evidence was provided by micro-Raman spectroscopy, which identified the characteristic organic groups of the particles as centralite, diphenylamine or their nitrated derivatives, which are indicative of GSR. PMID:25303642

Abrego, Zuriñe; Grijalba, Nagore; Unceta, Nora; Maguregui, Maite; Sanchez, Alicia; Fernández-Isla, Alberto; Goicolea, M Aranzazu; Barrio, Ramón J

2014-12-01

81

Investigating Age Resolution in Laser Ablation Geochronology  

NASA Astrophysics Data System (ADS)

Workshop on Data Handling in LA-ICP-MS U-Th-Pb Geochronology; Vancouver, British Columbia, Canada, 12-13 July 2008; Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) uranium-thorium-lead (U-Th-Pb) dating is an increasingly popular approach for determining the age of mineral grains and the timing of geological events. The spatial resolution offered by this technique allows detailed investigations of complex igneous and metamorphic processes, and the speed of data capture allows vast amounts of information to be gathered rapidly. Laser ablation U-Th-Pb dating is therefore becoming an increasingly influential technique to the geochronology community, providing cost-effective and ready access to age data for laboratories and end users worldwide. However, complications in acquiring, processing, and interpreting data can lead to inaccurate age information entering the literature. With the numbers of practitioners expanding rapidly, the need to standardize approaches and resolve difficulties (particularly involving the subjectivity in processing laser ablation U-Th-Pb data) is becoming important.

Horstwood, Matt; Kosler, Jan; Jackson, Simon; Pearson, Norman; Sylvester, Paul

2009-02-01

82

Solar cell contact formation using laser ablation  

DOEpatents

The formation of solar cell contacts using a laser is described. A method of fabricating a back-contact solar cell includes forming a poly-crystalline material layer above a single-crystalline substrate. The method also includes forming a dielectric material stack above the poly-crystalline material layer. The method also includes forming, by laser ablation, a plurality of contacts holes in the dielectric material stack, each of the contact holes exposing a portion of the poly-crystalline material layer; and forming conductive contacts in the plurality of contact holes.

Harley, Gabriel; Smith, David; Cousins, Peter

2012-12-04

83

Spectroscopic characterization of laser ablation brass plasma  

SciTech Connect

We present optical emission studies of the laser ablation brass plasma generated by the fundamental, second, and third harmonics of a neodymium doped yttrium aluminum garnet laser. The spectra predominantly reveal the spectral lines of the neutral and singly ionized copper and zinc. The excitation temperatures are determined by the Boltzmann plot method, whereas the electron number densities have been extracted from the Stark broadened line profiles. The spatial variations in the spectral line intensities and the plasma parameters at 1000, 500, and 100 mbar air pressures have been evaluated. Besides, the effect of the ambient gases (He, Ne, and Ar), the laser irradiance, and the laser wavelengths on the plasma parameters have been investigated.

Shaikh, Nek M. [Atomic and Molecular Physics Laboratory, Department of Physics, Quaid-i-Azam University, 45320 Islamabad (Pakistan); Institute of Physics, University of Sindh, 76080 Jamshoro (Pakistan); Hafeez, Sarwat; Kalyar, M. A.; Ali, R.; Baig, M. A. [Atomic and Molecular Physics Laboratory, Department of Physics, Quaid-i-Azam University, 45320 Islamabad (Pakistan)

2008-11-15

84

Nanosecond laser ablation for pulsed laser deposition of yttria  

NASA Astrophysics Data System (ADS)

A thermal model to describe high-power nanosecond pulsed laser ablation of yttria (Y2O3) has been developed. This model simulates ablation of material occurring primarily through vaporization and also accounts for attenuation of the incident laser beam in the evolving vapor plume. Theoretical estimates of process features such as time evolution of target temperature distribution, melt depth and ablation rate and their dependence on laser parameters particularly for laser fluences in the range of 6 to 30 J/cm2 are investigated. Calculated maximum surface temperatures when compared with the estimated critical temperature for yttria indicate absence of explosive boiling at typical laser fluxes of 10 to 30 J/cm2. Material ejection in large fragments associated with explosive boiling of the target needs to be avoided when depositing thin films via the pulsed laser deposition (PLD) technique as it leads to coatings with high residual porosity and poor compaction restricting the protective quality of such corrosion-resistant yttria coatings. Our model calculations facilitate proper selection of laser parameters to be employed for deposition of PLD yttria corrosion-resistive coatings. Such coatings have been found to be highly effective in handling and containment of liquid uranium.

Sinha, Sucharita

2013-09-01

85

Matrix effects in laser ablation molecular isotopic spectrometry  

NASA Astrophysics Data System (ADS)

Recently, it has been shown that laser-induced breakdown spectroscopy (LIBS) can be used for the detection of isotopes of elements via isotopic shifts in diatomic species in a technique known as laser ablation molecular isotopic spectrometry (LAMIS). While LAMIS works quite well for isotopic analysis of pure compounds under optimal conditions, it is desirable for it to be applicable for a variety of compounds and matrices. However, the LIBS plasma emission associated with LAMIS depends on several parameters, including the applied electric field of the laser pulse, the physical properties of the material being investigated, and the presence of additional elements other than the element of interest. In this paper, we address some of the pitfalls arising from these dependencies when using LAMIS for the determination of the relative isotopic abundance of boron-containing materials with varying chemical matrices.

Brown, Staci; Ford, Alan; Akpovo, Charlemagne C.; Martinez, Jorge; Johnson, Lewis

2014-11-01

86

Femtosecond laser ablation properties of borosilicate glass Adela Ben-Yakara)  

E-print Network

Femtosecond laser ablation properties of borosilicate glass Adela Ben-Yakara) Mechanical) We study the femtosecond laser ablation properties of borosilicate glass using atomic force. We present a detailed examination of the femtosecond laser ablation properties of borosilicate glass

Byer, Robert L.

87

What can We Learn about Atmospheric Meteor Ablation and Light Production from Laser Ablation?  

Microsoft Academic Search

Laboratory based laser ablation techniques can be used to study the size of the luminous region, predict spectral features,\\u000a estimate the luminous efficiency factor, and assess the role of chemically differentiated thermal ablation. A pulsed Nd:YAG\\u000a laser was used to ablate regions from ordinary and carbonaceous chondrite meteorites. CCD cameras and a digital spectroscope\\u000a were used to measure the size

R. L. Hawkes; E. P. Milley; J. M. Ehrman; R. M. Woods; J. D. Hoyland; C. L. Pettipas; D. W. Tokaryk

2008-01-01

88

Preparation of nanofluids using laser ablation in liquid technique  

SciTech Connect

In this work we report some results on thermal and transport properties of Ag-di water and Al-di water nanofluids that were prepared using Nd:yag laser to ablate Ag and Al in deionized water. The produced nanofluids were characterized using UV-VIS spectroscopy and TEM analysis. Our results on the UV-VIS spectra of the generated nanofluids demonstrated that using laser ablation in liquid we could generate stable colloids containing well-dispersed nanosized particles without use of any dispersants or surface reactive reagents. For Ag-di water nanofluids, the particles were spherical and the majority of the particles were in the 9 – 21 nm range with some big ones 23 - 26nm in size. The results on Al showed that the amplitude of the UV-VIS absorption spectra of Al-di water changed with time indicating that the ablated Al species reacts with water to yield an amorphous gel that transforms to the crystallized aluminum hydroxides with different shapes and sizes. The shapes were fibrous, triangular, rectangular, spherical shapes and joining of two pieces of triangles. In fact, these triangular and rectangular shapes were indeed pyramidal structures and hexagonal prisms, respectively.

Tran, P.X.; Soong, Yee

2007-06-01

89

Sulphur selective ablation by UV laser  

NASA Astrophysics Data System (ADS)

In this work we report the preliminary experimental results on the selective ablation of sulphur in ancient stones. The sulphur concentration was reduced after laser action. For this goal an excimer laser operating at 308 nm wavelength and time duration of 20 ns was used. In order to estimate the sulphur concentration before and after laser cleaning, a portable apparatus for energy-dispersive X-ray fluorescence (EDXRF) was utilised. The processed sample were characterized by an initial sulphur concentration of 2.8% w/w. After the laser treatment, sulphur concentration decreased after a total deposited energy of about 30 J/cm2 up to 1.2% w/w value. Due to the porosity of the stone, in fact, it is difficult to eliminate completely the S presence in the composition of the stones. It was also observed that after a few laser shots the initial black area of the stone became white showing in this way the great potential of the laser action on the cleaning process of the pietra leccese.

Lorusso, Antonella; Nassisi, Vincenzo; Belloni, Fabio; Buccolieri, Giovanni; Caretto, Giuseppe; Castellano, Alfredo

2005-06-01

90

RESEARCH Open Access Focal Laser Ablation of Prostate Cancer  

E-print Network

RESEARCH Open Access Focal Laser Ablation of Prostate Cancer: Numerical Simulation of Temperature between simulation and in vivo experiments of FLA for prostate cancer. Simulation is a promising planning surgical method. Keywords: Prostate cancer focal laser ablation, thermal damage, bioheat transfer

Paris-Sud XI, Université de

91

Pulsed laser ablation of solids and critical phenomena  

Microsoft Academic Search

We consider the possible manifestations of critical phenomena under pulsed laser ablation (PLA). The mechanism of phase explosion under nanosecond laser ablation is considered and the possibility of estimating the critical temperature from PLA experiments is discussed. A model based on the Euler equations and generalized van der Waals equation is developed to describe rarefaction shock waves (RSW) in near-critical

Nadezhda M Bulgakova; Alexander V Bulgakov; Igor M Bourakov; Natalia A Bulgakova

2002-01-01

92

Mechanism study of skin tissue ablation by nanosecond laser pulses  

NASA Astrophysics Data System (ADS)

Understanding the fundamental mechanisms in laser tissue ablation is essential to improve clinical laser applications by reducing collateral damage and laser pulse energy requirement. The motive of this dissertation is to study skin tissue ablation by nanosecond laser pulses in a wide spectral region from near-infrared to ultraviolet for a clear understanding of the mechanism that can be used to improve future design of the pulsed lasers for dermatology and plastic surgery. Multiple laser and optical configurations have been constructed to generate 9 to 12ns laser pulses with similar profiles at 1064. 532, 266 and 213nm for this study of skin tissue ablation. Through measurements of ablation depth as a function cf laser pulse energy, the 589nm spectral line in the secondary radiation from ablated skin tissue samples was identified as the signature of the occurrence of ablation. Subsequently, this spectral signature has been used to investigate the probabilistic process of the ablation near the threshold at the four wavelengths. Measurements of the ablation probability were conducted as a function of the electrical field strength of the laser pulse and the ablation thresholds in a wide spectral range from 1064nm to 213nm were determined. Histology analysis and an optical transmission method were applied in assessing of the ablation depth per pulse to study the ablation process at irradiance levels higher than threshold. Because more than 70% of the wet weight of the skin tissue is water, optical breakdown and backscattering in water was also investigated along with a nonlinear refraction index measurement using a z-scan technique. Preliminary studies on ablation of a gelatin based tissue phantom are also reported. The current theoretical models describing ablation of soft tissue ablation by short laser pulses were critically reviewed. Since none of the existing models was found capable of explaining the experimental results, a new plasma-mediated model was developed. A laser-induced and localized thermal ionization pathway has been investigated and it was found to have significant influence on the initial free electron density during plasma formation due to the combination of strong light absorption by chromophores and confined temperature rise in the chromophores. Good agreements have been found between the new plasma-mediated ablation model and experimental results. The implications of this dissertation research to the future improvement of laser systems in dermatology and plastic surgery are discussed.

Fang, Qiyin

93

Laser ablation loading of a surface-electrode ion trap  

E-print Network

We demonstrate loading by laser ablation of $^{88}$Sr$^+$ ions into a mm-scale surface-electrode ion trap. The laser used for ablation is a pulsed, frequency-tripled Nd:YAG with pulse energies of 1-10 mJ and durations of 3-5 ns. An additional laser is not required to photoionize the ablated material. The efficiency and lifetime of several candidate materials for the laser ablation target are characterized by measuring the trapped ion fluorescence signal for a number of consecutive loads. Additionally, laser ablation is used to load traps with a trap depth (40 meV) below where electron impact ionization loading is typically successful ($\\gtrsim$ 500 meV).

David R. Leibrandt; Robert J. Clark; Jaroslaw Labaziewicz; Paul Antohi; Waseem Bakr; Kenneth R. Brown; Isaac L. Chuang

2007-06-22

94

Laser ablation of aluminum from normal evaporation to phase explosion  

SciTech Connect

A study of laser ablation of Aluminum sample by nanosecond laser pulses considering two simultaneous mechanisms of normal evaporation and phase explosion is theoretically carried out. The temperature distribution in the sample is calculated by a one dimensional heat conduction equation. Ablation depth due to the evaporation and explosion is calculated as a function of laser pulse energies. Variation in some effective sample parameters during the laser ablation and their effects on laser ablation mechanisms are taken into account. At low irradiance, ablation is mainly due to the evaporation, while after a threshold intensity, the phase explosion becomes the dominant mechanism. Theoretical results of transition from the normal evaporation to the phase explosion are in good agreement with the experimental results.

Gragossian, A.; Tavassoli, S. H.; Shokri, B. [Laser and Plasma Research Institute, Shahid Beheshti University, G. C., Evin, Tehran 1983963113 (Iran, Islamic Republic of)

2009-05-15

95

Femtosecond laser ablation of brass in air and liquid media  

NASA Astrophysics Data System (ADS)

Laser ablation of brass in air, water, and ethanol was investigated using a femtosecond laser system operating at a wavelength of 785 nm and a pulse width less than 130 fs. Scanning electron and optical microscopy were used to study the efficiency and quality of laser ablation in the three ablation media at two different ablation modes. With a liquid layer thickness of 3 mm above the target, ablation rate was found to be higher in water and ethanol than in air. Ablation under water and ethanol showed cleaner surfaces and less debris re-deposition compared to ablation in air. In addition to spherical particles that are normally formed from re-solidified molten material, micro-scale particles with varying morphologies were observed scattered in the ablated structures (craters and grooves) when ablation was conducted under water. The presence of such particles indicates the presence of a non-thermal ablation mechanism that becomes more apparent when ablation is conducted under water.

Shaheen, M. E.; Gagnon, J. E.; Fryer, B. J.

2013-06-01

96

Revisiting the interplay between ablation, collisional, and radiative processes during ns-laser ablation  

SciTech Connect

A study of ns-laser ablation is presented, which focuses on the transient behavior of the physical processes that act in and above a copper sample. A dimensionless multiphase collisional radiative model describes the interplay between the ablation, collisional, and radiative mechanisms. Calculations are done for a 6 ns-Nd:YAG laser pulse operating at 532 nm and fluences up to 15 J/cm{sup 2}. Temporal intensity profiles as well as transmissivities are in good agreement with experimental results. It is found that volumetric ablation mechanisms and photo-processes both play an essential role in the onset of ns-laser induced breakdown.

Autrique, D. [Department of Physics and OPTIMAS Research Center, TU Kaiserslautern, 67653 Kaiserslautern (Germany) [Department of Physics and OPTIMAS Research Center, TU Kaiserslautern, 67653 Kaiserslautern (Germany); Department of Chemistry, University of Antwerp, 2610 Wilrijk (Belgium); Gornushkin, I. [Federal Institute for Materials Research and Testing - BAM, 12489 Berlin (Germany)] [Federal Institute for Materials Research and Testing - BAM, 12489 Berlin (Germany); Alexiades, V. [Department of Mathematics, University of Tennessee, Knoxville, Tennessee 37996-1320 (United States)] [Department of Mathematics, University of Tennessee, Knoxville, Tennessee 37996-1320 (United States); Chen, Z.; Bogaerts, A. [Department of Chemistry, University of Antwerp, 2610 Wilrijk (Belgium)] [Department of Chemistry, University of Antwerp, 2610 Wilrijk (Belgium); Rethfeld, B. [Department of Physics and OPTIMAS Research Center, TU Kaiserslautern, 67653 Kaiserslautern (Germany)] [Department of Physics and OPTIMAS Research Center, TU Kaiserslautern, 67653 Kaiserslautern (Germany)

2013-10-21

97

Diagnostics and applications of ultrashort pulsed laser ablation /  

E-print Network

ultra-short and high power pulsed laser system to study laser plasma interactions has attracted people will tell us the composition of the plasma plume and help us to study pulsed laser deposition. Eizel lens of plasma plume in pulsed laser ablation. In this work, we have designed and constructed Eizel lens and time

98

Energy efficiency of femtosecond laser ablation of polymer materials  

NASA Astrophysics Data System (ADS)

We present the results of an experimental study of the ablation spectral energy thresholds for a number of polymer materials ((C2F4) n , (CH2O) n ) exposed to femtosecond (?0.5 ~ 45-70 fs) laser pulses (? ~ 266, 400, 800 nm) under atmospheric conditions and under vacuum ( p ~ 10-2 Pa). We have analyzed the energy thresholds and the efficiency of optical, thermophysical, and gasdynamic processes in laser ablation vs. the laser pulse duration and photon energy.

Loktionov, E. Yu.; Ovchinnikov, A. V.; Protasov, Yu. Yu.; Protasov, Yu. S.; Sitnikov, D. S.

2012-03-01

99

The role of laser wavelength on plasma generation and expansion of ablation plumes in air  

NASA Astrophysics Data System (ADS)

We investigated the role of excitation laser wavelength on plasma generation and the expansion and confinement of ablation plumes at early times (0-500 ns) in the presence of atmospheric pressure. Fundamental, second, and fourth harmonic radiation from Nd:YAG laser was focused on Al target to produce plasma. Shadowgraphy, fast photography, and optical emission spectroscopy were employed to analyze the plasma plumes, and white light interferometry was used to characterize the laser ablation craters. Our results indicated that excitation wavelength plays a crucial role in laser-target and laser-plasma coupling, which in turn affects plasma plume morphology and radiation emission. Fast photography and shadowgraphy images showed that plasmas generated by 1064 nm are more cylindrical compared to plasmas generated by shorter wavelengths, indicating the role of inverse bremsstrahlung absorption at longer laser wavelength excitation. Electron density estimates using Stark broadening showed higher densities for shorter wavelength laser generated plasmas, demonstrating the significance of absorption caused by photoionization. Crater depth analysis showed that ablated mass is significantly higher for UV wavelengths compared to IR laser radiation. In this experimental study, the use of multiple diagnostic tools provided a comprehensive picture of the differing roles of laser absorption mechanisms during ablation.

Hussein, A. E.; Diwakar, P. K.; Harilal, S. S.; Hassanein, A.

2013-04-01

100

Use of laser ablation in quantitative analysis of the elemental composition of art pigments  

NASA Astrophysics Data System (ADS)

The ability to use laser ablation for preparation of art pigment samples in quantitative analysis of their elemental composition by atomic emission spectroscopy of inductively coupled plasma is shown. The proposed technique enables one to eliminate errors associated with both the influence of strong acids and the stoichiometric disruption in a sample.

Klyachkovskaya, E. V.; Muravitskaya, E. V.; Kozhukh, N. M.; Rozantsev, V. A.; Belkov, M. V.; Ershov-Pavlov, E. A.

2011-01-01

101

A fundamental study of excimer laser ablation using experimental and MD simulation method  

Microsoft Academic Search

This paper focuses on the effect of pulse duration on ablation rate and behavior of plume in excimer laser ablation. Experimental results of laser ablation demonstrate that the 200 ns pulse laser exhibits a four to five times larger ablation rate than that with 20 ns pulse for the same laser fluence. CCD photography reveals that the plume velocity exceeds

Kazuo Horiuchi; Masafumi Ishiyama; Tadashi Hasebe; Ken Yukimura; Yutaka Imaida

1998-01-01

102

On the influence of the mass ablated by a laser pulse on thin film morphology and optical properties  

NASA Astrophysics Data System (ADS)

To know and to control experimental parameters that play a role in laser ablation is vital to define film properties. Among the others, laser fluence is commonly used. Yet, when plasma expansion dynamics takes place through an ambient gas, the relation between the ablated mass per pulse and gas mass is critical and till now it was poorly investigated. While the gas mass is fixed by the pressure in the deposition chamber, the ablated mass is not unequivocally determined by the laser fluence. For a given fluence value the ablated mass changes as a function of the irradiated target area. Here, we show that nanostructured silver thin films deposited keeping unaltered the laser fluence, while changing in a controlled way the irradiated area and hence the ablated mass per pulse, display markedly differentiated morphological and optical properties, as evidenced by electron microscopy and UV-Vis and Raman spectroscopies.

Spadaro, M. C.; Fazio, E.; Neri, F.; Ossi, P. M.; Trusso, S.

2014-10-01

103

The impact of laser ablation on optical soft tissue differentiation for tissue specific laser surgery-an experimental ex vivo study  

PubMed Central

Background Optical diffuse reflectance can remotely differentiate various bio tissues. To implement this technique in an optical feedback system to guide laser surgery in a tissue-specific way, the alteration of optical tissue properties by laser ablation has to be taken into account. It was the aim of this study to evaluate the general feasibility of optical soft tissue differentiation by diffuse reflectance spectroscopy under the influence of laser ablation, comparing the tissue differentiation results before and after laser intervention. Methods A total of 70 ex vivo tissue samples (5 tissue types) were taken from 14 bisected pig heads. Diffuse reflectance spectra were recorded before and after Er:YAG-laser ablation. The spectra were analyzed and differentiated using principal component analysis (PCA), followed by linear discriminant analysis (LDA). To assess the potential of tissue differentiation, area under the curve (AUC), sensitivity and specificity was computed for each pair of tissue types before and after laser ablation, and compared to each other. Results Optical tissue differentiation showed good results before laser exposure (total classification error 13.51%). However, the tissue pair nerve and fat yielded lower AUC results of only 0.75. After laser ablation slightly reduced differentiation results were found with a total classification error of 16.83%. The tissue pair nerve and fat showed enhanced differentiation (AUC: 0.85). Laser ablation reduced the sensitivity in 50% and specificity in 80% of the cases of tissue pair comparison. The sensitivity of nerve–fat differentiation was enhanced by 35%. Conclusions The observed results show the general feasibility of tissue differentiation by diffuse reflectance spectroscopy even under conditions of tissue alteration by laser ablation. The contrast enhancement for the differentiation between nerve and fat tissue after ablation is assumed to be due to laser removal of the surrounding lipid-rich nerve sheath. The results create the basis for a guidance system to control laser ablation in a tissue-specific way. PMID:22704127

2012-01-01

104

Laser ablation system, and method of decontaminating surfaces  

DOEpatents

A laser ablation system comprising a laser head providing a laser output; a flexible fiber optic cable optically coupled to the laser output and transmitting laser light; an output optics assembly including a nozzle through which laser light passes; an exhaust tube in communication with the nozzle; and a blower generating a vacuum on the exhaust tube. A method of decontaminating a surface comprising the following steps: providing an acousto-optic, Q-switched Nd:YAG laser light ablation system having a fiber optically coupled output optics assembly; and operating the laser light ablation system to produce an irradiance greater than 1.times.10.sup.7 W/cm.sup.2, and a pulse width between 80 and 170 ns.

Ferguson, Russell L. (Idaho Falls, ID); Edelson, Martin C. (Ames, IA); Pang, Ho-ming (Ames, IA)

1998-07-14

105

Investigations on laser hard tissue ablation under various environments  

NASA Astrophysics Data System (ADS)

The purpose of this study was to investigate the effect of liquid environments upon laser bone ablation. A long-pulsed Er,Cr:YSGG laser was employed to ablate bovine bone tibia at various radiant exposures under dry, wet (using water or perfluorocarbon) and spray environmental conditions. Energy loss by the application of liquid during laser irradiation was evaluated, and ablation performance for all conditions was quantitatively measured by optical coherence tomography (OCT). Microscope images were also used to estimate thermal side effects in tissue after multiple-pulse ablation. Wet using water and spray conditions equally attenuated the 2.79 µm wavelength laser beam. Higher transmission efficiency was obtained utilizing a layer of perfluorocarbon. Dry ablation exhibited severe carbonization due to excessive heat accumulation. Wet condition using water resulted in similar ablation volume to the dry case without carbonization. The perfluorocarbon layer produced the largest ablation volume but some carbonization due to the poor thermal conductivity. Spray induced clean cutting with slightly reduced efficiency. Liquid-assisted ablation provided significant beneficial effects such as augmented material removal and cooling/cleaning effects during laser osteotomy.

Kang, H. W.; Oh, J.; Welch, A. J.

2008-06-01

106

Laser ablation methods for analysis of urinary calculi: Comparison study based on calibration pellets  

NASA Astrophysics Data System (ADS)

Methods based on laser ablation, such as Laser-Induced Breakdown Spectroscopy (LIBS) and Laser-Ablation Inductively Coupled Plasma Mass/Optical Emission Spectrometry (LA-ICP-MS/OES) are particularly suitable for urinary calculi bulk and micro analysis. Investigation of spatial distribution of matrix and trace elements can help to explain their emergence and growth. However, quantification is still very problematic and these methods are often used only for qualitative elemental mapping. There are no commercially available standards, which would correspond to the urinary calculi matrix. Internal standardization is also difficult, mainly due to different crystalline phases in one kidney stone. The aim of this study is to demonstrate the calibration capabilities and examine the limitations of laser ablation based techniques. Calibration pellets were prepared from powdered human urinary calculi with phosphate, oxalate and urate matrix. For this comparative study, the most frequently used laser-ablation based analytical techniques were chosen, such as LIBS and LA-ICP-MS. Moreover, some alternative techniques such as simultaneous LIBS-LA-ICP-OES and laser ablation LA-LIBS were also utilized.

Št?pánková, K.; Novotný, K.; Vašinová Galiová, M.; Kanický, V.; Kaiser, J.; Hahn, D. W.

2013-03-01

107

Dynamics of laser ablated colliding plumes  

SciTech Connect

We report the dynamics of single and two collinearly colliding laser ablated plumes of ZnO studied using fast imaging and the spectroscopic measurements. Two dimensional imaging of expanding plume and temporal evolution of various species in interacting zones of plumes are used to calculate plume front velocity, electron temperature, and density of plasma. The two expanding plumes interact with each other at early stage of expansion ({approx}20 ns) resulting in an interaction zone that propagates further leading to the formation of stagnation layer at later times (>150 ns) at the lateral collision front of two plumes. Colliding plumes have larger concentration of higher ionic species, higher temperature, and increased electron density in the stagnation region. A one-to-one correlation between the imaging and optical emission spectroscopic observations in interaction zone of the colliding plumes is reported.

Gupta, Shyam L.; Pandey, Pramod K.; Thareja, Raj K. [Department of Physics, Indian Institute of Technology, Kanpur-208016 (India)

2013-01-15

108

Formation of tribological structures by laser ablation  

NASA Astrophysics Data System (ADS)

Many technical applications can benefit from the use of tribological structures in minimizing abrasive material wear and energy consumption without the integration of additional materials in a working assembly. Especially in lubricated friction systems, the tribological character can be significantly improved through the addition of oriented and repetitive microstructure. In this study, experimental tests are discussed for a small range of structure dimensions to verify the effect of optimizing the tribological contact performance. A nanosecond pulsed fiber laser is used to create various test structures with different sizes and form. The quality of the fabricated surface pattern, particularly form correctness, feathering and material modification effects of the ablated area is characterized and optimized. The influence of pulse duration, pulse energy and pulse delay using normal pulsing is presented and compared to various burst modes.

Schilling, Niels; Paschke, Mike; Hendow, Sami T.; Klotzbach, Udo

2012-03-01

109

Amalgam ablation with the Er:YAG laser  

NASA Astrophysics Data System (ADS)

Any laser that will be used by dentist to replace the dental drill (handpiece) must remove dental hard tissues safely. These lasers must also have the ability to ablate the restorative dental materials which are present in the teeth being treated. Prior to any laser being used to treat humans a thorough knowledge of the effects of the laser treatment on dental materials must be understood. Cores of dental amalgam were created and sliced into thin wafers for this experiment. Ablation efficiency and thermal changes were evaluated with and without water. It appears as if the Er:YAG laser can effectively ablate amalgam dental material with and without water. The water prevents the temperature from increasing much above baseline and does not reduce efficiency of ablation.

Wigdor, Harvey A.; Visuri, Steven R.; Walsh, Joseph T., Jr.

1995-04-01

110

Tailored ablation processing of advanced biomedical hydroxyapatite by femtosecond laser pulses  

NASA Astrophysics Data System (ADS)

The micromachining of hydroxyapatite (HAp) is highly important for orthopedics and dentistry, since human bone and teeth consist mainly of HAp. We demonstrate ultrashort Ti:sapphire laser ablation of HAp, using pulse-widths of 50 fs, 500 fs, and 2 ps at a wavelength of 820 nm and at 1 kpps. The crucial medical issue is to preserve the chemical properties of the machined (ablated) surface. If the chemical properties of HAp change, the human bone or tooth cannot re-grow after laser processing. Using X-ray photoelectron spectroscopy, we observe chemical properties of HAp ablated in air. The HAp is ablated at laser fluences of 3.2 J/cm2 (6.4×1013 W/cm2 at 50 fs), 3.3 J/cm2 (6.6×1012 W/cm2 at 500 fs), and 9.6 J/cm2 (4.8×1012 W/cm2 at 2 ps), respectively. As a result it is found that the ablated surface is unchanged after laser ablation over the pulse-width range used in this experiment.

Ozono, K.; Obara, M.

111

Laser ablation dynamics in metals: The thermal regime  

NASA Astrophysics Data System (ADS)

We studied the laser ablation dynamics of steel in the thermal regime both experimentally and theoretically. The real-time monitoring of the process shows that the ablation rate depends on laser energy density and ambient pressure during the exposure time. We demonstrated that the ablation efficiency can be enhanced when the pressure is reduced with respect to the atmospheric pressure for a given laser fluence, reaching an upper limit despite of high-vacuum conditions. An analytical model based on the Hertz-Knudsen law reproduces all the experimental results.

Mezzapesa, F. P.; Columbo, L. L.; Brambilla, M.; Dabbicco, M.; Ancona, A.; Sibillano, T.; Scamarcio, G.

2012-07-01

112

Dynamics of laser driven, ablatively accelerated targets. Memorandum report  

Microsoft Academic Search

The characteristics of ablation plasma from planar targets, driven by long Nd:glass laser pulses (4 nsec, < 10 to the 14th power w\\/sq cm), and the velocity of the ablatively accelerated targets are experimentally studied. Ablation plasma diagnostics include arrays of time-of-flight ion collectors, plasma calorimeters, and ballistic pendula which directly measure the plasma velocity, energy, and momentum. The ballistic

Grun

1981-01-01

113

Dynamics of Laser-Driven Ablatively Accelerated Targets  

Microsoft Academic Search

The characteristics of ablation plasma from planar targets, driven by long Nd: glass laser pulses (4 nsec, < 10('14) W\\/cm('2)), and the velocity of the ablatively accelerated targets are experimentally studied. Ablation plasma diagnostics include arrays of time-of-flight ion collectors, plasma calorimeters, and ballistic pendula which directly measure the plasma velocity, energy, and momentum. The ballistic pendula have been tested

Jacob Grun

1981-01-01

114

Quantification of polyimide carbonization after laser ablation  

NASA Astrophysics Data System (ADS)

Polyimide was irradiated with a XeCl excimer laser (308 nm) and the ablated area and its surrounding were studied using transmission electron microscopy (TEM) and confocal Raman microscopy. Ring-like structures surrounding the ablated area were detected at all fluences. At fluences lower than 250 mJ/cm-2 the formation of conical structures was observed within the irradiated area. The width of the rings increases with fluence and only slightly with the number of pulses. The rings consist mainly of polycrystalline carbon with a relatively high bond angle disorder, with thickness decreasing radially from the crater edge. The thickness of the deposited carbon was determined from TEM analysis and calculated from the intensity ratios of Raman bands assigned to carbon and polyimide using a two layer model. Comparing the two results an estimate of the absorption coefficient of the deposited carbon could be obtained. On top of the cone structures carbon was detected with a higher degree of crystallinity and lower bond angle disorder as compared to the material deposited outside the crater. With energy dispersive x-ray analysis, calcium could be detected on top of the cones. Therefore, it can be assumed that the Ca impurities are causing the cone structures. The higher crystallinity of the carbon inside the irradiated area is probably due to a tempering-like process on top of the Ca compound which is heated upon laser irradiation or to a mixture of growth mechanisms similar to the ones suggested for the formation of carbon nanotubes on metal particles and carbon nanohorns without metal catalysis.

Raimondi, F.; Abolhassani, S.; Brütsch, R.; Geiger, F.; Lippert, T.; Wambach, J.; Wei, J.; Wokaun, A.

2000-09-01

115

Wetting and other physical characteristics of polycarbonate surface textured using laser ablation  

NASA Astrophysics Data System (ADS)

Surface texturing of polycarbonate glass is carried out for improved hydrophobicity via controlled laser ablation at the surface. Optical and physical characteristics of the laser treated layer are examined using analytical tools including optical, atomic force, and scanning electron microscopes, Fourier transform infrared spectroscopy, and X-ray diffraction. Contact angle measurements are carried out to assess the hydrophobicity of the laser treated surface. Residual stress in the laser ablated layer is determined using the curvature method, and microhardnes and scratch resistance are analyzed using a micro-tribometer. Findings reveal that textured surfaces compose of micro/nano pores with fine cavities and increase the contact angle to hydrophobicity such a way that contact angles in the range of 120° are resulted. Crystallization of the laser treated surface reduces the optical transmittance by 15%, contributes to residual stress formation, and enhances the microhardness by twice the value of untreated polycarbonate surface. In addition, laser treatment improves surface scratch resistance by 40%.

Yilbas, B. S.; Khaled, M.; Abu-Dheir, N.; Al-Aqeeli, N.; Said, S. A. M.; Ahmed, A. O. M.; Varanasi, K. K.; Toumi, Y. K.

2014-11-01

116

Silica nano-ablation using laser plasma soft x-rays  

NASA Astrophysics Data System (ADS)

We have investigated nano-ablation of silica glass and ablation process using focused laser plasma soft Xrays. Laser plasma soft X-rays were generated by irradiation of a Ta target with Nd:YAG laser light. The soft X-rays were focused on silica glass plates using an ellipsoidal mirror at fluences up to 1 J/cm2. In order to fabricate nano-trenches, a silica glass plate was irradiated with laser plasma soft X-rays through the windows of a line and space mask. We demonstrated fabrication of nano-trenches with a width of 50 nm. It should be noted that the feature size is more precise than that estimated from the thermal diffusion length for the 10-ns X-rays (i.e. 80 nm). Furthermore, the ablated area has a depth of 470 nm and a roughness of 1 nm after ten shots of irradiation. Thus, the X-ray irradiation technique have a significant feature of direct nanomachining. The ablation occurs at fluences F beyond a ablation threshould Fth and ablation depth per pulse D obeys the law D = 1/? ln(F/Fth), where ? is an effective absorption coefficient. These results suggest that absorbed energy is accumulated in the absorbed region without energy diffusion until ablation occurs. In addition, time-resolved mass spectroscopy revealed that silica glass is broken into atomic ions and atomic neutrals during ablation. Because Si+ and O+ ions have kinetic energies of 10-30 eV, non-thermal process such as Coulomb explosion may be driving force behind the ablation. Such non-thermal process enables us to fabricate nano-structures on silica glass.

Makimura, Tetsuya; Torii, Shuichi; Niino, Hiroyuki; Murakami, Kouichi

2009-05-01

117

Osteoid Osteoma: Experience with Laser- and Radiofrequency-Induced Ablation  

SciTech Connect

The purpose of this study was to analyze the clinical outcome of osteoid osteoma treated by thermal ablation after drill opening. A total of 17 patients and 20 procedures were included. All patients had typical clinical features (age, pain) and a typical radiograph showing a nidus. In 5 cases, additional histological specimens were acquired. After drill opening of the osteoid osteoma nidus, 12 thermal ablations were induced by laser interstitial thermal therapy (LITT) (9F Power-Laser-Set; Somatex, Germany) and 8 ablations by radiofrequency ablation (RFA) (RITA; StarBurst, USA). Initial clinical success with pain relief has been achieved in all patients after the first ablation. Three patients had an osteoid osteoma recurrence after 3, 9, and 10 months and were successfully re-treated by thermal ablation. No major complication and one minor complication (sensible defect) were recorded. Thermal ablation is a safe and minimally invasive therapy option for osteoid osteoma. Although the groups are too small for a comparative analysis, we determined no difference between laser- and radiofrequency-induced ablation in clinical outcome after ablation.

Gebauer, Bernhard [Charite, Medical University Berlin, Department of Radiology (Germany)], E-mail: bernhard.gebauer@charite.de; Tunn, Per-Ulf [Charite, Medical University Berlin, Department of Surgery and Surgical Oncology (Germany); Gaffke, Gunnar [Charite, Medical University Berlin, Department of Radiology (Germany); Melcher, Ingo [Charite, Medical University Berlin, Campus Virchow-Clinic, Department of Trauma and Reconstructive Surgery (Germany); Felix, Roland; Stroszczynski, Christian [Charite, Medical University Berlin, Department of Radiology (Germany)

2006-04-15

118

Laser ablation of paper: Raman identification of products  

NASA Astrophysics Data System (ADS)

Old paper samples are bleached using pulsed laser radiation with a wavelength of 532 nm. The ablation products of five paper samples that differ by composition and production dates are studied using Raman microspectroscopy. Cellulose, protein, calcite, titanium dioxide (anatase, rutile, and brookite), quartz, lazurite, bonattite, and dolomite are identified as ablation products.

Balakhnina, Irina; Brandt, Nikolay; Chikishev, Andrey; Rebrikova, Natalia; Yurchuk, Yuliya

2014-11-01

119

Acoustic online monitoring of IR laser ablation of burnt skin  

Microsoft Academic Search

In burn surgery necrotic tissue has to be removed prior to grafting. Tangential excision causes high blood loss and destruction of viable tissue. Pulsed infrared laser ablation can overcome both problems because of its high precision and the superficial coagulation of the remaining tissue. We investigated the ablation noise to realize an acoustic feedback system for a selective removal of

Kester Nahen; Alfred Vogel

1999-01-01

120

Enhancement of pulsed laser ablation in environmentally friendly liquid.  

PubMed

Enhancement of pulsed laser ablation can be achieved in acetic acid as an environmentally friendly liquid. This paper evaluates microholes and textured features induced by a nanosecond pulsed laser under different processing circumstances. The microholes are fabricated by laser drilling in acetic acid and found to be 100% deeper than in air. The textured features achieved in the liquid demonstrate a higher content of Copper and a lower content of Oxygen. The improvement of laser ablation efficiency in the liquid is attributed to the strong confinement of plasma plume accompanying with shockwave and cavitation bubbles. Meanwhile, the laser enhanced chemical etching by the weak acid plays a critical role. PMID:25321965

Luo, Fangfang; Guan, Yingchun; Ong, Weili; Du, Zheren; Ho, Ghimwei; Li, Fengping; Sun, Shufeng; Lim, Gniancher; Hong, Minghui

2014-10-01

121

Analysis and removal of ITER relevant materials and deposits by laser ablation  

NASA Astrophysics Data System (ADS)

The analysis of the deposition of eroded wall material on the plasma-facing materials in fusion devices is one of the crucial issues to maintain the plasma performance and to fulfill safety requirements with respect to tritium retention by co-deposition. Laser ablation with minimal damage to the plasma facing material is a promising method for in situ monitoring and removal of the deposition, especially for plasma-shadowed areas which are difficult to reach by other cleaning methods like plasma discharge. It requires the information of ablation process and the ablation threshold for quantitative analysis and effective removal of the different deposits. This paper presents systemic laboratory experimental analysis of the behavior of the ITER relevant materials, graphite, tungsten, aluminum (as a substitution of beryllium) and mixed deposits ablated by a Nd:YAG laser (1064 nm) with different energy densities (1-27 J/cm2, power density 0.3-3.9 GW/cm2). The mixed deposits consisted of W-Al-C layer were deposited on W substrate by magnetron sputtering and arc plasma deposition. The aim was to select the proper parameters for the quantitative analysis and for laser removal of the deposits by investigating the ablation efficiency and ablation threshold for the bulk materials and deposits. The comparison of the ablation and saturation energy thresholds for pure and mixed materials shows that the ablation threshold of the mixed layer depends on the concentration of the components. We propose laser induced breakdown spectroscopy for determination of the elemental composition of deposits and then we select the laser parameters for the layer removal. Comparison of quantitative analysis results from laboratory to that from TEXTOR shows reasonable agreements. The dependence of the spectra on plasma parameters and ambient gas pressure is investigated.

Xiao, Qingmei; Huber, Alexander; Philipps, Volker; Sergienko, Gennady; Gierse, Niels; Mertens, Philippe; Hai, Ran; Ding, Hongbin

2014-12-01

122

Absorption-Ablation-Excitation Mechanisms of Laser-Cluster Interactions in a Nanoaerosol System  

E-print Network

The absorption-ablation-excitation mechanism in laser-cluster interactions is investigated by measuring Rayleigh scattering of aerosol clusters along with atomic emission from phase-selective laser-induced breakdown spectroscopy (PS-LIBS). As the excitation laser intensity is increased beyond 0.16GW/cm2, the scattering cross-section of TiO_2 clusters begins to decrease, concurrent with the onset of atomic emission of Ti, indicating a scattering-to-ablation transition and the formation of nanoplasmas. To better clarify the process, time-resolved measurements of scattering signals are examined for different excitation laser intensities. For increasing laser intensities, the cross-sections of clusters decrease during a single pulse, evincing the shorter ablation delay time and larger ratios of ablation clusters. Assessment of the electron energy distribution during the ablation process is conducted by non-dimensionalizing the Fokker-Planck equation, with analogous Strouhal Sl_E, Peclet Pe_E, and Damkohler Da_E n...

