Science.gov

Sample records for ablative pulsed plasma

  1. Plasma mediated ablation of biological tissues with ultrashort laser pulses

    SciTech Connect

    Oraevsky, A.A. |; DaSilva, L.B.; Feit, M.D.

    1995-03-08

    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.

  2. Study of breakdown in an ablative pulsed plasma thruster

    SciTech Connect

    Huang, Tiankun; Wu, Zhiwen; Liu, Xiangyang; Xie, Kan; Wang, Ningfei; Cheng, Yue

    2015-10-15

    Breakdown in ablative pulsed plasma thrusters (APPTs) must be studied in order to design new types of APPTs and measure particular parameters. In this paper, we studied a parallel-plate ablative pulsed plasma thruster that used a coaxial semiconductor spark plug. By operating the APPT about 500 times with various capacitor voltages and electrode gaps, we measured and analyzed the voltage of the spark plug, the voltage between the electrodes, and the discharge current. These experiments revealed a time delay (∼1–10 μs) between spark plug ignition and capacitor discharge, which may affect the performance of high-pulsing-rate (>10 kHz) and double-discharge APPTs, and the measurements of some of the APPT parameters. The delay time decreased as the capacitor voltage increased, and it increased with an increasing electrode gap and increasing number of ignitions. We explain our results through a simple theoretical analysis.

  3. Characteristics of plasma properties in an ablative pulsed plasma thruster

    SciTech Connect

    Schoenherr, Tony; Nees, Frank; Arakawa, Yoshihiro; Komurasaki, Kimiya; Herdrich, Georg

    2013-03-15

    Pulsed plasma thrusters are electric space propulsion devices which create a highly transient plasma bulk in a short-time arc discharge that is expelled to create thrust. The transitional character and the dependency on the discharge properties are yet to be elucidated. In this study, optical emission spectroscopy and Mach-Zehnder interferometry are applied to investigate the plasma properties in variation of time, space, and discharge energy. Electron temperature, electron density, and Knudsen numbers are derived for the plasma bulk and discussed. Temperatures were found to be in the order of 1.7 to 3.1 eV, whereas electron densities showed maximum values of more than 10{sup 17} cm{sup -3}. Both values showed strong dependency on the discharge voltage and were typically higher closer to the electrodes. Capacitance and time showed less influence. Knudsen numbers were derived to be in the order of 10{sup -3}-10{sup -2}, thus, indicating a continuum flow behavior in the main plasma bulk.

  4. Plasma luminescence feedback control system for precise ultrashort pulse laser tissue ablation

    SciTech Connect

    Kim, B.M.; Feit, M.D.; Rubenchick, A.M.; Gold, D.M.; Darrown, C.B.; Da Silva, L.B.

    1998-01-01

    Plasma luminescence spectroscopy was used for precise ablation of bone tissue without damaging nearby soft tissue using ultrashort pulse laser (USPL). Strong contrast of the luminescence spectra between bone marrow and spinal cord provided the real time feedback control so that only bone tissue can be selectively ablated while preserving the spinal cord.

  5. Numerical studies of wall-plasma interactions and ionization phenomena in an ablative pulsed plasma thruster

    NASA Astrophysics Data System (ADS)

    Yang, Lei; Zeng, Guangshang; Tang, Haibin; Huang, Yuping; Liu, Xiangyang

    2016-07-01

    Wall-plasma interactions excited by ablation controlled arcs are very critical physical processes in pulsed plasma thrusters (PPTs). Their effects on the ionization processes of ablated vapor into discharge plasma directly determine PPT performances. To reveal the physics governing the ionization phenomena in PPT discharge, a modified model taking into account the pyrolysis effect of heated polytetrafluoroethylene propellant on the wall-plasma interactions was developed. The feasibility of the modified model was analyzed by creating a one-dimensional simulation of a rectangular ablative PPT. The wall-plasma interaction results based on this modified model were found to be more realistic than for the unmodified model; this reflects the dynamic changes of the inflow parameters during discharge in our model. Furthermore, the temporal and spatial variations of the different plasma species in the discharge chamber were numerically studied. The numerical studies showed that polytetrafluoroethylene plasma was mainly composed of monovalent ions; carbon and fluorine ions were concentrated in the upstream and downstream discharge chamber, respectively. The results based on this modified model were in good agreement with the experimental formation times of the various plasma species. A large number of short-lived and highly ionized carbon and fluorine species (divalent and trivalent ions) were created during initial discharge. These highly ionized species reached their peak density earlier than the singly ionized species.

  6. Modeling of gas ionization and plasma flow in ablative pulsed plasma thrusters

    NASA Astrophysics Data System (ADS)

    Huang, Tiankun; Wu, Zhiwen; Liu, Xiangyang; Xie, Kan; Wang, Ningfei; Cheng, Yue

    2016-12-01

    A one-dimensional model to study the gas ionization and plasma flow in ablative pulsed plasma thrusters(APPTs) is established in this paper. The discharge process of the APPT used in the LES-6 satellite is simulated to validate the model. The simulation results for the impulse bit and propellant utilization give values of 29.05 μN s and 9.56%, respectively, which are in good agreement with experimental results. To test the new ionization sub-model, the discharge process of a particular APPT, XPPT-1, is simulated, and a numerical result for the propellant utilization of 62.8% is obtained, which also agrees well with experiment. The gas ionization simulation results indicate that an APPT with a lower average propellant ablation rate and higher average electric field intensity between electrodes should have higher propellant utilization. The plasma density distribution between the electrodes of APPTs can also be obtained using the new model, and the numerical results show that the plasma generation and flow are discontinuous, which is in good agreement with past experimental results of high-speed photography. This model provides a new tool with which to study the physical mechanisms of APPTs and a reference for the design of high-performance APPTs.

  7. Opacity and atomic analysis of double pulse laser ablated Li plasma

    NASA Astrophysics Data System (ADS)

    Sivakumaran, V.; Joshi, H. C.; Kumar, Ajai

    2014-09-01

    Opacity effects for neutral and ionic emission lines of lithium have been investigated by Atomic Data Analysis Structure (ADAS). Line ratios and opacity corrected photon emissivity coefficients are calculated over a wide range of electron temperatures and densities. The experimentally measured temporal evolution of the line profiles of the over dense Li plasma formed in the double pulse laser ablation experiment have been explained using the ADAS analysis and the plasma parameters of the plasma plume under consideration have been estimated. These results could be projected as a diagnostic tool to estimate plasma parameters of an over dense lithium plasma.

  8. Infrared nanosecond laser-metal ablation in atmosphere: Initial plasma during laser pulse and further expansion

    SciTech Connect

    Wu, Jian; Wei, Wenfu; Li, Xingwen; Jia, Shenli; Qiu, Aici

    2013-04-22

    We have investigated the dynamics of the nanosecond laser ablated plasma within and after the laser pulse irradiation using fast photography. A 1064 nm, 15 ns laser beam was focused onto a target made from various materials with an energy density in the order of J/mm{sup 2} in atmosphere. The plasma dynamics during the nanosecond laser pulse were observed, which could be divided into three stages: fast expansion, division into the primary plasma and the front plasma, and stagnation. After the laser terminated, a critical moment when the primary plasma expansion transited from the shock model to the drag model was resolved, and this phenomenon could be understood in terms of interactions between the primary and the front plasmas.

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

    SciTech Connect

    Geohegan, D.B.

    1994-09-01

    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.

  10. Influence of the main pulse and prepulse intensity on high-order harmonic generation in silver plasma ablation

    SciTech Connect

    Elouga Bom, L. B.; Kieffer, J.-C.; Ozaki, T.; Ganeev, R. A.; Suzuki, M.; Kuroda, H.

    2007-03-15

    We present experimental studies of high-order harmonic generation in silver plasma ablation performed with the Ti:sapphire laser beams of the Advanced Laser Light Source (800 nm wavelength, 360 mJ total energy). We have independently varied the intensity of the prepulse (which creates the plasma ablation) and the intensity of the main pulse (which generates the harmonics), and studied their influence on the harmonic spectrum. We show here that the presence of doubly ionized atoms in the ablation, created either by a strong prepulse intensity or with the irradiation of the main pulse, is ineffective for the generation of harmonics.

  11. Surface modification of biomaterials by pulsed laser ablation deposition and plasma/gamma polymerization

    NASA Astrophysics Data System (ADS)

    Rau, Kaustubh R.

    Surface modification of stainless-steel was carried out by two different methods: pulsed laser ablation deposition (PLAD) and a combined plasma/gamma process. A potential application was the surface modification of endovascular stents, to enhance biocompatibility. The pulsed laser ablation deposition process, had not been previously reported for modifying stents and represented a unique and potentially important method for surface modification of biomaterials. Polydimethylsiloxane (PDMS) elatomer was studied using the PLAD technique. Cross- linked PDMS was deemed important because of its general use for biomedical implants and devices as well as in other fields. Furthermore, PDMS deposition using PLAD had not been previously studied and any information gained on its ablation characteristics could be important scientifically and technologically. The studies reported here showed that the deposited silicone film properties had a dependence on the laser energy density incident on the target. Smooth, hydrophobic, silicone-like films were deposited at low energy densities (100-150 mJ/cm2). At high energy densities (>200 mJ/cm2), the films had an higher oxygen content than PDMS, were hydrophilic and tended to show a more particulate morphology. It was also determined that (1)the deposited films were stable and extremely adherent to the substrate, (2)silicone deposition exhibited an `incubation effect' which led to the film properties changing with laser pulse number and (3)films deposited under high vacuum were similar to films deposited at low vacuum levels. The mechanical properties of the PLAD films were determined by nanomechanical measurements which are based on the Atomic Force Microscope (AFM). From these measurements, it was possible to determine the modulus of the films and also study their scratch resistance. Such measurement techniques represent a significant advance over current state-of-the-art thin film characterization methods. An empirical model for

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

    SciTech Connect

    Kato, Toru; Stauss, Sven; Kato, Satoshi; Urabe, Keiichiro; Terashima, Kazuo; Baba, Motoyoshi; Suemoto, Tohru

    2012-11-26

    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.

  13. [Doppler effect on width of characteristic line in plasma induced by pulsed laser ablating Al].

    PubMed

    Song, Yi-Zhong; He, An-Zhi

    2005-05-01

    Aluminum (Al) plasma was induced with a pulsed Nd: YAG laser beam ablating Al target in Ar. Time-resolved information of the plasma radiation was taken with time-resolved technique, and the spectra of the radiation were recorded with an optical multi-path analyzer (OMA III ), whereupon, time-resolved spectra of the plasma radiation induced by pulsed laser were acquired. Based on the experiment data, Al resonant double lines, Al I 396.15 nm, Al I 394.40 nm, were respectively fitted with Lorentz, Gauss and their linear integrated function (abbr. Integrated function), whereupon, Lorentz and Gauss elements were separated from the experiment data profile curve. By contrasting Lorentz with Gauss curve separated, it was found that the experiment curve mainly consisted of Lorentz element, a with little Gauss. By contrasting Lorentz with Integrated fitting curve for experiment data, a visual picture of the characteristic lines broadened by Doppler effect was exhibited. According to the visual picture, the increase of full half-high width of the characteristic line broadened by Doppler effect was estimated. It was about 2 x 10(-)3 -8 x 10(-3) nm, approximating the theoretical value 6.7 x 10(-)3 nm. As a result, Doppler effect on the width of characteristic lines in the plasma could be reasonably explained by curve fitting analysis and theoretical calculation.

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

    SciTech Connect

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

    2014-06-15

    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.

  15. In-vivo plasma-mediated ablation as a function of laser pulse width

    NASA Astrophysics Data System (ADS)

    Liu, Xinbing; Tien, An-Chun; Juhasz, Tibor; Irish, Barbara; Elner, Victor; Kurtz, Ron M.

    1997-06-01

    We evaluated in vivo wound healing responses to plasma- mediated ablation in skin as a function of laser pulsewidth and energy. Experiments utilized a regeneratively amplified Ti:Sapphire laser operating at 800 nm with pulsewidths varied from 7 ns to 100 fs. Skin incisions were created in mice by tightly focusing the laser beam on the tissue surface. Incisions of equal depth were compared at time points ranging from 6 hours to 3 weeks using standard histologic methods. Incision depth was proportional to pulse energy at each pulsewidth. Fluence threshold dependence on laser pulsewidth agreed with those predicted by ex vivo testing. Histologic analysis revealed minimal adjacent tissue damage at pulsewidths less than a few picoseconds and energies near the fluence threshold. Longer pulsewidths and higher fluence levels were associated with more significant collateral effects. These in vivo results suggest collateral tissue damage and secondary effects may be minimized by controlling laser pulsewidth and energy.

  16. Characteristics of a non-volatile liquid propellant in liquid-fed ablative pulsed plasma thrusters

    NASA Astrophysics Data System (ADS)

    Ling, William Yeong Liang; Schönherr, Tony; Koizumi, Hiroyuki

    2017-02-01

    In the past several decades, the use of electric propulsion in spacecraft has experienced tremendous growth. With the increasing adoption of small satellites in the kilogram range, suitable propulsion systems will be necessary in the near future. Pulsed plasma thrusters (PPTs) were the first form of electric propulsion to be deployed in orbit, and are highly suitable for small satellites due to their inherent simplicity. However, their lifetime is limited by disadvantages such as carbon deposition leading to thruster failure, and complicated feeding systems required due to the conventional use of solid propellants (usually polytetrafluoroethylene (PTFE)). A promising alternative to solid propellants has recently emerged in the form of non-volatile liquids that are stable in vacuum. This study presents a broad comparison of the non-volatile liquid perfluoropolyether (PFPE) and solid PTFE as propellants on a PPT with a common design base. We show that liquid PFPE can be successfully used as a propellant, and exhibits similar plasma discharge properties to conventional solid PTFE, but with a mass bit that is an order of magnitude higher for an identical ablation area. We also demonstrate that the liquid PFPE propellant has exceptional resistance to carbon deposition, completely negating one of the major causes of thruster failure, while solid PTFE exhibited considerable carbon build-up. Energy dispersive X-ray spectroscopy was used to examine the elemental compositions of the surface deposition on the electrodes and the ablation area of the propellant (or PFPE encapsulator). The results show that based on its physical characteristics and behavior, non-volatile liquid PFPE is an extremely promising propellant for use in PPTs, with an extensive scope available for future research and development.

  17. On the growth mechanism of nanoparticles in plasma during pulsed laser ablation in liquids

    NASA Astrophysics Data System (ADS)

    Taccogna, F.; Dell’Aglio, M.; Rutigliano, M.; Valenza, G.; De Giacomo, A.

    2017-04-01

    Particle-in-cell methodology is applied to study the simultaneous charging and coagulation of a nanoparticle, taking into account the self-consistent dynamics of surrounding plasma induced by laser ablation in liquid. The model uses, as an input, plasma temperature and electron number density which are experimentally obtained by high temporally resolved optical emission spectroscopy of the laser-induced plasma in water. Results show the important role of ions in the growth process and of the atom-induced evaporation process for the final nanoparticle size. The competition between different mechanisms of nanoparticle formation in the laser-induced plasma is finally discussed.

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

    SciTech Connect

    Nakahara, Sho; Stauss, Sven; Kato, Toru; Terashima, Kazuo; Sasaki, Takehiko

    2011-06-15

    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.

  19. INTERACTION OF LASER RADIATION WITH MATTER. LASER PLASMA: Laser microprocessing in a gas environment at a high repetition rate of ablative pulses

    NASA Astrophysics Data System (ADS)

    Klimentov, Sergei M.; Pivovarov, Pavel A.; Konov, Vitalii I.; Breitling, D.; Dausinger, F.

    2004-06-01

    The parameters of laser ablation of channels in steel are studied in a wide range of nanosecond pulse repetition rates f (5 Hz <= f <= 200 kHz). It is found that for f >= 4 kHz, the results of ablation in air are identical to those obtained under the action of single laser pulses in vacuum. The experimental data as well as the estimates of the parameters of laser plasma and the gas environment in the region of the laser action lead to the conclusion that there exists a long-lived region of hot rarefied gas, known as a fire ball in the theory of explosions. The emerging rarefaction reduces the screening effect of the surface plasma formed under the action of subsequent pulses. This makes it possible to use lasers with a high pulse repetition rate for attaining ablation conditions close to the conditions in vacuum without complicating the technology of microprocessing by using vacuum chambers and evacuating pumps.

  20. Atomic Processes in Emission Characteristics of a Lithium Plasma Plume Formed by Double-Pulse Laser Ablation

    NASA Astrophysics Data System (ADS)

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

    2013-03-01

    High resolution spectral analysis of lithium plasma formed by single and double laser ablation has been undertaken to understand the plume-laser interaction, especially at the early stages of the plasma plume. In order to identify different atomic processes in evolving plasma, time resolved spectral emission studies at different inter-pulse delays have been performed for ionic and neutral lithium lines emitting from different levels. Along with the enhancement in emission intensity, a large line broadening and spectral shift, especially in the case of excited state transition Li I 610.3 nm have been observed in the presence of the second pulse. This broadening and shift gradually decrease with increasing time delay. Another interesting feature is the appearance of a multi-component structure in the ionic line at 548.4 nm and these components change conversely into a single structure at the later stages of the plasma. The multi-component structures are correlated with the presence of different velocity (temperature) distributions in non-LTE conditions. Atomic analyses by computing photon emissivity coefficients with an ADAS code have been used to identify the above processes.

  1. Ablation of steel using picosecond laser pulses in burst mode

    NASA Astrophysics Data System (ADS)

    Lickschat, Peter; Demba, Alexander; Weissmantel, Steffen

    2017-02-01

    Results obtained in picosecond laser processing of steel applying the burst mode are presented. Using the burst mode, pulse trains, i.e., bursts, consisting of a number of picosecond pulses with an inter-pulse delay of 12.5 ns and 10 ps pulse duration are applied for material processing. Small cavities with sizes in the range of the laser beam diameter made by single-burst ablation are compared to quadratic cavities of 0.5 × 0.5 mm² produced by multiburst ablation and simultaneous scanning of the laser beam across the steel sample surface. The ablated volume per pulse within the burst was calculated either from the ablated volume per burst or from the ablation depth of the quadratic cavities. With the second to fourth pulses in the bursts, a reduction of the ablated volume per pulse in comparison with the first pulse in the bursts (i.e., to the use of single pulses) was found for both single- and multiburst ablation, which is assumed to be due to plasma shielding. By contrast, the ablated volume per pulse within the bursts increases for the fifth to eighth pulses. Heat accumulation effect and the influence of the heated plasma can be assumed to be the reason for these higher ablation rates. SEM micrographs also show that there is a higher melt ejection out of the laser processed area. This is indicated by the formation of bulges about the ablated area.

  2. Plasma-mediated ablation of biofilm contamination

    NASA Astrophysics Data System (ADS)

    Guo, Zhixiong; Wang, Xiaoliang; Huang, Huan

    2010-12-01

    Ultra-short pulsed laser removal of thin biofilm contamination on different substrates has been conducted via the use of plasma-mediated ablation. The biofilms were formed using sheep whole blood. The ablation was generated using a 1.2 ps ultra-short pulsed laser with wavelength centered at 1552 nm. The blood contamination was transformed into plasma and collected with a vacuum system. The single line ablation features have been measured. The ablation thresholds of blood contamination and bare substrates were determined. It is found that the ablation threshold of the blood contamination is lower than those of the beneath substrates including the glass slide, PDMS, and human dermal tissues. The ablation effects of different laser parameters (pulse overlap rate and pulse energy) were studied and ablation efficiency was measured. Proper ablation parameters were found to efficiently remove contamination with maximum efficiency and without damage to the substrate surface for the current laser system. Complete removal of blood contaminant from the glass substrate surface and freeze-dried dermis tissue surface was demonstrated by the USP laser ablation with repeated area scanning. No obvious thermal damage was found in the decontaminated glass and tissue samples.

  3. High excitation of the species in nitrogen-aluminum plasma generated by electron cyclotron resonance microwave discharge of N2 gas and pulsed laser ablation of Al target

    NASA Astrophysics Data System (ADS)

    Liang, Peipei; Li, Yanli; Cai, Hua; You, Qinghu; Yang, Xu; Huang, Feiling; Sun, Jian; Xu, Ning; Wu, Jiada

    2014-11-01

    A reactive nitrogen-aluminum plasma generated by electron cyclotron resonance (ECR) microwave discharge of N2 gas and pulsed laser ablation of an Al target is characterized spectroscopically by time-integrated and time-resolved optical emission spectroscopy (OES). The vibrational and rotational temperatures of N2 species are determined by spectral simulation. The generated plasma strongly emits radiation from a variety of excited species including ambient nitrogen and ablated aluminum and exhibits unique features in optical emission and temperature evolution compared with the plasmas generated by a pure ECR discharge or by the expansion of the ablation plume. The working N2 gas is first excited by ECR discharge and the excitation of nitrogen is further enhanced due to the fast expansion of the aluminum plume induced by target ablation, while the excitation of the ablated aluminum is prolonged during the plume expansion in the ECR nitrogen plasma, resulting in the formation of strongly reactive nitrogen-aluminum plasma which contains highly excited species with high vibrational and rotational temperatures. The enhanced intensities and the prolonged duration of the optical emissions of the combined plasma would provide an improved analytical capability for spectrochemical analysis.

  4. Formation of diatomic molecular radicals in reactive nitrogen-carbon plasma generated by electron cyclotron resonance discharge and pulsed laser ablation

    SciTech Connect

    Liang, Peipei; Li, Yanli; You, Qinghu; Cai, Hua; Yang, Xu; Sun, Jian; Xu, Ning; Wu, Jiada

    2014-04-15

    The reactive nitrogen-carbon plasma generated by electron cyclotron resonance (ECR) microwave discharge of N{sub 2} gas and pulsed laser ablation of a graphite target was characterized spectroscopically by time-integrated and time-resolved optical emission spectroscopy with space resolution for a study of gas-phase reactions and molecular radical formation in the plasma. The plasma exhibits very high reactivity compared with the plasma generated solely by ECR discharge or by pulsed laser ablation and contains highly excited species originally present in the ambient gaseous environment and directly ablated from the target as well as formed as the products of gas-phase reactions occurring in the plasma. The space distribution and the time evolution of the plasma emission give an access to the gas-phase reactions for the formation of C{sub 2} and CN radicals, revealing that C{sub 2} radicals are formed mainly in the region near the target while CN radicals can be formed in a much larger region not only in the vicinity of the target, but especially in the region near a substrate far away from the target.

  5. Formation of diatomic molecular radicals in reactive nitrogen-carbon plasma generated by electron cyclotron resonance discharge and pulsed laser ablation

    NASA Astrophysics Data System (ADS)

    Liang, Peipei; Li, Yanli; You, Qinghu; Cai, Hua; Yang, Xu; Sun, Jian; Xu, Ning; Wu, Jiada

    2014-04-01

    The reactive nitrogen-carbon plasma generated by electron cyclotron resonance (ECR) microwave discharge of N2 gas and pulsed laser ablation of a graphite target was characterized spectroscopically by time-integrated and time-resolved optical emission spectroscopy with space resolution for a study of gas-phase reactions and molecular radical formation in the plasma. The plasma exhibits very high reactivity compared with the plasma generated solely by ECR discharge or by pulsed laser ablation and contains highly excited species originally present in the ambient gaseous environment and directly ablated from the target as well as formed as the products of gas-phase reactions occurring in the plasma. The space distribution and the time evolution of the plasma emission give an access to the gas-phase reactions for the formation of C2 and CN radicals, revealing that C2 radicals are formed mainly in the region near the target while CN radicals can be formed in a much larger region not only in the vicinity of the target, but especially in the region near a substrate far away from the target.

  6. Direct measurements of sample heating by a laser-induced air plasma in pre-ablation spark dual-pulse laser-induced breakdown spectroscopy (LIBS).

    PubMed

    Register, Janna; Scaffidi, Jonathan; Angel, S Michael

    2012-08-01

    Direct measurements of temperature changes were made using small thermocouples (TC), placed near a laser-induced air plasma. Temperature changes up to ~500 °C were observed. From the measured temperature changes, estimates were made of the amount of heat absorbed per unit area. This allowed calculations to be made of the surface temperature, as a function of time, of a sample heated by the air plasma that is generated during orthogonal pre-ablation spark dual-pulse (DP) LIBS measurements. In separate experiments, single-pulse (SP) LIBS emission and sample ablation rate measurements were performed on nickel at sample temperatures ranging from room temperature to the maximum surface temperature that was calculated using the TC measurement results (500 °C). A small, but real sample temperature-dependent increase in both SP LIBS emission and the rate of sample ablation was found for nickel samples heated up to 500 °C. Comparison of DP LIBS emission enhancement values for bulk nickel samples at room temperature versus the enhanced SP LIBS emission and sample ablation rates observed as a function of increasing sample temperature suggests that sample heating by the laser-induced air plasma plays only a minor role in DP LIBS emission enhancement.

  7. Pulsed HF laser ablation of dentin

    NASA Astrophysics Data System (ADS)

    Papagiakoumou, Eirini I.; Papadopoulos, Dimitris N.; Makropoulou, Mersini I.; Khabbaz, Maruan G.; Serafetinides, Alexander A.

    2005-03-01

    The interaction of a TEA (Transversally Excited Atmospheric pressure) corona preionized oscillator double amplifier HF (hydrogen fluoride) laser beam with dentin tissue is reported. Pulses of 39 ns in the wavelength range of 2.65-3.35 μm and output energies in the range of 10-45 mJ, in a predominantly TEM00 beam were used to interact with dentin tissue. Ablation experiments were conducted with the laser beam directly focused on the tissue. Several samples of freshly extracted human teeth were used, cut longitudinally in facets of about 1mm thick and stored in phosphate buffered saline after being cleaned from the soft tissue remains. The experimental data (ablation thresholds, ablation rates) are discussed with respect to the ablation mechanism(s). Adequate tissue removal was observed and the ablation behavior was, in the greates part of the available fluences, almost linear. From the microscopic examination of teh samples, in a scanning electron microscope (SEM), the irradiated surfaces displayed oval craters (reflecting the laser beam shape) with absence of any melting or carbonization zone. It is suggested that the specific laser removes hard tissue by a combined photothermal and plasma mediated ablation mechanism, leaving a surface free from thermal damage and with a well-shaped crater.

  8. INTERACTION OF LASER RADIATION WITH MATTER. LASER PLASMA: Change in the ionisation state of a near-surface laser-produced aluminium plasma in double-pulse ablation modes

    NASA Astrophysics Data System (ADS)

    Burakov, V. S.; Bokhonov, A. F.; Nedel'ko, M. I.; Tarasenko, N. V.

    2003-12-01

    The near-surface plasma produced upon irradiation of an aluminium target by two successive laser pulses with nonresonance and resonance wavelengths is studied by the spectroscopic and probe-assisted methods. The feasibility of increasing the ion fraction in the laser-produced plasma in double-pulse ablation modes is demonstrated. The conditions are determined under which processes on the surface as well as selective excitation and ionisation in the plasma have a determining effect on the formation of its ionisation state.

  9. Mechanism study of skin tissue ablation by nanosecond laser pulses

    NASA Astrophysics Data System (ADS)

    Fang, Qiyin

    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

  10. Features of spatial distribution of the parameters on the initial section of a supersonic plasma jet, created by pulsed discharge in a capillary with ablative wall

    NASA Astrophysics Data System (ADS)

    Ageev, A. G.; Bityurin, V. A.; Chinnov, V. F.; Efimov, A. V.; Pashchina, A. S.

    2016-11-01

    The results of spectroscopic studies of the initial section of the supersonic plasma jet created by a pulsed discharge in the capillary with the ablative wall are presented. Features of the spatial distribution of the electron density and the intensity of the spectral components, which, in particular, caused by the high electron temperature in the hot central zone, exceeding the “normal” temperature, as well as significant non-isobaricity at the initial section of supersonic jet are revealed. The presence of the molecular components exhibiting their emission properties at the plasma jet periphery permit us to estimate the parameters of the plasma in the spatial domain, where “detached” shock waves of the supersonic jet are created.

  11. Computational modeling of ultra-short-pulse ablation of enamel

    SciTech Connect

    London, R.A.; Bailey, D.S.; Young, D.A.

    1996-02-29

    A computational model for the ablation of tooth enamel by ultra-short laser pulses is presented. The role of simulations using this model in designing and understanding laser drilling systems is discussed. Pulses of duration 300 sec and intensity greater than 10{sup 12} W/cm{sup 2} are considered. Laser absorption proceeds via multi-photon initiated plasma mechanism. The hydrodynamic response is calculated with a finite difference method, using an equation of state constructed from thermodynamic functions including electronic, ion motion, and chemical binding terms. Results for the ablation efficiency are presented. An analytic model describing the ablation threshold and ablation depth is presented. Thermal coupling to the remaining tissue and long-time thermal conduction are calculated. Simulation results are compared to experimental measurements of the ablation efficiency. Desired improvements in the model are presented.

  12. Ultrafast double-pulse ablation of fused silica

    SciTech Connect

    Chowdhury, Ihtesham H.; Xu Xianfan; Weiner, Andrew M.

    2005-04-11

    Ultrafast pump-probe experiments were used to study high-intensity ultrafast pulse-ablation dynamics in fused silica. Two laser pulses with varied time delay and pulse energy were used to irradiate fused silica samples and observe the transient reflectivity and transmissivity of the probe pulse. It was seen that the probe reflectivity initially increased due to the formation of free-electron plasma and then dropped to a low value within a period of about 10 ps caused by a rapid structural change at the surface. The time-resolved measurements of reflectivity and transmissivity were also related to atomic force microscopy measurements of the depth of the laser-ablated hole. It was seen that the depth peaked at zero delay between the pulses and decreased within a period of about 1 ps as the temporal separation between the pulses was increased caused by the screening by the plasma produced by the first pulse. When the temporal separation is about 100 ps or longer, evidence for melting and resolidification during double-pulse ablation was also observed in the form of ridges at the circumference of the ablated holes.

  13. Hydrodynamic Efficiency of Ablation Propulsion with Pulsed Ion Beam

    SciTech Connect

    Buttapeng, Chainarong; Yazawa, Masaru; Harada, Nobuhiro; Suematsu, Hisayuki; Jiang Weihua; Yatsui, Kiyoshi

    2006-05-02

    This paper presents the hydrodynamic efficiency of ablation plasma produced by pulsed ion beam on the basis of the ion beam-target interaction. We used a one-dimensional hydrodynamic fluid compressible to study the physics involved namely an ablation acceleration behavior and analyzed it as a rocketlike model in order to investigate its hydrodynamic variables for propulsion applications. These variables were estimated by the concept of ablation driven implosion in terms of ablated mass fraction, implosion efficiency, and hydrodynamic energy conversion. Herein, the energy conversion efficiency of 17.5% was achieved. In addition, the results show maximum energy efficiency of the ablation process (ablation efficiency) of 67% meaning the efficiency with which pulsed ion beam energy-ablation plasma conversion. The effects of ion beam energy deposition depth to hydrodynamic efficiency were briefly discussed. Further, an evaluation of propulsive force with high specific impulse of 4000s, total impulse of 34mN and momentum to energy ratio in the range of {mu}N/W was also analyzed.

  14. Multidiagnostic analysis of ultrafast laser ablation of metals with pulse pair irradiation

    NASA Astrophysics Data System (ADS)

    Amoruso, S.; Bruzzese, R.; Wang, X.; O'Connell, G.; Lunney, J. G.

    2010-12-01

    Copper targets are irradiated in the ablation regime by pairs of equal, time-delayed collinear laser pulses separated on a timescale going from ≈2 ps to ≈2 ns. The ablation plume is characterized by ion probe diagnostic, fast imaging, and temporally and spatially resolved optical emission spectroscopy. The variation in the ablation efficiency with the delay between the pulses is analyzed by measuring the ablation crater profile with a contact profilometer. The second laser pulse modifies the characteristics of the plasma plume produced by the first pulse and the ablation efficiency. The different mechanisms involved in double pulse ultrafast laser ablation are identified and discussed. The experimental findings are interpreted in the frame of a simple model of the interaction of the second pulse with the nascent ablation plume produced by the first pulse. This model yields consistent and quantitative agreement with the experimental findings predicting the observed experimental trends of the ablation depth reduction and ion yield increase with the delay between the pulses, as well as the characteristic timescale of the observed changes. The possibility of controlling the characteristics of the plumes produced during ultrafast laser ablation via an efficient coupling of the energy of the second pulse to the various ablation components produced by the first pulse is of particular interest in ultrafast pulsed laser deposition and microprobe analyses of materials.

  15. Pulsed infrared laser ablation and clinical applications

    NASA Astrophysics Data System (ADS)

    Chan, Kin Foong

    Sufficient light energy deposited in tissue can result in ablation and excessive thermal and mechanical damage to adjacent tissues. The goals of this research are to investigate the mechanisms of pulsed infrared laser ablation of tissue, to optimize laser parameters for minimizing unnecessary damage to healthy tissue, and to explore the potential of using pulsed infrared lasers for clinical applications, especially laser lithotripsy. A dual-channel optical low coherence reflectometer was implemented to measure the expansion and collapse velocities of a Q-switched Ho:YAG (λ = 2.12 μm) laser-induced cavitation in water. Cavitation wall velocities up to 11 m/s were measured with this technique, and the results were in fair agreement with those calculated from fast-flash photographic images. The dependence of ablation threshold fluence on calculus absorption was examined. Preliminary results indicated that the product of optical absorption and ablation threshold fluence, which is the heat of ablation, remained constant for a given urinary calculus type and laser pulse duration. An extended study examined the influence of optical absorption on pulsed infrared laser ablation. An analytical photothermal ablation model was applied and compared to experimental ablation results using an infrared free-electron laser at selected wavelengths between 2.12 μm and 6.45 μm Results were in good agreement with the model, and the ablation depths of urinary calculi were highly dependent upon the calculus optical absorption as well as light attenuation within the intrapulse ablation plume. An efficient wavelength for ablation corresponded to the wavelength of the Er:YAG laser (λ = 2.94 μm) suggested this laser should be examined for laser lithotripsy. Schlieren flash photography, acoustic transient measurements with a piezoelectric polyvinylidene-fluoride needle-hydrophone, mass loss measurements, and chemical analyses were employed to study the ablation mechanisms of the free

  16. Modeling of ablation threshold dependence on pulse duration for dielectrics with ultrashort pulsed laser

    NASA Astrophysics Data System (ADS)

    Sun, Mingying; Zhu, Jianqiang; Lin, Zunqi

    2017-01-01

    We present a numerical model of plasma formation in ultrafast laser ablation on the dielectrics surface. Ablation threshold dependence on pulse duration is predicted with the model and the numerical results for water agrees well with the experimental data for pulse duration from 140 fs to 10 ps. Influences of parameters and approximations of photo- and avalanche-ionization on the ablation threshold prediction are analyzed in detail for various pulse lengths. The calculated ablation threshold is strongly dependent on electron collision time for all the pulse durations. The complete photoionization model is preferred for pulses shorter than 1 ps rather than the multiphoton ionization approximations. The transition time of inverse bremsstrahlung absorption needs to be considered when pulses are shorter than 5 ps and it can also ensure the avalanche ionization (AI) coefficient consistent with that in multiple rate equations (MREs) for pulses shorter than 300 fs. The threshold electron density for AI is only crucial for longer pulses. It is reasonable to ignore the recombination loss for pulses shorter than 100 fs. In addition to thermal transport and hydrodynamics, neglecting the threshold density for AI and recombination could also contribute to the disagreements between the numerical and the experimental results for longer pulses.

  17. Optical feedback signal for ultrashort laser pulse ablation of tissue

    SciTech Connect

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

    1997-07-01

    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.

  18. Temperature dependent ablation threshold in silicon using ultrashort laser pulses

    NASA Astrophysics Data System (ADS)

    Thorstensen, Jostein; Erik Foss, Sean

    2012-11-01

    We have experimentally investigated the ablation threshold in silicon as a function of temperature when applying ultrashort laser pulses at three wavelengths. By varying the temperature of a silicon substrate from room temperature to 320 °C, we observe that the ablation threshold for a 3 ps pulse using a wavelength of 1030 nm drops from 0.43 J/cm2 to 0.24 J/cm2, a reduction of 43%. For a wavelength of 515 nm, the ablation threshold drops from 0.22 J/cm2 to 0.15 J/cm2, a reduction of 35%. The observed ablation threshold for pulses at 343 nm remains constant with temperature, at 0.10 J/cm2. These results indicate that substrate heating is a useful technique for lowering the ablation threshold in industrial silicon processing using ultrashort laser pulses in the IR or visible wavelength range. In order to investigate and explain the observed trends, we apply the two-temperature model, a thermodynamic model for investigation of the interaction between silicon and ultrashort laser pulses. Applying the two-temperature model implies thermal equilibrium between optical and acoustic phonons. On the time scales encountered herein, this need not be the case. However, as discussed in the article, the two-temperature model provides valuable insight into the physical processes governing the interaction between the laser light and the silicon. The simulations indicate that ablation occurs when the number density of excited electrons reaches the critical electron density, while the lattice remains well below vaporization temperature. The simulated laser fluence required to reach critical electron density is also found to be temperature dependent. The dominant contributor to increased electron density is, in the majority of the investigated cases, the linear absorption coefficient. Two-photon absorption and impact ionization also generate carriers, but to a lesser extent. As the linear absorption coefficient is temperature dependent, we find that the simulated reduction in

  19. Ablation of carbide materials with femtosecond pulses

    NASA Astrophysics Data System (ADS)

    Dumitru, Gabriel; Romano, Valerio; Weber, Heinz P.; Sentis, Marc; Marine, Wladimir

    2003-01-01

    The response of cemented tungsten carbide and of titanium carbonitride was investigated with respect to damage and ablation properties, under interaction with ultrashort laser pulses. These carbide materials present high microhardness and are of significant interest for tribological applications. The experiments were carried out in air with a commercial Ti:sapphire laser at energy densities on the target up to 6.5 J/cm 2. The irradiated target surfaces were analyzed with optical, SEM and AFM techniques and the damage and ablation threshold values were determined using the measured spot diameters and the calculated incident energy density distributions.

  20. Diagnostic characterization of ablation plasma ion implantation

    NASA Astrophysics Data System (ADS)

    Qi, B.; Gilgenbach, R. M.; Jones, M. C.; Johnston, M. D.; Lau, Y. Y.; Wang, L. M.; Lian, J.; Doll, G. L.; Lazarides, A.

    2003-06-01

    Experiments are reported in which two configurations for ablation-plasma-ion-implantation (APII) are characterized by diagnostics and compared. The first configuration oriented the target parallel to the deposition substrate. This orientation yielded ion-beam-assisted deposition of thin films. A delay (>5 μs) between laser and high voltage was necessary for this geometry to avoid arcing between negatively biased substrate and target. The second experimental configuration oriented the target perpendicular to the deposition substrate, reducing arcing, even for zero/negative delay between the laser and the high voltage pulse. This orientation also reduced neutral atom, ballistic deposition on the substrate resulting in a pure ion implantation mode. Ion density measurements were made by resonant laser diagnostics and Langmuir probes, yielding total ion populations in the range of 1014. Implanted ion doses were estimated by electrical diagnostics, and materials analysis, including x-ray energy dispersive spectroscopy and x-ray photoelectron spectroscopy, yielding implanted doses in the range 1012 ions/cm2 per pulse. This yields an APII efficiency of order 10% for implantation of laser ablated ions. Scaling of ion dose with voltage agrees well with a theory assuming the Child-Langmuir law and that the ion current at the sheath edge is due to the uncovering of the ions by the movement of the sheath. Thin film analysis showed excellent adhesion with smoother films for an accelerating voltage of -3.2 kV; higher voltages (-7.7 kV) roughened the film.

  1. Subsurface ablation of atherosclerotic plaque using ultrafast laser pulses

    PubMed Central

    Lanvin, Thomas; Conkey, Donald B.; Frobert, Aurelien; Valentin, Jeremy; Goy, Jean-Jacques; Cook, Stéphane; Giraud, Marie-Noelle; Psaltis, Demetri

    2015-01-01

    We perform subsurface ablation of atherosclerotic plaque using ultrafast pulses. Excised mouse aortas containing atherosclerotic plaque were ablated with ultrafast near-infrared (NIR) laser pulses. Optical coherence tomography (OCT) was used to observe the ablation result, while the physical damage was inspected in histological sections. We characterize the effects of incident pulse energy on surface damage, ablation hole size, and filament propagation. We find that it is possible to ablate plaque just below the surface without causing surface damage, which motivates further investigation of ultrafast ablation for subsurface atherosclerotic plaque removal. PMID:26203381

  2. Subsurface ablation of atherosclerotic plaque using ultrafast laser pulses.

    PubMed

    Lanvin, Thomas; Conkey, Donald B; Frobert, Aurelien; Valentin, Jeremy; Goy, Jean-Jacques; Cook, Stéphane; Giraud, Marie-Noelle; Psaltis, Demetri

    2015-07-01

    We perform subsurface ablation of atherosclerotic plaque using ultrafast pulses. Excised mouse aortas containing atherosclerotic plaque were ablated with ultrafast near-infrared (NIR) laser pulses. Optical coherence tomography (OCT) was used to observe the ablation result, while the physical damage was inspected in histological sections. We characterize the effects of incident pulse energy on surface damage, ablation hole size, and filament propagation. We find that it is possible to ablate plaque just below the surface without causing surface damage, which motivates further investigation of ultrafast ablation for subsurface atherosclerotic plaque removal.

  3. Ablation of boron carbide for high-order harmonic generation of ultrafast pulses in laser-produced plasma

    NASA Astrophysics Data System (ADS)

    Ganeev, R. A.; Suzuki, M.; Kuroda, H.

    2016-07-01

    We demonstrate the generation of harmonics up to the 27th order (λ=29.9 nm) of 806 nm radiation in the boron carbide plasma. We analyze the advantages and disadvantages of this target compared with the ingredients comprising B4C (solid boron and graphite) by studying the plasma emission and harmonic spectra from three species. We compare different schemes of the two-color pump of B4C plasma, particularly using the second harmonics of 806 nm laser and optical parametric amplifier (1310 nm) as the assistant fields, as well as demonstrate the sum and difference frequency generation using the mixture of the wavelengths of two laser sources. These studies showed the advantages of the two-color pump of B4C plasma leading to the stable harmonic generation and the growth of harmonic conversion efficiency. We also show that the coincidence of harmonic and plasma emission wavelengths in most cases does not cause the enhancement or decrease of the conversion efficiency of this harmonic. Our spatial characterization of harmonics shows their on-axis modification depending on the conditions of frequency conversion.

  4. Plasma-mediated ablation: An optical tool for submicrometer surgery on neuronal and vascular systems

    PubMed Central

    Tsai, Philbert S.; Blinder, Pablo; Migliori, Benjamin J.; Neev, Joseph; Jin, Yishi; Squier, Jeffrey A.; Kleinfeld, David

    2009-01-01

    Plasma-mediated ablation makes use of high energy laser pulses to ionize molecules within the first few femtoseconds of the pulse. This process leads to a submicrometer-sized bubble of plasma that can ablate tissue with negligible heat transfer and collateral damage to neighboring tissue. We review the physics of plasma-mediated ablation and its use as a tool to generate targeted insults at the subcellular level to neurons and blood vessels deep within nervous tissue. Illustrative examples from axon regeneration and microvascular research illustrate the utility of this tool. We further discuss the use of ablation as an integral part of automated histology. PMID:19269159

  5. Performance and Controllability of Pulsed Ion Beam Ablation Propulsion

    SciTech Connect

    Yazawa, Masaru; Buttapeng, Chainarong; Harada, Nobuhiro; Suematsu, Hisayuki; Jiang Weihua; Yatsui, Kiyoshi

    2006-05-02

    We propose novel propulsion driven by ablation plasma pressures produced by the irradiation of pulsed ion beams onto a propellant. The ion beam ablation propulsion demonstrates by a thin foil (50 {mu}mt), and the flyer velocity of 7.7 km/s at the ion beam energy density of 2 kJ/cm2 adopted by using the Time-of-flight method is observed numerically and experimentally. We estimate the performance of the ion beam ablation propulsion as specific impulse of 3600 s and impulse bit density of 1700 Ns/m2 obtained from the demonstration results. In the numerical analysis, a one-dimensional hydrodynamic model with ion beam energy depositions is used. The control of the ion beam kinetic energy is only improvement of the performance but also propellant consumption. The spacecraft driven by the ion beam ablation provides high performance efficiency with short-pulsed ion beam irradiation. The numerical results of the advanced model explained latent heat and real gas equation of state agreed well with experimental ones over a wide range of the incident ion beam energy density.

  6. Contact pulsed Nd:YAG ablation of human dentin: ablation rates and tissue effects

    NASA Astrophysics Data System (ADS)

    Harris, David M.; Yessik, Michael J.

    1994-09-01

    Dentin from freshly extracted human teeth was exposed to flashlamp pumped Nd:YAG pulses (100 microsecond(s) duration, 50 - 200 mJ/pulse) delivered through a flat cut fiberoptic in contact with the dentin surface. Ablation depth and volume were measured optically and confirmed with electron microscope morphometrics. Ablation depth increased with force applied at the fiber tip up to 5 - 10 g. Above this ablation depths were insensitive to applied force. Craters made in dental stone were deeper and narrower than those made in normal dentin. Ablation depths per pulse and volumes per pulse decrease as the number of pulses increase. This is more prominent for 200 mJ pulses. At 60 mJ the ablation depths are the same from 10 to 100 Hz repetition rates, although qualitative changes (collateral damage) are greater at higher repetition rates. A progressive increase in collateral damage is seen from the 1st through the 200th pulse.

  7. Thermal ablation of an aluminium film upon absorption of a femtosecond laser pulse

    SciTech Connect

    Bezhanov, S G; Kanavin, A P; Uryupin, S A

    2016-02-28

    We have found the time dependence of the ablation depth of aluminium irradiated by a femtosecond laser pulse. It is shown to what extent an increase in the radiation energy flux density leads to an increase in the quasi-stationary value of the ablation depth. By reducing the aluminium film thickness down to one hundred nanometres and less, the ablation depth significantly increases. At the same time, the quasi-stationary value of the ablation depth of a thin film is obtained due to the removal of heat from the focal spot region. (interaction of laser radiation with matter. laser plasma)

  8. Ultrashort pulse laser microsurgery system with plasma luminescence feedback control

    SciTech Connect

    Kim, B.M.; Feit, M.D.; Rubenchik, A.M.; Gold, D.M.; Darrow, C.B.; Da Silva, L.B.

    1997-11-10

    Plasma luminescence spectroscopy was used for precise ablation of bone tissue during ultrashort pulse laser (USPL) micro-spinal surgery. Strong contrast of the luminescence spectra between bone marrow and spinal cord provided the real time feedback control so that only bone tissue can be selectively ablated while preserving the spinal cord.

  9. Hydrodynamic model for ultra-short pulse ablation of hard dental tissue

    SciTech Connect

    London, R.A.; Bailey, D.S.; Young, D.A.; Alley, W.E.; Feit, M.D.; Rubenchik, A.M.; Neev, J.

    1996-02-29

    A computational model for the ablation of tooth enamel by ultra-short laser pulses is presented. The role of simulations using this model in designing and understanding laser drilling systems is discussed. Pulses of duration 300 fsec and intensity greater than 10{sup 12} W/cm{sup 2} are considered. Laser absorption proceeds via multi-photon initiated plasma mechanism. The hydrodynamic response is calculated with a finite difference method, using an equation of state constructed from thermodynamic functions including electronic, ion motion, and chemical binding terms. Results for the ablation efficiency are presented. An analytic model describing the ablation threshold and ablation depth is presented. Thermal coupling to the remaining tissue and long-time thermal conduction are calculated. Simulation results are compared to experimental measurements of the ablation efficiency. Desired improvements in the model are presented.

  10. Ablation characteristics of quantum square pulse mode dental erbium laser

    NASA Astrophysics Data System (ADS)

    Lukač, Nejc; Suhovršnik, Tomaž; Lukač, Matjaž; Jezeršek, Matija

    2016-01-01

    Erbium lasers are by now an accepted tool for performing ablative medical procedures, especially when minimal invasiveness is desired. Ideally, a minimally invasive laser cutting procedure should be fast and precise, and with minimal pain and thermal side effects. All these characteristics are significantly influenced by laser pulse duration, albeit not in the same manner. For example, high cutting efficacy and low heat deposition are characteristics of short pulses, while vibrations and ejected debris screening are less pronounced at longer pulse durations. We report on a study of ablation characteristics on dental enamel and cementum, of a chopped-pulse Er:YAG [quantum square pulse (QSP)] mode, which was designed to reduce debris screening during an ablation process. It is shown that in comparison to other studied standard Er:YAG and Er,Cr:YSGG laser pulse duration modes, the QSP mode exhibits the highest ablation drilling efficacy with lowest heat deposition and reduced vibrations, demonstrating that debris screening has a considerable influence on the ablation process. By measuring single-pulse ablation depths, we also show that tissue desiccation during the consecutive delivery of laser pulses leads to a significant reduction of the intrinsic ablation efficacy that cannot be fully restored under clinical settings by rehydrating the tooth using an external water spray.

  11. Experimental investigation on colloidal alumina nanoparticles produced by collinear nanosecond double-pulse laser ablation in liquid

    NASA Astrophysics Data System (ADS)

    Mahdieh, M. H.; Fattahi, B.; Akbari Jafarabadi, M.

    2017-01-01

    In this research, we investigated the effect of inter-pulse delay times on production of colloidal alumina nanoparticles by collinear double pulse laser ablation. In comparison to single pulse laser ablation, collinear double pulse laser ablation with inter-pulse delay times of 5, 10, 15 and 20 ns results in production of colloidal nanoparticles with smaller mean size and lower variance size distribution. In the case of 5 ns inter-pulse delay time, the highest concentration of nanoparticles was obtained due to more rapid cooling time of the plasma as a result of higher rate of nuclei generation than particle growth. The results also showed that the main pulse and the pre-pulse with 5 ns delay time have significant overlap and consequently such condition leads to maximum influence on the ablation.

  12. Enhanced filament ablation of metals based on plasma grating in air

    SciTech Connect

    Wang, Di; Liu, Fengjiang; Ding, Liangen; Yuan, Shuai; Zeng, Heping

    2015-09-15

    We demonstrate efficient ablation of metals with filamentary plasma grating generated by two intense blue femtosecond filaments and a third focused infrared pulse. This scheme leads to significant promotion of ablation efficiency on metal targets in air in comparison with single infrared or blue filament with equal pulse energy. The reason is that the blue plasma grating firstly provides stronger intensity and a higher density of background electrons, then the delayed infrared pulse accelerates local electrons inside the plasma grating. These two processes finally results in robustly increased electron density and highly ionized metallic atoms.

  13. Low-order harmonic generation in metal ablation plasmas in nanosecond and picosecond laser regimes

    SciTech Connect

    Lopez-Arias, M.; Oujja, M.; Sanz, M.; Castillejo, M.; Ganeev, R. A.; Boltaev, G. S.; Satlikov, N. Kh.; Tugushev, R. I.; Usmanov, T.

    2012-02-15

    Low-order harmonics, third and fifth, of IR (1064 nm) laser emission have been produced in laser ablation plasmas of the metals manganese, copper and silver. The harmonics were generated in a process triggered by laser ablation followed by frequency up-conversion of a fundamental laser beam that propagates parallel to the target surface. These studies were carried out in two temporal regimes by creating the ablation plasma using either nanosecond or picosecond pulses and then probing the plasma plume with pulses of the same duration. The spatiotemporal behavior of the generated harmonics was characterized and reveals the distinct composition and dynamics of the plasma species that act as nonlinear media, allowing the comparison of different processes that control the generation efficiency. These results serve to guide the choice of laser ablation plasmas to be used for efficient high harmonic generation of laser radiation.