Ren, Yihua; Zhang, Yiyang; Tse, Stephen D; Long, Marshall B

2014-01-01

123

Laser Ablation of Aluminium: Drops and Voids Johannes Roth1  

E-print Network

Laser Ablation of Aluminium: Drops and Voids Johannes Roth1 , Johannes Karlin1 , Christian Ulrich2 as a #12;2 Johannes Roth et al pollution. Or they can stay in the hole and fill it up. Void formation

Roth, Johannes

124

Selective material ablation by the TEA CO2 laser  

NASA Astrophysics Data System (ADS)

This paper reports two topics in the material processing using TEA CO2 lasers. We demonstrated selective ablation of hydrogenated amorphous silicon (a-Si:H) thin layer on a quartz substrate by the second harmonic (SH) radiation of TEA CO2 laser generated by AgGaSe2 nonlinear crystal. Si-H bonds contained in a-Si:H strongly absorb the 5 micrometers SH radiation and resulted in the selective ablation of the a-Si:H layer. The successful ablation processing of ethylenetetrafluoroethylene (ETFE) copolymer by the 9.6 micrometers fundamental wavelength TEA CO2 laser is also reported. Only ETFE thin film adhered to an aluminum substrate can be ablated by the TEA CO2 laser.

Sumiyoshi, Tetsumi; Shiratori, Akira; Ninomiya, Yutaka; Obara, Minoru

1995-03-01

125

Laser tattoo removal with preceding ablative fractional treatment  

NASA Astrophysics Data System (ADS)

A combined laser tattoo removal treatment, first the ablative fractional resurfacing (AFR) with an Er:YAG laser and then the q-switched (QSW) Nd:YAG laser treatment, was studied. Experiments show that significantly higher fluences can be used for the same tissue damage levels.

Cenci?, Boris; Možina, Janez; Jezeršek, Matija

2013-06-01

126

Tissue ablation through water with erbium: YAG lasers  

Microsoft Academic Search

The authors report the dynamics of vapor cavities generated by 200 mu s long Er:YAG laser pulses under water and in gelatin. Acoustic transients were detected at the beginning of the laser pulse and when the cavity collapsed. Cavity expansion and collapse, and the associated acoustic transients are possible ablation mechanisms with the Er:YAG laser. Shortening of the pulse duration

H. Loertscher; W. Q. Shi; W. S. Grundfest

1992-01-01

127

Momentum Transfer by Laser Ablation of Irregularly Shaped Space Debris  

SciTech Connect

Proposals for ground-based laser remediation of space debris rely on the creation of appropriately directed ablation-driven impulses to either divert the fragment or drive it into an orbit with a perigee allowing atmospheric capture. For a spherical fragment, the ablation impulse is a function of the orbital parameters and the laser engagement angle. If, however, the target is irregularly shaped and arbitrarily oriented, new impulse effects come into play. Here we present an analysis of some of these effects.

Liedahl, D A; Libby, S B; Rubenchik, A

2010-02-04

128

Discharge-aided reactive laser ablation for ultrafine powder production  

Microsoft Academic Search

Ultrafine alumina powder was produced by aluminum target ablation with a Nd:YAG laser beam (1064 nm wavelength; 340 mJ\\/pulse energy; 7 ns pulse duration; 10 pps repetition rate), in a 120 Torr O2 atmosphere. A theoretical approach for the ablation process, based on laser energy absorption and energy balance in the target, is used for comparison with the experimental production

Ioan Chis; A. Marcu; T. Yukawa; Dumitru Dragulinescu; Constantin Grigoriu; Dana Miu; Weihua Jiang; Kiyoshi Yatsui

1998-01-01

129

Laser ablation for the synthesis of carbon nanotubes  

DOEpatents

Single walled carbon nanotubes are produced in a novel apparatus by the laser-induced ablation of moving carbon target. The laser used is of high average power and ultra-fast pulsing. According to various preferred embodiments, the laser produces and output above about 50 watts/cm.sup.2 at a repetition rate above about 15 MHz and exhibits a pulse duration below about 10 picoseconds. The carbon, carbon/catalyst target and the laser beam are moved relative to one another and a focused flow of "side pumped", preheated inert gas is introduced near the point of ablation to minimize or eliminate interference by the ablated plume by removal of the plume and introduction of new target area for incidence with the laser beam. When the target is moved relative to the laser beam, rotational or translational movement may be imparted thereto, but rotation of the target is preferred.

Holloway, Brian C; Eklund, Peter C; Smith, Michael W; Jordan, Kevin C; Shinn, Michelle

2012-11-27

130

Laser ablation for the synthesis of carbon nanotubes  

NASA Technical Reports Server (NTRS)

Single walled carbon nanotubes are produced in a novel apparatus by the laser-induced ablation of moving carbon target. The laser used is of high average power and ultra-fast pulsing. According to various preferred embodiments, the laser produces an output above about 50 watts/cm.sup.2 at a repetition rate above about 15 MHz and exhibits a pulse duration below about 10 picoseconds. The carbon, carbon/catalyst target and the laser beam are moved relative to one another and a focused flow of side pumped, preheated inert gas is introduced near the point of ablation to minimize or eliminate interference by the ablated plume by removal of the plume and introduction of new target area for incidence with the laser beam. When the target is moved relative to the laser beam, rotational or translational movement may be imparted thereto, but rotation of the target is preferred.

Holloway, Brian C. (Inventor); Eklund, Peter C. (Inventor); Smith, Michael W. (Inventor); Jordan, Kevin C. (Inventor); Shinn, Michelle (Inventor)

2010-01-01

131

Laser ablation of iron: A comparison between femtosecond and picosecond laser pulses  

NASA Astrophysics Data System (ADS)

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.

Shaheen, M. E.; Gagnon, J. E.; Fryer, B. J.

2013-08-01

132

Transient Newton rings in dielectrics upon fs laser ablation  

E-print Network

We report the appearance of transient Newton rings in dielectrics (sapphire and lead-oxide glass) during ablation with single fs laser pulses. Employing femtosecond microscopy with 800 nm excitation and 400 nm illumination, we observe a characteristic ring pattern that dynamically changes for increasing delay times between pump and probe pulse. Such transient Newton rings have been previously observed in metals and semiconductors at fluences above the ablation threshold and were related to optical interference of the probe beam reflected at the front surface of the ablating layer and at the interface of the non-ablating substrate. Yet, it had been generally assumed that this phenomenon cannot be (and has not been) observed in dielectrics due to the different ablation mechanism and optical properties of dielectrics. The fact that we are able to observe them has important consequences for the comprehension of the ablation mechanisms in dielectrics and provides a new method for investigating these mechanisms in ...

Garcia-Lechuga, Mario; Hernandez-Rueda, Javier; Solis, Javier

2014-01-01

133

Laser Ablation Increases PEM/Catalyst Interfacial Area  

NASA Technical Reports Server (NTRS)

An investigational method of improving the performance of a fuel cell that contains a polymer-electrolyte membrane (PEM) is based on the concept of roughening the surface of the PEM, prior to deposition of a thin layer of catalyst, in order to increase the PEM/catalyst interfacial area and thereby increase the degree of utilization of the catalyst. The roughening is done by means of laser ablation under carefully controlled conditions. Next, the roughened membrane surface is coated with the thin layer of catalyst (which is typically platinum), then sandwiched between two electrode/catalyst structures to form a membrane/ele c t - rode assembly. The feasibility of the roughening technique was demonstrated in experiments in which proton-conducting membranes made of a perfluorosulfonic acid-based hydrophilic, protonconducting polymer were ablated by use of femtosecond laser pulses. It was found that when proper combinations of the pulse intensity, pulse-repetition rate, and number of repetitions was chosen, the initially flat, smooth membrane surfaces became roughened to such an extent as to be converted to networks of nodules interconnected by filaments (see Figure 1). In further experiments, electrochemical impedance spectroscopy (EIS) was performed on a pristine (smooth) membrane and on two laser-roughened membranes after the membranes were coated with platinum on both sides. Some preliminary EIS data were interpreted as showing that notwithstanding the potential for laser-induced damage, the bulk conductivities of the membranes were not diminished in the roughening process. Other preliminary EIS data (see Figure 2) were interpreted as signifying that the surface areas of the laser-roughened membranes were significantly greater than those of the smooth membrane. Moreover, elemental analyses showed that the sulfur-containing molecular groups necessary for proton conduction remained intact, even near the laser-roughened surfaces. These preliminary results can be taken as indications that laser-roughened PEMs should function well in fuel cells and, in particular, should exhibit current and power densities greater than those attainable by use of smooth membranes.

Whitacre, Jay; Yalisove, Steve

2009-01-01

134

Laser ablation of a platinum target in water. I. Ablation mechanisms  

SciTech Connect

This is the first in a series of three papers aimed at better understanding the processes that lead to nanomaterial formation during laser ablation of solid targets in liquids. Here we study the variation of the target surface morphology versus laser fluence and wavelength in order to suggest an ablation mechanism. A key finding is that an explosive ablation mechanism is prominent for a wide range of laser fluences for all wavelengths tested. Interestingly, however, ultraviolet (355 nm) and infrared (1064 nm) wavelengths show characteristically different explosive behaviors. In the infrared case, numerous large craters with diameters around 20 {mu}m form at localized points within the laser irradiated area. In contrast, ultraviolet ablation results in a striking transition to nanoscale surface roughness across the entire irradiated area. This texture is attributed to spinodal decomposition at the molten target surface. We propose that the wavelength and fluence dependence of the ablation craters can be explained by the amount of energy absorbed in the target. The consequences of the ablation mechanism for nanomaterial synthesis are discussed.

Nichols, William T.; Sasaki, Takeshi; Koshizaki, Naoto [Nanoarchitectonics Research Center, National Institute of Advanced Industrial Science and Technology (AIST), Central 5, 1-1-1 Higashi, Tsukuba, Ibaraki 305-8565 (Japan)

2006-12-01

135

Collinear double pulse laser ablation in water for the production of silver nanoparticles.  

PubMed

Experiments of collinear Double Pulse Laser Ablation in Liquid (DP-LAL) were carried out for studying the production mechanisms of nanoparticles (NPs) in water, which revealed the fundamental role of the cavitation bubble dynamics in the formation of aqueous colloidal dispersions. In this work, DP-LAL was used to generate silver nanoparticles (AgNPs) from a silver target submerged in water at atmospheric pressure and room temperature, by using the second harmonic (532 nm) of two Nd:YAG lasers. The second laser pulse was shot at different delay times (i.e. interpulse delay) during the bubble temporal evolution of the first laser induced bubble. Optical Emission Spectroscopy, Shadowgraph Images, Surface Plasmon Resonance absorption spectroscopy and Dynamic Light Scattering were carried out to study the behaviour of laser-induced plasma and cavitation bubbles during the laser ablation in liquid, to monitor the generation of AgNPs under different conditions, and for characterization of NPs. The results of DP-LAL were always compared with the corresponding ones obtained with Single Pulse Laser Ablation in Liquid (SP-LAL), so as to highlight the peculiarities of the two different techniques. PMID:24196485

Dell'Aglio, Marcella; Gaudiuso, Rosalba; ElRashedy, Remah; De Pascale, Olga; Palazzo, Gerardo; De Giacomo, Alessandro

2013-12-28

136

Mechanisms of Carbon Nanotube Production by Laser Ablation Process  

NASA Technical Reports Server (NTRS)

We will present possible mechanisms for nanotube production by laser oven process. Spectral emission of excited species during laser ablation of a composite graphite target is compared with that of laser irradiated C60 vapor. The similarities in the transient and spectral data suggest that fullerenes are intermediate precursors for nanotube formation. The confinement of the ablation products by means of a 25-mm diameter tube placed upstream of the target seems to improve the production and purity of nanotubes. Repeated laser pulses vaporize the amorphous/graphitic carbon and possibly catalyst particles, and dissociate fullerenes yielding additional feedstock for SWNT growth.

Scott, Carl D.; Arepalli, Sivaram; Nikolaev, Pavel; Smalley, Richard E.; Nocholson, Leonard S. (Technical Monitor)

2000-01-01

137

Histological analysis of a cornea following experimental femtosecond laser ablation.  

PubMed

: Corneal photorefractive surgery is currently performed by ablation of corneal stroma under the stromal flap. A stromal flap is created using a femtosecond (FS) laser or mechanical microkeratome, although the FS laser procedure is considered safer and more accurate. This review assesses and compares the use of FS laser versus mechanical microkeratome ablation for corneal stromal characteristics mainly examined by histology and cellular biological responses. Supporting data from our studies, using corneas of enucleated porcine eye globes, are included in this review. Histological analysis and experimental studies of cellular/tissue responses to FS laser irradiation should be further investigated, and the equipment used to perform these techniques should be improved. PMID:25289720

Sumioka, Takayoshi; Miyamoto, Takeshi; Takatsuki, Reiko; Okada, Yuka; Yamanaka, Osamu; Saika, Shizuya

2014-11-01

138

Moessbauer Study of Iron Films Produced by Laser Ablation  

SciTech Connect

Iron atoms evaporated by laser ablation were deposited on Al substrates and Si substrates. The iron and alloy (Fe-Al and Fe-Si) films thus formed were evaluated using Moessbauer spectroscopy in order to study their magnetic and chemical properties. Neat iron films (thicker than 50 nm) deposited on Al substrates at 10 K were found to have spin orientations parallel to the surface plane. Formation of Fe-Al alloy was observed at the boundary between the Fe-films and the Al substrate, and the composition of the Fe-Al alloy was a function of the Al substrate temperature during the deposition. Doublet absorption of FeAl was observed for the sample formed at 10 K, and distributed magnetic splitting with disordered compositions of Fe-Al alloy was observed for the samples formed at 293 K. When the sample was formed at 573 K, two sets of sextets with sharp absorptions were observed indicating the formation of Fe3Al. The films were also examined using scanning electron microscopy (SEM). Similarly, samples of laser-evaporated iron on Si substrates were studied, and alloys of Fe-Si were found. Fe3Si and FeSi were produced when the laser-deposition was performed on Si substrates at 573 K.

Namiki, Kentarou; Yokoyama, Daisuke; Yamada, Yasuhiro [Department of Chemistry, Tokyo University of Science, 1-3 Kagurazaka, Shinjuku-ku, Tokyo 162-8601 (Japan)

2005-04-26

139

Improving Consistency in Laser Ablation Geochronology  

NASA Astrophysics Data System (ADS)

Workshop on Data Handling in LA-ICP-MS U-Th-Pb Geochronology; San Francisco, California, 12-13 December 2009; The use of uranium-thorium-lead (U-Th-Pb) laser ablation-inductively coupled plasma mass spectrometry (LA-ICP-MS) geochronology involves rapid analysis of U-and Th-rich accessory minerals. It routinely achieves 1-2% precision for U-Th-Pb dates constituting detrital mineral age spectra and for dating igneous and metamorphic events. The speed and low setup and analysis cost of LA-ICP-MS U-Th-Pb geochronology has led to a proliferation of active laboratories. Tens of thousands of analyses are produced per month, but there is little agreement on how to transform these data into accurate U-Th-Pb dates. Recent interlaboratory blind comparisons of zircon samples indicate that resolvable biases exist among laboratories and the sources of bias are not fully understood. Common protocols of data reduction and reporting are essential for scientists to be able to compare and interpret these data accurately.

Horstwood, Matt; Gehrels, George; Bowring, James

2010-07-01

140

Ultrashort laser ablation of PMMA and intraocular lenses  

NASA Astrophysics Data System (ADS)

The use of intraocular lenses (IOLs) is the most promising method to restore vision after cataract surgery. Several new materials, techniques, and patterns have been studied for forming and etching IOLs to improve their optical properties and reduce diffractive aberrations. This study is aimed at investigating the use of ultrashort laser pulses to ablate the surface of PMMA and intraocular lenses, and thus provide an alternative to conventional techniques. Ablation experiments were conducted using various polymer substrates (PMMA samples, hydrophobic acrylic IOL, yellow azo dye doped IOL, and hydrophilic acrylic IOL consist of 25% H2O). The irradiation was performed using 100 fs pulses of 800 nm radiation from a regeneratively amplified Ti:sapphire laser system. We investigated the ablation efficiency and the phenomenology of the ablated patterns by probing the ablation depth using a profilometer. The surface modification was examined using a high resolution optical microscope (IOLs) or atomic force microscope—AFM (PMMA samples). It was found that different polymers exhibited different ablation characteristics, a result that we attribute to the differing optical properties of the materials. In particular, it was observed that the topography of the ablation tracks created on the hydrophilic intraocular lenses was smoother in comparison to those created on the PMMA and hydrophobic lens. The yellow doped hydrophobic intraocular lenses show higher ablation efficiency than undoped hydrophobic acrylic lenses.

Serafetinides, A. A.; Makropoulou, M.; Fabrikesi, E.; Spyratou, E.; Bacharis, C.; Thomson, R. R.; Kar, A. K.

2008-10-01

141

Efficient space propulsion engines based on laser ablation  

SciTech Connect

Recent results have shown laser momentum transfer coefficients C{sub m} as large as 700 dynes/J from visible and near-infrared laser pulses with heterogeneous targets. Using inexpensive target materials, it is now possible to deliver a 1-tonne satellite from LEO to GEO in 21 days using a 10-kW onboard laser ablation engine, or to maintain several 1-tonne GEO satellites on station from Earth indefinitely using a laser with 100-W average power.

Phipps, C.R.

1993-08-01

142

Femtosecond laser ablation of polytetrafluoroethylene (Teflon) in ambient air  

NASA Astrophysics Data System (ADS)

Teflon, polytetrafluorethylene (PTFE), is an important material in bioscience and medical application due to its special characteristics (bio-compatible, nonflammable, antiadhesive, and heat resistant). The advantages of ultrashort laser processing of Teflon include a minimal thermal penetration region and low processing temperatures, precision removal of material, and good-quality feature definition. In this paper, laser processing of PTFE in ambient air by a Ti:sapphire femtosecond laser (780 nm, 110 fs) is investigated. It is found that the pulse number on each irradiated surface area must be large enough for a clear edge definition and the ablated depth increases with the pulse number. The air ionization effect at high laser fluences not only degrades the ablated structures quality but also reduces the ablation efficiency. High quality microstructures are demonstrated with controlling laser fluence below a critical fluence to exclude the air ionization effect. The ablated microstructures show strong adhesion property to liquids and clear edges that are suitable for bio-implantation applications. Theoretical calculation is used to analyze the evolution of the ablated width and depth at various laser fluences.

Wang, Z. B.; Hong, M. H.; Lu, Y. F.; Wu, D. J.; Lan, B.; Chong, T. C.

2003-05-01

143

Plasma mediated ablation of biological tissues with ultrashort laser pulses  

SciTech Connect

Plasma mediated ablation of collagen gels and porcine cornea was studied at various laser pulse durations in the range from 350 fs to 1 ns at 1,053 nm wavelength. A time resolved stress detection technique was employed to measure transient stress profiles and amplitudes. Optical microscopy was used to characterize ablation craters qualitatively, while a wide band acoustic transducer helped to quantify tissue mechanical response and the ablation threshold. The ablation threshold was measured as a function of laser pulse duration and linear absorption coefficient. For nanosecond pulses the ablation threshold was found to have a strong dependence on the linear absorption coefficient of the material. As the pulse length decreased into the subpicosecond regime the ablation threshold became insensitive to the linear absorption coefficient. The ablation efficiency was found to be insensitive to both the laser pulse duration and the linear absorption coefficient. High quality ablation craters with no thermal or mechanical damage to surrounding material were obtained with 350 fs laser pulses. The mechanism of optical breakdown at the tissue surface was theoretically investigated. In the nanosecond regime, optical breakdown proceeds as an electron collisional avalanche ionization initiated by thermal seed electrons. These seed electrons are created by heating of the tissue by linear absorption. In the ultrashort pulse range, optical breakdown is initiated by the multiphoton ionization of the irradiated medium (6 photons in case of tissue irradiated at 1,053 nm wavelength), and becomes less sensitive to the linear absorption coefficient. The energy deposition profile is insensitive to both the laser pulse duration and the linear absorption coefficient.

Oraevsky, A.A. [Lawrence Livermore National Lab., CA (United States)]|[Rice Univ., Houston, TX (United States). Dept. of Electrical Engineering; DaSilva, L.B.; Feit, M.D. [Lawrence Livermore National Lab., CA (United States)] [and others

1995-03-08

144

Theory of shock wave propagation during laser ablation  

Microsoft Academic Search

Laser ablation consists of three coupled processes: (i) heat conduction within the solid, (ii) flow through a discontinuity layer (evaporation wave) attached to the solid surface, and (iii) shock wave expansion of the laser induced plume. In this paper, a one-dimensional solution for all three coupled processes is presented. The heat conduction and the evaporation wave are solved numerically. The

Zhaoyan Zhang; George Gogos

2004-01-01

145

Investigation of laser ablated plumes using fast photography  

Microsoft Academic Search

Fast photography is used to investigate the expansion dynamics of the laser ablated plasmas in various ambient atmospheres and laser energies. Dependence of plasma parameters such as velocity, temperature, density, and pressure on time and ambient atmosphere is presented. The measured vapor pressure and temperature decrease with the increase in ambient gas pressure. The images of the expanding plumes are

A. Misra; R. K. Thareja

1999-01-01

146

Growth of metal oxide nanoparticles using pulsed laser ablation technique  

Microsoft Academic Search

Nano particles exhibit physical and chemical properties distinctively different from that of bulk due to high number of surface atoms, surface energy and surface area to volume ratio. Laser is a unique source of radiation and has been applied in the synthesis of nano structured metal oxides. The pulsed laser ablation (PLA) technique in liquid medium has been proven an

M. A. Gondal; Q. A. Drmosh; Tawfik A. Saleh; Z. H. Yamani

2011-01-01

147

UV solid state laser ablation of intraocular lenses  

NASA Astrophysics Data System (ADS)

Commercially available intraocular lenses (IOLs) are manufactured from silicone and acrylic, both rigid (e.g. PMMA) and foldable (hydrophobic or hydrophilic acrylic biomaterials), behaving different mechanical and optical properties. Recently, the use of apodizing technology to design new diffractive-refractive multifocals improved the refractive outcome of these intraocular lenses, providing good distant and near vision. There is also a major ongoing effort to refine laser refractive surgery to correct other defects besides conventional refractive errors. Using phakic IOLs to treat high myopia potentially provides better predictability and optical quality than corneal-based refractive surgery. The aim of this work was to investigate the effect of laser ablation on IOL surface shaping, by drilling circular arrays of holes, with a homemade motorized rotation stage, and scattered holes on the polymer surface. In material science, the most popular lasers used for polymer machining are the UV lasers, and, therefore, we tried in this work the 3rd and the 5th harmonic of a Q-switched Nd:YAG laser (?=355 nm and ?=213 nm respectively). The morphology of the ablated IOL surface was examined with a scanning electron microscope (SEM, Fei - Innova Nanoscope) at various laser parameters. Quantitative measurements were performed with a contact profilometer (Dektak-150), in which a mechanical stylus scanned across the surface of gold-coated IOLs (after SEM imaging) to measure variations in surface height and, finally, the ablation rates were also mathematically simulated for depicting the possible laser ablation mechanism(s). The experimental results and the theoretical modelling of UV laser interaction with polymeric IOLs are discussed in relation with the physical (optical, mechanical and thermal) properties of the material, in addition to laser radiation parameters (laser energy fluence, number of pulses). The qualitative aspects of laser ablation at ?=213 nm reveal a smooth optical surface on the intraocular lens with no irregularities, observed with other wavelengths.

Apostolopoulos, A.; Lagiou, D. P.; Evangelatos, Ch.; Spyratou, E.; Bacharis, C.; Makropoulou, M.; Serafetinides, A. A.

2013-06-01

148

Optical properties of petal-like aggregated nanocrystalline zinc oxide synthesized by laser ablation  

SciTech Connect

Highlights: Black-Right-Pointing-Pointer Petal like ZnO nanocrystals are synthesized by high frequency laser ablation in water. Black-Right-Pointing-Pointer Optical band gap of ZnO nanocrystals was tunable by changing the laser pulse energy. Black-Right-Pointing-Pointer Nonlinear optical properties and limiting threshold were obtained by Z-scan technique. -- Abstract: The results of the investigations carried out on the third-order nonlinearity in zinc oxide (ZnO) nanocrystals (NCs) by Z-scan technique are included in this paper. ZnO NCs show negative nonlinearity and good nonlinear absorption behavior at 532 nm. The third-order optical susceptibility {chi}(3) increases with enlargement of NCs due to the size dependent enhancement of exciton oscillator strength. The synthesis of ZnO NCs was performed by laser ablation from a high-purity metallic target of Zn in distilled water medium. For the ablation process, a high frequency pulsed Nd:YAG laser was employed operating at 532 nm with 100 ns pulse duration. UV-vis absorption spectroscopy illustrated the enhancement of the size of ZnO NCs upon increasing the laser pulse energy applied in ablation process. Accordingly the corresponding optical band gap (E{sub g}) decrease by increasing the size of NCs. X-ray diffraction (XRD) associated with transmission electron microscopy (TEM) was utilized to characterize the crystalline phase and also for determining the ZnO NCs morphology.

Jafarkhani, P.; Chehrghani, A. [Iranian National Centre for Laser Science and Technology (INLC), PO Box: 14665-576, Tehran (Iran, Islamic Republic of)] [Iranian National Centre for Laser Science and Technology (INLC), PO Box: 14665-576, Tehran (Iran, Islamic Republic of); Torkamany, M.J., E-mail: mjtorkamany@inlc.ir [Iranian National Centre for Laser Science and Technology (INLC), PO Box: 14665-576, Tehran (Iran, Islamic Republic of)

2012-03-15

149

Gel-modulated photo ablation using noncontact photoacoustic spectroscopy control: a new concept  

NASA Astrophysics Data System (ADS)

Refractive gels, applied on the corneal surface in situ act as laser beam modulators. Depending upon their surface shape and absorbency, they can be used to reshape irregular surfaces or induce refractive effects. Three gels (Palm I Pallikaris, Greece; Refrax 33, Imperial, USA; Biomask, Maverick USA) have been investigated using Non Contact Photoacoustic Spectroscopy (NCPAS). Their use requires on line detection and monitoring of the ablation process, indicating when the gel is ablated and the corneal tissue is exposed to the incident laser pulse. NCPAS enables this on line control. With the gels in their present form, stable ablation rates where achieved only after 200 - 400 pulses, depending upon the gel. The typical frequency shift of the Fourier -- transformed time signal of NCPAS, observed for different target materials (gels, human, and porcine cornea) allowed the discrimination of the different gels as well as from human and porcine corneal tissue (epithelium and stroma). NCPAS discriminates and identifies even those gels with similar ablation rates, using the typical frequency shift (difference >= 1 kHz). Refractive gels in combination with a powerful on-line control such as NCPAS has a potential to be used as a low cost approach for reducing or minimizing the amount of surface bound corneal optical aberrations; it could thus bypass the complexity and costs of corneal reshaping systems, using topography or wavefront based customized treatment algorithms.

Jean, Benedikt J.; Bende, Thomas

2000-06-01

150

Nanoparticle plume dynamics in femtosecond laser ablation of gold  

NASA Astrophysics Data System (ADS)

This paper describes some recent results on femtosecond laser ablation of gold. We have studied both the fast vapour/plasma and slow nanoparticle plumes using Langmuir probe, time-resolved ICCD imaging and time-resolved optical absorption measurements. The nanoparticle plume dynamics was analysed by comparing the optical emission absorption measurements with an adiabatic isentropic model of ablation plume expansion, leading to an estimate of the amount of material in the nanoparticle plume.

O'Connell, G.; Donnelly, T.; Lunney, J. G.

2014-10-01

151

Nanometer thickness laser ablation for spatial control of cell attachment  

NASA Astrophysics Data System (ADS)

We demonstrate here a new method to control the location of cells on surfaces in two dimensions, which can be applied to a number of biomedical applications including diagnostic tests and tissue engineered medical devices. Two-dimensional control over cell attachment is achieved by generation of a spatially controlled surface chemistry that allows control over protein adsorption, a process which mediates cell attachment. Here, we describe the deposition of thin allylamine plasma polymer coatings on silicon wafer and perfluorinated poly(ethylene-co-propylene) substrates, followed by grafting of a protein resistant layer of poly(ethylene oxide). Spatially controlled patterning of the surface chemistry was achieved in a fast, one-step procedure by nanometer thickness controlled laser ablation using a 248 nm excimer laser. X-ray photoelectron spectroscopy and atomic force microscopy were used to confirm the production of surface chemistry patterns with a resolution of approximately 1 µm, which is significantly below the dimensions of a single mammalian cell. Subsequent adsorption of the extracellular matrix proteins collagen I and fibronectin followed by cell culture experiments using bovine corneal epithelial cells confirmed that cell attachment is controlled by the surface chemistry pattern. The method is an effective tool for use in a number of in vitro and in vivo applications.

Thissen, H.; Hayes, J. P.; Kingshott, P.; Johnson, G.; Harvey, E. C.; Griesser, H. J.

2002-10-01

152

Raman mapping of laser-induced changes and ablation of InAs nanowires  

NASA Astrophysics Data System (ADS)

Indium arsenic (InAs) nanowires were irradiated with a focused laser beam, followed by in situ Raman spectroscopy mapping and scanning electron microscopy imaging to investigate the changes of the nanowires due to laser irradiation. It was found that laser irradiation with the power intensity above a certain threshold causes arsenic (As) atoms to disintegrate from InAs and accumulate on the surface of the nanowire; the accumulated As atoms evaporate under the continued laser irradiation. This process reduces the As content in the nanowire. The reduction of As content, in turn, lowers the melting temperature of the nanowire locally and facilitates laser ablation, which eventually fractures the nanowire. The laser irradiation induced changes of the InAs nanowires are attributed to the local temperature rises due to the irradiation, as confirmed by the Raman peak shifts. The results from this work show that in situ Raman spectroscopy mapping can provide detailed information about the entire process of laser-induced change and ablation of InAs nanowires and has the potential to become a powerful tool for the characterization of laser modification of nanowires and other nanometer-sized objects.

He, Jiayu; Chen, Pingping; Lu, Wei; Dai, Ning; Zhu, Da-Ming

2014-06-01

153

Ion implantation induced by Cu ablation at high laser fluence  

NASA Astrophysics Data System (ADS)

High energy laser plasma-produced Cu ions have been implanted in silicon substrates placed at different distances and angles with respect to the normal to the surface of the ablated target. The implanted samples have been produced using the iodine high power Prague Asterix Laser System (PALS) using 438 nm wavelength irradiating in vacuum a Cu target. The high laser pulse energy (up to 230 J) and the short pulse duration (400 ps) produced a non-equilibrium plasma expanding mainly along the normal to the Cu target surface. Time-of-flight (TOF) technique was employed, through an electrostatic ion energy analyzer (IEA) placed along the target normal, in order to measure the ion energy, the ion charge state, the energy distribution and the charge state distribution. Ions had a Boltzmann energy distributions with an energy increasing with the charge state. At a laser fluence of the order of 6 × 10 6 J/cm 2, the maximum ion energy was about 600 keV and the maximum charge state was about 27+. In order to investigate the implantation processes, Cu depth profiles have been performed with Rutherford backscattering spectrometry (RBS) of 1.5 MeV helium ions, Auger electron spectroscopy (AES) with 3 keV electron beam and 1 keV Ar sputtering ions in combination with scanning electron microscopy (SEM). Surface analysis results indicate that Cu ions are implanted within the first surface layers and that the ion penetration ranges are in agreement with the ion energy measured with IEA analysis.

Torrisi, L.; Mezzasalma, A. M.; Gammino, S.; Badziak, J.; Parys, P.; Wolowski, J.; Laska, L.; Franco, G.

2006-10-01

154

Optical, structural and morphological properties of zirconia nanoparticles prepared by laser ablation in liquids  

NASA Astrophysics Data System (ADS)

Absorption, fluorescence and Raman spectra, the structural composition and morphology of zirconia nanoparticles synthesised via the laser ablation of a metal in water and aqueous solutions of the sodium dodecyl sulphate (SDS) surfactant have been studied using absorption spectroscopy, Raman spectroscopy, X-ray diffraction and scanning electron microscopy. The results demonstrate that, exposing zirconium to intense nanosecond laser pulses at a high repetition rate in these liquids, one can obtain stable cubic, tetragonal and monoclinic crystalline phases of nanozirconia with a particle size in the range 40 – 100 nm and a Zr – SDS organic – inorganic composite. The absorption and fluorescence of the synthesised zirconia strongly depend on the SDS concentration in the starting solution. The gas – vapour bubbles forming during ablation are shown to serve as templates for the formation of hollow nanoand microstructures.

Borodina, T. I.; Val'yano, G. E.; Gololobova, O. A.; Karpukhin, V. T.; Malikov, M. M.; Strikanov, D. A.

2014-09-01

155

Nanoscale patterning of graphene through femtosecond laser ablation  

NASA Astrophysics Data System (ADS)

We report on nanometer-scale patterning of single layer graphene on SiO2/Si substrate through femtosecond laser ablation. The pulse fluence is adjusted around the single-pulse ablation threshold of graphene. It is shown that, even though both SiO2 and Si have more absorption in the linear regime compared to graphene, the substrate can be kept intact during the process. This is achieved by scanning the sample under laser illumination at speeds yielding a few numbers of overlapping pulses at a certain point, thereby effectively shielding the substrate. By adjusting laser fluence and translation speed, 400 nm wide ablation channels could be achieved over 100 ?m length. Raster scanning of the sample yields well-ordered periodic structures, provided that sufficient gap is left between channels. Nanoscale patterning of graphene without substrate damage is verified with Scanning Electron Microscope and Raman studies.

Sahin, R.; Simsek, E.; Akturk, S.

2014-02-01

156

Ablative Laser Propulsion Using Multi-Layered Material Systems  

NASA Technical Reports Server (NTRS)

Experimental investigations are ongoing to study the force imparted to materials when subjected to laser ablation. When a laser pulse of sufficient energy density impacts a material, a small amount of the material is ablated. A torsion balance is used to measure the momentum produced by the ablation process. The balance consists of a thin metal wire with a rotating pendulum suspended in the middle. The wire is fixed at both ends. Recently, multi-layered material systems were investigated. These multi-layered materials were composed of a transparent front surface and opaque sub surface. The laser pulse penetrates the transparent outer surface with minimum photon loss and vaporizes the underlying opaque layer.

Nehls, Mary; Edwards, David; Gray, Perry; Schneider, T.

2002-01-01

157

Nanostructures synthesis by femtosecond laser ablation of glasses  

NASA Astrophysics Data System (ADS)

In this article, we investigate the variations in ablation dynamics that result in diverse nanostructures on SiO2 based glass samples. A three-dimensional fibrous nanoparticle agglomerate was observed on sodalime glass when exposed to femtosecond laser irradiation. The fused nanoparticles have diameters ranging from 30 nm to 70 nm. Long continuous nanofibers of extremely high aspect ratio (certain fibers up to 100 000:1) were obtained by exposing silica glass surface to femtosecond laser irradiation at MHz repetition rate in air. A nanostructure assembly comprising of nanofiber and nanoparticle agglomerates was also observed by ablating silica glass. From our experimental analysis, it was determined that variation in bandgap and material composition alters ablation dynamics and dictates the response of glass to femtosecond laser irradiation, ultimately leading to the formation of structures with varying morphology on silica and sodalime glass. The possible underlying mechanisms that produce such nanostructures on glass specimens have also been explored.

Vipparty, D.; Tan, B.; Venkatakrishnan, K.

2012-10-01

158

Mechanical and tribological properties of CN x films deposited by reactive pulsed laser ablation  

Microsoft Academic Search

We report the tribological, mechanical, structural and compositional characteristics of CNx films deposited by excimer laser (XeCl, ?=308 nm, ?FWHM=30 ns) ablation of a graphite target in N2 atmosphere. The influence of growth conditions on structural, morphological, tribological and mechanical properties of the CNx films has been examined by X-ray Photoelectron Spectroscopy (XPS), Transmission and Scanning Electron Microscopy (TEM and

A. Zocco; A. Perrone; E. Broitman; Zs. Czigany; L. Hultman; M. Anderle; N. Laidani

2002-01-01

159

Laser ablation behaviors of SiC–ZrC coated carbon\\/carbon composites  

Microsoft Academic Search

Laser ablation behaviors of carbon\\/carbon composites with an underlying SiC layer and a surface ZrC layer were investigated using a continuous wave CO2 laser. The laser powers varied from 100W to 2000W. The results indicate that the two-layer SiC–ZrC coating can improve the laser ablation resistance of the carbon\\/carbon composites. Three ablation regions can be identified. The ablation mechanisms in

Qiaomu Liu; Litong Zhang; Fengrui Jiang; Jia Liu; Laifei Cheng; Hui Li; Yiguang Wang

2011-01-01

160

Production of copper and brass nanoparticles upon laser ablation in liquids  

SciTech Connect

The production of nanoparticles upon ablation of copper and brass by pulsed radiation from Nd:YAG and copper lasers in water, ethanol, and acetone is studied. The nanoparticles were investigated by the methods of X-ray diffractometry, optical spectroscopy, and transmission electron microscopy. The produced copper and brass nanoparticles were shown to exhibit a plasmon resonance lying in the visible spectral range near 580 and 510 nm. The brass nanoparticles produced by ablation in ethanol have a shell approximately 10-nm thick for an average dimension of 20-30 nm. A chemical modification of ethanol was observed, which manifested itself in the appearance of intense UV absorption bands. Upon laser irradiation of brass nanoparticles in a liquid their absorption spectrum gradually transformed into the spectrum of copper nanoparticles. (interaction of laser radiation with matter)

Kazakevich, Pavel V; Simakin, Aleksandr V; Shafeev, Georgii A [Scientific Center for Wave Studies, A.M.Prokhorov General Physics Institute, Russian Academy of Sciences, Moscow (Russian Federation); Voronov, Valerii V [Laser Materials and Technology Research Center, A. M. Prokhorov General Physics Institute, Russian Academy of Sciences, Moscow (Russian Federation)

2004-10-31

161

Multi-wavelength enhancement of silicon Raman scattering by nanoscale laser surface ablation  

NASA Astrophysics Data System (ADS)

In this paper, we produce nanoholes on a silicon surface by laser ablation. Those nanoholes lead to a yield enhancement of light-matter interaction. Performing Raman spectroscopy on silicon, an enhancement of its main Raman mode is observed: it is twice higher with the nanoholes compared to a flat surface. Such a feature appears whatever the excitation wavelength (488, 514.5 and 632.8 nm) and the laser power, revealing a broad band light-matter interaction enhancement. In addition, no change in the position and shape of the main Raman mode of silicon is observed, suggesting that no structural damages are induced by laser ablation. These results clearly demonstrate the potentiality of such nanostructures for the further development of silicon photonics.

Merlen, A.; Sangar, A.; Torchio, P.; Kallepalli, L. N. D.; Grojo, D.; Utéza, O.; Delaporte, P.

2013-11-01

162

Optical time of flight studies of lithium plasma in double pulse laser ablation: Evidence of inverse Bremsstrahlung absorption  

NASA Astrophysics Data System (ADS)

The early stage of formation of lithium plasma in a collinear—double pulse laser ablation mode has been studied using optical time of flight (OTOF) spectroscopy as a function of inter-pulse delay time, the distance from the target surface and the fluence of the ablation lasers. The experimental TOF measurements were carried out for lithium neutral (670.8 nm and 610.3 nm), and ionic (548.4 nm and 478.8 nm) lines. These experimental observations have been compared with that for single pulse laser ablation mode. It is found that depending on the fluence and laser pulse shape of the first pre-ablation laser and the second main ablation laser, the plasma plume formation and its characteristic features can be described in terms of plume-plume or laser-plume interaction processes. Moreover, the enhancement in the intensity of Li neutral and ionic lines is observed when the laser-plume interaction is the dominant process. Here, we see the evidence of the role of inverse Bremsstrahlung absorption process in the initial stage of formation of lithium plasma in this case.

Sivakumaran, V.; Joshi, H. C.; Singh, R. K.; Kumar, Ajai

2014-06-01

163

Below-Band-Gap Laser Ablation Of Diamond For TEM  

NASA Technical Reports Server (NTRS)

Thin, electron-transparent layers of diamond for examination in transmission electron microscope (TEM) fabricated from thicker diamond substrates by using laser beam to ablate surface of substrate. Involves use of photon energy below band gap. Growing interest in use of diamond as bulk substrate and as coating material in variety of applications has given rise to increasing need for TEM for characterization of diamond-based materials. Below-band-gap laser ablation method helps to satisfy this need. Also applied in general to cutting and etching of diamonds.

George, Thomas; Foote, Marc C.; Vasquez, Richard P.; Fortier, Edward P.; Posthill, John B.

1995-01-01

164

Fundamental Mechanisms of Pulsed Laser Ablation of Biological Tissue  

NASA Astrophysics Data System (ADS)

The ability to cut and remove biological tissue with short pulsed laser light, a process called laser ablation, has the potential to revolutionize many surgical procedures. Ablation procedures using short pulsed lasers are currently being developed or used in many fields of medicine, including cardiology, ophthalmology, dermatology, dentistry, orthopedics, and urology. Despite this, the underlying physics of the ablation process is not well understood. In fact, there is wide disagreement over whether the fundamental mechanism is primarily photothermal, photomechanical, or photochemical. In this thesis, both experimental and theoretical techniques are developed to explore this issue. The photothermal model postulates that ablation proceeds through vaporization of the target material. The photomechanical model asserts that ablation is initiated when the laser-induced tensile stress exceeds the ultimate tensile strength of the target. I have developed a three dimensional model of the thermoelastic response of tissue to short pulsed laser irradiation which allows the time dependent stress distribution to be calculated given the optical, thermal and mechanical properties of the target. A complimentary experimental technique has been developed to verify this model, measure the needed physical properties of the tissue, and record the thermoelastic response of the tissue at the onset of ablation. The results of this work have been widely disseminated to the international research community and have led to significant findings which support the photomechanical model of ablation of tissue. First, the energy deposited in tissue is an order of magnitude less than that required for vaporization. Second, unlike the one-dimensional thermoelastic model of laser-induced stress generation that has appeared in the literature, the full three-dimensional model predicts the development of significant tensile stresses on the surface of the target, precisely where ablation is observed to occur. Third, although the laser-induced temperature rise is modest, the magnitude of the stresses is sufficient to initiate mechanically destructive phenomenon. In hard materials, including bone, a gradual weakening of material with each successive laser pulse is observed and correlated with the formation of permanent microcracks within the material. In meniscus, a representative soft tissue, the growth and collapse of mechanically destructive cavitation bubbles is observed. (Copies available exclusively from MIT Libraries, Rm. 14-0551, Cambridge, MA 02139-4307. Ph. 617 -253-5668; Fax 617-253-1690.).

Albagli, Douglas

165

Hydrodynamic simulations of metal ablation by femtosecond laser irradiation  

SciTech Connect

Ablation of Cu and Al targets has been performed with 170 fs laser pulses in the intensity range of 10{sup 12}-10{sup 14} W cm{sup -2}. We compare the measured removal depth with 1D hydrodynamic simulations. The electron-ion temperature decoupling is taken into account using the standard two-temperature model. The influence of the early heat transfer by electronic thermal conduction on hydrodynamic material expansion and mechanical behavior is investigated. A good agreement between experimental and numerical matter ablation rates shows the importance of including solid-to-vapor evolution of the metal in the current modeling of the laser matter interaction.

Colombier, J.P. [CEA/DAM Ile de France, Dept. de Physique Theorique et Appliquee, B.P. 12, 91680 Bruyeres-le-Chatel, (France); Laboratoire Traitement du Signal et Instrumentation (TSI), Universite Jean Monnet, UMR CNRS 5516, 42000 Saint-Etienne (France); Combis, P.; Bonneau, F. [CEA/DAM Ile de France, Dept. de Physique Theorique et Appliquee, B.P. 12, 91680 Bruyeres-le-Chatel (France); Le Harzic, R.; Audouard, E. [Laboratoire Traitement du Signal et Instrumentation (TSI), Universite Jean Monnet, UMR CNRS 5516, 42000 Saint-Etienne (France)

2005-04-15

166

Pulsed laser ablation of solids and critical phenomena  

NASA Astrophysics Data System (ADS)

We consider the possible manifestations of critical phenomena under pulsed laser ablation (PLA). The mechanism of phase explosion under nanosecond laser ablation is considered and the possibility of estimating the critical temperature from PLA experiments is discussed. A model based on the Euler equations and generalized van der Waals equation is developed to describe rarefaction shock waves (RSW) in near-critical matter. For a near-surface slab of a gold target heated above the critical point and expanding freely in vacuum, the evolution of the RSW has been studied. The possibility of RSW formation in stellar matter is discussed.

Bulgakova, Nadezhda M.; Bulgakov, Alexander V.; Bourakov, Igor M.; Bulgakova, Natalia A.

2002-09-01

167

Vibration testing based on impulse response excited by laser ablation  

NASA Astrophysics Data System (ADS)

This paper proposes an innovative vibration testing method based on impulse response excited by laser ablation. In conventional vibration testing using an impulse hammer, high-frequency elements of over tens of kilohertz are barely present in the excitation force. A pulsed high-power YAG laser is used in this study for producing an ideal impulse force on a structural surface. Illuminating a point on a metal with the well-focused YAG laser, laser ablation is caused by generation of plasma on the metal. As a result, an ideal impulse excitation force generated by laser ablation is applied to the point on the structure. Therefore, it is possible to measure high-frequency FRFs due to the laser excitation. A water droplet overlay on the metal is used to adjust the force magnitude of laser excitation. An aluminum block that has nine natural frequencies below 40 kHz is employed as a test piece. The validity of the proposed method is verified by comparing the FRFs of the block obtained by the laser excitation, impulse hammer, and finite element analysis. Furthermore, the relationship between accuracy of FRF measurements and sensitivity of sensors is investigated.

Kajiwara, Itsuro; Hosoya, Naoki

2011-10-01

168

Thermal melting and ablation of silicon by femtosecond laser radiation  

SciTech Connect

The space-time dynamics of thermal melting, subsurface cavitation, spallative ablation, and fragmentation ablation of the silicon surface excited by single IR femtosecond laser pulses is studied by timeresolved optical reflection microscopy. This dynamics is revealed by monitoring picosecond and (sub)nanosecond oscillations of probe pulse reflection, which is modulated by picosecond acoustic reverberations in the dynamically growing surface melt subjected to ablation and having another acoustic impedance, and by optical interference between the probe pulse replicas reflected by the spalled layer surface and the layer retained on the target surface. The acoustic reverberation periods change during the growth and ablation of the surface melt film, which makes it possible to quantitatively estimate the contributions of these processes to the thermal dynamics of the material surface. The results on the thermal dynamics of laser excitation are supported by dynamic measurements of the ablation parameters using noncontact ultrasonic diagnostics, scanning electron microscopy, atomic force microscopy, and optical interference microscopy of the modified regions appearing on the silicon surface after ablation.

Ionin, A. A.; Kudryashov, S. I., E-mail: sikudr@lebedev.ru; Seleznev, L. V.; Sinitsyn, D. V. [Russian Academy of Sciences, Lebedev Physical Institute (Russian Federation)] [Russian Academy of Sciences, Lebedev Physical Institute (Russian Federation); Bunkin, A. F.; Lednev, V. N.; Pershin, S. M. [Russian Academy of Sciences, General Physics Institute (Russian Federation)] [Russian Academy of Sciences, General Physics Institute (Russian Federation)

2013-03-15

169

CO{sub 2} Laser Ablation Propulsion Tractor Beams  

SciTech Connect

Manipulation of objects at a distance has already been achieved with no small measure of success in the realm of microscopic objects on the scale size of nanometers to micrometers in applications including laser trapping and laser tweezers. However, there has been relatively little effort to apply such remote control to macroscopic systems. A space tractor beam could be applied to a wide range of applications, including removal of orbital debris, facilitation of spacecraft docking, adjustment of satellite attitude or orbital position, etc. In this paper, an ablative laser propulsion tractor beam is demonstrated based on radiation from a CO{sub 2} laser. Cooperative, layered polymer targets were used for remote impulse generation using a CO{sub 2} laser. The use of a structured ablatant enabling switching between thrust directional parity (i.e., forward or reverse) and imparting torque to a remote target. Fluence-dependent results are presented in the context of polymer ablation modeling work and with consideration of confined ablation effects.

Sinko, John E. [Micro-Nano Global Center of Excellence, Graduate School of Engineering, Nagoya University, Furo-cho, Chikusa-ku, Nagoya, 464-8603 (Japan); Schlecht, Clifford A. [Institute for Materials and Complexity, Saint Louis, MO 63112 (United States)

2010-05-06

170

Laser ablation of liquid surface in air induced by laser irradiation through liquid medium  

Microsoft Academic Search

The pulse laser ablation of a liquid surface in air when induced by laser irradiation through a liquid medium has been experimentally\\u000a investigated. A supersonic liquid jet is observed at the liquid–air interface. The liquid surface layer is driven by a plasma\\u000a plume that is produced by laser ablation at the layer, resulting in a liquid jet. This phenomenon occurs only

Yuji Utsunomiya; Takashi Kajiwara; Takashi Nishiyama; Kunihito Nagayama; Shiro Kubota; Motonao Nakahara

2010-01-01

171

Cluster Generation Under Pulsed Laser Ablation Of Compound Semiconductors  

SciTech Connect

A comparative experimental study of pulsed laser ablation in vacuum of two binary semiconductors, zinc oxide and indium phosphide, has been performed using IR- and visible laser pulses with particular attention to cluster generation. Neutral and cationic Zn{sub n}O{sub m} and In{sub n}P{sub m} particles of various stoichiometry have been produced and investigated by time-of-flight mass spectrometry. At ZnO ablation, large cationic (n>9) and all neutral clusters are mainly stoichiometric in the ablation plume. In contrast, indium phosphide clusters are strongly indium-rich with In{sub 4}P being a magic cluster. Analysis of the plume composition upon laser exposure has revealed congruent vaporization of ZnO and a disproportionate loss of phosphorus by the irradiated InP surface. Plume expansion conditions under ZnO ablation are shown to be favorable for stoichiometric cluster formation. A delayed vaporization of phosphorus under InP ablation has been observed that results in generation of off-stoichiometric clusters.

Bulgakov, Alexander V.; Evtushenko, Anton B.; Shukhov, Yuri G. [Institute of Thermophysics SB RAS, Lavrentyev Ave. 1, 630090 Novosibirsk (Russian Federation); Ozerov, Igor; Marine, Wladimir [Universite de la Mediterranee, CINaM, UPR CNRS 3118, 13288 Marseille (France)

2010-10-08

172

Wavelength-Dependent Conformational Changes in Collagen after Mid-Infrared Laser Ablation of Cornea  

PubMed Central

We ablated porcine corneas with a free electron laser tuned to either 2.77 or 6.45 ?m, two matched wavelengths that predominantly target water and protein, respectively. The ejected nonvolatile debris and the crater left behind were examined by circular dichroism, Raman spectroscopy, and scanning electron microscopy to characterize the postablation conformation of collagen proteins. We found near-complete unfolding of collagen secondary and tertiary structure at either ablating wavelength. On the other hand, we found excess fibril swelling and evidence for excess cis-hydroxyproline in the 6.45-?m debris. These results support the hypothesis that the favorable ablative properties of protein-targeting wavelengths rest on selective heating of tissue proteins. PMID:17933877

Xiao, Yaowu; Guo, Mingsheng; Zhang, Peng; Shanmugam, Ganesh; Polavarapu, Prasad L.; Hutson, M. Shane

2008-01-01

173

Ablation-initiated Isotope-selective Atomic Absorption Spectroscopy of Lanthanide Elements  

SciTech Connect

For remote isotope analysis of low-decontaminated trans-uranium (TRU) fuel, absorption spectroscopy has been applied to a laser-ablated plume of lanthanide elements. To improve isotopic selectivity and detection sensitivity of the ablated species, various experimental conditions were optimized. Isotope-selective absorption spectra were measured by observing the slow component of the plume produced under low-pressure rare-gas ambient. The measured minimum line width of about 0.9 GHz was close to the Doppler width of the Gd atomic transition at room temperature. The relaxation rate of high-lying metastable state was found to be higher than that of the ground state, which suggests that higher analytical sensitivity can be obtained using low-lying state transition. Under helium gas environment, Doppler splitting was caused from particle motion. This effect was considered for optimization for isotope selection and analysis. Some analytical performances of this method were determined under optimum conditions and were discussed.

Miyabe, M.; Oba, M.; Iimura, H.; Akaoka, K.; Maruyama, Y.; Wakaida, I.; Watanabe, K. [Division of Environment and Radiation Science, Japan Atomic Energy Agency, Tokai-mura, Ibaraki-ken (Japan)

2009-03-17

174

High resolution selective multilayer laser processing by nanosecond laser ablation of metal nanoparticle films  

SciTech Connect

Ablation of gold nanoparticle films on polymer was explored using a nanosecond pulsed laser, with the goal to achieve feature size reduction and functionality not amenable with inkjet printing. The ablation threshold fluence for the unsintered nanoparticle deposit was at least ten times lower than the reported threshold for the bulk film. This could be explained by the combined effects of melting temperature depression, lower conductive heat transfer loss, strong absorption of the incident laser beam, and the relatively weak bonding between nanoparticles. The ablation physics were verified by the nanoparticle sintering characterization, ablation threshold measurement, time resolved ablation plume shadowgraphs, analysis of ablation ejecta, and the measurement and calculation of optical properties. High resolution and clean feature fabrication with small energy and selective multilayer processing are demonstrated.

Ko, Seung H.; Pan Heng; Hwang, David J.; Chung, Jaewon; Ryu, Sangil; Grigoropoulos, Costas P.; Poulikakos, Dimos [Laser Thermal Laboratory, Department of Mechanical Engineering, University of California, Berkeley, California 94720-1740 (United States); Laboratory of Thermodynamics in Emerging Technologies, Department of Mechanical and Process Engineering, ETH Zurich, 8092 Zurich (Switzerland)

2007-11-01

175

Laser ablative surface treatment for enhanced bonding of Ti-6Al-4V alloy.  

PubMed

Adhesive bonding offers many advantages over mechanical fastening, but requires certification before it can be incorporated in primary structures for commercial aviation without disbond-arrestment features or redundant load paths. Surface preparation is widely recognized as the key step to producing robust and predictable adhesive bonds. Surface preparation by laser ablation provides an alternative to the expensive, hazardous, polluting, and less precise practices used currently such as chemical-dip, manual abrasion and grit blast. This report documents preliminary testing of a surface preparation technique using laser ablation as a replacement for the chemical etch and abrasive processes currently applied to Ti-6Al-4V alloy adherends. Surface roughness and surface chemical composition were characterized using interference microscopy and X-ray photoelectron spectroscopy, respectively. A technique for fluorescence visualization was developed which allowed for quantitative failure mode analysis. Wedge crack extension testing in a hot, humid environment indicated the relative effectiveness of various surface treatments. Increasing ablation duty cycle reduced crack propagation and adhesive failure. Single lap shear testing showed an increase in strength and durability as laser ablation duty cycle and power were increased. Chemical analyses showed trends for surface chemical species, which correlated with improved bond strength and durability. PMID:23317556

Palmieri, Frank L; Watson, Kent A; Morales, Guillermo; Williams, Thomas; Hicks, Robert; Wohl, Christopher J; Hopkins, John W; Connell, John W

2013-02-01

176

Ablation scaling in laser-produced plasmas with laser intensity, laser wavelength, and target atomic number  

NASA Astrophysics Data System (ADS)

Layered target experiments at 1.06 ?m have been performed in order to measure the mass-ablation rate ? and the ablation pressure Pa as a function of absorbed laser intensity Ia, laser wavelength ?L, and target atomic number Z in steady-state ablation dominated by nonlocalized inverse bremsstrahlung absorption. The results can be expressed as ?exp(kg/ sec cm2)?65 [Ia(W/cm2)/1013]5/9 ?-4/9L(?m)Z1/4 and Pa(Mbar)?2.5[Ia(W/ cm 2)/ 1013]7/9 ?-2/9L(?m)Z1/8. The measured results show good agreement with theory for nonlocalized absorption and with data of others.

Dahmani, Faiz

1992-06-01

177

Laser ablation in a liquid-confined environment using a nanosecond laser pulse  

SciTech Connect

Laser ablation of aluminum metal with 1 ns, 800 nm pulse at low radiant exposures was investigated in air (dry) and water (wet) environments. Compared to dry ablation, an approximately eight times increase in material removal rate was associated with wet ablation. Based on optical reflectance and scanning electron microscope images, bubble formation/collapse was responsible for augmented acoustic pressure and ablation performance. Numerically simulated temperature distributions during wet ablation were consistent with the occurrence of explosive water vaporization near the critical temperature of water. Strong pressure emission during liquid vaporization and jet formation can account for enhanced ablation process. Radial expansion of bubbles minimized the redeposition of debris, leading to improvements in energy coupling to the target and ablation performance.

Kang, Hyun Wook [American Medical Systems, Minnetonka, Minnesota 55343 (United States); Lee, Ho [School of Mechanical Engineering, Kyungpook National University, Dae-gu 702-701 (Korea, Republic of); Welch, Ashley J. [Department of Biomedical Engineering, University of Texas at Austin, Austin, Texas 78712 (United States)

2008-04-15

178

Laser induced modification and ablation of InAs nanowires  

SciTech Connect

InAs nanowires were irradiated locally under an ambient condition using a focused laser beam, which led to laser ablation and thinning of the nanowires. We show that the laser beam can induce a reduction of the local As concentration in an InAs nanowire; the change leads to a significant decrease of local melting temperature of InAs, which results in the thinning and eventually breaking of the nanowire. The results indicate that chemical and mechanical modifications of an InAs nanowire can be accomplished by using a confocal laser beam, which may prove to be a convenient approach in fabricating nanostructural materials and nanodevices.

He Jiayu; Chen Pingping; Lu Wei; Dai Ning [Shanghai Institute of Technical Physics, Academy Science of China, Shanghai (China); Zhu Daming [Department of Physics, University of Missouri - Kansas City, Kansas City, Missouri 64110 (United States)

2012-05-01

179

Effects of laser ablated silver nanoparticles on Lemna minor.  

PubMed

The present study investigates and models the effect of laser ablated silver nanoparticles (AgNPs) on the development of the aquatic macrophyte Lemna minor. Toxic effects of five different AgNP concentrations (8, 16, 32, 96 and 128 ?g L(-1)) on L. minor were recorded over seven days under simulated natural conditions. Biosorption of AgNPs by L. minor was modeled using four sorption isotherms, and the sorption behavior was found to agree most closely with the Langmuir-Freundlich model (R(2)=0.997). While toxic effects of AgNPs could be observed in all models and concentrations, the greatest increase in toxicity was in the 8-32 ?g L(-1) range. Dry weight- and frond number-based inhibition experiments suggest that growth inhibition does not necessarily scale with AgNP concentration, and that slight fluctuations in inhibition rates exist over certain concentration ranges. Very close fits (R(2)=0.999) were obtained for all removal models, suggesting that the fluctuations are not caused by experimental variation. In addition, L. minor was found to be a successful bioremediation agent for AgNPs, and displayed higher removal rates for increasing AgNP doses. FT-IR spectroscopy suggests that carbonyl groups are involved in AgNP remediation. PMID:24529395

Üçüncü, Esra; Özkan, Alper D; Kur?ungöz, Canan; Ülger, Zeynep E; Ölmez, Tolga T; Tekinay, Turgay; Ortaç, Bülend; Tunca, Evren

2014-08-01

180

Laser ablation and selective excitation directed to trace element analysis  

Microsoft Academic Search

A trace (element) analyser based on laser ablation and selectively excited radiation is proposed as an ultramicro-ultratrace technique for quantitative element analysis. Measurements of trace quantities of chromium in samples of NBS standard reference material (steel), doped skim milk powder and doped flour were undertaken. There is a linear 45 deg slope for Log\\/Log plot dependence of signal versus concentration

V. H. S. Kwong

1980-01-01

181

Laser ablation assisted adhesive bonding of automotive structural composites  

SciTech Connect

Laser ablation has been evaluated as a surface pretreatment prior to adhesive bonding. In prior experimental work, it was observed that when adhesively bonded, composite, single lap shear samples fail, the fracture often occurs at either the adhesive/adherend interface or in the resin rich surface layer of the composite. These two areas represent the weakest portion of the joint. Laser ablation pretreatment generates areas where the resin on the composite surface is selectively removed leaving behind exposed reinforcing fibers which are the major load bearing members of the composite. In a subsequent adhesive bonding operation, this allows portions of the fibers to be encapsulated in the adhesive while other portions of the fiber remain in the composite resin. This type of pretreatment permits fibers to bridge and reinforce the interface between adhesive and adherend. A secondary benefit is the removal of surface contaminantes by pyrolysis. Microscopic observation of laser ablated surfaces indicates a prominent, fiber rich area. Results of the mechanical evaluation indicated that the lap shear strength for laser ablated samples was significantly higher than specimens with no pretreatment or with solvent cleaning only, but were slightly lower than specimens that were mechanically roughened and cleaned with solvents prior to bonding.

Boeman, R.G.; Paulauskas, F.L.; Warren, C.D.

1999-07-03

182

Mechanical properties of calcium phosphate coatings deposited by laser ablation  

Microsoft Academic Search

Amorphous calcium phosphate and crystalline hydroxyapatite coatings with different morphologies were deposited onto Ti–6Al–4V substrates by means of the laser ablation technique. The strength of adhesion of the coatings to the substrate and their mode of fracture were evaluated through the scratch test technique and scanning electron microscopy. The effect of wet immersion on the adhesion was also assessed. The

L Clèries; E Mart??nez; J. M Fernández-Pradas; G Sardin; J Esteve; J. L Morenza

2000-01-01

183

Elemental fractionation in laser ablation inductively coupled plasma mass spectrometry  

Microsoft Academic Search

The major challenge to the use of laser ablation sample introduction, combined with inductively coupled plasma mass spectrometry, is the problem of calibration. In the geological analysis of minerals, calibration is complicated by the extraordinarily wide variety of sample matrices which may be encountered. While there is a lack of mineral standards with well characterized concentrations near 1 g\\/g, the NIST

H. P. Longerich; D. Günther; S. E. Jackson

1996-01-01

184

Magnetically Guided Laser Ablation for High Specific Impulse Thrusters  

Microsoft Academic Search

Laser ablation has long been recognized as a method of obtaining very high temperature plasmas which can form a basis for ultra high specific impulse thrust devices. In the current work, research efforts were directed to explore the use of magnetic field with a strength of up to 4.5 Tesla to direct a laser (1064 nm YAG, 200-450 mJ\\/pulse) generated

S. H. Zaidi; T. W. Smith; R. Murray; L. Qian; R. B. Miles; K. Kremeyer

185

Laser-plasma interactions in 532 nm ablation of Si  

Microsoft Academic Search

Single-crystal Si was ablated by pulsed 532 nm laser radiation, and the volume of removed material and the time-resolved current of ejected ions were measured. These data were used to determine the ion fraction of ejected material. The ion fractions provide direct evidence that the break point is due to the laser-plasma interaction. This is confirmed by the speed distributions

Gyoowan Han; P. Terrence Murray

2000-01-01

186

Comparative study on laser tissue ablation between PV and HPS lasers  

NASA Astrophysics Data System (ADS)

Laser therapy for obstructive benign prostatic hyperplasia (BPH) has gained broad adoption due to effective tissue removal, immediate hemostasis, and minor complications. The aim of this study is to quantitatively compare ablation characteristics of PV (Photoselective Vaporization) and the newly introduced HPS (High Performance System) 532 nm lasers. Bovine prostatic tissues were ablated in vitro, using a custom-made scanning system. Laser-induced volume produced by two lasers was quantified as a function of applied power, fiber working distance (WD), and treatment speed. Given the same power of 80 W and speed of 4 mm/s, HPS created up to 50 % higher tissue ablation volume than PV did. PV induced a rapid decrease of ablation volume when WD increased from 0.5 mm to 3 mm while HPS yielded almost constant tissue removal up to 3 mm for both 80 W and 120 W. As the treatment speed increased, both lasers reached saturation in tissue ablation volume. Lastly, both PV and HPS lasers exhibited approximately 1 mm thick heat affected zone (HAZ) in this study although HPS created twice deeper ablation channels with a depth of up to 4 mm. Due to a smaller beam size and a higher output power, HPS maximized tissue ablation rate with minimal thermal effects to the adjacent tissue. Furthermore, more collimated beam characteristics provides more spatial flexibility and may even help to decrease the rate of fiber degradation associated with thermal damage from debris reattachment to the tip.

Kang, Hyun Wook; Jebens, David; Mitchell, Gerald; Koullick, Ed

2008-02-01

187

Morphological and structural studies of WO x thin films deposited by laser ablation  

NASA Astrophysics Data System (ADS)

Tungsten oxide is an interesting compound with many applications in gas sensors, electrochromic and photochromic devices. Thin films of tungsten oxide were obtained by pulsed laser deposition (PLD) and radio frequency assisted PLD (RF-PLD). A tungsten target was ablated in reactive oxygen atmosphere (0.01-0.05 mbar). The deposition parameters such as laser fluence, substrate temperature, radiofrequency power were varied, while different materials (Corning glass and silicon) have been used as substrates. The obtained films showed good adhesion to the substrate and uniform surface aspect, which are important properties for applications. X-ray diffraction, Auger electron, Raman spectroscopies and atomic force microscopy were used for characterization.

Filipescu, M.; Orlando, S.; Russo, V.; Lamperti, A.; Purice, A.; Moldovan, A.; Dinescu, M.

2007-07-01

188

Ablation by ultrashort laser pulses: Atomistic and thermodynamic analysis of the processes at the ablation threshold  

NASA Astrophysics Data System (ADS)

Ultrafast laser irradiation of solids may ablate material off the surface. We study this process for thin films using molecular-dynamics simulation and thermodynamic analysis. Both metals and Lennard-Jones (LJ) materials are studied. We find that despite the large difference in thermodynamical properties between these two classes of materials—e.g., for aluminum versus LJ the ratio Tc/Ttr of critical to triple-point temperature differs by more than a factor of 4—the values of the ablation threshold energy Eabl normalized to the cohesion energy, ?abl=Eabl/Ecoh , are surprisingly universal: all are near 0.3 with ±30% scattering. The difference in the ratio Tc/Ttr means that for metals the melting threshold ?m is low, ?m?abl . This thermodynamical consideration gives a simple explanation for the difference between metals and LJ. It explains why despite the universality in ?abl , metals thermomechanically ablate always from the liquid state. This is opposite to LJ materials, which (near threshold) ablate from the solid state. Furthermore, we find that immediately below the ablation threshold, the formation of large voids (cavitation) in the irradiated material leads to a strong temporary expansion on a very slow time scale. This feature is easily distinguished from the acoustic oscillations governing the material response at smaller intensities, on the one hand, and the ablation occurring at larger intensities, on the other hand. This finding allows us to explain the puzzle of huge surface excursions found in experiments at near-threshold laser irradiation.

Upadhyay, Arun K.; Inogamov, Nail A.; Rethfeld, Bärbel; Urbassek, Herbert M.

2008-07-01

189

Ablation by ultrashort laser pulses: Atomistic and thermodynamic analysis of the processes at the ablation threshold  

SciTech Connect

Ultrafast laser irradiation of solids may ablate material off the surface. We study this process for thin films using molecular-dynamics simulation and thermodynamic analysis. Both metals and Lennard-Jones (LJ) materials are studied. We find that despite the large difference in thermodynamical properties between these two classes of materials--e.g., for aluminum versus LJ the ratio T{sub c}/T{sub tr} of critical to triple-point temperature differs by more than a factor of 4--the values of the ablation threshold energy E{sub abl} normalized to the cohesion energy, {epsilon}{sub abl}=E{sub abl}/E{sub coh}, are surprisingly universal: all are near 0.3 with {+-}30% scattering. The difference in the ratio T{sub c}/T{sub tr} means that for metals the melting threshold {epsilon}{sub m} is low, {epsilon}{sub m}<{epsilon}{sub abl}, while for LJ it is high, {epsilon}{sub m}>{epsilon}{sub abl}. This thermodynamical consideration gives a simple explanation for the difference between metals and LJ. It explains why despite the universality in {epsilon}{sub abl}, metals thermomechanically ablate always from the liquid state. This is opposite to LJ materials, which (near threshold) ablate from the solid state. Furthermore, we find that immediately below the ablation threshold, the formation of large voids (cavitation) in the irradiated material leads to a strong temporary expansion on a very slow time scale. This feature is easily distinguished from the acoustic oscillations governing the material response at smaller intensities, on the one hand, and the ablation occurring at larger intensities, on the other hand. This finding allows us to explain the puzzle of huge surface excursions found in experiments at near-threshold laser irradiation.

Upadhyay, Arun K. [Department of Materials Science and Engineering, University of Michigan, Ann Arbor, Michigan 48109-2136 (United States); Inogamov, Nail A. [Landau Institute for Theoretical Physics, Russian Academy of Science, Kosygina 2, 117940 Moscow (Russian Federation); Rethfeld, Baerbel; Urbassek, Herbert M. [Fachbereich Physik, Universitaet Kaiserslautern, Erwin-Schroedinger-Strasse, D-67663 Kaiserslautern (Germany)

2008-07-15

190

Recent advances in laser ablation modelling for asteroid deflection methods  

NASA Astrophysics Data System (ADS)

Over the past few years, a series of studies have demonstrated the theoretical benefits of using laser ablation in order to mitigate the threat of a potential asteroid on a collision course with earth. Compared to other slow-push mitigation strategies, laser ablation allows for a significant reduction in fuel consumption since the ablated material is used as propellant. A precise modelling of the ablation process is however difficult due to the high variability in the physical parameters encountered among the different asteroids as well as the scarcity of experimental studies available in the literature. In this paper, we derive a new thermal model to simulate the efficiency of a laser-based detector. The useful material properties are first derived from thermochemical tables and equilibrium thermodynamic considerations. These properties are then injected in a 3D axisymetrical thermal model developed in Matlab. A temperature-dependent conduction flux is imposed on the exterior boundary condition that takes into account the balance between the incident power and the power losses due to the vaporization process across the Knudsen layer and the radiations respectively. A non-linear solver is finally used and the solution integrated over the ablation front to reconstruct the net thrust and the global mass flow. Compared to an initial 1D model, this new approach shows the importance of the parietal radiation losses in the case of a CW laser. Despite the low energy conversion efficiency, this new model still demonstrates the theoretical benefit of using lasers over more conventional low-thrust strategies.

Thiry, Nicolas; Vasile, Massimiliano

2014-09-01

191

A review of Thulium fiber laser ablation of kidney stones  

NASA Astrophysics Data System (ADS)

The clinical solid-state Holmium:YAG laser lithotripter (?=2120 nm) is capable of operating at high pulse energies, but its efficient operation is limited to low pulse rates during lithotripsy. The diode-pumped experimental Thulium Fiber Laser (?=1908 nm) is limited to low pulse energies, but can operate at high pulse rates. This review compares stone ablation threshold, ablation rate, and retropulsion effects for Ho:YAG and TFL. Laser lithotripsy complications also include optical fiber bending failure resulting in endoscope damage and low irrigation rates leading to poor visibility. Both problems are related to fiber diameter and limited by Ho:YAG laser multimode spatial beam profile. This study exploits TFL spatial beam profile for higher power transmission through smaller fibers. A short taper is also studied for expanding TFL beam at the distal tip of a small-core fiber. Stone mass loss, stone crater depths, fiber transmission losses, fiber burn-back, irrigation rates, and deflection through a flexible ureteroscope were measured for tapered fiber and compared with conventional fibers. The stone ablation threshold for TFL was four times lower than for Ho:YAG. Stone retropulsion with Ho:YAG increased linearly with pulse energy. Retropulsion with TFL was minimal at pulse rates < 150 Hz, then rapidly increased at higher pulse rates. TFL beam profile provides higher laser power through smaller fibers than Ho:YAG laser, potentially reducing fiber failure and endoscope damage and allowing greater irrigation rates for improved visibility and safety. Use of a short tapered distal fiber tip also allows expansion of the laser beam, resulting in decreased fiber tip damage compared to conventional fibers, without compromising fiber bending, stone ablation efficiency, or irrigation rates.

Fried, Nathaniel M.; Blackmon, Richard L.; Irby, Pierce B.

2011-02-01

192

Growth of SiO(x) nanowires by laser ablation.  

PubMed

Amorphous SiO(x) nanowires (NWs) were synthesized using laser ablation of silicon-containing targets. The influence of various parameters such as target composition, substrate type, substrate temperature and carrier gas on the growth process was studied. The NWs were characterized using high resolution scanning and transmission electron microscopes (HRSEM and HRTEM) with their attachments: electron dispersive spectroscopy (EDS) and energy electron loss spectroscopy (EELS). A metal catalyst was found essential for the NW growth. A growth temperature higher than 1000?°C was necessary for the NW formation using an Ar-based carrier gas at 500 Torr. The use of Ar-5%H(2) instead of pure Ar resulted in a higher yield and longer NWs. Application of a diffusion barrier on top of the Si substrate guaranteed the availability of metal catalyst droplets on the surface, essential for the NW growth. Ni was found to be a better catalyst than Au in terms of the NW yield and length. Two alternative sequences for the evolution of the amorphous SiO(x) NWs were considered: (a) the formation of Si NWs first and their complete oxidation afterwards, which seems to be doubtful, (b) the direct formation of SiO(x) NWs, which is more likely to occur. The direct formation mechanism was proposed to advance in three stages: preferential adsorption of SiO(x) clusters on the catalyst surface first, a successive surface diffusion to the catalyst droplet lower hemisphere, and finally the formation and growth of the NW between the catalyst and the substrate. PMID:21730706

Aharonovich, Igor; Tamir, Shoshana; Lifshitz, Yeshayahu

2008-02-13

193

Laser Spectroscopy of Transuranium Elements  

Microsoft Academic Search

The present paper aims to discuss the prospects for nuclear structure investigation of the transuranium elements by laser spectroscopy. The authors lay stress on two peculiarities of the nuclear structure in this region: the deformed shell closure at neutron number N = 152 and the appearance of superdeformed isomeric states. A laser spectroscopic experimental method is proposed for studying these

Yu. P. Gangrsky; D. V. Karaivanov; K. P. Marinova; B. N. Markov; Yu. E. Penionshkevich; S. G. Zemlyanoi

2005-01-01

194

Ultrafast laser induced breakdown spectroscopy for high spatial resolution chemical analysis  

NASA Astrophysics Data System (ADS)

Femtosecond laser induced breakdown spectroscopy (LIBS) was used to identify the spatial resolution limitations and assess the minimal detectable mass restrictions in laser-ablation based chemical analysis. The atomic emission of sodium (Na) and potassium (K) dopants in transparent dielectric Mica matrices was studied, to find that both these elements could be detected from 450 nm diameter ablation craters, full-width-at-half-maximum (FWHM). Under optimal conditions, mass as low as 220 ag was measured, demonstrating the feasibility of using laser-ablation based chemical analysis to achieve high spatial resolution elemental analysis in real-time and at atmospheric pressure conditions.

Zorba, Vassilia; Mao, Xianglei; Russo, Richard E.

2011-02-01

195

Pulsed laser ablation plasmas generated in CO{sub 2} under high-pressure conditions up to supercritical fluid  

SciTech Connect

Pulsed laser ablation of solids in supercritical media has a large potential for nanomaterials fabrication. We investigated plasmas generated by pulsed laser ablation of Ni targets in CO{sub 2} at pressures ranging from 0.1 to 16 MPa at 304.5 K. Plasma species were characterized by optical emission spectroscopy, and the evolution of cavitation bubbles and shockwaves were observed by time-resolved shadowgraph imaging. Ni and O atomic emissions decreased with increasing gas pressure; however, near the critical point the intensities reached local maxima, probably due to the enhancement of the plasma excitation and effective quenching resulting from the large density fluctuation.

Kato, Toru; Stauss, Sven; Kato, Satoshi; Urabe, Keiichiro; Terashima, Kazuo [Department of Advanced Materials Science, Graduate School of Frontier Sciences, University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8561 (Japan); Baba, Motoyoshi; Suemoto, Tohru [Division of Advanced Spectroscopy, Institute for Solid State Physics, The University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8581 (Japan)

2012-11-26

196

Infrared laser ablation atmospheric pressure photoionization mass spectrometry.  

PubMed

In this paper we introduce laser ablation atmospheric pressure photoionization (LAAPPI), a novel atmospheric pressure ion source for mass spectrometry. In LAAPPI the analytes are ablated from water-rich solid samples or from aqueous solutions with an infrared (IR) laser running at 2.94 ?m wavelength. Approximately 12 mm above the sample surface, the ablation plume is intercepted with an orthogonal hot solvent (e.g., toluene or anisole) jet, which is generated by a heated nebulizer microchip and directed toward the mass spectrometer inlet. The ablated analytes are desolvated and ionized in the gas-phase by atmospheric pressure photoionization using a 10 eV vacuum ultraviolet krypton discharge lamp. The effect of operational parameters and spray solvent on the performance of LAAPPI is studied. LAAPPI offers ~300 ?m lateral resolution comparable to, e.g., matrix-assisted laser desorption ionization. In addition to polar compounds, LAAPPI efficiently ionizes neutral and nonpolar compounds. The bioanalytical application of the method is demonstrated by the direct LAAPPI analysis of rat brain tissue sections and sour orange (Citrus aurantium) leaves. PMID:22242626

Vaikkinen, Anu; Shrestha, Bindesh; Kauppila, Tiina J; Vertes, Akos; Kostiainen, Risto

2012-02-01

197

Signal enhancement of lead and arsenic in soil using laser ablation combined with fast electric discharge  

NASA Astrophysics Data System (ADS)

In comparison to the traditional single pulse laser induced breakdown spectroscopy (SP-LIBS), a significant enhancement of atomic emission of lead and arsenic from laser plasma of soil has been demonstrated by the use of a laser ablation and fast pulse discharge plasma spectroscopy technique (LA-FPDPS). In this technique, a specifically designed high voltage and rapid discharge circuit was used to reheat the laser plasma and to enhance the plasma emission. A rapid and time damped alternating discharge current was observed with a short oscillating period ˜ 0.6 ?s and sustained for about 6 ?s. The peak intensities of Pb (283.31 nm) and As (286.04 nm) lines from soil plasma emission were greatly enhanced when compare to the traditional single pulse (SP) LIBS system. In addition, the precision of measurements in terms of the relative standard deviation (RSD) and the signal to noise ( S/ N) ratios were also improved. Scanning electron microscopy (SEM) images of the laser ablation regions indicated that the plasma reheating by the discharge spark was presumably the main mechanism for observed signal enhancement in the LA-FPDPS technique.

Kexue, L. I.; Zhou, Weidong; Shen, Qinmei; Shao, Jie; Qian, Huiguo

2010-05-01

198

Thrust Measurements in Ballistic Pendulum Ablative Laser Propulsion Experiments  

SciTech Connect

This paper describes a setup for thrust measurement in ablative laser propulsion experiments, based on a simple ballistic pendulum associated to an imaging system, which is being assembled at IEAv. A light aluminium pendulum holding samples is placed inside a 100 liters vacuum chamber with two optical windows: the first (in ZnSe) for the laser beam and the second (in fused quartz) for the pendulum visualization. A TEA-CO{sub 2} laser beam is focused to the samples providing ablation and transferring linear moment to the pendulum as a whole. A CCD video camera captures the oscillatory movement of the pendulum and the its trajectory is obtained by image processing. By fitting the trajectory of the pendulum to a dumped sinusoidal curve is possible to obtain the amplitude of the movement which is directly related to the momentum transfered to the sample.

Brazolin, H. [Instituto Tecnologico de Aeronautica 12.228-900-Sao Jose dos Campos (Brazil); Rodrigues, N. A. S.; Minucci, M. A. S. [Instituto de Estudos Avancados 12.228-001-Sao Jose dos Campos (Brazil)

2008-04-28

199

Comparative shock wave analysis during corneal ablation with an excimer laser, picosecond laser, and femtosecond laser  

NASA Astrophysics Data System (ADS)

With the event of topographic steep central islands following excimer laser surgery and the potential damage to the corneal endothelium, shock waves are playing an increasingly important role in laser refractive surgery. With this in mind, we performed a comparative shock wave analysis in corneal tissue using an excimer laser, picosecond laser, and femtosecond laser. We used a Lambda Physik excimer laser at 308 nm wavelength, a Nd:YLF picosecond laser at 1053 nm wavelength and a synchronously pumped linear cavity femtosecond laser at 630 nm wavelength. The pulse widths of the corresponding lasers were 8 ns, 18 ps, 150 fs, respectively. The energy density of irradiation was 2.5 to 8 times the threshold level being 2 J/cm2 (excimer laser), 86 J/cm2 (picosecond laser) and 10.3 J/cm2 (femtosecond laser). Shock wave dynamics were analyzed using time-resolved photography on a nanosecond time scale using the picosecond laser in corneal tissue, water and air. Shock wave dynamics using the femtosecond laser were studied in water only while the excimer laser induced shock wave during corneal ablation was studied in air only. We found the dynamics of shock waves to be similar in water and corneal tissue indicating that water is a good model to investigate shock wave effects in the cornea. The magnitude of the shock wave velocity and pressure decays over time to that of a sound wave. The distance over which it decays is 3 mm in air with the excimer laser and 600 - 700 micrometers in air with the picosecond laser. In water, the picosecond laser shock wave decays over a distance of 150 micrometers compared to the femtosecond laser shock wave which decays over a distance of 30 micrometers . Overall the excimer laser shock wave propagates 5 times further than that of the picosecond laser and the picosecond laser shock wave propagates 5 times further than that of the femtosecond laser. In this preliminary comparison, the time and distance for shock wave decay appears to be directly related to the laser pulse duration. The decay distance of the excimer laser shock waves appear to be 5 times longer than that of the picosecond laser in air while the picosecond laser shock wave distance appears to be 5 times longer than that of the femtosecond laser in water. The shorter shock wave distance of the picosecond laser is advantageous for corneal surgery by minimizing potential acoustic damage to the stromal and endothelial cells. Femtosecond lasers further minimize acoustic damage and their use should be considered in future corneal laser procedures.