  14. Carbon nanocrystals produced by pulsed laser ablation of carbon

    NASA Astrophysics Data System (ADS)

    Mangione, A.; Torrisi, L.; Picciotto, A.; Caridi, F.; Margarone, D.; Fazio, E.; La Mantia, A.; di Marco, G.

    2005-10-01

    Plasma laser ablation experiments were performed irradiating glassy-carbon targets placed in vacuum through a pulsed Nd:YAG laser operating at the second harmonic (532 nm), 9 ns pulse width and 10(9) W/cm(2) density power. Thin films of ablated carbon were deposited on silicon oxide substrates placed at different distances and angles with respect to the target. The analysis of the deposited material was carried out by using surface profiler, scanning electron microscopy (SEM), Fourier transform infrared (FT-IR) and Raman spectroscopy. Results show the evidence of carbon nanocrystals and nanostructures with dimension of the order of 100 nm deposited on the substrates together with a large amount of amorphous phase. The spectroscopic investigations and the SEM images indicate the formation of nanodiamond seeds as a nucleation process induced on the substrate surface. Nanostructures were investigated as a function of the laser intensity and angle distribution. Experimental results were compared with the literature data coming from nanodiamonds growth with different techniques. Experiments performed at Instituto Nazionale di Fisica Nucleare-Laboratori Nazionali del Sud (INFN-LNS) of Catania (Italy) and data analysis conducted at Dipartimento di Fisica and DFMTA of the Universita of Messina (Italy), CNR-ITIS of Messina and ST-Microelectronics of Catania will be presented and discussed.

  15. Effects of Two-Pulse Sequencing on Characteristics of Elementary Propellants for Ablative Laser Propulsion

    NASA Technical Reports Server (NTRS)

    Thompson, M. Shane; Pakhomov, Andrew V.; Herren, Kenneth A.

    2003-01-01

    This work continues on previous investigations of elementary propellants for Ablative Laser Propulsion (ALP). This paper details the experimental methods used for alignment of a non-colinear temporal pulse splitting apparatus. Spatial coincidence of the separate pulses is established, the pulses are delayed, and first data is reported on this pulse spacing effect on time-of-fight (TOF) measurements. This includes ion velocity and number density measurements, and this data is compared to results from a previous work. Also, first data on the experimental determination of the time required for the laser-induced plasma to become purely reflective to incident pulses is presented.

  16. Pulsed Plasma Accelerator Modeling

    NASA Technical Reports Server (NTRS)

    Goodman, M.; Kazeminezhad, F.; Owens, T.

    2009-01-01

    This report presents the main results of the modeling task of the PPA project. The objective of this task is to make major progress towards developing a new computational tool with new capabilities for simulating cylindrically symmetric 2.5 dimensional (2.5 D) PPA's. This tool may be used for designing, optimizing, and understanding the operation of PPA s and other pulsed power devices. The foundation for this task is the 2-D, cylindrically symmetric, magnetohydrodynamic (MHD) code PCAPPS (Princeton Code for Advanced Plasma Propulsion Simulation). PCAPPS was originally developed by Sankaran (2001, 2005) to model Lithium Lorentz Force Accelerators (LLFA's), which are electrode based devices, and are typically operated in continuous magnetic field to the model, and implementing a first principles, self-consistent algorithm to couple the plasma and power circuit that drives the plasma dynamics.

  17. Ablation-cooled material removal with ultrafast bursts of pulses

    NASA Astrophysics Data System (ADS)

    Kerse, Can; Kalaycıoğlu, Hamit; Elahi, Parviz; Çetin, Barbaros; Kesim, Denizhan K.; Akçaalan, Önder; Yavaş, Seydi; Aşık, Mehmet D.; Öktem, Bülent; Hoogland, Heinar; Holzwarth, Ronald; Ilday, Fatih Ömer

    2016-09-01

    The use of femtosecond laser pulses allows precise and thermal-damage-free removal of material (ablation) with wide-ranging scientific, medical and industrial applications. However, its potential is limited by the low speeds at which material can be removed and the complexity of the associated laser technology. The complexity of the laser design arises from the need to overcome the high pulse energy threshold for efficient ablation. However, the use of more powerful lasers to increase the ablation rate results in unwanted effects such as shielding, saturation and collateral damage from heat accumulation at higher laser powers. Here we circumvent this limitation by exploiting ablation cooling, in analogy to a technique routinely used in aerospace engineering. We apply ultrafast successions (bursts) of laser pulses to ablate the target material before the residual heat deposited by previous pulses diffuses away from the processing region. Proof-of-principle experiments on various substrates demonstrate that extremely high repetition rates, which make ablation cooling possible, reduce the laser pulse energies needed for ablation and increase the efficiency of the removal process by an order of magnitude over previously used laser parameters. We also demonstrate the removal of brain tissue at two cubic millimetres per minute and dentine at three cubic millimetres per minute without any thermal damage to the bulk.

  18. Ablation-cooled material removal with ultrafast bursts of pulses.

    PubMed

    Kerse, Can; Kalaycıoğlu, Hamit; Elahi, Parviz; Çetin, Barbaros; Kesim, Denizhan K; Akçaalan, Önder; Yavaş, Seydi; Aşık, Mehmet D; Öktem, Bülent; Hoogland, Heinar; Holzwarth, Ronald; Ilday, Fatih Ömer

    2016-09-01

    The use of femtosecond laser pulses allows precise and thermal-damage-free removal of material (ablation) with wide-ranging scientific, medical and industrial applications. However, its potential is limited by the low speeds at which material can be removed and the complexity of the associated laser technology. The complexity of the laser design arises from the need to overcome the high pulse energy threshold for efficient ablation. However, the use of more powerful lasers to increase the ablation rate results in unwanted effects such as shielding, saturation and collateral damage from heat accumulation at higher laser powers. Here we circumvent this limitation by exploiting ablation cooling, in analogy to a technique routinely used in aerospace engineering. We apply ultrafast successions (bursts) of laser pulses to ablate the target material before the residual heat deposited by previous pulses diffuses away from the processing region. Proof-of-principle experiments on various substrates demonstrate that extremely high repetition rates, which make ablation cooling possible, reduce the laser pulse energies needed for ablation and increase the efficiency of the removal process by an order of magnitude over previously used laser parameters. We also demonstrate the removal of brain tissue at two cubic millimetres per minute and dentine at three cubic millimetres per minute without any thermal damage to the bulk.

  19. Flyer Acceleration by Pulsed Ion Beam Ablation and Application for Space Propulsion

    SciTech Connect

    Harada, Nobuhiro; Buttapeng, Chainarong; Yazawa, Masaru; Kashine, Kenji; Jiang Weihua; Yatsui, Kiyoshi

    2004-02-04

    Flyer acceleration by ablation plasma pressure produced by irradiation of intense pulsed ion beam has been studied. Acceleration process including expansion of ablation plasma was simulated based on fluid model. And interaction between incident pulsed ion beam and a flyer target was considered as accounting stopping power of it. In experiments, we used ETIGO-II intense pulsed ion beam generator with two kinds of diodes; 1) Magnetically Insulated Diode (MID, power densities of <100 J/cm2) and 2) Spherical-focused Plasma Focus Diode (SPFD, power densities of up to 4.3 kJ/cm2). Numerical results of accelerated flyer velocity agreed well with measured one over wide range of incident ion beam energy density. Flyer velocity of 5.6 km/s and ablation plasma pressure of 15 GPa was demonstrated by the present experiments. Acceleration of double-layer target consists of gold/aluminum was studied. For adequate layer thickness, such a flyer target could be much more accelerated than a single layer. Effect of waveform of ion beam was also examined. Parabolic waveform could accelerate more efficiently than rectangular waveform. Applicability of ablation propulsion was discussed. Specific impulse of 7000{approx}8000 seconds and time averaged thrust of up to 5000{approx}6000N can be expected. Their values can be controllable by changing power density of incident ion beam and pulse duration.

  20. Size control of nanoparticles by multiple-pulse laser ablation

    NASA Astrophysics Data System (ADS)

    Yu, Jiaxin; Nan, Junyi; Zeng, Heping

    2017-04-01

    Bare nanoparticles synthesized by laser ablation in water have found their application in catalysis, spectroscopy and biomedical research fields. In this perspective, how to efficiently produce stable nanoparticles with controllable size is an important topic and has attracted a lot of interests. Here, we introduce a multiple-pulse laser as the ablation source. By changing the number of sub-pulses, the average size of nanoparticles can be tuned in a broad range from ∼120 nm to ∼4 nm. The demonstration in this article may offer a new approach to fabricate ultrafine nanostructures and also help the scientific study of the mechanism in laser ablation.

  1. Experimental measurement of ablation effects in plasma armature railguns

    SciTech Connect

    Parker, J.V.; Parsons, W.M.

    1986-01-01

    Experimental evidence supporting the importance of ablation in plasma armature railguns is presented. Experiments conducted using the HYVAX and MIDI-2 railguns are described. Several indirect effects of ablation are identified from the experimental results. An improved ablation model of plasma armature dynamics is proposed which incorporates the restrike process.

  2. Control of laser-ablation plasma potential with external electrodes

    SciTech Connect

    Isono, Fumika Nakajima, Mitsuo; Hasegawa, Jun; Kawamura, Tohru; Horioka, Kazuhiko

    2015-08-15

    The potential of a laser-ablation plasma was controlled stably up to +2 kV by using external ring electrodes. A stable electron sheath was formed between the plasma and the external electrodes by placing the ring electrodes away from the boundary of the drifting plasma. The plasma kept the potential for a few μs regardless of the flux change of the ablation plasma. We also found that the plasma potential changed with the expansion angle of the plasma from the target. By changing the distance between the plasma boundary and the external electrodes, we succeeded in controlling the potential of laser-ablation plasma.

  3. Rail gun performance and plasma characteristics due to wall ablation

    NASA Technical Reports Server (NTRS)

    Ray, P. K.

    1986-01-01

    The experiment of Bauer, et al. (1982) is analyzed by considering wall ablation and viscous drag in the plasma. Plasma characteristics are evaluated through a simple fluid-mechanical analysis considering only wall ablation. By equating the energy dissipated in the plasma with the radiation heat loss, the average properties of the plasma are determined as a function of time.

  4. Pulsed Plasma Thruster Contamination

    NASA Technical Reports Server (NTRS)

    Myers, Roger M.; Arrington, Lynn A.; Pencil, Eric J.; Carter, Justin; Heminger, Jason; Gatsonis, Nicolas

    1996-01-01

    Pulsed Plasma Thrusters (PPT's) are currently baselined for the Air Force Mightysat II.1 flight in 1999 and are under consideration for a number of other missions for primary propulsion, precision positioning, and attitude control functions. In this work, PPT plumes were characterized to assess their contamination characteristics. Diagnostics included planar and cylindrical Langmuir probes and a large number of collimated quartz contamination sensors. Measurements were made using a LES 8/9 flight PPT at 0.24, 0.39, 0.55, and 1.2 m from the thruster, as well as in the backflow region behind the thruster. Plasma measurements revealed a peak centerline ion density and velocity of approx. 6 x 10(exp 12) cm(exp -3) and 42,000 m/s, respectively. Optical transmittance measurements of the quartz sensors after 2 x 10(exp 5) pulses showed a rapid decrease in plume contamination with increasing angle from the plume axis, with a barely measurable transmittance decrease in the ultraviolet at 90 deg. No change in optical properties was detected for sensors in the backflow region.

  5. Periodic Phenomena In Laser-Ablation Plasma Plumes: A Self-Organization Scenario

    SciTech Connect

    Gurlui, S.; Sanduloviciu, M.; Mihesan, C.; Ziskind, M.; Focsa, C.

    2006-01-15

    Experimental evidence of the appearance of a proper periodic dynamics in a plasma plume created by pulsed laser ablation is considered as a hint for the presence of a self-organization scenario that explains similar phenomena observed in plasma diodes.

  6. Ablation of Myocardial Tissue With Nanosecond Pulsed Electric Fields

    PubMed Central

    Xie, Fei; Varghese, Frency; Pakhomov, Andrei G.; Semenov, Iurii; Xiao, Shu; Philpott, Jonathan; Zemlin, Christian

    2015-01-01

    Background Ablation of cardiac tissue is an essential tool for the treatment of arrhythmias, particularly of atrial fibrillation, atrial flutter, and ventricular tachycardia. Current ablation technologies suffer from substantial recurrence rates, thermal side effects, and long procedure times. We demonstrate that ablation with nanosecond pulsed electric fields (nsPEFs) can potentially overcome these limitations. Methods We used optical mapping to monitor electrical activity in Langendorff-perfused New Zealand rabbit hearts (n = 12). We repeatedly inserted two shock electrodes, spaced 2–4 mm apart, into the ventricles (through the entire wall) and applied nanosecond pulsed electric fields (nsPEF) (5–20 kV/cm, 350 ns duration, at varying pulse numbers and frequencies) to create linear lesions of 12–18 mm length. Hearts were stained either with tetrazolium chloride (TTC) or propidium iodide (PI) to determine the extent of ablation. Some stained lesions were sectioned to obtain the three-dimensional geometry of the ablated volume. Results In all animals (12/12), we were able to create nonconducting lesions with less than 2 seconds of nsPEF application per site and minimal heating (< 0.2°C) of the tissue. The geometry of the ablated volume was smoother and more uniform throughout the wall than typical for RF ablation. The width of the lesions could be controlled up to 6 mm via the electrode spacing and the shock parameters. Conclusions Ablation with nsPEFs is a promising alternative to radiofrequency (RF) ablation of AF. It may dramatically reduce procedure times and produce more consistent lesion thickness than RF ablation. PMID:26658139

  7. Influence of pulse duration on ultrashort laser pulse ablation of biological tissues.

    PubMed

    Kim, B M; Feit, M D; Rubenchik, A M; Joslin, E J; Celliers, P M; Eichler, J; Da Silva, L B

    2001-07-01

    Ablation characteristics of ultrashort laser pulses were investigated for pulse durations in the range of 130 fs-10 ps. Tissue samples used in the study were dental hard tissue (dentin) and water. We observed differences in ablation crater morphology for craters generated with pulse durations in the 130 fs-1 ps and the 5 ps-10 ps range. For the water experiment, the surface ablation and subsequent propagation of stress waves were monitored using Mach-Zehnder interferometry. For 130 fs-1 ps, energy is deposited on the surface while for longer pulses the beam penetrates into the sample. Both studies indicate that a transition occurs between 1 and 5 ps.

  8. Pulsed Tm:YAG laser ablation of knee joint tissues

    NASA Astrophysics Data System (ADS)

    Shi, Wei-Qiang; Vari, Sandor G.; Duffy, J. T.; Miller, J. M.; Weiss, Andrew B.; Fishbein, Michael C.; Grundfest, Warren S.

    1992-06-01

    We investigated the effect of a free-running 2.01 micron pulsed Tm:YAG laser on bovine knee joint tissues. Ablation rates of fresh fibrocartilage, hyaline cartilage, and bone were measured in saline as a function of laser fluence (160 - 640 J/cm2) and fiber core size (400 and 600 microns). All tissues could be effectively ablated and the ablation rate increased linearly with the increasing fluence. Use of fibers of different core sizes, while maintaining constant energy fluence, did not result in significant difference in ablation rate. Histology analyses of the ablated tissue samples reveal average Tm:YAG radiation induced thermal damage (denatunalization) zones ranging between 130 and 540 microns, depending on the laser parameters and the tissue type.

  9. Ultrashort pulse laser ablation of dielectrics: Thresholds, mechanisms, role of breakdown

    PubMed Central

    Mirza, Inam; Bulgakova, Nadezhda M.; Tomáštík, Jan; Michálek, Václav; Haderka, Ondřej; Fekete, Ladislav; Mocek, Tomáš

    2016-01-01

    In this paper, we establish connections between the thresholds and mechanisms of the damage and white-light generation upon femtosecond laser irradiation of wide-bandgap transparent materials. On the example of Corning Willow glass, evolution of ablation craters, their quality, and white-light emission were studied experimentally for 130-fs, 800-nm laser pulses. The experimental results indicate co-existence of several ablation mechanisms which can be separated in time. Suppression of the phase explosion mechanism of ablation was revealed at the middle of the irradiation spots. At high laser fluences, air ionization was found to strongly influence ablation rate and quality and the main mechanisms of the influence are analysed. To gain insight into the processes triggered by laser radiation in glass, numerical simulations have been performed with accounting for the balance of laser energy absorption and its distribution/redistribution in the sample, including bremsstrahlung emission from excited free-electron plasma. The simulations have shown an insignificant role of avalanche ionization at such short durations of laser pulses while pointing to high average energy of electrons up to several dozens of eV. At multi-pulse ablation regimes, improvement of crater quality was found as compared to single/few pulses. PMID:27991543

  10. Ultrashort pulse laser ablation of dielectrics: Thresholds, mechanisms, role of breakdown

    NASA Astrophysics Data System (ADS)

    Mirza, Inam; Bulgakova, Nadezhda M.; Tomáštík, Jan; Michálek, Václav; Haderka, Ondřej; Fekete, Ladislav; Mocek, Tomáš

    2016-12-01

    In this paper, we establish connections between the thresholds and mechanisms of the damage and white-light generation upon femtosecond laser irradiation of wide-bandgap transparent materials. On the example of Corning Willow glass, evolution of ablation craters, their quality, and white-light emission were studied experimentally for 130-fs, 800-nm laser pulses. The experimental results indicate co-existence of several ablation mechanisms which can be separated in time. Suppression of the phase explosion mechanism of ablation was revealed at the middle of the irradiation spots. At high laser fluences, air ionization was found to strongly influence ablation rate and quality and the main mechanisms of the influence are analysed. To gain insight into the processes triggered by laser radiation in glass, numerical simulations have been performed with accounting for the balance of laser energy absorption and its distribution/redistribution in the sample, including bremsstrahlung emission from excited free-electron plasma. The simulations have shown an insignificant role of avalanche ionization at such short durations of laser pulses while pointing to high average energy of electrons up to several dozens of eV. At multi-pulse ablation regimes, improvement of crater quality was found as compared to single/few pulses.

  11. Fast pulse nonthermal plasma reactor

    DOEpatents

    Rosocha, Louis A.

    2005-06-14

    A fast pulsed nonthermal plasma reactor includes a discharge cell and a charging assembly electrically connected thereto. The charging assembly provides plural high voltage pulses to the discharge cell. Each pulse has a rise time between one and ten nanoseconds and a duration of three to twenty nanoseconds. The pulses create nonthermal plasma discharge within the discharge cell. Accordingly, the nonthermal plasma discharge can be used to remove pollutants from gases or break the gases into smaller molecules so that they can be more efficiently combusted.

  12. Ablation Studies of Enamel Tissue Using Pulsed HF Laser

    DTIC Science & Technology

    2007-11-02

    and enamel has been successful. The reason is thought to be due to high absorption coefficients of hydroxyapatite [Ca10(Po4)6(OH2)] with a total...secondary absorption peak of hydroxyapatite lies, a less violent and cleaner ablation of enamel compared with its main absorption peak at 9.6 µm is...1 of 4 Ablation Studies of Enamel Tissue using Pulsed HF Laser M.E. Khosroshahi, B.A. Ghasemi Amirkabir University of Technology, School of

  13. Pulsed laser ablation of dental calculus in the near ultraviolet.

    PubMed

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

    2014-02-01

    Pulsed lasers emitting wavelengths near 400 nm can selectively ablate dental calculus without damaging underlying and surrounding sound dental hard tissue. Our results indicate that calculus ablation at this wavelength relies on the absorption of porphyrins endogenous to oral bacteria commonly found in calculus. Sub- and supragingival calculus on extracted human teeth, irradiated with 400-nm, 60-ns laser pulses at ≤8  J/cm2, exhibits a photobleached surface layer. Blue-light microscopy indicates this layer highly scatters 400-nm photons, whereas fluorescence spectroscopy indicates that bacterial porphyrins are permanently photobleached. A modified blow-off model for ablation is proposed that is based upon these observations and also reproduces our calculus ablation rates measured from laser profilometry. Tissue scattering and a stratified layering of absorbers within the calculus medium explain the gradual decrease in ablation rate from successive pulses. Depending on the calculus thickness, ablation stalling may occur at <5  J/cm2 but has not been observed above this fluence.

  14. Spectroscopic characterization of laser ablation brass plasma

    NASA Astrophysics Data System (ADS)

    Shaikh, Nek M.; Hafeez, Sarwat; Kalyar, M. A.; Ali, R.; Baig, M. A.

    2008-11-01

    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.

  15. Ablation-cooled material removal with ultrafast bursts of pulses

    NASA Astrophysics Data System (ADS)

    Ilday, F. Ömer; Kerse, C.; Kalaycioglu, H.; Elahi, P.; Yavas, S.; Kesim, D.; Akçaalan, Ö.; Çetin, B.; Öktem, B.; Asik, M.; Hoogland, H.; Holzwarth, R.

    Use of femtosecond pulses allows precise and thermal-damage-free material removal with broad applications. However, its potential is limited by low material removal speeds and complexity of the required lasers. The laser complexity arises from the high pulse energy threshold for ablation. Physics of the laser-material interaction precludes a straightforward scaling up of the removal rate by using more powerful lasers due to shielding and collateral damage from heat accumulation. Here, we exploit ablation cooling, a technique used in aerospace engineering since 1950's, to circumvent this limitation. We apply rapid successions of pulses from specially developed lasers to ablate the target material before the residual heat deposited by previous pulses diffuse away from the interaction region. This constitutes a new physical regime of laser-material interactions, where heat removal due to ablation is comparable to conduction. Proof-of-principle experiments demonstrate reduction of required pulse energies by 1000x, while simultaneously increasing efficiency and speed by 10x.

  16. Heat effects of metals ablated with femtosecond laser pulses

    NASA Astrophysics Data System (ADS)

    Hirayama, Yoichi; Obara, Minoru

    2002-09-01

    Heat effects of metallic bulk crystals of Au, Ag, Cu, and Fe ablated with femtosecond Ti:sapphire laser pulses is experimentally studied. As a result of X-ray diffraction (XRD) measurements, the XRD peak signal of the area ablated with Ti:sapphire laser is much smaller than that of the crystalline metal sample. While the crystal form of the metal sample is crystalline before laser ablation, the crystal form in the ablated area is partially changed into the amorphous form. The residual pulse energy that did not contribute to the ablation process remains, which leads to the formation of thin layer of melted phase. The melted layer is abruptly cooled down not to be re-crystallized, but to transform into amorphous form. It is evident that the area ablated with femtosecond laser is changed into amorphous metals. This mechanism would be the same as the melt-quenching generally used as the fabrication method of amorphous metals. This experimental result is consistent with the theoretical result.

  17. Contribution of material’s surface layer on charge state distribution in laser ablation plasma

    SciTech Connect

    Kumaki, Masafumi; Steski, Dannie; Kanesue, Takeshi; Ikeda, Shunsuke; Okamura, Masahiro; Washio, Masakazu

    2016-02-15

    To generate laser ablation plasma, a pulse laser is focused onto a solid target making a crater on the surface. However, not all the evaporated material is efficiently converted to hot plasma. Some portion of the evaporated material could be turned to low temperature plasma or just vapor. To investigate the mechanism, we prepared an aluminum target coated by thin carbon layers. Then, we measured the ablation plasma properties with different carbon thicknesses on the aluminum plate. The results showed that C{sup 6+} ions were generated only from the surface layer. The deep layers (over 250 nm from the surface) did not provide high charge state ions. On the other hand, low charge state ions were mainly produced by the deeper layers of the target. Atoms deeper than 1000 nm did not contribute to the ablation plasma formation.

  18. Pulse compression in plasma: Generation of femtosecond pulses without CPA

    SciTech Connect

    G. Shvets; N. J. Fisch; A. Pukhov; J. Meyer-ter-Vehn

    2000-07-20

    Laser pulses can be efficiently compressed to femtosecond duration when a smaller-frequency short pulse collides with high frequency long pulse in rare plasma, absorbing most of its energy. The mechanism of short pulse amplification is nonlinear superradiance.

  19. Pulsed laser ablation of pepsin on an inorganic substrate

    NASA Astrophysics Data System (ADS)

    Cicco, N.; Lopizzo, T.; Marotta, V.; Morone, A.; Verrastro, M.; Viggiano, V.

    2009-03-01

    Pressed pepsin pellets used as targets were ablated with the pulses of the Nd-YAG laser. The activity of the pepsin thin layer, deposited on a glass substrate, was successfully detected by analyzing the proteolytic degradation areas on the polyacrylamide gel (PA-gel) copolymerized with albumin from the hen egg white (ovalbumin), used as an enzymatic substrate.

  20. Laser ablation plasma-assisted stabilization of premixed methane/air flame

    NASA Astrophysics Data System (ADS)

    Li, Xiaohui; Yu, Yang; Peng, Jiangbo; Yu, Xin; Fan, Rongwei; Sun, Rui; Chen, Deying

    2016-01-01

    Laser ablation plasma has been applied to assist stabilization of premixed methane/air flames with a flow speed up to 15.3 m/s. The ablation plasma was generated using the 50 Hz, 1064 nm output of a Nd:YAG laser onto a tantalum slab. With the ablation plasma, the stabilization equivalence ratio has been extended to the fuel-leaner end and the blow off limits have been enhanced by from 3.6- to 14.8-folds for flames which can stabilize without the plasma. The laser pulse energy required for flameholding was reduced to 10 mJ, a 64 % reduction compared with that of gas breakdown plasma, which will ease the demand for high-power lasers for high-frequency plasma generation. The temporal evolutions of the flame kernels following the ablation plasma were investigated using the OH* chemiluminescence imaging approach, and the flame propagation speed ( v f) was measured from the flame kernel evolutions. With the ablation plasma, the v f with flow speed of 4.7-9.0 m/s and equivalence ratio of 1.4 has been enhanced from 0.175 m/s of laminar premixed methane/air flame to 2.79-4.52 and 1.59-5.46 m/s, respectively, in the early and late time following the ablation plasma. The increase in the combustion radical concentrations by the ablation plasma was thought to be responsible for the v f enhancement and the resulted flame stabilization.

  1. Ablation of carbon-doped liquid propellant in laser plasma propulsion

    NASA Astrophysics Data System (ADS)

    Zheng, Z. Y.; Liang, T.; Zhang, S. Q.; Gao, L.; Gao, H.; Zhang, Z. L.

    2016-04-01

    Carbon-doped liquid glycerol ablated by nanosecond pulse laser is investigated in laser plasma propulsion. It is found that the propulsion is much more correlated with the carbon content. The doped carbon can change the laser intensity and laser focal position so as to reduce the splashing quantity of the glycerol. Less consumption of the liquid volume results in a high specific impulse.

  2. Dynamics of Molecular Emission Features from Nanosecond, Femtosecond Laser and Filament Ablation Plasmas

    SciTech Connect

    Harilal, Sivanandan S.; Yeak, J.; Brumfield, Brian E.; Suter, Jonathan D.; Phillips, Mark C.

    2016-06-15

    The evolutionary paths of molecular species and nanoparticles in laser ablation plumes are not well understood due to the complexity of numerous physical processes that occur simultaneously in a transient laser-plasma system. It is well known that the emission features of ions, atoms, molecules and nanoparticles in a laser ablation plume strongly depend on the laser irradiation conditions. In this letter we report the temporal emission features of AlO molecules in plasmas generated using a nanosecond laser, a femtosecond laser and filaments generated from a femtosecond laser. Our results show that, at a fixed laser energy, the persistence of AlO is found to be highest and lowest in ns and filament laser plasmas respectively while molecular species are formed at early times for both ultrashort pulse (fs and filament) generated plasmas. Analysis of the AlO emission band features show that the vibrational temperature of AlO decays rapidly in filament assisted laser ablation plumes.

  3. Ultrashort-pulse laser ablation of nanocrystalline aluminum

    SciTech Connect

    Gill-Comeau, Maxime; Lewis, Laurent J.

    2011-12-01

    Molecular-dynamics simulations of the ablation of nanocrystalline Al films by ultrashort laser pulses in the low-fluence (no-ionization) regime (0-2.5 times the ablation threshold, F{sub th}) are reported. The simulations employ an embedded-atom method potential for the dynamics of the ions and a realistic two-temperature model for the electron gas (and its interactions with the ion gas), which confers different electronic properties to the monocrystalline solid, nanocrystalline solid, and liquid regions of the targets. The ablation dynamics in three nanocrystalline structures is studied: two dense targets with different crystallite sizes (d=3.1 and 6.2 nm on average) and a d=6.2 nm porous sample. The results are compared to the ablation of monocrystalline Al. Significant differences are observed, the nanocrystalline targets showing, in particular, a lower ablation threshold and a larger melting depth, and yielding pressure waves of higher amplitude than the monocrystalline targets. Furthermore, it is shown that nanocrystalline targets experience no residual stress associated with thermal expansion and lateral constraints, and that little crystal growth occurs in the solid during and after ablation. Laser-induced spallation of the back surface of the films is also investigated; we find, in particular, that the high-strain fracture resistance of nanocrystalline samples is significantly reduced in comparison to the crystalline material.

  4. Diagnostics of Pulsed Hydrogen Plasmas

    NASA Astrophysics Data System (ADS)

    Dubois, Jerome; Cunge, Gilles; Joubert, Olivier; Darnon, Maxime; Vallier, Laurent; Posseme, Nicolas; Etching Group Team

    2014-10-01

    Hydrogen plasmas present a great potential interest for new materials such as graphene or C-nanotubes. To modify or clean such ultrathin layers without damaging the material, low ion energy bombardment is required (conditions such as those obtained in pulsed ICP reactor). By contrast, for other applications the ion energy must be high, to get a significant etch rate for example. To assist the development of innovative processes in H2 plasmas, we have thus analyzed systematically CW and pulsed H2 plasmas both with and without RF bias power. In particular, we carry out time-resolved ion flux, and time-averaged ion energy measurements in different pulsing configurations. A large variety of ion energies and shapes of IVDF are reported depending on pulsing parameters. The IVDF are typically very broad (due to the low ion transit time of low mass ion through the sheath) and either bi or tri-modal (H +, H2 + and H3 + contributions). The time variations of the ion flux in pulsed plasmas also presents peculiar features that will be discussed. Finally, we show that a specific issue is associated to H2 plasmas: they reduce the chamber walls material therefore releasing impurities (O atoms...) in the plasma with important consequences on processes.

  5. Picosecond pulsed laser ablation and micromachining of 4H-SiC wafers

    NASA Astrophysics Data System (ADS)

    Molian, Pal; Pecholt, Ben; Gupta, Saurabh

    2009-02-01

    Ultra-short pulsed laser ablation and micromachining of n-type, 4H-SiC wafer was performed using a 1552 nm wavelength, 2 ps pulse, 5 μJ pulse energy erbium-doped fiber laser with an objective of rapid etching of diaphragms for pressure sensors. Ablation rate, studied as a function of energy fluence, reached a maximum of 20 nm per pulse at 10 mJ/cm 2, which is much higher than that achievable by the femtosecond laser for the equivalent energy fluence. Ablation threshold was determined as 2 mJ/cm 2. Scanning electron microscope images supported the Coulomb explosion (CE) mechanism by revealing very fine particulates, smooth surfaces and absence of thermal effects including melt layer formation. It is hypothesized that defect-activated absorption and multiphoton absorption mechanisms gave rise to a charge density in the surface layers required for CE and enabled material expulsion in the form of nanoparticles. Trenches and holes micromachined by the picosecond laser exhibited clean and smooth edges and non-thermal ablation mode for pulse repetition rates less than 250 kHz. However carbonaceous material and recast layer were noted in the machined region when the pulse repetition rate was increased 500 kHz that could be attributed to the interaction between air plasma and micro/nanoparticles. A comparison with femtosecond pulsed lasers shows the promise that picosecond lasers are more efficient and cost effective tools for creating sensor diaphragms and via holes in 4H-SiC.

  6. Investigation and spectral analysis of the plasma-induced ablation mechanism of dental hydroxyapatite

    NASA Astrophysics Data System (ADS)

    Niemz, M. H.

    1994-04-01

    Experiments on the ablation of dental substance performed with picosecond laser pulses are reported for the first time. A mode locked Nd:YLF oscillator laser was used to generate 25 ps pulses at a wavelength of 1.053 µm. These were seeded and amplified to pulse energies up to 1 mJ in a regenerative amplifier laser at repetition rates up to 1 kHz. Very precise cavities were ablated in the enamel of extracted human teeth by mounting the probes onto a computer controlled 3D translation stage. Scanning electron microscopy and dye penetration tests were performed there-after. In contrast to longer pulse durations, picosecond pulses ablate with no signs of thermal damage, if the laser pulses are spatially distributed over the target. Definitions of the physical mechanisms “plasma-induced ablation” and “photodisruption” are given. Furthermore, the generated plasma spark has been spectroscopically analyzed. Excitations of calcium and sodium have been observed. From the spectra, the plasma temperature and free electron density could be estimated. By converting part of the laser energy into the second harmonic using a LiNbO3 crystal, a reference amplitude was achieved for the spectra. With this reference signal, a clear distinction could be made between spectra obtained from healthy and caries infected teeth, thus enabling a better control of caries removal in the near future.

  7. Filamentation due to the Weibel Instability in two counterstreaming laser ablated plasmas

    NASA Astrophysics Data System (ADS)

    Dong, Quan-Li; Yuan, Dawei; Gao, Lan; Liu, Xun; Chen, Yangao; Jia, Qing; Hua, Neng; Qiao, Zhanfeng; Chen, Ming; Zhu, Baoqiang; Zhu, Jianqiang; Zhao, Gang; Ji, Hantao; Sheng, Zheng-Ming; Zhang, Jie

    2016-05-01

    Weibel-type filamentation instability was observed in the interaction of two counter streaming laser ablated plasma flows, which were supersonic, collisionless, and closely relevant to astrophysical conditions. The plasma flows were created by irradiating a pair of oppositely standing plastic (CH) foils with 1ns-pulsed laser beams of total energy of 1.7 kJ in two laser spots. With characteristics diagnosed in experiments, the calculated features of Weibel-type filaments are in good agreement with measurements.

  8. Experimental study on double-pulse laser ablation of steel upon multiple parallel-polarized ultrashort-pulse irradiations

    NASA Astrophysics Data System (ADS)

    Schille, Joerg; Schneider, Lutz; Kraft, Sebastian; Hartwig, Lars; Loeschner, Udo

    2016-07-01

    In this paper, double-pulse laser processing is experimentally studied with the aim to explore the influence of ultrashort pulses with very short time intervals on ablation efficiency and quality. For this, sequences of 50 double pulses of varied energy and inter-pulse delay, as adjusted between 400 fs and 18 ns by splitting the laser beam into two optical paths of different length, were irradiated to technical-grade stainless steel. The depth and the volume of the craters produced were measured in order to evaluate the efficiency of the ablation process; the crater quality was analyzed by SEM micrographs. The results obtained were compared with craters produced with sequences of 50 single pulses and energies equal to the double pulse. It is demonstrated that double-pulse processing cannot exceed the ablation efficiency of single pulses of optimal fluence, but the ablation crater surface formed smoother if inter-pulse delay was in the range between 10 ns and 18 ns. In addition, the influence of pulse duration and energy distribution between the individual pulses of the double pulse on ablation was studied. For very short inter-pulse delay, no significant effect of energy variation within the double pulse on removal rate was found, indicating that the double pulse acts as a big single pulse of equal energy. Further, the higher removal efficiency was achieved when double-pulse processing using femtosecond pulses instead of picosecond pulses.

  9. The absorption and radiation of a tungsten plasma plume during nanosecond laser ablation

    NASA Astrophysics Data System (ADS)

    Moscicki, T.; Hoffman, J.; Chrzanowska, J.

    2015-10-01

    In this paper, the effect of absorption of the laser beam and subsequent radiation on the dynamics of a tungsten plasma plume during pulsed laser ablation is analyzed. Different laser wavelengths are taken into consideration. The absorption and emission coefficients of tungsten plasma in a pressure range of 0.1-100 MPa and temperature up to 70 000 K are presented. The shielding effects due to the absorption and radiation of plasma may have an impact on the course of ablation. The numerical model that describes the tungsten target heating and the formation of the plasma and its expansion were made for 355 nm and 1064 nm wavelengths of a Nd:YAG laser. The laser beam with a Gaussian profile was focused to a spot size of 0.055 mm2 with a power density of 1 × 109 W/cm2 (10 ns full width half maximum pulse duration). The plasma expands into air at ambient pressure of 1 mPa. The use of the shorter wavelength causes faster heating of the target, thus the higher ablation rate. The consequences of a higher ablation rate are slower expansion and smaller dimensions of the plasma plume. The higher plasma temperature in the case of 1064 nm is due to the lower density and lower plasma radiation. In the initial phase of propagation of the plasma plume, when both the temperature and pressure are very high, the dominant radiation is emission due to photo-recombination. However, for a 1064 nm laser wavelength after 100 ns of plasma expansion, the radiation of the spectral lines is up to 46.5% of the total plasma radiation and should not be neglected.

  10. The absorption and radiation of a tungsten plasma plume during nanosecond laser ablation

    SciTech Connect

    Moscicki, T. Hoffman, J.; Chrzanowska, J.

    2015-10-15

    In this paper, the effect of absorption of the laser beam and subsequent radiation on the dynamics of a tungsten plasma plume during pulsed laser ablation is analyzed. Different laser wavelengths are taken into consideration. The absorption and emission coefficients of tungsten plasma in a pressure range of 0.1–100 MPa and temperature up to 70 000 K are presented. The shielding effects due to the absorption and radiation of plasma may have an impact on the course of ablation. The numerical model that describes the tungsten target heating and the formation of the plasma and its expansion were made for 355 nm and 1064 nm wavelengths of a Nd:YAG laser. The laser beam with a Gaussian profile was focused to a spot size of 0.055 mm{sup 2} with a power density of 1 × 10{sup 9 }W/cm{sup 2} (10 ns full width half maximum pulse duration). The plasma expands into air at ambient pressure of 1 mPa. The use of the shorter wavelength causes faster heating of the target, thus the higher ablation rate. The consequences of a higher ablation rate are slower expansion and smaller dimensions of the plasma plume. The higher plasma temperature in the case of 1064 nm is due to the lower density and lower plasma radiation. In the initial phase of propagation of the plasma plume, when both the temperature and pressure are very high, the dominant radiation is emission due to photo-recombination. However, for a 1064 nm laser wavelength after 100 ns of plasma expansion, the radiation of the spectral lines is up to 46.5% of the total plasma radiation and should not be neglected.

  11. Pulsed Electromagnetic Acceleration of Plasmas

    NASA Technical Reports Server (NTRS)

    Thio, Y. C. Francis; Cassibry, Jason T.; Markusic, Tom E.; Rodgers, Stephen L. (Technical Monitor)

    2002-01-01

    A major shift in paradigm in driving pulsed plasma thruster is necessary if the original goal of accelerating a plasma sheet efficiently to high velocities as a plasma "slug" is to be realized. Firstly, the plasma interior needs to be highly collisional so that it can be dammed by the plasma edge layer not (upstream) adjacent to the driving 'vacuum' magnetic field. Secondly, the plasma edge layer needs to be strongly magnetized so that its Hall parameter is of the order of unity in this region to ensure excellent coupling of the Lorentz force to the plasma. Thirdly, to prevent and/or suppress the occurrence of secondary arcs or restrike behind the plasma, the region behind the plasma needs to be collisionless and extremely magnetized with sufficiently large Hall parameter. This places a vacuum requirement on the bore conditions prior to the shot. These requirements are quantified in the paper and lead to the introduction of three new design parameters corresponding to these three plasma requirements. The first parameter, labeled in the paper as gamma (sub 1), pertains to the permissible ratio of the diffusive excursion of the plasma during the course of the acceleration to the plasma longitudinal dimension. The second parameter is the required Hall parameter of the edge plasma region, and the third parameter the required Hall parameter of the region behind the plasma. Experimental research is required to quantify the values of these design parameters. Based upon fundamental theory of the transport processes in plasma, some theoretical guidance on the choice of these parameters are provided to help designing the necessary experiments to acquire these data.

  12. Megavolt, Multigigawatt Pulsed Plasma Switch

    NASA Technical Reports Server (NTRS)

    Lee, Ja H.; Choi, Sang H.; Song, Kyo D.

    1996-01-01

    Plasma switch proposed for use in high-voltage, high-current pulse power system. Designed not only to out-perform conventional spark-gap switch but also relatively compact and lightweight. Features inverse-pinch configuration to prevent constriction of current sheets into filaments, plus multiple-ring-electrode structure to resist high-voltage breakdown.

  13. Adjustment of ablation shapes and subwavelength ripples based on electron dynamics control by designing femtosecond laser pulse trains

    NASA Astrophysics Data System (ADS)

    Yuan, Yanping; Jiang, Lan; Li, Xin; Wang, Cong; Lu, Yongfeng

    2012-11-01

    A quantum model is proposed to investigate femtosecond laser pulse trains processing of dielectrics by including the plasma model with the consideration of laser particle-wave duality. Central wavelengths (400 nm and 800 nm) strongly impact the surface plasmon field distribution, the coupling field intensity distribution (between the absorbed intensity and the surface plasma), and the distribution of transient localized free electron density in the material. This, in turn, significantly changes the localized transient optical/thermal properties during laser materials processing. The effects of central wavelengths on ablation shapes and subwavelength ripples are discussed. The simulation results show that: (1) ablation shapes and the spacing of subwavelength ripples can be adjusted by localized transient electron dynamics control using femtosecond laser pulse trains; (2) the adjustment of the radii of ablation shapes is stronger than that of the periods of subwavelength ripples.

  14. Ultrarelativistic electromagnetic pulses in plasmas

    NASA Technical Reports Server (NTRS)

    Ashour-Abdalla, M.; Leboeuf, J. N.; Tajima, T.; Dawson, J. M.; Kennel, C. F.

    1981-01-01

    The physical processes of a linearly polarized electromagnetic pulse of highly relativistic amplitude in an underdense plasma accelerating particles to very high energies are studied through computer simulation. An electron-positron plasma is considered first. The maximum momenta achieved scale as the square of the wave amplitude. This acceleration stops when the bulk of the wave energy is converted to particle energy. The pulse leaves behind as a wake a vacuum region whose length scales as the amplitude of the wave. The results can be explained in terms of a snow plow or piston-like action of the radiation on the plasma. When a mass ratio other than unity is chosen and electrostatic effects begin to play a role, first the ion energy increases faster than the electron energy and then the electron energy catches up later, eventually reaching the same value.

  15. Plume dynamics from UV pulsed ablation of Al and Ti

    NASA Astrophysics Data System (ADS)

    Bauer, William; Perram, Glen; Haugan, Timothy

    2016-12-01

    Pulsed laser ablation of Al and Ti with a < 3.3 J/cm2 KrF laser and Ar background pressure of up to 1 Torr was performed to study the ablated plume. Mass loss experiments revealed the number of ablated atoms per pulse increases by 30% for Ti and 20% for Al as pressure decreases from 1 Torr to vacuum. Optical emission imaging performed using a gated ICCD revealed a strong dependence of shock front parameters, defined by the Sedov-Taylor blast and classical drag models, on background pressure. Spatially resolved optical emission spectroscopy from Al I, Al II, Ti I, and Ti II revealed ion temperatures of 104 K that decreased away from the target surface along the surface normal and neutral temperatures of 103 K independent of target distance. Comparison between kinetic energy in the shock and internal excitation energy reveals that nearly 100% of the energy is partitioned into shock front kinetic energy and 1% into internal excitation.

  16. Nanosecond laser ablation for pulsed laser deposition of yttria

    NASA Astrophysics Data System (ADS)

    Sinha, Sucharita

    2013-09-01

    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.

  17. Critical Fluences And Modeling Of CO{sub 2} Laser Ablation Of Polyoxymethylene From Vaporization To The Plasma Regime

    SciTech Connect

    Sinko, John E.; Phipps, Claude R.; Tsukiyama, Yosuke; Ogita, Naoya; Sasoh, Akihiro; Umehara, Noritsugu; Gregory, Don A.

    2010-05-06

    A CO{sub 2} laser was operated at pulse energies up to 10 J to ablate polyoxymethylene targets in air and vacuum conditions. Critical effects predicted by ablation models are discussed in relation to the experimental data, including specifically the threshold fluences for vaporization and critical plasma formation, and the fluence at which the optimal momentum coupling coefficient is found. Finally, we discuss a new approach for modeling polymers at long wavelengths, including a connection formula that links the vaporization and plasma regimes for laser ablation propulsion.

  18. Condensation of ablation plumes in the irradiation of metals by high-intensity nanosecond laser pulses at atmospheric pressure

    SciTech Connect

    Kozadaev, K V

    2016-01-31

    The Anisimov–Luk'yanchuk model is adapted for describing the condensation of vapour-plasma plumes produced in the irradiation of metal targets by high-intensity (10{sup 8} – 10{sup 10} W cm{sup -2}) nanosecond (10 – 100 ns) pulses at atmospheric pressure. The resultant data suggest that the initial stages of the development of metal ablation plumes correspond with a high degree of accuracy to the Zel'dovich–Raizer theory of dynamic condensation; however, at the stage of the ablation plume decay, the liquid-droplet phase is formed primarily by coalescence of 'nuclei'. (interaction of laser radiation with matter. laser plasma)

  19. Aerospace applications of pulsed plasmas

    NASA Astrophysics Data System (ADS)

    Starikovskiy, Andrey

    2012-10-01

    The use of a thermal equilibrium plasma for combustion control dates back more than a hundred years to the advent of internal combustion (IC) engines and spark ignition systems. The same principles are still applied today to achieve high efficiency in various applications. Recently, the potential use of nonequilibrium plasma for ignition and combustion control has garnered increasing interest due to the possibility of plasma-assisted approaches for ignition and flame stabilization. During the past decade, significant progress has been made toward understanding the mechanisms of plasma chemistry interactions, energy redistribution and the nonequilibrium initiation of combustion. In addition, a wide variety of fuels have been examined using various types of discharge plasmas. Plasma application has been shown to provide additional combustion control, which is necessary for ultra-lean flames, high-speed flows, cold low-pressure conditions of high-altitude gas turbine engine (GTE) relight, detonation initiation in pulsed detonation engines (PDE) and distributed ignition control in homogeneous charge-compression ignition (HCCI) engines, among others. The present paper describes the current understanding of the nonequilibrium excitation of combustible mixtures by electrical discharges and plasma-assisted ignition and combustion. Nonequilibrium plasma demonstrates an ability to control ultra-lean, ultra-fast, low-temperature flames and appears to be an extremely promising technology for a wide range of applications, including aviation GTEs, piston engines, ramjets, scramjets and detonation initiation for pulsed detonation engines. To use nonequilibrium plasma for ignition and combustion in real energetic systems, one must understand the mechanisms of plasma-assisted ignition and combustion and be able to numerically simulate the discharge and combustion processes under various conditions.

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

    SciTech Connect

    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.; Chang, T.D.; Neev, J.

    1996-05-01

    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.

  1. Coupling effects of the number of pulses, pulse repetition rate and fluence during laser PMMA ablation

    NASA Astrophysics Data System (ADS)

    Liu, Z. Q.; Feng, Y.; Yi, X.-S.

    2000-10-01

    Poly(methyl methacrylate) (PMMA) was ablated using a 248-nm long-pulsed KrF excimer laser operating at a pulse repetition rate (PRR) of 2 and 10 Hz, and fluence varying from 0.4 to 2 J/cm 2. The coupling effects of multiple shots, PRR, and fluence are found and discussed on the etching depth data and topography of PMMA. An increase in either PRR, or fluence or the number of pulses can accelerate the etching efficiency in terms of ablation rate, as a result of strengthened thermal effects. Quality of the craters such as roughness, porosity and contamination is sensitively dependent on the specific laser operating conditions. Basically, increasing the PRR and the number of pulses gives rise to a crater with smoother and less porous bottom.

  2. Electronegative Plasma Instabilities in Industrial Pulsed Plasmas

    NASA Astrophysics Data System (ADS)

    Pribyl, Patrick; Hansen, Anders; Gekelman, Walter

    2016-10-01

    Electronegative gases that are important for industrial etch processes have a series of instabilities that occur at process relevant conditions. These have been studied since the 1990s, but are becoming a much more important today as plasma reactors are being pushed to produce ever finer features, and tight control of the etch process is becoming crucial. The experiments are being done in a plasma etch tool that closely simulates a working industrial device. ICP coils in different configurations are driven by a pulsed RF generators operating at 2-5 MHz. A computer controlled automated probe drive can access a volume above the substrate. The probe can be a Langmuir probe, a ``Bdot'' probe, or an emissive probe the latter used for more accurate determination of plasma potential. A microwave interferometer is available to measure line-averaged electron density. The negative ion instability is triggered depending upon the gas mix (Ar,SF6) , pressure and RF power. The instability can be ``burned through'' by rapidly pulsing the RF power. In this study we present measurements of plasma current and density distribution over the wafer before, after and during the rapid onset of the instability. Work suported by NSF-GOALI Award and done at the BAPSF.

  3. Shock wave mediated plume chemistry for molecular formation in laser ablation plasmas

    SciTech Connect

    Harilal, Sivanandan S.; Brumfield, Brian E.; Cannon, Bret D.; Phillips, Mark C.

    2016-02-16

    Laser ablation is used in a variety of applications albeit formation mechanisms of molecules and nanoclusters are not well understood. We investigated the formation mechanisms of AlO molecules during complex interactions between an Al laser plume expanding into ambient air at atmospheric pressure levels. To produce the plasma a high-purity Al target was ablated using 1064 nm, 6 ns laser pulses. Our results show that the plasma chemistry leading to the formation of AlO is mediated by shock waves. During the early times of plasma expansion, the generated shock waves at the plume edges act as a barrier for the combustion process and the molecular formation is prevalent after the shockwave collapse. The temporally and spatially resolved contour mapping of Al and AlO highlight the formation routes and persistence of species in the plasma and its relation to plume hydrodynamics.

  4. A spectroscopic study of laser ablation plasma from Mo target

    NASA Astrophysics Data System (ADS)

    Jakubowska, Katarzyna; Kubkowska, Monika; Blagoev, Alexander; Rosiński, Marcin; Parys, Piotr; Gąsior, Paweł

    2014-05-01

    The goal of this contribution is to present time-resolved optical spectroscopy studies of laser ablation of the Mo target with ˜ 3.5 ns, 0.4 J pulses delivered by the Nd-YAG laser system at 1.06 μm. The sample was placed in a vacuum chamber under 5 × 10-5 mbar pressure and irradiated, with power densities varied up to 22.7 GW cm-2. The ion emission from the plasma plume was measured using an electrostatic ion energy analyzer (IEA) and ion collector, which allowed us to estimate the ion kinetic energy and charge independent of the applied power densities. The signal collected by the IEA indicated the presence of molybdenum ions up to eight-ion charge. Simultaneously after the ion emission, the optical spectra acquired within 2 μs of exposure time were observed in the wavelength range from 200 to 1000 nm with a Mechelle 5000 spectrometer equipped with an iCCD (iStar) detector. The plasma electron temperature was estimated from a Boltzmann plot based on the registered spectra as well as from the ion measurements.