Krueger, Ronald R.; Juhasz, Tibor

1995-05-01

200

Laser ablation of silicon in water with nanosecond and femtosecond pulses  

Microsoft Academic Search

We describe laser ablation of Si under water by 5 ns, 355 nm and 100 fs, 800 nm pulses. Compared to that in air, an approximately twofold improvement in the ablation rate is found in water for femtosecond and nanosecond pulses. For higher laser irradiances, the plasma that forms at the water-air interface hampers further improvement of the ablation rate.

Jun Ren; Michael Kelly; Lambertus Hesselink

2005-01-01

201

Next generation Er:YAG fractional ablative laser  

NASA Astrophysics Data System (ADS)

Pantec Biosolutions AG presents a portable fractional ablative laser system based on a miniaturized diode pumped Er:YAG laser. The system can operate at repetition rates up to 500 Hz and has an incorporated beam deflection unit. It is smaller, lighter and cost efficient compared to systems based on lamp pumped Er:YAG lasers and incorporates a skin layer detection to guarantee precise control of the microporation process. The pulse parameters enable a variety of applications in dermatology and in general medicine, as demonstrated by first results on transdermal drug delivery of FSH (follicle stimulating hormone).

Heinrich, A.; Vizhanyo, A.; Krammer, P.; Summer, S.; Gross, S.; Bragagna, T.; Böhler, C.

2011-03-01

202

Microsecond laser ablation of thrombus and gelatin under clear liquids: Contact versus noncontact  

Microsoft Academic Search

Laser thrombolysis is a procedure for removing blood clots in occluded arteries using pulsed laser energy. The laser light is delivered through an optical fiber to the thrombus. The ablation process is profoundly affected by whether the optical fiber tip is inside a catheter or is in contact with the thrombus. This study measured ablation efficiency of 1-?s laser pulses

HanQun Shangguan; Lee W. Casperson; Scott A. Prahl

1996-01-01

203

Higher Order Chemistry Models in the CFD Simulation of Laser-Ablated Carbon Plumes  

NASA Technical Reports Server (NTRS)

Production of single-walled carbon nanotubes (SWNT) has taken place for a number of years and by a variety of methods such as laser ablation, chemical vapor deposition, and arc-jet ablation. Yet, little is actually understood about the exact chemical kinetics and processes that occur in SWNT formation. In recent time, NASA Johnson Space Center has devoted a considerable effort to the experimental evaluation of the laser ablation production process for SWNT originally developed at Rice University. To fully understand the nature of the laser ablation process it is necessary to understand the development of the carbon plume dynamics within the laser ablation oven. The present work is a continuation of previous studies into the efforts to model plume dynamics using computational fluid dynamics (CFD). The ultimate goal of the work is to improve understanding of the laser ablation process, and through that improved understanding, refine the laser ablation production of SWNT.

Greendyke, R. B.; Creel, J. R.; Payne, B. T.; Scott, C. D.

2005-01-01

204

Noble metal nanoparticles produced by nanosecond laser ablation  

NASA Astrophysics Data System (ADS)

Silver and gold thin films were deposited by pulsed laser ablation in a controlled Ar atmosphere at pressures between 10 and 100 Pa. Different morphologies, ranging from isolated nanoparticle arrays up to nanostructured thin films were observed. Fast imaging of the plasma allowed deducing the expansion dynamics of the ablated plume. Plasma velocity and volume were used together with the measured average ablated mass per pulse as input parameters in a model to estimate the average size of nanoparticles grown in the plume. The nanoparticle size is expected to decrease from 4 nm down to 1 nm with decreasing Ar pressure between 100 and 10 Pa: this was confirmed by transmission electron micrographs which indicate a reduced dispersion of particle size over narrow size ranges. The production of substrates for surface enhanced Raman scattering whose performances critically depend on nanoparticle size, shape, and structure is discussed.

Ossi, P. M.; Neri, F.; Santo, N.; Trusso, S.

2011-09-01

205

Laser induced breakdown spectroscopy inside liquids: Processes and analytical aspects  

NASA Astrophysics Data System (ADS)

This paper provides an overview of the laser induced breakdown spectroscopy (LIBS) inside liquids, applied for detection of the elements present in the media itself or in the submerged samples. The processes inherent to the laser induced plasma formation and evolution inside liquids are discussed, including shockwave generation, vapor cavitation, and ablation of solids. Types of the laser excitation considered here are single pulse, dual pulse and multi-pulse. The literature relative to the LIBS measurements and applications inside liquids is reviewed and the most relevant results are summarized. Finally, we discuss the analytical aspects and release some suggestions for improving the LIBS sensitivity and accuracy in liquid environment.

Lazic, V.; Jovi?evi?, S.

2014-11-01

206

IR laser ablative and conventional decomposition of poly(vinyl phenyl ketone): Different processes and different products  

Microsoft Academic Search

Pulsed IR laser ablation of poly(vinyl phenyl ketone) results in the formation of CO, C1–C4 hydrocarbons, benzene, styrene and phenylacetylene and affords deposition of polymeric films that were examined by EDX-SEM, FTIR, UV and NMR spectroscopies and gel-permeation chromatography. It is revealed that the structure of the films is affected by laser fluence and their Mw distribution is almost identical

Dana Pokorná; Jan Šubrt; Anna Galíková; Josef Pola

2007-01-01

207

Synthesis efficiency of heavy carbon clusters from ETFE ablated by different numbers of laser pulse in vacuum  

Microsoft Academic Search

We have carried out mass spectral analysis of positive ions produced by laser ablation of a copolymer of ethylene and tetrafluoroethylene (ETFE: [?CH2?CH2?CF2?CF2?]n) in vacuum using time-of-flight mass spectrometry (TOF-MS). The surfaces of the ETFE targets irradiated by different numbers of laser pulse were analyzed by X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). Heavy carbon cluster ions Cn+

K. Shibagaki; N. Takada; K. Sasaki; K. Kadota

2002-01-01

208

Growth and structure of fullerene-like CNx thin films produced by pulsed laser ablation of graphite in nitrogen  

Microsoft Academic Search

The growth and structure of fullerene-like CNx films produced by laser ablation of graphite in low pressure nitrogen were investigated. Deposition conditions were selected based on investigations of CN and C2 concentration at the condensation surface, vibrational temperature of CN radicals, and kinetic energies of atomic and molecular species. Films were characterized with x-ray photoelectron spectroscopy, Raman spectroscopy, high-resolution transmission

A. A. Voevodin; J. G. Jones; J. S. Zabinski; Zs. Czigany; L. Hultman

2002-01-01

209

Excimer laser surface ablation: a review of recent literature.  

PubMed

The aim was to review the recently published literature on excimer laser surface ablation procedures, including photorefractive keratectomy (PRK), laser sub-epithelial keratomileusis (LASEK), microkeratome-assisted PRK (epi-LASIK) and trans-epithelial (laser-assisted) PRK, to help elucidate where and how surface ablation may best fit into current refractive surgical practice. The emphasis was on publications within the last three years and included systemic reviews, meta-analyses and randomised controlled trials. Where such evidence did not exist, selective large series cohort studies, case-controlled studies and case series with follow-up preferably greater than six months were examined and included. Refractive and visual outcomes are excellent and comparable to those after LASIK even in complex cases after previous corneal surgery. Indeed, surface ablation combined with corneal collagen cross-linking may be used in selected eyes with biomechanical instability, where LASIK is contraindicated. In addition, there is evidence to suggest that there may be less induction of higher order aberrations with surface techniques. Long-term stability and safety appear to be extremely satisfactory. The literature supports the use of modern excimer laser surface treatments, with outcomes comparable to those after LASIK and evidence of less induction of higher-order aberrations. Follow-up studies at 10 to 20 years indicate excellent stability and safety. PMID:23656608

O'Brart, David P S

2014-01-01

210

Emission features of femtosecond laser ablated carbon plasma in ambient helium  

NASA Astrophysics Data System (ADS)

We investigated the optical emission features of plasmas produced by 800 nm, 40 fs ultrafast laser pulses on a carbon target in the presence of ambient helium or nitrogen gases at varied pressures. Fast photography employing intensified charge coupled device, optical emission spectroscopy, and temporally spatially resolved optical time of flight emission spectroscopy were used as diagnostic tools. Spatio-temporal contours of excited neutral, ionic, as well as molecular carbon species in the plume were obtained using time of flight emission spectroscopy. These contours provided detailed account of molecular species evolution and expansion dynamics and indicate that three-body recombination is a major mechanism for carbon dimers generation in ultrafast laser ablation plumes in the presence of ambient gas. A systematic comparison of the emission features from ns and fs laser ablation carbon plumes as well as their expansion in ambient helium is also given. C2 vibrational temperatures were estimated during carbon plasma expansion with lower values in ambient helium compared to nitrogen and showed decreasing values with respect to space and ambient gas pressure.

Al-Shboul, K. F.; Harilal, S. S.; Hassanein, A.

2013-04-01

211

KrF laser ablation of a polyethersulfone film: Effect of pulse duration on structure formation  

NASA Astrophysics Data System (ADS)

Polyethersulfone (PES) films were processed with KrF laser irradiation of different pulse durations ( ?). Scanning electron microscopy (SEM) and Raman spectroscopy were employed for the examination of the morphology and chemical composition of the irradiated surfaces, respectively. During ablation with 500 fs and 5 ps pulses, localized deformations (beads), micro-ripple and conical structures were observed on the surface depending on the irradiation fluence ( F) and the number of pulses ( N). In addition, the number density of the structures is affected by the irradiation parameters ( ?, F, N). Furthermore, at longer pulse durations ( ? = 30 ns), conical structures appear at lower laser fluence values, which are converted into columnar structures upon irradiation at higher fluences. The Raman spectra collected from the top of the structures following irradiation at different pulse durations revealed graphitization of the ns laser treated areas, in contrast to those processed with ultra-short laser pulses.

Pazokian, Hedieh; Selimis, Alexandros; Stratakis, Emmanuel; Mollabashi, Mahmoud; Barzin, Jalal; Jelvani, Saeid

2011-10-01

212

Pico- and nanosecond laser ablation of mixed tungsten / aluminium films  

E-print Network

In order to extend the investigation of laser-assisted cleaning of ITER-relevant first mirror materials to the picosecond regime, a commercial laser system delivering 10 picosecond pulses at 355 nm at a frequency of up to 1 MHz has been used to investigate the ablation of mixed aluminium (oxide) / tungsten (oxide) layers deposited on poly- and nanocrystalline molybdenum as well as nanocrystalline rhodium mirrors. Characterization before and after cleaning using scanning electron microscopy (SEM) and spectrophotometry shows heavy dust formation, resulting in a degradation of the reflectivity. Cleaning using a 5 nanosecond pulses at 350 and 532 nm, on the other hand, proved very promising. The structure of the film remnants suggests that in this case buckling was the underlying removal mechanism rather than ablation. Repeated coating and cleaning using nanosecond pulses is demonstrated.

Wisse, M; Steiner, R; Mathys, D; Stumpp, A; Joanny, M; Travere, J M; Meyer, E

2014-01-01

213

Pre-ignition laser ablation of nanocomposite energetic materials  

SciTech Connect

Laser ignition of energetic material composites was studied for initiation with heating rates from 9.5 Multiplication-Sign 10{sup 4} to 1.7 Multiplication-Sign 10{sup 7} K/s. This is a unique heating rate regime for laser ignition studies because most studies employ either continuous wave CO{sub 2} lasers to provide thermal ignition or pulsed Nd:YAG lasers to provide shock ignition. In this study, aluminum (Al) and molybdenum trioxide (MoO{sub 3}) nanoparticle powders were pressed into consolidated pellets and ignited using a Nd:YAG laser (1064 nm wavelength) with varied pulse energy. Results show reduced ignition delay times corresponding to laser powers at the ablation threshold for the sample. Heating rate and absorption coefficient were determined from an axisymmetric heat transfer model. The model estimates absorption coefficients from 0.1 to 0.15 for consolidated pellets of Al + MoO{sub 3} at 1064 nm wavelength. Ablation resulted from fracturing caused by a rapid increase in thermal stress and slowed ignition of the pellet.

Stacy, S. C.; Massad, R. A.; Pantoya, M. L. [Department of Mechanical Engineering, Texas Tech University, Lubbock, Texas 79409 (United States)] [Department of Mechanical Engineering, Texas Tech University, Lubbock, Texas 79409 (United States)

2013-06-07

214

Dynamics of multiple plumes in laser ablation: Modeling of the shielding effect  

NASA Astrophysics Data System (ADS)

The scattering and absorption of laser radiation by previously ablated plumes in laser ablation (known as the shielding effect) dramatically affect the efficiency of laser ablation process. The ablated plumes consisting of water vapor, droplets, and particles are modeled as a gas-particle equilibrium mixture by solution of the Euler equations combined with the transport equation for the ratio of heat capacities. Shielding effect on the overall ablated mass by multiple plumes is studied for a wide range of concentration of particles in vaporized plumes, various laser repetition rates, scattering, and absorption of laser energy. The shielding phenomenon is studied for short sequences of discrete plumes to focus on the shielding effect of individual plumes. The results of numerical modeling were compared to experimental results of laser-induced water explosive vaporization. Ablation rate was calculated for a single ablated plume and for the sequence of six laser pulses at the repetition rates of 0.33 and 1MHz at which gas dynamics interactions between plumes are strong but plumes have not yet form a continuous jet. A single ablated plume has an initial semispherical shape which transforms into mushroomlike cloud with a thin stem and a ring vortex as it was observed in experiments with water and cornea ablation. For the plume with a given ablated mass, the longer ejection of plume with smaller density produces the plume with smaller shielding capacity. For multiple laser pulses, the velocity of ejected mixture increases from the center of the target to its periphery because of the shielding effect. The ablated mass of the current plume depends on the attenuation of the incident laser beam energy caused by the propagation of laser beam through previously ablated plumes. In the case of laser energy absorption, the ablation rate per pulse exceeds 2-2.5 times the rate obtained for the laser energy scattering.

Zinovik, Igor; Povitsky, Alex

2006-07-01

215

Experimental and theoretical investigations of femtosecond laser ablation of aluminum in vacuum  

SciTech Connect

We used time-gated optical emission spectroscopy to investigate the characteristics of aluminum plumes and their vacuum expansion after femtosecond laser ablation at different fluences. The prominent feature is the presence of two main classes of species in the plume: very fast Al atoms and ions preceding the plume bulk essentially constituted of much slower Al nanoparticles expanding with a ten times smaller average velocity. Atomic force microscopy of deposited Al nanoparticles evidenced an average size of about 10 nm with a pretty narrow size distribution. These results and the peculiar feature of nanoparticle formation during femtosecond laser irradiation of matter were very satisfactorily interpreted and reproduced by molecular-dynamics simulation of the process. Finally, the analysis of the dependence on laser fluence of the ablation process showed an initial logarithmic increase of ablation yield, up to about 500 mJ/cm{sup 2}, followed by a sudden and very steep increase at higher fluences. According to our numerical calculations, this latter feature can be ascribed to the increase of the overheated material volume due to electron heat diffusion.

Amoruso, S.; Bruzzese, R.; Vitiello, M.; Nedialkov, N.N.; Atanasov, P.A. [Coherentia-Istituto Nazionale per la Fisica della Materia (INFM) and Dipartimento di Scienze Fisiche, Universita degli Studi di Napoli Federico II, Complesso Universitario di Monte S. Angelo, I-80126 Naples (Italy); Institute of Electronics, Bulgarian Academy of Sciences, 72, Tsaridradsko shose Boulevard, Sofia 1784 (Bulgaria)

2005-08-15

216

Synthesis of higher diamondoids by pulsed laser ablation plasmas in supercritical CO{sub 2}  

SciTech Connect

Pulsed laser ablation (wavelength 532 nm; fluence 18 J/cm{sup 2}; pulse width 7 ns; repetition rate 10 Hz) of highly oriented pyrolytic graphite was conducted in adamantane-dissolved supercritical CO{sub 2} with and without cyclohexane as a cosolvent. Micro-Raman spectroscopy of the products revealed the presence of hydrocarbons possessing sp{sup 3}-hybridized carbons similar to diamond structures. The synthesis of diamantane and other possible diamondoids consisting of up to 12 cages was confirmed by gas chromatography-mass spectrometry. Furthermore, gas chromatography-mass spectrometry measurements of samples before and after pyrolysis treatment indicate the synthesis of the most compact decamantane, namely, superadamantane. It is thought that oxidant species originating from CO{sub 2} during pulsed laser ablation might lead to the selective dissociation of C-H bonds, enabling the synthesis of low H/C ratio molecules. Therefore, laser ablation in supercritical CO{sub 2} is proposed as a practical method for synthesizing diamondoids.

Nakahara, Sho; Stauss, Sven; Kato, Toru; Terashima, Kazuo [Department of Advanced Materials Science, Graduate School of Frontier Sciences, University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, 277-8561 Chiba (Japan); Sasaki, Takehiko [Department of Complexity Science and Engineering, Graduate School of Frontier Sciences, The University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, 277-8561 Chiba (Japan)

2011-06-15

217

Excimer laser ablation of plasma polymers for cell and tissue culture applications  

NASA Astrophysics Data System (ADS)

The two-dimensional control of cell adhesion is desired for a number of cell- and tissue culture applications. Thus, a suitable method for the two-dimensional control over surface chemistry, which leads to the display of cell-adhesive and non-adhesive signals is required. In our study, allylamine plasma polymer (ALAPP) deposition has been used to provide a cell-adhesive substrate, while additional grafting of poly(ethylene oxide) (PEO) on ALAPP surfaces has been used to prevent cell adhesion. Two-dimensional control over the surface chemistry was achieved using excimer laser ablation. Ablation experiments were carried out using a 248 nm excimer laser with energy densities of 17 - 1181 mJ/cm2 and 1 - 16 pulses per area. Results obtained by X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM) show controlled thickness ablation of the plasma polymer and the additional PEO graft polymer. Cell culture experiments using bovine corneal epithelial cells show that two-dimensional control of cell adhesion can be achieved by using appropriate masks in the laser beam.

Thissen, Helmut; Hayes, Jason P.; Hartley, Patrick G.; Johnson, Graham; Harvey, Erol C.; Griesser, Hans J.

2001-04-01

218

Modeling of laser ablation and fragmentation of human calculi  

SciTech Connect

The large-scale radiation-hydrodynamics computer code LASNEX, has been used to model experimental results in the laser ablation and fragmentation of renal and biliary calculi. Recent experiments have demonstrated laser ablation and fragmentation of human calculi in vitro and in vivo. In the interaction, laser light incident upon the calculus is of sufficient intensity to produce a plasma (a hot ionized gas). The physical picture which emerges is as follows. The plasma couples to acoustic and shear waves which then propagate through the dense stone material, causing spall and fracture by reflection from material discontinuities or boundaries. Experiments have thus far yielded data on the interaction against which models can be tested. Data on the following have been published: (1) light emission, (2) absorption and emission spectra, (3) fragmentation efficiency, (4) cavitation bubble dynamics and (5) mass removal. We have performed one dimensional simulations of the laser-matter interaction to elucidate the important physical mechanisms. We find that good quantitative fits between simulation and experiment are obtained for visible light emission, electron temperature, electron density, plasma pressure and cavitation bubble growth. With regard to mass removal, experiment and simulation are consistent with each other and give an excellent estimate of the ablation threshold. The modeling indicates that a very small ablation layer at the surface of the calculus is responsible for significant mass loss by fragmentation within the bulk of the calculus. With such quantitative fits in hand, we believe this type of modeling can now be applied to the study of other procedures involving plasma formation of interest to the medical community. 25 refs., 7 figs.

Gitomer, S.; Jones, R.D.; Howsare, C.

1989-01-01

219

Growth of epitaxial thin films by pulsed laser ablation  

SciTech Connect

High-quality, high-temperature superconductor (HTSc) films can be grown by the pulsed laser ablation (PLA) process. This article provides a detailed introduction to the advantages and curent limitations of PLA for epitaxial film growth. Emphasis is placed on experimental methods and on exploitation of PLA to control epitaxial growth at either the unit cell or the atomic-layer level. Examples are taken from recent HTSc film growth. 33 figs, 127 refs. (DLC)

Lowndes, D.H.

1992-01-01

220

Growth of epitaxial thin films by pulsed laser ablation  

SciTech Connect

High-quality, high-temperature superconductor (HTSc) films can be grown by the pulsed laser ablation (PLA) process. This article provides a detailed introduction to the advantages and curent limitations of PLA for epitaxial film growth. Emphasis is placed on experimental methods and on exploitation of PLA to control epitaxial growth at either the unit cell or the atomic-layer level. Examples are taken from recent HTSc film growth. 33 figs, 127 refs. (DLC)

Lowndes, D.H.

1992-10-01

221

Optical feedback signal for ultrashort laser pulse ablation of tissue  

SciTech Connect

An optical feedback system for controlled precise tissue ablation is discussed. Our setup includes an ultrashort pulse laser (USPL), and a diagnostic system using analysis of either tissue fluorescence or plasma emission luminescence. Current research is focused on discriminating hard and soft tissues such as bone and spinal cord during surgery using either technique. Our experimental observations exhibit considerable spectroscopic contrast between hard and soft tissue, and both techniques offer promise for a practical diagnostic system.

Kim, B.-M.; Feit, M.D.; Rubenchik, A.M.; Mammini, B.M.; Da Silva, L.B.

1997-07-01

222

Laser Ablation Inductively Coupled Plasma Mass Spectrometry: Principles and Applications  

Microsoft Academic Search

The application of laser ablation inductively plasma mass spectrometry (LA?ICP?MS) to the determination of major, minor, and trace elements as well as isotope?ratio measurements offers superior technology for direct solid sampling in analytical chemistry. The advantages of LA?ICP?MS include direct analysis of solids; no chemical dissolution is necessary, reduced risk of contamination, analysis of small sample mass, and determination of

N. S. Mokgalaka; J. Gardea-Torresdey

2006-01-01

223

Comparison of soft and hard tissue ablation with sub-ps and ns pulse lasers  

SciTech Connect

Tissue ablation with ultrashort laser pulses offers several unique advantages. The nonlinear energy deposition is insensitive to tissue type, allowing this tool to be used for soft and hard tissue ablation. The localized energy deposition lead to precise ablation depth and minimal collateral damage. This paper reports on efforts to study and demonstrate tissue ablation using an ultrashort pulse laser. Ablation efficiency and extent of collateral damage for 0.3 ps and 1000 ps duration laser pulses are compared. Temperature measurements of the rear surface of a tooth section is also presented.

Da Silva, L.B.; Stuart, B.C.; Celliers, P.M.; Feit, M.D.; Glinsky, M.E.; Heredia, N.J.; Herman, S.; Lane, S.M.; London, R.A.; Matthews, D.L.; Perry, M.D.; Rubenchik, A.M. [Lawrence Livermore National Lab., CA (United States); Chang, T.D. [Veterans Administration Hospital, Martinez, CA (United States); Neev, J. [Beckman Laser Inst. and Medical Clinic, Irvine, CA (United States)

1996-05-01

224

Update On CO2 Laser Ablation Of Polyoxymethylene At 101 kPa  

NASA Astrophysics Data System (ADS)

Recent work has brought about a renewed interest in CO2 laser ablation studies of polyoxymethylene, due to its potential as a test target for enhancing modern understanding of the laser ablation process. In this paper, new results taken in air at atmosphere pressure are reported, including data measured at institutions in Germany and Japan, which increase the body of literature data on CO2 laser ablation of polyoxymethylene. The results are discussed in terms of aerospace parameters such as the momentum coupling coefficient and specific impulse, and are compared to a previous literature study. The threshold fluence is specified for ablation of polyoxymethylene by CO2 laser radiation. Fluences higher (and lower) than previously tested for CO2 laser ablation were studied herein, and record specific impulse values for CO2 laser ablation of flat polyoxymethylene are also reported here.

Sinko, John E.; Scharring, Stefan; Ogita, Naoya; Sasoh, Akihiro; Eckel, Hans-Albert; Röser, Hans-Peter

2010-10-01

225

Modeling of Plume Dynamics in Laser Ablation  

Microsoft Academic Search

The aim of this study is to find thermal conditions for the formation of carbon annotates in a laser furnace. The proposed model includes a multi-species formulation for concentration of chemical components combined with the compressible Euler equations. An axisymmetric unsteady computational gas dynamic model of plume expansion into ambiance has been developed. In the present work, the system of

Diomar Lobao; Alex Povitsky

2003-01-01

226

Laser-assisted ablation of corneal-like material using focused femtosecond laser pulses  

NASA Astrophysics Data System (ADS)

In this article we investigate laser-assisted ablation of Hydroxy Ethyl Methacrylate (Hydro-gel) material using 30 femtosecond laser pulses delivered from a Ti:Sapphire multipass amplifier with a repetition rate of 1 kHz. Measurements of the crater depth, width and removed volume as a function of laser pulse energy and pulse number were made for stationary and translated ablation. Based on laser fluence, crater profile, collateral damage and translation speed, optimal laser parameters for efficient micromachining were defined. The results presented in this paper will be important for future developments in laser ophthalmology, where insight into the optimal laser parameters for corneallike surgery will decrease both processing time and collateral tissue damage.

Kohli, Vikram; Yu, Deli; Elezzabi, Abulhakem Y.

2007-02-01

227

Furnace geometry effects on plume dynamics in laser ablation for nanotube synthesis  

Microsoft Academic Search

Laser ablation (LA) has become a popular method for production of carbon nanotubes where formation of gaseous carbon plume and liberation of catalyst particles are caused by the laser pulse. The plume dynamics in laser ablation is somewhat similar to point explosion where a large amount of energy is liberated in a small volume. The aim of this study is

Diomar Cesar Lobão; Alex Povitsky

2004-01-01

228

Characteristics of Droplets Ejected from Liquid Propellants Ablated by Laser Pulses in Laser Plasma Propulsion  

NASA Astrophysics Data System (ADS)

The angular distribution and pressure force of droplets ejected from liquid water and glycerol ablated by nanosecond laser pulses are investigated under different viscosities in laser plasma propulsion. It is shown that with increasing viscosity, the distribution angles present a decrease tendency for two liquids, and the angular distribution of glycerol is smaller than that of water. A smaller distribution leads to a higher pressure force generation. The results indicate that ablation can be controlled by varying the viscosity of liquid propellant in laser plasma propulsion.

Zheng, Zhiyuan; Gao, Hua; Fan, Zhenjun; Xing, Jie

2014-03-01

229

Lasers in Surgery and Medicine 44:805814 (2012) Femtosecond Plasma Mediated Laser Ablation Has  

E-print Network

Medicine, Department of Surgery, Plastic and Reconstructive Surgery Division, Stanford University SchoolLasers in Surgery and Medicine 44:805­814 (2012) Femtosecond Plasma Mediated Laser Ablation Has post- surgery. However, at 8 weeks post-surgery, there was no significant difference. In the drill

Palanker, Daniel

230

Measurement of energy conversion efficiency during laser ablation by a multiple laser beam deflection probe  

Microsoft Academic Search

We have developed a novel multiple-pass laser beam deflection (LBD) arrangement for detection of acoustic and weak shock waves in fluids. The arrangement gives us the possibility to acquire temporally resolved information (signal waveforms) on single and non-reproducible events in several points of space. We have applied the new arrangement to investigate spherical shocks generated during laser ablation of metallic

Janez Diaci; Janez Možina

1996-01-01

231

Applications and mechanisms of laser ablation for elemental analysis of nuclear wastes and contaminated soils  

SciTech Connect

Survey methods for compositional analysis of nuclear wastes and contaminated soils are under development to support characterization prior to treatment and continued monitoring during remediation. Laser ablation in conjunction with optical spectroscopy and mass spectroscopy are attractive because of the safety and convenience of minimal sample handling and very small sampling volume. However, the signal intensities in analytic applications depend sensitively on the physical state of the sample (e.g., particle morphology, defect concentration, impurities, and presence of liquids). In this work, the authors examine how solid and condensed state properties of the sample affect the laser-substrate interaction, and the dynamic electronic, physical, and chemical processes which ultimately generate the signals that are detected for analytic purposes.

Langford, S.C.; Dickinson, J.T. [Washington State Univ., Pullman, WA (United States)

1996-12-31

232

Laser spectroscopy on a ``shoestring''  

NASA Astrophysics Data System (ADS)

The advent of tunable lasers has had a profound influence on both experimental and theoretical physics. Unfortunately, since these laser systems are typically hazardous and expensive, the physics student at the undergraduate or first-year graduate level has no real familiarity with their application in modern physics; and thus cannot fully appreciate their significance. Tunable single mode laser diodes, however, may offer a remedy to this situation. To demonstrate their applicability, we have designed a relatively simple and inexpensive experiment of laser diode spectroscopy in an atomic beam which illustrates the effect of hyperfine structure and the isotope shift in the rubidium D1 transition (52S1/2-52P1/2). Furthermore, this experiment demonstrates the possibility of investigating basic physics without major expenditures for laser systems and laboratory facilities.

Camparo, J. C.; Klimcak, C. M.

1983-12-01

233

Generation of Cd1-xZnxS nanoparticles by laser ablation in liquids  

NASA Astrophysics Data System (ADS)

Approximately spherical nanoparticles of the II-VI semiconductor materials Cd1-xZnxS have been produced successfully by laser ablation of the bulk material in several liquids. The non-stabilized suspensions of particles are characterized by absorption spectroscopy and transmission electron microscopy (TEM). The procedure is not strongly size-selective, radii of 7±3 nm were found for Cd1-xZnxS by transmission electron microscopy. Acetonitrile stabilizes the particles for several days up to weeks. Prolonged irradiation leads effectively to a reduction in particles size, in which particle agglomeration may play an important role. Ablation in degassed liquids does not have a significant effect on the absorption of the suspended particles.

Jafarov, M. A.; Nasirov, E. F.; Jafarli, R.

2014-08-01

234

Spectroscopic evidence of positive clusters in Ag colloids obtained by laser ablation in aqueous solutions  

NASA Astrophysics Data System (ADS)

We have found evidence of positive cluster formation during the laser ablation process of a silver target in aqueous solutions. In particular, by employing in situ shot-by-shot UV-vis spectroscopy in the early stages of the ablation, we observed a weak and unstable absorption band around 266 nm and a more stable one around 290 nm, which could be assigned to charged clusters like Ag{3/2+} and Ag{4/2+}, respectively. Surface-enhanced Raman scattering experiments performed with a test molecule adsorbed on a silver colloid obtained in pure water were compatible with the presence of Ag{4/2+} active sites on the surface of the Ag nanoparticles.

Giorgetti, E.; Marsili, P.; Muniz-Miranda, M.; Gellini, C.; Giammanco, F.

2014-10-01

235

Laser ablation of hard tissue: correlation between the laser beam parameters and the post-ablative tissue characteristics  

NASA Astrophysics Data System (ADS)

Hard dental tissue laser applications, such as preventive treatment, laser diagnosis of caries, laser etching of enamel, laser decay removal and cavity preparation, and more recently use of the laser light to enlarge the root canal during the endodontic therapy, have been investigated for in vitro and in vivo applications. Post-ablative surface characteristics, e.g. degree of charring, cracks and other surface deformation, can be evaluated using scanning electron microscopy. The experimental data are discussed in relevance with the laser beam characteristics, e.g. pulse duration, beam profile, and the beam delivery systems employed. Techniques based on the laser illumination of the dental tissues and the subsequent evaluation of the scattered fluorescent light will be a valuable tool in early diagnosis of tooth diseases, as carious dentin or enamel. The laser induced autofluorescence signal of healthy dentin is much stronger than that of the carious dentin. However, a better understanding of the transmission patterns of laser light in teeth, for both diagnosis and therapy is needed, before the laser procedures can be used in a clinical environment.

Serafetinides, Alexandros A.; Makropoulou, Mersini I.; Khabbaz, Maruan

2003-11-01

236

Laser microprobe and resonant laser ablation for depth profile measurements of hydrogen isotope atoms contained in graphite  

Microsoft Academic Search

We measured the depth profile of hydrogen atoms in graphite by laser microprobing combined with resonant laser ablation. Deuterium-implanted graphite was employed for the measurements. The sample was ablated by a tunable laser with a wavelength corresponding to the resonant wavelength of1S-2S of deuterium with two-photon excitation. The ablated deuterium was ionized by a 2 + 1 resonant ionization process.

Masafumi Yorozu; Tatsuya Yanagida; Terunobu Nakajyo; Yasuhiro Okada; Akira Endo

2001-01-01

237

Development of intercavitary laser spectroscopy  

Microsoft Academic Search

Development of the Technique. Among the numerous applications of the techniques and instruments of quantum electronics in science and technology, an important position is assumed by applications in which problems of spectral analysis are solved and the possibilities and the means of modern spectroscopy are enhanced. The tendency to use monochromatic laser radiation for probing in weakly absorbing media has

V. S. Burakov

1981-01-01

238

Laser ablation characteristics of yttria-doped zirconia in the nanosecond and femtosecond regimes  

NASA Astrophysics Data System (ADS)

The laser ablation characteristics of yttria-stabilized zirconia (YSZ) have been investigated as a function of the target microstructure and dopant level for different nanosecond- [ArF, KrF, and XeCl excimers; Nd:YAG (yttrium aluminum garnet) (fourth harmonic)] and femtosecond-laser sources [Ti:sapphire (fundamental and third harmonic)]. Particle ejection, which compromises the quality of coatings prepared by pulsed laser deposition (PLD), was analyzed in detail. Nanosecond-laser pulses cause a severe thermomechanical surface cracking and exfoliation of micron-sized fragments on a microsecond to millisecond time scale in the case of 8-9.5 mol % Y2O3-doped, fully stabilized zirconia (8YSZ and 9.5YSZ) targets. As a consequence of the intrinsic material brittleness, fully stabilized YSZ coatings deposited by PLD contained particles for all tested conditions. Lower doped partially stabilized zirconia (3YSZ) exhibits a superior fracture toughness attributed to a laser-induced partial transition to the monoclinic phase, detected by Raman spectroscopy, which enables the deposition of particle-free dense thin films by conventional PLD using nanosecond-UV laser radiation at moderate fluences of 1.2-1.5 J/cm2. The ablation dynamics of ultrashort laser pulses differ fundamentally from the nanosecond regime as evidenced, e.g., by time-resolved shadowgraphy and light scattering experiments. Femtosecond pulses prevent the exfoliation of micron-sized fragments but result invariably in a pronounced ejection of submicron particles. The resulting PLD coatings are porous and reveal a large surface roughness as they consist of an agglomeration of nanoparticles. Femtosecond-NIR pulses provide a factor of 2.5-10 higher material removal rates compared to nanosecond- and femtosecond-UV pulses. The ablation metrics, i.e., threshold fluence and effective absorptivity, mainly depend on the laser wavelength while the pulse duration, target microstructure, and dopant level are of minor importance. Evidence is presented that incubation effects play a significant role in nanosecond- and femtosecond-laser ablations of YSZ enabling material removal at comparatively low fluences for sub-bandgap photon energies.

Heiroth, S.; Koch, J.; Lippert, T.; Wokaun, A.; Günther, D.; Garrelie, F.; Guillermin, M.

2010-01-01

239

Mass spectroscopic characterization of yttrium-containing metallofullerene YC82 using resonant laser ablation  

SciTech Connect

In this paper, resonant laser ablation time-of-flight mass spectroscopy (RLA-TOF-MS) has been used to mass spectroscopic characterization of yttrium-containing fullerenes. Solvent soluble, yttrium-containing fullerenes are extracted from yttrium/carbon soot produced by the carbon-arc fullerene generation method. The RLA-TOF mass spectra indicate the presence of YC82. The metallofullerences YC60, YC70, Y2C82 and a series of Y2C2n are not observed by RLA-TOF-MS. This result is consistent with the ESR spectral result reported by Shinohara et al.

Wang Shiliang; Tian Jiahe; Dai Songtao; Chen Dieyan; Luo Chuping; Tan Haisong; Gan Liangbing; Huang Chunhui [Laser Single Atom Detection Laboratory, Department of Physics, Tsinghua University, Beijing 100084 (China); State Key Laboratory of Rare Earth Material Chemistry and Applications, Peking University, Beijing 100871 (China)

1995-04-01

240

Doppler Free Laser Spectroscopy  

NSDL National Science Digital Library

In this experiment you will use a technique known as saturation-absorption spectroscopy to study the hyperfine structure (hfs) of rubidium. This particular method is designed to overcome the limitations imposed by the Doppler-broadening of spectral lines while avoiding the need to work at low temperatures.

2012-01-09

241

Pulsed laser ablation of borax target in vacuum and hydrogen DC glow discharges  

NASA Astrophysics Data System (ADS)

The aim of our experiment was to produce a material with B sbnd H bonds for applications in hydrogen storage and generation. By using KrF excimer laser ( ? = 248 nm) ablation of borax (Na 2B 4O 7) target, thin films were deposited on KBr and silicon substrates. Ablation was performed both in vacuum and in hydrogen atmosphere. DC glow discharge technique was utilized to enhance hydrogen gas ionization. Experiments were performed using laser fluence from 5 to 20 J/cm 2. Films were deposited under gas pressure of 1 × 10 -5 to 5 × 10 -2 mbar and substrate temperatures of 130-450 °C. Scanning electron microscopy analysis of films showed presence of circular particulates. Film thickness, roughness and particulates number increased with increase in laser fluence. Energy dispersive X-ray spectroscopy analysis shows that sodium content in the particulates is higher than in the target. This effect is discussed in terms of atomic arrangements (both at surface and bulk) in systems where ionic and covalent bonds are present and by looking at the increased surface/bulk ratio of the particulates with respect to the deposited films. The Fourier transform infrared spectroscopy measurements showed presence of B sbnd O stretching and B sbnd O sbnd B bending bonds. Possible reasons for absence of B sbnd H bonds are attributed to binding enthalpy of the competing molecules.

Kale, A. N.; Miotello, A.; Mosaner, P.

2006-09-01

242

Nanoparticle preparation of quinacridone and ?-carotene using near-infrared laser ablation of their crystals  

NASA Astrophysics Data System (ADS)

Quinacridone nanoparticles with a mean size of about 200 nm are successfully prepared using nanosecond near-infrared (NIR) laser ablation of its microcrystalline powders in heavy water. The absorption spectra of the formed colloidal solutions depend on the excitation wavelengths, which is eventually ascribed to number and energy of absorbed photons. ?-carotene has low photostability and is easily decomposed upon UV/VIS laser ablation of its solid, while its nanoparticles are prepared utilizing this NIR laser ablation technique. The advantage of nanoparticle preparation by NIR laser ablation is discussed.

Yuyama, K.; Sugiyama, T.; Asahi, T.; Ryo, S.; Oh, I.; Masuhara, H.

2010-12-01

243

On the Feasibility of Depth Profiling of Animal Tissue by Ultrashort Pulse Laser Ablation  

PubMed Central

Experiments were performed to examine the feasibility of MS depth profiling of animal tissue by ~75 fs, 800 nm laser pulses to expose underlying layers of tissue for subsequent MS analysis. Matrix assisted laser desorption ionization mass spectrometry (MALDI-MS) was used to analyze phospholipids and proteins from both intact bovine eye lens tissue and tissue ablated by ultrashort laser pulses. Laser desorption postionization (LDPI-MS) with 10.5 eV single photon ionization was also used to analyze cholesterol and other small molecules in the tissue before and after laser ablation. Scanning electron microscopy was applied to examine the ablation patterns in the tissue and estimate the depth of the ablation craters. Ultrashort pulse laser ablation was found able to remove a layer of several tens of micrometers from the surface of eye lens tissue while leaving the underlying tissue relatively undamaged for subsequent MS analysis. MS analysis of cholesterol, phospholipids, peptides, and various unidentified species did not reveal any chemical damage caused by ultrashort pulse laser ablation for analytes smaller than ~6 kDa. However, a drop in intensity of larger protein ions was detected by MALDI-MS following laser ablation. An additional advantage was that ablated tissue displayed up to an order of magnitude higher signal intensities than intact tissue when subsequently analyzed by MS. These results support the use of ultrashort pulse laser ablation in combination with MS analysis to permit depth profiling of animal tissue. PMID:22482364

Milasinovic, Slobodan; Liu, Yaoming; Bhardwaj, Chhavi; Melvin, Blaze M.T.; Gordon, Robert J.; Hanley, Luke

2012-01-01

244

Laser spectroscopy of sputtered atoms  

SciTech Connect

The use of laser radiation to study the sputtering process is of relatively recent origin. Much has been learned from this work about the basic physics of the sputtering process itself through measurements of velocity and excited state distributions of sputtered atoms and the effects of adsorbates on substrate sputtering yields. Furthermore, the identification, characterization, and sensitive detection of sputtered atoms by laser spectroscopy has led to the development of in situ diagnostics for impurity fluxes in the plasma edge regions of tokamaks and of ultrasensitive methods (ppB Fe in Si) for surface analysis with ultralow (picocoulomb) ion fluences. The techniques involved in this work, laser fluorescence and multiphoton resonance ionization spectroscopy, will be described and illustrations given of results achieved up to now. 55 refs., 5 figs., 1 tab.

Gruen, D.M.; Pellin, M.J.; Young, C.E.; Calaway, W.F.

1985-01-01

245

Femtosecond pulsed laser ablation deposition of tantalum carbide  

NASA Astrophysics Data System (ADS)

In this work a frequency-doubled Nd:glass laser with a pulse duration of 250 fs has been used to ablate a TaC target and to deposit thin films on silicon. The results have been compared with those previously obtained by nanosecond pulsed laser deposition and evidence of large differences in the plasma characteristics has been revealed. In particular, in the femtosecond and nanosecond plumes the energy and the velocity of neutral and ionized particles are very different. The features of femtosecond ablation include the delayed emission from the target of large and slow particles. The characteristics of the femtosecond plasma are clearly related to the morphology and composition of the deposited films and the results show a nanostructure consisting of a large number of spherical particles, with a mean diameter of about 50 nm, with a stoichiometry corresponding to Ta 2C. To explain these features, an ablation-deposition mechanism, related to the ejection of hot particles from the target, is proposed.

Teghil, R.; De Bonis, A.; Galasso, A.; Villani, P.; Santagata, A.

2007-12-01

246

Production of nanoparticles by laser-induced ablation of metals in liquids  

SciTech Connect

The production of noble metal (Ag and Au) nanoparticles upon the ablation of metal targets in liquids (H{sub 2}O, C{sub 2}H{sub 5}OH, etc.) caused by irradiation by a copper vapour laser is studied. The nanoparticles emerging in a liquid are investigated using X-ray diffractometry, optical absorption spectroscopy, and high-resolution transmission electron microscopy. The colloidal nanoparticle solutions exhibits a distinct plasmon resonance at 520 and 400 nm for Au and Ag, respectively. It is shown that the proximity of laser wavelength to the resonance makes it possible to decrease the dimension of nanoparticles by irradiating the colloidal solution. The size distribution function of nanoparticles is simulated taking into account the production, coagulation, and splitting of nanopartiles in the laser beam. (special issue devoted to the memory of academician a m prokhorov)

Bozon-Verduraz, F; Brayner, R [ITODYS, Universite Paris (France); Voronov, Valerii V [Laser Materials and Technology Research Center, A. M. Prokhorov General Physics Institute, Russian Academy of Sciences, Moscow (Russian Federation); Kirichenko, N A; Simakin, Aleksandr V; Shafeev, Georgii A [Wave Research Centre, A.M. Prokhorov General Physics Institute, Russian Academy of Sciences, Moscow (Russian Federation)

2003-08-31

247

Laser ablation in a running hall effect thruster for space propulsion  

NASA Astrophysics Data System (ADS)

Hall Effect Thrusters (HETs) are promising electric propulsion devices for the station-keeping of geostationary satellites (more than 120 in orbit to date). Moreover, they can offer a cost-effective solution for interplanetary journey, as proved by the recent ESA SMART-1 mission to the Moon. The main limiting factor of the HETs lifetime is the erosion of the annular channel ceramics walls. In order to provide a better understanding of the energy deposition on the insulated walls, a laser irradiation study has been carried out on a PPS100-ML thruster during its run in the PIVOINE-2G ground test facility (CNRS Orléans, France). Two distinct approaches have been followed: continuous wave fiber laser irradiation (generation of thermal defects) and nanosecond pulsed laser ablation (generation of topological defects). The irradiated zones have been monitored in situ by IR thermography and optical emission spectroscopy and further investigated ex situ by scanning electron microscopy and profilometry.

Balika, L.; Focsa, C.; Gurlui, S.; Pellerin, S.; Pellerin, N.; Pagnon, D.; Dudeck, M.

2013-07-01

248

Split-ring resonators manufactured on conductive layer by selective laser ablation  

NASA Astrophysics Data System (ADS)

In this paper an alternative method of manufacturing SRR structures through the selective removal of a thin layer of silver-palladium deposited on the surface of the Al2O3 ceramic by laser ablation process using nanosecond Nd:YAG laser (1064 nm) was presented. The SRR structures array were subject to transmittance measurements using the TDS (Time Domain Spectroscopy). Both electric and magnetic resonances were observed at frequencies determined by the structural parameters of the SRR. In case of the E field perpendicular to an SRR structure and one resonance area for 0.56 THz with the E field parallel to the structure, two characteristic resonant dips for 0.31 THz and 0.62 THz were obtained. Studies have confirmed that using selective laser removal process enables the preparation of the resonant structure in the range of THz.

Koziol, Pawe?; Anto?czak, Arkadiusz J.; Szymczyk, Patrycja E.; Stepak, Bogusz; ?azarek, ?ukasz; Wójcik, Micha? R.; Walczakowski, Micha?; Abramski, Krzysztof M.

2014-08-01

249

Single molecule laser spectroscopy.  

PubMed

In this article, we discussed some single molecule spectroscopy techniques and methods. We have chosen the simplicity in this survey based on our laboratory experience in this field. We concentrated on the imaging by both techniques the wide field and the scanning microscopes. Other imaging enhancements on the technique like extended resolution wide field, the total internal reflection imaging, and its derivatives are also reviewed. In addition to the imaging techniques, some diffusion techniques also are discussed like fluorescence correlation spectroscopy. The related methods like Forester resonance transfer, photo-induced electron transfer and anisotropy (steady state and time decay) are also discussed. In addition, we elucidated some simple details about the theory behind the FCS and its resulting curve fitting. This review is preceded by general introduction and ended with the conclusion. PMID:25156641

Atta, Diaa; Okasha, Ali

2015-01-25

250

Ablation of selected conducting layers by fiber laser  

NASA Astrophysics Data System (ADS)

Laser Direct Writing (LDW) are used in the manufacture of electronic circuits, pads, and paths in sub millimeter scale. They can also be used in the sensors systems. Ablative laser writing in a thin functional layer of material deposited on the dielectric substrate is one of the LDW methods. Nowadays functional conductive layers are composed from graphene paint or nanosilver paint, indium tin oxide (ITO), AgHTTM and layers containing carbon nanotubes. Creating conducting structures in transparent layers (ITO, AgHT and carbon nanotubes layers) may have special importance e.g. for flexi electronics. The paper presents research on the fabrication of systems of paths and appropriate pattern systems of paths and selected electronic circuits in AgHTTM and ITO layers deposited on glass and polymer substrates. An influence of parameters of ablative fiber laser treatment in nanosecond regime as well as an influence of scanning mode of laser beam on the pattern fidelity and on electrical parameters of a generated circuit was investigated.

Pawlak, Ryszard; Tomczyk, Mariusz; Walczak, Maria

2014-08-01

251

Stable isotope laser spectroscopy  

NASA Technical Reports Server (NTRS)

Recent advances in semiconductor laser technology have produced a reliable lightweight device ideally suited for a spacecraft high resolution molecular spectrometer. Lead-salt tunable diode lasers (TDL) emit in several spectral modes, each with a very narrow linewidth of -0.0003/cm. This spectral resolution is much narrower than typical Doppler broadened molecular linewidths in the mid-IR range. Thus it is possible to detect individual rotational lines within the vibrational band and measure their intensity, which can be used to determine gas concentration. The narrow spectral lines of any impurity gas tend to lie between the narrow lines of the gas of interest. This represents a major advantage over the accepted gas chromatograph mass spectrometer (GCMS) technique for measuring gas concentrations and isotope ratios. The careful and extensive gas purification procedures required to remove impurities for reliable GCMS measurements will not be required for an IR laser gas analysis. The infrared laser gas analysis technique is being developed to measure stable isotopic ratios of gases such as CO2, CH4, N2O, and NH3. This will eventually lead to development of instruments capable of in situ istopic measurements on planets such as Mars. The carbon (C-12, C-13) isotope ratio is indicative of the type of carbon fixation mechanisms (e.g., photosynthesis, respiration) in operation on a planet, while the nitrogen (N-14, N-15) isotope ratio can probably be used to date nitrogen-bearing Martian samples. The absorbance ratio of two adjacent lines of CO2 in the 2300/cm (4.3 micron) region of the spectrum was measured. The precision of the measurement is presently better than 1 percent and significant improvement is anticipated as rapid sweep-integration techniques and computer controlled data acquistion capabilities are incorporated.

Becker, J. F.; Yaldaei, Ramil; Mckay, Christopher P.

1989-01-01

252

Real-time measurement of ArF excimer laser corneal tissue ablation rates using cross-  

E-print Network

between several cross-correlation metrics and the directly measured corneal ablation rate, yieldingReal-time measurement of ArF excimer laser corneal tissue ablation rates using cross- correlation refractive surgery. © 2011 Optical Society of America OCIS codes: (170.1020) Ablation of tissue; (170

Hahn, David W.

253

Simulation of laser interaction with ablative plasma and hydrodynamic behavior of laser supported plasma  

SciTech Connect

When an intense laser beam irradiates on a solid target, ambient air ionizes and becomes plasma, while part of the target rises in temperature, melts, vaporizes, ionizes, and yet becomes plasma. A general Godunov finite difference scheme WENO (Weighted Essentially Non-Oscillatory Scheme) with fifth-order accuracy is used to simulate 2-dimensional axis symmetrical laser-supported plasma flow field in the process of laser ablation. The model of the calculation of ionization degree of plasma and the interaction between laser beam and plasma are considered in the simulation. The numerical simulations obtain the profiles of temperature, density, and velocity at different times which show the evolvement of the ablative plasma. The simulated results show that the laser energy is strongly absorbed by plasma on target surface and that the velocity of laser supported detonation (LSD) wave is half of the ideal LSD value derived from Chapman-Jouguet detonation theory.

Tong Huifeng; Yuan Hong [Institute of Fluid Physics, Chinese Academy of Engineering Physics, P.O. Box 919-101, Mianyang, Sichuan 621900 (China); Tang Zhiping [CAS Key Laboratory for Mechanical Behavior and Design of Materials, Department of Mechanics and Mechanical Engineering, University of Science and Technology of China, Hefei 230026 (China)

2013-01-28

254

Simulation of laser interaction with ablative plasma and hydrodynamic behavior of laser supported plasma  

NASA Astrophysics Data System (ADS)

When an intense laser beam irradiates on a solid target, ambient air ionizes and becomes plasma, while part of the target rises in temperature, melts, vaporizes, ionizes, and yet becomes plasma. A general Godunov finite difference scheme WENO (Weighted Essentially Non-Oscillatory Scheme) with fifth-order accuracy is used to simulate 2-dimensional axis symmetrical laser-supported plasma flow field in the process of laser ablation. The model of the calculation of ionization degree of plasma and the interaction between laser beam and plasma are considered in the simulation. The numerical simulations obtain the profiles of temperature, density, and velocity at different times which show the evolvement of the ablative plasma. The simulated results show that the laser energy is strongly absorbed by plasma on target surface and that the velocity of laser supported detonation (LSD) wave is half of the ideal LSD value derived from Chapman-Jouguet detonation theory.

Tong, Huifeng; Yuan, Hong; Tang, Zhiping

2013-01-01

255

Testing of concrete by laser ablation  

DOEpatents

A method of testing concrete in a structure in situ, by: directing a succession of pulses of laser radiation at a point on the structure so that each pulse effects removal of a quantity of concrete and transfers energy to the concrete; detecting a characteristic of energy which has been transferred to the concrete; determining, separately from the detecting step, the total quantity of concrete removed by the succession of pulses; and calculating a property of the concrete on the basis of the detected energy characteristic and the determined total quantity of concrete removed.

Flesher, Dann J. (Benton City, WA); Becker, David L. (Kennewick, WA); Beem, William L. (Kennewick, WA); Berry, Tommy C. (Kennewick, WA); Cannon, N. Scott (Kennewick, WA)

1997-01-01

256

Testing of concrete by laser ablation  

DOEpatents

A method is disclosed for testing concrete in a structure in situ, by: directing a succession of pulses of laser radiation at a point on the structure so that each pulse effects removal of a quantity of concrete and transfers energy to the concrete; detecting a characteristic of energy which has been transferred to the concrete; determining, separately from the detecting step, the total quantity of concrete removed by the succession of pulses; and calculating a property of the concrete on the basis of the detected energy characteristic and the determined total quantity of concrete removed. 1 fig.

Flesher, D.J.; Becker, D.L.; Beem, W.L.; Berry, T.C.; Cannon, N.S.

1997-01-07

257

Laser ablative synthesis of carbon nanotubes  

DOEpatents

An improved method for the production of single walled carbon nanotubes that utilizes an RF-induction heated side-pumped synthesis chamber for the production of such. Such a method, while capable of producing large volumes of carbon nanotubes, concurrently permits the use of a simplified apparatus that allows for greatly reduced heat up and cool down times and flexible flowpaths that can be readily modified for production efficiency optimization. The method of the present invention utilizes a free electron laser operating at high average and peak fluence to illuminate a rotating and translating graphite/catalyst target to obtain high yields of SWNTs without the use of a vacuum chamber.

Smith, Michael W. (Newport News, VA); Jordan, Kevin (Newport News, VA); Park, Cheol (Yorktown, VA)

2010-03-02

258

Ablation of Silicone Rubber Using UV-Nanosecond and IR-Femtosecond Lasers  

NASA Astrophysics Data System (ADS)

Silicone rubber was ablated by an ArF laser, the forth harmonics of Nd:YAG, and a Ti:sapphire laser for microdrilling. The fs-Ti:sapphire laser ablated the sample at a rate higher than those of the other lasers, in the fluence range of approximately 0.15-2.0 J/cm2. No chemical denaturation was observed after irradiation using each laser. The UV-ArF laser ablated the irradiated area precisely, making the surface flat and smooth.

Fukami, Yuko; Okoshi, Masayuki; Inoue, Narumi

2004-07-01

259

Effects of laser parameters on pulsed Er-YAG laser skin ablation  

Microsoft Academic Search

Previous studies demonstrated that pulsed 2.94m Er-YAG laser radiation allows a precise etching of organic tissue with only minimal thermal damage. This makes the Er-YAG laser a promising tool for the careful removal of superficial skin lesions. In order to provide optimized laser parameters for potential clinical use and to enhance our understanding of the mid-infrared ablation process, we measured

Raimund Hibst; Roland Kaufmann

1991-01-01

260

The influence of laser wavelength and fluence on palladium nanoparticles produced by pulsed laser ablation in deionized water  

NASA Astrophysics Data System (ADS)

Homogeneous spherical palladium (Pd) nanoparticles were synthesized by pulsed laser ablation of a solid Pd foil target submerged in deionized water, without the addition of any external chemical surfactant. The influence of laser wavelength (355, 532, and 1064 nm) and fluence (8.92, 12.74, and 19.90 J/cm2) on nucleation, growth, and aggregation of Pd nanoparticles were systematically studied. Microstructural and optical properties of the obtained nanoparticles were studied by field emission transmission electron microscopy (FETEM), energy dispersive X-ray spectroscopy, and UV-vis spectroscopy. FETEM micrographs indicate that the average nanocrystallite sizes are relatively low (3-6 nm) and homogeneous for the particles synthesized at the laser wavelengths of 355 and 532 nm. However, at a laser wavelength of 1064 nm, the average nanocrystallite size is relatively large and inhomogeneous in nature. Moreover, we observe that the mean diameter and production rate of particles increases with an increase in laser fluence. The selected area electron diffraction patterns obtained from isolated Pd nanoparticles show the characteristic diffused electron diffraction rings of polycrystalline materials with a face-centered cubic structure. Absorbance spectrum of the synthesized nanoparticle solution shows a broad absorption band, which corresponds to a typical inter-band transition of a metallic system, indicating the production of pure palladium nanoparticles. The present work provides new insights into the effect of laser wavelength and fluence on the control of size and aggregation of palladium nanoparticles in the liquid medium.

Kim, Jinil; Amaranatha Reddy, D.; Ma, Rory; Kim, Tae Kyu

2014-11-01

261

Nanosecond and femtosecond laser ablation of brass: Particulate and ICPMS measurements  

SciTech Connect

Femtosecond and nanosecond lasers were compared for ablating brass alloys. All operating parameters from both lasers were equal except for the pulse duration. The ablated aerosol vapor was collected on silicon substrates for particle size measurements or sent into an inductively coupled plasma mass spectrometer. The diameters and size distribution of particulates were measured from scanning electron microscope (SEM) images of the collected ablated aerosol. SEM measurements showed that particles ablated using nanosecond pulses were single spherical entities ranging in diameter from several micrometers to several hundred nanometers. Primary particles ablated using femtosecond ablation were {approx}100 nm in diameter but formed large agglomerates. ICPMS showed enhanced signal intensity and stability using femtosecond compared to nanosecond laser ablation.

Liu, C.; Mao, X.L.; Mao, S.; Zeng, X.; Greif, R.; Russo, R.E.

2003-11-01

262

Peak polarity overturn for charged particles in laser ablation process  

SciTech Connect

The charged particles emitted during laser ablation off a brass target are detected using a metal probe in air. A special phenomenon is found in the recorded signals: following a giant electromagnetic peak observed immediately after the emission of the pulsed laser, a minor peak occurs whose polarity merely depends on the distance between the probe and the laser focal spot on the target. Under the condition of our experiment, the overturn point is 1.47 mm, i.e., the minor peak remains negative when the probe distance is less than 1.47 mm; it becomes positive while the probe is set at a distance beyond 1.47 mm. A hypothesis is proposed to explain the overturn that takes the flight behavior of the charged particles both in plasma and propagating shock wave into consideration.

Zhang, P.; Ji, Y. J.; Lai, X. M.; Bian, B. M.; Li, Z. H. [Department of Information Physics and Engineering, Nanjing University of Science and Technology, Nanjing 210094 (China)

2006-07-01

263

Evaluation of the analytical capability of NIR femtosecond laser ablation-inductively coupled plasma mass spectrometry.  

PubMed

A laser ablation-inductively coupled plasma-mass spectrometric (LA-ICPMS) technique utilizing a titanium-sapphire (TiS) femtosecond laser (fs-laser) has been developed for elemental and isotopic analysis. The signal intensity profile, depth of the ablation pit and level of elemental fractionation were investigated in order to evaluate the analytical capability of the present fs-laser ablation-ICPMS technique. The signal intensity profile of (57)Fe, obtained from iron sulfide (FeS(2)), demonstrated that the resulting signal intensity of (57)Fe achieved by the fs-laser ablation was almost 4-times higher than that obtained by ArF excimer laser ablation under a similar energy fluence (5 J/cm(2)). In fs-laser ablation, there is no significant difference in a depth of the ablation pit between glass and zircon material, while in ArF laser ablation, the resulting crater depth on the zircon crystal was almost half the level than that obtained for glass material. Both the thermal-induced and particle size-related elemental fractionations, which have been thought to be main sources of analytical error in the LA-ICPMS analysis, were measured on a Harvard 91500 zircon crystal. The resulting fractionation indexes on the (206)Pb/(238)U (f(Pb/U)) and (238)U/(232)Th (f(U/Th)) ratios obtained by the present fs-laser ablation system were significantly smaller than those obtained by a conventional ArF excimer laser ablation system, demonstrative of smaller elemental fractionation. Using the present fs-laser ablation technique, the time profile of the signal intensity of (56)Fe and the isotopic ratios ((57)Fe/(54)Fe and (56)Fe/(54)Fe) have been measured on a natural pyrite (FeS(2)) sample. Repeatability in signal intensity of (56)Fe achieved by the fs-laser ablation system was significantly better than that obtained by ArF excimer laser ablation. Moreover, the resulting precision in (57)Fe/(54)Fe and (56)Fe/(54)Fe ratio measurements could be improved by the fs-laser ablation system. The data obtained here clearly demonstrate that, even with the fundamental wavelength (NIR operating at 780 nm), the fs-laser ablation system has the potential to become a significant tool for in-situ elemental and isotopic analysis of geochemical samples including heavy minerals and metallic materials. PMID:18332541

Hirata, Takafumi; Kon, Yoshiaki

2008-03-01

264

Simulation of nanosecond pulsed laser ablation of copper samples: A focus on laser induced plasma radiation  

NASA Astrophysics Data System (ADS)

A thermal model for nanosecond pulsed laser ablation of Cu in one dimension and in ambient gas, He at 1 atm, is proposed in which equations concerning heat conduction in the target and gas dynamics in the plume are solved. These equations are coupled to each other through the energy and mass balances at interface between the target and the vapor and also Knudsen layer conditions. By assumption of local thermal equilibrium, Saha-Eggert equations are used to investigate plasma formation. The shielding effect of the plasma, due to photoionization and inverse bremsstrahlung processes, is considered. Bremsstrahlung and blackbody radiation and spectral emissions of the plasma are also investigated. Spatial and temporal distribution of the target temperature, number densities of Cu and He, pressure and temperature of the plume, bremsstrahlung and blackbody radiation, and also spectral emissions of Cu at three wavelengths (510, 516, and 521 nm) are obtained. Results show that the spectral power of Cu lines has the same pattern as CuI relative intensities from National Institute of Standard and Technology. Investigation of spatially integrated bremsstrahlung and blackbody radiation, and also Cu spectral emissions indicates that although in early times the bremsstrahlung radiation dominates the two other radiations, the Copper spectral emission is the dominant radiation in later times. It should be mentioned that the blackbody radiation has the least values in both time intervals. The results can be used for prediction of the optimum time and position of the spectral line emission, which is applicable in some time resolved spectroscopic techniques such as laser induced breakdown spectroscopy. Furthermore, the results suggest that for distinguishing between the spectral emission and the bremsstrahlung radiation, a spatially resolved spectroscopy can be used instead of the time resolved one.

Aghaei, M.; Mehrabian, S.; Tavassoli, S. H.

2008-09-01

265

Plasma properties of laser-ablated strontium target  

SciTech Connect

Optical emission spectroscopy is used to characterize the laser-produced strontium plasma by using the fundamental, second, and third harmonics of a Nd:YAG laser. Variations in the electron temperature (T{sub e}) and number density (N{sub e}) as a function of distance, laser irradiance, and ambient gas pressure have been studied by using the emission lines of neutral strontium. In addition, absorption mechanisms responsible for the variation of the electron temperature and number density and the dependence of the spectral line intensities on the ambient gas pressure and laser irradiance are discussed.

Hafeez, S.; Shaikh, Nek M.; Rashid, Baber; Baig, M. A. [Atomic and Molecular Physics Laboratory, Department of Physics, Quaid-i-Azam University, 45320 Islamabad (Pakistan)

2008-04-15

266

High-resolution ablation of amorphous polymers using CO2 laser irradiation  

NASA Astrophysics Data System (ADS)

Etching of various amorphous polymers by the application of CO2 laser radiation (10.6 ?m) is described. By passage of the radiation through a high-resolution mask in contact with the polymer surface, this ablation can produce images having submicron resolution and good edge acuity. The laser intensity required for ablation is compared for various thermoplastic and thermosetting polymers. Below the required level of intensity, no ablation is observed, but the laser irradiation can result in thermal crystallization. The energy necessary to induce ablation with infrared radiation is comparable to that required for UV decomposition.

Sonnenschein, Mark F.; Roland, C. Michael

1990-07-01

267

Comparative study of gelatin ablation by free-running and Q-switch modes of Er:YAG laser  

Microsoft Academic Search

To optimize the laser ablation of soft wet tissues by Er:YAG laser radiation at 2.94 micrometers the dynamics of ablation is investigated by high-speed photography techniques. Gelatin as model material is used.

Vitaly I. Konov; Lev A. Kulevsky; Alexei V. Lukashev; Vladimir P. Pashinin; Alexander S. Silenok

1991-01-01

268

Treatment of lymphangioma circumscriptum using fractional carbon dioxide laser ablation.  

PubMed

Lymphangioma circumscriptum remains a challenging entity to treat given anatomic considerations and a significant tendency for recurrence regardless of the modality selected. Surgical excision offers the greatest potential for definitive management but is often beset by procedural morbidity and suboptimal cosmetic outcomes. A range of palliative options have been reported for the treatment of lymphangioma circumscriptum, with varying degrees of associated efficacy and morbidity. This report describes the novel use of fractional carbon dioxide laser ablation for the treatment of lymphangioma circumscriptum, with promising cosmetic results and durable symptomatic relief. PMID:23758048

Shumaker, Peter R; Dela Rosa, Kristina M; Krakowski, Andrew

2013-01-01

269

Laser Ablation of Metals Johannes Roth, Carolina Trichet, Hans-Rainer-Trebin, and Steffen Sonntag  

E-print Network

Laser Ablation of Metals Johannes Roth, Carolina Trichet, Hans-Rainer-Trebin, and Steffen Sonntag. The interaction of the laser light with the electrons is described by a continuum equation and #12;2 Johannes Roth

Roth, Johannes

270

Visual laser ablation of the prostate (VLAP) with the prostascope  

NASA Astrophysics Data System (ADS)

Introduction: Laser ablation of the prostatic tissue or laser prostatectomy, is used as an alternative method to traditional endoscopic resection of the prostate. The usual side-firing Nd:YAG laser fiber for the treatment of obstructive symptoms has operational difficulties, a high cost and often poor early results. Materials: We describe the laser coagulation of the prostate using a 600-um bare fiber inserted in a modified Albarran bridge which included at the tip, a new gold-plated deflectable reflector. The complete device passes through a 21Fr.rigid cysto- urethroscope. The system and the fiber can be used for several dozen treatments. The dosimetry was 2000 J per 1 cc of prostatic tissue. Methods: VLAP using the prostascope was performed on more than 70 men in one institution, and 150 in a second one, for obstructive symptoms due to benign prostatic hyperplasia. The parameter included AUA symptom score, flow rate, residual volume and complications. Data were obtained preoperatively and 1, 3, 6 and 12 months after treatment. Discussion: According to our data VLAP with this system is a save, minimal invasive and effective treatment. Results are comparable to other non-contact laser devices. As the gold-plated reflector is inexpensive and the standard bare fiber can be used repeatedly, the cost is less than of an usual side-firing laser fiber.

Mattioli, Stefano; Cremona, M.; Ackaert, K. J.

1997-12-01

271

Effects of plasma confinement on the femtosecond laser ablation of silicon  

NASA Astrophysics Data System (ADS)

We investigated the femtosecond laser ablation of silicon in a confined condition by covering the surface of a silicon wafer with a glass slide. The ablation was carried out by either irradiating the focused spot with different numbers of pulses or by scanning the laser beam on the surface of the silicon wafer. The morphology of the ablated surface was characterized by scanning electron microscope. For laser fluences much larger than the ablation threshold of silicon, cylindrical holes were generated in the confined ablation, in sharp contrast to the conical holes observed in the ablation performed in open air. Accordingly, grooves with U-shaped and V-shaped cross sections were achieved in the ablations carried out in the confined condition and in open air, respectively. For laser fluences close to the ablation threshold of silicon, the difference in the morphology of micro- and nanostructures obtained by these two ablation methods became not pronounced and two-dimensional nanohole arrays were created on the surface of silicon wafer. While the period of the nanohole arrays in the direction of the laser polarization was found to be close to the laser wavelength, the period in the direction perpendicular to the laser polarization was observed to be more than two times of the laser wavelength. In addition, the distribution of erupted nanoparticles was also found to be different in the two ablation processes. A ring-shaped distribution of nanoparticles was observed in the open air ablation while a monotonic decrease of nanoparticle density along the radial direction was found in the confined ablation.

Zhang, Chengyun; Yao, Jianwu; Lan, Sheng; Trofimov, Vyacheslav A.; Lysak, Tatiana M.

2013-11-01

272

The role of laser wavelength on plasma generation and expansion of ablation plumes in air  

E-print Network

and surface melting, ablation and plasma formation, laser-plasma interaction, shock wave for- mation craters. Our results indicated that excitation wavelength plays a crucial role in laser-target and laser-plasma. The presence of an ambient gas dramatically affects the laser-target and laser plasma coupling, as well

Harilal, S. S.

273

Formation and properties of metal colloids and colloidal nano-alloys by laser ablation and irradiation of metals in liquids  

NASA Astrophysics Data System (ADS)

We have successfully synthesized noble metal colloids by laser ablation of metal targets in liquids and Au/Ag colloidal nano-alloys with a wide range of compositions by a re-irradiation of mixed colloidal suspensions. Optical extinction spectra as well as electron microscopy data can give a clear picture of the structure and properties of the obtained particles, while an X-ray photoelectron spectroscopy is used for an estimation of the clusters' composition.

Compagnini, G.; Messina, E.; Puglisi, O.

274

Biomedical applications of laser spectroscopy  

NASA Astrophysics Data System (ADS)

Very soon after the invention of the laser, the use of the thermal effects of the radiation was introduced. Such techniques have been refined and the laser is now routinely used for treatment in many specialities. Photodynamic therapy (PDT) is a non-thermal modality employing the combination of a tumor-seeking agent and activating laser light. During the last 15 years laser spectroscopic techniques have also been developed providing powerful means for non-intrusive medical diagnostics of tissue in real time. At the beginning only few groups were involved in exploratory work, but successively the field has developed now to occupy a large number of research teams, which meet at large specialized conferences. We will here consider three aspects of laser diagnostics: fluorescence, Raman and near-IR, and elastic scattering spectroscopy, and we will also briefly discuss PDT. The activity in the field is very extensive, and rather than trying to give a full overview, illustrations from work performed at the Lund University Medical Laser Center will be given.

Svanberg, Sune

1999-07-01

275

Measurement of depth profile of hydrogen isotope atom contained in solid material using resonant laser ablation  

Microsoft Academic Search

The depth profile of hydrogen isotope atoms was measured by using mass spectrometry combined with resonant laser ablation. A graphite sample was implanted with deuterium by a cyclotron and was employed for the measurements. The graphite sample was ablated by a tunable laser which wavelength was corresponding to the resonant wavelength of 1S - 2S for deuterium with two- photon

Masafumi Yorozu; Yasuhiro Okada; Terunobu Nakajyo; Akira Endo

1999-01-01

276

Nanoscale patterning of graphene through femtosecond laser ablation R. Sahin, E. Simsek, and S. Akturk  

E-print Network

graphene sheets can easily be produced using standard chemical vapor deposition (CVD) method.5 High spatial works on the issue, Kalita et al. use the fs laser ablation method to produce 5 lm width grapheneNanoscale patterning of graphene through femtosecond laser ablation R. Sahin, E. Simsek, and S

Simsek, Ergun

277

Laser Ablation (LA-ICPMS) at the Institute of Mineralogy, University of WÃrzburg  

NSDL National Science Digital Library

This website from the University of Wuerzburg briefly describes laser ablation, the most versatile in-situ solid sampling technique for ICP mass spectrometry. The website also features a section detailing applications for laser ablation inductively coupled plasma mass spectrometry (LA-ICPMS), including trace element concentration and chemical zoning, and others.

University of Wü Institute of Mineralogy; Rzburg; Wãrzburg, University O.

278

Application of the laser ablation for conservation of historical paper documents  

Microsoft Academic Search

Laser ablation was applied for surface cleaning and spectroscopic diagnostics of historical paper documents and model samples in the framework of the conservation projects. During cleaning the spectra of ablation products were recorded by means of the LIBS technique which allowed for nearly non-destructive identification of surface layers such as contaminants, substrate and pigments. For consecutive laser pulses a strong

A. Kaminska; M. Sawczak; K. Komar; G. ?liwi?ski

2007-01-01

279

Clinical outcomes following percutaneous magnetic resonance image guided laser ablation of symptomatic uterine fibroids  

Microsoft Academic Search

BACKGROUND: Fibroids are common benign tumours of the uterus. Percutaneous magnetic resonance (MR) image guided laser ablation provides a minimally invasive, day-case alternative to surgery for the treatment of symptomatic fibroids. METHODS: Women with symptomatic fibroids wishing to avoid surgery were treated with laser ablation. MR thermal mapping ensured that maximal safe energy was applied. Fibroid volume was measured at

J. T. Hindley; P. A. Law; M. Hickey; S. C. Smith; D. L. Lamping; W. M. W. Gedroyc; L. Regan

2002-01-01

280

Determination of intratest variability of trace elements in foraminifera by laser ablation inductively coupled  

E-print Network

inductively coupled plasma-mass spectrometry E. C. Hathorne, O. Alard, R. H. James, and N. W. Rogers, Mg, Mn, Cu, Zn, Sr and Ba) within foraminifera tests using laser ablation inductively coupled plasma of trace elements in foraminifera by laser ablation inductively coupled plasma-mass spectrometry, Geochem

Demouchy, Sylvie

281

Major element analysis of natural silicates by laser ablation ICP-MS Munir Humayun,*a  

E-print Network

Major element analysis of natural silicates by laser ablation ICP-MS Munir Humayun,*a Fred A (EMP) analysis to provide complementary information on major element constituents. Here, we present a method for laser ablation ICP-MS analysis of major elements in silicate glasses and minerals that, when

Weston, Ken

282

Improved Analytical Characterization of Solid Waste-Forms by Fundamental Development of Laser Ablation Technology  

Microsoft Academic Search

Laser ablation (LA) with inductively coupled plasma mass spectrometry (ICP-MS) has been demonstrated as a viable technology for sample characterization within the EM complex. Laser ablation systems have been set up at the Hanford Site, Savannah River Plant, the Pu immobilization program (MD), Los Alamos, and at numerous other DOE facilities. Characterization of elemental and isotopic chemical constituents is an

Richard E

2000-01-01

283

A Hybrid MD-DSMC Model of Picosecond Laser Ablation and Desorption  

E-print Network

model of the evolution of a plume generated by laser ablation of an organic solid is presented interaction cross sections. The MD breathing sphere model [15], used for simulation of the initial stageA Hybrid MD-DSMC Model of Picosecond Laser Ablation and Desorption Michael I. Zeifman* , Barbara J

Zhigilei, Leonid V.

284

Stable carbon and oxygen isotope analysis of fossil tooth enamel using laser ablation  

Microsoft Academic Search

A technique is described whereby the ?13C and ?18O values of fossil tooth enamel can be measured in situ using laser ablation techniques. The laser heats the sample and forms CO2 from structural carbonate apatite. The ?18O values obtained with this method are equal to those of the phosphate oxygen due to the high temperature of reaction during ablation. Analytical

Thure E. Cerling; Zachary D. Sharp

1996-01-01

285

Phase explosion in atmospheric pressure infrared laser ablation from water-rich targets  

E-print Network

Phase explosion in atmospheric pressure infrared laser ablation from water-rich targets Zhaoyang pressure. It incorporates the nonlinear absorption of water and the phase explosion due to superheating explosion on laser ablation dynamics, and it is relevant for the preparative, analytical, and medical

Vertes, Akos

286

Comparison of holmium:YAG and thulium fiber laser lithotripsy: ablation thresholds, ablation rates, and retropulsion effects  

NASA Astrophysics Data System (ADS)

The holmium:YAG (Ho:YAG) laser lithotriptor is capable of operating at high pulse energies, but efficient operation is limited to low pulse rates (~10 Hz) during lithotripsy. On the contrary, the thulium fiber laser (TFL) is limited to low pulse energies, but can operate efficiently at high pulse rates (up to 1000 Hz). This study compares stone ablation threshold, ablation rate, and retropulsion for the two different Ho:YAG and TFL operation modes. The TFL (? = 1908 nm) was operated with pulse energies of 5 to 35 mJ, 500-?s pulse duration, and pulse rates of 10 to 400 Hz. The Ho:YAG laser (? = 2120 nm) was operated with pulse energies of 30 to 550 mJ, 350-?s pulse duration, and a pulse rate of 10 Hz. Laser energy was delivered through 200- and 270-?m-core optical fibers in contact mode with human calcium oxalate monohydrate (COM) stones for ablation studies and plaster-of-Paris stone phantoms for retropulsion studies. The COM stone ablation threshold for Ho:YAG and TFL measured 82.6 and 20.8 J/cm2, respectively. Stone retropulsion with the Ho:YAG laser linearly increased with pulse energy. Retropulsion with TFL was minimal at pulse rates less than 150 Hz, then rapidly increased at higher pulse rates. For minimal stone retropulsion, Ho:YAG operation at pulse energies less than 175 mJ at 10 Hz and TFL operation at 35 mJ at 100 Hz is recommended, with both lasers producing comparable ablation rates. Further development of a TFL operating with both high pulse energies of 100 to 200 mJ and high pulse rates of 100 to 150 Hz may also provide an alternative to the Ho:YAG laser for higher ablation rates, when retropulsion is not a primary concern.

Blackmon, Richard L.; Irby, Pierce B.; Fried, Nathaniel M.

2011-07-01

287

Process and structures for fabrication of solar cells with laser ablation steps to form contact holes  

DOEpatents

Contact holes of solar cells are formed by laser ablation to accomodate various solar cell designs. Use of a laser to form the contact holes is facilitated by replacing films formed on the diffusion regions with a film that has substantially uniform thickness. Contact holes may be formed to deep diffusion regions to increase the laser ablation process margins. The laser configuration may be tailored to form contact holes through dielectric films of varying thickness.

Harley, Gabriel; Smith, David D; Dennis, Tim; Waldhauer, Ann; Kim, Taeseok; Cousins, Peter John

2013-11-19

288

An observation of ablation effect of soft biotissue by pulsed Er:YAG laser  

NASA Astrophysics Data System (ADS)

Because of the unique properties with regard to the absorption in organic tissue, pulsed Er:YAG laser has found most interest for various application in medicine, such as dermatology, dentistry, and cosmetic surgery. However, consensus regarding the optimal parameters for clinical use of this tool has not been reached. In this paper, the laser ablation characteristics of soft tissue by Er:YAG laser irradiation was studied. Porcine skin tissue in vitro was used in the experiment. Laser fluences ranged from 25mJ/mm2 to 200mJ/mm2, repetition rates was 5Hz, spot sizes on the tissue surface was 2mm. The ablation effects were assessed by the means of optical microscope, ablation diameters and depths were measured with reading microscope. It was shown that the ablation of soft biotissue by pulsed Er:YAG laser was a threshold process. With appropriate choice of irradiation parameters, high quality ablation with clean, sharp cuts following closely the spatial contour of the incident beam can be achieved. The curves of ablation crater diameter and depth versus laser fluence were obtained, then the ablation threshold and ablation yield were calculated subsequently, and the influence of the number of pulses fired into a crater on ablation crater depth was also discussed.

Zhang, Xianzeng; Xie, Shusen; Ye, Qing; Zhan, Zhenlin

2007-02-01

289

Hard tissue ablation with a spray-assisted mid-IR laser  

NASA Astrophysics Data System (ADS)

The objective of this study was to understand the dominant mechanism(s) for dental enamel ablation with the application of water spray. A free-running Er,Cr:YSGG (yttrium, scandium, gallium, garnet) laser was used to ablate human enamel tissue at various radiant exposures. During dental ablation, distilled water was sprayed on the sample surface, and these results were compared to ablation without a spray (dry ablation). In order to identify dominant ablation mechanisms, transient acoustic waves were compared to ablation thresholds and the volume of material removed. The ablation profile and depth were measured using optical coherence tomography (OCT). Irregular surface modification, charring and peripheral cracks were associated with dry ablation, whereas craters for spray samples were relatively clean without thermal damage. In spite of a 60% higher ablation threshold for spray associated irradiations owing to water absorption, acoustic peak pressures were six times higher and ablation volume was up to a factor of 2 larger compared to dry ablation. The enhanced pressure and ablation performance of the spray-assisted process was the result of rapid water vaporization, material ejection with recoil stress, interstitial water explosion and possibly liquid-jet formation. With water cooling and abrasive/disruptive mechanical effects, the spray ablation can be a safe and efficient modality for dental treatment.

Kang, H. W.; Rizoiu, I.; Welch, A. J.

2007-12-01

290

Investigation of the particle size distribution of the ejected material generated during the single femtosecond laser pulse ablation of aluminium  

NASA Astrophysics Data System (ADS)

Single femtosecond laser pulses are employed to ablate an aluminium target in vacuum, and the particle size distribution of the ablated material deposited on a mica substrate is examined with atomic force microscopy (AFM). The recorded AFM images show that these particles have a mean radius of several tens of nanometres. It is also determined that the mean radius of these deposited nanoparticles increases when the laser fluence at the aluminium target increases from 0.44 J/cm2 to 0.63 J/cm2. The mechanism of the laser-induced nanoparticle generation is thought to be photomechanical tensile stress relaxation. Raman spectroscopy measurements confirm that the nanoparticles thus produced have the same structure as the bulk aluminium.

Wu, Han; Zhang, Nan; Zhu, Xiaonong

2014-10-01

291

Model polyimide films: Synthesis, characterization, and deposition by resonant infrared laser ablation  

NASA Astrophysics Data System (ADS)

A new deposition technique for high performance polymer films, resonant infrared laser ablation (RIR-LA) is presented. Ultraviolet laser deposition techniques have been shown to cause decomposition and depolymerization of the deposited polymer films. We hypothesized that the infrared radiation would be a gentler technique compared to ultraviolet radiation and should leave the polymer structure intact. We proposed a technique where a solution-based polymeric precursor is frozen in liquid nitrogen, placed in vacuum chamber, and ablated by a rastered infrared laser beam. Then the ejected material is collected on a substrate forming a thin polymeric film. First we tested the technique on a 15 weight % pyromellitic dianhydride-co-4,4'-oxidianiline (PMDA-ODA) in N-methylpyrrolidinone (NMP), the polymeric precursor to polyimide. PMDA-ODA is converted to polyimide by a thermal cure near 250 °C. Fourier transform infrared spectroscopy results confirmed that the PMDA-ODA was transferred intact and without curing by RIR-LA. Molecular weight studies show that only a small portion of the original molecular weight is lost, allowing for the preservation of strength and structural properties. The technique was then tested with other polymers including polyamide imide and polyether imide. Both polymers were successfully transferred intact with no signs of curing. Polyamide imide boasts an even lower cure temperature than polyimide at only 150°C, illustrating how effective RIR-LA is at avoiding thermal transformations.