  5. Experimental scaling law for mass ablation rate from a Sn plasma generated by a 1064 nm laser

    SciTech Connect

    Burdt, Russell A.; Yuspeh, Sam; Najmabadi, Farrokh; Sequoia, Kevin L.; Tao Yezheng; Tillack, Mark S.

    2009-08-01

    The ablation depth in planar Sn targets irradiated with a pulsed 1064 nm laser was investigated over laser intensities from 3x10{sup 11} to 2x10{sup 12} W/cm{sup 2}. The ablation depth was measured by irradiating a thin layer of Sn evaporated onto a Si wafer, and looking for signatures of Si ions in the expanding plasma with spectroscopic and particle diagnostics. It was found that ablation depth scales with laser intensity to the (5/9)th power, which is consistent with analytical models of steady-state laser ablation, as well as empirical formulae from previous studies of mass ablation rate in overlapping parameter space. In addition, the scaling of mass ablation rate with atomic number of the target as given by empirical formulae in previous studies using targets such as C and Al, are shown to remain valid for the higher atomic number of the target (Z=50) used in these experiments.

  6. Plasma shape control by pulsed solenoid on laser ion source

    DOE PAGES

    Sekine, M.; Ikeda, S.; Romanelli, M.; ...

    2015-05-28

    A Laser ion source (LIS) provides high current heavy ion beams with a very simple mechanical structure. Plasma is produced by a pulsed laser ablation of a solid state target and ions are extracted by an electric field. It was difficult to manipulate the beam parameters of a LIS, since the plasma condition could only be adjusted by the laser irradiation condition. To enhance flexibility of LIS operation, we employed a pulsed solenoid in the plasma drift section and investigated the effect of the solenoid field on singly charged iron beams. The experimentally obtained current profile was satisfactorily controlled bymore » the pulsed magnetic field. Thus, this approach may also be useful to reduce beam emittance of a LIS.« less

  7. Plasma shape control by pulsed solenoid on laser ion source

    SciTech Connect

    Sekine, M.; Ikeda, S.; Romanelli, M.; Kumaki, M.; Fuwa, Y.; Kanesue, T.; Hayashizaki, N.; Lambiase, R.; Okamura, M.

    2015-05-28

    A Laser ion source (LIS) provides high current heavy ion beams with a very simple mechanical structure. Plasma is produced by a pulsed laser ablation of a solid state target and ions are extracted by an electric field. It was difficult to manipulate the beam parameters of a LIS, since the plasma condition could only be adjusted by the laser irradiation condition. To enhance flexibility of LIS operation, we employed a pulsed solenoid in the plasma drift section and investigated the effect of the solenoid field on singly charged iron beams. The experimentally obtained current profile was satisfactorily controlled by the pulsed magnetic field. Thus, this approach may also be useful to reduce beam emittance of a LIS.

  8. Plasma shape control by pulsed solenoid on laser ion source

    NASA Astrophysics Data System (ADS)

    Sekine, M.; Ikeda, S.; Romanelli, M.; Kumaki, M.; Fuwa, Y.; Kanesue, T.; Hayashizaki, N.; Lambiase, R.; Okamura, M.

    2015-09-01

    A Laser ion source (LIS) provides high current heavy ion beams with a very simple mechanical structure. Plasma is produced by a pulsed laser ablation of a solid state target and ions are extracted by an electric field. However, it was difficult to manipulate the beam parameters of a LIS, since the plasma condition could only be adjusted by the laser irradiation condition. To enhance flexibility of LIS operation, we employed a pulsed solenoid in the plasma drift section and investigated the effect of the solenoid field on singly charged iron beams. The experimentally obtained current profile was satisfactorily controlled by the pulsed magnetic field. This approach may also be useful to reduce beam emittance of a LIS.

  9. Investigation of nanoparticle formation in a plasma produced by femtosecond laser ablation of gold

    SciTech Connect

    Spiga, P.; Hermann, J.; Itina, T.; Grojo, D.; Neamtu, D.; Pailharey, D.; Marine, W.

    2005-10-31

    The formation of nanoparticles in a plasma produced by the interaction of ultrashort laser pulses with gold has been investigated. Three different experimental techniques were employed. (i) The plume expansion was characterized using fast imaging with the aid of an intensified charge-coupled device. (ii) The plasma composition was analyzed using time- and space-resolved optical emission spectroscopy. (iii) The ablated material was deposited on mica substrates and analyzed by means of atomic force microscopy. As a result, the size-distribution and the overall number of nanoparticles were determined as a function of the laser energy density incident on the target surface. The detection of particles with sizes in the nanometer range supports theoretical modeling according to which phase explosion is the dominant mechanism of metal ablation by ultrashort laser pulses.

  10. Third harmonic generation in air ambient and laser ablated carbon plasma

    SciTech Connect

    Singh, Ravi Pratap Gupta, Shyam L.; Thareja, Raj K.

    2015-12-15

    We report the third harmonic generation of a nanosecond laser pulse (1.06 μm) in air ambient and in the presence of nanoparticles from laser ablated carbon plasma. Significant decrease in the threshold of third harmonic generation and multi-fold increment in the intensity of generated third harmonic is observed in presence of carbon plasma. The third harmonic in air is due to the quasi-resonant four photon process involving vibrationally excited states of molecular ion of nitrogen due to electron impact ionization and laser pulse. Following optical emission spectroscopic observations we conclude that the presence of C{sub 2} and CN in the ablated plume play a vital role in the observed third harmonic signals.

  11. Surface Modification of ICF Target Capsules by Pulsed Laser Ablation

    SciTech Connect

    Carlson, Lane C.; Johnson, Michael A.; Bunn, Thomas L.

    2016-06-30

    Topographical modifications of spherical surfaces are imprinted on National Ignition Facility (NIF) target capsules by extending the capabilities of a recently developed full surface (4π) laser ablation and mapping apparatus. The laser ablation method combines the precision, energy density and long reach of a focused laser beam to pre-impose sinusoidal modulations on the outside surface of High Density Carbon (HDC) capsules and the inside surface of Glow Discharge Polymer (GDP) capsules. Sinusoidal modulations described in this paper have sub-micron to 10’s of microns vertical scale and wavelengths as small as 30 μm and as large as 200 μm. The modulated patterns are created by rastering a focused laser fired at discrete capsule surface locations for a specified number of pulses. The computer program developed to create these raster patterns uses inputs such as laser beam intensity profile, the material removal function, the starting surface figure and the desired surface figure. The patterns are optimized to minimize surface roughness. Lastly, in this paper, simulated surfaces are compared with actual ablated surfaces measured using confocal microscopy.

  12. Surface Modification of ICF Target Capsules by Pulsed Laser Ablation

    DOE PAGES

    Carlson, Lane C.; Johnson, Michael A.; Bunn, Thomas L.

    2016-06-30

    Topographical modifications of spherical surfaces are imprinted on National Ignition Facility (NIF) target capsules by extending the capabilities of a recently developed full surface (4π) laser ablation and mapping apparatus. The laser ablation method combines the precision, energy density and long reach of a focused laser beam to pre-impose sinusoidal modulations on the outside surface of High Density Carbon (HDC) capsules and the inside surface of Glow Discharge Polymer (GDP) capsules. Sinusoidal modulations described in this paper have sub-micron to 10’s of microns vertical scale and wavelengths as small as 30 μm and as large as 200 μm. The modulatedmore » patterns are created by rastering a focused laser fired at discrete capsule surface locations for a specified number of pulses. The computer program developed to create these raster patterns uses inputs such as laser beam intensity profile, the material removal function, the starting surface figure and the desired surface figure. The patterns are optimized to minimize surface roughness. Lastly, in this paper, simulated surfaces are compared with actual ablated surfaces measured using confocal microscopy.« less

  13. Spectroscopy Measurements on Ablation Testing in High Enthalpy Plasma Flows

    DTIC Science & Technology

    2010-11-01

    stagnation point, are located on the ablative material sample. 3.5 InfraRed THERMOGRAPHY Surface temperature measurement is a topic of great concern...high temperature material at two different narrow wavelengths. The temperature is calculated by building the ratio of the radiation intensities. The...this work is to develop the capability of testing and characterization of ablative materials exposed to high enthalpy plasma flows including both

  14. A survey of pulse shape options for a revised plastic ablator ignition design

    SciTech Connect

    Clark, D. S.; Milovich, J. L.; Hinkel, D. E.; Salmonson, J. D.; Peterson, J. L.; Berzak Hopkins, L. F.; Eder, D. C.; Haan, S. W.; Jones, O. S.; Marinak, M. M.; Robey, H. F.; Smalyuk, V. A.; Weber, C. R.

    2014-11-15

    Recent experimental results using the “high foot” pulse shape for inertial confinement fusion ignition experiments on the National Ignition Facility (NIF) [Moses et al., Phys. Plasmas 16, 041006 (2009)] have shown encouraging progress compared to earlier “low foot” experiments. These results strongly suggest that controlling ablation front instability growth can significantly improve implosion performance even in the presence of persistent, large, low-mode distortions. Simultaneously, hydrodynamic growth radiography experiments have confirmed that ablation front instability growth is being modeled fairly well in NIF experiments. It is timely then to combine these two results and ask how current ignition pulse shapes could be modified to improve one-dimensional implosion performance while maintaining the stability properties demonstrated with the high foot. This paper presents such a survey of pulse shapes intermediate between the low and high foot extremes in search of an intermediate foot optimum. Of the design space surveyed, it is found that a higher picket version of the low foot pulse shape shows the most promise for improved compression without loss of stability.

  15. Imaging the ultrafast Kerr effect, free carrier generation, relaxation and ablation dynamics of Lithium Niobate irradiated with femtosecond laser pulses

    NASA Astrophysics Data System (ADS)

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

    2014-09-01

    The interaction of high-power single 130 femtosecond (fs) laser pulses with the surface of Lithium Niobate is experimentally investigated in this work. The use of fs-resolution time-resolved microscopy allows us to separately observe the instantaneous optical Kerr effect induced by the pulse and the generation of a free electron plasma. The maximum electron density is reached 550 fs after the peak of the Kerr effect, confirming the presence of a delayed carrier generation mechanism. We have also observed the appearance of transient Newton rings during the ablation process, related to optical interference of the probe beam reflected at the front and back surface of the ablating layer. Finally, we have analyzed the dynamics of the photorefractive effect on a much longer time scale by measuring the evolution of the transmittance of the irradiated area for different fluences below the ablation threshold.

  16. Imaging the ultrafast Kerr effect, free carrier generation, relaxation and ablation dynamics of Lithium Niobate irradiated with femtosecond laser pulses

    SciTech Connect

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

    2014-09-21

    The interaction of high-power single 130 femtosecond (fs) laser pulses with the surface of Lithium Niobate is experimentally investigated in this work. The use of fs-resolution time-resolved microscopy allows us to separately observe the instantaneous optical Kerr effect induced by the pulse and the generation of a free electron plasma. The maximum electron density is reached 550 fs after the peak of the Kerr effect, confirming the presence of a delayed carrier generation mechanism. We have also observed the appearance of transient Newton rings during the ablation process, related to optical interference of the probe beam reflected at the front and back surface of the ablating layer. Finally, we have analyzed the dynamics of the photorefractive effect on a much longer time scale by measuring the evolution of the transmittance of the irradiated area for different fluences below the ablation threshold.

  17. Near-critical phase explosion promoting breakdown plasma ignition during laser ablation of graphite.

    PubMed

    Ionin, A A; Kudryashov, S I; Seleznev, L V

    2010-07-01

    Removal rate, air shock, and ablative recoil pressure parameters were measured as a function of laser intensity I(peak) during nanosecond laser ablation of graphite. Surface vaporization of molten graphite at low intensities I(peak)<0.15 GW/cm(2) was observed to transform into its near-critical phase explosion (intense homogeneous boiling) at the threshold intensity I(PE)≈0.15 GW/cm(2) in the form of a drastic, correlated rise of removal rate, air shock, and ablative recoil pressure magnitudes. Just above this threshold (I(peak)≥0.25 GW/cm(2)), the explosive mass removal ended up with saturation of the removal rate, much slower increase of the air and recoil pressure magnitudes, and appearance of a visible surface plasma spark. In this regime, the measured far-field air shock pressure amplitude exhibits a sublinear dependence on laser intensity (∝I(peak)(4/9)), while the source plasma shock pressure demonstrates a sublinear trend (∝I(peak)(3/4)), both indicating the subcritical character of the plasma. Against expectations, in this regime the plasma recoil pressure increases versus I(peak) superlinearly (∝I(peak)(1.1)), rather than sublinearly (∝I(peak)(3/4)), with the mentioned difference related to the intensity-dependent initial spatial plasma dimensions within the laser waist on the graphite surface and to the plasma formation time during the heating laser pulse (overall, the pressure source effect). The strict coincidence of the phase explosion, providing high (kbar) hydrodynamic pressures of ablation products, and the ignition of ablative laser plasma in the carbon plume may indicate the ablative pressure-dependent character of the underlying optical breakdown at the high plume pressures, initiating the plasma formation. The experimental data evidence that the spatiotemporal extension of the plasma in the laser plume and ambient air during the heating laser pulse is supported by fast lateral electron and radiative heat conduction (laser

  18. Effects of pulsed CO2 laser in caries selective ablation

    NASA Astrophysics Data System (ADS)

    Colojoara, Carmen; David, Ion; Marinovici, Mariana

    1995-03-01

    We have evaluated the effect of pulsed carbon dioxide laser in the treatment for deep carious decay. The so called `caries profonda' is still a problem for conservative dentistry. A `Valvfivre' Master 20S carbon dioxide laser was pulsed to determine the effects on dentine and for testing the properties of softened dentine in selective ablation. Laser treatment parameters were from 1 to 2 W, 50 to 150 ms, 200 to 320 Hz. Fifteen human teeth samples were exposed to irradiation: extracted third molar were exposed to CO2 pulsed laser to determine in vitro the effects on pulp morphology. The tissue samples were analyzed histologically and by means of scanning electron microscopy for evidence of thermal damage. Next, we have evaluated the morphologic changes in vivo on 10 cases in patients with deep carious decay. Pulsed infrared lasers are capable of inducing physical and chemical changes in dentine structure. The results showed an artificially sclerosing and micro-hardness on the remaining dentine. CO2 laser can vaporized carious dentine.

  19. Investigation of early plasma evolution induced by ultrashort laser pulses.

    PubMed

    Hu, Wenqian; Shin, Yung C; King, Galen B

    2012-07-02

    Early plasma is generated owing to high intensity laser irradiation of target and the subsequent target material ionization. Its dynamics plays a significant role in laser-material interaction, especially in the air environment(1-11). Early plasma evolution has been captured through pump-probe shadowgraphy(1-3) and interferometry(1,4-7). However, the studied time frames and applied laser parameter ranges are limited. For example, direct examinations of plasma front locations and electron number densities within a delay time of 100 picosecond (ps) with respect to the laser pulse peak are still very few, especially for the ultrashort pulse of a duration around 100 femtosecond (fs) and a low power density around 10(14) W/cm(2). Early plasma generated under these conditions has only been captured recently with high temporal and spatial resolutions(12). The detailed setup strategy and procedures of this high precision measurement will be illustrated in this paper. The rationale of the measurement is optical pump-probe shadowgraphy: one ultrashort laser pulse is split to a pump pulse and a probe pulse, while the delay time between them can be adjusted by changing their beam path lengths. The pump pulse ablates the target and generates the early plasma, and the probe pulse propagates through the plasma region and detects the non-uniformity of electron number density. In addition, animations are generated using the calculated results from the simulation model of Ref. (12) to illustrate the plasma formation and evolution with a very high resolution (0.04 ~ 1 ps). Both the experimental method and the simulation method can be applied to a broad range of time frames and laser parameters. These methods can be used to examine the early plasma generated not only from metals, but also from semiconductors and insulators.

  20. Investigation of Early Plasma Evolution Induced by Ultrashort Laser Pulses

    PubMed Central

    Hu, Wenqian; Shin, Yung C.; King, Galen B.

    2012-01-01

    Early plasma is generated owing to high intensity laser irradiation of target and the subsequent target material ionization. Its dynamics plays a significant role in laser-material interaction, especially in the air environment1-11. Early plasma evolution has been captured through pump-probe shadowgraphy1-3 and interferometry1,4-7. However, the studied time frames and applied laser parameter ranges are limited. For example, direct examinations of plasma front locations and electron number densities within a delay time of 100 picosecond (ps) with respect to the laser pulse peak are still very few, especially for the ultrashort pulse of a duration around 100 femtosecond (fs) and a low power density around 1014 W/cm2. Early plasma generated under these conditions has only been captured recently with high temporal and spatial resolutions12. The detailed setup strategy and procedures of this high precision measurement will be illustrated in this paper. The rationale of the measurement is optical pump-probe shadowgraphy: one ultrashort laser pulse is split to a pump pulse and a probe pulse, while the delay time between them can be adjusted by changing their beam path lengths. The pump pulse ablates the target and generates the early plasma, and the probe pulse propagates through the plasma region and detects the non-uniformity of electron number density. In addition, animations are generated using the calculated results from the simulation model of Ref. 12 to illustrate the plasma formation and evolution with a very high resolution (0.04 ~ 1 ps). Both the experimental method and the simulation method can be applied to a broad range of time frames and laser parameters. These methods can be used to examine the early plasma generated not only from metals, but also from semiconductors and insulators. PMID:22806170

  1. Ablation experiment and threshold calculation of titanium alloy irradiated by ultra-fast pulse laser

    SciTech Connect

    Zheng, Buxiang; Jiang, Gedong; Wang, Wenjun Wang, Kedian; Mei, Xuesong

    2014-03-15

    The interaction between an ultra-fast pulse laser and a material's surface has become a research hotspot in recent years. Micromachining of titanium alloy with an ultra-fast pulse laser is a very important research direction, and it has very important theoretical significance and application value in investigating the ablation threshold of titanium alloy irradiated by ultra-fast pulse lasers. Irradiated by a picosecond pulse laser with wavelengths of 1064 nm and 532 nm, the surface morphology and feature sizes, including ablation crater width (i.e. diameter), ablation depth, ablation area, ablation volume, single pulse ablation rate, and so forth, of the titanium alloy were studied, and their ablation distributions were obtained. The experimental results show that titanium alloy irradiated by a picosecond pulse infrared laser with a 1064 nm wavelength has better ablation morphology than that of the green picosecond pulse laser with a 532 nm wavelength. The feature sizes are approximately linearly dependent on the laser pulse energy density at low energy density and the monotonic increase in laser pulse energy density. With the increase in energy density, the ablation feature sizes are increased. The rate of increase in the feature sizes slows down gradually once the energy density reaches a certain value, and gradually saturated trends occur at a relatively high energy density. Based on the linear relation between the laser pulse energy density and the crater area of the titanium alloy surface, and the Gaussian distribution of the laser intensity on the cross section, the ablation threshold of titanium alloy irradiated by an ultra-fast pulse laser was calculated to be about 0.109 J/cm{sup 2}.

  2. Pulsed plasma etching for semiconductor manufacturing

    NASA Astrophysics Data System (ADS)

    Economou, Demetre J.

    2014-07-01

    Power-modulated (pulsed) plasmas have demonstrated several advantages compared to continuous wave (CW) plasmas. Specifically, pulsed plasmas can result in a higher etching rate, better uniformity, and less structural, electrical or radiation (e.g. vacuum ultraviolet) damage. Pulsed plasmas can also ameliorate unwanted artefacts in etched micro-features such as notching, bowing, micro-trenching and aspect ratio dependent etching. As such, pulsed plasmas may be indispensable in etching of the next generation of micro-devices with a characteristic feature size in the sub-10 nm regime. This work provides an overview of principles and applications of pulsed plasmas in both electropositive (e.g. argon) and electronegative (e.g. chlorine) gases. The effect of pulsing the plasma source power (source pulsing), the electrode bias power (bias pulsing), or both source and bias power (synchronous pulsing), on the time evolution of species densities, electron energy distribution function and ion energy and angular distributions on the substrate is discussed. The resulting pulsed plasma process output (etching rate, uniformity, damage, etc) is compared, whenever possible, to that of CW plasma, under otherwise the same or similar conditions.

  3. A new sealed RF-excited CO2 laser for enamel ablation operating at 9.4μm with pulse duration of 26 μs

    NASA Astrophysics Data System (ADS)

    Chan, Kenneth H.; Jew, Jamison M.; Fried, Daniel

    2016-02-01

    Several studies over the past 20 years have identified that carbon dioxide lasers operating at wavelengths between 9.3 and 9.6-μm with pulse durations near 20-µs are ideal for hard tissue ablation. Those wavelengths are coincident with the peak absorption of the mineral phase and the pulse duration is close to the thermal relaxation time of the deposited energy of a few microseconds to minimize peripheral thermal damage and long enough to minimize plasma shielding effects to allow efficient ablation at practical rates. The desired pulse duration near 20-μs has been difficult to achieve since it is too long for TEA lasers and too short for RF-excited lasers for efficient operation. Recently, Coherent Inc. (Santa Clara, CA) developed the J5-V laser for microvia drilling which can produce laser pulses greater than 100 mJ in energy at 9.4-μm with a pulse duration of 26-µs and it can achieve pulse repetition rates of 3 KHz. We report the first results using this laser to ablate enamel and dentin. The onset of plasma shielding does not occur until the fluence exceeds 100 J/cm2 allowing efficient ablation at rates exceeding 50-μm per pulse. This laser is ideally suited for the selective ablation of carious lesions.

  4. Nanosecond pulsed laser ablation of Ge investigated by employing photoacoustic deflection technique and SEM analysis

    NASA Astrophysics Data System (ADS)

    Yaseen, Nazish; Bashir, Shazia; Shabbir, Muhammad Kaif; Jalil, Sohail Abdul; Akram, Mahreen; Hayat, Asma; Mahmood, Khaliq; Haq, Faizan-ul; Ahmad, Riaz; Hussain, Tousif

    2016-06-01

    Nanosecond pulsed laser ablation phenomena of single crystal Ge (100) has been investigated by employing photoacoustic deflection as well as SEM analysis techniques. Nd: YAG laser (1064 nm, 10 ns, 1-10 Hz) at various laser fluences ranging from 0.2 to 11 J cm-2 is employed as pump beam to ablate Ge targets. In order to evaluate in-situe ablation threshold fluence of Ge by photoacoustic deflection technique, Continuous Wave (CW) He-Ne laser (632 nm, power 10 mW) is employed as a probe beam. It travels parallel to the target surface at a distance of 3 mm and after passing through Ge plasma it causes deflection due to density gradient of acoustic waves. The deflected signal is detected by photodiode and is recorded by oscilloscope. The threshold fluence of Ge, the velocity of ablated species and the amplitude of the deflected signal are evaluated. The threshold fluence of Ge comes out to be 0.5 J cm-2 and is comparable with the analytical value. In order to compare the estimated value of threshold with ex-situe measurements, the quantitative analysis of laser irradiated Ge is performed by using SEM analysis. For this purpose Ge is exposed to single and multiple shots of 5, 10, 50 and 100 at various laser fluences ranging from 0.2 to 11 J cm-2. The threshold fluence for single and multiple shots as well as incubation coefficients are evaluated. It is observed that the value of incubation co-efficient decreases with increasing number of pulses and is therefore responsible for lowering the threshold fluence of Ge. SEM analysis also reveals the growth of various features such as porous structures, non-uniform ripples and blisters on the laser irradiated Ge. It is observed that both the fluence as well as number of laser shots plays a significant role for the growth of these structures.

  5. Filamentation due to the Weibel instability in two counterstreaming laser ablated plasmas

    SciTech Connect

    Dong, Quan -Li; Yuan, Dawei; Gao, Lan; Liu, Xun; Chen, Yangao; Jia, Qing; Hua, Neng; Qiao, Zhanfeng; Chen, Ming; Zhu, Baoqiang; Zhu, Jianqiang; Zhao, Gang; Ji, Hantao; Sheng, Zheng -Ming; Zhang, Jie

    2016-05-01

    Weibel-type filamentation instability was observed in the interaction of two counter streaming laser ablated plasma flows, which were supersonic, collisionless, and closely relevant to astrophysical conditions. The plasma flows were created by irradiating a pair of oppositely standing plastic (CH) foils with 1ns-pulsed laser beams of total energy of 1.7 kJ in two laser spots. Finally, with characteristics diagnosed in experiments, the calculated features of Weibel-type filaments are in good agreement with measurements.

  6. Resonant laser ablation of metals detected by atomic emission in a microwave plasma and by inductively coupled plasma mass spectrometry.

    PubMed

    Cleveland, Danielle; Stchur, Peter; Hou, Xiandeng; Yang, Karl X; Zhou, Jack; Michel, Robert G

    2005-12-01

    It has been shown that an increase in sensitivity and selectivity of detection of an analyte can be achieved by tuning the ablation laser wavelength to match that of a resonant gas-phase transition of that analyte. This has been termed resonant laser ablation (RLA). For a pulsed tunable nanosecond laser, the data presented here illustrate the resonant enhancement effect in pure copper and aluminum samples, chromium oxide thin films, and for trace molybdenum in stainless steel samples, and indicate two main characteristics of the RLA phenomenon. The first is that there is an increase in the number of atoms ablated from the surface. The second is that the bandwidth of the wavelength dependence of the ablation is on the order of 1 nm. The effect was found to be virtually identical whether the atoms were detected by use of a microwave-induced plasma with atomic emission detection, by an inductively coupled plasma with mass spectrometric detection, or by observation of the number of laser pulses required to penetrate through thin films. The data indicate that a distinct ablation laser wavelength dependence exists, probably initiated via resonant radiation trapping, and accompanied by collisional broadening. Desorption contributions through radiation trapping are substantiated by changes in crater morphology as a function of wavelength and by the relatively broad linewidth of the ablation laser wavelength scans, compared to gas-phase excitation spectra. Also, other experiments with thin films demonstrate the existence of a distinct laser-material interaction and suggest that a combination of desorption induced by electronic transition (DIET) with resonant radiation trapping could assist in the enhancement of desorption yields. These results were obtained by a detailed inspection of the effect of the wavelength of the ablation laser over a narrow range of energy densities that lie between the threshold of laser-induced desorption of species and the usual analytical

  7. Effects of Liquid Medium and Ablation Wavelength on the Properties of Cadmium Sulfide Nanoparticles Formed by Pulsed-Laser Ablation.

    PubMed

    García Guillén, Grisel; Zuñiga Ibarra, Veronica Anahi; Mendivil Palma, Maria Isabel; Krishnan, Bindu; Avellaneda Avellaneda, David; Shaji, Sadasivan

    2016-11-03

    Pulsed-laser ablation in liquid (PLAL) is a green synthesis technique to obtain semiconductor nanomaterials in colloidal form. Herein, cadmium sulfide (CdS) nanoparticles were synthesized by the pulsed-laser ablation of a CdS target in different liquid media by using λ=532 and 1064 nm outputs from a pulsed (10 ns, 10 Hz) Nd:YAG laser at different ablation fluence values. The morphology, structure, crystalline phase, elemental composition, optical, and luminescent properties of CdS nanomaterials were analyzed by using transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), UV/Vis absorption spectroscopy, and fluorescence spectroscopy. By changing the liquid medium and ablation wavelength, CdS nanoparticles with different morphology and size were formed, as demonstrated by using TEM analysis. The crystallinity and chemical states of the ablation products were confirmed by using XRD and XPS analyses. The optical bandgap of the CdS nanoparticles was dependent on the ablation wavelength and the fluence. These nanocolloids presented different green emissions, which implied the presence of several emission centers. CdS nanocolloids in distilled water catalyzed the photocatalytic decay of methylene blue dye under light irradiation from a solar simulator.

  8. Ablation and analysis of small cell populations and single cells by consecutive laser pulses

    NASA Astrophysics Data System (ADS)

    Shrestha, Bindesh; Nemes, Peter; Vertes, Akos

    2010-10-01

    Laser ablation of single cells through a sharpened optical fiber is used for the detection of metabolites by laser ablation electrospray ionization (LAESI) mass spectrometry (MS). Ablation of the same Allium cepa epidermal cell by consecutive pulses indicates the rupture of the cell wall by the second shot. Intracellular sucrose heterogeneity is detected by subsequent laser pulses pointing to rupturing the vacuolar membrane by the third exposure. Ion production by bursts of laser pulses shows that the drying of ruptured A. cepa cells occurs in ˜50 s at low pulse rates (10 pulses/s bursts) and significantly faster at high pulse rates (100 pulses/s bursts). These results point to the competing role of cytoplasm ejection and evaporative drying in diminishing the LAESI-MS signal in ˜50 s or 100 laser pulses, whichever occurs first.

  9. Laser ablation inductively coupled plasma mass spectrometry measurement of isotope ratios in depleted uranium contaminated soils.

    PubMed

    Seltzer, Michael D

    2003-09-01

    Laser ablation of pressed soil pellets was examined as a means of direct sample introduction to enable inductively coupled plasma mass spectrometry (ICP-MS) screening of soils for residual depleted uranium (DU) contamination. Differentiation between depleted uranium, an anthropogenic contaminant, and naturally occurring uranium was accomplished on the basis of measured 235U/238U isotope ratios. The amount of sample preparation required for laser ablation is considerably less than that typically required for aqueous sample introduction. The amount of hazardous laboratory waste generated is diminished accordingly. During the present investigation, 235U/238U isotope ratios measured for field samples were in good agreement with those derived from gamma spectrometry measurements. However, substantial compensation was required to mitigate the effects of impaired pulse counting attributed to sample inhomogeneity and sporadic introduction of uranium analyte into the plasma.

  10. Irreversible electroporation ablation area enhanced by synergistic high- and low-voltage pulses

    PubMed Central

    2017-01-01

    Irreversible electroporation (IRE) produced by a pulsed electric field can ablate tissue. In this study, we achieved an enhancement in ablation area by using a combination of short high-voltage pulses (HVPs) to create a large electroporated area and long low-voltage pulses (LVPs) to ablate the electroporated area. The experiments were conducted in potato tuber slices. Slices were ablated with an array of four pairs of parallel steel electrodes using one of the following four electric pulse protocols: HVP, LVP, synergistic HVP+LVP (SHLVP) or LVP+HVP. Our results showed that the SHLVPs more effectively necrotized tissue than either the HVPs or LVPs, even when the SHLVP dose was the same as or lower than the HVP or LVP doses. The HVP and LVP order mattered and only HVPs+LVPs (SHLVPs) treatments increased the size of the ablation zone because the HVPs created a large electroporated area that was more susceptible to the subsequent LVPs. Real-time temperature change monitoring confirmed that the tissue was non-thermally ablated by the electric pulses. Theoretical calculations of the synergistic effects of the SHLVPs on tissue ablation were performed. Our proposed SHLVP protocol provides options for tissue ablation and may be applied to optimize the current clinical IRE protocols. PMID:28253331

  11. Experimental investigation of vapor shielding effects induced by ELM-like pulsed plasma loads using the double plasma gun device

    NASA Astrophysics Data System (ADS)

    Sakuma, I.; Kikuchi, Y.; Kitagawa, Y.; Asai, Y.; Onishi, K.; Fukumoto, N.; Nagata, M.

    2015-08-01

    We have developed a unique experimental device of so-called double plasma gun, which consists of two magnetized coaxial plasma gun (MCPG) devices, in order to clarify effects of vapor shielding on material erosion due to transient events in magnetically confined fusion devices. Two ELM-like pulsed plasmas produced by the two MCPG devices were injected into a target chamber with a variable time difference. For generating ablated plasmas in front of a target material, an aluminum foil sample in the target chamber was exposed to a pulsed plasma produced by the 1st MCPG device. The 2nd pulsed plasma was produced with a time delay of 70 μs. It was found that a surface absorbed energy measured by a calorimeter was reduced to ∼66% of that without the Al foil sample. Thus, the reduction of the incoming plasma energy by the vapor shielding effect was successfully demonstrated in the present experiment.

  12. Computational study of nanosecond pulsed laser ablation and the application to momentum coupling

    SciTech Connect

    Yuan Hong; Tong Huifeng; Li Mu; Sun Chengwei

    2012-07-15

    During the evaporation and ablation of a matter induced by intensive laser radiation, the vapor plasma is ejected from the surface of the target which induces the recoil pressure and impulse in the target. Impulse coupling of laser beams with matter has been extensively studied as the basis of laser propulsion and laser clearing space debris. A one-dimensional (1D) bulk absorption model to simulate the solid target ablated directly by the laser beam is presented; numerical calculation of impulse acting on the target in vacuum with different laser parameters is performed with fluid dynamics theory and 1D Lagrange difference scheme. The calculated results of the impulse coupling coefficients are in good agreement with the experimental results and Phipps' empirical value. The simulated results show that the mechanical coupling coefficients decrease with the increment of laser intensity when the laser pulses generate plasma. The present model can be applied when the laser intensity is 10{sup 8} - 10{sup 10} W/cm{sup 2}, which will provide a guide to the study of momentum coupling of laser beams with matter.

  13. Reflection of nanosecond Nd:YAG laser pulses in ablation of metals.

    PubMed

    Benavides, O; Lebedeva, O; Golikov, V

    2011-10-24

    Hemispherical total reflectivity of copper, nickel, and tungsten in ablation by nanosecond Nd:YAG laser pulses in air of atmospheric pressure is experimentally studied as a function of laser fluence in the range of 0.1-100 J/cm(2). Our experiment shows that at laser fluences below the plasma formation threshold the reflectivity of mechanically polished metals remains virtually equal to the table room-temperature reflectivity values. The hemispherical total reflectivity of the studied metals begins to drop at a laser fluence of the plasma formation threshold. With increasing laser fluence above the plasma formation threshold the reflectivity sharply decreases to a low value and then remains unchanged with further increasing laser fluence. Computation of the surface temperature at the plasma formation threshold fluence reveals that its value is substantially below the melting point that indicates an important role of the surface nanostructural defects in the plasma formation on a real sample due to their enhanced heating caused by both plasmonic absorption and plasmonic nanofocusing.

  14. Harmonic generation by atomic and nanoparticle precursors in a ZnS laser ablation plasma

    NASA Astrophysics Data System (ADS)

    Oujja, M.; Lopez-Quintas, I.; Benítez-Cañete, A.; de Nalda, R.; Castillejo, M.

    2017-01-01

    Harmonic generation of a driving laser propagating across a laser ablation plasma serves for the diagnosis of multicomponent plumes. Here we study the contribution of atomic and nanoparticle precursors to the generation of coherent ultraviolet and vacuum ultraviolet light as low-order harmonics of the fundamental emission (1064 nm) of a Q-switched Nd:YAG laser in a nanosecond infrared ZnS laser ablation plasma. Odd harmonics from the 3rd up to the 9th order (118.2 nm) have been observed with distinct temporal and spatial characteristics which were determined by varying the delay between the ablation and driving nanosecond pulses and by spatially scanning the plasma with the focused driving beam propagating parallel to the target. At short distances from the target surface (≤1 mm), the harmonic intensity displays two temporal components peaked at around 250 ns and 10 μs. While the early component dies off quickly with increasing harmonic order and vanishes for the 9th order, the late component is notably intense for the 7th harmonic and is still clearly visible for the 9th. Spectral analysis of spontaneous plume emissions help to assign the origin of the two components. While the early plasma component is mainly constituted by neutral Zn atoms, the late component is mostly due to nanoparticles, which upon interaction with the driving laser are subject to breakup and ionization. With the aid of calculations of the phase matching integrals within the perturbative model of optical harmonic generation, these results illustrate how atom and nanoparticle populations, with differing temporal and spatial distributions within the ablation plasma, contribute to the nonlinear medium.

  15. Minimization of thermomechanical side effects in IR ablation by use of Q-switched double pulses

    NASA Astrophysics Data System (ADS)

    Vogel, Alfred; Schmidt, Peter; Flucke, Barbara

    2001-07-01

    Holmium laser pulses (λ= 2.1 m) are often used for medical laser applications inside the human body, because they can be transmitted through low-OH quartz fibers, and they are relatively well absorbed in water and biological tissues. However, large thermal damage zones were observed after application of free-running holmium laser pulses for arthroscopic surgery. The aim of our study is to reduce thermal damage without introducing additional mechanical damage and without impairing the hemostatic action of the laser radiation. For that purpose we use double pulses from a custom-made acousto-optically Q- switched thulium laser (λ = 2.0 μm) that can emit pulses with energies of up to 150 mJ. The penetration depth of the thulium laser radiation (170 μm) as well as the thermal damage zone are only half as large as that of the holmium laser. The use of Q-switched pulses creates stress confinement conditions leading to a more efficient ablation than with free running pulses. For a given ablation depth, the residual heat deposited in the tissue is therefore smaller than with free running pulses and, hence, also the thermal damage zone. This reduction of thermal damage is possible even though the free-running pulses already fulfil the condition for thermal confinement. The thermal damage zone was only 100 μm for the Q-switched thulium pulses but 200 μm for the free-running pulses. The degree of thermal damage was, in addition, much more severe for the free-running pulses. Q-switched pulses lead to an explosive ablation of the target material. In a liquid environment, this gives rise to the formation of cavitation effects, we release a pre-pulse with small energy (40 mJ) before each ablation pulse of up to 150 mJ. The pre-pulse produces a small cavity that is then filled by the ablation products of the main pulse. The ablation pulse is emitted about 100 μs after the pre-pulse when the bubble is maximally expanded. This way, no additional cavitation effects are induced

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

    NASA Astrophysics Data System (ADS)

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

    2007-02-01

    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.

  17. Heat-affected zone of metals ablated with femtosecond laser pulses

    NASA Astrophysics Data System (ADS)

    Hirayama, Yoichi; Obara, Minoru

    2003-07-01

    The melted area is found on the surface ablated by nanosecond and picosecond laser pulses. However, the heat effect is little on the ablated surface in the case of femtosecond laser due to non-thermal ablation process. Heat-affected zone of metallic bulk crystal ablated with femtosecond Ti:sapphire laser pulses is experimentally studied. As a result of XRD (X-ray diffraction) measurements, the XRD peak signal of the area ablated with Ti:sapphire laser becomes smaller than that of the crystalline metal sample. While the crystallinity of the metal sample is crystalline before the laser ablation, the crystallinity in the ablated area is partially changed into the amorphous form. Because the residual pulse energy that is not used for the ablation process remains, leading to the formation of thin layer of melt phase. The melt layer is abruptly cooled down not to be re-crystallized, but to transform into the amorphous form. It is evident that the area ablated with femtosecond laser is changed into the amorphous metal. Additionally XRD measurements and AR+ etching are performed alternately to measure the thickness of the amorphous layer. In the case of iron, the thickness is measured to be 1 μm approximately, therefore heat-affected zone is quite small.

  18. A multiphase model for pulsed ns-laser ablation of copper in an ambient gas

    SciTech Connect

    Autrique, D.; Chen, Z.; Alexiades, V.; Bogaerts, A.; Rethfeld, B.

    2012-07-30

    Laser ablation in an ambient gas is nowadays used in a growing number of applications, such as chemical analysis and pulsed laser deposition. Despite the many applications, the technique is still poorly understood. Therefore models describing the material evolution in time during short pulse laser irradiation can be helpful to unravel the puzzle and finally result in the optimization of the related applications. In the present work, a copper target is immersed in helium, initially set at atmospheric pressure and room temperature. Calculations are performed for a Gaussian-shaped laser pulse with a wavelength of 532 nm, full width at half maximum of 6 ns, and laser fluences up to 10 J/cm{sup 2}. In order to describe the transient behaviour in and above the copper target, hydrodynamic equations are solved. An internal energy method accounting for pressure relaxation is applied for the description of the target. In the plume domain a set of conservation equations is solved, assuming local thermodynamic equilibrium. Calculated crater depths and transmission profiles are compared with experimental results and similar trends are found. Our calculations indicate that for the laser fluence regime under study, explosive boiling could play a fundamental role in the plasma formation of metals under ns-pulsed laser irradiation.

  19. Approximate theory of highly absorbing polymer ablation by nanosecond laser pulses

    NASA Astrophysics Data System (ADS)

    Furzikov, N. P.

    1990-04-01

    Surface interference, nonlinearly saturated instability of laser-induced thermodestruction, and subsequent oscillation of absorption mode permit the description of analytical ablation thresholds and depths per pulse of polymers having high absorption at laser wavelengths, e.g., polyimide and poly(ethylene terephtalate). Inverse problem solution for polycarbonate and ablation invariant designing are also realized.

  20. Ablation of high-Z material dust grains in edge plasmas of magnetic fusion devices

    SciTech Connect

    Marenkov, E. D.; Krasheninnikov, S. I.

    2014-12-15

    The model, including shielding effects of high-Z dust grain ablation in tokamak edge plasma, is presented. In a contrast to shielding models developed for pellets ablation in a hot plasma core, this model deals with the dust grain ablation in relatively cold edge plasma. Using some simplifications, a closed set of equations determining the grain ablation rate Γ is derived and analyzed both analytically and numerically. The scaling law for Γ versus grain radius and ambient plasma parameters is obtained and confirmed by the results of numerical solutions. The results obtained are compared with both dust grain models containing no shielding effects and the pellet ablation models.

  1. Role of Wavelength and Pulse Structure in the Ablation of Tissue and Gelatin

    NASA Astrophysics Data System (ADS)

    Tribble, Jerri Ann

    The goal of these measurements has been to investigate the wavelength dependence of infrared laser induced tissue ablation. Fourier transform infrared spectroscopy of tissues guided the selection of wavelengths to which the Vanderbilt Free-Electron Laser (FEL) was tuned in order to study ablation rates and residual thermal damage in tissues including neural, ocular and dermal. Targeting FEL radiation to the amide II mode of proteins leads to tissue ablation characterized by minimal collateral damage while maintaining a substantial ablation rate. To account for these observations, a novel ablation mechanism has been proposed based on compromising tissue through resonant denaturation of structural proteins, which was tested using dynamic measurements on mechanical (ns) time scales of ablation of gelatin by FEL radiation. Simultaneous measurements of ejected material using a continuous HeNe probe beam tangential to the gelatin surface and the concomitant stress wave in the bulk of the sample provide an intriguing dynamical picture of the ablation event generated by infrared radiation of different wavelengths and different macropulse durations. By varying the macropulse duration from 60 to 200 ns with a broadband infrared Pockels cell, it is evident in both ejecta data and the stress transient data that the bulk of the ablation occurs after the end of the laser pulse. The most significant difference between ablation induced by different laser wavelengths, however, appears during the laser pulse, at the onset of ablation.

  2. The effect of polarization on ultrashort pulsed laser ablation of thin metal films

    NASA Astrophysics Data System (ADS)

    Venkatakrishnan, K.; Tan, B.; Stanley, P.; Sivakumar, N. R.

    2002-08-01

    Ultrashort pulse lasers have proven to have superior advantages over conventional continuous wave and long pulse lasers for ablation of thin metal films. Though several investigations have been carried out to understand the phenomena of ultrashort pulse laser machining, the effect of the beam polarization on ablation of thin metal films has been seldom investigated. In this article, we report our recent observations on how the shape of the machined feature and also the damage threshold of the material varies according to the polarization of the ultrashort pulse laser beam. Based on this we have explained how the polarization of the beam controls the laser cutting rate, kerf width, edge quality, and ablation depth of the ablated feature.

  3. Development of double-pulse lasers ablation system for generating gold ion source under applying an electric field

    NASA Astrophysics Data System (ADS)

    Khalil, A. A. I.

    2015-12-01

    Double-pulse lasers ablation (DPLA) technique was developed to generate gold (Au) ion source and produce high current under applying an electric potential in an argon ambient gas environment. Two Q-switched Nd:YAG lasers operating at 1064 and 266 nm wavelengths are combined in an unconventional orthogonal (crossed-beam) double-pulse configuration with 45° angle to focus on a gold target along with a spectrometer for spectral analysis of gold plasma. The properties of gold plasma produced under double-pulse lasers excitation were studied. The velocity distribution function (VDF) of the emitted plasma was studied using a dedicated Faraday-cup ion probe (FCIP) under argon gas discharge. The experimental parameters were optimized to attain the best signal to noise (S/N) ratio. The results depicted that the VDF and current signals depend on the discharge applied voltage, laser intensity, laser wavelength and ambient argon gas pressure. A seven-fold increases in the current signal by increasing the discharge applied voltage and ion velocity under applying double-pulse lasers field. The plasma parameters (electron temperature and density) were also studied and their dependence on the delay (times between the excitation laser pulse and the opening of camera shutter) was investigated as well. This study could provide significant reference data for the optimization and design of DPLA systems engaged in laser induced plasma deposition thin films and facing components diagnostics.

  4. Effect of nanosecond pulse laser ablation on the surface morphology of Zr-based metallic glass

    NASA Astrophysics Data System (ADS)

    Zhu, Yunhu; Fu, Jie; Zheng, Chao; Ji, Zhong

    2016-09-01

    In this study, we investigated the ripple patterns formation on the surface of Zr41.2Ti13.8Cu12.5Ni10Be22.5 (vit1) bulk metallic glass using a nanosecond pulse laser ablation in air with a wavelength of 1064 nm. The strong thermal ablation phenomenon could be observed on vit1 BMG surface at laser energy of 200 mJ as a result of the adhibition of confining overlay. Many periodic ripples had formed on the edge of the ablated area at laser energy of 400 mJ because of the high intensity pulsed laser beam. The underlying mechanism of the periodic ripples formation could be explained by the K-H hydrodynamic instability theory. It had been shown that laser ablation with 600 mJ and 200 pulses results in the formation of many micro-cracks on the ablated area. Further analysis showed that the spatial occupation of the laser ablated area and the spacing between two adjacent ripples increased as the laser energy and the number of incident laser pulses increasing. The surface ripples feature on the edge of ablated area became more obvious with increasing laser pulses, but it was not correlated closely with the laser energies variation.

  5. Plasma confinement to enhance the momentum coupling coefficient in ablative laser micro-propulsion: a novel approach

    NASA Astrophysics Data System (ADS)

    Ahmad, Muhammad Raza; Jamil, Yasir; Qaiser Zakaria, M.; Hussain, Tousif; Ahmad, Riaz

    2015-07-01

    We introduce for the first time the novel idea of manipulating the momentum coupling coefficient using plasma confinement and shock wave reflection from the cavity walls. The plasma was confined using cylindrical geometries of various cavity aspect ratios to manipulate the momentum coupling coefficient (C m ). The Nd: YAG laser (532 nm, 5 ns pulse duration) was focused on the ferrite sample surface to produce plasma in a region surrounded by cylindrical cavity walls. The multiple reflections of the shockwaves from the cavity walls confined the laser-induced plasma to the central region of the cavity that subsequently resulted in a significant enhancement of the momentum coupling coefficient values. The plasma shielding effect has also been observed for particular values of laser fluencies and cavity aspect ratios. Compared with the direct ablation, the confined ablation provides an effective way to obtain high C m values.

  6. A Langmuir Probe Diagnostic for Use in Inhomogeneous, Time-Varying Plasmas Produced by High-Energy Laser Ablation

    SciTech Connect

    Patterson, J R; Emig, J A; Fournier, K B; Jenkins, P P; Trautz, K M; Seiler, S W; Davis, J F

    2012-05-01

    Langmuir probes (LP) are used extensively to characterize plasma environments produced by radio frequency, pulsed plasma thrusters, and laser ablation. We discuss here the development of a LP diagnostic to examine high-density, high-temperature inhomogeneous plasmas such as those that can be created at the University of Rochester's Laboratory for Laser Energetics OMEGA facility. We have configured our diagnostic to examine the velocity of the plasma expanding from the target. We observe velocities of approximately 16-17 cm/{micro}s, with individual LP currents displaying complex structures, perhaps due to the multiple atomic species and ionization states that exist.

  7. Laser ablation of single-crystalline silicon by radiation of pulsed frequency-selective fiber laser

    NASA Astrophysics Data System (ADS)

    Veiko, V. P.; Skvortsov, A. M.; Huynh, C. T.; Petrov, A. A.

    2015-07-01

    We have studied the process of destruction of the surface of a single-crystalline silicon wafer scanned by the beam of a pulsed ytterbium-doped fiber laser radiation with a wavelength of λ = 1062 nm. It is established that the laser ablation can proceed without melting of silicon and the formation of a plasma plume. Under certain parameters of the process (radiation power, beam scan velocity, and beam overlap density), pronounced oxidation of silicon microparticles with the formation of a characteristic loose layer of fine powdered silicon dioxide has been observed for the first time. The range of lasing and beam scanning regimes in which the growth of SiO2 layer takes place is determined.

  8. Laser ablated copper plasmas in liquid and gas ambient

    SciTech Connect

    Kumar, Bhupesh; Thareja, Raj K.

    2013-05-15

    The dynamics of copper ablated plasma plumes generated using laser ablation of copper targets in both liquid (de-ionized water) and gas (air) ambients is reported. Using time and space resolved visible emission spectroscopy (450-650 nm), the plasma plumes parameters are investigated. The electron density (n{sub e}) determined using Stark broadening of the Cu I (3d{sup 10}4d{sup 1} {sup 2}D{sub 3/2}-3d{sup 10}4p{sup 1} {sup 2}P{sub 3/2} at 521.8 nm) line is estimated and compared for both plasma plumes. The electron temperature (T{sub e}) was estimated using the relative line emission intensities of the neutral copper transitions. Field emission scanning electron microscopy and energy dispersive x-ray spectral analysis of the ablated copper surface indicated abundance of spherical nanoparticles in liquid while those in air are amalgamates of irregular shapes. The nanoparticles suspended in the confining liquid form aggregates and exhibit a surface plasmon resonance at ∼590 nm.

  9. Influence of Surface Radius Curvature on Laser Plasma Propulsion with Ablation Water Propellant

    NASA Astrophysics Data System (ADS)

    Liang, Tian; Zheng, Zhiyuan; Zhang, Siqi; Tang, Weichong; Xiao, Ke; Liang, Wenfei; Gao, Lu; Gao, Hua

    2016-10-01

    The surface shape of liquid water is well controlled during nanosecond pulse laser ablation plasma propulsion. In this study, we measured the effect of the shape on the coupling coefficient and the specific impulse. We found that the coupling coefficient and specific impulse could be optimized by varying the surface convexity. Based on the analysis of the surface radius curvature, we demonstrate that the convex surface changes the laser focal positions to achieve high efficiency. supported by National Natural Science Foundation of China (No. 10905049) and Fundamental Research Funds for the Central Universities of China (Nos. 53200859165, 2562010050)

  10. Inductively Coupled Plasma: Fundamental Particle Investigations with Laser Ablation and Applications in Magnetic Sector Mass Spectrometry

    SciTech Connect

    Saetveit, Nathan Joe

    2008-01-01

    Particle size effects and elemental fractionation in laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) are investigated with nanosecond and femtosecond laser ablation, differential mobility analysis, and magnetic sector ICP-MS. Laser pulse width was found to have a significant influence on the LA particle size distribution and the elemental composition of the aerosol and thus fractionation. Emission from individual particles from solution nebulization, glass, and a pressed powder pellet are observed with high speed digital photography. The presence of intact particles in an ICP is shown to be a likely source of fractionation. A technique for the online detection of stimulated elemental release from neural tissue using magnetic sector ICP-MS is described. Detection limits of 1 μg L-1 or better were found for P, Mn, Fe, Cu, and Zn in a 60 μL injection in a physiological saline matrix.