Dygert, Nicole Leigh

292

Rapid in-situ analysis of liquid steel by laser-induced breakdown spectroscopy  

Microsoft Academic Search

Laser-induced breakdown spectroscopy (LIBS) denotes a technique where a pulsed laser beam is used to ablate small amounts of the target material. The characteristic optical emission line intensities of the excited species in the laser-generated plasma allow a quantitative chemical analysis of the target material. LIBS is a fast, non-contact method allowing large working distances between the sample under investigation

J. Gruber; J. Heitz; H. Strasser; D. Bäuerle; N. Ramaseder

2001-01-01

293

Fabrication of high-density pitch adapters by laser ablation  

NASA Astrophysics Data System (ADS)

High Energy Physics experiments make extensive use of micro-strip silicon sensors for tracking purposes. However, the high granularity of the modern detectors makes the connection between the segmented sensor channels and the readout electronics very complex. Enhancing the complexity, a direct connection is not possible in most of the cases due to the mismatch between the detector pad pitch and the electronics. A new method based on laser technology is presented for the fabrication of pitch adapters. In this new method the high-density metal traces are manufactured by means of laser ablation of the metal layer deposited on top of a substrate. Glass, Kapton and Silicon substrates were metal coated and tested for the fabrication of pitch adapters. Finally, a metal-on-glass prototype has been successfully manufactured and tested for electrical conductivity, bondability and metrology. Detectors have been assembled using this pitch adapters design and tested in particle beams at CERN.

Rey-García, F.; Bao-Varela, C.; Pérez, E.; Rodríguez, P.; Gallas, A.; de la Fuente, G. F.

2014-05-01

294

Laser ablation and the unzipping of addition polymer  

NASA Astrophysics Data System (ADS)

Ability to control decomposition path and products for addition polymers is important in many applications ranging from thin film fabrication and basic understanding of reaction kinetics to evaluating the feasibility of thermal routes for the recycling of addition polymers. Laser ablation, a technique widely used to deposit thin films of a variety of inorganic materials, can also be used as a simple and highly versatile method for the deposition of thin polymer films of materials that are difficult to process and studying decomposition kinetics as well. In situ studies of the products formed by the laser/polymer interaction suggest that, as in standard pyrolysis, decomposition of poly(tetrafluoroethylene), poly(methylmethacrylate), and poly(?-methyl styrene) proceeds via chain unzipping leading to monomer. Unexpectedly, high monomer yields are also observed for addition polymers that pyrolyze by random scission producing little or no monomer. Examples of such materials presented here include poly(vinylfluoride) and polypropylene.

Blanchet, Graciela B.

1996-10-01

295

Laser ablation of dental calculus at 400 nm using a Ti:sapphire laser  

NASA Astrophysics Data System (ADS)

A Nd:YAG laser-pumped, frequency-doubled Ti:sapphire laser is used for selective ablation of calculus. The laser provides <=25 mJ at 400 nm (60-ns pulse width, 10-Hz repetition rate). The laser is coupled into an optical multimode fiber coiled around a 4-in.-diam drum to generate a top-hat output intensity profile. With coaxial water cooling, this is ideal for efficient, selective calculus removal. This is in stark contrast with tightly focused Gaussian beams that are energetically inefficient and lead to irreproducible results. Calculus is well ablated at high fluences >=2J/cm2 stalling occurs below this fluence because of photobleaching. Healthy hard tissue is not removed at fluences <=3 J/cm2.

Schoenly, Joshua E.; Seka, Wolf; Rechmann, Peter

2009-02-01

296

Background gas collisional effects on expanding fs and ns laser ablation plumes  

NASA Astrophysics Data System (ADS)

The collisional effects of a background gas on expanding ultrafast and short pulse laser ablation plumes were investigated by varying background pressure from vacuum to atmospheric pressure levels. For producing Cu ablation plumes, either 40 fs, 800 nm pulses from a Ti: Sapphire laser or 6 ns, 1,064 nm pulses from a Nd:YAG laser were used. The role of background pressure on plume hydrodynamics, spectral emission features, absolute line intensities, signal to background ratios and ablation craters was studied. Though the signal intensities were found to be maximum near to atmospheric pressure levels, the optimum signal to background ratios are observed ~20-50 Torr for both ns and fs laser ablation plumes. The differences in laser-target and laser-plasma couplings between ns and fs lasers were found to be more engraved in the crater morphologies and plasma hydrodynamic expansion features.

Harilal, S. S.; Farid, N.; Freeman, J. R.; Diwakar, P. K.; LaHaye, N. L.; Hassanein, A.

2014-10-01

297

TiC and TaC deposition by pulsed laser ablation: a comparative approach  

NASA Astrophysics Data System (ADS)

Titanium and tantalum monocarbides have been evaporated by means of doubled Nd-YAG laser and deposited on oriented silicon substrates. The gaseous phase and the deposited films have been characterised by mass spectrometry, optical imaging (ICCD camera) and electron microscopy analysis (SEM, TEM), X-ray diffraction, X-ray photoelectron spectroscopy (XPS), respectively. The major differences between the two systems, observed in the gas phase analysis concern the plume composition and morphology which are strictly related to the films characteristics. In fact, while in the case of TiC it is possible to identify several evaporation mechanisms as a function of the laser fluence leading to different film composition, the ablation of TaC can be interpreted mainly in terms of a single process. The steps of the film growth were also studied for both systems.

Teghil, R.; D'Alessio, L.; Zaccagnino, M.; Ferro, D.; Marotta, V.; De Maria, G.

2001-03-01

298

Direct Drive Beryllium Ablator Capsules for the Omega Laser  

NASA Astrophysics Data System (ADS)

We are designing direct drive beryllium ablator capsules for the Omega laser as part of our effort to develop beryllium ablator ignition capsules for the National Ignition Facility (NIF). The main goals for this experimental campaign is to develop the fabrication expertise for roughly NIF size capsules and obtain experimental data on how the copper- brazed joint between the beryllium hemispheres affects the implosion. Our proposed design calls for an 1180 micron outisde diameter capsule with 40 micron thick beryllium walls containing 50 atm of deuterium gas. Some of the capsules will also have 0.05 atm of argon. We plan to image the joints with argon fluorescence from inside the capsule. Our plan is to use a 1 ns square pulse with 30 kJ of laser energy. With this drive, we expect the convergence ratio to be about 6.5 to 7. Depending on the capsule design details, we expect that the peak temperature will be 490 ± 40 eV, and the neutron yield will be anywhere from 1× 10^8 to 8× 10^8 neutrons. Some of the uncertainty comes from whether or not we use argon and questions about how much mix the copper-brazed joint will cause. The yield also depends strongly on which beryllium alloy we use. We calculate better implosions in direct drive with pure beryllium, but requirements on allowable grain size may force us to use copper-doped beryllium, which would reduce the yield by about 50%.

Bradley, P. A.; Wilson, D. C.; Cobble, J. A.; Murphy, T. J.; Cooley, J. C.; Salazar, M. A.; Rivera Nobile, G., Jr.

2001-10-01

299

Manufacture of miniature bioparticle electromanipulators by excimer laser ablation  

NASA Astrophysics Data System (ADS)

Multilevel microelectrode structures have been produced using excimer laser ablation techniques to obtain devices for the electro-manipulation of bioparticles using traveling electric field dielectrophoresis effects. The system used to make these devices operates with a krypton fluoride excimer laser at a wavelength of 248 nm and with a repetition rate of 100 Hz. The laser illuminates a chrome-on-quartz mask which contains the patterns for the particular electrode structure being made. The mask is imaged by a high- resolution lens onto the sample. Large areas of the mask pattern are transferred to the sample by using synchronized scanning of the mask and workpiece with sub-micron precision. Electrode structures with typical sizes of approximately 10 micrometers are produced and a multi-level device is built up by ablation of electrode patterns and layered insulators. To produce a traveling electric field suitable for the manipulation of bioparticles, a linear array of 10 micrometers by 200 micrometers microelectrodes, placed at 20 micrometers intervals, is used. The electric field is created by energizing each electrode with a sinusoidal voltage 90 degree(s) out of phase with that applied to the adjacent electrode. On exposure to the traveling electric field, bioparticles become electrically polarized and experience a linear force and so move along the length of the linear electrode array. The speed and direction of the particles is controlled by the magnitude and frequency of the energizing signals. Such electromanipulation devices have potential uses in a wide range of biotechnological diagnostic and processing applications. Details of the overall laser projection system are presented together with data on the devices which have been manufactured so far.

Gower, Malcolm C.; Harvey, Erol C.; Rizvi, Nadeem H.; Rumsby, Phil T.; Burt, Julian P.; Talary, Mark S.; Tame, John A.; Pethig, Ron

1998-06-01

300

Laser ablation and high precision patterning of biomaterials and intraocular lenses  

NASA Astrophysics Data System (ADS)

The use of intraocular lenses (IOL) is the most promising method for restoring excellent vision in cataract surgery. In addition, multifocal intraocular lenses for good distant and near vision are investigated. Several new materials, techniques and patterns are studied for the formation and etching of intraocular lenses in order to improve their optical properties and reduce the diffractive aberrations. As pulsed laser ablation is well established as a universal tool for surface processing of organic polymer materials, this study was focused in using laser ablation with short and ultra short laser pulses for surface modification of PMMA and intraocular lenses, instead of using other conventional techniques. The main advantage of using very short laser pulses, e.g. of ns, ps or fs duration, is that heat diffusion into the polymer material is negligible. As a result high precision patterning of the sample, without thermal damage of the surroundings, becomes possible. In this study, laser ablation was performed using commercially available hydrophobic acrylic IOLs, hydrophilic acrylic IOLs, and PMMA IOLs, with various diopters. We investigated the ablation efficiency and the phenomenology of the etched patterns by testing the ablation rate, versus laser energy fluence, at several wavelengths and the surface modification with atomic force microscopy (AFM), or scanning electron microscopy (SEM). The irradiated polymers have different optical properties, at the applied wavelengths, and therefore, present different ablation behaviour and morphology of the laser ablated crater walls and surrounding surfaces. The experimental results, some theoretical assumptions for mathematical modeling of the relevant ablation mechanisms are discussed.

Serafetinides, A. A.; Spyratou, E.; Makropoulou, M.

2010-10-01

301

High-speed machining of glass materials by laser-induced plasma-assisted ablation using a 532-nm laser  

NASA Astrophysics Data System (ADS)

In this communication, we report a high-speed machining of glass materials by a novel laser ablation technique using a conventional visible laser for the first time. A high-quality micrograting structure is fabricated in fused quartz by laser-induced plasma-assisted ablation (LIPAA) using a second harmonic of Q-switched Nd+:YAG laser (532 nm). The plasma generated from a silver (Ag) target by the laser irradiation effectively assists in ablation of the fused quartz substrate by the same laser beam, although the laser beam is transparent to the substrate. A grating with a cross-sectional shape like a square-wave (period 20 ?m) is achieved using the mask projection technique. The ablation rate reaches several tens nm/pulse. In addition, LIPAA is applied to high-speed hole drilling (700 ?m in diameter) of fused-quartz (0.5 mm thick) and Pyrex glass (0.5 mm thick).

Zhang, J.; Sugioka, K.; Midorikawa, K.

302

Single-shot ablation threshold of chromium using UV femtosecond laser pulses  

NASA Astrophysics Data System (ADS)

Single-shot ablation threshold for thin chromium film was studied using 266 nm, femtosecond laser pulses. Chromium is a useful material in the nanotechnology industry and information on ablation threshold using UV femtosecond pulses would help in precise micromachining of the material. The ablation threshold was determined by measuring the ablation crater diameters as a function of incident laser pulse energy. Absorption of 266 nm light on the chromium film was also measured under our experimental conditions, and the absorbed energy single-shot ablation threshold fluence was 46 ± 5 mJ/cm2. The experimental ablation threshold fluence value was compared to time-dependent heat flow calculations based on the two temperature model for ultrafast laser pulses. The model predicts a value of 31.6 mJ/cm2 which is qualitatively consistent with the experimentally obtained value, given the simplicity of the model.

Banerjee, S. P.; Fedosejevs, R.

2014-07-01

303

Hydrodynamic modeling of femtosecond laser ablation of metals in vacuum and in liquid  

NASA Astrophysics Data System (ADS)

We numerically examine the mechanisms involved in nanoparticle formation by laser ablation of metallic targets in vacuum and in liquid. We consider the very early ablation stage providing initial conditions for much longer plume expansion processes. In the case of ultrashort laser ablation, the initial population of primary nanoparticles is formed at this stage. When a liquid is present, the dynamics of the laser plume expansion differs from that in vacuum. Low compressibility of the ambient liquid results in strong confinement conditions. As a result, ablation threshold rises drastically, the ablated material is compressed, part of it becomes supersaturated and the backscattered material additionally heats the target. The extension of a molten layer leads to the additional ablation at a later stage also favoring nanoparticle formation. The obtained results thus explain recent experimental findings and help to predict the role of the experimental parameters. The performed analysis indicates ways of a control over nanoparticle synthesis.

Povarnitsyn, Mikhail E.; Itina, Tatiana E.

2014-10-01

304

Morphological features of silicon substrate by using different frequency laser ablation in air and water  

NASA Astrophysics Data System (ADS)

The interaction of the nanosecond laser (FWHM = 30 ns, ? = 355 nm) and monocrystalline silicon is investigated in air and water. Conventional optical and scanning electron microscopes are used to characterize surface ablation of the monocrystalline silicon. A numerical model is used to ascertain the time of the bubble motion in water. Morphological features of the laser-induced crater are different under various environments and frequencies. More debris is found when using high frequency ablation, and a larger zone is affected by heat when using low frequency ablation in air. There is no debris found in water, and the morphology of craters is better in low frequency ablation than that in high frequency ablation because bubbles generated by high frequency ablation affect laser transmission.

Xu, J. Y.; Hu, H.; Lei, Y. L.

2014-10-01

305

Characterization of the laser ablation plasma used for the deposition of amorphous carbon  

NASA Astrophysics Data System (ADS)

The plasma produced by laser ablation of a graphite target was studied by means of optical emission spectroscopy and a Langmuir planar probe. Laser ablation was performed using a Nd:YAG laser with emission at the fundamental line with pulse length of 28 ns. In this work, we report the behavior of the mean kinetic energy of plasma ions and the plasma density, as a function of the laser fluence (J/cm 2), and the target to probe (substrate) distance. The characterized regimes were employed to deposit amorphous carbon at different values of kinetic energy of the ions and plasma density. The mean kinetic energy of the ions could be changed from 40 to 300 eV, and the plasma density could be varied from 1 × 10 12 to 7 × 10 13 cm -3. The main emitting species were C + (283.66, 290.6, 299.2 and 426.65 nm) and C ++ (406.89 and 418.66 nm) with the C + (426.65 nm) being the most intense and that which persisted for the longest times. Different combinations of the plasma parameters yield amorphous carbon with different structures. Low levels (about 40 eV) of ion energy produce graphitic materials, while medium levels (about 200 eV) required the highest plasma densities in order to increase the C sbnd C sp 3 bonding content and therefore the hardness of the films. The structure of the material was studied by means of Raman spectroscopy, and the hardness and elastic modulus by depth sensitive nanoindentation.

Camps, Enrique; Escobar-Alarcón, L.; Castrejón-Sánchez, V. H.; Camacho-López, M. A.; Muhl, Stephen

2007-10-01

306

3D photomechanical model of tooth enamel ablation by Er-laser radiation  

NASA Astrophysics Data System (ADS)

The three-dimensional (3D) photomechanical model of human tooth enamel ablation is described. It takes into account: the structural peculiarities of enamel, Er-laser beam energy spatial distribution and laser radiation attenuation in the tissue. Dynamics change of enamel coefficient of absorption during ablation is also discussed. We consider the 3D photomechanical model of incomplete removal (modification) of the enamel rods by the pressure of water contained in the enamel pores and heated by laser radiation, and complete removal (ablation) of the enamel rods as result of hydroxyapatite heated by laser radiation and evaporation. Modeling results are in close agreement with the experimental results.

Belikov, Andrey V.; Shatilova, Ksenia V.; Skrypnik, Alexei V.

2014-02-01

307

Ablation algorithms and corneal asphericity in myopic correction with excimer lasers  

NASA Astrophysics Data System (ADS)

The purpose of this work is studying a corneal asphericity change after a myopic refractive correction by mean of excimer lasers. As the ablation profile shape plays a key role in the post-op corneal asphericity, ablation profiles of recent lasers should be studied. The other task of this research was to analyze operation (LASIK) outcomes of one of the lasers with generic spherical ablation profile and to compare an asphericity change with theoretical predictions. The several correction methods, like custom generated aspherical profiles, may be utilized for mitigation of unwanted effects of asphericity change. Here we also present preliminary results of such correction for one of the excimer lasers.

Iroshnikov, Nikita G.; Larichev, Andrey V.; Yablokov, Michail G.

2007-06-01

308

Synthesis of oxidation resistant lead nanoparticle films by modified pulsed laser ablation  

NASA Astrophysics Data System (ADS)

Thin layers of lead nanoparticles have been produced by a modified pulsed laser ablation (PLA) process in which smaller nanoparticles were swept out of the ablation chamber by a stream of flowing Ar. Large (?m-sized) particles, which are usually deposited during the standard PLA process, were successfully eliminated from the deposit. The nanoparticles deposited on room temperature substrates were well distributed, and the most probable particle diameter was in the order of 30 nm. Since lead is highly reactive, the nanoparticles formed in Ar were quickly oxidized upon exposure to air. A small partial pressure of H2S gas was subsequently added to the effluent, downstream from the ablation chamber, and this resulted in the formation of nanoparticle deposits that were surprisingly oxidation resistant. The properties of the nanoparticle films (as determined by transmission electron microscopy, scanning electron microscopy, x-ray diffraction, x-ray photoelectron spectroscopy, and conductivity measurements) are reported, and the mechanism of the oxidation retardation process is discussed.

Shin, Eunsung; Murray, P. Terrence; Subramanyam, Guru; Malik, Hans K.; Schwartz, Kenneth L.

2012-07-01

309

Silicon and zinc telluride nanoparticles synthesized by pulsed laser ablation: Size distributions and nanoscale structure  

SciTech Connect

Size distributions of Si and ZnTe nanoparticles produced by low energy density ArF (193 nm) pulsed laser ablation into ambient gases were measured as a function of the gas pressure and target-substrate separation, D{sub ts}, using atomic force microscopy (AFM) and high resolution scanning electron microscopy (HRSEM). For low energy density (Ed = 1.04 J/cm{sup 2}) ablation of Si into He at pressures of 0.5, 1.5, 4 and 10 torr, large nanoparticles were most numerous at D{sub ts} = 10 mm, with smaller nanoparticles found at 20 mm and 40 mm. For each D{sub ts} value a maximum of the mean nanoparticle diameter occurred for a He pressure near 6 torr, in contrast to other recent measurements in which the size of Si nanoparticles increased monotonically with the He pressure. High resolution Z-contrast transmission electron microscopy (HRZTEM) and electron energy loss spectroscopy (EELS) revealed that ZnTe nanoparticles formed by ablation into nitrogen at E{sub d} = 0.74 J/cm{sup 2} consisted of a crystalline ZnTe core surrounded by an amorphous ZnO shell. Growth defects and surface steps were clearly visible in the ZnTe crystalline core. The dependences of the mean diameter of ZnTe nanocrystals on nitrogen pressure and D{sub ts}, were qualitatively similar to those found for Si in He.

Lowndes, D.H.; Rouleau, C.M.; Duscher, G. [and others

1997-08-01

310

Particle Generation by Pulsed Excimer Laser Ablation in Liquid: Hollow Structures and Laser-Induced Reactions  

NASA Astrophysics Data System (ADS)

Pulsed laser ablation of solid targets in liquid media is a powerful method to fabricate micro-/nanoparticles, which has attracted much interest in the past decade. It represents a combinatorial library of constituents and interactions, and one can explore disparate regions of parameter space with outcomes that are impossible to envision a priori. In this work, a pulsed excimer laser (wavelength 248 nm, pulse width 30 ns) has been used to ablate targets in liquid media with varying laser fluences, frequencies, ablation times and surfactants. It is observed that hollow particles could be fabricated by excimer laser ablation of Al, Pt, Zn, Mg, Ag, Si, TiO2, and Nb2O5 in water or aqueous solutions. The hollow particles, with sizes from tens of nanometers to micrometers, may have smooth and continuous shells or have morphologies demonstrating that they were assembled from nanoparticles. A new mechanism has been proposed to explain the formation of these novel particle geometries. They were formed on laser-produced bubbles through bubble interface pinning by laser-produced solid species. Considering the bubble dynamics, thermodynamic and kinetic requirements have been discussed in the mechanism that can explain some phenomena associated with the formation of hollow particles, especially (1) larger particles are more likely to be hollow particles; (2) Mg and Al targets have stronger tendency to generate hollow particles; and (3) the 248 nm excimer laser is more beneficial to fabricate hollow particles in water than other lasers with longer wavelengths. The work has also demonstrated the possiblities to fabricate novel nanostructures through laser-induced reactions. Zn(OH)2/dodecyl sulfate flower-like nanostructures, AgCl cubes, and Ag2O cubes, pyramids, triangular plates, pentagonal rods and bars have been obtained via reactions between laser-produced species with water, electrolyes, or surfactant molecules. The underlying mechanisms of forming these structures have been discussed. The experimental results and the associated mechanisms developed in my research, and described in this thesis, have enriched the current understanding of particle generation by pulsed laser ablation in liquid. In so doing, my research has expanded the mechanistic routes for novel, or designer, nanoparticle geometries. Within the combinatorial and non-equilibrium environment provided by the unique experimental arrangement, the basic laws of material science still apply. Understanding and utilizing the laws will help researchers to fabricate new nanostructures by this and other methods providing similar environment.

Yan, Zijie

311

Ablation par laser pulse de revetements antierosion pour le domaine aeronautique  

NASA Astrophysics Data System (ADS)

Erosion resistant coatings (ERCs) are frequently used to protect aircraft engine components against erosion, and therefore, to extend their lifetime and reduce maintenance cost. However, after many hours in service, certain areas of the coating will begin to deteriorate. Given that such components are generally very costly, it is desirable to replace only the coating instead of the part itself. This research is part of the MANU 4 project, supported by CRIAQ and NSERC, which aims to study the feasibility of stripping an erosion-resistant coating deposited on a titanium-based alloy with three different techniques: wet chemical etching, plasma etching and pulse laser ablation. This thesis focuses more specifically on the etching with a pulsed laser of a 20-mum thick TiAlN ERC deposited on a Ti-6Al-4V substrate. This work compares the suitability of two pulsed lasers: a femtosecond Ti:Sapphire laser emitting at 800 nm and a nanosecond KrF excimer laser centred at 248 nm. These two lasers were chosen since they are frequently used for micromachining applications and allow us to study the effect of the wavelength and pulse duration. Preliminary findings have allowed us to identify four most critical variables that influence the etch rate and the surface roughness: (i) beam size, (ii) laser power, (iii) stage speed, and (iv) step distance between scanned lines. For each laser, optimal etching conditions were obtained by varying a single parameter at a time. Final results show that the higher energy per pulse offered by the excimer laser allows one to increase by one order of magnitude the etch rate, but almost doubles, from 1 mum to 1.8 mum, the surface roughness, in comparison with results obtained with the Ti:Sapphire laser. Compared with other techniques, pulse laser ablation has the potential to offer very high selectivity. In this regard, plume emission spectroscopy was studied as an in situ technique to monitor the etching progress and determine the precise moment when the laser beam reaches the surface of the substrate. Despite chemical similarities between the coating and the substrate, we show that it is possible to monitor the decrease of the nitrogen line with respect to the titanium reference peak in order to diagnose, in real time, when the etching process should stop. Yet, more effort is still needed to define more precisely the etch stop criteria as a function of the applied laser fluence. Finally, several surface characterization techniques were used to assess the effects of the stripping process on the surface of the substrate after ablation. Contact profilometry has confirmed that the surface roughness is increased to 1-2 mum, compared to the 0.6 mum average roughness of the coating before stripping. EDX and XRD measurements have also confirmed the presence of oxides at the surface of the substrate, a consequence of the oxidation of titanium during the ablation process at atmospheric pressure. Finally, nanoindentation measurements of the polished cross-section of the etched samples have shown that the hardness is not significantly affected during the etching process.

Ragusich, Alexis

312

INTERACTION OF LASER RADIATION WITH MATTER. LASER PLASMA: Smoothing of ablation pressure nonuniformities in the laser-plasma corona during heating of laser fusion targets  

Microsoft Academic Search

A method for smoothing ablation pressure nonuniformities during heating of laser fusion targets is described which utilises an extra laser pulse preceding the main pulse. Theoretical and experimental data are presented on heating of thin (3-10 mum) foils (simulating the target shell) by a spatially nonuniform laser beam. In the experiments, the laser pulse width at half maximum was 2

M. A. Zhurovich; O. A. Zhitkova; I. G. Lebo; Yu A. Mikhailov; G. V. Sklizkov; Aleksandr N. Starodub; V. F. Tishkin

2009-01-01

313

Ablation parameters in KrF laser/plasma interaction: An experimental study  

NASA Astrophysics Data System (ADS)

Experimental measurements of ablation parameters in a KrF laser produced aluminum plasma are presented for the laser intensity range of 1011-1013 W/cm2. Plasma created from large focal spots shows single broad ion current pulses as compared to two groups of ions observed from small focal spots. Detailed analysis of the velocity distributions of emitted ions is carried out to understand this behavior and its effect on measurements of the ablation parameters. Scalings with laser intensity of the mass ablation rate (?˜I0.42L) and of the ablation pressure (Pa˜I0.81L) giving ?=1.5×105 g cm-2 sec-1 and Pa=5.5 Mbar at a laser intensity of 1013 W/cm2 are obtained. The results are found to be in good agreement with the predictions of a plasma ablation model based on inverse bremsstrahlung dominated absorption.

Gupta, P. D.; Tsui, Y. Y.; Popil, R.; Fedosejevs, R.; Offenberger, A. A.

1987-01-01

314

Fabrication of Fresnel microlens with excimer laser contour ablation  

NASA Astrophysics Data System (ADS)

Laser micromachining systems based on excimer lasers are usually oriented to work with mask projection regime because of the low pulse repetition rate as well as large beam aperture of the laser source. In case of fabricating of the complex 3D structures, this approach introduces a number of limitations. Alternative solution might be usage of direct writing laser mode. Some examples of the so called contour ablation approach for fabricating microlenses with an absolutely monotonically changing cross-sectional profile are presented in the literature. Based on this idea and introducing new variables like automatic mask selection as well as optimizing process algorithms led us to obtain more versatile method for shape approximation. Hence, there were fabricated structures with cross-sectional profiles described as functions that are monotonic on specified intervals such as Fresnel microlenses. In this paper we describe approximation of process parameters for obtaining desired cross-sectional profiles and finally fabrication of few exemplary microlenses. All structures were characterized by a digital optical microscopy and compared to the given profiles. The accuracy of reproduction of the desired structures at the level of single microns was achieved.

Wójcik, Micha? R.; Anto?czak, Arkadiusz J.; Kozio?, Pawe? E.; ?azarek, ?ukasz K.; Stepak, Bogusz D.; Abramski, Krzysztof M.

2014-08-01

315

Doppler-shifted optical absorption characterization of plume-lateral expansion in laser ablation of a cerium target  

NASA Astrophysics Data System (ADS)

The temporal evolution of the ablation plume of cerium was investigated by absorption spectroscopy. Cerium oxide pellets were ablated in a helium atmosphere by second-harmonic radiation (532 nm) from a Nd:YAG laser at a fluence of 0.5 J/cm2. The lateral velocity (expansion velocity horizontal to the sample surface) of the plume was determined from the magnitude of the Doppler splitting of the absorption spectra measured close to the sample surface. The lateral velocities of neutral and singly ionized atoms were systematically investigated by varying several parameters, such as ambient gas pressure, ablation laser fluence, observation timing, and observation height. In addition, temporal profiles of the absorption signal were measured by detuning the probe laser frequency from the atomic resonant frequency in order to obtain the temporal variation of the velocity. On the basis of the drag force model, the slowing coefficients for atomic and ionic species in a helium atmosphere were evaluated along with lateral velocity in a vacuum. This study may help in understanding the plume dynamics effect on deposited film properties as well as optimizing experimental conditions for ablation-based spectroscopic analysis.

Miyabe, M.; Oba, M.; Iimura, H.; Akaoka, K.; Maruyama, Y.; Ohba, H.; Tampo, M.; Wakaida, I.

2012-12-01

316

Atomistic investigation of ablation of amorphous polystyrene under femtosecond laser pulse  

NASA Astrophysics Data System (ADS)

In the present work we elucidate the thermodynamic mechanisms of femtosecond (fs) laser ablation of amorphous polystyrene by means of molecular dynamics (MD) simulations. The effects of extrinsic parameter of laser pulse intensity and intrinsic parameter of molecular architecture on the laser ablation are further studied. Simulation results show that the laser ablation-induced polymeric material removal is achieved by evaporation from the surface and expansion within the bulk. Furthermore, inter-chain sliding and intra-chain change also play important roles in the microscopic deformation of the material. It is found that both the laser pulse intensity and the arrangement of phenyl groups have significant influence on the fs laser ablation of polystyrene.

Huang, YanHua; Song, ChengWei; Zhang, JunJie; Sun, Tao

2014-09-01

317

Theoretical modeling of laser ablation of quaternary bronze alloys: case studies comparing femtosecond and nanosecond LIBS experimental data.  

PubMed

A model, formerly proposed and utilized to understand the formation of laser induced breakdown spectroscopy (LIBS) plasma upon irradiation with nanosecond laser pulses at different fluences and wavelengths, has been extended to the irradiation with femtosecond laser pulses in order to control the fractionation mechanisms which heavily affect the application of laser-ablation-based microanalytical techniques. The model takes into account the different chemico-physical processes occurring during the interaction of an ultrashort laser pulse with a metallic surface. In particular, a two-temperature description, relevant to the electrons and lattice of the substrate, respectively, has been introduced and applied to different ternary and quaternary copper-based alloys subjected to fs and ns ablation both in the visible (527 nm) and in the UV (248 nm). The model has been found able to reproduce the shorter plasma duration experimentally found upon fs laser ablation. Kinetic decay times of several copper (major element) emission lines have been examined together with those relevant to the main plasma parameters. The plasma experimental temperature, derived assuming a Boltzmann distribution, and the electron density following the Saha equation have been compared with the corresponding theoretical data. A satisfactory description of plasma parameters and main matrix constituent composition has been obtained in the time window where local thermal equilibrium was assumed for LIBS data analysis. Improved analytical capabilities are predicted upon delayed detection of plasma emission in femtosecond LIBS, in relation to the better LOD achieved and to the improved data reproducibility expected. Results support the utilization of ultrafast laser sources for trace detection, despite the residual fractionation occurring in the examined range of fluences which affects the linearity of experimental calibration curves built for tin and lead after internal standardization on copper. The validation of model results by experimental data allowed highlighting, from first principles, of the ablation mechanisms for the two temporal regimes and information on how this affects the accurate microanalysis of Cu-based alloys. PMID:19817368

Fornarini, Lucilla; Fantoni, Roberta; Colao, Francesco; Santagata, Antonio; Teghil, Roberto; Elhassan, Asmaa; Harith, Mohamed A

2009-12-31

318

Smoothing of ablation pressure nonuniformities in the laser-plasma corona during heating of laser fusion targets  

Microsoft Academic Search

A method for smoothing ablation pressure nonuniformities during heating of laser fusion targets is described which utilises an extra laser pulse preceding the main pulse. Theoretical and experimental data are presented on heating of thin (3–10 ?m) foils (simulating the target shell) by a spatially nonuniform laser beam. In the experiments, the laser pulse width at half maximum was 2

M A Zhurovich; O A Zhitkova; I G Lebo; Yu A Mikhailov; G V Sklizkov; Aleksandr N Starodub; V F Tishkin

2009-01-01

319

Smoothing of ablation pressure nonuniformities in the laser-plasma corona during heating of laser fusion targets  

Microsoft Academic Search

A method for smoothing ablation pressure nonuniformities during heating of laser fusion targets is described which utilises an extra laser pulse preceding the main pulse. Theoretical and experimental data are presented on heating of thin (3-10 m) foils (simulating the target shell) by a spatially nonuniform laser beam. In the experiments, the laser pulse width at half maximum was 2

M A Zhurovich; Yu A Mikhailov; G V Sklizkov; Aleksandr N Starodub; O A Zhitkova; I G Lebo; V F Tishkin

2009-01-01

320

A comparison of nanosecond and femtosecond laser-induced plasma spectroscopy of brass samples  

Microsoft Academic Search

The ablation of brass samples in argon shield gas by 170 fs and 6 ns laser pulses has been studied by optical emission spectroscopy of the evolving plasmas. Differences observed in the temporal behavior of the spectral line intensities are explained by the shielding effect of the Ar plasma for ns-pulses and the free expansion of the plasma of the

V. Margetic; A Pakulev; A Stockhaus; M Bolshov; K Niemax; R Hergenröder

2000-01-01

321

Modeling of plume dynamics with shielding in laser ablation of carbon  

NASA Astrophysics Data System (ADS)

The process of laser ablation of carbon in presence of background gas is simulated numerically. The plume dynamics in laser ablation is important to study for many reasons including temperature of plume particles and shielding of target by previously ablated plumes. Shielding leads directly to the change in energy deposition of incident laser pulse at the target surface and in turn influences the ablation dynamics and amount of material removed. Carbon ablation is studied for single and multiple laser hits typical for synthesis of nanotubes. Two models of correction of ablated velocity and pressure resulting from shielding effect are proposed and investigated. Numerical modeling of this plume dynamics and its integral effect of shielding is challenging due to inherent high nonlinearity of the problem. Some of available numerical techniques handles nonlinearity but are dissipative, e.g. Godunov type schemes. Other techniques are less dissipative but fail to account for strong nonlinearity typical for initial stages of ablation, e.g. the ENO-Roe. To effectively model this highly nonlinear plume dynamics a combination of two of above mentioned schemes is developed so as the numerical evaluation of fluxes is close to their physical values and the scheme has minimum dissipation. The non-monotonic behavior of ablated mass as a function of time duration between two laser pulses is studied.

Pathak, Kedar; Povitsky, Alex

2007-05-01

322

Simulation of Laser Interaction with Ablative Plasma and ydrodynamic of Laser Supported Plasma(LSP)  

NASA Astrophysics Data System (ADS)

A general Godunov finite difference schemes-WENO(Weighted Essentially Non-Oscillatory) Schemes which have fifth-order accuracy was used to make a numerical calculation for 2-dimensional axis symmetrical laser-supported plasma flow field under laser ablated solid target. The models of the calculation of ionization degree of plasma and the interaction between laser beam and plasma and the simplified eos(equation of state) of plasma were considered in the simulation. The plasma field parameters during and after laser duration variation with time are also obtained. The simulation results show that the laser beam power was strong absorbed by plasma of target surface, and the velocity of LSD(Laser Supported Detonation) wave is half of ideal LSD value which derived from C-J detonation theory.

Huifeng, Tong; Zhiping, Tang

2011-06-01

323

Alternatives to excimer laser refractive surgery: UV and mid-infrared laser ablation of intraocular lenses and porcine cornea  

NASA Astrophysics Data System (ADS)

Despite the fact that the laser applications in human ophthalmology are well established, further research is still required, for better and predictable ablation dosimetry on both cornea tissue and intraocular lenses. Further studies for alternative laser sources to the well established excimer lasers, such as UV or mid-infrared solid state lasers, have been proposed for refractive surgery. The precise lens ablation requires the use of laser wavelengths possessing a small optical penetration depth in the cornea and in the synthetic lenses, in order to confine the laser energy deposition to a small volume. In order to eliminate some very well known problems concerning the reshaping of cornea and the modification of the optical properties of the intraocular lenses, ablation experiments of ex vivo porcine cornea, acrylic PMMA and hydrophilic lenses were conducted with an Er:YAG laser (2.94 ?m) and the fifth harmonic of a Nd:YAG laser (213 nm). The morphology of cornea was recorded using a cornea topography system before and immediately after the ablation. Histology analysis of the specimens was obtained, in order to examine the microscopic appearance of the ablated craters and the existence of any thermal damage caused by the mid-infrared and UV laser irradiation. The macroscopic morphology of the intraocular lens craters was inspected with an optical transmission microscope. Measurements of the ablation rates of the lenses were performed and simulated by a mathematical model.

Serafetinides, A. A.; Makropoulou, M.; Spyratou, E.; Bacharis, C.

2007-03-01

324

Comparison of silver nanoparticles confined in nanoporous silica prepared by chemical synthesis and by ultra-short pulsed laser ablation in liquid  

NASA Astrophysics Data System (ADS)

Hexagonally ordered mesoporous silica materials, MCM-41 and SBA-15, have been synthesized and loaded with Ag nanoparticles, utilizing both chemical synthesis and ultra-short pulsed laser ablation in liquid. In laser ablation, a silver target, immersed in aqueous suspension of ordered mesoporous silica SBA-15, was irradiated by ultra-short laser pulses to generate silver nanoparticles. For comparison, samples of similar silver contents were prepared either by incorporating silver into the SBA-15 during a hydrothermal synthesis or by introducing silver in MCM-41 by template ion-exchange. Samples were characterized by XRD, N2 physisorption, TEM and UV-vis spectroscopy. All preparations contained significant amount of 5-50 nm size silver agglomerates on the outer surface of the silica particles. The laser ablation process did not cause significant destruction of the SBA-15 structure and metallic silver (Ag0) nanoparticles were mainly generated. It is demonstrated that by laser ablation in aqueous silica suspension smaller and more uniform metallic silver particles can be produced and loaded on the surface of the silica support than by synthesis procedures. Catalytic properties of the samples have been tested in the total oxidation of toluene. Because of its favorable Ag dispersity, the Ag/SBA-15 catalyst, generated by the laser ablation method, had better catalytic stability and, relative to its Ag load, higher activity than the conventional Ag/SBA-15 preparations.

Szegedi, Á.; Popova, M.; Valyon, J.; Guarnaccio, A.; De Stefanis, A.; De Bonis, A.; Orlando, S.; Sansone, M.; Teghil, R.; Santagata, A.

2014-10-01

325

Precise ablation of dental hard tissues with ultra-short pulsed lasers. Preliminary exploratory investigation on adequate laser parameters.  

PubMed

This study aimed to evaluate the possibility of introducing ultra-short pulsed lasers (USPL) in restorative dentistry by maintaining the well-known benefits of lasers for caries removal, but also overcoming disadvantages, such as thermal damage of irradiated substrate. USPL ablation of dental hard tissues was investigated in two phases. Phase 1--different wavelengths (355, 532, 1,045, and 1,064 nm), pulse durations (picoseconds and femtoseconds) and irradiation parameters (scanning speed, output power, and pulse repetition rate) were assessed for enamel and dentin. Ablation rate was determined, and the temperature increase measured in real time. Phase 2--the most favorable laser parameters were evaluated to correlate temperature increase to ablation rate and ablation efficiency. The influence of cooling methods (air, air-water spray) on ablation process was further analyzed. All parameters tested provided precise and selective tissue ablation. For all lasers, faster scanning speeds resulted in better interaction and reduced temperature increase. The most adequate results were observed for the 1064-nm ps-laser and the 1045-nm fs-laser. Forced cooling caused moderate changes in temperature increase, but reduced ablation, being considered unnecessary during irradiation with USPL. For dentin, the correlation between temperature increase and ablation efficiency was satisfactory for both pulse durations, while for enamel, the best correlation was observed for fs-laser, independently of the power used. USPL may be suitable for cavity preparation in dentin and enamel, since effective ablation and low temperature increase were observed. If adequate laser parameters are selected, this technique seems to be promising for promoting the laser-assisted, minimally invasive approach. PMID:22565342

Bello-Silva, Marina Stella; Wehner, Martin; Eduardo, Carlos de Paula; Lampert, Friedrich; Poprawe, Reinhart; Hermans, Martin; Esteves-Oliveira, Marcella

2013-01-01

326

Spindle Assembly and Architecture: From Laser Ablation to Microtubule Nucleation  

NASA Astrophysics Data System (ADS)

Spindles are arrays of microtubules that segregate chromosomes during cell division. It has been difficult to validate models of spindle assembly due to a lack of information on the organization of microtubules in these structures. Here we present a novel method, based on femtosecond laser ablation, capable of measuring the detailed architecture of spindles. We used this method to study the metaphase spindle and find that microtubules are shortest near poles and become progressively longer towards the center of the spindle. These data, in combination with mathematical modeling, high resolution imaging, and biochemical perturbations, are sufficient to reject previously proposed mechanisms of spindle assembly. Our results support a new model of spindle assembly in which microtubule polymerization dynamics are not spatially regulated, microtubule transport locally sorts microtubules -- determining their proper organization in the spindle without moving them appreciable distances --, and the profile of microtubule nucleation controls the length of the spindle.

Needleman, Daniel; Brugues, Jan; Nuzzo, Valeria; Mazur, Eric

2012-02-01

327

Laser Ablation of Gallium Arsenide in Different Solutions  

SciTech Connect

The optical, structural, and nonlinear optical characteristics of GaAs nanoparticles obtained by laser ablation in different liquids were investigated. Thermally induced self-defocusing in GaAs solutions was observed using both a high pulse repetition rate and nanosecond pulses. In studying the nonlinear optical characteristics of GaAs solutions using picosecond and femtosecond pulses, two-photon absorption was observed. The nonlinear absorption coefficient of an aqueous GaAs solution measured by the Z-scan technique and the nonlinear susceptibility of GaAs nanoparticles were, respectively, 0.7 x 10{sup -9} cm W{sup -1} and 2 x 10{sup -9} esu at a wavelength of 795 nm.

Ganeev, R.A.; Kuroda, H. [Institute for Solid State Physics, University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8581 (Japan); Ryasnyanskii, A.I. [Samarkand State University, Samarkand, 703004 (Uzbekistan)

2005-12-15

328

Fabrication of pillared PLGA microvessel scaffold using femtosecond laser ablation  

PubMed Central

One of the persistent challenges confronting tissue engineering is the lack of intrinsic microvessels for the transportation of nutrients and metabolites. An artificial microvascular system could be a feasible solution to this problem. In this study, the femtosecond laser ablation technique was implemented for the fabrication of pillared microvessel scaffolds of polylactic-co-glycolic acid (PLGA). This novel scaffold facilitates implementation of the conventional cell seeding process. The progress of cell growth can be observed in vitro by optical microscopy. The problems of becoming milky or completely opaque with the conventional PLGA scaffold after cell seeding can be resolved. In this study, PLGA microvessel scaffolds consisting of 47 ?m × 80 ?m pillared branches were produced. Results of cell culturing of bovine endothelial cells demonstrate that the cells adhere well and grow to surround each branch of the proposed pillared microvessel networks. PMID:22605935

Wang, Hsiao-Wei; Cheng, Chung-Wei; Li, Ching-Wen; Chang, Han-Wei; Wu, Ping-Han; Wang, Gou-Jen

2012-01-01

329

Iron carbide nanoparticles produced by laser ablation in organic solvent  

NASA Astrophysics Data System (ADS)

Laser ablation of iron in an organic solvent (pentane, hexane, or decane) was performed using an air-tight cell to produce iron carbide nanoparticles. Mössbauer spectra of the nanoparticles were obtained at room temperature. They revealed that the nanoparticles consisted of two paramagnetic components and magnetic components. The two paramagnetic components were a high-spin Fe(II) species and an amorphous iron carbide containing a large amount of carbon. Whereas the magnetic components measured at room temperature exhibited superparamagnetism, those measured at low temperature were fitted by a combination of four sextets, which were assigned to Fe7 C 3. The Fe7 C 3 yield was higher in higher molecular weight solvents. Transmission electron microscopy (TEM) images of the samples showed that the nanoparticles were spherical with diameters in the range 10-100 nm.

Matsue, T.; Yamada, Y.; Kobayashi, Y.

2012-03-01

330

Synthesis of magnetic nanoparticles by pulsed laser ablation  

NASA Astrophysics Data System (ADS)

Magnetic nanoparticles were prepared by laser ablation of Fe foil in ethanol. The nanoparticles consisted of Fe3O4 and Fe3C and were superparamagnetic with a saturation magnetization Ms = 124 emu/g. Zero field cooled (ZFC) measurements collected at an applied field of 50 Oe displayed a maximum magnetic susceptibility at 120 K with a broad distribution. Field cooled (FC) measurements collected during cooling and heating showed a thermal hysteresis indicative of temperature dependent magnetic viscosity. The magnetic viscosity was calculated from thermoremanent magnetization (TRM) plots and it increased with decreasing temperature. The activation volume of these non uniform magnetic states was calculated from TRM measurements and it was found to decrease with decreasing temperature. The decrease in activation diameters was interpreted as a decrease in exchange length, and hence a decrease in particle-particle interactions.

Franzel, L.; Bertino, M. F.; Huba, Z. J.; Carpenter, E. E.

2012-11-01

331

Synthesis of stable silver colloids by laser ablation in water  

NASA Astrophysics Data System (ADS)

The stable colloid with silver nanoparticles has been produced by irradiation of metal target in deionized water by pulse 1064 nm laser. The dependences of the nanoparticle size and colloid stability on fluence, ablation time, surface conditions of the target, and thickness of the water layer have been studied. The sizes and shape of nanoparticles have been measured by dynamic light scattering and by scanning electron microscopy. It has been shown that decrease of the water layer thickness above the target surface leads to increase of the colloid stability. The proper number of treatment cycles allowed to prepare the target surface for production of the nanoparticles with average size about 34 nm obtained by statistical analysis of the scanning electron microscope images. Several methods have been used to increase the colloid stability: (1) increase of the laser fluence, (2) decrease of the water layer thickness above the target surface, (3) the treatment of the target surface by laser beam scanning. The subsequent increase of the colloid concentration by partial drying slightly enhanced the nanoparticle size. The optimized synthesis conditions and drying parameters allowed to produce the pure colloid with concentration about 0.5 g/l and stability over a month of almost spherical silver nanoparticles with typical size 45±5 nm.

Tyurnina, Anastasiya E.; Shur, Vladimir Y.; Kozin, Roman V.; Kuznetsov, Dmitry K.; Mingaliev, Evgeny A.

2013-11-01

332

Iron isotope composition of particles produced by UV-femtosecond laser ablation of natural oxides, sulfides, and carbonates.  

PubMed

The need for femtosecond laser ablation (fs-LA) systems coupled to MC-ICP-MS to accurately perform in situ stable isotope analyses remains an open question, because of the lack of knowledge concerning ablation-related isotopic fractionation in this regime. We report the first iron isotope analysis of size-resolved, laser-induced particles of natural magnetite, siderite, pyrrhotite, and pyrite, collected through cascade impaction, followed by analysis by solution nebulization MC-ICP-MS, as well as imaging using electron microscopy. Iron mass distributions are independent of mineralogy, and particle morphology includes both spheres and agglomerates for all ablated phases. X-ray spectroscopy shows elemental fractionation in siderite (C-rich agglomerates) and pyrrhotite/pyrite (S-rich spheres). We find an increase in (56)Fe/(54)Fe ratios of +2‰, +1.2‰, and +0.8‰ with increasing particle size for magnetite, siderite, and pyrrhotite, respectively. Fe isotope differences in size-sorted aerosols from pyrite ablation are not analytically resolvable. Experimental data are discussed using models of particles generation by Hergenröder and elemental/isotopic fractionation by Richter. We interpret the isotopic fractionation to be related to the iron condensation time scale, dependent on its saturation in the gas phase, as a function of mineral composition. Despite the isotopic variations across aerosol size fractions, total aerosol composition, as calculated from mass balance, confirms that fs-LA produces a stoichiometric sampling in terms of isotopic composition. Specifically, both elemental and isotopic fractionation are produced by particle generation processes and not by femtosecond laser-matter interactions. These results provide critical insights into the analytical requirements for laser-ablation-based stable isotope measurements of high-precision and accuracy in geological samples, including the importance of quantitative aerosol transport to the ICP. PMID:24261311

d'Abzac, Francois-Xavier; Beard, Brian L; Czaja, Andrew D; Konishi, Hiromi; Schauer, James J; Johnson, Clark M

2013-12-17

333

High-temperature transuranium organometallic species from laser ablation of actinide–polymer mixtures  

Microsoft Academic Search

Pulsed laser ablation of dispersions of f-element compounds in polymers produces novel `high-temperature' organometallic complex ions. The M+–L from reactions of metal ions (M+) with polymer fragments (L) in the ablation plume are identified by time-of-flight mass spectrometry. Compositions and abundances of M+–L from ablation of UO2 and lanthanides in polyimide (PI) reflected distinctive f-element chemistries; we report here on

John K Gibson

1998-01-01

334

INTERACTION OF LASER RADIATION WITH MATTER. LASER PLASMA: Laser ablation plume dynamics in nanoparticle synthesis  

NASA Astrophysics Data System (ADS)

The dynamics of the plume ejected from the surface of solid targets (YSZ, Nd:YAG and graphite) by a CO2 laser pulse with a duration of ~500 ?s (at the 0.03 level), energy of 1.0-1.3 J and peak power of 6-7 kW have been studied using high-speed photography of the plume luminescence and shadow. The targets were used to produce nanopowders by laser evaporation. About 200 ?s after termination of the pulse, shadowgraph images of the plumes above the YSZ and Nd:YAG targets showed dark straight tracks produced by large particles. The formation of large (~10 ?m) particles is tentatively attributed to cracking of the solidified melt at the bottom of the ablation crater. This is supported by the fact that no large particles are ejected from graphite, which sublimes without melting. Further support to this hypothesis is provided by numerical 3D modelling of melt cooling in craters produced by laser pulses of different shapes.

Osipov, V. V.; Platonov, V. V.; Lisenkov, V. V.

2009-06-01

335

Preparation of nano-size particles of silver with femtosecond laser ablation in water  

NASA Astrophysics Data System (ADS)

Nano-size particles of Ag were prepared by laser ablation in water with femtosecond laser pulses at 800 nm. The formation efficiency and the size of colloidal particles were compared with those of colloidal particles prepared by nanosecond laser pulses. The formation efficiency for femtosecond pulses was significantly lower than that for nanosecond pulses. The size of colloids prepared by femtosecond pulses were less dispersed than that of colloids prepared by nanosecond pulses. The shape of the craters on the targets suggested that ablation process was different between femtosecond and nanosecond ablation. In addition, it was found that the ablation efficiency for femtosecond ablation in water was lower than that in air, while that for nanosecond pulses was similar in both water and air.

Tsuji, Takeshi; Kakita, Toshihiko; Tsuji, Masaharu

2003-02-01

336

Wavelength dependence of boron nitride ablation by TEA CO2 lasers  

NASA Astrophysics Data System (ADS)

Transversely excited atmospheric (TEA) CO2 laser ablation of boron nitride ceramics in both cubic and hexagonal phases (cBN, hBN) was demonstrated. A TEA CO2 laser oscillating at a wavelength of 9.2 ?m, which coincides with a TO-phonon spectrum of the cBN, could ablate the cBN ceramics more efficiently than with 10 ?m band radiation. The hBN samples were also ablated well with 9.2 ?m laser irradiation, however, the ablated site color changed to black due to a boron rich phase left on the surface. In the case of hBN sintered with Al2O3 and SiO2, the ablation threshold fluence is determined by the one of Al2O3, which is the highest threshold among the three elements.

Sumiyoshi, Tetsumi; Tomita, Hiroyuki; Takahashi, Akihisa; Obara, Minoru; Ishii, Katsunori

1996-05-01

337

Comparison of separation performance of laser-ablated and wet-etched microfluidic devices  

PubMed Central

Laser ablation of glass allows for production of microfluidic devices without the need of hydrofluoric acid and photolithography. The goal of this study was to compare the separation performance of microfluidic devices produced using a low-cost laser ablation system and conventional wet etching. During laser ablation, cracking of the glass substrate was prevented by heating the glass to 300°C. A range of laser energy densities was found to produce channel depths ranging from 4 – 35 ?m and channel widths from 118 – 162 ?m. The electroosmotic flow velocity was lower in laser-ablated devices, 0.110 ± 0.005 cm s?1, as compared to wet-etched microfluidic chips, 0.126 ± 0.003 cm s?1. Separations of both small and large molecules performed on both wet- and laser-ablated devices were compared by examining limits of detection, theoretical plate count, and peak asymmetry. Laser-induced fluorescence detection limits were 10 pM fluorescein for both types of devices. Laser-ablated and wet-etched microfluidic chips had reproducible migration times with ? 2.8% RSD and peak asymmetries ranging from 1.0 – 1.8. Numbers of theoretical plates were between 2.8- and 6.2-fold higher on the wet-etched devices compared to laser-ablated devices. Nevertheless, resolution between small and large analytes was accomplished, which indicates that laser ablation may find an application in pedagogical studies of electrophoresis or microfluidic devices, or in settings where hydrofluoric acid cannot be used. PMID:20827468

Baker, Christopher A.; Bulloch, Rayford; Roper, Michael G.

2010-01-01

338

Laser hydrothermal reductive ablation of titanium monoxide: Hydrated TiO particles with modified Ti/O surface  

SciTech Connect

IR laser- and UV laser-induced ablation of titanium monoxide (TM) in hydrogen (50 Torr) is compared to the same process induced in vacuum and shown to result in deposition of hydrated surface modified nanostructured titanium suboxide films. Complementary analyses of the films deposited in vacuum and in hydrogen by Fourier transform infrared, Raman and X-ray photoelectron spectroscopy, X-ray diffraction and electron microscopy allowed to determine different features of both films and propose a mechanism of surface modification of ejected particles, which involves hydrothermal reduction of TM and subsequent reactions of evolved water. The films exert good adhesion to metal and quartz surfaces and are hydrophobic in spite of having their surface coated with adsorbed water. - Graphical abstract: Laser ablation of titanium monoxide (TiO) in hydrogen involves a sequence of H{sub 2} and H{sub 2}O eliminations and additions and yields hydrated amorphous nanostructured titanium suboxide which is richer in oxygen than TiO. Highlights: Black-Right-Pointing-Pointer IR and UV laser ablated particles of titanium monoxide (TiO) undergo amorphization. Black-Right-Pointing-Pointer Films deposited in vacuum have TiO stoichiometry and are oxidized in atmosphere. Black-Right-Pointing-Pointer Films deposited in hydrogen are hydrated and have more O in topmost layers. Black-Right-Pointing-Pointer Films modification in hydrogen is explained by reactions in hydrogen plasma.

Blazevska-Gilev, Jadranka [Laboratory of Laser Chemistry, Institute of Chemical Process Fundamentals, ASCR, Prague 16502 (Czech Republic); University St.Cyril and Methodious, Skopje 1000, Former Yugoslav Republic of Macedonia (Macedonia, The Former Yugoslav Republic of); Jandova, Vera [Laboratory of Laser Chemistry, Institute of Chemical Process Fundamentals, ASCR, Prague 16502 (Czech Republic); Kupcik, Jaroslav [Laboratory of Laser Chemistry, Institute of Chemical Process Fundamentals, ASCR, Prague 16502 (Czech Republic); Institute of Inorganic Chemistry, ASCR, Rez 25068 (Czech Republic); Bastl, Zdenek [J. Heyrovsky Institute of Physical Chemistry, ASCR, Prague 18223 (Czech Republic); Subrt, Jan; Bezdicka, Petr [Institute of Inorganic Chemistry, ASCR, Rez 25068 (Czech Republic); Pola, Josef, E-mail: pola@icpf.cas.cz [Laboratory of Laser Chemistry, Institute of Chemical Process Fundamentals, ASCR, Prague 16502 (Czech Republic)

2013-01-15

339

Laser-induced breakdown spectroscopy of tantalum plasma  

SciTech Connect

Laser Induced Breakdown spectroscopy (LIBS) of Tantalum (Ta) plasma has been investigated. For this purpose Q-switched Nd: YAG laser pulses (?? 1064 nm, ?? 10 ns) of maximum pulse energy of 100 mJ have been employed as an ablation source. Ta targets were exposed under the ambient environment of various gases of Ar, mixture (CO{sub 2}: N{sub 2}: He), O{sub 2}, N{sub 2}, and He under various filling pressure. The emission spectrum of Ta is observed by using LIBS spectrometer. The emission intensity, excitation temperature, and electron number density of Ta plasma have been evaluated as a function of pressure for various gases. Our experimental results reveal that the optical emission intensity, the electron temperature and density are strongly dependent upon the nature and pressure of ambient environment. The SEM analysis of the ablated Ta target has also been carried out to explore the effect of ambient environment on the laser induced grown structures. The growth of grain like structures in case of molecular gases and cone-formation in case of inert gases is observed. The evaluated plasma parameters by LIBS analysis such as electron temperature and the electron density are well correlated with the surface modification of laser irradiated Ta revealed by SEM analysis.

Khan, Sidra; Bashir, Shazia; Hayat, Asma; Khaleeq-ur-Rahman, M.; Faizan–ul-Haq [Centre for Advanced Studies in Physics, GC University, Lahore (Pakistan)] [Centre for Advanced Studies in Physics, GC University, Lahore (Pakistan)

2013-07-15

340

LASER ABLATION SYNTHESIS OF ZINC OXIDE CLUSTERS: A NEW FAMILY OF FULLERENES?  

E-print Network

1 LASER ABLATION SYNTHESIS OF ZINC OXIDE CLUSTERS: A NEW FAMILY OF FULLERENES? Alexander V to fullerenes. A local abundance minimum at n = 13 provides an additional evidence for the presence in the ablation plume of fullerene-like (ZnO)n clusters. #12;2 Recently much interest has been shown in Zn

Paris-Sud XI, Université de

341

Laser flash photography of cold cavitation-driven ablation in tissues  

Microsoft Academic Search

Plasma mediated ablation of collagen gels and porcine cornea was studied at various laser pulse durations in the range from 350 fs to 1 ns at 1053 nm wavelength. A time resolved stress detection technique was employed to measure transient stress profiles and amplitudes. Optical microscopy was used to characterize ablation craters qualitatively, while a wide band acoustic transducer helped

Alexander A. Oraevsky; Rinat O. Esenaliev; Steven L. Jacques; Frank K. Tittel

1995-01-01

342

Modeling CO{sub 2} laser ablation impulse of polymers in vapor and plasma regimes  

SciTech Connect

An improved model for CO{sub 2} laser ablation impulse in polyoxymethylene and similar polymers is presented that describes the transition effects from the onset of vaporization to the plasma regime in a continuous fashion. Several predictions are made for ablation behavior.

Sinko, John E. [Micro-Nano Global Center of Excellence, Graduate School of Engineering, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8603 (Japan); Phipps, Claude R. [Photonic Associates LLC, 200A Ojo de la Vaca Road, Santa Fe, New Mexico 87508 (United States)

2009-09-28

343

Pressure effects during excimer laser ablation of magnesium diboride targets  

Microsoft Academic Search

The expansion dynamics and kinetics of the plasma produced by excimer laser irradiation of MgB2 in Ar background gas has been studied by space- and time-resolved optical emission spectroscopy. The experimental results show that there is a distance-related pressure threshold above which the expansion dynamics changes from a free expansion to a shock wave regime, causing both a considerable increase

S. Amoruso; M. Armenante; R. Bruzzese; N. Spinelli; R. Velotta; M. Vitiello; X. Wang

2003-01-01

344

Formation of periodic structures upon laser ablation of metal targets in liquids  

SciTech Connect

Experimental data on the formation of ordered microstructures produced upon ablation of metal targets in liquids irradiated by a copper vapour laser or a pulsed Nd:YAG laser are presented. The structures were obtained on brass, bronze, copper, and tungsten substrates immersed in distilled water or ethanol. As a result of multiple-pulse laser ablation by a scanning beam, ordered microcones with pointed vertexes are formed on the target surface. The structures are separated by deep narrow channels. The structure period was experimentally shown to increase linearly with diameter of the laser spot on the target surface. (interaction of laser radiation with matter)

Kazakevich, Pavel V; Simakin, Aleksandr V; Shafeev, Georgii A [A.M. Prokhorov General Physics Institute, Russian Academy of Sciences, Moscow (Russian Federation)

2005-09-30

345

The FTICRMS laser microprobe: Speciation of surfaces in resonant laser ablation/ionization (RLA)  

NASA Astrophysics Data System (ADS)

The coupling of a tunable laser with a laser microprobe FT-ICR-MS prototype developed at the University of Metz made it possible to carry out the first RLA-FTICRMS experiment, which combines the selectivity and the sensitivity of two photon resonant laser ablation/ionization and the high accuracy mass measurement. This technique is a tool for the direct analysis of organic (or inorganic) traces on surfaces. The selectivity of the element's detection depends on the choice of resonant line, and on the screen effect of gazeous plume emitted by the laser pulse. In fact, the resonant two photons processes are most effective when the laser power density is lower than 5.108 W/cm2 because the gaseous cloud is relatively transparent in this condition.

Muller, Jean-François; Krier, Gabriel; Aubriet, Frédéric; Vernex-Loset, Lionel; Courrier, Benoît

2001-08-01

346

Third order optical nonlinearity and diffraction pattern of Ni nanoparticles prepared by laser ablation  

NASA Astrophysics Data System (ADS)

In this article we studied all-optical Kerr effect of Ni nanoparticles immersed in ethanol using z-scan method. The nanoparticles were prepared by high frequency pulsed laser ablation. UV-Visible optical absorption spectroscopy and SEM observation were employed for characterization and studying the morphology of Ni nanoparticles. Analysis of scanning electron microscopy (SEM) images showed that the synthesized nanoparticles shape were dominantly spherical, varying from 19 nm to 40 nm for 1 mJ pulse energy. The nonlinear absorption and refraction indices were measured using open- and closed-aperture z-scan techniques, with both CW and pulsed irradiations. In both regimes results were studied. Furthermore, diffraction rings pattern as a result of nonlinear refraction was observed. We suggested an opportunity to form a new nonlinear-optical media for nonlinear optical applications.

Alikhani, S.; Tajalli, H.; Koushki, E.

2013-01-01

347

Excited states time evolution on a laser-ablated molybdenum plume  

NASA Astrophysics Data System (ADS)

The dynamics of the excited states on a laser-ablated Mo plume was studied, both in air and in vacuum, by emission spectroscopy along the plume expansion axis. The emission related to ionized atoms occurs in the beginning of the plume expansion, near the metal surface, and is predominantly ultraviolet emission. In the middle of the plasma plume, it takes place the electron transitions between excited states of neutral atoms, and in the end of the plume, the visible emission is to transitions to the ground state of neutral molybdenum atoms. It was possible to determine plume parameters such as plasma expansion velocity of (5.0 ± 0.7) km/s at atmospheric pressure and (4.0 ± 0.7) km/s in vacuum, and the plasma duration that was (160 ± 14) ns at atmospheric pressure and (138 ± 18) ns in vacuum.

Sternberg, E. M. A.; Rodrigues, N. A. S.; Sbampato, M. E.; Amorim, J.; Silveira, C. A. B.

2014-09-01

348

In situ photography of picosecond laser ablation of nickel D.A. Willis1  

E-print Network

In situ photography of picosecond laser ablation of nickel D.A. Willis1 , X. Xu* School. The fundamental and second harmonic wavelengths were used for the pump and probe beams, respectively. The probe

Xu, Xianfan

349

Slit Skiascopic-guided Ablation Using the Nidek Laser  

Microsoft Academic Search

PURPOSE: To present the approach of using a scanning slit refractometer (the ARK 10000) in con- junction with a corneal topography system to guide customized corneal ablation. This diagnostic system is coupled with the Nidek EC-5000 system which combines scanning slit and a scanning small area ablation (1.0 mm) to perform a customized ablation. METHODS: The ARK 10000 diagnostic system

Scott MacRae; Masanao Fujieda

2000-01-01

350

Visualization of microsecond laser ablation of porcine clot and gelatin under a clear liquid  

Microsoft Academic Search

Laser thrombolysis uses microsecond laser pulses to remove thrombus-blocked arteries in the heart and the brain. Rapidly expanding and collapsing vapor bubbles are formed upon absorption of the laser energy by the thrombus. The goal of this study was to visualize the process of ablation and assess the effects of pulse repetition rate. The differences between contact versus non-contact of

Ujwal S. Sathyam; Alan Shearin; Scott A. Prahl

1996-01-01

351

Preparation and morphology control of silver colloids by laser ablation in water  

Microsoft Academic Search

Nano-size colloids of silver were prepared by laser ablation in water in various conditions of laser pulses, such as wavelength, intensity, and pulse duration. The formation efficiency, the size, and the size distribution of colloids were varied with these conditions. It was suggested that interaction between laser pulses and colloidal particles plays important roles in the formation process. It is

T. Tsuji; N. Watanabe; T. Kakita; M. Tsuji

2003-01-01

352

Preparation of nano-size particles of silver with femtosecond laser ablation in water  

Microsoft Academic Search

Nano-size particles of Ag were prepared by laser ablation in water with femtosecond laser pulses at 800nm. The formation efficiency and the size of colloidal particles were compared with those of colloidal particles prepared by nanosecond laser pulses. The formation efficiency for femtosecond pulses was significantly lower than that for nanosecond pulses. The size of colloids prepared by femtosecond pulses

Takeshi Tsuji; Toshihiko Kakita; Masaharu Tsuji

2003-01-01

353

Internal structure and expansion dynamics of laser ablation plumes into ambient gases  

E-print Network

:YAG laser. The diagnostic tools include fast photography of overall visible plume emission using a 2 ns- pendent on irradiation conditions such as incident laser in- tensity and pulse duration, laser wavelength scattering.17 Fast photography adds another dimen- sion to ablation diagnostics by providing two

Harilal, S. S.

354

Modeling of the ablation source in laser-ultrasonics  

NASA Astrophysics Data System (ADS)

For the excitation of ultrasound by optical irradiation two principal mechanisms play a role. One of them, the so-called thermoplastic effect has been quantitatively described by several groups. In this work, a quantitative model describing the second effect, the excitation of ultrasonic signals by evaporation of the surface of the material onto which the laser pulses impinges, is presented. The evaporation, the expansion of the evaporated material as well as the interaction with the optical radiation is treated in a one-dimensional model. The pressure exerted on the surface of the specimen which results from the expanding vaporized material is used as source for the generation of the ultrasonic signals in the material or component insonified. There is an optical intensity at which the broadband ultrasonic signals exhibit maximal amplitude. The amplitude of the ultrasonic signals calculated using the model presented and the amount of ablated material are compared with experimental results. Despite the simplifications made, the agreement between theory and experiment is excellent for steel and satisfactory for aluminum. The results of this work can be used to optimize the parameters for a laser-based ultrasonic inspection system.

Hoffmann, A.; Arnold, W.

2000-05-01

355

Particle formation by infrared laser ablation of MALDI matrix compounds.  

PubMed

The concentration and size distribution of particles ablated from the infrared matrix-assisted laser desorption/ionization matrix compounds succinic acid (butanedioic acid), ?-cyano-4-hydroxycinnamic acid, and glycerol were measured using an aerodynamic particle sizer combined with a scanning mobility particle sizer. The two sizing instruments together had a sizing range to from 10?nm to 20?µm. Thin layers of the matrix compounds were irradiated with fluences between 6.0 and 9.5?kJ/m(2) and wavelengths between 2.8 and 3.0?µm. The distribution of particles was characterized by a large concentration of clusters in the 20-nm-diameter range and large component of mass in the range of coarse particle with diameters greater than 1?µm. The wavelength dependence revealed a blue shift for the maximum particle production that is attributed to heating and disruption of the hydrogen bonds in the matrix that shifts the absorption to shorter wavelengths. This blue shift has been observed previously in infrared matrix-assisted laser desorption/ionization. PMID:25044838

Musapelo, Thabiso; Murray, Kermit K

2014-07-01

356

Excimer laser ablation for spatially controlled protein patterns  

NASA Astrophysics Data System (ADS)

Two-dimensional control over the location of proteins on surfaces is desired for a number of applications including diagnostic tests and tissue engineered medical devices. Many of these applications require patterns of specific proteins that allow subsequent two-dimensionally controlled cell attachment. The ideal technique would allow the deposition of specific protein patterns in areas where cell attachment is required, with complete prevention of unspecific protein adsorption in areas where cells are not supposed to attach. In our study, collagen I was used as an example for an extracellular matrix protein known to support the attachment of bovine corneal epithelial cells. An allylamine plasma polymer was deposited on a silicon wafer substrate, followed by grafting of poly(ethylene oxide). Two-dimensional control over the surface chemistry was achieved using a 248 nm excimer laser. Results obtained by XPS and AFM show that the combination of extremely low-fouling surfaces with excimer laser ablation can be used effectively for the production of spatially controlled protein patterns with a resolution of less than 1 micrometers . Furthermore, it was shown that bovine corneal epithelial cell attachment followed exactly the created protein patterns. The presented method is an effective tool for a number of in vitro and in vivo applications.

Thissen, Helmut; Hayes, Jason P.; Kingshott, Peter; Johnson, Graham; Harvey, Erol C.; Griesser, Hans J.

2001-11-01

357

Focal Laser Ablation of Prostate Cancer: Definition, Needs, and Future  

PubMed Central

Current challenges and innovations in prostate cancer management concern the development of focal therapies that allow the treatment of only the cancer areas sparing the rest of the gland to minimize the potential morbidity. Among these techniques, focal laser ablation (FLA) appears as a potential candidate to reach the goal of focusing energy delivery on the identified targets. The aim of this study is to perform an up-to-date review of this new therapeutic modality. Relevant literature was identified using MEDLINE database with no language restrictions (entries: focal therapy, laser interstitial thermotherapy, prostate cancer, FLA) and by cross-referencing from previously identified studies. Precision, real-time monitoring, MRI compatibility, and low cost of integrated system are principal advantages of FLA. Feasibility and safety of this technique have been reported in phase I assays. FLA might eventually prove to be a middle ground between active surveillance and radical treatment. In conclusion, FLA may have found a role in the management of prostate cancer. However, further trials are required to demonstrate the oncologic effectiveness in the long term. PMID:22666240

Colin, Pierre; Mordon, Serge; Nevoux, Pierre; Marqa, Mohammed Feras; Ouzzane, Adil; Puech, Philippe; Bozzini, Gregory; Leroux, Bertrand; Villers, Arnauld; Betrouni, Nacim

2012-01-01

358

Laser spectroscopy at IGISOL IV  

NASA Astrophysics Data System (ADS)

The IGISOL (Ion Guide Isotope Separator On-Line) facility at the University of Jyväskylä accelerator laboratory has been upgraded and relocated to a purpose built laboratory. The new laboratory includes a dedicated MCC30 proton/deuteron cyclotron, which in conjunction with beams from the K130 cyclotron, will greatly increase the beam time available at the facility. Full off-line commissioning of the laser spectroscopy beam-line was achieved in February 2013 and on-line commissioning with radioactive beams was achieved in May 2013. Optical hyperfine resonance spectra were obtained for previously studied radioactive molybdenum isotopes and used to investigate our long term stability, efficiency and ability to successfully reproduce previous results from IGISOL III. A preliminary spectrum for the previously unmeasurable Mo was collected, displaying the improved capabilities of the new facility. Both data-sets show that the laser-line is ready for future experiments. The IGISOL IV beams are cleaner and have a higher radioactive content compared to similar experiments at IGISOL III.

Dicker, A. R.; Campbell, P.; Cheal, B.; Gorelov, D.; Hakala, J.; Johnson, D. J. S.; Jokinen, A.; Kolhinen, V.; Koponen, J.; Moore, I. D.; Penttilä, H.; Pohjalainen, I.; Reponen, M.; Rinta-Antila, S.; Sonnenschein, V.; Voss, A.

2014-06-01

359

A Laser Ablation Method for the Synthesis of Crystalline Semiconductor Nanowires  

Microsoft Academic Search

A method combining laser ablation cluster formation and vapor-liquid-solid ( VLS) growth was developed for the synthesis of semiconductor nanowires. In this process, laser ablation was used to prepare nanometer-diameter catalyst clusters that define the size of wires produced by VLS growth. This approach was used to prepare bulk quantities of uniform single-crystal silicon and germanium nanowires with diameters of

Alfredo M. Morales; Charles M. Lieber

1998-01-01

360

Formation of Au(III)DNA Coordinate Complex by Laser Ablation of Au Nanoparticles in Solution  

Microsoft Academic Search

We discovered that an Au(III)-DNA coordinate complex, Au(III)(DNA-base)2(amine)l, are formed by laser ablation of Au nanoparticles in an aqueous solution containing DNA molecules in the presence of amines and multi-valent cations, where l represents an unknown ligand (either amine or water). Optical absorption spectrum of the solution after laser ablation exhibited a 360 nm absorption peak assigned to ligand?Au(III) charge

Yoshihiro Takeda; Tamotsu Kondow; Fumitaka Mafuné

2005-01-01

361

X-ray Diffraction of Permalloy Nanoparticles Fabricated by Laser Ablation in Water  

SciTech Connect

Permalloy (NiFeMo) nanoparticles were fabricated by laser ablation of bulk material in water with a UV pulsed laser. Transmission electron microscope images showed that approximately spherical particles about 50 nm in diameter were formed in the ablation process. All diffraction peaks corresponding to the bulk material were present in the nanoparticles. In addition to these peaks several new peaks were observed in the nanoparticles, which were attributed to nickel oxide.

Musaev, O.; Midgley, A; Muthu, D; Wrobel, J; Kruger, M

2009-01-01

362

Local wettability tuning with laser ablation redeposits on PDMS  

NASA Astrophysics Data System (ADS)

In this paper, we present a method to locally control the wettability behavior of PDMS surfaces by excimer laser ablation. In the ablation process, a micrometer scale roughness is formed in the irradiated regions while a nanometer scale roughness is formed by the redeposits surrounding the irradiated regions. The increase in surface roughness results in a change of the wettability behavior of the PDMS surface. By using a hexagonal pattern and tuning the patterning pitch, two different wetting behaviors were realized. A pitch smaller than 300 ?m resulted in a superhydrophobic surface with an advancing contact angle of ?adv = 165° and a receding contact angle of ?rec = 160°. A pitch between 300 and 500 ?m resulted in a sticky superhydrophobic surface with ?adv = 120-150° and ?rec = 80°. The contact angle hysteresis for the latter was larger than for untreated PDMS resulting in very sticky surfaces with high sliding angles. This gives the method great versatility since the two wetting behaviors are very different. By combining both behaviors, local surface features like pinning sites, non-wetting sites, barriers and guides can all be fabricated by a single method. As an application demonstrator of the method, we show that drops can be caught and released depending on size and tilting angle by creating slippery surfaces with sticky barriers. Additionally, the method is ideal for rapid prototyping as it consist of only a single step. It is a direct write method requiring no lithographic mask. Also the process works in ambient atmosphere, so it can be used for temperature or pressure sensitive applications.

van Pelt, Stijn; Frijns, Arjan; Mandamparambil, Rajesh; den Toonder, Jaap

2014-06-01

363

Spectroscopic study on the enhanced excitation of an electron cyclotron resonance nitrogen plasma by pulsed laser ablation of an aluminum target.  

PubMed

The influence of pulsed laser ablation of an aluminum target on the nitrogen plasma produced by electron cyclotron resonance (ECR) microwave discharge has been studied by optical emission spectroscopy (OES) with time and space resolution. The continuous wave (CW) feature of the optical emissions from the ECR nitrogen plasma turns to vary with time and space due to pulsed laser ablation and the expansion of the ablation-induced aluminum plume in the nitrogen plasma. The optical emissions from the nitrogen plasma increase significantly and the emission intensity of nitrogen molecular ions is observed to be more than 20 times higher with the target being ablated in comparison to the case without target ablation. The comparison of the optical emissions from the nitrogen plasma with those from the aluminum plume indicates that the excitation enhancement of the nitrogen plasma occurs in the region where the aluminum plume is expanding, revealing that the expansion of the aluminum plume leads to the excitation enhancement of the nitrogen plasma. Relevant mechanisms responsible for the excitation enhancement of the nitrogen plasma through hybrid processes of ECR microwave discharge and pulsed laser ablation are also discussed. PMID:19007469

Tang, J Y; Zhang, W; Sun, J; Xu, N; Ge, C; Wu, J D

2008-11-01

364

Human cornea wound healing in organ culture after Er:YAG laser ablation  

NASA Astrophysics Data System (ADS)

Purpose: To study the healing process in cultured human corneas after Er:YAG laser ablation. Methods: Human cadaver corneas within 24 hours post mortem were ablated with a Q- switched Er:YAG laser at 2.94 micrometer wavelength. The radiant exposure was 500 mJ/cm2. The cornea was cultured on a tissue supporting frame immediately after the ablation. Culture media consisted of 92% minimum essential media, 8% fetal bovine serum, 0.125% HEPES buffer solution, 0.125% gentamicin, and 0.05% fungizone. The entire tissue frame and media container were kept in an incubator at 37 degrees Celsius and 5% CO2. Serial macroscopic photographs of the cultured corneas were taken during the healing process. Histology was performed after 30 days of culture. Results: A clear ablated crater into the stroma was observed immediately after the ablation. The thickness of thermal damage ranges between 1 and 25 micrometer. Haze development within the crater varies from the third day to the fourteenth day according to the depth and the roughness of the crater. Histologic sections of the cultured cornea showed complete re- epithelization of the lased area. Loose fibrous tissue is observed filling the ablated space beneath the epithelium. The endothelium appeared unaffected. Conclusions: The intensity and time of haze development appears dependent upon the depth of the ablation. Cultured human corneas may provide useful information regarding the healing process following laser ablation.

Shen, Jin-Hui; Joos, Karen M.; Robinson, Richard D.; Shetlar, Debra J.; O'Day, Denis M.

1998-06-01

365

Confocal Microscopy-Guided Laser Ablation for Superficial and Early Nodular Basal Cell Carcinoma  

PubMed Central

Importance Laser ablation is a rapid and minimally invasive approach for the treatment of superficial skin cancers, but efficacy and reliability vary owing to lack of histologic margin control. High-resolution reflectance confocal microscopy (RCM) may offer a means for examining margins directly on the patient. Observations We report successful elimination of superficial and early nodular basal cell carcinoma (BCC) in 2 cases-, using RCM imaging to guide Er-:YAG laser ablation. Three-dimensional (3-D) mapping is feasible with RCM-, to delineate the lateral border and thickness of the tumor. Thus, the surgeon may deliver laser fluence and passes with localized control—ie, by varying the ablation parameters in sub-lesional areas with specificity that is governed by the 3-D topography of the BCC. We further demonstrate intra-operative detection of residual BCC after initial laser ablation and complete removal of remaining tumor by additional passes. Both RCM imaging and histologic sections confirm the final clearance of BCC. Conclusions and Relevance Confocal microscopy may enhance the efficacy and reliability of laser tumor ablation. This report represents a new translational application for RCM imaging, which, when combined with an ablative laser, may one day provide an efficient and cost-effective treatment for BCC. PMID:24827701

Chen, Chih-Shan Jason; Sierra, Heidy; Cordova, Miguel; Rajadhyaksha, Milind

2014-01-01

366

Bubble formation induced by nanosecond laser ablation in water and its diagnosis by optical transmission technique  

NASA Astrophysics Data System (ADS)

In this paper, bubble formation and ablation rate in laser ablation of a thin-film aluminum target are studied. The target was an aluminum thin-film coated on a quartz substrate and interacted by a nanosecond Nd:YAG laser beam in ambient air and distilled water. Measuring optical transmission of a He-Ne beam through the ablation region shows that the ablation rate in water is higher than that in ambient air. The results also show that an initial peak appears in the transmission signal which is an evidence for bubble formation in water. Analyzing the data is useful for monitoring the bubble formation in water and relatively estimating the ablation rate.

Mahdieh, M. H.; Akbari Jafarabadi, M.

2014-09-01

367

Absorption coefficient of aluminum near the critical point and the consequences on high-power nanosecond laser ablation  

SciTech Connect

During nanosecond laser ablation, the absorption coefficient determines the laser energy deposition in the target, the accurate knowledge of which near the material critical point is crucial for understanding the fundamental physics of high-power nanosecond laser ablation. In this letter, the absorption coefficient of aluminum near the critical point is calculated through the Drude model based on the measured electrical conductivity data, and its effect on laser ablation is investigated numerically using a heat transfer model. The result supports the experimental observations that phase explosion occurs for the ablation of aluminum by sufficiently intense laser pulses, and the model predicted phase explosion threshold is consistent with experimental measurements.

Wu Benxin; Shin, Yung C. [Center for Laser-based Manufacturing, School of Mechanical Engineering, Purdue University, West Lafayette, Indiana 47907 (United States)

2006-09-11

368

Effect of oblique force source induced by laser ablation on ultrasonic generation.  

PubMed

The effect of asymmetry caused by oblique line-shaped laser ablation on the generation of ultrasonic waves in metal, especially the effect of transverse component of the ablation force source on the ultrasonic waves is analyzed. Due to the oblique force source, the displacements of shear wave increase obviously by the enhanced shear force, the energy concentration area of longitudinal wave deflects to the small range centered on the incident direction while that of shear wave is approximately perpendicular to incident direction. In addition, surface wave enhances in the direction of transverse power flow. Furthermore, some ultrasonic characteristics under vortex laser ablation condition are inferred. PMID:24514978

Guo, Yuning; Yang, Dexing; Chang, Ying; Gao, Wei

2014-01-13

369

Ultrafast laser ablation and machining large-size structures on porcine bone.  