  11. Modeling of beam-target interaction during pulsed electron beam ablation of graphite: Case of melting

    NASA Astrophysics Data System (ADS)

    Ali, Muddassir; Henda, Redhouane

    2017-02-01

    A one-dimensional thermal model based on a two-stage heat conduction equation is employed to investigate the ablation of graphite target during nanosecond pulsed electron beam ablation. This comprehensive model accounts for the complex physical phenomena comprised of target heating, melting and vaporization upon irradiation with a polyenergetic electron beam. Melting and vaporization effects induced during ablation are taken into account by introducing moving phase boundaries. Phase transition induced during ablation is considered through the temperature dependent thermodynamic properties of graphite. The effect of electron beam efficiency, power density, and accelerating voltage on ablation is analyzed. For an electron beam operating at an accelerating voltage of 15 kV and efficiency of 0.6, the model findings show that the target surface temperature can reach up to 7500 K at the end of the pulse. The surface begins to melt within 25 ns from the pulse start. For the same process conditions, the estimated ablation depth and ablated mass per unit area are about 0.60 μm and 1.05 μg/mm2, respectively. Model results indicate that ablation takes place primarily in the regime of normal vaporization from the surface. The results obtained at an accelerating voltage of 15 kV and efficiency factor of 0.6 are satisfactorily in good accordance with available experimental data in the literature.

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

    SciTech Connect

    Tong Huifeng; Yuan Hong; Tang Zhiping

    2013-01-28

    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.

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

    NASA Astrophysics Data System (ADS)

    Tong, Huifeng; Yuan, Hong; Tang, Zhiping

    2013-01-01

    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.

  14. Plasma Emission Spectra of Opuntia Nopalea Obtained with Microsecond Laser Pulses

    NASA Astrophysics Data System (ADS)

    Ponce, L.; Flores, T.; Arronte, A.; Flores, A.

    2008-04-01

    Laser-induced Plasma Spectroscopy was performed during the spines ablation of Opuntia by using Nd:YAG microsecond laser pulses. The results show strong absorption in Glochids that causes the intense electronic noise on the spectra. This process is consider suitable for practical elimination of spines in alimentary products like opuntia.

  15. Plasma Emission Spectra of Opuntia Nopalea Obtained with Microsecond Laser Pulses

    SciTech Connect

    Ponce, L.; Flores, T.; Arronte, A.; Flores, A.

    2008-04-15

    Laser-induced Plasma Spectroscopy was performed during the spines ablation of Opuntia by using Nd:YAG microsecond laser pulses. The results show strong absorption in Glochids that causes the intense electronic noise on the spectra. This process is consider suitable for practical elimination of spines in alimentary products like opuntia.

  16. Responses of polymers to laser plasma EUV light beyond ablation threshold and micromachining

    NASA Astrophysics Data System (ADS)

    Makimura, Tetsuya; Torii, Shuichi; Okazaki, Kota; Nakamura, Daisuke; Takahashi, Akihiko; Niino, Hiroyuki; Okada, Tatsuo; Murakami, Kouichi

    2011-06-01

    We have investigated responses of PDMS, PMMA and acrylic block copolymers (BCP) to EUV light from laserproduced plasma beyond ablation thresholds and micromachining. We generated wide band EUV light around 100 eV by irradiation of Ta targets with Nd:YAG laser light. In addition, narrow band EUV light at 11 and 13 nm were generated by irradiation of solid Xe and Sn targets, respectively, with pulsed CO2 laser light. The generated EUV light was condensed onto samples, using an ellipsoidal mirror. The EUV light was incident through windows of contact masks on the samples. We found that through-holes with a diameter of 1 μm can be fabricated in PDMS sheets with thicknesses of 10 μm. PDMS sheets are ablated if they are irradiated with EUV light beyond a threshold power density, while PDMS surfaces were modified by irradiation with the narrow band EUV light at lower power densities. Effective ablation of PMMA sheets can be applied to a LIGA-like process for fabricating micro-structures of metals using the practical apparatus. Furthermore, BCP sheets were ablated to have micro-structures. Thus, we have developed a practical technique for microma chining of PMMA, PDMS and BCP sheets in a micrometer scale.

  17. Numerical study of the thermal ablation of wet solids by ultrashort laser pulses

    SciTech Connect

    Perez, Danny; Beland, Laurent Karim; Deryng, Delphine; Lewis, Laurent J.; Meunier, Michel

    2008-01-01

    The ablation by ultrashort laser pulses at relatively low fluences (i.e., in the thermal regime) of solids wetted by a thin liquid film is studied using a generic numerical model. In comparison with dry targets, the liquid is found to significantly affect ablation by confining the solid and slowing down the expansion of the laser-heated material. These factors affect the relative efficiency of the various ablation mechanisms, leading, in particular, to the complete inhibition of phase explosion at lower fluences, a reduced ablation yield, and significant changes in the composition of the plume. As a consequence, at fluences above the ablation threshold, the size of the ejected nanoclusters is lower in presence of the liquid. Our results provide a qualitative understanding of the effect of wetting layers on the ablation process.

  18. Experimental and Computational Studies of High Energy Density Plasma Streams Ablated from Fine Wires

    SciTech Connect

    Greenly, John B.; Seyler, Charles

    2014-03-30

    Experimental and computational studies of high energy density plasma streams ablated from fine wires. Laboratory of Plasma Studies, School of Electrical and Computer Engineering, Cornell University. Principal Investigators: Dr. John B. Greenly and Dr. Charles E. Seyler. This report summarizes progress during the final year of this project to study the physics of high energy density (HED) plasma streams of 10^17-10^20/cm3 density and high velocity (~100-500 km/s). Such streams are produced from 5-250 micrometer diameter wires heated and ionized by a 1 MA, 250 ns current pulse on the COBRA pulsed power facility at Cornell University. Plasma is ablated from the wires and is driven away to high velocity by unbalanced JxB force. A wire, or an array of wires, can persist as an essentially stationary, continuous source of this streaming plasma for >200 ns, even with driving magnetic fields of many Tesla and peak current densities in the plasma of many MA/cm2. At the heart of the ablation stream generation is the continuous transport of mass from the relatively cold, near-solid-density wire "core" into current-carrying plasma within 1 mm of the wire, followed by the magnetic acceleration of that plasma and its trapped flux to form a directed stream. In the first two years of this program, an advancing understanding of ablation physics led to the discovery of several novel wire ablation experimental regimes. In the final year, one of these new HED plasma regimes has been studied in quantitative detail. This regime studies highly reproducible magnetic reconnection in strongly radiating plasma with supersonic and superalfvenic flow, and shock structures in the outflow. The key discovery is that very heavy wires, e.g. 250 micrometer diameter Al or 150 micrometer Cu, behave in a qualitatively different way than the lighter wires typically used in wire-array Z-pinches. Such wires can be configured to produce a static magnetic X-point null geometry that stores magnetic and

  19. Stark broadening measurements in plasmas produced by laser ablation of hydrogen containing compounds

    NASA Astrophysics Data System (ADS)

    Burger, Miloš; Hermann, Jörg

    2016-08-01

    We present a method for the measurement of Stark broadening parameters of atomic and ionic spectral lines based on laser ablation of hydrogen containing compounds. Therefore, plume emission spectra, recorded with an echelle spectrometer coupled to a gated detector, were compared to the spectral radiance of a plasma in local thermal equilibrium. Producing material ablation with ultraviolet nanosecond laser pulses in argon at near atmospheric pressure, the recordings take advantage of the spatially uniform distributions of electron density and temperature within the ablated vapor. By changing the delay between laser pulse and detector gate, the electron density could be varied by more than two orders of magnitude while the temperature was altered in the range from 6,000 to 14,000 K. The Stark broadening parameters of transitions were derived from their simultaneous observation with the hydrogen Balmer alpha line. In addition, assuming a linear increase of Stark widths and shifts with electron density for non-hydrogenic lines, our measurements indicate a change of the Stark broadening-dependence of Hα over the considered electron density range. The presented results obtained for hydrated calcium sulfate (CaSO4ṡ2H2O) can be extended to any kind of hydrogen containing compounds.

  20. Designing solid propellant pulsed plasma thrusters

    NASA Technical Reports Server (NTRS)

    Guman, W. J.

    1975-01-01

    In this paper fundamental definitions and a few semiempirical correlations of experimental data of solid propellant pulsed plasma thrusters are used to illustrate the design analysis of such propulsion systems. The design analysis presented facilitates the design of a thruster to meet a specific performance level and provides the spacecraft designer with a methodology to select a pulsed plasma propulsion system to meet his mission requirements.

  1. INFN - P.L.A.I.A. PROJECT (Plasma Laser Ablation for Ion Acceleration)

    NASA Astrophysics Data System (ADS)

    Torrisi, L.; Gammino, S.; Andò, L.; Ciavola, G.; Mezzasalma, A. M.; Nassisi, V.; Wolowski, J.; Parys, P.; Laska, L.; Krasa, J.; Boody, F. P.

    2004-10-01

    The INFN-Gr.V PLAIA (Plasma Laser Ablation for Ion Acceleration) Project is presented and discussed. The project is developing at LNS of Catania, Messina and Lecce Laboratories as Italian centers of research and it see as European partners the PALS Laboratory of Prague and the group of researchers coordinated by Prof. Wolowsky from IPPLM of Warsaw. PLAIA concerns the study of pulsed plasma produced by pulsed lasers and some special applications of this physics to the new generation of ion sources. Different lasers are employed at LNS of Catania, LEA of Lecce and PALS of Prague. Their fluences range from about 10 J/cm2 for the excimer lasers of LEA up to about 100 kj/cm2 for the iodine laser of PALS. The Nd:Yag laser of LNS, operating at 1064 nm, 9 ns pulse width and 900 mJ maximum pulse energy shows peculiar properties, specially if it is employed at 30 Hz repetition rate, at which it may produce stabile current of ions ejected from a dense plasma. Such laser has the optimum compromise between power density and repetition rate to be used as injector of ions in ECR sources or as source of a new generation of ion implanters which can be employed to accelerate multi-energetic ion beams useful to treat the surface of different materials. Results and projects are discussed in detail.

  2. Single and double long pulse laser ablation of aluminum induced in air and water ambient

    NASA Astrophysics Data System (ADS)

    Akbari Jafarabadi, Marzieh; Mahdieh, Mohammad Hossein

    2017-02-01

    In this paper, single pulse and double pulse laser ablation of an aluminum target in two interaction ambient was investigated experimentally. The interaction was performed by nanosecond Nd:YAG laser beam in air and four depths (i.e. 9, 13, 17, and 21 mm) of distilled water ambient. The irradiation was carried out in single and collinear double pulse configurations in both air and liquid ambient. Crater geometry (depth and diameter) was measured by an optical microscope. The results indicated that the crater geometry strongly depends on both single pulse and double pulse configurations and interaction ambient. In single pulse regime, the crater diameter is higher for all water depths compared to that of air. However, the crater depth, depend on water depth, is higher or lower than the crater depth in air. In double pulse laser ablation, there are greater values for both crater diameters and crater depths in the water.

  3. Dynamic absorption and scattering of water and hydrogel during high-repetition-rate (>100 MHz) burst-mode ultrafast-pulse laser ablation

    PubMed Central

    Qian, Zuoming; Covarrubias, Andrés; Grindal, Alexander W.; Akens, Margarete K.; Lilge, Lothar; Marjoribanks, Robin S.

    2016-01-01

    High-repetition-rate burst-mode ultrafast-laser ablation and disruption of biological tissues depends on interaction of each pulse with the sample, but under those particular conditions which persist from previous pulses. This work characterizes and compares the dynamics of absorption and scattering of a 133-MHz repetition-rate, burst-mode ultrafast-pulse laser, in agar hydrogel targets and distilled water. The differences in energy partition are quantified, pulse-by-pulse, using a time-resolving integrating-sphere-based device. These measurements reveal that high-repetition-rate burst-mode ultrafast-laser ablation is a highly dynamical process affected by the persistence of ionization, dissipation of plasma plume, neutral material flow, tissue tensile strength, and the hydrodynamic oscillation of cavitation bubbles. PMID:27375948

  4. Pulsed laser ablation of complex oxides: The role of congruent ablation and preferential scattering for the film stoichiometry

    SciTech Connect

    Wicklein, S.; Koehl, A.; Dittmann, R.; Sambri, A.; Amoruso, S.; Wang, X.; Bruzzese, R.

    2012-09-24

    By combining structural and chemical thin film analysis with detailed plume diagnostics and modeling of the laser plume dynamics, we are able to elucidate the different physical mechanisms determining the stoichiometry of the complex oxides model material SrTiO{sub 3} during pulsed laser deposition. Deviations between thin film and target stoichiometry are basically a result of two effects, namely, incongruent ablation and preferential scattering of lighter ablated species during their motion towards the substrate in the O{sub 2} background gas. On the one hand, a progressive preferential ablation of the Ti species with increasing laser fluence leads to a regime of Ti-rich thin film growth at larger fluences. On the other hand, in the low laser fluence regime, a more effective scattering of the lighter Ti plume species results in Sr rich films.

  5. Influence of effective number of pulses on the morphological structure of teeth and bovine femur after femtosecond laser ablation.

    PubMed

    Nicolodelli, Gustavo; Lizarelli, Rosane de Fátima Zanirato; Bagnato, Vanderlei Salvador

    2012-04-01

    Femtosecond lasers have been widely used in laser surgery as an instrument for contact-free tissue removal of hard dental, restorative materials, and osseous tissues, complementing conventional drilling or cutting tools. In order to obtain a laser system that provides an ablation efficiency comparable to mechanical instruments, the laser pulse rate must be maximal without causing thermal damage. The aim of this study was to compare the different morphological characteristics of the hard tissue after exposure to lasers operating in the femtosecond pulse regime. Two different kinds of samples were irradiated: dentin from human extracted teeth and bovine femur samples. Different procedures were applied, while paying special care to preserving the structures. The incubation factor S was calculated to be 0.788±0.004 for the bovine femur bone. These results indicate that the incubation effect is still substantial during the femtosecond laser ablation of hard tissues. The plasma-induced ablation has reduced side effects, i.e., we observe less thermal and mechanical damage when using a superficial femtosecond laser irradiation close to the threshold conditions. In the femtosecond regime, the morphology characteristics of the cavity were strongly influenced by the change of the effective number of pulses.

  6. Myocardial tissue ablation by single high-energy laser pulses for ELR and TMR

    NASA Astrophysics Data System (ADS)

    Theisen, Dirk; Brinkmann, Ralf; Stubbe, Hans-Martin; Birngruber, Reginald

    1999-02-01

    The objective of this study is to compare the ablation sites induced by two different laser and application systems for myocardial laser revascularization. One system used was an 800 W CO2 laser, which is clinically established for transmyocardial laser revascularization (TMR). The second system was a self-designed Holmium laser emitting single high energy pulses for the minimal invasive approach of endocardial laser revascularization (ELR), whereby the laser light is transmitted via optical fiber into the left ventricle to ablate the myocardial channels from the inside. The laser energy was applied to Polyacrylamide (PAA) as transparent tissue phantom and in water as blood phantom. The ablation dynamics were investigated by high speed flash photography recording a picture series of a single event. Reperfused ex- vivo porcine hearts were treated to quantify differences in the thermal-mechanical damage ranges by polarization light microscopy. Ablation dynamics in water revealed oscillatory changes of the axial length of the steam bubbles between 3 mm and 12 mm during the CO2 laser pulse. For the Holmium laser pulse a maximal axial and lateral length of 5 mm was observed. The lateral dimensions of the bubbles were maximal 1 mm with the CO2- and 3.5 mm with the Holmium laser system. In PAA bubbles also collapse during the laser pulse which affects the size of the ablated channels. Using 12 J Holmium laser pulses for ablation of PAA, channel depths around 7 mm were found. Single Holmium laser pulses demonstrate ablations comparable in size and thermal- mechanical collateral damage to those achieved with the standard CO2 laser. The results are very encouraging for single pulse ELR and demonstrate the potential of a catheter based minimal invasive procedure for laser heart reperfusion.

  7. Electrosensitization assists cell ablation by nanosecond pulsed electric field in 3D cultures

    PubMed Central

    Muratori, Claudia; Pakhomov, Andrei G.; Xiao, Shu; Pakhomova, Olga N.

    2016-01-01

    Previous studies reported a delayed increase of sensitivity to electroporation (termed “electrosensitization”) in mammalian cells that had been subjected to electroporation. Electrosensitization facilitated membrane permeabilization and reduced survival in cell suspensions when the electric pulse treatments were split in fractions. The present study was aimed to visualize the effect of sensitization and establish its utility for cell ablation. We used KLN 205 squamous carcinoma cells embedded in an agarose gel and cell spheroids in Matrigel. A local ablation was created by a train of 200 to 600 of 300-ns pulses (50 Hz, 300–600 V) delivered by a two-needle probe with 1-mm inter-electrode distance. In order to facilitate ablation by engaging electrosensitization, the train was split in two identical fractions applied with a 2- to 480-s interval. At 400–600 V (2.9–4.3 kV/cm), the split-dose treatments increased the ablation volume and cell death up to 2–3-fold compared to single-train treatments. Under the conditions tested, the maximum enhancement of ablation was achieved when two fractions were separated by 100 s. The results suggest that engaging electrosensitization may assist in vivo cancer ablation by reducing the voltage or number of pulses required, or by enabling larger inter-electrode distances without losing the ablation efficiency. PMID:26987779

  8. Femtosecond-pulse laser ablation of dental hydroxyapatite and single-crystalline fluoroapatite

    NASA Astrophysics Data System (ADS)

    Krüger, J.; Kautek, W.; Newesely, H.

    Laser microdrilling of healthy human enamel and dentine using 300 fs pulses at a wavelength of 615 nm and 3 Hz repetition rate leads to an enhanced structuring quality in comparison with nanosecond-laser results. Microcracking and damage to neighboring tissue can be reduced. Ablation threshold fluences for 100 laser pulses of 0.3 Jcm-2 (human dentine), 0.6 Jcm-2 (human enamel) and 0.8 Jcm-2 (single crystalline fluoroapatite) could be determined. Ablation depths per pulse below 1 μm were observed.

  9. Modeling of plasma distortions by laser-induced ablation spectroscopy (LIAS) and implications for the interpretation of LIAS measurements

    NASA Astrophysics Data System (ADS)

    Tokar, M. Z.; Gierse, N.; Philipps, V.; Samm, U.

    2015-09-01

    For the interpretation of the line radiation observed from laser induced ablation spectroscopy (LIAS) such parameters as the density and temperature of electrons within very compact clouds of atoms and singly charged ions of ablated material have to be known. Compared to the local plasma conditions prior to the laser pulse, these can be strongly changed during LIAS since new electrons are generated by the ionisation of particles ejected from the irradiated target. Because of their transience and spatial inhomogeneity it is technically difficult to measure disturbances induced in the plasma by LIAS. To overcome this uncertainty a numerical model has been elaborated, providing a self-consistent description for the spreading of ablated particles and accompanying modifications in the plasma. The results of calculations for LIAS performed on carbon-containing targets in Ohmic and additionally heated discharges in the tokamak TEXTOR are presented. Due to the increase in the electron density the ‘ionisation per photon’ ratio, S/XB factor, is significantly enhanced compared to unperturbed plasma conditions. The impact of the amount of material ablated and of the plasma conditions before LIAS on the level of the S/XB-enhancement is investigated.

  10. Transient Shock Formation of Pulsed Electrothermal Plasma Discharge Confined in an Extended Bore

    NASA Astrophysics Data System (ADS)

    Kim, Kyoungjin; Kwak, Ho Sang; Park, Joong-Youn

    An electrothermal gun possesses a great potential to be an efficient source of pulsed plasma discharge for nanomaterials production or thermal plasma spray coatings. A plasma discharge by intense pulsed power is numerically studied utilizing time-dependent gas dynamics equations which are solved by FCT (flux-corrected transport) algorithm in two-dimensional domain of the interior capillary bore region and the external region of extended bore. Plasma conditions at the bore exit, mass ablation of polycarbonate bore wall, and degree of ionization are determined at different levels of transient arc current profile. As a way to controlling the plasma discharge, the extended bore at the capillary exit is considered and the flow pattern of pulsed plasma discharge in the extended bore exhibit complex shock structure from slightly to highly underexpanded jet depending on the level of arc current profiles. Flow instability of oscillating Mach disk is found at higher level of arc current profile cases.

  11. The effects of pulse duration on ablation pressure driven by laser radiation

    SciTech Connect

    Zhou, Lei; Li, Xiao-Ya Zhu, Wen-Jun; Wang, Jia-Xiang; Tang, Chang-Jian

    2015-03-28

    The effects of laser pulse duration on the ablation pressure induced by laser radiation are investigated using Al target. Numerical simulation results using one dimensional radiation hydro code for laser intensities from 5×10{sup 12}W/cm{sup 2} to 5×10{sup 13}W/cm{sup 2} and pulse durations from 0.5 ns to 20 ns are presented. These results suggest that the laser intensity scaling law of ablation pressure differs for different pulse durations. And the theoretical analysis shows that the effects of laser pulse duration on ablation pressure are mainly caused by two regimes: the unsteady-state flow and the radiative energy loss to vacuum.

  12. Hyperthermal Pulsed-Laser Ablation Beams for Film Deposition and Surface Microstructural Engineering

    SciTech Connect

    Lowndes, D.H.

    1999-11-08

    This paper presents an overview of pulsed-laser ablation for film deposition and surface microstructure formation. By changing the ambient gas pressure from high vacuum to several Torr (several hundred Pa) and by selecting the pulsed-laser wavelength, the kinetic energy of ablated atoms/ions can be varied from several hundred eV down to {approximately}0.1 eV and films ranging from superhard to nanocrystalline may be deposited. Furthermore, cumulative (multi-pulse) irradiation of a semiconductor surface (e.g. silicon) in an oxidizing gas (0{sub 2}, SF{sub 6}) et atmospheric pressure can produce dense, self-organized arrays of high-aspect-ratio microcolumns or microcones. Thus, a wide range of materials synthesis and processing opportunities result from the hyperthermal flux and reactive growth conditions provided by pulsed-laser ablation.

  13. Plasma in a Pulsed Discharge Environment

    NASA Technical Reports Server (NTRS)

    Remy, J.; Bienier, L.; Salama, F.

    2005-01-01

    The plasma generated in a pulsed slit discharge nozzle is used to form molecular ions in an astrophysically relevant environment. The plasma has been characterized as a glow discharge in the abnormal regime. Laboratory studies help understand the formation processes of polycyclic aromatic hydrocarbon (PAH) ions that are thought to be the source of the ubiquitous unidentified infrared bands.

  14. Rapid ablation of dental hard tissue using promoter-assisted pulsed Nd:YAG laser

    NASA Astrophysics Data System (ADS)

    Frederickson, Christopher J.; Lu, Quiang; Hayes, Donald J.; Wallace, David B.; Grove, Michael E.; Bell, Brent A.; Motamedi, Massoud; Rastegar, Sohi; Wright, C. G.; Arcoria, Charles J.

    1997-05-01

    Nd:YAG lasers have been used previously for selective removal of various material from teeth. To permit ablation of healthy enamel with the Nd:YAG laser, we have adopted a strategy in which micro-drops of photoabsorptive 'promoters' are placed on the enamel to enhance absorption of individual laser pulses. Ink-jet technology dispenses the micro-drops with micron- and millisecond-scale precision. Various promoters using drug and cosmetic dyes, indocyanine green, or carbon-black pigments have been studied. Typical ablation parameters are 1.064 micrometers ; 20-180 mJ per pulse; 100 microsecond(s) ; 10-30 pulses/sec; 0.2-2.0 nl drops. Recent results from the program include: (1) For a variety of promoters, a monotonic relationship obtains between absorption coefficient at 1.064 micrometers and the efficiency of ablation of enamel. (2) With different promoter volumes, the efficiency of ablation rises, plateaus, then falls with increasing volume. (3) At drilling rates of 30 pulses/sec, ablation efficiency approaches rates of 0.1 mm3/sec. LM and SEM observations show a glassy 'pebbled' crater surface indicative of hydroxyapatite that has cooled, condensed, and solidified on the crater walls. Together these results favor the view that a micro-drop promoter-assisted Nd:YAG drill can five clinically useful ablations hard dental tissue.

  15. Relativistic laser pulse compression in magnetized plasmas

    SciTech Connect

    Liang, Yun; Sang, Hai-Bo Wan, Feng; Lv, Chong; Xie, Bai-Song

    2015-07-15

    The self-compression of a weak relativistic Gaussian laser pulse propagating in a magnetized plasma is investigated. The nonlinear Schrödinger equation, which describes the laser pulse amplitude evolution, is deduced and solved numerically. The pulse compression is observed in the cases of both left- and right-hand circular polarized lasers. It is found that the compressed velocity is increased for the left-hand circular polarized laser fields, while decreased for the right-hand ones, which is reinforced as the enhancement of the external magnetic field. We find a 100 fs left-hand circular polarized laser pulse is compressed in a magnetized (1757 T) plasma medium by more than ten times. The results in this paper indicate the possibility of generating particularly intense and short pulses.

  16. Laser ablation of skull tissue using transverse excited 9.6-μm CO2 lasers with pulse durations of 1-100 μs

    NASA Astrophysics Data System (ADS)

    Fried, Nathaniel M.; Fried, Daniel

    2000-06-01

    Craniotomy using a drill and saw frequently results in fragmentation of the skull plate. Lasers have the potential to remove the skull plate intact. TE CO2 lasers operating at the peak absorption wavelength of bone ((lambda) equals 9.6 micrometer) and with pulse durations of 5 - 10 microseconds, approximately the thermal relaxation time in hard tissue, produced high ablation rates and minimal peripheral thermal damage. Both thick (2 mm) and thin (250 micrometer) bovine skull samples were perforated and the ablation rates calculated. Results were compared with Q-switched and free- running Er:YAG lasers ((lambda) equals 2.94 micrometer, (tau) p equals 150 ns and 150 microseconds). The CO2 laser perforated thick sections at ablation rates of 10 - 15 micrometer per pulse and fluences of approximately 6 J/cm2. There was no discernible thermal damage and no need for water irrigation during ablation. Pulse durations >= 20 microseconds resulted in significant tissue charring which increased with the pulse duration. Although the Er:YAG laser produced ablation rates of approximately 100 micrometer per pulse, fluences > 30 J/cm2 were required to perforate thick samples, and thermal damage measured 25 - 40 micrometer. In summary, the novel 5 - 10 microsecond pulse length of the TE CO2 laser is long enough to avoid a marked reduction in the ablation rate due to plasma formation and short enough to avoid peripheral thermal damage through thermal diffusion during the laser pulse. Further studies with the TE CO2 laser are warranted for potential clinical application craniotomy procedures.

  17. Simulation of femtosecond pulsed laser ablation of metals

    NASA Astrophysics Data System (ADS)

    Davydov, R. V.; Antonov, V. I.

    2016-11-01

    In this paper a mathematical model for femtosecond laser ablation of metals is proposed, based on standard two-temperature model connected with 1D hydrodynamic equations. Wide-range equation of state has been developed. The simulation results are compared with experimental data for aluminium and copper. A good agreement for both metals with numerical results and experiment shows that this model can be employed for choosing laser parameters to better accuracy in nanoparticles production by ablation of metals.

  18. Laser ablated zirconium plasma: A source of neutral zirconium

    SciTech Connect

    Yadav, Dheerendra; Thareja, Raj K.

    2010-10-15

    The authors report spectroscopic investigations of laser produced zirconium (Zr) plasma at moderate laser fluence. At low laser fluence the neutral zirconium species are observed to dominate over the higher species of zirconium. Laser induced fluorescence technique is used to study the velocity distribution of ground state neutral zirconium species. Two-dimensional time-resolved density distributions of ground state zirconium is mapped using planner laser induced fluorescence imaging and total ablated mass of neutral zirconium atoms is estimated. Temporal and spatial evolutions of electron density and temperature are discussed by measuring Stark broadened profile and ratio of intensity of emission lines, respectively.

  19. Atomistic investigation of ablation of amorphous polystyrene under femtosecond laser pulse

    NASA Astrophysics Data System (ADS)

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

    2015-03-01

    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.

  20. Investigations of the damage mechanisms during ultrashort pulse laser ablation of dental tissue

    NASA Astrophysics Data System (ADS)

    Domke, Matthias; Wick, Sebastian; Laible, Maike; Rapp, Stephan; Kuznetsova, Julia; Homann, Christian; Huber, Heinz P.; Sroka, Ronald

    2015-07-01

    Several investigations of dental tissue ablation with ultrashort pulsed lasers suggest that these lasers enable precise and selective material removal and reduce the formation of micro cracks and thermal effects, when compared to ns-pulses. In this study, two damage mechanisms are presented occurring during ablation of dentin using a laser emitting pulses of a duration of 380 fs at a wavelength of 1040 nm. First, it was found that nano cracks appear around the craters after single fs-pulse ablation. These cracks are directed to the crater and cross the dentinal tubules. Transient investigation of the single fs-pulse ablation process by pump-probe microscopy suggest that the driving mechanism could be a pressure wave that is released after stress confinement. Second, squared ablation holes were created by moving the laser focus at scan speeds between 0.5 mm/s and 2.0 m/s and fluences up to 14 J/cm2. It was found that deep cracks appear at the edges of the squared holes, if the scan speed is about 0.5 m/s. The fluence has only a minor impact on the crack formation. The crack propagation was investigated in the depth using x-ray micro tomography and optical coherence tomography. It was found that these cracks appear in the depth down to the dental pulp. These findings suggest that fast scanning of the laser beam is the key for damage free processing using ultrashort pulse lasers. Then, ablation rates of about 2.5 - 3.5 mm3/min/W can be achieved in dentine with pulse durations of 380 fs.

  1. Heat accumulation in ultra-short pulsed scanning laser ablation of metals.

    PubMed

    Bauer, Franziska; Michalowski, Andreas; Kiedrowski, Thomas; Nolte, Stefan

    2015-01-26

    High average laser powers can have a serious adverse impact on the ablation quality in ultra-short pulsed laser material processing of metals. With respect to the scanning speed, a sharp transition between a smooth, reflective and an uneven, dark ablated surface is observed. Investigating the influence of the sample temperature, it is experimentally shown that this effect stems from heat accumulation. In a numerical heat flow simulation, the critical scanning speed indicating the change in ablation quality is determined in good agreement with the experimental data.

  2. Spectroscopic study of emission coal mineral plasma produced by laser ablation

    NASA Astrophysics Data System (ADS)

    Vera, L. P.; Pérez, J. A.; Riascos, H.

    2014-05-01

    Spectroscopic analysis of plasma produced by laser ablation of coal samples using 1064 nm radiation pulses from a Q-switched Nd:YAG on different target under air ambient, was performed. The emission of molecular band systems such as C2 Swan System (d3Πg→a3Πu), the First Negative System N2 (Band head at 501,53 nm) and emission lines of the C I, C II, were investigated using the optical emission spectroscopy technique. The C2 molecular spectra (Swan band) were analyzed to determine vibrational temperature (0,62 eV); the density and electron temperature of the plasma have been evaluated using Stark broadening and the intensity of the nitrogen emission lines N II, the found values of 1,2 eV and 2,2 x1018 cm-3 respectively.

  3. Determination of ablation threshold for composite resins and amalgam irradiated with femtosecond laser pulses

    NASA Astrophysics Data System (ADS)

    Freitas, A. Z.; Freschi, L. R.; Samad, R. E.; Zezell, D. M.; Gouw-Soares, S. C.; Vieira, N. D., Jr.

    2010-03-01

    The use of laser for caries removal and cavity preparation is already a reality in the dental clinic. The objective of the present study was to consider the viability of ultrashort laser pulses for restorative material selective removal, by determining the ablation threshold fluence for composite resins and amalgam irradiated with femtosecond laser pulses. Lasers pulses centered at 830 nm with 50 fs of duration and 1 kHz of repetition rate, with energies in the range of 300 to 770 μJ were used to irradiate the samples. The samples were irradiated using two different geometrical methods for ablation threshold fluence determinations and the volume ablation was measured by optical coherence tomography. The shape of the ablated surfaces were analyzed by optical microscopy and scanning electron microscopy. The determined ablation threshold fluence is 0.35 J/cm2 for the composite resins Z-100 and Z-350, and 0.25 J/cm2 for the amalgam. These values are half of the value for enamel in this temporal regime. Thermal damages were not observed in the samples. Using the OCT technique (optical coherence tomography) was possible to determine the ablated volume and the total mass removed.

  4. Laser Ablation of Biological Tissue Using Pulsed CO{sub 2} Laser

    SciTech Connect

    Hashishin, Yuichi; Sano, Shu; Nakayama, Takeyoshi

    2010-10-13

    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 CO{sub 2} laser (wavelength: 10.6 {mu}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.

  5. Experimental verification of the ablation pressure dependence upon the laser intensity at pulsed irradiation of metals

    NASA Astrophysics Data System (ADS)

    Krasyuk, I. K.; Semenov, A. Yu; Stuchebryukhov, I. A.; Khishchenko, K. V.

    2016-11-01

    Experiments for verification of a functional dependence of the ablation pressure on the irradiated surface of a target upon the laser intensity in a range from 1.2 to 350 TW/cm2 have been carried out. For that, at some intensities of the laser irradiation, time intervals between the laser pulse maximum and the moment of the shock-wave front arrival to the rear surface of the target were measured, which are dependent on the ablation pressure. Two schemes of the measurements were used. At the first scheme, at higher laser intensities, the front arrival moment is determined via an electron-optical camera when the rear surface begins glowing. At the second scheme, the front arrival moment is recorded when a probe laser pulse changes the character of the reflection by the rear surface of the irradiated target. Results of measurements are in agreement with the ablation pressure dependence upon the laser pulse intensity within 20%.

  6. Damage in materials following ablation by ultrashort laser pulses: A molecular-dynamics study

    SciTech Connect

    Bouilly, Delphine; Perez, Danny; Lewis, Laurent J.

    2007-11-01

    The formation of craters following femtosecond- and picosecond-pulse laser ablation in the thermal regime is studied using a generic two-dimensional numerical model based on molecular-dynamics simulations and the Lennard-Jones potential. Femtosecond pulses are found to produce very clean craters through a combination of etching of the walls and the formation of a very thin heat affected zone. Our simulations also indicate that dislocations are emitted continuously during all of the ablation process (i.e., for hundreds of ps). For picosecond pulses, we observe much thicker heat affected zones which result from melting and recrystallization following the absorption of the light. In this case also, continuous emission of dislocations--though fewer in number--takes place throughout the ablation process.

  7. Visualization of liquid-assisted hard tissue ablation with a pulsed CO2 laser

    NASA Astrophysics Data System (ADS)

    Li, X. W.; Chen, C. G.; Zhang, X. Z.; Zhan, Z. L.; Xie, S. S.

    2015-01-01

    To investigate the characteristics of liquid-mediated hard tissue ablation induced by a pulsed CO2 laser with a wavelength of 10.6 μm, a high speed camera was used to monitor the interaction between water, tissue and laser irradiation. The results showed that laser irradiation can directly impact on tissue through a vapor channel formed by the leading part of the laser pulse. The ablation debris plays a key role in liquid-assisted laser ablation, having the ability to keep the vapor channel open to extend actuation time. The runoff effect induced by vortex convection liquid flow can remove the tissue that obstructs the effect of the next laser pulse.

  8. Numerical analysis of laser ablation and damage in glass with multiple picosecond laser pulses.

    PubMed

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

    2013-04-08

    This study presents a novel numerical model for laser ablation and laser damage in glass including beam propagation and nonlinear absorption of multiple incident ultrashort laser pulses. The laser ablation and damage in the glass cutting process with a picosecond pulsed laser was studied. The numerical results were in good agreement with our experimental observations, thereby revealing the damage mechanism induced by laser ablation. Beam propagation effects such as interference, diffraction and refraction, play a major role in the evolution of the crater structure and the damage region. There are three different damage regions, a thin layer and two different kinds of spikes. Moreover, the electronic damage mechanism was verified and distinguished from heat modification using the experimental results with different pulse spatial overlaps.

  9. Temperature response of biological materials to pulsed non-ablative CO2 laser irradiation.

    PubMed

    Brugmans, M J; Kemper, J; Gijsbers, G H; van der Meulen, F W; van Gemert, M J

    1991-01-01

    This paper presents surface temperature responses of various tissue phantoms and in vitro and in vivo biological materials in air to non-ablative pulsed CO2 laser irradiation, measured with a thermocamera. We studied cooling off behavior of the materials after a laser pulse, to come to an understanding of heat accumulation and related thermal damage during (super) pulsed CO2 laser irradiation. The experiments show a very slow decay of temperatures in the longer time regime. This behavior is well predicted by a simple model for one-dimensional heat flow that considers the CO2 laser radiation as producing a heat flux on the material surface. The critical pulse repetition frequency for which temperature accumulation is sufficiently low is estimated at about 5 Hz. Although we have not investigated the ablative situation, our results suggest that very low pulse frequencies in microsurgical procedures may be recommended.

  10. Cold Atmospheric Plasma for Selectively Ablating Metastatic Breast Cancer Cells

    PubMed Central

    Wang, Mian; Holmes, Benjamin; Cheng, Xiaoqian; Zhu, Wei; Keidar, Michael; Zhang, Lijie Grace

    2013-01-01

    Traditional breast cancer treatments such as surgery and radiotherapy contain many inherent limitations with regards to incomplete and nonselective tumor ablation. Cold atomospheric plasma (CAP) is an ionized gas where the ion temperature is close to room temperature. It contains electrons, charged particles, radicals, various excited molecules, UV photons and transient electric fields. These various compositional elements have the potential to either enhance and promote cellular activity, or disrupt and destroy them. In particular, based on this unique composition, CAP could offer a minimally-invasive surgical approach allowing for specific cancer cell or tumor tissue removal without influencing healthy cells. Thus, the objective of this research is to investigate a novel CAP-based therapy for selectively bone metastatic breast cancer treatment. For this purpose, human metastatic breast cancer (BrCa) cells and bone marrow derived human mesenchymal stem cells (MSCs) were separately treated with CAP, and behavioral changes were evaluated after 1, 3, and 5 days of culture. With different treatment times, different BrCa and MSC cell responses were observed. Our results showed that BrCa cells were more sensitive to these CAP treatments than MSCs under plasma dose conditions tested. It demonstrated that CAP can selectively ablate metastatic BrCa cells in vitro without damaging healthy MSCs at the metastatic bone site. In addition, our study showed that CAP treatment can significantly inhibit the migration and invasion of BrCa cells. The results suggest the great potential of CAP for breast cancer therapy. PMID:24040051

  11. Evolution of laser pulse shape in a parabolic plasma channel

    NASA Astrophysics Data System (ADS)

    Kaur, M.; Gupta, D. N.; Suk, H.

    2017-01-01

    During high-intensity laser propagation in a plasma, the group velocity of a laser pulse is subjected to change with the laser intensity due to alteration in refractive index associated with the variation of the nonlinear plasma density. The pulse front sharpened while the back of the pulse broadened due to difference in the group velocity at different parts of the laser pulse. Thus the distortion in the shape of the laser pulse is expected. We present 2D particle-in-cell simulations demonstrating the controlling the shape distortion of a Gaussian laser pulse using a parabolic plasma channel. We show the results of the intensity distribution of laser pulse in a plasma with and without a plasma channel. It has been observed that the plasma channel helps in controlling the laser pulse shape distortion. The understanding of evolution of laser pulse shape may be crucial while applying the parabolic plasma channel for guiding the laser pulse in plasma based accelerators.

  12. Planarization of Isolated Defects on ICF Target Capsule Surfaces by Pulsed Laser Ablation

    SciTech Connect

    Alfonso, Noel; Carlson, Lane C.; Bunn, Thomas L.

    2016-08-09

    Demanding surface quality requirements for inertial confinement fusion (ICF) capsules motivated the development of a pulsed laser ablation method to reduce or eliminate undesirable surface defects. The pulsed laser ablation technique takes advantage of a full surface (4π) capsule manipulation system working in combination with an optical profiling (confocal) microscope. Based on the defect topography, the material removal rate, the laser pulse energy and its beam profile, a customized laser raster pattern is derived to remove the defect. The pattern is a table of coordinates and number of pulses that dictate how the defect will be vaporized until its height is level with the capsule surface. This paper explains how the raster patterns are optimized to minimize surface roughness and how surface roughness after laser ablation is simulated. The simulated surfaces are compared with actual ablated surfaces. Large defects are reduced to a size regime where a tumble finishing process produces very high quality surfaces devoid of high mode defects. The combined polishing processes of laser ablation and tumble finishing have become routine fabrication steps for National Ignition Facility capsule production.

  13. Planarization of Isolated Defects on ICF Target Capsule Surfaces by Pulsed Laser Ablation

    DOE PAGES

    Alfonso, Noel; Carlson, Lane C.; Bunn, Thomas L.

    2016-08-09

    Demanding surface quality requirements for inertial confinement fusion (ICF) capsules motivated the development of a pulsed laser ablation method to reduce or eliminate undesirable surface defects. The pulsed laser ablation technique takes advantage of a full surface (4π) capsule manipulation system working in combination with an optical profiling (confocal) microscope. Based on the defect topography, the material removal rate, the laser pulse energy and its beam profile, a customized laser raster pattern is derived to remove the defect. The pattern is a table of coordinates and number of pulses that dictate how the defect will be vaporized until its heightmore » is level with the capsule surface. This paper explains how the raster patterns are optimized to minimize surface roughness and how surface roughness after laser ablation is simulated. The simulated surfaces are compared with actual ablated surfaces. Large defects are reduced to a size regime where a tumble finishing process produces very high quality surfaces devoid of high mode defects. The combined polishing processes of laser ablation and tumble finishing have become routine fabrication steps for National Ignition Facility capsule production.« less

  14. Effect of the pulse repetition rate on fiber-assisted tissue ablation

    NASA Astrophysics Data System (ADS)

    Kang, Hyun Wook

    2016-07-01

    The effect of the pulse repetition rate on ablation performance was evaluated ex vivo at various fiber sweeping speeds for an effective 532-nm laser prostatectomy. Three pulse repetition rates (7.5, 15, and 30 kHz) at 100 W were delivered to bovine liver tissue at three sweeping speeds (2, 4, and 6 mm/s) to achieve bulky tissue removal. Ablation performance was quantitatively compared in terms of the ablation volume and the coagulation thickness. The lowest pulse repetition rate of 7.5 kHz attained the highest ablation volume (101.5 ± 12.0 mm3) and the thinnest coagulation (0.7 ± 0.1 mm) along with superficial carbonization. The highest pulse repetition rate of 30 kHz was associated with the least tissue removal (65.8 ± 5.0 mm3) and the deepest thermal denaturation (1.1 ± 0.2 mm). Quantitative evaluations of laser parameters can be instrumental in facilitating ablation efficiency and maintaining hemostatic coagulation during treatment of large-sized benign prostate hyperplasia.

  15. Laser ablation of GaAs in liquid: the role of laser pulse duration

    NASA Astrophysics Data System (ADS)

    De Bonis, Angela; Galasso, Agostino; Santagata, Antonio; Teghil, Roberto

    2016-01-01

    The synthesis of gallium arsenide (GaAs) nanoparticles has attracted wide scientific and technological interest due to the possibility of tuning the GaAs NP (nanoparticle) band gap across the visible spectrum and their consequent use in optoelectronic devices. In recent years, laser ablation in liquid (LAL) has been widely used for the preparation of colloidal solutions of semiconducting and metallic nanoparticles, thanks to its flexibility. With the aim of highlighting the key role played by laser pulse duration on the ablation mechanism and on the properties of the obtained materials, laser ablation of a gallium arsenide target in acetone was performed using laser sources operating in two different temporal regimes: Nd:glass laser (λ   =  527 nm, pulse duration of 250 fs and frequency repetition rate of 10 Hz) and Nd:YAG laser (λ   =  532 nm, pulse duration of 7 ns and frequency repetition rate of 10 Hz). The ablation process was studied following the dynamics of the laser induced shock waves (SWs) and cavitation bubbles (CBs) by fast shadowgraphy, showing that CB dimension and lifetime is related to the laser pulse length. A characterization of the obtained materials by TEM (transmission electron microscopy) and microRaman spectroscopy have shown that quite spherical gallium oxide/GaAs nanoparticles can be obtained by nanosecond laser ablation. On the other hand, pure polycrystalline GaAs nanoparticles can be produced by using an ultrashort laser source.

  16. An improved three-dimensional two-temperature model for multi-pulse femtosecond laser ablation of aluminum

    SciTech Connect

    Zhang, Jinping; Chen, Yuping Hu, Mengning; Chen, Xianfeng

    2015-02-14

    In this paper, an improved three-dimensional two-temperature model for multi-pulse femtosecond laser ablation of aluminum was proposed and proved in our experiment. Aiming to achieve hole-drilling with a high ratio of depth/entrance diameter in vacuum, this model can predict the depth and radius of the drilled holes precisely when employing different laser parameters. Additionally, for multi-pulse laser ablation, we found that the laser fluence and number of pulses are the dominant parameters and the multi-pulse ablation threshold is much lower than the single-pulse one, which will help to obtain high-quality holes.

  17. Pulsed Energy Systems for Generating Plasmas

    NASA Technical Reports Server (NTRS)

    Rose, M. Franklin; Shotts, Z.

    2005-01-01

    This paper will describe the techniques needed to electrically generate highly ionized dense plasmas for a variety of applications. The components needed in pulsed circuits are described in terms of general performance parameters currently available from commercial vendors. Examples of pulsed systems using these components are described and technical data from laboratory experiments presented. Experimental data are given for point designs, capable of multi-megawatt power levels.

  18. Destruction of monocrystalline silicon with nanosecond pulsed fiber laser accompanied by the oxidation of ablation microparticles

    NASA Astrophysics Data System (ADS)

    Veiko, V. P.; Skvortsov, A. M.; Huynh, C. T.; Petrov, A. A.

    2013-11-01

    In this work, we report an observation of process of local destruction monocrystalline silicon with a scanning beam irradiation of pulse ytterbium fiber laser with a wavelength λ= 1062 nm, accompanied by the oxidation of ablation microparticles. It is shown that depending on the power density of irradiation was observed a large scatter size of the microparticles. From a certain average power density is observed beginning oxidation particulate emitted from the surface of the irradiated area. By varying the parameters of the laser beam such as scanning speed, pulse repetition rate, overlap of laser spot, radiation dose can be achieved almost complete oxidation of all formed during the ablation of microparticles.

  19. Dynamics of plasma expansion and shockwave formation in femtosecond laser-ablated aluminum plumes in argon gas at atmospheric pressures

    SciTech Connect

    Miloshevsky, Alexander; Harilal, Sivanandan S.; Miloshevsky, Gennady Hassanein, Ahmed

    2014-04-15

    Plasma expansion with shockwave formation during laser ablation of materials in a background gasses is a complex process. The spatial and temporal evolution of pressure, temperature, density, and velocity fields is needed for its complete understanding. We have studied the expansion of femtosecond (fs) laser-ablated aluminum (Al) plumes in Argon (Ar) gas at 0.5 and 1 atmosphere (atm). The expansion of the plume is investigated experimentally using shadowgraphy and fast-gated imaging. The computational fluid dynamics (CFD) modeling is also carried out. The position of the shock front measured by shadowgraphy and fast-gated imaging is then compared to that obtained from the CFD modeling. The results from the three methods are found to be in good agreement, especially during the initial stage of plasma expansion. The computed time- and space-resolved fields of gas-dynamic parameters have provided valuable insights into the dynamics of plasma expansion and shockwave formation in fs-pulse ablated Al plumes in Ar gas at 0.5 and 1 atm. These results are compared to our previous data on nanosecond (ns) laser ablation of Al [S. S. Harilal et al., Phys. Plasmas 19, 083504 (2012)]. It is observed that both fs and ns plumes acquire a nearly spherical shape at the end of expansion in Ar gas at 1 atm. However, due to significantly lower pulse energy of the fs laser (5 mJ) compared to pulse energy of the ns laser (100 mJ) used in our studies, the values of pressure, temperature, mass density, and velocity are found to be smaller in the fs laser plume, and their time evolution occurs much faster on the same time scale. The oscillatory shock waves clearly visible in the ns plume are not observed in the internal region of the fs plume. These experimental and computational results provide a quantitative understanding of plasma expansion and shockwave formation in fs-pulse and ns-pulse laser ablated Al plumes in an ambient gas at atmospheric pressures.

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

    SciTech Connect

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

    2008-07-15

    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.

  1. Femtosecond pulse laser ablation of chromium: experimental results and two-temperature model simulations

    NASA Astrophysics Data System (ADS)

    Saghebfar, M.; Tehrani, M. K.; Darbani, S. M. R.; Majd, A. E.

    2017-01-01

    In this work, the results of experimental and computational single- and multi-shot ablation threshold and the incubation effect of chromium metal sample, irradiated by ultrashort laser pulses, are presented. The experimental value of the ablation threshold is determined based on D2 method by measuring the outer ablation crater diameters as a function of incident laser pulse energy using 800 nm, 30 fs, laser pulses. The value of 0.19 ± 0.04 (J/cm2 ), is obtained for the single-shot ablation threshold fluence. The experimental results are compared with time-dependent heat flow calculations based on the two-temperature model and the effect of number and separation time of two consecutive laser pulses with the same total fluence is studied for the Cr target. Moreover, the role of pulse width and absorbed fluence in thermal equilibrium time between electrons and lattice is investigated in two-temperature model. The thermal equilibrium between electron and lattice is established after a few picoseconds for low fluences and after a few tens of picoseconds at higher fluences.

  2. Effect of inter-pulse delay time on production and size properties of colloidal nanoparticles prepared by collinear double-pulse laser ablation in liquid

    NASA Astrophysics Data System (ADS)

    Fattahi, Behzad; Mahdieh, Mohammah Hossein

    2016-08-01

    The influence of inter-pulse delay times (0-20 ns) between two collinear sequential nanosecond pulses on the production and size properties (mean size and size distribution) of colloidal nanoparticles prepared by pulsed laser ablation of a silver target in a distilled water medium has been studied. Various laser fluences at different inter-pulse delay times between two collinear pulses were used. Furthermore, for a better understanding of the effect of the double-pulse and single-pulse mode, experiments were performed. The characterization of the synthesized colloidal nanoparticles was investigated using scanning electron microscopy (SEM) and UV-vis absorption spectroscopy. Our results showed that 5 ns time-delayed double-pulse laser ablation results in the production of nanoparticles with the highest concentration among the other time-delayed ablation experiments and even more than single-pulse-mode experiments. It also found that using a double-pulse approach with inter-pulse delay times in the range of 0-20 ns leads to the production of nanoparticles with smaller mean sizes and narrower size distributions in comparison to single-pulse-mode laser ablation. The effect of time overlapping between two pulses in the case of double-pulse ablation was analyzed.

  3. Synthesis of Diamond Films with Pulsed Plasmas.

    DTIC Science & Technology

    1991-08-01

    can be used also reduces the amount of reactants that can be dissociated which may adversely effect the film’s growth rate as well as quality. The use...not specifically address the optimization of temperature, to determine if a temperature effect did exist with pulsed-plasma depositions, the... effect the growth rate and quality of the diamond film. Baseline films obtained with CW formed plasmas had growth rates and film quality that exceeded any

  4. Doping He droplets by laser ablation with a pulsed supersonic jet source

    SciTech Connect

    Katzy, R.; Singer, M.; Izadnia, S.; LaForge, A. C. Stienkemeier, F.

    2016-01-15

    Laser ablation offers the possibility to study a rich number of atoms, molecules, and clusters in the gas phase. By attaching laser ablated materials to helium nanodroplets, one can gain highly resolved spectra of isolated species in a cold, weakly perturbed system. Here, we present a new setup for doping pulsed helium nanodroplet beams by means of laser ablation. In comparison to more well-established techniques using a continuous nozzle, pulsed nozzles show significant differences in the doping efficiency depending on certain experimental parameters (e.g., position of the ablation plume with respect to the droplet formation, nozzle design, and expansion conditions). In particular, we demonstrate that when the ablation region overlaps with the droplet formation region, one also creates a supersonic beam of helium atoms seeded with the sample material. The processes are characterized using a surface ionization detector. The overall doping signal is compared to that of conventional oven cell doping showing very similar dependence on helium stagnation conditions, indicating a comparable doping process. Finally, the ablated material was spectroscopically studied via laser induced fluorescence.

  5. Ablation of NIF Targets and Diagnostic Components by High Power Lasers and X-Rays from High Temperature Plasmas

    SciTech Connect

    Eder, D.C; Anderson, A.T.; Braun, D.G; Tobin, M.T.

    2000-04-19

    The National Ignition Facility (NIF) will consist of 192 laser beams that have a total energy of up to 1.8 MJ in the 3rd harmonic ({lambda} = 0.35 {micro}m) with the amount of 2nd harmonic and fundamental light depending on the pulse shape. Material near best focus of the 3rd harmonic light will be vaporized/ablated very rapidly, with a significant fraction of the laser energy converted into plasma x rays. Additional plasma x rays can come from imploding/igniting capsule inside Inertial Confinement Fusion (ICF) hohlraums. Material from outer portions of the target, diagnostic components, first-wall material, and optical components, are ablated by the plasma x rays. Material out to a radius of order 3 cm from target center is also exposed to a significant flux of 2nd harmonic and fundamental laser light. Ablation can accelerate the remaining material to high velocities if it has been fragmented or melted. In addition, the high velocity debris wind of the initially vaporized material pushes on the fragments/droplets and increases their velocity. The high velocity shrapnel fragments/droplets can damage the fused silica shields protecting the final optics in NIF. We discuss modeling efforts to calculate vaporization/ablation, x-ray generation, shrapnel production, and ways to mitigate damage to the shields.

  6. Ablation Resistance of C/C Composites with Atmospheric Plasma-Sprayed W Coating

    NASA Astrophysics Data System (ADS)

    Zhou, Zhe; Wang, Yuan; Gong, Jieming; Ge, Yicheng; Peng, Ke; Ran, Liping; Yi, Maozhong

    2016-12-01

    To improve the ablation resistance of carbon/carbon (C/C) composites, tungsten (W) coating with thickness of 1.2 mm was applied by atmospheric plasma spraying. The antiablation property of the coated composites was evaluated by oxyacetylene flame ablation experiments. The phase composition of the coating was investigated by a combination of x-ray diffraction analysis and scanning electron microscopy with energy-dispersive x-ray spectroscopy analysis. The ablation resistance of the coated C/C substrates was compared with that of uncoated C/C composites and C/C-CuZr composites after ablation for 30 s. The properties of the coated C/C composites after ablation time of 10, 30, 60, 90, 120, and 180 s were further studied. The results indicated that the mass and linear ablation rates of the W-coated C/C composites were lower than those of uncoated C/C or C/C-CuZr composites after ablation for 30 s. The coating exhibited heat stability after 120 s of ablation, with mass loss and linear ablation rates of 7.39 × 10-3 g/s and 3.50 × 10-3 mm/s, respectively. However, the W coating became ineffective and failed after ablation for 180 s. Three ablation regions could be identified, in which the ablation mechanism of the coating changed from thermochemical to thermophysical erosion to mechanical scouring with increasing ablation time.

  7. Resonant infrared ablation of polystyrene with single picosecond pulses generated by an optical parametric amplifier

    NASA Astrophysics Data System (ADS)

    Duering, Malte; Haglund, Richard; Luther-Davies, Barry

    2014-01-01

    We report on resonant infrared laser ablation of polystyrene using single 8 ps pulses at a wavelength of 3.31 μm generated by a MgO:PPLN optical parametric amplifier pumped by a Nd:YLF laser. We determined the single-pulse ablation threshold to be 0.46 J/cm2, about a factor of five smaller than in previous free-electron-laser studies. Time-resolved imaging of the laser-target interaction reveals that the detailed dynamics of the ablation process begin with thermal expansion of a large volume of hot material from which a less dense plume of polymeric material evaporates. This plume disappears on a time scale of 0.75 μs and the hot polymer material recedes back into the crater from which it was expelled. Subsequently, and on a much longer time scale, structural alterations in the ablation crater continue to evolve for at least another millisecond. Our results suggest that single picosecond pulses are effective for the ablation of polymers and exhibit dynamics similar to those observed in studies using a free-electron laser.

  8. Modeling and Simulation of Ablation-Controlled Plasmas

    NASA Astrophysics Data System (ADS)

    Kundrapu, Madhusudhan N.

    Ablation and plasma formation in high energy laser target interactions and arc discharges are studied numerically. Each of the two processes is modeled separately due to the type of energy source and the resulting flow eld. Ablation of the target material and plasma formation are coupled to obtain evaporation rate, temperature distribution, velocity eld, and species concentration self-consistently. Laser ablation is studied in the perspective of directed energy applications, where beam size varies from few centimeters to tens of centimeters with energies extending up to 10 kW/cm2. Because of this high energy deposition, the evaporated material expands to supersonic speeds into the free space. Due to the large spot sizes and associated supersonic flow, one dimensional Euler equations are considered to be sufficient for modeling the plume. Instead, more emphasis was given to evaporation model, by introducing Knudsen layer kinetics at the plume target interface, and plasma shielding. The evaporation rate is validated with results from the experiments and simulations are carried out to nd the in fluence of laser beam frequency on evaporation rates. The evaporation model used in this work is found to be more accurate than the widely used model based on sonic speed assumption. The optimum beam wavelength for Al surfaces is found to be 850 nm. Attenuation of telemetry data by plasma is a concern for the testing of directed energy systems. Electrostatic approach for the mitigation of communication attenuation is analyzed to obtain the fluency limits up to which the approach can be implemented. It is found from sheath calculations that uninterrupted telemetry can be achieved through Al plasma for fluences below 4 J/cm2 at a background pressure of 1 atm, using a maximum bias voltage of 10 kV . Arc discharge ablation is modeled for the synthesis of nanoparticles. The electric arc generated between the electrodes, placed inside a Helium chamber, evaporates the catalyst

  9. Synthesis of CaWO4 nanocolloidal suspension via pulsed laser ablation and its optical properties

    NASA Astrophysics Data System (ADS)

    Ryu, Jeong Ho; Park, Gyeong Seon; Kim, Kang Min; Lim, Chang Sung; Yoon, Jong-Won; Shim, Kwang Bo

    2007-09-01

    Pulsed laser ablation (PLA) in the liquid phase was successfully employed to synthesize calcium tungstate (CaWO4) nanocolloidal suspension. The crystalline phase, particle morphology and laser ablation mechanism for the colloidal nanoparticles were investigated using XRD, TEM and SEM. The obtained colloidal suspension consisted of well-dispersed CaWO4 nanoparticles which showed a spherical shape with sizes ranging from 5 to 30 nm. The laser ablation and the nanoparticle forming process were discussed under consideration of the photo-ablation mechanism, where the nanoparticles were generated by rapid condensation of the plume in high pressured ethanol vapor. The optical properties of the prepared CaWO4 colloidal nanoparticles were analyzed in detail using XPS, Raman spectroscopy, UV-Vis spectroscopy and PL spectrophotometry. The optical band gap was estimated by Tauc and Menths law.

  10. Vaporization and deposition of an intact polyimide precursor by resonant infrared pulsed laser ablation

    NASA Astrophysics Data System (ADS)

    Dygert, N. L.; Schriver, K. E.; Haglund, R. F., Jr.

    2006-02-01

    Poly(amic acid) (PAA), a precursor to polyimide, was successfully deposited on substrates without reaching curing temperature, by resonant infrared pulsed laser ablation. The PAA was prepared by dissolving pyromellitic dianhydride and 4, 4' oxidianiline in the polar solvent N-methyl pyrrolidinone (NMP). RIR-PLD transferred material showed two distinct geometries, droplets and string-like moieties. The unaltered nature of the deposited PAA was confirmed by Fourier transform infrared spectroscopy (FTIR). Thermal curing was achieved by heating for one hour on a 250°C hotplate, and the transformation to polyimide was demonstrated from changes in the FTIR spectrum following curing. Plume shadowgraphy showed very clear contrasts in the ablation mechanism between ablation of the solvent alone and the ablation of the PAA, with additional contrast shown between the various resonant frequencies used.

  11. Plasma-Pulse-Acceleration Experiments

    DTIC Science & Technology

    1987-06-01

    W. Pucher, Testing a new Type of Circuit Breaker for HVDC , Direct Current, Feb. 1966, pp. 3 - 6 /10/ D. Kind, E. Marx, K. Mollenhoff, J. Salge... breakers /4, 5/, exploding wires /6/, plasma jet tubes /7/, and high pressure radiation sources /8/. In particular current limiting circuit breakers ...length, radius, shaping, material to be evaporated etc.). Here it is possible to transfer design criteria from current-limiting circuit breakers and

  12. Pulsed laser ablation of polymers for display applications

    NASA Astrophysics Data System (ADS)

    Pedder, James E. A.; Holmes, Andrew S.; Booth, Heather J.

    2008-02-01

    Laser micromachining by ablation is a well established technique used for the production of 2.5D and 3D features in a wide variety of materials. The fabrication of stepped, multi-level, structures can be achieved using a number of binary mask projection techniques using excimer lasers. Alternatively, direct-writing of complex 2.5D features can easily be achieved with solid-state lasers. Excimer laser ablation using half-tone masks allows almost continuous surface relief and the generation of features with low surface roughness. We have developed techniques to create large arrays of repeating micro-optical structures on polymer substrates. Here, we show our recent developments in laser structuring with the combination of half-tone and binary mask techniques.

  13. Ablation and nanostructuring of metals by femtosecond laser pulses

    SciTech Connect

    Ashitkov, S I; Komarov, P S; Ovchinnikov, A V; Struleva, E V; Agranat, M B; Zhakhovskii, V V; Inogamov, N A

    2014-06-30

    Using an interferometric continuous monitoring technique, we have investigated the motion of the surface of an aluminium target in the case of femtosecond laser ablation at picosecond time delays relative to the instant of laser exposure. Measurements of the temporal target dispersion dynamics, molecular dynamics simulation results and the morphology of the ablation crater have demonstrated a thermomechanical (spall) nature of the disruption of the condensed phase due to the cavitation-driven formation and growth of vapour phase nuclei upon melt expansion, followed by the formation of surface nanostructures upon melt solidification. The tensile strength of heated aluminium in a condensed state has been determined experimentally at an expansion rate of ∼10{sup 9} s{sup -1}. (extreme light fields and their applications)

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

    NASA Astrophysics Data System (ADS)

    Huifeng, Tong; Zhiping, Tang

    2011-06-01

    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.

  15. Bone tissue heating and ablation by short and ultrashort laser pulses

    NASA Astrophysics Data System (ADS)

    Letfullin, Renat R.; Rice, Colin E. W.; George, Thomas F.

    2010-02-01

    Biological hard tissues, such as those found in bone and teeth, are complex tissues that build a strong mineral structure over an organic matrix framework. The laser-matter interaction for bone hard tissues holds great interest to laser surgery and laser dentistry; the use of short/ultrashort pulses, in particular, shows interesting behaviors not seen in continuous wave lasers. High laser energy densities in ultrashort pulses can be focused on a small irradiated surface (spot diameter is 10-50 μm) leading to rapid temperature rise and thermal ablation of the bone tissue. Ultrashort pulses, specifically those in the picosecond and femtosecond ranges, impose several challenges in modeling bone tissue response. In the present paper we perform time-dependent thermal simulations of short and ultrashort pulse laser-bone interactions in singlepulse and multipulse (set of ultrashort pulses) modes of laser heating. A comparative analysis for both radiation modes is discussed for laser heating of different types of the solid bone on the nanosecond, picosecond and femtosecond time scales. It is shown that ultrashort laser pulses with high energy densities can ablate bone tissue without heating tissues bordering the ablation creator. This reaction is particularly desirable as heat accumulation and thermal damage are the main factors affecting tissue regrowth rates, and thus patient recovery times.

  16. Surface roughness and wettability of dentin ablated with ultrashort pulsed laser

    NASA Astrophysics Data System (ADS)

    Liu, Jing; Lü, Peijun; Sun, Yuchun; Wang, Yong

    2015-05-01

    The aim of this study was to evaluate the surface roughness and wettability of dentin following ultrashort pulsed laser ablation with different levels of fluence and pulse overlap (PO). Twenty-five extracted human teeth crowns were cut longitudinally into slices of approximately 1.5-mm thick and randomly divided into nine groups of five. Samples in groups 1 to 8 were ablated with an ultrashort pulsed laser through a galvanometric scanning system. Samples in group 9 were prepared using a mechanical rotary instrument. The surface roughness of samples from each group was then measured using a three-dimensional profile measurement laser microscope, and wettability was evaluated by measuring the contact angle of a drop of water on the prepared dentin surface using an optical contact angle measuring device. The results showed that both laser fluence and PO had an effect on dentin surface roughness. Specifically, a higher PO decreased dentin surface roughness and reduced the effect of high-laser fluence on decreasing the surface roughness in some groups. Furthermore, all ablated dentin showed a contact angle of approximately 0 deg, meaning that laser ablation significantly improved wettability. Adjustment of ultrashort pulsed laser parameters can, therefore, significantly alter dentin surface roughness and wettability.

  17. Deposition of Fluorinated Diamond-Like-Carbon Films by Exposure of Electrothermal Pulsed Plasmas

    NASA Astrophysics Data System (ADS)

    Kimura, Takashi; Iida, Masayasu

    2011-08-01

    Thin amorphous carbon films are deposited on silicon substrates by exposure to pulsed plasmas where the feed gas is mainly generated from the ablation of an insulator. An electrothermal pulsed plasma thruster with a discharge room in an insulator rod is used as the pulsed plasma for the ablation of the insulator, and the material of the insulator rod is poly(tetrafluoroethylene) (PTFE). The pulsed plasma, in which the estimated electron density is on the order of 1022-1023 m-3, is generated by the stored energy in the capacitor. The deposition rate, which depends on the stored energy, is lower than 1 nm per pulse in our experiment. The maximum hardness measured using a nanoindenter is about 7 GPa at a stored energy of about 2.7 J, beyond which the hardness of the films decreases with the increase in stored energy. Raman spectroscopy is also carried out to examine the formation of fluorinated diamond-like carbon films. In addition, the influence of dilution gas on the properties of the deposited films is also investigated.

  18. Laser-induced back-ablation of aluminum thin films using picosecond laser pulses

    SciTech Connect

    BULLOCK, A B

    1999-05-26

    Experiments were performed to understand laser-induced back-ablation of Al film targets with picosecond laser pulses. Al films deposited on the back surface of BK-7 substrates are ablated by picosecond laser pulses propagating into the Al film through the substrate. The ablated Al plume is transversely probed by a time-delayed, two-color sub-picoseond (500 fs) pulse, and this probe is then used to produce self-referencing interferograms and shadowgraphs of the Al plume in flight. Optical emission from the Al target due to LIBA is directed into a time-integrated grating spectrometer, and a time-integrating CCD camera records images of the Al plume emission. Ablated Al plumes are also redeposited on to receiving substrates. A post-experimental study of the Al target and recollected deposit characteristics was also done using optical microscopy, interferometry, and profilometry. In this high laser intensity regime, laser-induced substrate ionization and damage strongly limits transmitted laser fluence through the substrate above a threshold fluence. The threshold fluence for this ionization-based transmission limit in the substrate is dependent on the duration of the incident pulse. The substrate ionization can be used as a dynamic control of both transmitted spatial pulse profile and ablated Al plume shape. The efficiency of laser energy transfer between the laser pulse incident on the Al film and the ablated Al plume is estimated to be of order 5% and is a weak function of laser pulsewidth. The Al plume is highly directed. Low plume divergence ({theta}{sub divergence} < 5{sup o}) shows the ablated plume temperature to be very low at long time delays ( T << 0.5 eV at delays of 255 ns). Spectroscopic observations and calculations indicate that, in early time (t < 100 ps), the Al film region near the substrate/metal interface is at temperatures of order 0.5 eV. Interferograms of Al plumes produced with 0.1 {micro}m films show these plumes to be of high neutral atom

  19. Powerful laser pulse absorption in partly homogenized foam plasma

    NASA Astrophysics Data System (ADS)

    Cipriani, M.; Gus'kov, S. Yu.; De Angelis, R.; Andreoli, P.; Consoli, F.; Cristofari, G.; Di Giorgio, G.; Ingenito, F.; Rupasov, A. A.

    2016-03-01

    The internal volume structure of a porous medium of light elements determines unique features of the absorption mechanism of laser radiation; the characteristics of relaxation and transport processes in the produced plasma are affected as well. Porous materials with an average density larger than the critical density have a central role in enhancing the pressure produced during the ablation by the laser pulse; this pressure can exceed the one produced by target direct irradiation. The problem of the absorption of powerful laser radiation in a porous material is examined both analytically and numerically. The behavior of the medium during the process of pore filling in the heated region is described by a model of viscous homogenization. An expression describing the time and space dependence of the absorption coefficient of laser radiation is therefore obtained from the model. A numerical investigation of the absorption of a nanosecond laser pulse is performed within the present model. In the context of numerical calculations, porous media with an average density larger than the critical density of the laser-produced plasma are considered. Preliminary results about the inclusion of the developed absorption model into an hydrodynamic code are presented.

  20. A Pulsed Plasma Thruster Using Dimethyl Ether as Propellant

    NASA Astrophysics Data System (ADS)

    Masui, Souichi; Okada, Terumasa; Kitatomi, Makoto; Kakami, Akira; Tachibana, Takeshi

    The pulsed plasma thruster (PPT), has attracted attention again as a micro-thruster because of its compactness, light weight, and comparatively low power consumption. On the other hand, the propellant utilization efficiency of a conventinal Teflon PPT is relatively low among electric propulsion devices because a propellant that originates from late-time ablation produces negligible thrust. The liquid propellant PPT (LP-PPT), in which water or ethanol is fed with an injector, was proposed to overcome these difficulties. Thrust measurements show that a LP-PPT provides higher specific impulses than a conventional PPT. However, water requires temperature management for propellant storage due to its relatively high freezing point. Moreover, even if ethanol, which has a sufficiently low freezing point, is used as propellant, a pressurant is necessary, as well as water, because the vapor pressures are insufficient for self-pressurization. In this study, we propose to use dimethyl ether (DME) as the propellant. DME, which has a freezing point of 131 K at 1 atm and a vapor pressure of 6 atm at 298 K, can be stored in tanks as a liquid, and requires no feeding pressurant. We designed a DME pulsed plasma thruster to evaluate performance. Thrust measurement yielded a specific impulse of 430 s for a coaxial type at a capacitor-stored energy of 13 J.

  1. Synthesis of silver nanoparticles by laser ablation in ethanol: A pulsed photoacoustic study

    NASA Astrophysics Data System (ADS)

    Valverde-Alva, M. A.; García-Fernández, T.; Villagrán-Muniz, M.; Sánchez-Aké, C.; Castañeda-Guzmán, R.; Esparza-Alegría, E.; Sánchez-Valdés, C. F.; Llamazares, J. L. Sánchez; Herrera, C. E. Márquez

    2015-11-01

    The pulsed photoacoustic (PA) technique was used to study the synthesis by laser ablation of silver nanoparticles (Ag-NPs) in ethanol. PA technique allowed to determine the production rate per laser pulse and concentration of synthesized Ag-NPs. The samples were produced by using a pulsed Nd:YAG laser with 1064 nm of wavelength and 7 ns of pulse duration. The laser pulse energy varied from 10 to 100 mJ. Transmission electron microscopy micrographs demonstrated that the obtained nanoparticles were spherical with an average size close to 10 nm. The absorption spectra of the colloids showed a plasmon absorption peak around 400 nm. The PA analyses showed a significant reduction of the production rate of Ag-NPs during the first hundreds of laser pulses. For a higher number of pulses this rate was kept almost constant. Finally, we found that the root mean square (RMS) value of the PA signal was proportional to the laser pulse fluence on the target surface. Thus PA technique was useful to monitor the ablation process.

  2. The effect of ultrafast laser wavelength on ablation properties and implications on sample introduction in inductively coupled plasma mass spectrometry

    SciTech Connect

    LaHaye, N. L.; Harilal, S. S.; Diwakar, P. K.; Hassanein, A.; Kulkarni, P.

    2013-07-14

    We investigated the role of femtosecond (fs) laser wavelength on laser ablation (LA) and its relation to laser generated aerosol counts and particle distribution, inductively coupled plasma-mass spectrometry (ICP-MS) signal intensity, detection limits, and elemental fractionation. Four different NIST standard reference materials (610, 613, 615, and 616) were ablated using 400 nm and 800 nm fs laser pulses to study the effect of wavelength on laser ablation rate, accuracy, precision, and fractionation. Our results show that the detection limits are lower for 400 nm laser excitation than 800 nm laser excitation at lower laser energies but approximately equal at higher energies. Ablation threshold was also found to be lower for 400 nm than 800 nm laser excitation. Particle size distributions are very similar for 400 nm and 800 nm wavelengths; however, they differ significantly in counts at similar laser fluence levels. This study concludes that 400 nm LA is more beneficial for sample introduction in ICP-MS, particularly when lower laser energies are to be used for ablation.

  3. Thyristor stack for pulsed inductive plasma generation

    SciTech Connect

    Teske, C.; Jacoby, J.; Schweizer, W.; Wiechula, J.

    2009-03-15

    A thyristor stack for pulsed inductive plasma generation has been developed and tested. The stack design includes a free wheeling diode assembly for current reversal. Triggering of the device is achieved by a high side biased, self supplied gate driver unit using gating energy derived from a local snubber network. The structure guarantees a hard firing gate pulse for the required high dI/dt application. A single fiber optic command is needed to achieve a simultaneous turn on of the thyristors. The stack assembly is used for switching a series resonant circuit with a ringing frequency of 30 kHz. In the prototype pulsed power system described here an inductive discharge has been generated with a pulse duration of 120 {mu}s and a pulse energy of 50 J. A maximum power transfer efficiency of 84% and a peak power of 480 kW inside the discharge were achieved. System tests were performed with a purely inductive load and an inductively generated plasma acting as a load through transformer action at a voltage level of 4.1 kV, a peak current of 5 kA, and a current switching rate of 1 kA/{mu}s.

  4. Thyristor stack for pulsed inductive plasma generation.

    PubMed

    Teske, C; Jacoby, J; Schweizer, W; Wiechula, J

    2009-03-01

    A thyristor stack for pulsed inductive plasma generation has been developed and tested. The stack design includes a free wheeling diode assembly for current reversal. Triggering of the device is achieved by a high side biased, self supplied gate driver unit using gating energy derived from a local snubber network. The structure guarantees a hard firing gate pulse for the required high dI/dt application. A single fiber optic command is needed to achieve a simultaneous turn on of the thyristors. The stack assembly is used for switching a series resonant circuit with a ringing frequency of 30 kHz. In the prototype pulsed power system described here an inductive discharge has been generated with a pulse duration of 120 micros and a pulse energy of 50 J. A maximum power transfer efficiency of 84% and a peak power of 480 kW inside the discharge were achieved. System tests were performed with a purely inductive load and an inductively generated plasma acting as a load through transformer action at a voltage level of 4.1 kV, a peak current of 5 kA, and a current switching rate of 1 kA/micros.

  5. A unified model to determine the energy partitioning between target and plasma in nanosecond laser ablation of silicon

    SciTech Connect

    Galasso, G.; Kaltenbacher, M.; Tomaselli, A.; Scarpa, D.

    2015-03-28

    In semiconductor industry, pulsed nanosecond lasers are widely applied for the separation of silicon wafers. Here, the high intensities employed activate a cascade of complex multi-physical and multi-phase mechanisms, which finally result in the formation of a laser induced plasma, shielding the target from the incoming laser beam. Such induced plasma plume, by preventing the laser to effectively reach the target, reduces the overall efficiency and controllability of the ablation process. Modelling can be a useful tool in the optimization of industrial laser applications, allowing a deeper understanding of the way the laser energy distributes between target and induced plasma. Nevertheless, the highly multi-physical character of laser ablation poses serious challenges on the implementation of the various mechanisms underlying the process within a common modelling framework. A novel strategy is here proposed in order to simulate in a simplified, yet physically consistent way, a typical industrial application as laser ablation of silicon wafers. Reasonable agreement with experimental findings is obtained. Three fundamental mechanisms have been identified as the main factors influencing the accuracy of the numerical predictions: the transition from evaporative to volumetric mass removal occurring at critical temperature, the collisional and radiative processes underlying the initial plasma formation stage and the increased impact of the liquid ejection mechanism when a sub-millimeter laser footprint is used.

  6. Pulsed plasma thruster ignitor plug ignition characteristics

    NASA Technical Reports Server (NTRS)

    Brady, M. E.; Aston, G.

    1982-01-01

    The operating characteristics of the semiconductor spark gap ignitor plug used to initiate the discharge in a pulsed plasma thruster are investigated. Current and voltage waveform measurements for the ignitor plug alone, and for the plug mounted in the thruster cathode indicate an average dynamic impedance of 0.2 ohms for a wide range of operating conditions, and a trigger circuit energy transfer efficiency to the plug on the order of 25%. Two modes of trigger ignition are found which are related to the rise time of the applied voltage pulse. Analysis of plasma characteristics reveals plug erosion to occur primarily in the semiconductor and anode regions, by mechanisms including plug metal embrittlement, plasma sputtering and vaporization caused by the discharge current pulse. Measurements also indicate a plume velocity on the order of 1580,000 cm/sec which increases with trigger circuit stored energy. The results establish levels of performance for future applications of semiconductor spark gap ignitor plugs in plasma devices.

  7. Pulsed-DC DBD Plasma Actuators

    NASA Astrophysics Data System (ADS)

    Duong, Alan; McGowan, Ryan; Disser, Katherine; Corke, Thomas; Matlis, Eric

    2016-11-01

    A new powering system for dielectric barrier discharge (DBD) plasma actuators that utilizes a pulsed-DC waveform is presented. The plasma actuator arrangement is identical to most typical AC-DBD designs with staggered electrodes that are separated by a dielectric insulator. However instead of an AC voltage input to drive the actuator, the pulsed-DC utilizes a DC voltage source. The DC source is supplied to both electrodes, and remains constant in time for the exposed electrode. The DC source for the covered electrode is periodically grounded for very short instants and then allowed to rise to the source DC level. This process results in a plasma actuator body force that is significantly larger than that with an AC-DBD at the same voltages. The important characteristics used in optimizing the pulsed-DC plasma actuators are presented. Time-resolved velocity measurements near the actuator are further used to understand the underlying physics of its operation compared to the AC-DBD. Supported by NASA Glenn RC.

  8. Laser-induced fluorescence analysis of plasmas for epitaxial growth of YBiO3 films with pulsed laser deposition

    NASA Astrophysics Data System (ADS)

    Orsel, Kasper; Groenen, Rik; Bastiaens, Bert; Koster, Gertjan; Rijnders, Guus; Boller, Klaus-J.

    2016-12-01

    We record the two-dimensional laser-induced fluorescence (LIF) on multiple plasma constituents in a YBiO3 plasma. This allows us to directly link the influence of oxygen present in the background gas during pulsed laser deposition to the oxidation of plasma species as well as the formation of epitaxial YBiO3 films. With spatiotemporal LIF mapping of the plasma species (Y, YO, Bi, and BiO) in different background gas compositions, we find that little direct chemical interaction takes place between the plasma plume constituents and the background gas. However, a strong influence of the background gas composition can be seen on the YBO film growth, as well as a strong correlation between the oxygen fraction in the background gas and the amount of YO in the plasma plume. We assign this correlation to a direct interaction between the background gas and the target in between ablation pulses. In an O2 background, an oxygen-rich surface layer forms in between ablation pulses, which provides additional oxygen for the plasma plume during target ablation. This differs from our previous observations in STO and LAO plasmas, where species oxidation primarily takes place during propagation of the plasma plume towards the substrate.

  9. Two-Pulsed Technique for Ablative Laser Propulsion: Force Measurement in Vacuum

    NASA Technical Reports Server (NTRS)

    Herren, Kenneth A.; Cohen, Timothy; Lin, Jun; Pakhomov, Andrew V.

    2004-01-01

    This is a continuation of studies using a two-pulsed technique for Ablative Laser Propulsion (ALP) extended to force measurements in vacuum. Aluminum samples were ablated using pairs of laser pulses, each of 100 ps width, 532 nm wavelength and 5 mJ energy. The pulses were temporally separated in the 0 - 0.67 ns range. The force imparted on Al targets was measured in situ by means of a piezoelectric force gauge. The preliminary results confirm the previously reported oscillatory behavior of ion velocity and number density observed by means of a time-of-flight energy analyzer. The uncertainties of presented measurements and future directions for the study are discussed.

  10. Non-thermal ablation of expanded polytetrafluoroethylene with an intense femtosecond-pulse laser.

    PubMed

    Hashida, M; Mishima, H; Tokita, S; Sakabe, S

    2009-07-20

    Ablation of expanded polytetrafluoroethylene without disruption of the fine porous structure is demonstrated using an intense femtosecond-pulse laser. As a result of laser-matter interactions near ablation threshold fluence, high-energy ions are emitted, which cannot be produced by thermal dissociation of the molecules. The ion energy is produced by Coulomb explosion of the elements of (-CF(2)-CF(2)-)(n) and the energy spectra of the ions show contributions from the Coulomb explosions of the ions rather than those of thermal expansion to generate high-energy ions. The dependence of ion energy on the laser fluence of a 180-fs pulse, compared with that of a 400-ps pulse, also suggests that the high-energy ions are accelerated by Coulomb explosion.

  11. Effect of dry and wet ambient environment on the pulsed laser ablation of titanium

    NASA Astrophysics Data System (ADS)

    Ali, Nisar; Bashir, Shazia; Umm-i-Kalsoom; Akram, Mahreen; Mahmood, Khaliq

    2013-04-01

    Surface and structural properties of the laser irradiated titanium targets have been investigated under dry and wet ambient environments. For this purpose KrF Excimer laser of wavelength 248 nm, pulse duration of 20 ns and repetition rate of 20 Hz has been employed. The targets were exposed for various number of laser pulses ranging from 500 to 2000 in the ambient environment of air, de-ionized water and propanol at a fluence of 3.6 J/cm2. The surface morphology, chemical composition and crystallographical analysis were performed by using Scanning Electron Microscope (SEM), Energy Dispersive X-ray Spectroscopy (EDS) and X-ray Diffraction (XRD), respectively. For both central and peripheral ablated areas, significant difference in surface morphology has been observed in case of dry and wet ambient conditions. Large sized and diffused grains are observed in case of dry ablation. Whereas, in case of wet ablation, small sized, and well defined grains with distinct grain boundaries and significantly enhanced density are revealed. This difference is ascribed to the confinement effects of the liquid. The peripheral ablated area shows redeposition in case of dry ablation whereas small sized grain like structures are formed in case of wet ablation. EDS analysis exhibits variation in chemical composition under both ambient conditions. When the targets are treated in air environment, enhancement of the oxygen as well as nitrogen content is observed while in case of de-ionized water and propanol only increase in content of oxygen is observed. X-ray diffraction analysis exhibits formation of oxides and nitrides in case of air, whereas, in case of de-ionized water and propanol only oxides along with hydrides are formed. For various number of laser pulses the variation in the peak intensity, crystallinity and d-spacing is observed under both ambient conditions.

  12. Experimental and Analytical Investigation of Cemented Tungsten Carbide Ultra-Short Pulse Laser Ablation

    NASA Astrophysics Data System (ADS)

    Urbina, J. P. Calderón; Daniel, C.; Emmelmann, C.

    Ultra-short pulse laser processing of hard materials, such as cemented tungsten carbide, requires an accurate and agile experimental and analytical investigation to obtain adequate information and setting parameters to maximize ablation rate. Therefore, this study presents a systematic approach which, first, experimentally searches for the variables with the most significant influence on the objective using a design of experiments method; and second, analyzes by means of existing ablation theory the interaction of the material and laser taking into account the Beer-Lambert law and incubation effect.Therefore, this places a basis for future analytical-experimental validation of the examined material.

  13. Pulsed electromagnetic acceleration of exploded wire plasmas

    SciTech Connect

    Peratt, A.L.; Koert, P.

    1983-11-01

    A simple analysis of the dynamic state of a current-conducting high-density plasma column, resulting from an exploded wire between the conductors of a rail-gun accelerator or one or more wires strung between the anode and cathode conductors in a pulsed-power generator diode, is given on the basis of a one-dimensional magnetohydrodynamics model. Spatial distributions of the current density, magnetic field, temperature, and particle density are calculated as well as the temporal current, voltage, and impedance histories. The model self-consistently treats the accelerator load transition through its solid, melt, vapor, and plasma states in the presence of its supply source and feed network. Once formed and accelerated, the plasma state calculations show expansion cooling across the self-induced magnetic field if the Bennett condition is not satisfied. The model predictions are compared to two experimental situations. The first involves the delivery of some hundreds of Joules of stored energy to the wire load. For this case, good agreement between the calculated and observed plasma state is obtained. The second situation involves the delivery of many thousands of Joules to the wire load. For this case and dependent upon the wire mass, diameter, number of wires exploded, their separation, and the pulsed energy electrical wave shapes, the magnetohydrodynamic results can be qualitatively incorrect. The necessity of an electromagnetic particle simulation approach is indicated in order to resolve the magnetic rope-like structure and filamentation observed in the very energetic plasmas.

  14. Ablation Study of WC and PCD Composites Using 10 Picosecond and 1 Nanosecond Pulse Durations at Green and Infrared Wavelengths

    NASA Astrophysics Data System (ADS)

    Eberle, Gregory; Wegener, Konrad

    An ablation study is carried out to compare 10 picosecond and 1 nanosecond pulse durations as well as 532 nanometre and 1064 nanometre wavelengths at each corresponding pulse duration. All laser parameters are kept constant in order to understand the influence of pulse duration and wavelength independently. The materials processed according to the electronic band structure are a metal and an insulator/metal composite, i.e. tungsten carbide and polycrystalline diamond composite respectively. After laser processing said materials, the ablation rate and surface roughness are determined. Analysis into the ablation behaviour between the various laser parameters and the materials processed is given, with a particular emphasis on the graphitisation of diamond.

  15. Low- and high-order harmonic generation in the extended plasmas produced by laser ablation of zinc and manganese targets

    SciTech Connect

    Ganeev, R. A.; Baba, M.; Suzuki, M.; Yoneya, S.; Kuroda, H.

    2014-12-28

    The systematic studies of the harmonic generation of ultrashort laser pulses in the 5-mm-long Zn and Mn plasmas (i.e., application of nanosecond, picosecond, and femtosecond pulses for ablation, comparison of harmonic generation from atomic, ionic, and cluster-contained species of plasma, variation of plasma length, two-color pump of plasmas, etc.) are presented. The conversion efficiency of the 11th–19th harmonics generated in the Zn plasma was ∼5 × 10{sup −5}. The role of the ionic resonances of Zn near the 9th and 10th harmonics on the enhancement of harmonics is discussed. The enhancement of harmonics was also analyzed using the two-color pump of extended plasmas, which showed similar intensities of the odd and even harmonics along the whole range of generation. The harmonics up to the 107th order were demonstrated in the case of manganese plasma. The comparison of harmonic generation in the 5-mm-long and commonly used short (≤0.5 mm) plasma plumes showed the advanced properties of extended media.

  16. CO2 laser pulse shortening by laser ablation of a metal target.

    PubMed

    Donnelly, T; Mazoyer, M; Lynch, A; O'Sullivan, G; O'Reilly, F; Dunne, P; Cummins, T

    2012-03-01

    A repeatable and flexible technique for pulse shortening of laser pulses has been applied to transversely excited atmospheric (TEA) CO(2) laser pulses. The technique involves focusing the laser output onto a highly reflective metal target so that plasma is formed, which then operates as a shutter due to strong laser absorption and scattering. Precise control of the focused laser intensity allows for timing of the shutter so that different temporal portions of the pulse can be reflected from the target surface before plasma formation occurs. This type of shutter enables one to reduce the pulse duration down to ~2 ns and to remove the low power, long duration tails that are present in TEA CO(2) pulses. The transmitted energy is reduced as the pulse duration is decreased but the reflected power is ~10 MW for all pulse durations. A simple laser heating model verifies that the pulse shortening depends directly on the plasma formation time, which in turn is dependent on the applied laser intensity. It is envisaged that this plasma shutter will be used as a tool for pulse shaping in the search for laser pulse conditions to optimize conversion efficiency from laser energy to useable extreme ultraviolet (EUV) radiation for EUV source development.

  17. CO2 laser pulse shortening by laser ablation of a metal target

    NASA Astrophysics Data System (ADS)

    Donnelly, T.; Mazoyer, M.; Lynch, A.; O'Sullivan, G.; O'Reilly, F.; Dunne, P.; Cummins, T.

    2012-03-01

    A repeatable and flexible technique for pulse shortening of laser pulses has been applied to transversely excited atmospheric (TEA) CO2 laser pulses. The technique involves focusing the laser output onto a highly reflective metal target so that plasma is formed, which then operates as a shutter due to strong laser absorption and scattering. Precise control of the focused laser intensity allows for timing of the shutter so that different temporal portions of the pulse can be reflected from the target surface before plasma formation occurs. This type of shutter enables one to reduce the pulse duration down to ˜2 ns and to remove the low power, long duration tails that are present in TEA CO2 pulses. The transmitted energy is reduced as the pulse duration is decreased but the reflected power is ˜10 MW for all pulse durations. A simple laser heating model verifies that the pulse shortening depends directly on the plasma formation time, which in turn is dependent on the applied laser intensity. It is envisaged that this plasma shutter will be used as a tool for pulse shaping in the search for laser pulse conditions to optimize conversion efficiency from laser energy to useable extreme ultraviolet (EUV) radiation for EUV source development.

  18. A new sealed RF-excited CO2 laser for enamel ablation operating at 9.4-μm with a pulse duration of 26-μs.

    PubMed

    Chan, Kenneth H; Jew, Jamison M; Fried, Daniel

    2016-02-13

    Several studies over the past 20 years have shown that carbon dioxide lasers operating at wavelengths between 9.3 and 9.6-μm with pulse durations near 20-μs are ideal for hard tissue ablation. Those wavelengths are coincident with the peak absorption of the mineral phase. The pulse duration is close to the thermal relaxation time of the deposited energy of a few microseconds which is short enough to minimize peripheral thermal damage and long enough to minimize plasma shielding effects to allow efficient ablation at practical rates. The desired pulse duration near 20-μs has been difficult to achieve since it is too long for transverse excited atmospheric pressure (TEA) lasers and too short for radio-frequency (RF) excited lasers for efficient operation. Recently, Coherent Inc. (Santa Clara, CA) developed the Diamond J5-V laser for microvia drilling which can produce laser pulses greater than 100-mJ in energy at 9.4-μm with a pulse duration of 26-μs and it can achieve pulse repetition rates of 3 KHz. We report the first results using this laser to ablate dental enamel. Efficient ablation of dental enamel is possible at rates exceeding 50-μm per pulse. This laser is ideally suited for the selective ablation of carious lesions.

  19. Experimental Investigation of Molecular Species Formation in Metal Plasmas During Laser Ablation

    NASA Astrophysics Data System (ADS)

    Radousky, H.; Crowhurst, J.; Rose, T.; Armstrong, M.; Stavrou, E.; Zaug, J.; Weisz, D.; Azer, M.; Finko, M.; Curreli, D.

    2016-10-01

    Atomic and molecular spectra on metal plasmas generated by laser ablation have been measured using single, nominally 6-7 ns pulses at 1064 nm, and with energies less than 50 mJ. The primary goal for these studies is to constrain the physical and chemical mechanisms that control the distribution of radionuclides in fallout after a nuclear detonation. In this work, laser emission spectroscopy was used to obtain in situdata for vapor phase molecular species as they form in a controlled oxygen atmosphere for a variety of metals such as Fe, Al, as well as preliminary results for U. In particular, the ablation plumes created from these metals have been imaged with a resolution of 10 ns, and it is possible to observe the expansion of the plume out to 0.5 us. These data serve as one set of inputs for a semi-empirical model to describe the chemical fractionation of uranium during fallout formation. Prepared by LLNL under Contract DE-AC52-07NA27344. This project was sponsored by the Department of the Defense, Defense Threat Reduction Agency, under Grant Number HDTRA1-16-1-0020.

  20. Influence of consecutive picosecond pulses at 532 nm wavelength on laser ablation of human teeth

    NASA Astrophysics Data System (ADS)

    Mirdan, Balsam M.; Antonelli, Luca; Batani, Dimitri; Jafer, Rashida; Jakubowska, Katarzyna; Tarazi, Saad al; Villa, Anna Maria; Vodopivec, Bruno; Volpe, Luca

    2014-07-01

    The interaction of 40 ps pulse duration laser emitting at 532 nm wavelength with human dental tissue (enamel, dentin, and dentin-enamel junction) has been investigated. The crater profile and the surface morphology have been studied by using a confocal auto-fluorescence microscope (working in reflection mode) and a scanning electron microscope. Crater profile and crater morphology were studied after applying consecutive laser pulses and it was found that the ablation depth increases with the number of consecutive pulses, leaving the crater diameter unchanged. We found that the thermal damage is reduced by using short duration laser pulses, which implies an increased retention of restorative material. We observe carbonization of the irradiated samples, which does not imply changes in the chemical composition. Finally, the use of 40 ps pulse duration laser may become a state of art in conservative dentistry.

  1. Landau damping of a driven plasma wave from laser pulses

    SciTech Connect

    Bu Zhigang; Ji Peiyong

    2012-01-15

    The interaction between a laser pulse and a driven plasma wave with a phase velocity approaching the speed of light is studied, and our investigation is focused on the Gaussian laser pulse. It is demonstrated that when the resonance condition between the plasma wave and the laser pulse is satisfied, the Landau damping phenomenon of the plasma wave originated from the laser pulse will emerge. The dispersion relations for the plasma waves in resonance and non-resonance regions are obtained. It is proved that the Landau damping rate for a driven plasma wave is {gamma}>0 in the resonance region, so the laser pulse can produce an inverse damping effect, namely Landau growth effect, which leads an instability for the plasma wave. The Landau growth means that the energy is transmitted from the laser pulse to the plasma wave, which could be an effective process for enhancing the plasma wave.

  2. Long Pulse ECH Plasma in LHD

    SciTech Connect

    Kubo, S.; Yoshimura, Y.; Shimozuma, T.; Igami, H.; Notake, T.; Kumazawa, R.; Seki, T.; Saito, K.; Nakamura, Y.; Mutoh, T.; Ohkubo, K.

    2005-09-26

    Demonstration of a long pulse or a steady state operation of ECH and sustainment of non-collapsed plasma only by ECH is important in LHD from both the confinement device and the heating system engineering points of view. A gyrotron with a diamond output window is introduced and operated at the power level of 150 kW for more than 1 hour after modification of the cooling and evacuation system of the ECH transmission line. The power of about 110 kW injected into LHD is used to sustain the plasma with the electron density of 1.5 x 1018 m-3 and central temperature of more than 1.0 keV for 3900 sec. The gas puffing rate is carefully controlled so that the plasma density does not exceed the critical value above which the plasma collapsed for given injection power, magnetic configuration and wall condition of LHD. The results of gyrotron operation, transmission system modification for long pulse and optimizations of the magnetic field configuration of LHD and gas puffing for a given injection condition are discussed.

  3. Long Pulse ECH Plasma in LHD

    NASA Astrophysics Data System (ADS)

    Kubo, S.; Yoshimura, Y.; Shimozuma, T.; Igami, H.; Notake, T.; Kumazawa, R.; Seki, T.; Saito, K.; Nakamura, Y.; Mutoh, T.; LHD Experimental Group

    2005-09-01

    Demonstration of a long pulse or a steady state operation of ECH and sustainment of non-collapsed plasma only by ECH is important in LHD from both the confinement device and the heating system engineering points of view. A gyrotron with a diamond output window is introduced and operated at the power level of 150 kW for more than 1 hour after modification of the cooling and evacuation system of the ECH transmission line. The power of about 110 kW injected into LHD is used to sustain the plasma with the electron density of 1.5 × 1018 m-3 and central temperature of more than 1.0 keV for 3900 sec. The gas puffing rate is carefully controlled so that the plasma density does not exceed the critical value above which the plasma collapsed for given injection power, magnetic configuration and wall condition of LHD. The results of gyrotron operation, transmission system modification for long pulse and optimizations of the magnetic field configuration of LHD and gas puffing for a given injection condition are discussed.

  4. A compact non-differential approach for modeling laser ablation plasma dynamics

    NASA Astrophysics Data System (ADS)

    Irimiciuc, S. A.; Gurlui, S.; Nica, P.; Focsa, C.; Agop, M.

    2017-02-01

    Various differentiable physical models are frequently used to describe the dynamics of laser-produced plasma plumes (e.g., kinetic models, two-fluid models, etc.). Given the complexity of all the phenomena involved in the laser-matter interactions, it is required to introduce the laser ablation plasma dynamic variable dependencies both on the space-time coordinates and on the resolution scales. Therefore, an adequate theoretical approach may be the use of non-differentiable physical models (fractal models). Continuing our previous work on the fractal hydrodynamic model for laser ablation plasma dynamics, we propose here a compact version for the analysis of the spatial and temporal evolution of some plasma dynamic variables, such as velocities, currents, number densities, or temperatures. Moreover, the influence of external factors on the ablation plasma dynamics is considered. The predictions of this model are compared with the experimental data obtained by using a Langmuir probe on an Aluminum laser-produced plasma.

  5. Cavitation effect of holmium laser pulse applied to ablation of hard tissue underwater.

    PubMed

    Lü, Tao; Xiao, Qing; Xia, Danqing; Ruan, Kai; Li, Zhengjia

    2010-01-01

    To overcome the inconsecutive drawback of shadow and schlieren photography, the complete dynamics of cavitation bubble oscillation or ablation products induced by a single holmium laser pulse [2.12 microm, 300 micros (FWHM)] transmitted in different core diameter (200, 400, and 600 microm) fibers is recorded by means of high-speed photography. Consecutive images from high-speed cameras can stand for the true and complete process of laser-water or laser-tissue interaction. Both laser pulse energy and fiber diameter determine cavitation bubble size, which further determines acoustic transient amplitudes. Based on the pictures taken by high-speed camera and scanned by an optical coherent microscopy (OCM) system, it is easily seen that the liquid layer at the distal end of the fiber plays an important role during the process of laser-tissue interaction, which can increase ablation efficiency, decrease heat side effects, and reduce cost.

  6. Patterned graphene ablation and two-photon functionalization by picosecond laser pulses in ambient conditions

    SciTech Connect

    Bobrinetskiy, I. I. Otero, N.; Romero, P. M.; Emelianov, A. V.

    2015-07-27

    Direct laser writing is a technology with excellent prospects for mask-less processing of carbon-based nanomaterials, because of the wide range of photoinduced reactions that can be performed on large surfaces with submicron resolution. In this paper, we demonstrate the use of picoseconds laser pulses for one-step ablation and functionalization of graphene. Varying the parameters of power, pulse frequency, and speed, we demonstrated the ablation down to 2 μm width and up to mm-long lines as well as functionalization with spatial resolution less than 1 μm with linear speeds in the range of 1 m/s. Raman and atomic-force microscopy studies were used to indicate the difference in modified graphene states and correlation to the changes in optical properties.

  7. A novel laser ablation plasma thruster with electromagnetic acceleration

    NASA Astrophysics Data System (ADS)

    Zhang, Yu; Zhang, Daixian; Wu, Jianjun; He, Zhen; Zhang, Hua

    2016-10-01

    A novel laser ablation plasma thruster accelerated by electromagnetic means was proposed and investigated. The discharge characteristics and thrust performance were tested with different charged energy, structural parameters and propellants. The thrust performance was proven to be improved by electromagnetic acceleration. In contrast with the pure laser propulsion mode, the thrust performance in electromagnetic acceleration modes was much better. The effects of electrodes distance and the off-axis distance between ceramic tube and cathode were tested, and it's found that there were optimal structural parameters for achieving optimal thrust performance. It's indicated that the impulse bit and specific impulse increased with increasing charged energy. In our experiments, the thrust performance of the thruster was optimal in large charged energy modes. With the charged energy 25 J and the use of metal aluminum, a maximal impulse bit of 600 μNs, a specific impulse of approximate 8000 s and thrust efficiency of about 90% were obtained. For the PTFE propellant, a maximal impulse bit of about 350 μNs, a specific impulse of about 2400 s, and thrust efficiency of about 16% were obtained. Besides, the metal aluminum was proven to be the better propellant than PTFE for the thruster.

  8. Gold fingerprinting by laser ablation inductively coupled plasma mass spectrometry

    NASA Astrophysics Data System (ADS)

    Watling, R. John; Herbert, Hugh K.; Delev, Dianne; Abell, Ian D.

    1994-02-01

    Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) has been applied to the characterization of the trace element composition "fingerprint" of selected gold samples from Western Australia and South Africa. By comparison of the elemental associations it is possible to relate gold to a specific mineralizing event, mine or bullion sample. This methodology facilitates identification of the provenance of stolen gold or gold used in salting activities. In this latter case, it is common for gold from a number of sources to be used in the salting process. Consequently, gold in the prospect being salted will not come from a single source and identification of multiple sources for this gold will establish that salting has occurred. Preliminary results also indicate that specific elemental associations could be used to identify the country of origin of gold. The technique has already been applied in 17 cases involving gold theft in Western Australia, where it is estimated that up to 2% of gold production is "relocated" each year as a result of criminal activities.

  9. Antimullerian Hormone Level and Endometrioma Ablation Using Plasma Energy

    PubMed Central

    Bubenheim, Michael; Auber, Mathieu; Marpeau, Loïc; Puscasiu, Lucian

    2014-01-01

    Objective: To investigate the impact of ovarian endometrioma vaporization using plasma energy on antimullerian hormone (AMH) level. Method: We report a prospective, noncomparative series (NCT01596985). Twenty-two patients with unilateral ovarian endometriomas ≥30 mm, with no surgical antecedent and no ongoing pregnancy, underwent vaporization of ovarian endometriomas using plasma energy during the period of November 29, 2010 to November 28, 2012. We assessed AMH levels before surgery, 3 months postoperatively, and at the end of follow-up. Results: The mean length of postoperative follow-up was 18.2 ± 8 months. AMH level significantly varied through the 3 assessments performed in the study, as the mean values ± SD were 3.9 ± 2.6 ng/mL before the surgery, 2.3 ± 1.1 ng/mL at 3 months, and 3.1 ± 2.2 ng/mL at the end of the follow-up (P = .001). There was a significant increase from 3 months postoperatively to the end of follow-up (median change 0.7 ng/mL, P = .01). Seventy-one percent of patients had an AMH level >2 ng/mL at the end of the follow-up versus 76% before the surgery (P = 1). During the postoperative follow-up, 11 patients tried to conceive, of whom 8 (73%) became pregnant. Conclusions: The ablation of unilateral endometriomas is followed in a majority of cases by a significant decrease in AMH level 3 months after surgery. In subsequent months, this level progressively increases, raising questions about the real factors that impact postoperative ovarian AMH production. PMID:25392649

  10. Pulsed Electromagnetic Acceleration of Plasma: A Review

    NASA Technical Reports Server (NTRS)

    Thio, Y. C. Francis; Turchi, Peter J.; Markusic, Thomas E.; Cassibry, Jason T.; Sommer, James; Rodgers, Stephen L. (Technical Monitor)

    2002-01-01

    Much have been learned in the acceleration mechanisms involved in accelerating a plasma electromagnetically in the laboratory over the last 40 years since the early review by Winston Bostik of 1963, but the accumulated understanding is very much scattered throughout the literature. This literature extends back at least to the early sixties and includes Rosenbluth's snowplow model, discussions by Ralph Lovberg, Colgate's boundary-layer model of a current sheet, many papers from the activity at Columbia by Robert Gross and his colleagues, and the relevant, 1-D unsteady descriptions developed from the U. of Maryland theta-pinch studies. Recent progress on the understanding of the pulsed penetration of magnetic fields into collisionless or nearly collisionless plasmas are also be reviewed. Somewhat more recently, we have the two-dimensional, unsteady results in the collisional regime associated with so-called wall-instability in large radius pinch discharges and also in coaxial plasma guns (e.g., Plasma Flow Switch). Among other things, for example, we have the phenomenon of a high- density plasma discharge propagating in a cooaxial gun as an apparently straight sheet (vs paraboloid) because mass re-distribution (on a microsecond timescale) compensates for the 1/r- squared variation of magnetic pressure. We will attempt to collate some of this vast material and bring some coherence tc the development of the subject.