PubMed

When using ultrafast laser ablation in some orthopedic applications where precise cutting/drilling is required with minimal damage to collateral tissue, it is challenging to produce large-sized and deep holes using a tightly focused laser beam. The feasibility of producing deep, millimeter-size structures under different ablation strategies is investigated. X-ray computed microtomography was employed to analyze the morphology of these structures. Our results demonstrated the feasibility of producing holes with sizes required in clinical applications using concentric and helical ablation protocols. PMID:23884158

An, Ran; Khadar, Ghadeer W; Wilk, Emilia I; Emigh, Brent; Haugen, Harold K; Wohl, Gregory R; Dunlop, Brett; Anvari, Mehran; Hayward, Joseph E; Fang, Qiyin

2013-07-01

370

Laser Spectroscopy for Atmospheric and Environmental Sensing  

PubMed Central

Lasers and laser spectroscopic techniques have been extensively used in several applications since their advent, and the subject has been reviewed extensively in the last several decades. This review is focused on three areas of laser spectroscopic applications in atmospheric and environmental sensing; namely laser-induced fluorescence (LIF), cavity ring-down spectroscopy (CRDS), and photoluminescence (PL) techniques used in the detection of solids, liquids, aerosols, trace gases, and volatile organic compounds (VOCs). PMID:22303184

Fiddler, Marc N.; Begashaw, Israel; Mickens, Matthew A.; Collingwood, Michael S.; Assefa, Zerihun; Bililign, Solomon

2009-01-01

371

Laser ablation threshold dependence on pulse duration for fused silica and corneal tissues: experiments and modeling  

NASA Astrophysics Data System (ADS)

The surface ablation threshold fluence of fused silica and two porcine cornea layers, the epithelium and the stroma, is characterized as a function of the laser pulse duration in the range of 100 fs-5 ps for a wavelength of 800 nm (Ti:sapphire laser system). The plateaulike region observed between 100 fs and 1 ps for the corneal layers indicates that for use in laser surgery, laser pulse durations chosen within this range should be practically equivalent. Our model predicts that the ablation threshold will decrease rapidly for pulse durations in the low end of the femtosecond regime.

Giguère, Dominic; Olivié, Gilles; Vidal, François; Toetsch, Stéphanie; Girard, Guillaume; Ozaki, Tsuneyuki; Kieffer, Jean-Claude; Nada, Ossama; Brunette, Isabelle

2007-06-01

372

Multimodal optical characterisation of collagen photodegradation by femtosecond infrared laser ablation.  

PubMed

Collagen is a structural component of the human body, as a connective tissue it can become altered as a result of pathophysiological conditions. Although the collagen degradation mechanism is not fully understood, it plays an important role in ageing, disease progression and applications in therapeutic laser treatments. To fully understand the mechanism of collagen alteration, in our study photo-disruptive effects were induced in collagen I matrix by point-irradiation with a femtosecond Ti-sapphire laser under controlled laser ablation settings. This was followed by multi-modal imaging of the irradiated and surrounding areas to analyse the degradation mechanism. Our multi-modal methodology was based on second harmonic generation (SHG), scanning electron microscope (SEM), autofluorescence (AF) average intensities and the average fluorescence lifetime. This allowed us to quantitatively characterise the degraded area into four distinct zones: (1) depolymerised zone in the laser focal spot as indicated by the loss of SHG signal, (2) enhanced crosslinking zone in the inner boundary of the laser induced cavity as represented by the high fluorescence ring, (3) reduced crosslinking zone formed the outer boundary of the cavity as marked by the increased SHG signal and (4) native collagen. These identified distinct zones were in good agreement with the expected photochemical changes shown using Raman spectroscopy. In addition, imaging using polarisation-resolved SHG (p-SHG) revealed both a high degree of fibre re-orientation and a SHG change in tensor ratios around the irradiation spot. Our multi-modal optical imaging approach can provide a new methodology for defining distinct zones that can be used in a clinical setting to determine suitable thresholds for applying safe laser treatments without affecting the surrounding tissues. Furthermore this technique can be extended to address challenges observed in collagen based tissue engineering and used as a minimally invasive diagnostic tool to characterise diseased and non-diseased collagen rich tissues. PMID:25318007

Manickavasagam, A; Hirvonen, L M; Melita, L N; Chong, E Z; Cook, R J; Bozec, L; Festy, F

2014-12-01

373

Preferential vaporization and plasma shielding during nano-second laser ablation  

NASA Astrophysics Data System (ADS)

Preferential removal of components from mixed material targets and plasma shielding are studied by using inductively coupled plasma-atomic emission spectrometry (ICP-AES) during UV nano-second laser ablation. The ICP emission intensity for Cu and Zn during ablation of brass samples varies versus laser power density. A model using thermal evaporation and inverse Bremsstrahlung processes is presented. The model shows that plasma shielding occurs at approximately 0.3 GW/cm 2, in agreement with experimental data for change in the mass ablation rate. The good agreement of model and experimental data suggest that thermal effects are important during nano-second laser ablation for power density less than 0.3 GW/cm 2.

Mao, Xianglei; Chan, Wing-Tat; Caetano, Manuel; Shannon, Mark A.; Russo, Richard E.

1996-04-01

374

Comparison of transcatheter laser and direct-current shock ablation of endocardium near tricuspid anulus  

NASA Astrophysics Data System (ADS)

Forty to eighty percent of the patients with accessory pathways (APs) manifest themselves by tachyarrhythmias. Many of these patients needed either life-long medical therapy or surgery. In order to avoid the discomfort and expenses in surgical procedures, closed chest percutaneous catheter ablation of APs became a potentially desirable therapeutic approach. Many investigations indicated that ablation of right APs by transcatheter direct current (dc) shock could cause life-threatening arrhythmias, right coronary arterical (RCA) spasm, etc. With the development of transcatheter laser technique, it has been used in drug-incurable arrhythmias. The results show that laser ablation is much safer than surgery and electric shock therapy. The purpose of this study is to explore the effectiveness, advantages, and complications with transcatheter Nd:YAG laser and dc shock in the ablation of right atrioventricular accessory pathways in the atrium near the tricuspid annulus (TA) in 20 dogs.

Zhang, Yu-Zhen; Wang, Shi-Wen; Li, Junheng

1993-03-01

375

Ablation of ionic crystals induced by capillary-discharge XUV laser  

NASA Astrophysics Data System (ADS)

Single crystals of two fluorides (LiF and CaF2) and a tungstate (PbWO4) were irradiated by nanosecond pulses of 46.9- nm radiation provided by 10-Hz capillary-discharge Ne-like Ar laser (CDL). The damage threshold was determined in LiF using the CDL beam focused by a Sc/Si multilayer-coated spherical mirror. Irradiated samples have been investigated by Nomarski (DIC - Differential Interference Contrast) microscopy and optical (WLI - white light intereferometry) profiler. After an exposure by a certain number of CDL pulses, an ablation rate can be calculated from WLI measured depth of the crater created by the XUV ablation. Potential use of XUV ablation of ionic crystals in pulsed laser deposition (PLD) of thin layers of such a particular material, which is difficult to ablate by conventional UV-Vis- NIR lasers, is discussed in this contribution.

Pira, Peter; Burian, Tomáš; Vyšín, Ludék; Chalupský, Jaromír; Lan?ok, Ján; Wild, Jan; St?ižík, Michal; Zelinger, Zden?k; Rocca, Jorge J.; Juha, Libor

2011-06-01

376

Transmission of 1064 nm laser radiation during ablation with an ultra-short pulse laser (USPL) system  

NASA Astrophysics Data System (ADS)

During ablation of oral hard tissue with an USPL system a small amount of the incident laser power does not contribute to the ablation process and is being transmitted. Partial transmission of ultra-short laser pulses could potentially affect the dental pulp. The aim of this study was to assess the transmission during ablation and to deduce possible risks for the patient. The study was performed with an Nd:YVO4 laser, emitting pulses with a duration of 8 ps at a wavelength of 1064 nm. A repetition rate of 500 kHz and an average power of 9 W were chosen to achieve high ablation efficiency. A scanner system created square cavities with an edge length of 1 mm. Transmission during ablation of mammoth ivory and dentin slices with a thickness of 2 mm and 5 mm was measured with a power meter, placed directly beyond the samples. Effects on subjacent blood were observed by ablating specimens placed in contact to pork blood. In a separate measurement the temperature increase during ablation was monitored using an infrared camera. The influence of transmission was assessed by tuning down the laser to the corresponding power and then directly irradiating the blood. Transmission during ablation of 2 mm specimens was about 7.7% (ivory) and 9.6% (dentin) of the incident laser power. Ablation of specimens directly in contact to blood caused coagulation at longer irradiation times (t~18s). Direct irradiation of blood with the transmitted power provoked bubbling and smoke formation. Temperature measurements identified heat generation as the main reason for the observed coagulation.

Schelle, Florian; Meister, Jörg; Oehme, Bernd; Frentzen, Matthias

2012-01-01

377

Surface ablation of PLLA induced by KrF excimer laser  

NASA Astrophysics Data System (ADS)

The surface characterization of PLLA (poly-L-lactic-acid) and its ablation due to excimer laser treatment is introduced in this paper. The main focus is to determine surface wettability and morphology changes in combination with changes of surface chemistry. The ablation loss and the determination of ablation threshold were used to study the biopolymer stability when treated to different laser fluences and pulse counts. The surface polarity was estimated using goniometry. AFM (atomic force microscopy) was used to determine the polymer surface morphology and roughness. The excimer laser has a strong effect on the polymer ablation. The thickness loss is strongly dependent on the laser fluence and number of pulses. For the fluences up to 30 mJ cm-2 and 6000 pulses achieved ablation about 5 ?m. The glass transition temperature and melting point were determined for the pristine and laser treated films. The increasing pulsed laser fluence leads to the major changes in roughness and morphology. The surface chemistry depends strongly on number of laser pulses.

Slepi?ka, P.; Michaljani?ová, I.; Sajdl, P.; Fitl, P.; Švor?ík, V.

2013-10-01

378

Laser structuring of metallic mold inserts by using ?s, ns, and ps-laser ablation  

NASA Astrophysics Data System (ADS)

Bio-inspired surfaces targeting functional characteristics such as anti-reflectivity, self-cleaning effects or a drag reduction are of significant interest to industry. In this feasibility study, process chains for the mass production of so-called shark skin structured surfaces are investigated. Due to their drag reduction properties, such bio-inspired surfaces are of relevance to a number of applications in which particular aqua- and aerodynamic characteristics are required. The design of the shark skin structure relies on a bio-mimetic analytical model to generate the 3D surface model necessary to achieve the targeted surface functionality. The process chains presented combine laser ablation as a method for micro structuring masters for high throughput replication employing injection molding. In particular, three different process chains that rely on micro second (?s), nano second (ns) and pico second (ps) laser ablation systems to pattern mold inserts were investigated. Then, these inserts were integrated into a tool for micro injection molding and replication trials were carried out. The results show that all three laser sources can be utilized to create this kind of micro cavities. This research indicates that these micro structures can be replicated successfully, but further work is required to optimize the replication and laser structuring process.

Scholz, Steffen G.; Kolew, Alexander; Griffiths, Christian

2012-03-01

379

High Spatial Resolution Fe isotope analysis by femtosecond Laser Ablation  

NASA Astrophysics Data System (ADS)

In-situ isotopic analysis of geological samples has shown the importance of retrieving isotopic information on the micron scale from isolated mineral grains in complex samples or those that contain multiple isotopic components. Recent studies of magnetite, hematite, and pyrite using femtosecond laser ablation (fs-LA) report sampled volumes (Vs) down to ~6×103?m3, with internal and external reproducibility of ~0.12‰ (2SE) and ~0.20‰ (2SD) respectively [1-3]. We have improved the spatial resolution of fs-LA measurements by a factor of ~10 with the same analytical uncertainty as that cited above. These improvements were made by: (1) using a more efficient ablation cell and (2) improving the electronics of the Faraday detectors. Two cell geometries manufactured by Photon Machines (San Diego, CA, USA) have been studied for aerosol Particle Size Distribution (PSD) and Fe isotope composition under He gas flows of ~0.6L.min-1: the Frame cell (~20cc, ~2s washout time) and the two volumes HelEx cell (inner volume ~7cc, ~0.7s washout time). The measured PSDs are independent of the substrate (hematite, magnetite, pyrite, pyrrhotite, and siderite) or the laser wavelength (?=198 and 263nm). The Frame cell produced a monomodal PSD, centered on an aerodynamic diameter (da) of ~0.25?m, whereas the HelEx cell produced a bi-modal PSD with peaks at da<0.056?m and 0.14?m. The finer aerosols produced by the HelEx cell are interpreted to reflect its faster extraction, limiting collisions and agglomeration, as well as inhomogeneous transport losses and attendant incomplete ionization in the plasma torch. LA-MC-ICP-MS analyses of magnetite using the Frame cell (Vs~1.5×104?m3, 40×10s on peak integrations) yield internal and external precisions of 0.12‰ (2SE) and 0.25‰ (2SD, n=61) respectively [1]. In contrast, the HelEx cell (Vs~5.5×103mm3, 40×5s on peak integrations) provides internal and external precisions of 0.10‰ (2SE) and 0.20‰ (2SD, n=115). A new generation of high-ohm resistors boards (IsotopX, Middlewich, UK) for Faraday detectors has been evaluated, using a 1010ohm resistor for 56Fe and 1011ohm for 54Fe. The new setup improved internal precision for conventional analysis by ~33%, and precision is independent of the on-peak integration time between 1 and 10s. The same improvement is noted for fs-LA using the HelEx cell, where spatial resolution entirely depends on the acquisition time. Hence, we were able to reduce Vs to ~6×102?m3 by performing analyses over only 50s (1s on peak integration), which still yields internal and external precisions of 0.11‰ (2SE) and 0.28‰ (2SD, n=28). In conclusion, and considering similar internal and external precisions, reducing the particle residence time in the ablation cell improves the spatial resolution by a factor of ~3. On the other hand, being able to integrate the signal over only 1s cycles improves the spatial resolution by a factor of ~9 with the same precisions as the currently published data. 1. Czaja, A.D., et al., Earth and Planetary Science Letters, 2013. 363: p. 192-203. 2. Steinhoefel, G., et al., Geochimica et Cosmochimica Acta, 2009. 73(18): p. 5343-5360. 3. Yoshiya, K., et al., Precambrian Research, 2012. 212-213: p. 169-193.

Johnson, C.; Beard, B. L.; d'Abzac, F.

2013-12-01

380

Fully Automated Laser Ablation Liquid Capture Sample Analysis using NanoElectrospray Ionization Mass Spectrometry  

SciTech Connect

RATIONALE: Laser ablation provides for the possibility of sampling a large variety of surfaces with high spatial resolution. This type of sampling when employed in conjunction with liquid capture followed by nanoelectrospray ionization provides the opportunity for sensitive and prolonged interrogation of samples by mass spectrometry as well as the ability to analyze surfaces not amenable to direct liquid extraction. METHODS: A fully automated, reflection geometry, laser ablation liquid capture spot sampling system was achieved by incorporating appropriate laser fiber optics and a focusing lens into a commercially available, liquid extraction surface analysis (LESA ) ready Advion TriVersa NanoMate system. RESULTS: Under optimized conditions about 10% of laser ablated material could be captured in a droplet positioned vertically over the ablation region using the NanoMate robot controlled pipette. The sampling spot size area with this laser ablation liquid capture surface analysis (LA/LCSA) mode of operation (typically about 120 m x 160 m) was approximately 50 times smaller than that achievable by direct liquid extraction using LESA (ca. 1 mm diameter liquid extraction spot). The set-up was successfully applied for the analysis of ink on glass and paper as well as the endogenous components in Alstroemeria Yellow King flower petals. In a second mode of operation with a comparable sampling spot size, termed laser ablation/LESA , the laser system was used to drill through, penetrate, or otherwise expose material beneath a solvent resistant surface. Once drilled, LESA was effective in sampling soluble material exposed at that location on the surface. CONCLUSIONS: Incorporating the capability for different laser ablation liquid capture spot sampling modes of operation into a LESA ready Advion TriVersa NanoMate enhanced the spot sampling spatial resolution of this device and broadened the surface types amenable to analysis to include absorbent and solvent resistant materials.

Lorenz, Matthias [ORNL] [ORNL; Ovchinnikova, Olga S [ORNL] [ORNL; Van Berkel, Gary J [ORNL] [ORNL

2014-01-01

381

Toward laser ablation Accelerator Mass Spectrometry of actinides  

NASA Astrophysics Data System (ADS)

A project to measure neutron capture cross sections of a number of actinides in a reactor environment by Accelerator Mass Spectrometry (AMS) at the ATLAS facility of Argonne National Laboratory is underway. This project will require the precise and accurate measurement of produced actinide isotopes in many (>30) samples irradiated in the Advanced Test Reactor at Idaho National Laboratory with neutron fluxes having different energy distributions. The AMS technique at ATLAS is based on production of highly-charged positive ions in an electron cyclotron resonance (ECR) ion source followed by acceleration in the ATLAS linac and mass-to-charge (m/q) measurement at the focus of the Fragment Mass Analyzer. Laser ablation was selected as the method of feeding the actinide material into the ion source because we expect it will have higher efficiency and lower chamber contamination than either the oven or sputtering techniques, because of a much narrower angular distribution of emitted material. In addition, a new multi-sample holder/changer to allow quick change between samples and a computer-controlled routine allowing fast tuning of the accelerator for different beams, are being developed. An initial test run studying backgrounds, detector response, and accelerator scaling repeatability was conducted in December 2010. The project design, schedule, and results of the initial test run to study backgrounds are discussed.

Pardo, R. C.; Kondev, F. G.; Kondrashev, S.; Nair, C.; Palchan, T.; Scott, R.; Seweryniak, D.; Vondrasek, R.; Paul, M.; Collon, P.; Deibel, C.; Youinou, G.; Salvatores, M.; Palmotti, G.; Berg, J.; Fonnesbeck, J.; Imel, G.

2013-01-01

382

Silver Nanoparticles Obtained by Laser Ablation Using Different Stabilizers  

NASA Astrophysics Data System (ADS)

We have synthesized silver nanoparticles by laser ablation in water using three stabilizers: hexadecyltrimethylammonium (CTAB) surfactant, polyamidoamine dendrimer second generation (PAMAM 2G) and polyamidoamine dendrimer fourth generation (PAMAM 4G) at different concentrations. We obtained spherical nanoparticles with narrow size distributions and average sizes ranging from 6 to 20 nm depending on the type of stabilizer and its concentration. For all cases the highest stabilizer concentration yielded the lowest average particle size; 15.5, 9.5, and 5.6 nm for CTAB, PAMAM 2G and PAMAM 4G respectively. We have also studied the stability of the nanoparticle colloids over a period of 30 days. Only the colloids of CTAB 10-3 M, all the concentrations of PAMAM 4G and pure water were stable after this time. This is explained in terms of steric hindrance of the stabilizer molecules and particle charge from Zeta potential measurements. All the results from transmission electron microscopy correlate well with those observed from the ultraviolet and visible spectra of each sample in terms of absorbance, peak width and peak maximum.

Olea-Mejía, Oscar; Pote-Orozco, Héctor; Camacho-López, Marco A.; Olea-Cardoso, Oscar; López-Castañares, Rafael; Vilchis-Néstor, Alfredo R.

2013-11-01

383

Compact And Robust Laser Impulse Measurement Device, With Ultrashort Pulse Laser Ablation Results  

SciTech Connect

An impulse measurement device and analysis package was conceived, designed, constructed, tested, and demonstrated to be capable of: measuring nanoNewton-seconds to milliNewton-seconds of impulse due to laser-ablation; being transported as carry-on baggage; set-up and tear-down times of less than an hour; target exchange times of less than two minutes (targets can be ablated at multiple positions for thousands of shots); measurements in air and in vacuum; error of just a few percent; repeatability over a wide range of potential systematic error sources; and time between measurements, including ring-down and analysis, of less than 30 seconds. The instrument consists of a cantilever (i.e. leaf spring), whose time-dependent displacement/oscillation is measured and analyzed to determine the impulse imparted by a laser pulse to a target. These shapes are readily/commercially available, and any target material can be used, provided it can be fashioned in the form of a cantilever, or as a coating/film/tape, suitable for mounting on a cantilever of known geometry. The instrument was calibrated both statically and dynamically, and measurements were performed on brass, steel, and Aluminum, using laser pulses of {approx}7 ns, {approx}500 ps, and {approx}500 fs. The results agree well with those published in the literature, with surface effects, atmosphere, and pre-/post-pulses demonstrating interesting effects and indicating areas for further study. These parameters should be carefully controlled and held constant during a series of measurements. The impulse imparted by ablation due to laser filaments in air was also explored.

Kremeyer, Kevin; Lapeyre, John; Hamann, Steven [Physics, Materials, and Applied Mathematics Research, L.L.C. PM and AM Research in Collaboration with AFRL 1665 E. 18th Street, Suite 112 Tucson, AZ, 85719 (United States)

2008-04-28

384

Standard addition method for laser ablation ICPMS using a spinning platform.  

PubMed

A method has been developed for the fast and easy determination of Pb, Sr, Ba, Ni, Cu, and Zn, which are of geological and environmental interest, in solid samples by laser ablation inductively coupled plasma mass spectrometry (LA-ICPMS) using a spinning sample platform. The platform, containing a sample and a standard, is spun during the ablation, allowing the quasi-simultaneous ablation of both materials. The aerosols resulting from the ablation of sample and standard were mixed in the ablation cell allowing quantification of analytes by standard additions. The proportion of standard versus sample of the mixing can be increased by performing the ablation further from the axis of rotation. The ablated masses have been determined using a new strategy based on isotope dilution analysis. This spinning laser ablation method has been applied to the Allende meteorite and four powdered standard reference materials (SRMs) fused in lithium borate glasses: two sediments as well as a soil and a rock material. SRM 612 (Trace Elements in Glass) was also analyzed despite having a matrix slightly different from the glass standard obtained by lithium borate fusion. The deviation from the certified values was found to be less than 15% for most of the mass fractions for all the elements and samples studied, with an average precision of 10%. These results demonstrate the validity of the proposed method for the direct and fast analysis of solid samples of different matrixes by standard additions, using a single standard sample. PMID:23418996

Claverie, Fanny; Malherbe, Julien; Bier, Naomi; Molloy, John L; Long, Stephen E

2013-04-01

385

Explosive detection using infrared laser spectroscopy  

Microsoft Academic Search

Stand-off and extractive explosive detection methods for short distances are investigated using mid-infrared laser spectroscopy. A quantum cascade laser (QCL) system for TATP-detection by open path absorption spectroscopy in the gas phase was developed. In laboratory measurements a detection limit of 5 ppm*m was achieved. For explosives with lower vapor pressure an extractive hollow fiber based measurement system was investigated.

J. Hildenbrand; J. Herbst; J. Wöllenstein; A. Lambrecht

2009-01-01

386

Synthesis and characterization of gold graphene composite with dyes as model substrates for decolorization: a surfactant free laser ablation approach.  

PubMed

A facile surfactant free laser ablation mediated synthesis (LAMS) of gold-graphene composite is reported here. The material was characterized using transmission electron microscopy, field emission scanning electron microscopy, energy dispersive X-ray spectroscopy, powdered X-ray diffraction, Raman spectroscopy, Zeta potential measurements and UV-Visible spectroscopic techniques. The as-synthesized gold-graphene composite was effectively utilized as catalyst for decolorization of 4 important textile and laser dyes. The integration of gold nanoparticles (AuNPs) with high surface area graphene has enhanced the catalytic activity of AuNPs. This enhanced activity is attributed to the synergistic interplay of pristine gold's electronic relay and ?-? stacking of graphene with the dyes. This is evident when the Rhodamine B (RB) reduction rate of the composite is nearly twice faster than that of commercial citrate capped AuNPs of similar size. In case of Methylene blue (MB) the rate of reduction is 17,000 times faster than uncatalyzed reaction. This synthetic method opens door to laser ablation based fabrication of metal catalysts on graphene for improved performance without the aid of linkers and surfactants. PMID:24967542

Sai Siddhardha, R S; Lakshman Kumar, V; Kaniyoor, Adarsh; Sai Muthukumar, V; Ramaprabhu, S; Podila, Ramakrishna; Rao, A M; Ramamurthy, Sai Sathish

2014-12-10

387

Synthesis and characterization of gold graphene composite with dyes as model substrates for decolorization: A surfactant free laser ablation approach  

NASA Astrophysics Data System (ADS)

A facile surfactant free laser ablation mediated synthesis (LAMS) of gold-graphene composite is reported here. The material was characterized using transmission electron microscopy, field emission scanning electron microscopy, energy dispersive X-ray spectroscopy, powdered X-ray diffraction, Raman spectroscopy, Zeta potential measurements and UV-Visible spectroscopic techniques. The as-synthesized gold-graphene composite was effectively utilized as catalyst for decolorization of 4 important textile and laser dyes. The integration of gold nanoparticles (AuNPs) with high surface area graphene has enhanced the catalytic activity of AuNPs. This enhanced activity is attributed to the synergistic interplay of pristine gold's electronic relay and ?-? stacking of graphene with the dyes. This is evident when the Rhodamine B (RB) reduction rate of the composite is nearly twice faster than that of commercial citrate capped AuNPs of similar size. In case of Methylene blue (MB) the rate of reduction is 17,000 times faster than uncatalyzed reaction. This synthetic method opens door to laser ablation based fabrication of metal catalysts on graphene for improved performance without the aid of linkers and surfactants.

Sai Siddhardha, R. S.; Lakshman Kumar, V.; Kaniyoor, Adarsh; Sai Muthukumar, V.; Ramaprabhu, S.; Podila, Ramakrishna; Rao, A. M.; Ramamurthy, Sai Sathish

2014-12-01

388

Aerosol measurements with laser-induced breakdown spectroscopy  

E-print Network

laser-induced breakdown spectroscopy measurements, Applied Physics Letters,by giant-pulse laser. Applied Physics Letters, vol. 3, no.Laser-Induced Breakdown Spectroscopy Measurements,” Applied Physics Letters,

Lithgow, Gregg Arthur

2007-01-01

389

Applications of lasers to the solution of environmental problems  

SciTech Connect

This presentation will focus on current work in the Ames Laboratory where laser ablation is being used for both analytical sampling and metal surface cleaning. Examples will be presented demonstrating the utility of optical spectroscopy for monitoring laser ablation processes.

Allen, L.; Pang, H.-M.; Edelson, M.C.

1995-12-31

390

Comparison between geometrically focused pulses versus filaments in femtosecond laser ablation of steel and titanium alloys  

NASA Astrophysics Data System (ADS)

Kerr self-focusing of high-power ultrashort laser pulses in atmosphere may result in a structure or structures of high intensity that can propagate over long distances with little divergence. Filamentation has garnered significant interest in the nonlinear optics community due to its unique properties. Salient features of filaments include a central region of intense laser power (greater than the ionization threshold of the propagation medium) and a low temperature plasma column that lasts up to nanoseconds in duration after the passage of the laser pulse. Steel and titanium samples are ablated by filaments and by sharply focused sub-picosecond laser pulses. We then performed metrology on the samples to compare the ablation features in addition to modeling of the plasma ablation process. Ablation with filaments leads to a wider range of material responses as compared to ablation with sharply focused pulse. This results in potential complications for applications of filament ablation that depends on the rate of material removal and spectroscopic analysis.

Valenzuela, Anthony; Munson, Chase; Porwitzky, Andrew; Weidman, Matthew; Richardson, Martin

2014-08-01

391

Using FT-IR Spectroscopy to Elucidate the Structures of Ablative Polymers  

NASA Technical Reports Server (NTRS)

The composition and structure of an ablative polymer has a multifaceted influence on its thermal, mechanical and ablative properties. Understanding the molecular level information is critical to the optimization of material performance because it helps to establish correlations with the macroscopic properties of the material, the so-called structure-property relationship. Moreover, accurate information of molecular structures is also essential to predict the thermal decomposition pathways as well as to identify decomposition species that are fundamentally important to modeling work. In this presentation, I will describe the use of infrared transmission spectroscopy (FT-IR) as a convenient tool to aid the discovery and development of thermal protection system materials.

Fan, Wendy

2011-01-01

392

Nd:YAG laser ablation characteristics of thin CIGS solar cell films  

NASA Astrophysics Data System (ADS)

This work reports that the ablation characteristics of thin CuIn1- x Ga x Se2 (CIGS) solar cell film differ significantly with elemental composition and laser pulse energy. From in situ shadowgraphs measured during Nd:YAG laser (1,064 nm) irradiation of CIGS films and crater morphologies, it was found that strong surface evaporation is dominant for low Ga concentration films of which band gap is well below the photon energy. As the band gap of CIGS film becomes close to or over the laser photon energy due to increased Ga content, surface absorption diminishes and at low laser energy, laser heating of the film plays an important role. It is demonstrated that for the CIGS films with Ga/(Ga + In) ratio being approximately over 0.2, the laser irradiation leads to solid phase removal of the film due to thermomechanical fracture at low laser energy but to ablative evaporation at elevated energy.

Lee, S. H.; Kim, C. K.; In, J. H.; Kim, D. S.; Ham, H. J.; Jeong, S. H.

2013-12-01

393

Atomic Spectroscopy with Laser Diodes and Undergraduates  

NASA Astrophysics Data System (ADS)

Laser spectroscopy provides powerful techniques for exploring numerous topics in atomic/molecular/optical physics and beyond. Investigations of atomic and molecular splittings, planetary atmospheres, nuclear shapes, ultrafast processes, exotic matter, plasma parameters, photoacoustic effects, and molecular dynamics via quantum control constitute a minuscule sampling of present day applications of laser spectroscopy. While diode lasers cannot fulfill many requirements regarding wavelength, power, and/or energy, their compactness, longevity, efficiency, reliability, quietude, ease of use, and low cost often make diodes the laser of choice for a given application of laser spectroscopy. In fact, the cost and spatial requirements of diode laser systems are so modest that an investigator, even when forced to operate on a tight budget, can maintain and usefully employ as many as a dozen independent diode laser systems. This talk will elaborate on several of these points and describe some unexpected results in recent measurements of fine-structures and Zeeman splittings in excited states of alkali and rare gas atoms via two- and three-step laser excitation spectroscopy.

Brandenberger, John R.

2004-03-01

394

Formation of wide bandgap cerium oxide nanoparticles by laser ablation in aqueous solution  

NASA Astrophysics Data System (ADS)

Cerium oxide nanoparticles were produced by laser ablation in an aqueous solution. Submicron-sized cerium oxide particles were size-reduced by pulsed-laser irradiation into those having diameters of 3.6 nm. It was found that the bandgap of the nanoparticle was larger and the Ce3+ concentration within it was higher than those prepared by other conventional methods. These characteristic structures are likely to originate from additional defect sites in the nanoparticles produced by laser ablation, where O2- ions have a lower coordination with Ce ions, resulting in removal of O atoms and reduction of Ce4+ into Ce3+.

Takeda, Yoshihiro; Mafuné, Fumitaka

2014-04-01

395

The effect of laser wavelength on the ablation rate of carbon  

NASA Astrophysics Data System (ADS)

The ablation of graphite is studied as a function of laser fluence for 355, 532 and 1,064 nm wavelength generated by a nanosecond Nd:YAG laser. It has been found that in the case of lower wavelengths, the transition from the thermal ablation to the phase explosion takes place at lower laser fluences. The change of crater shape due to the effect of deep drilling in the proximity of the phase explosion threshold was observed. The calculations of plasma radiation flux to the target surface were made, and the considerable increase of absorbed energy density was found in the case of 355 nm wavelength.

Hoffman, J.; Chrzanowska, J.; Kucharski, S.; Moscicki, T.; Mihailescu, I. N.; Ristoscu, C.; Szymanski, Z.

2014-10-01

396

A matrix isolation FTIR investigation of laser-ablated uranium oxide in argon and nitrogen matrices  

Microsoft Academic Search

Uranium oxide was laser-ablated using the second harmonic of a Nd : YAG laser, and the products studied after trapping them\\u000a in Ar and N2 matrices. The species obtained in the Ar matrix were UO, UO2 and UO3, which represent the primary products of laser ablation. Charge transfer complexes, (UO\\u000a 2\\u000a +\\u000a ) (O\\u000a 2\\u000a ?\\u000a ) and (UO\\u000a 2

K Sankaran; K Sundararajan; K S Viswanathan

1999-01-01

397

Morphology of femtosecond-laser-ablated borosilicate glass surfaces Adela Ben-Yakara)  

E-print Network

Morphology of femtosecond-laser-ablated borosilicate glass surfaces Adela Ben-Yakara) and Robert L August 2003 We study the morphology of borosilicate glass surface machined by femtosecond laser pulses of multiple overlapping craters leads to surface roughness. We carried out experiments on borosilicate glass 1

Byer, Robert L.

398

Morphology of Femtosecond Laser Ablated Borosilicate Glass Surfaces Adela Ben-Yakar and Robert L. Byer  

E-print Network

Morphology of Femtosecond Laser Ablated Borosilicate Glass Surfaces Adela Ben-Yakar and Robert L the morphology of borosilicate glass surface machined by femtosecond laser pulses. Our observations show have been used to machine microchannels in transparent glasses such as borosilicate glass and fused

Harkin, Anthony

399

Characteristics of Plasma Shock Waves Generated in the Pulsed Laser Ablation Process  

Microsoft Academic Search

We modify the Sedov theory to describe plasma shock waves generated in a pulsed laser ablating process. We also study the propagation characteristics of plasma shock waves during the preparation process of functional thin films deposited by a pulsed laser. In particular, we discuss in detail the temporal behaviour of energy causing the difference of the propagation characteristics between the

Zhi-Hua Li; Duan-Ming Zhang; Bo-Ming Yu; Li Guan

2002-01-01

400

Stability, size and optical properties of silver nanoparticles prepared by laser ablation in different carrier media  

Microsoft Academic Search

We studied the effects of the surrounding liquid environment on the size and optical properties of silver nanoparticles prepared by laser ablation by a pulsed Nd:YAG laser operated at 1064 nm. The silver targets used were kept in acetone, water and ethanol. TEM observations and optical extinction were employed for characterization of particle size, shape and optical properties, respectively. Nano

R. M. Tilaki; A. Iraji Zad; S. M. Mahdavi

2006-01-01

401

Stability, size and optical properties of silver nanoparticles prepared by laser ablation in different carrier media  

Microsoft Academic Search

We studied the effects of the surrounding liquid environment on the size and optical properties of silver nanoparticles prepared by laser ablation by a pulsed Nd:YAG laser operated at 1064 nm. The silver targets used were kept in acetone, water and ethanol. TEM observations and optical extinction were employed for characterization of particle size, shape and optical properties, respectively. Nano silver

R. M. Tilaki; A. Iraji zad; S. M. Mahdavi

2006-01-01

402

Laser ablation threshold dependence on pulse duration for fused silica and corneal tissues: experiments and modeling  

Microsoft Academic Search

The surface ablation threshold fluence of fused silica and two porcine cornea layers, the epithelium and the stroma, is characterized as a function of the laser pulse duration in the range of 100 fs-5 ps for a wavelength of 800 nm (Ti:sapphire laser system). The plateaulike region observed between 100 fs and 1 ps for the corneal layers indicates that

Dominic Giguère; Gilles Olivié; François Vidal; Stéphanie Toetsch; Guillaume Girard; Tsuneyuki Ozaki; Jean-Claude Kieffer; Ossama Nada; Isabelle Brunette

2007-01-01

403

Experimental investigation on spectral-energy efficiency of femtosecond laser ablation of metals  

SciTech Connect

Results of investigation on spectral-energy thresholds, rates, and mass flow rates of laser ablation of structural materials (Cu, Ti, Zr, Nb, Mo) of high-energy photonics are presented. The data were obtained by means of an experimental diagnostic module developed for study of multifactor interaction processes between UV-near IR femtosecond laser pulse radiation and condensed media in vacuum.

Loktionov, E. Yu., E-mail: stcpe@bmstu.ru [Bauman Moscow State Technical University (Russian Federation); Ovchinnikov, A. V. [Russian Academy of Sciences, Joint Institute for High Temperatures (Russian Federation); Protasov, Yu. Yu. [Bauman Moscow State Technical University (Russian Federation); Sitnikov, D. S. [Russian Academy of Sciences, Joint Institute for High Temperatures (Russian Federation)

2011-12-15

404

Dentin ablation-rate measurements in endodontics witj HF and CO2 laser radiation  

NASA Astrophysics Data System (ADS)

Recent studies focused on the ability of the laser light to enlarge the root canal during the endodontic therapy. The aim of this research is the experimental and theoretical study of the ablation rate of two infrared laser wavelengths on dentin. Thirty freshly extracted human teeth were longitudinally sectioned at thicknesses ranged from 0.5 to 2 mm, and irradiated on the root canal dentin. The measured ablation rates in dentinal wall of the root canal showed that the HF laser at 2.9 micrometer can more effectively penetrate into the tissue, whereas the carbon dioxide laser at 10.6 micrometer leads to high thermal damage of the ablation crater surroundings.

Makropoulou, Mersini I.; Serafetinides, Alexander A.; Khabbaz, Marouan; Sykaras, Sotirios; Tsikrikas, G. N.

1996-01-01

405

A theoretical model of the femtosecond laser ablation of semiconductors considering inverse bremsstrahlung absorption  

NASA Astrophysics Data System (ADS)

The mechanism of the femtosecond laser ablation of semiconductors is investigated. The collision process of free electrons in a conduction band is depicted by the test particle method, and a theoretical model of nonequilibrium electron transport on the femtosecond timescale is proposed based on the Fokker—Planck equation. This model considers the impact of inverse bremsstrahlung on the laser absorption coefficient, and gives the expressions of electron drift and diffusion coefficients in the presence of screened Coulomb potential. Numerical simulations are conducted to obtain the nonequilibrium distribution function of the electrons. The femtosecond laser ablation thresholds are then calculated accordingly, and the results are in good agreement with the experimental results. This is followed by a discussion on the impact of laser parameters on the ablation of semiconductors.

Xiaohui, Lin; Chibin, Zhang; Weisong, Ren; Shuyun, Jiang; Quanhui, Ouyang

2012-04-01

406

Models For Laser Ablation Mass Removal And Impulse Generation In Vacuum  

SciTech Connect

To the present day, literature efforts at modeling laser propulsion impulse often used empirical models. Recently, a simple physical approach was demonstrated to be effective for predicting many practical properties of laser ablative impulse generation under vacuum. The model used photochemical mass removal and energy conservation to predict parameters such as the peak momentum coupling coefficient, the optimal fluence position at which this maximum is reached, and various critical properties related to the laser ablation threshold. Although the current model understanding is not complete, improvements in the treatment of mass removal and ambient pressure are expected to allow this type of model to be broadly applicable to many diverse applications using laser ablation impulse generation. In this paper, we also introduce an alternative formulation of the model incorporating photothermal mass removal. Implications and limitations of the model formulation in its initial stage of development are discussed, particularly concerning critical fluence effects and directions for improvement.

Sinko, John E. [Micro-Nano Global Center of Excellence, Graduate School of Engineering, Nagoya University, Furo-cho, Chikusa-ku, Nagoya, Aichi, 464-8603 (Japan); Gregory, Don A. [Department o Physics, University of Alabama in Huntsville, OB-201B John Wright Dr., Huntsville, AL 35899 (United States)

2010-05-06

407

One-step synthesis of hybrid inorganic-organic nanocomposite coatings by novel laser adaptive ablation deposition technique  

NASA Astrophysics Data System (ADS)

A novel approach for one-step synthesis of hybrid inorganic-organic nanocomposite coatings by new modification of Pulsed Laser Deposition technology called Laser Adaptive Ablation Deposition (LAAD) is presented. Hybrid nanocomposite coatings including Mg- Rapamycin and Mg- Desoximetasone were produced by UV TEA N2 laser under low vacuum (0.1 Pa) and room temperature onto substrates from SS 316L, KCl and NaCl. The laser fluence for Mg alloy was 1, 8 J/cm2 and for Desoximetasone 0,176 J/cm2 and for Rapamycin 0,118 J/cm2 were respectively. The threedimensional two-segmented single target was used to adapt the interaction of focused laser beam with inorganic and organic material. Magnesium alloy nanoparticles with sizes from 50 nm to 250 nm were obtained in organic matrices. The morphology of nanocomposites films were studied by Bright field / Fluorescence optical microscope and Scanning Electron Microscope (SEM). Fourier Transform Infrared (FTIR) spectroscopy measurements were applied in order to study the functional properties of organic component before and after the LAAD process. Energy Dispersive X-ray Spectroscopy (EDX) was used for identification of Mg alloy presence in hybrid nanocomposites coatings. The precise control of process parameters and particularly of the laser fluence adjustment enables transfer on materials with different physical chemical properties and one-step synthesis of complex inorganic- organic nanocomposites coatings.

Serbezov, Valery; Sotirov, Sotir

2013-03-01

408

Time-resolved study of back side ablated molybdenum thin films by ultrashort laser pulses  

NASA Astrophysics Data System (ADS)

Ultrashort laser pulses are used to ablate a thin molybdenum layer from glass by irradiating the metal film through the transparent substrate. The trajectories of ablated molybdenum fragments are recorded using a shadowgraphic setup with a time resolution in the nanosecond range. In addition, the shape of collected molybdenum fragments is examined as a function of applied fluence. It is confirmed that in a fluence regime close to the ablation threshold one single disc is ablated as a whole and its velocity is determined in the order of 50 ms-1. In a second fluence regime, partial melting at the center of the disc is found and small melt droplets are recorded on their flight. Mo fragments ablated in this regime feature a ring-like structure with a brittle fracture at the outer and a molten appearance at the inner edge.

Bartl, Dominik; Michalowski, Andreas; Hafner, Margit; Letsch, Andreas; Nolte, Stefan; Tünnermann, Andreas

2013-01-01

409

Femtosecond laser ablation of dielectric materials in the optical breakdown regime: Expansion of a transparent shell  

NASA Astrophysics Data System (ADS)

Phase transition pathways of matter upon ablation with ultrashort laser pulses have been considered to be understood long-since for metals and semiconductors. We provide evidence that also certain dielectrics follow the same pathway, even at high pulse energies triggering optical breakdown. Employing femtosecond microscopy, we observe a charact