  11. Analysis of process parameter for the ablation of optical glasses with femto- and picosecond laser pulses

    NASA Astrophysics Data System (ADS)

    Schindler, Christian; Friedrich, Maria; Bliedtner, Jens

    2016-03-01

    Experiments with an ultrashort pulsed laser system emitting pulses ranging from 350 fs to 10 ps and a maximum average power of 50 W at 1030 nm are presented. The laser beam gets deflected by a galvanometric scan-system with maximum scan speed of 2500 mm/s and focused by F-theta lenses onto the substrates. By experiments the influences of pulse energy, fluence, laser wavelength, pulse length and material conditions on the target figures is analyzed. These are represented by the material characteristics mean squared roughness, ablation depths as well as the microcrack distribution in depth. The experimental procedure is applied onto a series of fused silica and SF6 samples.

  12. Laser ablation plasmas for diagnostics of structured electronic and optical materials during or after laser processing

    NASA Astrophysics Data System (ADS)

    Russo, Richard E.; Bol'shakov, Alexander A.; Yoo, Jong H.; González, Jhanis J.

    2012-03-01

    Laser induced plasma can be used for rapid optical diagnostics of electronic, optical, electro-optical, electromechanical and other structures. Plasma monitoring and diagnostics can be realized during laser processing in real time by means of measuring optical emission that originates from the pulsed laser-material interaction. In post-process applications, e.g., quality assurance and quality control, surface raster scanning and depth profiling can be realized with high spatial resolution (~10 nm in depth and ~3 μm lateral). Commercial instruments based on laser induced breakdown spectrometry (LIBS) are available for these purposes. Since only a laser beam comes in direct contact with the sample, such diagnostics are sterile and non-disruptive, and can be performed at a distance, e.g. through a window. The technique enables rapid micro-localized chemical analysis without a need for sample preparation, dissolution or evacuation of samples, thus it is particularly beneficial in fabrication of thin films and structures, such as electronic, photovoltaic and electro-optical devices or circuits of devices. Spectrum acquisition from a single laser shot provides detection limits for metal traces of ~10 μg/g, which can be further improved by accumulating signal from multiple laser pulses. LIBS detection limit for Br in polyethylene is 90 μg/g using 50-shot spectral accumulation (halogen detection is a requirement for semiconductor package materials). Three to four orders of magnitude lower detection limits can be obtained with a femtosecond laser ablation - inductively coupled plasma mass spectrometer (LA-ICP-MS), which is also provided on commercial basis. Laser repetition rate is currently up to 20 Hz in LIBS instruments and up to 100 kHz in LA-ICP-MS.

  13. Laser-ablation sampling for inductively coupled plasma distance-of-flight mass spectrometry

    SciTech Connect

    Gundlach-Graham, Alexander W.; Dennis, Elise; Ray, Steven J.; Enke, Christie G.; Barinaga, Charles J.; Koppenaal, David W.; Hieftje, Gary M.

    2015-01-01

    An inductively coupled plasma distance-of-flight mass spectrometer (ICP-DOFMS) has been coupled with laser-ablation (LA) sample introduction for the elemental analysis of solids. ICP-DOFMS is well suited for the analysis of laser-generated aerosols because it offers both high-speed mass analysis and simultaneous multi-elemental detection. Here, we evaluate the analytical performance of the LA-ICP-DOFMS instrument, equipped with a microchannel plate-based imaging detector, for the measurement of steady-state LA signals, as well as transient signals produced from single LA events. Steady-state detection limits are 1 mg g1, and absolute single-pulse LA detection limits are 200 fg for uranium; the system is shown capable of performing time-resolved single-pulse LA analysis. By leveraging the benefits of simultaneous multi-elemental detection, we also attain a good shot-to-shot reproducibility of 6% relative standard deviation (RSD) and isotope-ratio precision of 0.3% RSD with a 10 s integration time.

  14. Pulsed Inductive Plasma Acceleration: Performance Optimization Criteria

    NASA Technical Reports Server (NTRS)

    Polzin, Kurt A.

    2014-01-01

    Optimization criteria for pulsed inductive plasma acceleration are developed using an acceleration model consisting of a set of coupled circuit equations describing the time-varying current in the thruster and a one-dimensional momentum equation. The model is nondimensionalized, resulting in the identification of several scaling parameters that are varied to optimize the performance of the thruster. The analysis reveals the benefits of underdamped current waveforms and leads to a performance optimization criterion that requires the matching of the natural period of the discharge and the acceleration timescale imposed by the inertia of the working gas. In addition, the performance increases when a greater fraction of the propellant is initially located nearer to the inductive acceleration coil. While the dimensionless model uses a constant temperature formulation in calculating performance, the scaling parameters that yield the optimum performance are shown to be relatively invariant if a self-consistent description of energy in the plasma is instead used.

  15. Determination of the temporal structure of femtosecond laser pulses by means of laser-induced air plasma

    NASA Astrophysics Data System (ADS)

    Zhang, Nan; Bao, Wen-Xia; Yang, Jing-Hui; Zhu, Xiao-Nong

    2013-05-01

    A new approach is presented to reveal the temporal structure of femtosecond laser pulses by recording the corresponding time-resolved shadowgraphs of the laser-induced air plasma. It is shown that the temporal structures of femtosecond laser pulses, normally not observable by the ordinary intensity autocorrelator, can be detected through intuitively analyzing the ultrafast evolution process of the air plasma induced by the femtosecond laser pulses under examination. With this method, existence of pre- and post-pulses has been clearly unveiled within the time window of ±150 fs in reference with the main 50-fs laser pulses output from a commercial 1-kHz femtosecond laser amplifier. The unique advantage of the proposed method is that it can directly provide valuable information about the pulse temporal structures' effect on the laser-induced ionization or material ablation.

  16. A comparative study on reflection of nanosecond Nd-YAG laser pulses in ablation of metals in air and in vacuum.

    PubMed

    Benavides, O; May, L de la Cruz; Gil, A Flores

    2013-06-03

    A comparative study on reflection of nanosecond Nd-YAG laser pulses in ablation of aluminum in air and in vacuum under the same other experimental conditions is performed. We find that, hemispherical total reflectivity of aluminum undergoes a sharp drop at the plasma formation threshold both in the air and in vacuum. The initial large value (0.8) of aluminum reflectivity decreases to a level of about 0.14 and 0.24 for ablation in the air and in vacuum, respectively. These decreased reflectivity values remain virtually unchanged with further increasing laser fluence. The reflectivity drop in the air is observed to be sharper than in vacuum. Our study indicates that the reflectivity drop is predominantly caused by absorption of the laser light in plasma. Nano/micro-structural defects present on practical sample surfaces play the important role in the plasma formation, especially for the ablation in the air, where the plasma formation threshold is found to be by a factor of 3 smaller than in vacuum.

  17. Propagation of chirped laser pulses in a plasma channel

    SciTech Connect

    Jha, Pallavi; Malviya, Amita; Upadhyay, Ajay K.

    2009-06-15

    Propagation of an initially chirped, Gaussian laser pulse in a preformed parabolic plasma channel is analyzed. A variational technique is used to obtain equations describing the evolution of the phase shift and laser spot size. The effect of initial chirp on the laser pulse length and intensity of a matched laser beam propagating in a plasma channel has been analyzed. The effective pulse length and chirp parameter of the laser pulse due to its interaction with plasma have been obtained and graphically depicted. The resultant variation in laser frequency across the laser pulse is discussed.

  18. INTERACTION OF LASER RADIATION WITH MATTER. LASER PLASMA: Percolation upon expansion of nanosecond-pulse-produced laser plasma into a gas

    NASA Astrophysics Data System (ADS)

    Kask, Nikolai E.; Michurin, Sergei V.; Fedorov, Gennadii M.

    2005-01-01

    Spectral studies of a plasma expanding into the ambient gas upon ablation of various targets by nanosecond laser pulses of moderate intensities are performed. It is found that the dependences of the intensities of spectral lines on the pressure of the buffer gas and the target composition have a threshold character typical of percolation. It is ascertained that a three-dimensional percolation occurs in plasma, and its threshold is determined by the atomic density of the metal component contained in the target. It is shown that percolation clusters, existing at temperatures higher than the boiling temperature of the target material, affect the plasma absorption ability, temperature, and spectral continuum of plasma emission.

  19. Silver nanoparticles generated by pulsed laser ablation in supercritical CO2 medium

    NASA Astrophysics Data System (ADS)

    Machmudah, Siti; Sato, Takayuki; Wahyudiono; Sasaki, Mitsuru; Goto, Motonobu

    2012-03-01

    Pulsed laser ablation (PLA) has been widely employed in industrial and biological applications and in other fields. The environmental conditions in which PLA is conducted are important parameters that affect both the solid particle cloud and the deposition produced by the plume. In this work, the generation of nanoparticles (NPs) has been developed by performing PLA of silver (Ag) plates in a supercritical CO2 medium. Ag NPs were successfully generated by allowing the selective generation of clusters. Laser ablation was performed with an excitation wavelength of 532 nm under various pressures and temperatures of CO2 medium. On the basis of the experimental result, both surface of the irradiated Ag plate and structure of Ag NPs were significantly affected by the changes in supercritical CO2 pressure and temperature. With increasing irradiation pressure, plume deposited in the surrounding crater created by the ablation was clearly observed. In Field Emission Scanning Electron Microscopy (FE-SEM) the image of the generated Ag NPs on the silicon wafer and the morphology of Ag particles were basically a sphere-like structure. Ag particles contain NPs with large-varied diameter ranging from 5 nm to 1.2 μm. The bigger Ag NPs melted during the ablation process and then ejected smaller spherical Ag NPs, which formed nanoclusters attached on the molten Ag NPs. The smaller Ag NPs were also formed around the bigger Ag NPs. Based on the results, this new method can also be used to obtain advanced nano-structured materials.

  20. Structure of diamondlike carbon films deposited by femtosecond and nanosecond pulsed laser ablation

    NASA Astrophysics Data System (ADS)

    Sikora, A.; Garrelie, F.; Donnet, C.; Loir, A. S.; Fontaine, J.; Sanchez-Lopez, J. C.; Rojas, T. C.

    2010-12-01

    The characterization of diamondlike carbon (DLC) films is a challenging subject, considering the diversity of carbon-based nanostructures depending on the deposition process. We propose to combine multiwavelength (MW) Raman spectroscopy and electron energy-loss spectroscopy (EELS) to probe the structural disorder and the carbon hybridizations of DLC films deposited by pulsed laser ablation performed either with a nanosecond laser (film labeled ns-DLC), either with a femtosecond laser (film labeled fs-DLC). Such deposition methods allow to reach a rather high carbon sp3 hybridization but with some significant differences in terms of structural disorder and carbonaceous chain configurations. MW Raman investigations, both in the UV and visible range, is a popular and nondestructive way to probe the structural disorder and the carbon hybridizations. EELS allows the determination of the carbon plasmon energy in the low-loss energy region of the spectra, as well as the fine structure of the ionization threshold in the high-loss energy region. The paper shows that the combination of MW Raman and EELS is a powerful way to elucidate the nanostructure of DLC films. Complementary nanoindentation investigations allow to correlate the analytical results with the mechanical properties of the films. The ns-DLC film presents a stronger sp3-bonded C character (74%-85%) with a significant content of sp2 chains, whereas the fs-DLC contains less sp3 bonds (35%-50%) with a significant content of sp2-bonded C rings. The ns-DLC film exhibits a higher proportion of disordered sp2 C mainly in the form of chains. Comparatively, the fs-DLC exhibits a predominance of more ordered sp2 C structures in the form of graphitic aggregates whose size has been estimated near three aromatic rings. The film characteristics are in agreement with their mechanical properties. We also propose a correlation between the nanostructure and composition of the films with the deposition mechanisms. The difference

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

    NASA Astrophysics Data System (ADS)

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

    2013-04-01

    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.

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

    SciTech Connect

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

    2013-04-14

    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.

  3. Controlling the oxidation processes of Zn nanoparticles produced by pulsed laser ablation in aqueous solution

    NASA Astrophysics Data System (ADS)

    Camarda, P.; Messina, F.; Vaccaro, L.; Buscarino, G.; Agnello, S.; Gelardi, F. M.; Cannas, M.

    2016-09-01

    We used online UV-VIS optical absorption and photoluminescence spectra, acquired during and after pulsed laser ablation of a Zinc plate in aqueous solution, to investigate the effect of the laser repetition rate and liquid environment on the oxidation processes of the produced nanoparticles. A transient Zn/ZnO core-shell structure was revealed by the coexistence of an absorption peak around 5.0 eV due to Zn surface plasmon resonance and of an edge at 3.4 eV coming from wurtzite ZnO. The growth kinetics of ZnO at the various repetition rates, selectively probed by the excitonic emission at 3.3 eV, began immediately at the onset of laser ablation and was largely independent of the repetition rate. In addition, we detected an emission at 2.3 eV related to oxygen vacancies, which began to grow after a number of pulses increasing with the used repetition rate. Optical absorption spectra during and after ablation in a mixture of water and ethanol (0%-100%) revealed that the oxidation kinetics of Zn nanoparticles slows down from about 900 s in pure water to at least one week in pure ethanol.

  4. Growth of anatase and rutile phase TiO2 nanoparticles using pulsed laser ablation in liquid: Influence of surfactant addition and ablation time variation

    NASA Astrophysics Data System (ADS)

    Chaturvedi, Amita; Joshi, M. P.; Mondal, P.; Sinha, A. K.; Srivastava, A. K.

    2017-02-01

    Titanium dioxide (TiO2) nanoparticles were grown using nanosecond pulsed laser ablation of Ti target in DI water and in 0.001 M sodium dodecyl sulfate (SDS) surfactant aqueous solution. Growth was carried out with varying ablation times i. e. 30 min, 60 min and 90 min. The objective of our study was to investigate the influence of variations in liquid ambience conditions on the growth of the nanoparticles in a pulsed laser ablation in liquid (PLAL) process. Size, composition and optical properties of the grown TiO2 nanoparticles were investigated using transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), optical absorption, photoluminescence (PL) spectroscopy and X-ray diffraction (XRD) studies. The obtained nanoparticles of TiO2 were found almost spherical in shape and polycrystalline in nature in both the liquid mediums i.e. DI water and aqueous solution of surfactant. Nanoparticles number density was also found to increase with increasing ablation time in both the liquid mediums. However crystalline phase of the grown TiO2 nanoparticles differs with the change in liquid ambience conditions. Selected area electron diffraction (SAED), PL and XRD studies suggest that DI water ambience is favorable for the growth of anatase phase TiO2 nanoparticles for all ablation times. While Surfactant added water ambience is favorable for the growth of rutile phase TiO2 nanoparticles but for shorter ablation times of 30 min and 60 min only, for longer ablation time of 90 min anatase phase was also observed along with the rutile phase TiO2 nanoparticles. The formation of anatase phase in DI water and rutile and anatase phase in aqueous solution of surfactant is explained on the basis of varying thermodynamic conditions with the two different liquid ambiences and different ablation times.

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

    NASA Astrophysics Data System (ADS)

    Yan, Zijie

    2011-12-01

    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

  6. EVOLUTION OF FAST MAGNETOACOUSTIC PULSES IN RANDOMLY STRUCTURED CORONAL PLASMAS

    SciTech Connect

    Yuan, D.; Li, B.; Pascoe, D. J.; Nakariakov, V. M.; Keppens, R. E-mail: bbl@sdu.edu.cn

    2015-02-01

    We investigate the evolution of fast magnetoacoustic pulses in randomly structured plasmas, in the context of large-scale propagating waves in the solar atmosphere. We perform one-dimensional numerical simulations of fast wave pulses propagating perpendicular to a constant magnetic field in a low-β plasma with a random density profile across the field. Both linear and nonlinear regimes are considered. We study how the evolution of the pulse amplitude and width depends on their initial values and the parameters of the random structuring. Acting as a dispersive medium, a randomly structured plasma causes amplitude attenuation and width broadening of the fast wave pulses. After the passage of the main pulse, secondary propagating and standing fast waves appear. Width evolution of both linear and nonlinear pulses can be well approximated by linear functions; however, narrow pulses may have zero or negative broadening. This arises because narrow pulses are prone to splitting, while broad pulses usually deviate less from their initial Gaussian shape and form ripple structures on top of the main pulse. Linear pulses decay at an almost constant rate, while nonlinear pulses decay exponentially. A pulse interacts most efficiently with a random medium with a correlation length of about half of the initial pulse width. This detailed model of fast wave pulses propagating in highly structured media substantiates the interpretation of EIT waves as fast magnetoacoustic waves. Evolution of a fast pulse provides us with a novel method to diagnose the sub-resolution filamentation of the solar atmosphere.

  7. Analysis of Sterilization Effect of Atmospheric Pressure Pulsed Plasma

    SciTech Connect

    Ekem, N.; Akan, T.; Pat, S.; Akgun, Y.; Kiremitci, A.; Musa, G.

    2007-04-23

    We have developed a new technology, the High Voltage Atmospheric Pressure Pulsed Plasma (HVAPPP), for bacteria killing. The aim of this paper is to present a simple device to generate plasma able to kill efficiently bacteria.

  8. Influence of plasma parameters and substrate temperature on the structural and optical properties of CdTe thin films deposited on glass by laser ablation

    SciTech Connect

    Quiñones-Galván, J. G.; Santana-Aranda, M. A.; Pérez-Centeno, A.; Camps, Enrique; Campos-González, E.; Guillén-Cervantes, A.; Santoyo-Salazar, J.; Zelaya-Angel, O.; Hernández-Hernández, A.

    2015-09-28

    In the pulsed laser deposition of thin films, plasma parameters such as energy and density of ions play an important role in the properties of materials. In the present work, cadmium telluride thin films were obtained by laser ablation of a stoichiometric CdTe target in vacuum, using two different values for: substrate temperature (RT and 200 °C) and plasma energy (120 and 200 eV). Structural characterization revealed that the crystalline phase can be changed by controlling both plasma energy and substrate temperature; which affects the corresponding band gap energy. All the thin films showed smooth surfaces and a Te rich composition.

  9. Elemental fractionation in 785 nm picosecond and femtosecond laser ablation inductively coupled plasma mass spectrometry

    NASA Astrophysics Data System (ADS)

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

    2015-05-01

    Elemental fractionation and ICP-MS signal response were investigated for two different pulse width laser beams originating from the same laser system. Femtosecond and picosecond laser beams at pulse widths of 130 fs and 110 ps, respectively, and wavelength of 785 nm were used to ablate NIST 610 synthetic glass and SRM 1107 Naval Brass B at the same spot for 800 to 1000 laser pulses at different repetition rates (5 to 50 Hz). Elemental fractionation was found to depend on repetition rate and showed a trend with femtosecond laser ablation that is opposite to that observed in picosecond laser ablation for most measured isotopes. ICP-MS signal intensity was higher in femtosecond than picosecond LA-ICP-MS in both NIST 610 and naval brass when ablation was conducted under the same fluence and repetition rate. The differences in signal intensity were partly related to differences in particle size distribution between particles generated by femtosecond and picosecond laser pulses and the consequent differences in transport and ionization efficiencies. The main reason for the higher signal intensity resulting from femtosecond laser pulses was related to the larger crater sizes compared to those created during picosecond laser ablation. Elemental ratios measured using 66Zn/63Cu, 208Pb/238U, 232Th/238U, 66Zn/232Th and 66Zn/208Pb were found to change with the number of laser pulses with data points being more scattered in picosecond than femtosecond laser pulses. Reproducibility of replicate measurements of signal intensities, fractionation and elemental ratios was better for fs-LA-ICP-MS (RSD ~ 3 to 6%) than ps-LA-ICP-MS (RSD ~ 7 to 11%).

  10. Terahertz refractive anisotropy on femtosecond laser pulse ablated semi-insulating gallium arsenide surface

    NASA Astrophysics Data System (ADS)

    Zhao, Zhenyu; Song, Zhiqiang; Bai, Feng; Shi, Wangzhou; Zhao, Quan-Zhong

    2017-04-01

    We present an artificial variation of THz refractive index ellipse from isotropy to anisotropy at the surface of <100>-oriented semi-insulating gallium arsenide (SI-GaAs) via femtosecond pulse laser ablation. The refractive index ellipse is determined by the frequency and the polarization of incident THz radiation. The THz wave is localized in the gap of columns of micro-ripples when the polarization of THz is parallel to the micro-ripples, while no electric energy localization occurs when the polarization of THz is perpendicular to the micro-ripples. We found that the laser ablation process can induce a periodic distribution of n-type GaAs at the surface of SI-GaAs. These n-type GaAs micro-ripples work as plasmonic resonators, which are proposed to be the origin of the induced refractive index anisotropy.

  11. Solid-like ablation propulsion generation in nanosecond pulsed laser interaction with carbon-doped glycerol

    NASA Astrophysics Data System (ADS)

    Zheng, Zhi-Yuan; Zhang, Si-Qi; Liang, Tian; Qi, Jing; Tang, Wei-Chong; Xiao, Ke; Gao, Lu; Gao, Hua; Zhang, Zi-Li

    2017-03-01

    A solid-like propellant of carbon-doped glycerol ablated by a nanosecond pulsed laser is investigated. The results show that the specific impulse increases with increasing carbon content, and a maximum value of 228 s is obtained. The high specific impulse is attributed to the low ablated mass loss that occurs at high carbon content. More importantly, with increasing carbon content, the properties of the doped glycerol approach to those of a solid. These results indicate that propulsion at the required coupling coefficient and specific impulse can be realized by doping a liquid propellant with an absorber. Project supported by the Fundamental Research Funds for the Central Universities, China (Grant Nos. 53200859165 and 2562010050).

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

    PubMed

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

    2013-01-01

    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.

  13. Heat generation caused by ablation of dental hard tissues with an ultrashort pulse laser (USPL) system.

    PubMed

    Braun, Andreas; Krillke, Raphael Franz; Frentzen, Matthias; Bourauel, Christoph; Stark, Helmut; Schelle, Florian

    2015-02-01

    Heat generation during the removal of dental hard tissues may lead to a temperature increase and cause painful sensations or damage dental tissues. The aim of this study was to assess heat generation in dental hard tissues following laser ablation using an ultrashort pulse laser (USPL) system. A total of 85 specimens of dental hard tissues were used, comprising 45 specimens of human dentine evaluating a thickness of 1, 2, and 3 mm (15 samples each) and 40 specimens of human enamel with a thickness of 1 and 2 mm (20 samples each). Ablation was performed with an Nd:YVO4 laser at 1,064 nm, a pulse duration of 9 ps, and a repetition rate of 500 kHz with an average output power of 6 W. Specimens were irradiated for 0.8 s. Employing a scanner system, rectangular cavities of 1-mm edge length were generated. A temperature sensor was placed at the back of the specimens, recording the temperature during the ablation process. All measurements were made employing a heat-conductive paste without any additional cooling or spray. Heat generation during laser ablation depended on the dental hard tissue (enamel or dentine) and the thickness of the respective tissue (p < 0.05). Highest temperature increase could be observed in the 1-mm thickness group for enamel. Evaluating the 1-mm group for dentine, a significantly lower temperature increase could be measured (p < 0.05) with lowest values in the 3-mm group (p < 0.05). A time delay for temperature increase during the ablation process depending on the material thickness was observed for both hard tissues (p < 0.05). Employing the USPL system to remove dental hard tissues, heat generation has to be considered. Especially during laser ablation next to pulpal tissues, painful sensations and potential thermal injury of pulp tissue might occur.

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

    PubMed

    Hirata, Takafumi; Kon, Yoshiaki

    2008-03-01

    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

  15. Carbon isotope separation and molecular formation in laser-induced plasmas by laser ablation molecular isotopic spectrometry.

    PubMed

    Dong, Meirong; Mao, Xianglei; Gonzalez, Jhanis J; Lu, Jidong; Russo, Richard E

    2013-03-05

    Laser ablation molecular isotopic spectrometry (LAMIS) recently was reported for rapid isotopic analysis by measuring molecular emission from laser-induced plasmas at atmospheric pressure. This research utilized the LAMIS approach to study C2 molecular formation from laser ablation of carbon isotopic samples in a neon gas environment at 0.1 MPa. The isotopic shift for the Swan system of the C2 Δν = 1 band was chosen for carbon isotope analysis. Temporal and spatial resolved measurements of (12)C2, (12)C(13)C, and (13)C2 show that C2 forms from recombination reactions in the plasma. A theoretical simulation was used to determine the temperature from the molecular bands and to extract the isotopic ratio of (12)C/(13)C derived from (12)C2, (12)C(13)C, and (13)C2. Our data show that the ratio of (12)C/(13)C varies with time after the laser pulse and with distance above the sample. (12)C/(13)C deviates from the nominal ratio (2:1) at early times and closest to the sample surface. These measurements provide understanding of the chemical processes in the laser plasma and analytical improvement using LAMIS.

  16. Combination of fiber-guided pulsed erbium and holmium laser radiation for tissue ablation under water

    NASA Astrophysics Data System (ADS)

    Pratisto, Hans; Frenz, Martin; Ith, Michael; Altermatt, Hans J.; Jansen, E. Duco; Weber, Heinz P.

    1996-07-01

    Because of the high absorption of near-infrared laser radiation in biological tissue, erbium lasers and holmium lasers emitting at 3 and 2 mu m, respectively, have been proven to have optimal qualities for cutting or welding and coagulating tissue. To combine the advantages of both wavelengths, we realized a multiwavelength laser system by simultaneously guiding erbium and holmium laser radiation by means of a single zirconium fluoride (ZrF4) fiber. Laser-induced channel formation in water and poly(acrylamide) gel was investigated by the use of a time-resolved flash-photography setup, while pressure transients were recorded simultaneously with a needle hydrophone. The shapes and depths of vapor channels produced in water and in a submerged gel after single erbium and after combination erbium-holmium radiation delivered by means of a 400- mu m ZrF4 fiber were measured. Transmission measurements were performed to determine the amount of pulse energy available for tissue ablation. The effects of laser wavelength and the delay time between pulses of different wavelengths on the photomechanical and photothermal responses of meniscal tissue were evaluated in vitro by the use of histology. It was observed that the use of a short (200- mu s, 100-mJ) holmium laser pulse as a prepulse to generate a vapor bubble through which the ablating erbium laser pulse can be transmitted (delay time, 100 mu s) increases the cutting depth in meniscus from 450 to 1120 mu m as compared with the depth following a single erbium pulse. The results indicate that a combination of erbium and holmium laser radiation precisely and efficiently cuts tissue under water with 20-50- mu m collateral tissue damage. wave, cavitation, channel formation, infrared-fiber-delivery system, tissue damage, cartilage.

  17. Plasma Sensor Measurements in Pulse Detonation Engines

    NASA Astrophysics Data System (ADS)

    Matlis, Eric; Marshall, Curtis; Corke, Thomas; Gogineni, Sivaram

    2014-11-01

    Measurements have been conducted in a pulse detonation and rotating detonation engine using a newly developed plasma sensor. This sensor relies on the novel approach of using an ac-driven, weakly-ionized electrical discharge as the main sensing element. The advantages of this approach include a native high bandwidth of 1 MHz without the need for electronic frequency compensation, a dual-mode capability that provides sensitivity to multiple flow parameters, including velocity, pressure, temperature, and gas-species, and a simple and robust design making it very cost effective. The sensor design is installation-compatible with conventional sensors commonly used in gas-turbine research such as the Kulite dynamic pressure sensor while providing much better longevity. Developmental work was performed in high temperature facilities that are relevant to the propulsion and high-speed research community. This includes tests performed in a J85 augmentor at full afterburner and pulse-detonation engines at the University of Cincinnati (UC) at temperatures approaching 2760°C (5000°F).

  18. Measurement of ablation threshold of oxide-film-coated aluminium nanoparticles irradiated by femtosecond laser pulses

    NASA Astrophysics Data System (ADS)

    Chefonov, O. V.; Ovchinnikov, A. V.; Il'ina, I. V.; Agranat, M. B.

    2016-03-01

    We report the results of experiments on estimation of femtosecond laser threshold intensity at which nanoparticles are removed from the substrate surface. The studies are performed with nanoparticles obtained by femtosecond laser ablation of pure aluminium in distilled water. The attenuation (or extinction, i.e. absorption and scattering) spectra of nanoparticles are measured at room temperature in the UV and optical wavelength ranges. The size of nanoparticles is determined using atomic force microscopy. A new method of scanning photoluminescence is proposed to evaluate the threshold of nanoparticle removal from the surface of a glass substrate exposed to IR femtosecond laser pulses with intensities 1011 - 1013 W cm-2.

  19. Thin films deposited by femtosecond pulsed laser ablation of tungsten carbide

    NASA Astrophysics Data System (ADS)

    De Bonis, A.; Teghil, R.; Santagata, A.; Galasso, A.; Rau, J. V.

    2012-09-01

    Ultra-short Pulsed Laser Deposition has been applied to the production of thin films from a tungsten carbide target. The gaseous phase obtained by the laser ablation shows a very weak primary plume, in contrast with a very strong secondary one. The deposited films, investigated by Scanning Electron Microscopy, Atomic Force Microscopy, X-Ray Photoelectron Spectroscopy and X-Ray Diffraction, present a mixture of WC and other phases with lower carbon content. All films are amorphous, independently from the substrate temperature. The characteristics of the deposits have been explained in terms of thermal evaporation and cooling rate of molten particles ejected from the target.

  20. Green synthesis of selenium nanoparticles by excimer pulsed laser ablation in water

    NASA Astrophysics Data System (ADS)

    Van Overschelde, O.; Guisbiers, G.; Snyders, R.

    2013-10-01

    Pure selenium nanoparticles were successfully synthesized by Liquid Phase - Pulsed Laser Ablation (LP-PLA) in de-ionized water. Excimer laser (248 nm) operating at low fluence (F ˜ 1 J/cm2) was used to generate colloidal solutions of selenium nanoparticles. The obtained selenium nanoparticles were characterized by UV-visible spectroscopy, Raman spectroscopy, Dynamic Light Scattering, and Transmission Electron Microscopy. We describe the multi-modal size distributions generated and use the centrifugation method to isolate the smallest nanoparticles (˜60 nm in diameter).

  1. Pulsed laser ablation of Ni in vacuum and N{sub 2} atmosphere at various fluences

    SciTech Connect

    Shazia Bashir; Shazaib Khurshid; Mahreen Akram; Nisar Ali; Umm-i-Kalsoom; Shahbaz Ahmad; Daniel Yousaf

    2015-07-31

    Mechanisms of Ni ablation in vacuum and N{sub 2} atmosphere at various fluences ranging from 2.1 J cm{sup -2} to 3.4 J cm{sup -2} are studied by using a KrF excimer laser. The formation of various conical microstructures, ripples, large-sized irregular shaped cavities and pits is found. It is shown that no new phases are formed in the case of Ni ablation in vacuum, while new phases of nitrides and nitrooxides appear in the N{sub 2} environment. The microhardness analysis of targets irradiated in vacuum shows a decreasing trend with increasing fluence, whereas in the case of the N{sub 2} environment, a monotonic increase in hardness with increasing fluence is observed. (interaction of laser radiation with matter. laser plasma)

  2. Computational analysis of a pulsed inductive plasma accelerator

    NASA Astrophysics Data System (ADS)

    Corpening, Jeremy H.

    The pulsed inductive plasma accelerator allows for ionization of a cold gas propellant to plasma and acceleration of plasma with the same current pulse and without plasma contact with any part. This is beneficial since erosion is never a problem and lifetimes are limited only by the amount of carried propellant. To date, work involving the pulsed inductive plasma accelerator concept has been largely experimental with minimal computational analysis. The goal of the present research was to develop a computational tool using Maxwell's equations coupled with the Navier-Stokes fluid equations to fully analyze a pulsed inductive plasma accelerator. A plasma model was developed using the Saha equation and partition functions to calculate all required thermodynamic properties. The solution to Maxwell's equations was verified accurate and then coupled computations with propellant plasma were conducted. These coupled computations showed good order of magnitude accuracy with a simple onedimensional model however failed when the plasma began to accelerate due to the Lorentz force. The electric field, magnetic field, current density, and Lorentz force were all aligned in the proper vector directions. The computational failure occurred due to rapid, fictitious increases in the induced electric field in the vacuum created between the accelerating plasma and drive coil. Possible solutions to this problem are to decrease the time step and refine the grid density. Although complete acceleration of propellant plasma has yet to be computationally computed, this study has shown successful coupled computations with Maxwell and Navier-Stokes equations for a pulsed inductive plasma accelerator.

  3. Energy coupling to the plasma in repetitive nanosecond pulse discharges

    SciTech Connect

    Adamovich, Igor V.; Nishihara, Munetake; Choi, Inchul; Uddi, Mruthunjaya; Lempert, Walter R.

    2009-11-15

    A new analytic quasi-one-dimensional model of energy coupling to nanosecond pulse discharge plasmas in plane-to-plane geometry has been developed. The use of a one-dimensional approach is based on images of repetitively pulsed nanosecond discharge plasmas in dry air demonstrating that the plasma remains diffuse and uniform on a nanosecond time scale over a wide range of pressures. The model provides analytic expressions for the time-dependent electric field and electron density in the plasma, electric field in the sheath, sheath boundary location, and coupled pulse energy. The analytic model predictions are in very good agreement with numerical calculations. The model demonstrates that (i) the energy coupled to the plasma during an individual nanosecond discharge pulse is controlled primarily by the capacitance of the dielectric layers and by the breakdown voltage and (ii) the pulse energy coupled to the plasma during a burst of nanosecond pulses decreases as a function of the pulse number in the burst. This occurs primarily because of plasma temperature rise and resultant reduction in breakdown voltage, such that the coupled pulse energy varies approximately proportionally to the number density. Analytic expression for coupled pulse energy scaling has been incorporated into the air plasma chemistry model, validated previously by comparing with atomic oxygen number density measurements in nanosecond pulse discharges. The results of kinetic modeling using the modified air plasma chemistry model are compared with time-resolved temperature measurements in a repetitively pulsed nanosecond discharge in air, by emission spectroscopy, and purely rotational coherent anti-Stokes Raman spectroscopy showing good agreement.

  4. Spectroscopic characterization of the plasmas formed during the deposition of ZnO and Al-doped ZnO films by plasma-assisted pulsed laser deposition

    NASA Astrophysics Data System (ADS)

    Liang, Peipei; Cai, Hua; Yang, Xu; Li, Hui; Zhang, Wu; Xu, Ning; Sun, Jian; Wu, Jiada

    2016-11-01

    An oxygen-zinc plasma and an oxygen-zinc-aluminum plasma are formed by pulsed laser ablation of a Zn target or pulsed laser co-ablation of a Zn target and an Al target in an electron cyclotron resonance (ECR) discharge-generated oxygen plasma for the deposition of ZnO and Al-doped ZnO (AZO) films. The plasmas are characterized spectroscopically by time-integrated and time-resolved optical emission spectroscopy. Both the oxygen-zinc plasma and the oxygen-zinc-aluminum plasma contain excited species originally present in the working O2 gas and energetic species ablated from the targets. The optical emission of the oxygen-zinc-aluminum plasma is abundant in the emission bands of oxygen molecular ions and the emission lines of mono-atomic oxygen, zinc and aluminum atoms and atomic ions. The time-integrated spectra as well as the time-resolved spectra of the plasma emission indicate that the oxygen species in the ECR oxygen plasma experience additional excitation by the expanding ablation plumes, and the ablated species are excited frequently when traveling accompanying the plume expansion in the oxygen plasma, making the formed plasma highly excited and very reactive, which plays an important role in the reactive growth of ZnO matrix and the in-situ doping of Al into the growing ZnO matrix. The deposited ZnO and AZO films were evaluated for composition analysis by energy dispersive X-ray spectroscopy, structure characterization by X-ray diffraction and optical transmission measurement. The deposited ZnO is slightly rich in O. The Al concentration of the AZO films can be controlled and varied simply by changing the repetition rate of the laser used for Al target ablation. Both the ZnO and the AZO films are featured with hexagonal wurtzite crystal structure and exhibit high optical transparency in a wide spectral region. Al doping results in an improvement in the ultraviolet transparency, a blue shift in the absorption edge and a widening of the band gap.

  5. Adiabat shape Laser Pulses for ablation front instability control and high fuel compression

    NASA Astrophysics Data System (ADS)

    Milovich, Jose; Jones, O. S.; Berzak-Hopkins, L.; Clark, D. S.; Baker, K. L.; Casey, D. T.; Macphee, A. G.; Peterson, J. L.; Robey, H. F.; Smalyuk, V. A.; Weber, C. R.

    2014-10-01

    At the end of the NIC campaign a large body of experimental evidence showed that the point-design implosions driven by low-adiabat pulses had a high degree of mix. To reduce instability a high-adiabat (~3 × higher picket drive) design was fielded in the National Ignition Facility (NIF). The experimental results from this campaign have shown considerable improvement in performance (10 × neutron yields) over the point design with little evidence of mix. However, the adiabat of the implosions may be too high to achieve ignition for the available laser energy. To overcome this difficulty, and to take advantage of the high-picket drives, we have developed hybrid laser pulses that combined the virtue of both designs. These pulses can be thought of achieving adiabat shaping, where the ablator is set in a higher adiabat for instability control, while the fuel is maintained at a lower adiabat favoring higher fuel compression. Using these pulses, recent experiments at the NIF have indeed shown reduced growth rates. In this talk we will present the design of high-yield low-growth DT ignition experiments using these adiabat-shaped pulses. Work performed under the auspices of the U.S. D.O.E. by LLNL under contract DE-AC52-07NA27344.

  6. Two-dimensional space-resolved emission spectroscopy of laser ablation plasma in water

    SciTech Connect

    Matsumoto, Ayumu; Tamura, Ayaka; Fukami, Kazuhiro; Ogata, Yukio H.; Sakka, Tetsuo

    2013-02-07

    We developed a method for two-dimensional space-resolved emission spectroscopy of laser-induced plasma in water to investigate the spatial distribution of atomic species involved in the plasma. Using this method, the laser ablation plasma produced on a Cu target in 5 mM NaCl aqueous solution was examined. The emission spectrum varied considerably depending on the detecting position. The temperature and the atomic density ratio N{sub Na}/N{sub Cu} at various detecting positions were evaluated by fitting emission spectra to a theoretical model based on the Boltzmann distribution. We are successful in observing even a small difference between the distributions of the plasma parameters along the directions vertical and horizontal to the surface. The present approach gives direct information for sound understanding of the behavior of laser ablation plasma produced on a solid surface in water.

  7. Comparison of femtosecond and nanosecond laser ablation inductively coupled plasma mass spectrometry for uranium isotopic measurements

    SciTech Connect

    Havrilla, George Joseph; McIntosh, Kathryn Gallagher; Judge, Elizabeth; Dirmyer, Matthew R.; Campbell, Keri; Gonzalez, Jhanis J.

    2016-10-20

    Feasibility tests were conducted using femtosecond and nanosecond laser ablation inductively coupled plasma mass spectrometry for rapid uranium isotopic measurements. The samples used in this study consisted of a range of pg quantities of known 235/238 U solutions as dried spot residues of 300 pL drops on silicon substrates. The samples spanned the following enrichments of 235U: 0.5, 1.5, 2, 3, and 15.1%. In this direct comparison using these particular samples both pulse durations demonstrated near equivalent data can be produced on either system with respect to accuracy and precision. There is no question that either LA-ICP-MS method offers the potential for rapid, accurate and precise isotopic measurements of U10Mo materials whether DU, LEU or HEU. The LA-ICP-MS equipment used for this work is commercially available. The program is in the process of validating this work for large samples using center samples strips from Y-12 MP-1 LEU-Mo Casting #1.

  8. Ultra-fast Movies Resolve Ultra-short Pulse Laser Ablation and Bump Formation on Thin Molybdenum Films

    NASA Astrophysics Data System (ADS)

    Domke, Matthias; Rapp, Stephan; Huber, Heinz

    For the monolithic serial interconnection of CIS thin film solar cells, 470 nm molybdenum films on glass substrates must be separated galvanically. The single pulse ablation with a 660 fs laser at a wavelength of 1053 nm is investigated in a fluence regime from 0.5 to 5.0 J/cm2. At fluences above 2.0 J/cm2 bump and jet formation can be observed that could be used for creating microstructures. For the investigation of the underlying mechanisms of the laser ablation process itself as well as of the bump or jet formation, pump probe microscopy is utilized to resolve the transient ablation behavior.

  9. Non-thermal, pulsed electric field cell ablation: A novel tool for regenerative medicine and scarless skin regeneration.

    PubMed

    Golberg, Alexander; Broelsch, G Felix; Bohr, Stefan; Mihm, Martin C; Austen, William G; Albadawi, Hassan; Watkins, Michael T; Yarmush, Martin L

    2013-09-01

    High voltage, short pulsed electric fields (PEF) is a non-thermal ablation method, in which defined PEF irreversibly destabilize cell membranes, while preserving other tissue components such as the extracellular matrix (ECM). In the present report, we show that PEF ablated rat skin retains its microvascular blood supply and ECM structure. Complete regeneration of epidermis, hair follicles, sebaceous glands, and the panniculus carnosusis observed two months after the ablation. Our results clearly indicate that non-thermal PEF has the potential to be a powerful and novel tool for scarless tissue regeneration.

  10. Non-thermal, pulsed electric field cell ablation: A novel tool for regenerative medicine and scarless skin regeneration

    PubMed Central

    Golberg, Alexander; Broelsch, G. Felix; Bohr, Stefan; Mihm, Martin C.; Austen, William G.; Albadawi, Hassan; Watkins, Michael T.; Yarmush, Martin L.

    2014-01-01

    High voltage, short pulsed electric fields (PEF) is a non-thermal ablation method, in which defined PEF irreversibly destabilize cell membranes, while preserving other tissue components such as the extracellular matrix (ECM). In the present report, we show that PEF ablated rat skin retains its microvascular blood supply and ECM structure. Complete regeneration of epidermis, hair follicles, sebaceous glands, and the panniculus carnosusis observed two months after the ablation. Our results clearly indicate that non-thermal PEF has the potential to be a powerful and novel tool for scarless tissue regeneration. PMID:24999487

  11. Escape of carbon element in surface ablation of cobalt cemented tungsten carbide with pulsed UV laser

    NASA Astrophysics Data System (ADS)

    Li, Tiejun; Lou, Qihong; Dong, Jingxing; Wei, Yunrong; Liu, Jingru

    2001-03-01

    Surface ablation of cobalt cemented tungsten carbide hardmetal has been carried out in this work using a 308 nm, 30 ns XeCl excimer laser. The surface phase transformation on different pulse number of laser shots has been investigated by means of XRD and microphotography as well as AES at laser fluence of 2.5 J/cm 2. The experimental results showed that the phase structure of irradiated area has partly transformed from original WC to β-WC 1- x, then to α-W 2C and CW 3, and finally to W crystal. It is suggested that the formation of non-stoichiometric tungsten carbide should result from the escaping of carbon element due to accumulated heating of surface by pulsed laser irradiation.

  12. Direct surface engineering of silicon nanoparticles prepared by collinear double-pulse ns laser ablation

    NASA Astrophysics Data System (ADS)

    Mahdieh, M. H.; Momeni, A.

    2017-01-01

    In this paper we study the photoluminescence properties of colloidal silicon nanoparticles (Si NPs) in distilled water, with the aim of clarifying the role of surface characteristics on the emission properties. We will show that double-pulse ns laser ablation (DPLA) of a silicon target in water with different inter-pulse delay times of i.e. 5 and 10 ns can result in production of colloidal Si NPs with different PL emission intensities at the visible spectral range of 550-650 nm. The results reveal that DPLA process at the different delay times can induce different oxide related surface characteristics on the Si NPs through the direct surface engineering of the nanoparticles. A detailed analysis of the PL emissions using the stochastic quantum confinement model explained that the different emission behaviors of the colloids are associated with the oxide-related surface states which are contributed as radiative centers in the PL process.

  13. Synthesis by pulsed laser ablation of 2D nanostructures for advanced biomedical sensing

    NASA Astrophysics Data System (ADS)

    Trusso, S.; Zanchi, C.; Bombelli, A.; Lucotti, A.; Tommasini, M.; de Grazia, U.; Ciusani, E.; Romito, L. M.; Ossi, P. M.

    2016-05-01

    Au nanoparticle arrays with controlled nanostructure were produced by pulsed laser ablation on glass. Such substrates were optimized for biomedical sensing by means of SERS keeping fixed all process parameters but the laser pulse (LP) number that is a key deposition parameter. It allows to fine-tune the Au surface nanostructure with a considerable improvement in the SERS response towards the detection of apomorphine in blood serum (3.3 × 10-6 M), when LP number is increased from 1 × 104 to 2 × 104. This result is the starting point to correlate the intensity of selected SERS signals of apomorphine to its concentration in the blood of patients with Parkinson's disease.

  14. Bismuth Oxide Thin Films Deposited on Silicon Through Pulsed Laser Ablation, for Infrared Detectors

    NASA Astrophysics Data System (ADS)

    Condurache-Bota, Simona; Constantinescu, Catalin; Tigau, Nicolae; Praisler, Mirela

    2016-12-01

    Infrared detectors are used in many human activities, from industry to military, telecommunications, environmental studies and even medicine. Bismuth oxide thin films have proved their potential for optoelectronic applications, but their uses as infrared sensors have not been thoroughly studied so far. In this paper, pulsed laser ablation of pure bismuth targets within a controlled oxygen atmosphere is proposed for the deposition of bismuth oxide films on Si (100) substrates. Crystalline films were obtained, whose uniformity depends on the deposition conditions (number of laser pulses and the use of a radio-frequency (RF) discharge of the oxygen inside the deposition chamber). The optical analysis proved that the refractive index of the films is higher than 3 and that their optical bandgap is around 1eV, recommending them for infrared applications.

  15. Boron nitride nano-structures produced by pulsed laser ablation in acetone

    NASA Astrophysics Data System (ADS)

    Nistor, L. C.; Epurescu, G.; Dinescu, M.; Dinescu, G.

    2010-11-01

    Different phases of boron nitride (BN) nano-structures are synthesized from an hBN ceramic target immersed in acetone, by ablation with a high power pulsed Nd: YAG laser. Transmission electron microscopy (TEM) and electron diffraction (ED) are used to identify the morphology and structure of the prepared colloidal suspensions. It is revealed that by varying solely a single experimental parameter, i.e. the laser pulse fluency, a large variety of BN nano-structures can be produced: nanotubes, very thin graphene-like foils, nano-curls and nano-particles, all with the hexagonal graphite-like hBN structure, as well as high pressure BN phases: orthorhombic explosion E-BN nano-rods, or cubic diamond-like cBN nano-particles.

  16. Influence of water layer thickness on hard tissue ablation with pulsed CO2 laser

    NASA Astrophysics Data System (ADS)

    Zhang, Xianzeng; Zhan, Zhenlin; Liu, Haishan; Zhao, Haibin; Xie, Shusen; Ye, Qing

    2012-03-01

    The theory of hard tissue ablation reported for IR lasers is based on a process of thermomechanical interaction, which is explained by the absorption of the radiation in the water component of the tissue. The microexplosion of the water is the cause of tissue fragments being blasted from hard tissue. The aim of this study is to evaluate the influence of the interdependence of water layer thickness and incident radiant exposure on ablation performance. A total of 282 specimens of bovine shank bone were irradiated with a pulse CO2 laser. Irradiation was carried out in groups: without a water layer and with a static water layer of thickness ranging from 0.2 to 1.2 mm. Each group was subdivided into five subgroups for different radiant exposures ranging from 18 to 84 J/cm2, respectively. The incision geometry, surface morphology, and microstructure of the cut walls as well as thermal injury were examined as a function of the water layer thickness at different radiant exposures. Our results demonstrate that the additional water layer is actually a mediator of laser-tissue interaction. There exists a critical thickness of water layer for a given radiant exposure, at which the additional water layer plays multiple roles, not only acting as a cleaner to produce a clean cut but also as a coolant to prevent bone heating and reduce thermal injury, but also helping to improve the regularity of the cut shape, smooth the cut surface, and enhance ablation rate and efficiency. The results suggest that desired ablation results depend on optimal selection of both water layer thickness and radiant exposure.

  17. Influence of water layer thickness on hard tissue ablation with pulsed CO2 laser.

    PubMed

    Zhang, Xianzeng; Zhan, Zhenlin; Liu, Haishan; Zhao, Haibin; Xie, Shusen; Ye, Qing

    2012-03-01

    The theory of hard tissue ablation reported for IR lasers is based on a process of thermomechanical interaction, which is explained by the absorption of the radiation in the water component of the tissue. The microexplosion of the water is the cause of tissue fragments being blasted from hard tissue. The aim of this study is to evaluate the influence of the interdependence of water layer thickness and incident radiant exposure on ablation performance. A total of 282 specimens of bovine shank bone were irradiated with a pulse CO(2) laser. Irradiation was carried out in groups: without a water layer and with a static water layer of thickness ranging from 0.2 to 1.2 mm. Each group was subdivided into five subgroups for different radiant exposures ranging from 18 to 84 J/cm(2), respectively. The incision geometry, surface morphology, and microstructure of the cut walls as well as thermal injury were examined as a function of the water layer thickness at different radiant exposures. Our results demonstrate that the additional water layer is actually a mediator of laser-tissue interaction. There exists a critical thickness of water layer for a given radiant exposure, at which the additional water layer plays multiple roles, not only acting as a cleaner to produce a clean cut but also as a coolant to prevent bone heating and reduce thermal injury, but also helping to improve the regularity of the cut shape, smooth the cut surface, and enhance ablation rate and efficiency. The results suggest that desired ablation results depend on optimal selection of both water layer thickness and radiant exposure.

  18. Impulse calculation and characteristic analysis of space debris by pulsed laser ablation

    NASA Astrophysics Data System (ADS)

    Wang, Chenglin; Zhang, Yan; Wang, Kunpeng

    2016-11-01

    Ablation by high-energy pulsed laser provides recoil impulse that results in the de-orbiting and atmospheric re-entry of space debris, which may be the best method of clearing space debris in the size range of 1-10 cm. Both the magnitude and direction of the recoil impulse depend on the shape and orientation of the target and serve as the foundation for studying orbital evolution and evaluating removal effects. However, how to calculate the recoil impulse and analyze the features of recoil impulse have not received sufficient attention in the literature. Based on certain assumed conditions, a general numerical method is proposed to calculate the recoil impulse of free motion debris under a set of laser pulses. Selecting cylindrical debris as the research target, we derive an analytical method to calculate the ablation-driven impulse. Moreover, the characteristics of single impulses changing over time and the total impulse are examined using analytical expressions. Finally, simulation experiments are conducted to validate both the numerical and analytical methods.

  19. AFM and pulsed laser ablation methods for Cultural Heritage: application to archeometric analysis of stone artifacts

    NASA Astrophysics Data System (ADS)

    Barberio, M.; Veltri, S.; Stranges, F.; Bonanno, A.; Xu, F.; Antici, P.

    2015-09-01

    In this paper, we introduce the use of the atomic force microscope (AFM) and of the pulsed laser ablation as methods for morphological diagnostic with nanoscale precision of archeological artifacts and corrosive patina removal from stone artifacts. We test our methodology on stone artifacts extracted from the Church of Sotterra (located in Calabria, South Italy). The AFM microscopy was compared with different petrographic, chemical, optical and morphological analysis methods for identifying the textural characteristics, evaluating the state of preservation and formulating some hypotheses about the provenance and composition of the impurity patina located on the artifact surfaces. We demonstrate that with the nanometric precision obtained with AFM microscopy, it is possible to distinguish the different states of preservation, much better than using conventional petrographic methods. The surface's roughness is evaluated from very small artifact's fragments, reducing the coring at micrometric scale with a minimal damage to the artworks. After the diagnosis, we performed restoration tests using the pulsed laser ablation (PLA) method and compared it with the more common micro-sandblasting under dry conditions. We find that the PLA is highly effective for the removal of the surficial patina, with a control of a few hundreds of nanometers in the cleaning of surface, without introducing chemical or morphological damages to the artifacts. Moreover, PLA can be easily implemented in underwater conditions; this has the great advantage that stone and pottery artifacts for marine archeological sites do not need to be removed from the site.

  20. Intense isolated attosecond pulse generation from relativistic laser plasmas using few-cycle laser pulses

    SciTech Connect

    Ma, Guangjin; Dallari, William; Borot, Antonin; Tsakiris, George D.; Veisz, Laszlo; Krausz, Ferenc; Yu, Wei

    2015-03-15

    We have performed a systematic study through particle-in-cell simulations to investigate the generation of attosecond pulse from relativistic laser plasmas when laser pulse duration approaches the few-cycle regime. A significant enhancement of attosecond pulse energy has been found to depend on laser pulse duration, carrier envelope phase, and plasma scale length. Based on the results obtained in this work, the potential of attaining isolated attosecond pulses with ∼100 μJ energy for photons >16 eV using state-of-the-art laser technology appears to be within reach.

  1. Plasma Discharge Process in a Pulsed Diaphragm Discharge System

    NASA Astrophysics Data System (ADS)

    Duan, Jianjin; Hu, Jue; Zhang, Chao; Wen, Yuanbin; Meng, Yuedong; Zhang, Chengxu

    2014-12-01

    As one of the most important steps in wastewater treatment, limited study on plasma discharge process is a key challenge in the development of plasma applications. In this study, we focus on the plasma discharge process of a pulsed diaphragm discharge system. According to the analysis, the pulsed diaphragm discharge proceeds in seven stages: (1) Joule heating and heat exchange stage; (2) nucleated site formation; (3) plasma generation (initiation of the breakdown stage); (4) avalanche growth and plasma expansion; (5) plasma contraction; (6) termination of the plasma discharge; and (7) heat exchange stage. From this analysis, a critical voltage criterion for breakdown is obtained. We anticipate this finding will provide guidance for a better application of plasma discharges, especially diaphragm plasma discharges.

  2. Quantitative Analysis of Plasma Ablation Using Inverse Wire Array Z-pinches

    SciTech Connect

    Harvey-Thompson, A. J.; Lebedev, S. V.; Bland, S. N.; Chittenden, J. P.; Hall, G. N.; Ning, C.; Suzuki-Vidal, F.; Bott, S. C.

    2009-01-21

    An inverse (exploding) wire array configuration, in which the wires form a cylinder around a current carrying electrode on axis, was used to study the ablation phase of the pinch. This configuration allows the parameters of the plasma from individual wires of the array to be measured as the ablated plasma streams propagate in the outward radial direction. The density distribution and the evolution of the natural mode of modulation of the ablation was measured with interferometry and soft x-ray imaging. Measurements of the voltage across the array, which in this configuration is determined by the private magnetic flux around the individual wires, allows information on the localisation of the current to be obtained.

  3. Thrust Stand Measurements of a Conical Pulsed Inductive Plasma Thruster

    NASA Technical Reports Server (NTRS)

    Hallock, Ashley K.; Polzin, Kurt A.; Emsellem, Gregory D.

    2012-01-01

    Pulsed inductive plasma thrusters [1-3] are spacecraft propulsion devices in which electrical energy is capacitively stored and then discharged through an inductive coil. The thruster is electrodeless, with a time-varying current in the coil interacting with a plasma covering the face of the coil to induce a plasma current. Propellant is accelerated and expelled at a high exhaust velocity (O(10-100 km/s)) by the Lorentz body force arising from the interaction of the magnetic field and the induced plasma current. While this class of thruster mitigates the life-limiting issues associated with electrode erosion, pulsed inductive plasma thrusters can su er from both high pulse energy requirements imposed by the voltage demands of inductive propellant ionization, and low propellant utilization efficiencies. The Microwave Assisted Discharge Inductive Plasma Accelerator (MAD-IPA)[4], shown in Fig. 1 is a pulsed inductive plasma thruster that is able to operate at lower pulse energies by partially ionizing propellant with an electron cyclotron resonance (ECR) discharge inside a conical inductive coil whose geometry serves to potentially increase propellant and plasma plume containment relative to at coil geometries. The ECR plasma is created with the use of permanent mag- nets arranged to produce a thin resonance region along the inner surface of the coil, restricting plasma formation and, in turn, current sheet formation to areas of high magnetic coupling to the driving coil.

  4. Plasma regimes in high power pulsed magnetron sputtering

    NASA Astrophysics Data System (ADS)

    de Los Arcos, Teresa

    2013-09-01

    High Power Pulsed Magnetron Sputtering (HPPMS) is a relatively recent variation of magnetron sputtering where high power is applied to the magnetron in short pulses. The result is the formation of dense transient plasmas with a high fraction of ionized species, ideally leading to better control of film growth through substrate bias. However, the broad range of experimental conditions accessible in pulsed discharges results in bewildering variations in current and voltage pulse shapes, pulse power densities, etc, which represent different discharge behaviors, making it difficult to identify relevant deposition conditions. The complexity of the plasma dynamics is evident. Within each pulse, plasma characteristics such as plasma composition, density, gas rarefaction, spatial distribution, degree of self-sputtering, etc. vary with time. A recent development has been the discovery that the plasma emission can self-organize into well-defined regions of high and low plasma emissivity above the racetrack (spokes), which rotate in the direction given by the E ×B drift and that significantly influence the transport mechanisms in HPPMS. One seemingly universal characteristic of HPPMS plasmas is the existence of well defined plasma regimes for different power ranges. These regimes are clearly differentiated in terms of plasma conductivity, plasma composition and spatial plasma self-organization. We will discuss the global characteristics of these regimes in terms of current-voltage characteristics, energy-resolved QMS and OES analysis, and fast imaging. In particular we will discuss how the reorganization of the plasma emission into spokes is associated only to specific regimes of high plasma conductivity. We will also briefly discuss the role of the target in shaping the characteristics of the HPPMS plasma, since sputtering is a surface-driven process. This work was supported by the Deutsche Forschungsgemeinschaft (DFG) within the framework of the SFB-TR87.

  5. INTERACTION OF LASER RADIATION WITH MATTER: Effect of the pulse duration on graphitisation of diamond during laser ablation

    NASA Astrophysics Data System (ADS)

    Kononenko, Vitalii V.; Kononenko, Taras V.; Pimenov, S. M.; Sinyavskii, M. N.; Konov, Vitalii I.; Dausinger, F.

    2005-03-01

    Processes of graphitisation of laser-irradiated polycrystalline diamond surface exposed to multipulse irradiation are studied experimentally. The thickness of the laser-modified layer as a function of the laser-pulse duration ranging from 100 fs to 1.5 μs and the effect of the radiation wavelength on this thickness are studied. It is shown that the diamond graphitisation during multipulse laser ablation is a thermally stimulated process. The dependences of the diamond-ablation rates on the radiation energy density under the action of laser pulses of various durations are presented.

  6. Wall ablation of heated compound-materials into non-equilibrium discharge plasmas

    NASA Astrophysics Data System (ADS)

    Wang, Weizong; Kong, Linghan; Geng, Jinyue; Wei, Fuzhi; Xia, Guangqing

    2017-02-01

    The discharge properties of the plasma bulk flow near the surface of heated compound-materials strongly affects the kinetic layer parameters modeled and manifested in the Knudsen layer. This paper extends the widely used two-layer kinetic ablation model to the ablation controlled non-equilibrium discharge due to the fact that the local thermodynamic equilibrium (LTE) approximation is often violated as a result of the interaction between the plasma and solid walls. Modifications to the governing set of equations, to account for this effect, are derived and presented by assuming that the temperature of the electrons deviates from that of the heavy particles. The ablation characteristics of one typical material, polytetrafluoroethylene (PTFE) are calculated with this improved model. The internal degrees of freedom as well as the average particle mass and specific heat ratio of the polyatomic vapor, which strongly depends on the temperature, pressure and plasma non-equilibrium degree and plays a crucial role in the accurate determination of the ablation behavior by this model, are also taken into account. Our assessment showed the significance of including such modifications related to the non-equilibrium effect in the study of vaporization of heated compound materials in ablation controlled arcs. Additionally, a two-temperature magneto-hydrodynamic (MHD) model accounting for the thermal non-equilibrium occurring near the wall surface is developed and applied into an ablation-dominated discharge for an electro-thermal chemical launch device. Special attention is paid to the interaction between the non-equilibrium plasma and the solid propellant surface. Both the mass exchange process caused by the wall ablation and plasma species deposition as well as the associated momentum and energy exchange processes are taken into account. A detailed comparison of the results of the non-equilibrium model with those of an equilibrium model is presented. The non-equilibrium results

  7. Transmission of 1064 nm laser radiation during ablation with an ultra-short pulse laser (USPL) system

    NASA Astrophysics Data System (ADS)

    Schelle, Florian; Meister, Jörg; Oehme, Bernd; Frentzen, Matthias

    2012-01-01

    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.

  8. Group velocity and pulse lengthening of mismatched laser pulses in plasma channels

    SciTech Connect

    Schroeder, Carl; Benedetti, Carlo; Esarey, Eric; van Tilborg, Jeroen; Leemans, Wim

    2011-07-07

    Analytic solutions are presented to the non-paraxial wave equation describing an ultra-short, low-power, laser pulse propagating in aplasma channel. Expressions for the laser pulse centroid motion and laser group velocity are derived, valid for matched and mismatchedpropagation in a parabolic plasma channel, as well as in vacuum, for an arbitrary Laguerre-Gaussian laser mode. The group velocity of amismatched laser pulse, for which the laser spot size is strongly oscillating, is found to be independent of propagation distance andsignificantly less than that of a matched pulse. Laser pulse lengthening of a mismatched pulse owing to laser mode slippage isexamined and found to dominate over that due to dispersive pulse spreading for sufficiently long pulses. Analytic results are shown tobe in excellent agreement with numerical solutions of the full Maxwell equations coupled to the plasma response. Implications for plasmachannel diagnostics are discussed.

  9. External Pulsed Plasma Propulsion (EPPP) Analysis Maturation

    NASA Technical Reports Server (NTRS)

    Bonometti, Joesph A.; Morton, P. Jeff; Schmidt, George R. (Technical Monitor)

    2000-01-01

    External Pulsed Plasma Propulsion (EPPP) systems are at the stage of engineering infancy with evolving paradigms for application. performance and general characteristics. Recent efforts have focused on an approach that employs existing technologies with near term EPPP development for usage in interplanetary exploration and asteroid/comet deflection. if mandated. The inherent advantages of EPPP are discussed and its application to a variety of propulsion concepts is explored. These include, but are not limited to, utilizing energy sources such as fission. fusion and antimatter, as well as, improved chemical explosives. A mars mission scenario is presented as a demonstration of its capability using existing technologies. A suggested alternate means to improve EPPP efficiencies could also lead to a heavy lift (non-nuclear) launch vehicle capability. Conceivably, true low-cost, access to space is possible using advanced explosive propellants and/or coupling the EPPP vehicle to a "beam propellant" concept. EPPP systems appear to offer an approach that can potentially cover ETO through interstellar transportation capability. A technology roadmap is presented that shows mutual benefits pertaining to a substantial number of existing space propulsion and research areas.

  10. Evaluation of Pulsed Plasma Thruster Micropulsing

    NASA Technical Reports Server (NTRS)

    Arrington, Lynn

    2004-01-01

    This paper evaluates the concept of pulsed plasma thruster (PPT) micropulsing. Micropulsing was a premise behind a power processing unit (PPU) and an energy storage unit (ESU) design that for certain mission profiles, it was advantageous to operate a PPT at lower energy but higher frequency rather than at a higher energy but lower frequency. This premise allows for reductions in the ESU volume and mass without paying a penalty in thrust. To complete the evaluation, an independent spark plug initiation unit, a high voltage power supply and a variety of mica foil capacitors at 2.6, 5, 10, and 20 capacitance were used to conduct a series of tests on a single PPT to map performance levels of thrust, impulse bit, efficiency and specific impulse over a comparable power range. Testing at NASA Glenn Research Center was conducted with breadboard PPT hardware. The test results showed that operating in the lower energy ESU micropulsing mode produced similar thrust levels to a higher energy ESU operating at high power level. Further testing however showed a reduction in specific impulse and efficiency when the smaller capacitances were used at the highest power levels. This would require more fuel mass for a mission that was predominately high power, potentially negating the ESU mass savings. Therefore, micropulsing is advantageous where most of a mission profile occurs at low power, but retains the ability to conduct high thrust maneuvers when necessary.

  11. Matrix-assisted resonant infrared pulsed laser ablation of electroluminescent dendrimers

    NASA Astrophysics Data System (ADS)

    Torres-Pagan, Ricardo Daniel

    The deposition techniques for polymer thin films in organic light emitting diodes are limited to wet methods since molecular pyrolysis prevents the use of dry vacuum thermal evaporation methods. Wet methods have critical limitations such as poor thickness control, drying patterns and re-dissolution of previous layers. In this work, a novel approach, Matrix-Assisted Resonant Infrared Pulsed Laser Ablation (RIM-PLA) has been studied as an alternative deposition method for electroluminescent polymer films. RIM-PLA was successfully used for the deposition of two model dendrimers: fluorescent and phosphorescent Ir-cored. A free-electron laser was tuned to resonance frequencies for the vibrational modes of two solid matrix solvents: chloroform (C-H stretch; C-H bending) and toluene (C-H stretch; C=C stretch). The temperature-dependent absorption coefficients for each resonance mode were measured. Targets made from flash-frozen, low-concentration solutions of the dendrimers were irradiated at each frequency while varying fluence and exposure times. The molecular structure integrity of the targets was characterized. The deposited films were characterized to assess structure fidelity, roughness and topography, and luminance. All RIM-PLA deposited films were compared with spin-coated films. The ablation characteristics for each mode were found to be dependent on the solvent and not the dendrimer. Calculations from a temperature-rise model show that FEL pulsed-irradiation results in heating rates on the order of 108--109 K/s, resulting in metastable condensed targets. Thermodynamic and kinetic relations were used to calculate the relevance of three ablation mechanisms: normal vaporization, normal boiling and phase explosion. The latter mechanism has a critical threshold (> 0.8 Tc) for each solvent, and proceeds through spinodal decay followed by rapid homogeneous nucleation of vapor bubbles within the focal volume. For both chloroform modes, the primary ablation mechanism was

  12. Plasma lenses for ultrashort multi-petawatt laser pulses

    SciTech Connect

    Palastro, J. P.; Gordon, D.; Hafizi, B.; Johnson, L. A.; Peñano, J.; Hubbard, R. F.; Helle, M.; Kaganovich, D.

    2015-12-15

    An ideal plasma lens can provide the focusing power of a small f-number, solid-state focusing optic at a fraction of the diameter. An ideal plasma lens, however, relies on a steady-state, linear laser pulse-plasma interaction. Ultrashort multi-petawatt (MPW) pulses possess broad bandwidths and extreme intensities, and, as a result, their interaction with the plasma lens is neither steady state nor linear. Here, we examine nonlinear and time-dependent modifications to plasma lens focusing, and show that these result in chromatic and phase aberrations and amplitude distortion. We find that a plasma lens can provide enhanced focusing for 30 fs pulses with peak power up to ∼1 PW. The performance degrades through the MPW regime, until finally a focusing penalty is incurred at ∼10 PW.

  13. Plasma lenses for ultrashort multi-petawatt laser pulses

    NASA Astrophysics Data System (ADS)

    Palastro, J. P.; Gordon, D.; Hafizi, B.; Johnson, L. A.; Peñano, J.; Hubbard, R. F.; Helle, M.; Kaganovich, D.

    2015-12-01

    An ideal plasma lens can provide the focusing power of a small f-number, solid-state focusing optic at a fraction of the diameter. An ideal plasma lens, however, relies on a steady-state, linear laser pulse-plasma interaction. Ultrashort multi-petawatt (MPW) pulses possess broad bandwidths and extreme intensities, and, as a result, their interaction with the plasma lens is neither steady state nor linear. Here, we examine nonlinear and time-dependent modifications to plasma lens focusing, and show that these result in chromatic and phase aberrations and amplitude distortion. We find that a plasma lens can provide enhanced focusing for 30 fs pulses with peak power up to ˜1 PW. The performance degrades through the MPW regime, until finally a focusing penalty is incurred at ˜10 PW.

  14. Laser ablation efficiency during the production of Ag nanoparticles in ethanol at a low pulse repetition rate (1-10 Hz)

    NASA Astrophysics Data System (ADS)

    Valverde-Alva, M. A.; García-Fernández, T.; Esparza-Alegría, E.; Villagrán-Muniz, M.; Sánchez-Aké, C.; Castañeda-Guzmán, R.; de la Mora, M. B.; Márquez-Herrera, C. E.; Sánchez Llamazares, J. L.

    2016-10-01

    We studied the effect of the repetition rate of laser pulses (RRLP) in the range from 1-10 Hz in the production of silver nanoparticles (Ag-NPs) by laser ablation in ethanol. Laser pulses with a duration of 7 ns, a wavelength of 1064 nm and an energy of 60 mJ were used to ablate a 99.99% pure silver target immersed in 10 ml of ethanol. Transmittance analysis and atomic absorption spectroscopy were used to study the silver concentration in the colloidal solutions. The ablation process was studied by measuring the transmission of the laser pulses through the colloid. It is shown that for a fixed number of laser pulses (NLP) the ablation efficiency, in terms of the ablated silver mass per laser pulse, increases with the RRLP. This result contradicts what had previously been established in the literature.

  15. Experimental and theoretical investigation of the effect of laser parameters on laser ablation and laser-induced plasma formation

    NASA Astrophysics Data System (ADS)

    Stancalie, Andrei; Ciobanu, Savu-Sorin; Sporea, Dan

    2016-04-01

    We report results from a wide range of laser operating conditions, typical for laser induced breakdown spectroscopy (LIBS) and laser ablation (LA) experiments on copper metallic target, which form the basis of further systematically investigation of the effect of laser irradiance, pulse duration and wavelength, on the target, plume and plasma behavior, during and after laser-solid interaction. In the LA experiment, the laser beam was focused through a 25 cm focal length convergent lens on a plane copper target in air, at atmospheric pressure. The target was rotated in order to have fresh areas under laser irradiance. In the LIBS experiment, the Applied Photonics LIBS-6 instrument allowed modifying the laser irradiance at the sample surface by changing the pulse energy or the laser focusing distance. For the duration of the laser pulse, the power density at the surface of the target material exceeds 109 W/cm2 using only a compact laser device and simple focusing lenses. The plasma parameters were experimentally estimated from spectroscopic data generated by the plasma itself, namely by the line intensities and their ratio which reflect the relative population of neutral or ionic excited species in the plasma. The fitting of the Saha-Boltzmann plot to a straight line provides an apparent ionization temperature, whose value depends on the lines used in the plots. For the typical conditions of LA and LIBS, the temperature can be so high that Cu+ ions are formed. The first-order ionization of Cu (i.e., the ratio of Cu+/Cu0 ) is calculated.

  16. Population Inversions in Ablation Plasmas Generated by Intense Electron Beams.

    DTIC Science & Technology

    1986-11-30

    beam driven carbon anode plasmas. Diode closure results ..,.in three phases of beam-plasma evolution which are summarized below: Stage I: Deposited...enough for anode plasma forma- tion before the diode shorts. Spectroscopic data for noncrowbarred shots (dose 1 500-800 J/g) indicate the presence of CII...inconsistent with previously proposed kinetic mechanisms for the N2 laser pumped by helium. With a simple- model of the chemical kinetics, we have shown

  17. Physics and Dynamics of Current Sheets in Pulsed Plasma Thrusters

    DTIC Science & Technology

    2007-11-02

    pulsed plasma thruster. A simple experiment would involve measuring the impulse bit of a coaxial gas-fed pulsed plasma thruster operated in both positive...Princeton, NJ, 2002. [2] J. Marshal. Performance of a hydromagnetic plasma gun . The Physics of Fluids, 3(1):134–135, January-February 1960. [3] R.G. Jahn...Jahn and K.E. Clark. A large dielecteic vacuum facility. AIAA Jour- nal, 1966. [16] L.C. Burkhardt and R.H. Lovberg. Current sheet in a coaxial plasma

  18. Pulsed operation of low-power plasma thruster

    NASA Astrophysics Data System (ADS)

    Bugrova, A. I.; Desyatskov, A. V.; Korobkin, Yu. V.; Lipatov, A. S.; Kharchevnikov, V. K.

    2010-10-01

    Integral and local characteristics of the laboratory model of a low-power plasma thruster operating in a pulsed regime have been experimentally studied. Rectangular pulses of discharge current with the leading and trailing fronts not exceeding 1 ms have been obtained. At an average supplied electric power of ˜150 W, the propulsion efficiency amounted to 35%. The plasma concentration, electron temperature, and potential distributions in the output plasma jet have been measured using an electric probe. These measurements showed that a well formed plasma jet with a small divergence angle exists behind the thruster edge.

  19. High-Speed, Integrated Ablation Cell and Dual Concentric Injector Plasma Torch for Laser Ablation-Inductively Coupled Plasma Mass Spectrometry.

    PubMed

    Douglas, David N; Managh, Amy J; Reid, Helen J; Sharp, Barry L

    2015-11-17

    In recent years, laser ablation-inductively coupled plasma mass spectrometry (LA-ICPMS) has gained increasing importance for biological analysis, where ultratrace imaging at micrometer resolution is required. However, while undoubtedly a valuable research tool, the washout times and sensitivity of current technology have restricted its routine and clinical application. Long periods between sampling points are required to maintain adequate spatial resolution. Additionally, temporal signal dispersion reduces the signal-to-noise ratio, which is a particular concern when analyzing discrete samples, such as individual particles or cells. This paper describes a novel, two-volume laser ablation cell and integrated ICP torch designed to minimize aerosol dispersion for fast, efficient sample transport. The holistic design utilizes a short, continuous diameter fused silica conduit, which extends from the point of ablation, through the ICP torch, and into the base of the plasma. This arrangement removes the requirement for a dispersive component for argon addition, and helps to keep the sample on axis with the ICP cone orifice. Hence, deposition of sample on the cones is theoretically reduced with a resulting improvement in the absolute sensitivity (counts per unit mole). The system described here achieved washouts of 1.5, 3.2, and 4.9 ms for NIST 612 glass, at full width half, 10%, and 1% maximum, respectively, with an 8-14-fold improvement in absolute sensitivity, compared to a single volume ablation cell. To illustrate the benefits of this performance, the system was applied to a contemporary bioanalytical challenge, specifically the analysis of individual biological cells, demonstrating similar improvements in performance.

  20. Process Performances of 2 ns Pulsed Discharge Plasma

    NASA Astrophysics Data System (ADS)

    Matsumoto, Takao; Wang, Douyan; Namihira, Takao; Akiyama, Hidenori

    2011-08-01

    Pulsed discharge plasmas have been used to treat exhaust gases. Since pulse duration and the rise time of applied voltage to the discharge electrode has a strong influence on the energy efficiency of pollutant removal, the development of a short-pulse generator is of paramount importance for practical applications. In this work, it is demonstrated that the non thermal plasma produced by the 2 ns pulsed discharge has a higher energy efficiency than the 5 ns pulsed discharge plasma for NO removal and ozone generation. Typically, the NO removal efficiency was 1.0 mol kW-1 h-1 for 70% NO removal (initial NO concentration = 200 ppm, gas flow = 10 L/min). Meanwhile, the ozone yield was 500 g kW-1 h-1 for 20 g/m3 ozone concentration in the case of oxygen feeding. These energy efficiencies are the highest in the literature.

  1. A nonlinear plasma retroreflector for single pulse Compton backscattering

    NASA Astrophysics Data System (ADS)

    Palastro, J. P.; Kaganovich, D.; Gordon, D.; Hafizi, B.; Helle, M.; Penano, J.; Ting, A.

    2015-02-01

    Compton scattered x-rays can be generated using a configuration consisting of a single ultrashort laser pulse and a shaped gas target. Upon ionization the gas target serves as a plasma mirror that reflects the incident pulse providing a counter-propagating electromagnetic wiggler. While plasma mirrors are often conceived as linear Fresnel reflectors, we demonstrate that for high-intensity, ultrashort laser pulses the reflection results from two distinct nonlinear mechanisms. At lower densities, the reflection arises from the emission of an electromagnetic pulse during the saturation of the absolute Raman instability at the quarter critical surface. At higher densities the reflection of the pulse from the critical surface sets up a density fluctuation that acts as a Bragg-like reflector. These mechanisms, occurring in a non-perturbative regime of laser-plasma interactions, are examined numerically in order to characterize the Compton scattered radiation.

  2. Pulsed laser ablation of ferroelectric composites for phased array antenna applications

    NASA Astrophysics Data System (ADS)

    Sengupta, S.; Green, S. M.

    1998-05-01

    Low loss composites have been fabricated in thick and thin film forms for a broad range of frequency applications. The thin film composites of barium strontium titanium oxide (BSTO) have been primarily developed by the pulsed laser ablation (PLA) method. This deposition technique has produced high quality thin films of BSTO composites on various substrates [S. Sengupta, L.C. Sengupta, W.E. Kosik, Pulsed laser deposition of ferroelectric thin films in conjunction with superconducting oxides, IEEE Cat# 94CH3416-5, 431][Analysis of ferroelectric thin films deposited by the pulsed laser deposition method on oxide and fluoride substrates, IEEE Cat# 94CH3416-5, 70][S. Sengupta, D.P. Vijay, S.B. Desu, Thin films of novel ferroelectric composites, Proceedings of MRS, 361, 1995, 545][S. Sengupta, L.C. Sengupta, Novel pyroelectric sensor materials, submitted to the Special Issue on Sensors and Actuators of the IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control]. The objective of this work is to elucidate the PLA deposition parameters of the BSTO composite thin films. The material characterization and the electronic parameters of the thin films will also be presented. Finally, the patterning techniques required to fabricate the BSTO composite thin film phase shifters will be discussed. Some preliminary results of the phase shifter characterization will also be presented.

  3. Pulsed laser generation of ultrasound in a metal plate between the melting and ablation thresholds

    SciTech Connect

    Every, A. G.; Utegulov, Z. N.; Veres, I. A.

    2015-03-31

    The generation of ultrasound in a metal plate exposed to nanosecond pulsed laser heating, sufficient to cause melting but not ablation, is treated. Consideration is given to the spatial and temporal profiles of the laser pulse, penetration of the laser beam into the sample, the evolution of the melt pool, and thermal conduction in the melt and surrounding solid. The excitation of the ultrasound takes place over a few nanoseconds, and occurs predominantly within the thermal diffusion length of a micron or so beneath the surface. Because of this, the output of the thermal simulations can be represented as axially symmetric transient radial and normal surface force distributions. The epicentral displacement response at the opposite surface to these forces is obtained by two methods, the one based on the elastodynamic Green’s functions for plate geometry determined by the Cagniard generalized ray method, and the other using a finite element numerical method. The two approaches are in very close agreement. Numerical simulations are reported of the epicentral displacement response of a 3.12mm thick tungsten plate irradiated with a 4 ns pulsed laser beam with Gaussian spatial profile, at intensities below and above the melt threshold. Comparison is made between results obtained using available temperature dependent thermophysical data, and room temperature materials constants except near the melting point.

  4. Endometrial thermal balloon ablation using a high temperature, pulsed system: a mathematical model.

    PubMed

    Reinders, Daniel M; Baldwin, Susan A; Bert, Joel L

    2003-12-01

    A new endometrial thermal balloon ablation treatment for menorrhagia is modeled mathematically to predict its efficacy and safety. A device preheats a fluid to 173 degrees C within a reservoir external to the uterus, and then pulses this fluid without further heating between the reservoir and the balloon for 2.1 min of treatment time. The model predicted this treatment to result in consistent immediate tissue death (coagulation) depths of 3.4 +/- 0.1 mm for uterine cavities of 7 to 26 mL, and that eventual necrosis (tissue death that would occur 1-5 days post burn) may occur to depths of 6.5 +/- 0.2 mm. Whereas, burn depths varied with uterine cavity volume when a low temperature treatment (constant 75 degrees C for 15 min) was modeled (2.3-2.9 mm and 6.8-8.2 mm, for immediate tissue death and eventual necrosis respectively). Similarly, the high temperature, pulsed treatment was less sensitive to blood perfusion rate than the low temperature treatment. Predicted eventual necrosis depth was 1.5 mm less for the high temperature, pulsed treatment than that predicted for a low temperature treatment (constant 87 degrees C for 7 min) for the same immediate tissue death depth (3.5 mm), indicating that the new high temperature treatment may result in less damage to non targeted tissues.

  5. Selective Ablation of Thin Films with Picosecond-Pulsed Lasers for Solar Cells

    NASA Astrophysics Data System (ADS)

    Račiukaitis, G.; Gečys, P.; Gedvilas, M.; Regelskis, K.; Voisiat, B.

    2010-10-01

    Functional thin-films are of high importance in modern electronics for flat panel displays, photovoltaics, flexible and organic electronics. Versatile technologies are required for patterning thin-film materials on rigid and flexible substrates. The large-area applications of thin films such as photovoltaics need high speed and simple to use techniques. Ultra-short laser processing with its flexibility is one of the ways to achieve high quality material etching but optimization of the processes is required to meet specific needs of the applications. Lasers with picosecond pulse duration were applied in selective ablation of conducting, semi-conducting and isolating films in the complex multilayered thin-film solar cells based on amorphous Si and CuInxGa(1-x)Se2 (CIGS) deposited on glass and polymer substrates. Modeling of energy transition between the layers and temperature evolution was performed to understand the processes. Selection of the right laser wavelength was important to keep the energy coupling in a well defined volume at the interlayer interface. Ultra-short pulses ensured high energy input rate into absorbing material permitting peeling of the layers with no influence on the remaining material. Use of high repetition rate lasers with picosecond pulse duration offers new possibilities for high quality and efficiency patterning of advanced materials for thin-film electronics.

  6. Determination of bromine and tin compounds in plastics using laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS).

    PubMed

    İzgi, Belgin; Kayar, Murat

    2015-07-01

    The polybrominated flame retardants and organotin compounds were screened in terms of bromine and tin content using laser ablation inductively coupled plasma mass spectrometry in plastics. The calibration standards were prepared using the fused-disk technique, and all samples were investigated under optimal conditions. Using a central composite experimental design, laser parameters, laser energy, pulse rate, scan rate and spot size were identified. The detection limits of the method were 1000 mgkg(-1) and 1600 mgkg(-1) for bromide and tin, whereas the relative standard deviation (%) values of the analysis were 9% and 6% (n=3) for ERM EC681k with 770 ± 70 mgkg(-1) Br and 86 ± 6 mgkg(-1) Sn respectively, and 106-115% of Br and 102-104% of Sn were observed for the tetrabromobisphenol A and butyltin trichloride spike plastics, respectively.

  7. Pulse plasma carburizing and high pressure gas quenching -- Industrial applications

    SciTech Connect

    Preisser, F.; Schnatbaum, F.

    1995-12-31

    Pulse plasma carburizing with high pressure gas quenching up to 20 bar is the newly developed case hardening process now available in production size equipment. The first part of results demonstrates the tremendous potential of high pressure gas quenching for successful hardening of case hardening steels. The second part opens a window to glance at the pulse plasma carburizing of complex shaped parts. Both processes improve economical data and performance of carburizing processes.

  8. Microwave Frequency Transitions Requiring Laser Ablated Uranium Metal Discovered Using Chirp-Pulse Fourier Transform Spectroscopy

    NASA Astrophysics Data System (ADS)

    Long, B. E.; Cooke, S. A.

    2014-06-01

    A rod of depleted uranium metal (mp = 1,132° C) has been ablated with the fundamental operating frequency of a Nd:YAG laser. The resulting ablation plume of uranium was then mixed with argon gas and expanded between the transmit/receive horn antennae of a chirp-pulse Fourier transform microwave spectrometer. The recorded spectra show nine strong transitions which are not present when the laser is not used in the experimental procedure. A series of experiments in which the backing gas conditions were altered provides evidence that the nine observed transitions are carried by the same species. Should the transitions be from one species it is most likely an asymmetric top. The transitions persist even when ultra-pure argon is used as the sole backing gas. The oxide coating of the uranium metal likely provides a source of oxygen and, presently, the ``top" candidate for the unknown molecule is UO_3, which is known to have C_2v symmetry. Double resonance experiments are planned to aid transition assignments. A plausible explanation for an elusive assignment to date is the presence of pseudo-rotation.

  9. Pulse thermal processing of functional materials using directed plasma arc

    DOEpatents

    Ott, Ronald D.; Blue, Craig A.; Dudney, Nancy J.; Harper, David C.

    2007-05-22

    A method of thermally processing a material includes exposing the material to at least one pulse of infrared light emitted from a directed plasma arc to thermally process the material, the pulse having a duration of no more than 10 s.

  10. Inhibition of Candida albicans biofilm by pure selenium nanoparticles synthesized by pulsed laser ablation in liquids.

    PubMed

    Guisbiers, Grégory; Lara, Humberto H; Mendoza-Cruz, Ruben; Naranjo, Guillermo; Vincent, Brandy A; Peralta, Xomalin G; Nash, Kelly L

    2016-10-25

    Selenoproteins play an important role in the human body by accomplishing essential biological functions like oxido-reductions, antioxidant defense, thyroid hormone metabolism and immune response; therefore, the possibility to synthesize selenium nanoparticles free of any contaminants is exciting for future nano-medical applications. This paper reports the first synthesis of selenium nanoparticles by femtosecond pulsed laser ablation in de-ionized water. Those pure nanoparticles have been successfully used to inhibit the formation of Candida albicans biofilms. Advanced electron microscopy images showed that selenium nanoparticles easily adhere on the biofilm, then penetrate into the pathogen, and consequently damage the cell structure by substituting with sulfur. 50% inhibition of Candida albicans biofilm was obtained at only 25 ppm. Finally, the two physical parameters proved to affect strongly the viability of Candida albicans are the crystallinity and particle size.

  11. Luminescent amorphous silicon carbide ultrafine nanoparticles fabricated by pulsed-laser ablation

    NASA Astrophysics Data System (ADS)

    Zhu, Jun; Hu, Shan; Wang, Wei; Xia, Wei-wei; Chen, Hai-tao; Chen, Xiao-bing

    2017-04-01

    Bulk quantities of amorphous silicon carbide(SiC) ultrafine nanoparticles have been prepared via pulsed-laser ablation on a polished 3C-SiC polycrystalline target immersed in de-ionized water. The diameter of the nanoparticles is 10 ± 2.0 nm. The surface of the nanoparticles binds to the -H and -OH groups in water, suggesting that the ultrafine nanoparticles are hydrophilic. A direct band gap energy of 5.3 eV and an indirect band gap energy of 2.4 eV were determined via the ultraviolet-visible absorption characterization, which implies that the nanoparticles are of SiC. As excited at 320 nm, the suspension exhibited strong and stable violet emissions centered at 430 nm.

  12. Pulsed laser ablation in liquids: Impact of the bubble dynamics on particle formation.

    PubMed

    Reich, Stefan; Schönfeld, Patrick; Wagener, Philipp; Letzel, Alexander; Ibrahimkutty, Shyjumon; Gökce, Bilal; Barcikowski, Stephan; Menzel, Andreas; Dos Santos Rolo, Tomy; Plech, Anton

    2017-03-01

    Pulsed laser ablation in liquids (PLAL) is a multiscale process, involving multiple mutually interacting phenomena. In order to synthesize nanoparticles with well-defined properties it is important to understand the dynamics of the underlying structure evolution. We use visible-light stroboscopic imaging and X-ray radiography to investigate the dynamics occurring during PLAL of silver and gold on a macroscopic scale, whilst X-ray small angle scattering is utilized to deepen the understanding on particle genesis. By comparing our results with earlier reports we can elucidate the role of the cavitation bubble. We find that symmetry breaking at the liquid-solid interface is a critical factor for bubble motion and that the bubble motion acts on the particle distribution as confinement and retraction force to create secondary agglomerates.

  13. The shape effect of space debris on recoil impulse by pulsed laser ablation

    NASA Astrophysics Data System (ADS)

    Wang, Chenglin; Zhang, Yan; Wang, Kunpeng

    2016-10-01

    Removing space debris by high-energy pulsed laser may be the most effective way to mitigate the threat posed by the increasing space debris. Laser ablation of a thin surface layer causes recoil impulse, which will lower the orbit perigee of space debris and accelerate the atmospheric capture. When the laser beam vertically irradiates a flat debris, it requires a certain laser fluence to reach the optimal impulse coupling, and the recoil impulse is parallel to the laser beam. However, the incident laser fluence varies in different parts of a non-flat surface. We have taken the shape effect into account to propose a numerical method of calculating the recoil impulse. Taking cylinder debris as the target, we have compared the recoil impulse in different laser fluences through simulation experiments, which implies that a higher laser fluence than the optimal one is needed to obtain a larger recoil impulse for irregularly shaped space debris.

  14. Measurement of ablation threshold of oxide-film-coated aluminium nanoparticles irradiated by femtosecond laser pulses

    SciTech Connect

    Chefonov, O V; Ovchinnikov, A V; Il'ina, I V; Agranat, M B

    2016-03-31

    We report the results of experiments on estimation of femtosecond laser threshold intensity at which nanoparticles are removed from the substrate surface. The studies are performed with nanoparticles obtained by femtosecond laser ablation of pure aluminium in distilled water. The attenuation (or extinction, i.e. absorption and scattering) spectra of nanoparticles are measured at room temperature in the UV and optical wavelength ranges. The size of nanoparticles is determined using atomic force microscopy. A new method of scanning photoluminescence is proposed to evaluate the threshold of nanoparticle removal from the surface of a glass substrate exposed to IR femtosecond laser pulses with intensities 10{sup 11} – 10{sup 13} W cm{sup -2}. (interaction of laser radiation with matter)

  15. RAPID COMMUNICATION: ? thin film bilayers grown by pulsed laser ablation deposition

    NASA Astrophysics Data System (ADS)

    Singh, S. K.; Palmer, S. B.; McK Paul, D.; Lees, M. R.

    1996-09-01

    We have grown superconducting thin films of 0022-3727/29/9/044/img2 (Y-123) on 0022-3727/29/9/044/img3 (PCMO) buffer layers and PCMO overlayers on Y-123 thin films using pulsed laser ablation deposition. For both sets of films below 50 K, the Y-123 layer is superconducting and the zero-field cooled PCMO layer is insulating. The application of a magnetic field of 8 T results in an insulator - metal transition in the PCMO layer. This field-induced conducting state is stable in zero magnetic field at low temperature. The PCMO layer can be returned to an insulating state by annealing above 100 K. This opens the way for the construction of devices incorporating these oxide materials in which the electronic properties of key components such as the substrate or the barrier layer can be switched in a controlled way by the application of a magnetic field.

  16. Synthesis and characterization of uncoated and cysteamine-coated gold nanoparticles by pulsed laser ablation

    NASA Astrophysics Data System (ADS)

    Shukri, Wan Norsyuhada Wan; Bidin, Noriah; Islam, Shumaila; Krishnan, Ganesan; Bakar, Mohamad Aizat Abu; Affandi, Mohd Syafiq

    2016-10-01

    Gold nanoparticles and cysteamine-coated gold nanoparticles are physically synthesized using the pulsed laser ablation in liquid technique, which is rapid, simple, and efficient one-step synthesis. UV-Vis analysis shows that the absorption band after cysteamine coating is shifted toward the lower wavelength range around ˜234 nm as compared to gold nanoparticles' absorption band around ˜520 nm. Moreover, the change in the color of the solution is due to the aggregation of nanoparticles after cysteamine coating. From transmission electron microscopy, cysteamine coating of ˜1 nm thickness on gold nanoparticles is successfully carried out with narrow pore size distributions. Energy-dispersive x-ray spectroscopy analysis confirms the presence of cysteamine coating. Attenuated total reflectance Fourier transform infrared spectroscopy analysis also confirms the bond linkage between gold and cysteamine species.

  17. Photoemission Studies of Metallic Photocathodes Prepared by Pulsed Laser Ablation Deposition Technique

    SciTech Connect

    Fasano, V.; Lorusso, A.; Perrone, A.; De Rosa, H.; Cultrera, L.

    2010-11-10

    We present the results of our investigation on metallic films as suitable photocathodes for the production of intense electron beams in RF photoinjector guns. Pulsed laser ablation deposition technique was used for growing Mg and Y thin films onto Si and Cu substrates in high vacuum and at room temperature.Different diagnostic methods were used to characterize the thin films deposited on Si with the aim to optimize the deposition process. Photoelectron performances were investigated on samples deposited on Cu substrate in an ultra high vacuum photodiode chamber at 10{sup -7} Pa. Relatively high quantum efficiencies have been obtained for the deposited films, comparable to those of corresponding bulks. Samples could stay for several months in humid open air before being tested in a photodiode cell. The deposition process and the role of the photocathode surface contamination and its influence on the photoelectron performances are presented and discussed.

  18. The Post-Processing Effects due to Pulsed Laser Ablation of Paper

    NASA Astrophysics Data System (ADS)

    Kaminska, A.; Sawczak, M.; Cieplnski, M.; Sliwinski, G.

    For contemporary samples the effect of pulsed laser ablation applied at wavelengths selected from the range UV — near IR of 266, 355, 532 and 1064 nm were investigated. All the samples were made by the same method and of the same material, i.e. mixture of pure cotton cellulose and wood-pulp. Results of the colorimetric measurements indicate the most effective surface cleaning at 532 nm for the artificially soiled samples. An artificial aging resulted in neglectable changes in lightness and yellowness of the laser cleaned laboratory soiled samples but influenced the changes in non soiled samples. Marked changes were noticed due to 266 nm, 355 nm and 1064 nm irradiation and were ascribed to the photochemical damage of the cellulose fibres and to enhanced absorption of the laser radiation by the soil particles.

  19. Depth profiling and imaging capabilities of an ultrashort pulse laser ablation time of flight mass spectrometer

    PubMed Central

    Cui, Yang; Moore, Jerry F.; Milasinovic, Slobodan; Liu, Yaoming; Gordon, Robert J.; Hanley, Luke

    2012-01-01

    An ultrafast laser ablation time-of-flight mass spectrometer (AToF-MS) and associated data acquisition software that permits imaging at micron-scale resolution and sub-micron-scale depth profiling are described. The ion funnel-based source of this instrument can be operated at pressures ranging from 10−8 to ∼0.3 mbar. Mass spectra may be collected and stored at a rate of 1 kHz by the data acquisition system, allowing the instrument to be coupled with standard commercial Ti:sapphire lasers. The capabilities of the AToF-MS instrument are demonstrated on metal foils and semiconductor wafers using a Ti:sapphire laser emitting 800 nm, ∼75 fs pulses at 1 kHz. Results show that elemental quantification and depth profiling are feasible with this instrument. PMID:23020378

  20. Portable nanosecond pulsed air plasma jet

    SciTech Connect

    Walsh, J. L.; Kong, M. G.

    2011-08-22

    Low-temperature atmospheric pressure plasmas are of great importance in many emerging biomedical and materials processing applications. The redundancy of a vacuum system opens the gateway for highly portable plasma systems, for which air ideally becomes the plasma-forming gas and remote plasma processing is preferred to ensure electrical safety. Typically, the gas temperature observed in air plasma greatly exceeds that suitable for the processing of thermally liable materials; a large plasma-sample distance offers a potential solution but suffers from a diluted downstream plasma chemistry. This Letter reports a highly portable air plasma jet system which delivers enhanced downstream chemistry without compromising the low temperature nature of the discharge, thus forming the basis of a powerful tool for emerging mobile plasma applications.

  1. Thermal ablation of plasma-facing surfaces in tokamak disruptions: Sensitivity to particle kinetic energy

    SciTech Connect

    Ehst, D.A.; Hassanein, A.

    1996-02-01

    Ablation damage to solid targets with high heat flux impulses is generally greater high-energy electron beam heat sources compared to low-energy plasma guns. This sensitivity to incoming particle kinetic energy is explored with computer modelling; a fast-running routine (DESIRE) is developed for initial scoping analysis and is found to be in reasonable agreement with several experiments on graphite and tungsten targets. If tokamak disruptions are characterized by particle energies less than {approximately}1 keV, then we expect plasma guns are a better analogue than electron beams for simulating disruption behavior and testing candidate plasma-facing materials.

  2. A Study of Burst-Mode Ultrafast-Pulse Laser Ablation on Soft Tissues and Tissue-Proxies

    NASA Astrophysics Data System (ADS)

    Qian, Zuoming

    This thesis research presents an experimental study of both the physics mechanisms and biological effects of burst-mode ultrafast-pulse laser ablation. A 3D living-cell-culture tissue-proxy based on agar hydrogel was developed, and this tissue-proxy was used to quantify the cellular necrosis range, to identify the types of cellular death, and to measure the volume of material removal post burst-mode laser ablation. The potential hazards of cellular DNA damage were also evaluated. A time-resolving energy-partition diagnostics system was designed and built for characterizing the dynamic scattering and absorption of pulses during burst-mode ablation. Such characterizations were carried out on soda-lime glass, aluminum, porcine tissues, distilled water, and agar gels using this diagnostic system. Each type of target materials displayed distinct features in their absorption patterns. An array of characteristics of the absorption and their relation to the ablation dynamics were analyzed, and valuable insight about the burst-mode ablation process was gained. The characterization of the dynamic absorptions allowed the evaluation of the roles of different physics mechanisms in the resulting cellular damage and material removal.

  3. Electron cyclotron resonance plasma assisted pulsed laser deposition for compound host film synthesis and in situ doping

    SciTech Connect

    Lu, Y.F.; Sun, J.; Yu, D.; Shi, L.Q.; Dong, Z.B.; Wu, J.D.

    2006-05-15

    We developed a method for compound host film synthesis and in situ doping based on plasma assisted pulsed laser deposition by coablation of two targets with two pulsed laser beams. The feasibility of this method was demonstrated by the preparation of Er-doped GaN films. In the reactive nitrogen environment and with the assistance of nitrogen plasma generated from electron cyclotron resonance microwave discharge, the ablation of a polycrystalline GaAs target resulted in the reactive deposition of a GaN host film, whereas the ablation of a metallic Er target provided the host with Er atoms for in situ doping in the growing GaN host film. Hexagonal GaN films were formed on a silicon substrate as the host and Er was incorporated into the host with controlled concentration. We found that the composition of the compound host could be adjusted by varying the laser fluence on the target for host deposition or the energy of the plasma stream bombarding the growing host film. The dopant concentration could also be independently controlled to vary in a wide range by changing the pulse repetition ratio of the two laser beams or the laser fluence on the target for dopant supply. It was also proved that doping of very low concentrations could be easily realized by simply adjusting the pulse repetition rate and the fluence of the second laser.

  4. Maximum available flux of charged particles from the laser ablation plasma

    NASA Astrophysics Data System (ADS)

    Sakai, Yasuo; Itagaki, Tomonobu; Horioka, Kazuhiko

    2016-12-01

    The laser ablation plasma was characterized for high-flux sources of ion and electron beams. An ablation plasma was biased to a positive or a negative high voltage, and the fluxes of charged particles through a pair of extraction electrodes were measured as a function of the laser intensity IL. Maximum available fluxes and the ratios of electron and ion beam currents Je/Ji were evaluated as a function of the laser irradiance. The ion and the electron fluxes increased with a laser intensity and the current ratio was around 40 at IL = 1.3 × 108 W/cm2 which monotonically decreased with an increase of the laser intensity. The current ratios Je/Ji were correlated to the parameters of ablation plasma measured by the electrostatic probes. The results showed that the ion fluxes are basically enhanced by super-sonically drifting ions in the plasma and the electron fluxes are also enhanced by the drift motion together with a reduction of the sheath potential due to the enhanced ion flux to the surrounding wall.

  5. The effect of applied electric field on pulsed radio frequency and pulsed direct current plasma jet array

    SciTech Connect

    Hu, J. T.; Liu, X. Y.; Liu, J. H.; Xiong, Z. L.; Liu, D. W.; Lu, X. P.; Iza, F.; Kong, M. G.

    2012-06-15

    Here we compare the plasma plume propagation characteristics of a 3-channel pulsed RF plasma jet array and those of the same device operated by a pulsed dc source. For the pulsed-RF jet array, numerous long life time ions and metastables accumulated in the plasma channel make the plasma plume respond quickly to applied electric field. Its structure similar as 'plasma bullet' is an anode glow indeed. For the pulsed dc plasma jet array, the strong electric field in the vicinity of the tube is the reason for the growing plasma bullet in the launching period. The repulsive forces between the growing plasma bullets result in the divergence of the pulsed dc plasma jet array. Finally, the comparison of 309 nm and 777 nm emissions between these two jet arrays suggests the high chemical activity of pulsed RF plasma jet array.

  6. Xenon plasma sustained by pulse-periodic laser radiation

    SciTech Connect

    Rudoy, I. G.; Solovyov, N. G.; Soroka, A. M.; Shilov, A. O.; Yakimov, M. Yu.

    2015-10-15

    The possibility of sustaining a quasi-stationary pulse-periodic optical discharge (POD) in xenon at a pressure of p = 10–20 bar in a focused 1.07-μm Yb{sup 3+} laser beam with a pulse repetition rate of f{sub rep} ⩾ 2 kHz, pulse duration of τ ⩾ 200 μs, and power of P = 200–300 W has been demonstrated. In the plasma development phase, the POD pulse brightness is generally several times higher than the stationary brightness of a continuous optical discharge at the same laser power, which indicates a higher plasma temperature in the POD regime. Upon termination of the laser pulse, plasma recombines and is then reinitiated in the next pulse. The initial absorption of laser radiation in successive POD pulses is provided by 5p{sup 5}6s excited states of xenon atoms. This kind of discharge can be applied in plasma-based high-brightness broadband light sources.

  7. Thrust efficiency optimization of the pulsed plasma thruster SIMP-LEX

    NASA Astrophysics Data System (ADS)

    Nawaz, Anuscheh; Albertoni, Riccardo; Auweter-Kurtz, Monika

    2010-08-01

    The effect of electric parameters on the thrust efficiency of an ablative pulsed plasma thruster was studied. Analytically, it was shown that a higher efficiency can be obtained by increasing energy of a bank of capacitors. This can be achieved by changing the inductance per distance of the plasma sheet, or reducing the resistance of the circuit and the mass bit. Further, an optimum discharge time was found when the capacitance and the inductance were varied. A low initial inductance increases the thrust efficiency. Experimentally, these trends can be verified by comparing two thrusters: SIMP-LEX and ADD SIMP-LEX, with their different initial inductances. For ADD SIMP-LEX, the optimal thrust efficiency for different capacities was determined to be 31% at 60μF for a 17 J configuration.

  8. Plasma formation and dynamics in conical wire arrays in the Llampudken pulsed power generator

    SciTech Connect

    Muñoz, C. Gonzalo E-mail: fveloso@fis.puc.cl; Valenzuela, Vicente E-mail: fveloso@fis.puc.cl; Veloso, Felipe E-mail: fveloso@fis.puc.cl; Favre, Mario E-mail: fveloso@fis.puc.cl; Wyndham, Edmund E-mail: fveloso@fis.puc.cl

    2014-12-15

    Plasma formation and dynamics from conical wire array is experimentally studied. Ablation from the wires is observed, forming plasma accumulation at the array axis and subsequently a jet outflow been expelled toward the top of the array. The arrays are composed by 16 equally spaced 25μ diameter tungsten wires. Their dimensions are 20mm height, with base diameters of 8mm and 16mm top diameter. The array loads are design to be overmassed, hence no complete ablation of the wires is observed during the current rise. The experiments have been carried out in the Llampudken. pulsed power generator (∼350kA in ∼350ns). Plasma dynamics is studied in both side-on and end-on directions. Laser probing (shadowgraphy) is achieved using a frequency doubled Nd:YAG laser (532nm, 12ps FWHM) captured by CCD cameras. Pinhole XUV imaging is captured using gated microchannel plate cameras with time resolution ∼5ns. Results on the jet velocity and the degree of collimation indicating the plausibility on the use of these jets as comparable to the study astrophysically produced jets are presented and discussed.

  9. Modulation instability of laser pulse in magnetized plasma

    SciTech Connect

    Jha, Pallavi; Kumar, Punit; Raj, Gaurav; Upadhyaya, Ajay K.

    2005-12-15

    Modulation instability of a laser pulse propagating through transversely magnetized underdense plasma is studied. It is observed that interaction of laser radiation with plasma in the presence of uniform magnetic field results in an additional perturbed transverse plasma current density along with the relativistic and ponderomotive nonlinear current densities, thus affecting the modulational interaction. In the plane wave limit it is observed that modulational interaction is more stable for magnetized plasma as compared to the unmagnetized case. The analysis shows that there is a significant reduction in the growth rate of modulation instability over a given range of unstable wave numbers due to magnetization of plasma.

  10. Plasma absorption evidence via chirped pulse spectral transmission measurements

    SciTech Connect

    Jedrkiewicz, Ottavia; Minardi, Stefano; Couairon, Arnaud; Jukna, Vytautas; Selva, Marco; Di Trapani, Paolo

    2015-06-08

    This work aims at highlighting the plasma generation dynamics and absorption when a Bessel beam propagates in glass. We developed a simple diagnostics allowing us to retrieve clear indications of the formation of the plasma in the material, thanks to transmission measurements in the angular and wavelength domains. This technique featured by the use of a single chirped pulse having the role of pump and probe simultaneously leads to results showing the plasma nonlinear absorption effect on the trailing part of the pulse, thanks to the spectral-temporal correspondence in the measured signal, which is also confirmed by numerical simulations.

  11. Interaction of nanosecond ultraviolet laser pulses with reactive dusty plasma

    NASA Astrophysics Data System (ADS)

    van de Wetering, F. M. J. H.; Oosterbeek, W.; Beckers, J.; Nijdam, S.; Gibert, T.; Mikikian, M.; Rabat, H.; Kovačević, E.; Berndt, J.

    2016-05-01

    Even though UV laser pulses that irradiate a gas discharge are small compared to the plasma volume (≲3%) and plasma-on time (≲6 × 10-6%), they are found to dramatically change the discharge characteristics on a global scale. The reactive argon-acetylene plasma allows the growth of nanoparticles with diameters up to 1 μm, which are formed inside the discharge volume due to spontaneous polymerization reactions. It is found that the laser pulses predominantly accelerate and enhance the coagulation phase and are able to suppress the formation of a dust void.

  12. Propagation of intense laser pulses in strongly magnetized plasmas

    SciTech Connect

    Yang, X. H. Ge, Z. Y.; Xu, B. B.; Zhuo, H. B.; Ma, Y. Y.; Shao, F. Q.; Yu, W.; Xu, H.; Yu, M. Y.; Borghesi, M.

    2015-06-01

    Propagation of intense circularly polarized laser pulses in strongly magnetized inhomogeneous plasmas is investigated. It is shown that a left-hand circularly polarized laser pulse propagating up the density gradient of the plasma along the magnetic field is reflected at the left-cutoff density. However, a right-hand circularly polarized laser can penetrate up the density gradient deep into the plasma without cutoff or resonance and turbulently heat the electrons trapped in its wake. Results from particle-in-cell simulations are in good agreement with that from the theory.

  13. Plasma and Cavitation Dynamics during Pulsed Laser Microsurgery in vivo

    SciTech Connect

    Hutson, M. Shane; Ma Xiaoyan

    2007-10-12

    We compare the plasma and cavitation dynamics underlying pulsed laser microsurgery in water and in fruit fly embryos (in vivo)--specifically for nanosecond pulses at 355 and 532 nm. We find two key differences. First, the plasma-formation thresholds are lower in vivo --especially at 355 nm--due to the presence of endogenous chromophores that serve as additional sources for plasma seed electrons. Second, the biological matrix constrains the growth of laser-induced cavitation bubbles. Both effects reduce the disrupted region in vivo when compared to extrapolations from measurements in water.

  14. Thrust Stand Measurements of a Conical Inductive Pulsed Plasma Thruster

    NASA Technical Reports Server (NTRS)

    Hallock, Ashley K.; Polzin, Kurt A.

    2013-01-01

    Inductive Pulsed Plasma Thrusters (iPPT) spacecraft propulsion devices in which electrical energy is capacitively stored and then discharged through an inductive coil. The thruster is electrodeless, with a time-varying current in the coil interacting with a plasma covering the face of the coil to induce a plasma current Propellant is accelerated and expelled at a high exhaust velocity (O(10 -- 100 km/s)) by the Lorentz body force arising from the interaction of the magnetic field and the induced plasma current. While this class of thruster mitigates the life-limiting issues associated with electrode erosion, inductive pulsed plasma thrusters can suffer from both high pulse energy requirements imposed by the voltage demands of inductive propellant ionization, and low propellant utilization efficiencies. While this class of thruster mitigates the life-limiting issues associated with electrode erosion, inductive pulsed plasma thrusters can suffer from both high pulse energy requirements imposed by the voltage demands of inductive propellant ionization, and low propellant utilization efficiencies. A conical coil geometry may offer higher propellant utilization efficiency over that of a at inductive coil, however an increase in propellant utilization may be met with a decrease in axial electromagnetic acceleration, and in turn, a decrease in the total axially-directed kinetic energy imparted to the propellant.

  15. Plasma Switch for High-Power Active Pulse Compressor

    SciTech Connect

    Hirshfield, Jay L.

    2013-11-04

    Results are presented from experiments carried out at the Naval Research Laboratory X-band magnicon facility on a two-channel X-band active RF pulse compressor that employed plasma switches. Experimental evidence is shown to validate the basic goals of the project, which include: simultaneous firing of plasma switches in both channels of the RF circuit, operation of quasi-optical 3-dB hybrid directional coupler coherent superposition of RF compressed pulses from both channels, and operation of the X-band magnicon directly in the RF pulse compressor. For incident 1.2 ?s pulses in the range 0.63 ? 1.35 MW, compressed pulses of peak powers 5.7 ? 11.3 MW were obtained, corresponding to peak power gain ratios of 8.3 ? 9.3. Insufficient bakeout and conditioning of the high-power RF circuit prevented experiments from being conducted at higher RF input power levels.

  16. Filamentation of a relativistic short pulse laser in a plasma

    NASA Astrophysics Data System (ADS)

    Kumar, Naveen; Tripathi, V. K.; Sawhney, B. K.

    2006-06-01

    An intense short pulse laser propagating through a plasma undergoes filamentation instability under the combined effects of relativistic mass variation and ponderomotive force-induced electron density depression. These two nonlinearities superimpose each other. In a tenuous plasma, the filament size scales as {\\sim}( c / \\omega _p\\; a_0 ) \\sqrt 2 \\gamma _0^{1/2} , where ω p is the plasma frequency, a0 is the normalized laser amplitude and γ 0 is the relativistic gamma factor.

  17. Evolution of chirped laser pulses in a magnetized plasma channel

    SciTech Connect

    Jha, Pallavi; Hemlata,; Mishra, Rohit Kumar

    2014-12-15

    The propagation of intense, short, sinusoidal laser pulses in a magnetized plasma channel has been studied. The wave equation governing the evolution of the radiation field is set up and a variational technique is used to obtain the equations describing the evolution of the laser spot size, pulse length and chirp parameter. Numerical methods are used to analyze the simultaneous evolution of these parameters. The effect of the external magnetic field on initially chirped as well as unchirped laser pulses on the spot size, pulse length and chirping has been analyzed.

  18. Optical emission spectroscopy observations of fast pulsed capillary discharge plasmas

    NASA Astrophysics Data System (ADS)

    Avaria, G.; Ruiz, M.; Guzmán, F.; Favre, M.; Wyndham, E. S.; Chuaqui, H.; Bhuyan, H.

    2014-05-01

    We present time resolved optical emission spectroscopic (OES) observations of a low energy, pulsed capillary discharage (PCD). The optical emission from the capillary plasma and plasma jets emitted from the capillary volume was recorded with with a SpectraPro 275 spectrograph, fitted with a MCP gated OMA system, with 15 ns time resolution. The discharge was operated with different gases, including argon, nitrogen, hydrogen and methane, in a repetitive pulsed discharge mode at 10-50 Hz, with, 10-12 kV pulses applied at the cathode side. The time evolution of the electron density was measured using Stark broadening of the Hβ line. Several features of the capillary plasma dynamics, such as ionization growth, wall effects and plasma jet evolution, are inferred from the time evolution of the optical emission.

  19. Long-pulse plasma discharge on the Large Helical Device

    NASA Astrophysics Data System (ADS)

    Kumazawa, R.; Mutoh, T.; Saito, K.; Seki, T.; Nakamura, Y.; Kubo, S.; Shimozuma, T.; Yoshimura, Y.; Igami, H.; Ohkubo, K.; Takeiri, Y.; Oka, Y.; Tsumori, K.; Osakabe, M.; Ikeda, K.; Nagaoka, K.; Kaneko, O.; Miyazawa, J.; Morita, S.; Narihara, K.; Shoji, M.; Masuzaki, S.; Kobayashi, M.; Ogawa, H.; Goto, M.; Morisaki, T.; Peterson, B. J.; Sato, K.; Tokuzawa, T.; Ashikawa, N.; Nishimura, K.; Funaba, H.; Chikaraishi, H.; Watari, T.; Watanabe, T.; Sakamoto, M.; Ichimura, M.; Takase, Y.; Notake, T.; Takeuchi, N.; Torii, Y.; Shimpo, F.; Nomura, G.; Takahashi, C.; Yokota, M.; Kato, A.; Zhao, Y.; Kwak, J. G.; Yoon, J. S.; Yamada, H.; Kawahata, K.; Ohyabu, N.; Ida, K.; Nagayama, Y.; Noda, N.; Komori, A.; Sudo, S.; Motojima, O.; LHD experiment Group

    2006-03-01

    A long-pulse plasma discharge of more than 30 min duration was achieved on the Large Helical Device (LHD). A plasma of ne = 0.8 × 1019 m-3 and Ti0 = 2.0 keV was sustained with PICH = 0.52 MW, PECH = 0.1 MW and averaged PNBI = 0.067 MW. The total injected heating energy was 1.3 GJ. One of the keys to the success of the experiment was a dispersion of the local plasma heat load to divertors, accomplished by sweeping the magnetic axis inward and outward. Causes limiting the long pulse plasma discharge are discussed. An ion impurity penetration limited further long-pulse discharge in the 8th experimental campaign (2004).

  20. Thermal nonlinear optical properties of TiO2 nanocrystals prepared through pulsed laser ablation

    NASA Astrophysics Data System (ADS)

    Moslehirad, F.; Majles Ara, M. H.; Torkamany, M. J.; Afsary, M.; Ghorannevis, M.; Sabbaghzadeh, J.

    2013-05-01

    Titanium dioxide (TiO2) nanoparticles (NPs) were synthesized using the pulsed laser ablation method by irradiating a titanium target immersed in distilled water with 1064 nm, Nd:YAG (yttrium aluminum garnet) laser pulses. The indirect band gap of the NPs was estimated with the aid of ultraviolet/visible spectroscopy. Transmission electron microscopy showed the NPs to be spherical in shape and to vary from 5 to 50 nm. The average size of the NPs and their crystalline phases were determined by means of x-ray diffraction analysis. The thermal conductivity of the nano-TiO2 colloids was measured at a temperature of 25 °C. The single-beam z-scan technique was employed to obtain the nonlinear index of refraction (n2) and the nonlinear absorption coefficient (β) under continuous wave He-Ne laser excitation at different input powers. Thermo-optical coefficients of the NPs were calculated using the z-scan results.

  1. Phase transformation during surface ablation of cobalt-cemented tungsten carbide with pulsed UV laser

    NASA Astrophysics Data System (ADS)

    Li, T.; Lou, Q.; Dong, J.; Wei, Y.; Liu, J.

    Surface ablation of cobalt-cemented tungsten carbide hard metal has been carried out in this work using a 308 nm, 20 ns XeCl excimer laser. Surface microphotography and XRD, as well as an electron probe have been used to investigate the transformation of phase and microstructure as a function of the pulse-number of laser shots at a laser fluence of 2.5 J/cm2. The experimental results show that the microstructure of cemented tungsten carbide is transformed from the original polygonal grains of size 3 μm to interlaced large, long grains with an increase in the number of laser shots up to 300, and finally to gross grains of size 10 μm with clear grain boundaries after 700 shots of laser irradiation. The crystalline structure of the irradiated area is partly transformed from the original WC to βWC1-x, then to αW2C and CW3, and finally to W crystal. It is suggested that the undulating `hill-valley' morphology may be the result of selective removal of cobalt binder from the surface layer of the hard metal. The formation of non-stoichiometric tungsten carbide may result from the escape of elemental carbon due to accumulated heating of the surface by pulsed laser irradiation.

  2. Topics in high voltage pulsed power plasma devices and applications

    NASA Astrophysics Data System (ADS)

    Chen, Hao

    Pulsed power technology is one of the tools that is used by scientists and engineers nowadays to produce gas plasmas. The transient ultra high power is able to provide a huge pulse of energy which is sometimes greater than the ionization energy of the gas, and therefore separates the ions and electrons to form the plasma. Sometimes, the pulsed power components themselves are plasma devices. For example, the gas type switches can "turn on" the circuit by creating the plasma channel between the switch electrodes. Mini Back Lighted Thyratron, or as we call it, mini-BLT, is one of these gas type plasma switches. The development of the reduced size and weight "mini-BLT" is presented in this dissertation. Based on the operation characteristics testing of the mini-BLT, suggestions of optimizing the design of the switch are proposed. All the factors such as the geometry of the hollow electrodes and switch housing, the gas condition, the optical triggering source, etc. are necessary to consider when we design and operate the mini-BLT. By reducing the diameter of the cylindrical gas path between the electrodes in the BLT, a novel high density plasma source is developed, producing the plasma in the "squeezed" capillary. The pulsed power generator, of course, is inevitably used to provide the ionization energy for hydrogen gas sealed in the capillary. Plasma diagnostics are necessarily analyzed and presented in detail to properly complete and understand the capillary plasma. This high density plasma source (1019 cm-3) has the potential applications in the plasma wakefield accelerator. The resonant oscillation behavior of the particles in plasmas allows for dynamically generated accelerating electric fields that have orders of magnitude larger than those available in the conventional RF accelerators. Finally, the solid state switches are introduced as a comparison to the gas type switch. Pulsed power circuit topologies such as the Marx Bank, magnetic pulse compression and diode

  3. Pulsed-Plasma Disinfection of Water Containing Escherichia coli

    NASA Astrophysics Data System (ADS)

    Satoh, Kohki; MacGregor, Scott J.; Anderson, John G.; Woolsey, Gerry A.; Fouracre, R. Anthony

    2007-03-01

    The disinfection of water containing the microorganism, Escherichia coli (E. coli) by exposure to a pulsed-discharge plasma generated above the water using a multineedle electrode (plasma-exposure treatment), and by sparging the off-gas of the pulsed plasma into the water (off-gas-sparging treatment), is performed in the ambient gases of air, oxygen, and nitrogen. For the off-gas-sparging treatment, bactericidal action is observed only when oxygen is used as the ambient gas, and ozone is found to generate the bactericidal action. For the plasma-exposure treatment, the density of E. coli bacteria decreases exponentially with plasma-exposure time for all the ambient gases. It may be concluded that the main contributors to E. coli inactivation are particle species produced by the pulsed plasma. For the ambient gases of air and nitrogen, the influence of acidification of the water in the system, as a result of pulsed-plasma exposure, may also contribute to the decay of E. coli density.

  4. Preparation of germanium doped plasma polymerized coatings as ICF target ablators

    SciTech Connect

    Brusasco, R M; Saculla, M D; Cook, R C

    1994-10-05

    Targets for Inertial Confinement Fusion (ICF) experiments at the Lawrence Livermore National Laboratory (LLNL) utilize an organic (CH) ablator coating prepared by plasma polymerization. Some of these experiments require a mid-Z dopant in the ablator coating to modify the opacity of the shell. Bromine had been used in the past, but the surface finish of brominated CH degrades rapidly with time upon exposure to air. This paper describes the preparation and characterization of plasma polymer layers containing germanium as a dopant at concentrations of between 1.25 and 2.25 atom percent. The coatings are stable in air and have an rms surface roughness of 7--9 nm (modes 10--1,000) which is similar to that obtained with undoped coatings. High levels of dopant result in cracking of the inner mandrel during target assembly. Possible explanations for the observed cracking behavior will be discussed.

  5. Nonlinear spectrum of the ablative Rayleigh-Taylor instability in laser-accelerated planar plasmas

    SciTech Connect

    Keskinen, M. J.; Schmitt, A.

    2007-01-15

    A model for the nonlinear spectrum of the ablative Rayleigh-Taylor instability in laser-accelerated planar plasmas has been developed for a wide range of Froude numbers and scale sizes. It is found that the spectrum can be characterized by an inverse power law with spectral index of approximately 2 in the limit of small-wavenumber spectrum cutoffs and small-scale density gradient scale lengths. Comparison of the model spectrum with recent experimental observations is made with good agreement.

  6. Charge Exchange and Ablation Rates of a Titanium Wire Plasma Corona

    SciTech Connect

    Terry, Robert E.

    2009-01-21

    Wire ablation rates are important features in any examination of precursors or transparent mode implosions of wire arrays. When ion temperatures in a Ti wire plasma corona exceed a few eV, the process of resonant charge exchange competes with elastic scattering. Ions pushed into the corona from an anode bias wire array can be expected to drive a fast neutral wind into the surrounding volume, while a cathode bias wire array would not show the strong neutral wind.

  7. Fractal hydrodynamic model of high-fluence laser ablation plasma expansion

    SciTech Connect

    Agop, M.; Nica, P.; Gurlui, S.; Focsa, C.

    2010-10-08

    Optical/electrical characterization of transient plasmas generated by high-fluence (up to 1 kJ/cm{sup 2}) laser ablation of various targets revealed as a general feature the splitting of the plume in two structures. In order to account for this behavior, a new fractal hydrodynamic model has been developed in a non-differentiable space-time. The model successfully retrieves the kinetics of the two structures.

  8. Generation of thorium ions by laser ablation and inductively coupled plasma techniques for optical nuclear spectroscopy

    NASA Astrophysics Data System (ADS)

    Troyan, V. I.; Borisyuk, P. V.; Khalitov, R. R.; Krasavin, A. V.; Lebedinskii, Yu Yu; Palchikov, V. G.; Poteshin, S. S.; Sysoev, A. A.; Yakovlev, V. P.

    2013-10-01

    Single- and double-charged 232Th and 229Th ions were produced by laser ablation of solid-state thorium compounds and by inductively coupled plasma techniques with mass-spectrometry analysis from liquid solutions of thorium. The latter method was found to be more applicable for producing ions of radioactive 229Th for laser experiments when searching for the energy value of the isomeric nuclear transition.

  9. 2-D MHD numerical simulations of EML plasma armatures with ablation

    NASA Astrophysics Data System (ADS)

    Boynton, G. C.; Huerta, M. A.; Thio, Y. C.

    1993-01-01

    We use a 2-D) resistive MHD code to simulate an EML plasma armature. The energy equation includes Ohmic heating, radiation heat transport and the ideal gas equation of state, allowing for variable ionization using the Saha equations. We calculate rail ablation taking into account the flow of heat into the interior of the rails. Our simulations show the development of internal convective flows and secondary arcs. We use an explicit Flux Corrected Transport algorithm to advance all quantities in time.

  10. Magneto hydrodynamics simulations of pulsed high density plasmas in electromagnetic guns

    NASA Astrophysics Data System (ADS)

    Sitaraman, Hariswaran; Raja, Laxminarayan

    2011-10-01

    Electromagnetic guns are a class of devices which uses the Lorentz force to accelerate bulk plasma/conducting solids to velocities ~ km/s. This idea has been widely used in electromagnetic rail guns and in space propulsion systems. The electrically conducting region is typically a pulsed high density thermal plasma which interacts with the bounding solid surface resulting in ablation and materials chemical degradation. We perform a numerical modeling study of the plasma in an electromagnetic gun to understand the discharge physics and in particular study the plasma-surface interactions. The resistive Magneto hydrodynamics (MHD) equations which include the mass, momentum and energy equations for a conducting fluid along with the Maxwell's equations is used for this study. These equations constitute a stiff system with strong coupling between fluid dynamics and electromagnetics. The equations are solved on an unstructured mesh using a cell-centered finite volume formulation. Details of important species in the plasma and the particle and energy flux distribution at the solid boundaries are presented and the consequent plasma-surface interactions under varying operating conditions are discussed.

  11. A Performance Comparison of Pulsed Plasma Thruster Electrode Configurations

    NASA Technical Reports Server (NTRS)

    Arrington, Lynn A.; Haag, Tom W.; Pencil, Eric J.; Meckel, Nicole J.

    1997-01-01

    Pulsed plasma thrusters are currently planned on two small satellite missions and proposed for a third. In these missions, the pulsed plasma thruster's unique characteristics will be used variously to provide propulsive attitude control, orbit raising, translation, and precision positioning. Pulsed plasma thrusters are attractive for small satellite applications because they are essentially stand alone devices which eliminate the need for toxic and/or distributed propellant systems. Pulsed plasma thrusters also operate at low power and over a wide power range without loss of performance. As part of the technical development required for the noted missions, an experimental program to optimize performance with respect to electrode configuration was undertaken. One of the planned missions will use pulsed plasma thrusters for orbit raising requiring relatively high thrust and previously tested configurations did not provide this. Also, higher capacitor energies were tested than previously tried for this mission. Multiple configurations were tested and a final configuration was selected for flight hardware development. This paper describes the results of the electrode optimization in detail.

  12. Interaction of UV laser pulses with reactive dusty plasmas

    NASA Astrophysics Data System (ADS)

    van de Wetering, Ferdi; Beckers, Job; Nijdam, Sander; Oosterbeek, Wouter; Kovacevic, Eva; Berndt, Johannes

    2016-09-01

    This contribution deals with the effects of UV photons on the synthesis and transport of nanoparticles in reactive complex plasmas (capacitively coupled RF discharge). First measurements showed that the irradiation of a reactive acetylene-argon plasma with high-energy, ns UV laser pulses (355 nm, 75 mJ pulse energy, repetition frequency 10Hz) can have a large effect on the global discharge characteristics. One particular example concerns the formation of a dust void in the center of the discharge. At sufficiently high pulse energies, this formation of a dust free region - which occurs without laser irradiation-is totally suppressed. Moreover the experiments indicate that the laser pulses influence the early stages of the particle formation. Although the interaction between the laser and the plasma is not yet fully understood, it is remarkable that these localized nanosecond laser pulses can influence the plasma on a global scale. Besides new insights into fundamental problems, this phenomenon opens also new possibilities for the controlled manipulation of particle growth and particle transport in reactive plasmas.

  13. Population Inversions in Ablation Plasmas Generated by Intense Electron Beams.

    DTIC Science & Technology

    1988-11-01

    light weight design, and moderate cost. The Soviets have investigated intense proton beam pumped plasma lasers , however, the University of Michigan...interpretations have been verified by moving the position of the probe laser beam away from the surface of the anode (from 0.1 cm to 0.4 cm) and noting the changes...Properties Effects on Ultraviolet Laser induced Flashover of Angled Plastic insulators in Vacuum", C.L. Ensloe and R. M. Gilgenbach, IEEE 3 Trans. on

  14. Plasma detector for TEA CO2 laser pulse measurement

    NASA Astrophysics Data System (ADS)

    Ichikawa, Y.; Yamanaka, M.; Mitsuishi, A.; Fujita, S.; Yamanaka, T.; Yamanaka, C.; Tsunawaki, Y.; Iwasaki, T.; Takai, M.

    1983-10-01

    Laser-pulse evolution can be detected by measuring the emf generated by fast electrons in a laser-produced plasma when the laser radiation is focused onto a solid metal target in a vacuum. Using this phenomenon a 'plasma detector' is constructed, and its characteristics for the TEA CO2 laser radiation of intensity 10 to the 9th to 10 to the 10th W/sq cm are investigated experimentally. The plasma detector operates at room temperature and is strong against laser damages. For the evacuated plasma detector down to 0.1 torr, a maximum output voltage of 90 V and a rise time shorter than 1 ns are observed. The plasma detector, therefore, can be used as a power monitor for laser pulses and as a trigger voltage source.

  15. Temporal evolution of liquid-assisted hard bio-tissue ablation with infrared pulsed lasers under a liquid environment

    NASA Astrophysics Data System (ADS)

    Chen, Faner; Li, Qiang; Hua, Mingxin; Zhan, Zhenlin; Xie, Shusen; Zhang, Xianzeng

    2016-10-01

    Liquid-assisted hard biotissue ablation with the pulsed lasers takes advantages in precision and compatibility than mechanical tools in traditional surgery. The objective of this study was to monitor the dynamic process of the cavitation bubble evolution induced by Ho:YAG laser under water and identify the opening time of channel formation between the fiber tip to the target tissue surface. A free-running Ho:YAG laser was used in the experiment. The wavelength was 2.1 μm with a pulse duration of 350 us and pulse energy varied from 500 mJ to 2000 mJ. The high-speed camera (PCO. dimax, Germany, PCO) applied to monitor the whole ablation process was setting at a frame rate of 52000 frames/s. The results showed that the cavitation bubble induced by laser energy experienced an oscillation process including occurrence, expansion, contraction and subsequent collapse. A channel connected the fiber tip and target tissue surface was formed during the dynamic process which allowed the following pulse energy transmitted through the channel with a relative low absorption and directly interacted with the target tissue. The beginning time of channel formation, as well as the duration of channel opening, as functions of incident laser energy were also presented. A micro-explosion was observed near the tissue surface during the bubble collapse, which may contribute to produce a clean cut, reduce the thermal injury and improve the morphology of ablation crater.

  16. Reduction of picosecond laser ablation threshold and damage via nanosecond pre-pulse for removal of dielectric layers on silicon solar cells

    NASA Astrophysics Data System (ADS)

    Brand, A. A.; Meyer, F.; Nekarda, J.-F.; Preu, R.

    2014-10-01

    Laser microstructuring of thin dielectric layers on sensitive electronic devices, such as crystalline silicon solar cells, requires a careful design of the laser ablation process. For instance, degradation of the substrate's crystallinity can vastly decrease minority carrier lifetime and consequently impair the efficiency of such devices. Short-pulse laser ablation seems well suited for clean and spatially confined structuring because of the small heat-affected zone in the remaining substrate material [Dube and Gonsiorawski in Conference record of the twenty first IEEE photovoltaic specialists conference, 624-628 1990]. The short-time regimes, however, generate steep temperature gradients that can lead to amorphization of the remaining silicon surface. By `heating' the substrate via a non-ablative laser pulse in the nanosecond regime before the actual ablation pulse occurs we are able to prevent amorphization of the surface of the silicon solar cell substrate, while lowering the ablation thresholds of a SiNx layer on crystalline silicon wafers.

  17. Synthesis of nanoparticles by pulsed laser ablation in air: a versatile means for flexible synthesis and separation

    NASA Astrophysics Data System (ADS)

    Zhou, R.; Huang, T. T.; Lin, S. D.

    2016-11-01

    In this work, various types of pure nanoparticles are synthesized by pulsed laser ablation. A novel method using laser ablation is presented to synthesize and separate different sizes of nanoparticles. Laser ablation is applied as a physical and environmental friendly method to generate a variety of nanoparticles in air-based environments. By tuning laser beam horizontal and placing target materials vertically to the substrate, nanoparticles can be generated and separated automatically depending on their sizes. The size distribution is evaluated by optical microscope and nanoparticles are counted according to their diameters. The diameter of the particles ranges from 30nm to 5000nm. This work provides a versatile means to collect many types of uniform functional nanoparticles for a wide range of applications.

  18. A Study of Test Techniques for Evaluating Ablative Plasma Engines in Vacuum Test Cells

    DTIC Science & Technology

    1981-10-01

    windows as shown. A small light source was placed at the plasma engine face and the spectrometer was adjusted until the image of the source was...engine pulses. Since the flat face of the calorimeter is completely immersed in the plasma , then if the energy transfer is independent of the...that the plasma impinged on the’ outer surface as the apex faced the engine or on the inner surface as the open base faced the engine. Three

  19. Endometrial ablation

    MedlinePlus

    Hysteroscopy-endometrial ablation; Laser thermal ablation; Endometrial ablation-radiofrequency; Endometrial ablation-thermal balloon ablation; Rollerball ablation; Hydrothermal ablation; Novasure ablation

  20. INPIStron switched pulsed power for dense plasma pinches

    NASA Technical Reports Server (NTRS)

    Han, Kwang S.; Lee, Ja H.

    1993-01-01

    The inverse plasma switch INPIStron was employed for 10kJ/40kV capacitor bank discharge system to produce focused dense plasmas in hypocycloidal-pinch (HCP) devices. A single unit and an array of multiple HCP's were coupled as the load of the pulsed power circuit. The geometry and switching plasma dynamics were found advantageous and convenient for commutating the large current pulse from the low impedance transmission line to the low impedance plasma load. The pulse power system with a single unit HCP, the system A, was used for production of high temperature plasma focus and its diagnostics. The radially running down plasma dynamics, revealed in image converter photographs, could be simulated by a simple snow-plow model with a correction for plasma resistivity. The system B with an array of 8-HCP units which forms a long coaxial discharge chamber was used for pumping a Ti-sapphire laser. The intense UV emission from the plasma was frequency shifted with dye-solution jacket to match the absorption band of the Ti crystal laser near 500 nm. An untuned laser pulse energy of 0.6 J/pulse was obtained for 6.4 kJ/40 kV discharge, or near 103 times of the explosion limit of conventional flash lamps. For both systems the advantages of the INPIStron were well demonstrated: a single unit is sufficient for a large current (greater than 50 kA) without increasing the system impedance, highly reliable and long life operation and implied scalability for the high power ranges above I(sub peak) = 1 MA and V(sub hold) = 100 kV.

  1. Global Modeling of Uranium Molecular Species Formation Using Laser-Ablated Plasmas

    NASA Astrophysics Data System (ADS)

    Curreli, Davide; Finko, Mikhail; Azer, Magdi; Armstrong, Mike; Crowhurst, Jonathan; Radousky, Harry; Rose, Timothy; Stavrou, Elissaios; Weisz, David; Zaug, Joseph

    2016-10-01

    Uranium is chemically fractionated from other refractory elements in post-detonation nuclear debris but the mechanism is poorly understood. Fractionation alters the chemistry of the nuclear debris so that it no longer reflects the chemistry of the source weapon. The conditions of a condensing fireball can be simulated by a low-temperature plasma formed by vaporizing a uranium sample via laser heating. We have developed a global plasma kinetic model in order to model the chemical evolution of U/UOx species within an ablated plasma plume. The model allows to track the time evolution of the density and energy of an uranium plasma plume moving through an oxygen atmosphere of given fugacity, as well as other relevant quantities such as average electron and gas temperature. Comparison of model predictions with absorption spectroscopy of uranium-ablated plasmas provide preliminary insights on the key chemical species and evolution pathways involved during the fractionation process. This project was sponsored by the DoD, Defense Threat Reduction Agency, Grant HDTRA1-16-1-0020. This work was performed in part under the auspices of the U.S. DoE by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.

  2. Depth profile analysis of various titanium based coatings on steel and tungsten carbide using laser ablation inductively coupled plasma--"time of flight" mass spectrometry.

    PubMed

    Bleiner, D; Plotnikov, A; Vogt, C; Wetzig, K; Günther, D

    2000-01-01

    A homogenized 193 nm ArF* laser ablation system coupled to an inductively coupled plasma-"Time of Flight"-mass spectrometer (LA-ICP-TOFMS) was tested for depth profiling analysis on different single-layer Ti based coatings on steel and W carbides. Laser parameters, such as repetition rate, pulse energy and spatial resolution were tested to allow optimum depth related calibration curves. The ablation process using a laser repetition rate of 3 Hz, 120 microm crater diameter, and 100 mJ output energy, leads to linear calibration curves independent of the drill time or peak area used for calibrating the thickness of the layer. The best depth resolution obtained (without beam splitter) was 0.20 microm per laser shot. The time resolution of the ICP-TOFMS of 102 ms integration time per isotope was sufficient for the determination of the drill time of the laser through the coatings into the matrix with better than 2.6% RSD (about 7 microm coating thickness, n = 7). Variation of the volume of the ablation cell was not influencing the depth resolution, which suggests that the depth resolution is governed by the ablation process. However, the application on the Ti(N,C) based single layer shows the potential of LA-ICP-TOFMS as a complementary technique for fast depth determinations on various coatings in the low to medium microm region.

  3. Pulsed and CW adjustable 1942 nm single-mode all-fiber Tm-doped fiber laser system for surgical laser soft tissue ablation applications.

    PubMed

    Huang, Yize; Jivraj, Jamil; Zhou, Jiaqi; Ramjist, Joel; Wong, Ronnie; Gu, Xijia; Yang, Victor X D

    2016-07-25

    A surgical laser soft tissue ablation system based on an adjustable 1942 nm single-mode all-fiber Tm-doped fiber laser operating in pulsed or CW mode with nitrogen assistance is demonstrated. Ex vivo ablation on soft tissue targets such as muscle (chicken breast) and spinal cord (porcine) with intact dura are performed at different ablation conditions to examine the relationship between the system parameters and ablation outcomes. The maximum laser average power is 14.4 W, and its maximum peak power is 133.1 W with 21.3 μJ pulse energy. The maximum CW power density is 2.33 × 106 W/cm2 and the maximum pulsed peak power density is 2.16 × 107 W/cm2. The system parameters examined include the average laser power in CW or pulsed operation mode, gain-switching frequency, total ablation exposure time, and the input gas flow rate. The ablation effects were measured by microscopy and optical coherence tomography (OCT) to evaluate the ablation depth, superficial heat-affected zone diameter (HAZD) and charring diameter (CD). Our results conclude that the system parameters can be tailored to meet different clinical requirements such as ablation for soft tissue cutting or thermal coagulation for future applications of hemostasis.

  4. Spatial and Temporal Investigations of Laser Ablation Plasma Plume Density and Composition

    NASA Astrophysics Data System (ADS)

    Iratcabal, Jeremy; Bach, Bernhard; Beatty, Cuyler; Dutra, Eric; Darling, Timothy; Wiewior, Piotr; Covington, Aaron

    2016-10-01

    Laser ablation of solid targets with laser intensities of the order of 108-1011 W/cm2 provides a rich platform for investigating the density and composition of coexisting molecular, atomic, and ion species in the resulting plasma plume. Experiments measuring the spatial- and temporal-evolution of laser ablation plumes have been performed to simultaneously characterize the multiple parameters related to the energy and momentum partitioning of the incident laser energy as the ablation process occurs. The temperature, density, and relative populations of different molecular, atomic, and ion species can be determined by the simultaneous measurement of optical and charged particle spectroscopy, fast imaging cameras, and optical interferometric diagnostics. Additionally, background gas pressure, density, and species were carefully varied. A comparison of density measurements obtained with multiple interferometric, spectroscopic, and fast imaging diagnostics for a carbon ablation plume expanding into vacuum and into background gases with different Reynolds numbers will be presented. Atomic, molecular, and ion species population evolution will be presented as measured with optical and charged particle spectroscopy. This work was supported by the U.S. DOE NNSA Cooperative Agreement No. DE-NA0002075 and National Securities Technologies, LLC under Contract No. DE-AC52-06NA25946/subcontract No. 165819.

  5. Investigation of effect of solenoid magnet on emittances of ion beam from laser ablation plasma

    NASA Astrophysics Data System (ADS)

    Ikeda, Shunsuke; Romanelli, Mark; Cinquegrani, David; Sekine, Megumi; Kumaki, Masafumi; Fuwa, Yasuhiro; Kanesue, Takeshi; Okamura, Masahiro; Horioka, Kazuhiko

    2014-02-01

    A magnetic field can increase an ion current of a laser ablation plasma and is expected to control the change of the plasma ion current. However, the magnetic field can also make some fluctuations of the plasma and the effect on the beam emittance and the emission surface is not clear. To investigate the effect of a magnetic field, we extracted the ion beams under three conditions where without magnetic field, with magnetic field, and without magnetic field with higher laser energy to measure the beam distribution in phase space. Then we compared the relations between the plasma ion current density into the extraction gap and the Twiss parameters with each condition. We observed the effect of the magnetic field on the emission surface.

  6. Investigation of effect of solenoid magnet on emittances of ion beam from laser ablation plasma.

    PubMed

    Ikeda, Shunsuke; Romanelli, Mark; Cinquegrani, David; Sekine, Megumi; Kumaki, Masafumi; Fuwa, Yasuhiro; Kanesue, Takeshi; Okamura, Masahiro; Horioka, Kazuhiko

    2014-02-01

    A magnetic field can increase an ion current of a laser ablation plasma and is expected to control the change of the plasma ion current. However, the magnetic field can also make some fluctuations of the plasma and the effect on the beam emittance and the emission surface is not clear. To investigate the effect of a magnetic field, we extracted the ion beams under three conditions where without magnetic field, with magnetic field, and without magnetic field with higher laser energy to measure the beam distribution in phase space. Then we compared the relations between the plasma ion current density into the extraction gap and the Twiss parameters with each condition. We observed the effect of the magnetic field on the emission surface.

  7. Synchronous pulsing plasma utilization in dummy poly gate removal process

    NASA Astrophysics Data System (ADS)

    Huang, Ruixuan; Meng, Xiao-Ying; Han, Qiu-Hua; Zhang, Hai-Yang

    2015-03-01

    When CMOS technology reaches 28/20nm node and beyond, several new schemes are implemented such as High K metal gate (HKMG) which can enhance the device performance and has better control of device current leakage. Dummy poly gate removal (DPGR) process is introduced for HKMG, and works as a key process to control the work function of metal gate and threshold voltage (Vt) shift. In dry etch technology, conventional continuous wave (CW) plasma process has been widely used, however, it may not be capable for some challenging process in 28nm node and beyond. In DPGR process for HKMG scheme, CW scheme may result in plasma damage of gate oxide/capping layer for its inherent high electron temperature (Te) and ion energy while synchronous pulsing scheme is capable to simultaneously pulse both source and bias power, which could achieve lower Te, independent control of ion and radical flux, well control the loading of polymer deposition on dense/ isolate features. It's the first attempt to utilize synchronous pulsing plasma in DPGR process. Experiment results indicate that synchronous pulsing could provide less silicon recess under thin gate oxide which is induced by the plasma oxidation. Furthermore, the loading of HK capping layer loss between long channel and short channel can be well controlled which plays a key role on transistor performance, such as leakage and threshold voltage shift. Additionally, it has been found that synchronous pulsing could distinctly improve ILD loss when compared with CW, which is helpful to broaden the whole process window.

  8. Chirped pulse Raman amplification in warm plasma: towards controlling saturation.

    PubMed

    Yang, X; Vieux, G; Brunetti, E; Ersfeld, B; Farmer, J P; Hur, M S; Issac, R C; Raj, G; Wiggins, S M; Welsh, G H; Yoffe, S R; Jaroszynski, D A

    2015-08-20

    Stimulated Raman backscattering in plasma is potentially an efficient method of amplifying laser pulses to reach exawatt powers because plasma is fully broken down and withstands extremely high electric fields. Plasma also has unique nonlinear optical properties that allow simultaneous compression of optical pulses to ultra-short durations. However, current measured efficiencies are limited to several percent. Here we investigate Raman amplification of short duration seed pulses with different chirp rates using a chirped pump pulse in a preformed plasma waveguide. We identify electron trapping and wavebreaking as the main saturation mechanisms, which lead to spectral broadening and gain saturation when the seed reaches several millijoules for durations of 10's - 100's fs for 250 ps, 800 nm chirped pump pulses. We show that this prevents access to the nonlinear regime and limits the efficiency, and interpret the experimental results using slowly-varying-amplitude, current-averaged particle-in-cell simulations. We also propose methods for achieving higher efficiencies.

  9. Chirped pulse Raman amplification in warm plasma: towards controlling saturation

    PubMed Central

    Yang, X.; Vieux, G.; Brunetti, E.; Ersfeld, B.; Farmer, J. P.; Hur, M. S.; Issac, R. C.; Raj, G.; Wiggins, S. M.; Welsh, G. H.; Yoffe, S. R.; Jaroszynski, D. A.

    2015-01-01

    Stimulated Raman backscattering in plasma is potentially an efficient method of amplifying laser pulses to reach exawatt powers because plasma is fully broken down and withstands extremely high electric fields. Plasma also has unique nonlinear optical properties that allow simultaneous compression of optical pulses to ultra-short durations. However, current measured efficiencies are limited to several percent. Here we investigate Raman amplification of short duration seed pulses with different chirp rates using a chirped pump pulse in a preformed plasma waveguide. We identify electron trapping and wavebreaking as the main saturation mechanisms, which lead to spectral broadening and gain saturation when the seed reaches several millijoules for durations of 10’s – 100’s fs for 250 ps, 800 nm chirped pump pulses. We show that this prevents access to the nonlinear regime and limits the efficiency, and interpret the experimental results using slowly-varying-amplitude, current-averaged particle-in-cell simulations. We also propose methods for achieving higher efficiencies. PMID:26290153

  10. Single and Multi-Pulse Low-Energy Conical Theta Pinch Inductive Pulsed Plasma Thruster Performance

    NASA Technical Reports Server (NTRS)

    Hallock, A. K.; Martin, A. K.; Polzin, K. A.; Kimberlin, A. C.; Eskridge, R. H.

    2013-01-01

    Impulse bits produced by conical theta-pinch inductive pulsed plasma thrusters possessing cone angles of 20deg, 38deg, and 60deg, were quantified for 500J/pulse operation by direct measurement using a hanging-pendulum thrust stand. All three cone angles were tested in single-pulse mode, with the 38deg model producing the highest impulse bits at roughly 1 mN-s operating on both argon and xenon propellants. A capacitor charging system, assembled to support repetitively-pulsed thruster operation, permitted testing of the 38deg thruster at a repetition-rate of 5 Hz at power levels of 0.9, 1.6, and 2.5 kW. The average thrust measured during multiple-pulse operation exceeded the value obtained when the single-pulse impulse bit is multiplied by the repetition rate.

  11. Interaction physics of multipicosecond Petawatt laser pulses with overdense plasma.

    PubMed

    Kemp, A J; Divol, L

    2012-11-09

    We study the interaction of intense petawatt laser pulses with overdense plasma over several picoseconds, using two- and three-dimensional kinetic particle simulations. Sustained irradiation with non-diffraction-limited pulses at relativistic intensities yields conditions that differ qualitatively from what is experimentally available today. Nonlinear saturation of laser-driven density perturbations at the target surface causes recurrent emissions of plasma, which stabilize the surface and keep absorption continuously high. This dynamics leads to the acceleration of three distinct groups of electrons up to energies many times the laser ponderomotive potential. We discuss their energy distribution for applications like the fast-ignition approach to inertial confinement fusion.

  12. Photoacoustic monitoring of the pulsed laser ablation of glochids on prickly pear fruit

    NASA Astrophysics Data System (ADS)

    Arronte, M.; Flores, T.; Ponce, L.; Ortega-Martínez, E.

    2006-02-01

    The use of the photoacoustic technique for real time monitoring of the efficiency and cleaning sites localization during the laser assisted removal of the spiky glochids from prickly pear fruit is proposed. Prickly pear areoles were irradiated with high energy microsecond Nd: YAG laser sequence of pulses up to the entirely removal of the glochids agglomerate. Strong selective absorption of the laser radiation leads to the formation of a high pressure plasma. The photoacoustic experiments were done in open air conditions using a standard electret transducer. Results obtained from photoacoustic signal analysis display high sensibility and signal to noise ratio for in situ monitoring of the process.

  13. Modified surface morphology in surface ablation of cobalt-cemented tungsten carbide with pulsed UV laser radiation

    NASA Astrophysics Data System (ADS)

    Li, Tiejun; Lou, Qihong; Dong, Jingxing; Wei, Yunrong; Liu, Jingru

    2001-03-01

    Surface ablation of cobalt-cemented tungsten carbide hardmetal has been carried out in this work using a 308 nm, 20 ns XeCl excimer laser. The influence of ablation rate, surface roughness, surface micromorphology as well as surface phase structure on laser conditions including laser irradiance and pulse number have been investigated. The experimental results showed that the ablation rate and surface roughness were controlled by varying the number of pulses and laser irradiance. The microstructure and crystalline structure of irradiated surface layer varied greatly with different laser conditions. After 300 shots of laser irradiation at irradiance of 125 MW/cm 2, the surface micromorphology characterizing a uniform framework pattern of "hill-valleys". With the increment of laser shots at laser irradiance of 125 MW/cm 2, the microstructure of cemented tungsten carbide transformed from original polygon grains with the size of 3 μm to interlaced large and long grains after 300 shots of laser irradiation, and finally to gross grains with the size of 10 μm with clear grain boundaries after 700 shots. The crystalline structure of irradiated area has partly transformed from original WC to β-WC 1- x, then to α-W 2C and CW 3, and finally to W crystal. At proper laser irradiance and pulse number, cobalt binder has been selectively removed from the surface layer of hardmetal. It has been demonstrated that surface ablation with pulsed UV laser should be a feasible way to selectively remove cobalt binder from surface layer of cemented tungsten carbide hardmetal.

  14. Analysis of tungsten carbide coatings by UV laser ablation inductively coupled plasma atomic emission spectrometry

    NASA Astrophysics Data System (ADS)

    Kanicky, V.; Otruba, V.; Mermet, J.-M.

    2000-06-01

    Tungsten carbide coatings (thickness 0.1-0.2 mm) containing 8.0, 12.2, 17.2 and 22.9% Co were studied with laser ablation inductively coupled plasma atomic emission spectrometry (LA-ICP-AES). Composition of these plasma sprayed deposits on steel disks was determined using X-ray fluorescence spectrometry and electron microprobe energy/wavelength dispersive X-ray spectrometry. The coatings were ablated by means of a Q-switched Nd:YAG laser at 266 nm (10 Hz, 10 mJ per shot) coupled to an ICP echelle-based spectrometer equipped with a segmented charge-coupled device detector. Non-linear dependences of cobalt lines intensities on the Co percentage were observed both at a single spot ablation and at a sample translation. This behaviour could be attributed to a complex phase composition of the system W-C-Co. However, employing tungsten as internal standard the linear calibration was obtained for studied analytical lines Co II 228.616 nm, Co II 230.786 nm, Co II 236.379 nm and Co II 238.892 nm.

  15. Hook spectroscopy as an atomic number density diagnostic applied to laser-ablated copper plasmas

    SciTech Connect

    Zerkle, D.K.; Sappey, A.D.; Gamble, T.K.

    1993-11-01

    Hook spectroscopy has been used to determine the absolute number density of ground state copper atoms in laser-ablated plasma plumes. An ablation laser power flux of {approximately} 1.5 GW/cm{sup 2} is applied to a solid copper target in a background gas, producing a plasma plume suitable for studying homogeneous copper vapor condensation. Density is measured at post-ablation time delays ranging from 10 {mu}s to 3 ms with 25 torr of argon as the background gas. Planar laser-induced fluorescence (PLEF) images containing relative density information are used in conjunction with the hook spectra to resolve spatially the absolute density within the plume. Copper atom densities thus measured ranged from 1.9 {times} 10{sup 15} cm{sup {minus}3} at a delay of 10 {mu}s to 2.7 {times} 10{sup 13} cm{sup {minus}3} at 3 ms delay in 25 torr of argon The decrease in density is due to the condensation of copper vapor to form fine particulate. As a combustion diagnostic, the hook method may prove extremely useful for the determination of metal impurity density in coal fired flames as well as a single -- shot OH density and temperature diagnostic.

  16. Inductively coupled plasma mass spectrometry with a twin quadrupole instrument using laser ablation sample introduction and monodisperse dried microparticulate injection

    SciTech Connect

    Allen, Lloyd A.

    1996-10-17

    The focus of this dissertation is the use of a twin quadrupole inductively coupled plasma mass spectrometer (ICP-MS) for the simultaneous detection of two m/z values. The twin quadrupole ICP-MS is used with laser ablation sample introduction in both the steady state (10 Hz) and single pulse modes. Steady state signals are highly correlated and the majority of flicker noise cancels when the ratio is calculated. Using a copper sample, the isotope ratio 63Cu+/65Cu+ is measured with a relative standard deviation (RSD) of 0.26%. Transient signals for single laser pulses are also obtained. Copper isotope ratio measurements for several laser pulses are measured with an RSD of 0.85%. Laser ablation (LA) is used with steel samples to assess the ability of the twin quadrupole ICP-MS to eliminate flicker noise of minor components of steel samples. Isotopic and internal standard ratios are measured in the first part of this work. The isotope ratio 52Cr+/53Cr+ (Cr present at 1.31 %) can be measured with an RSD of 0.06 % to 0.1 %. For internal standard elements, RSDs improve from 1.9 % in the Cr+ signal to 0.12% for the ratio of 51V+ to 52Cr+. In the second part of this work, one mass spectrometer is scanned while the second channel measures an individual m/z value. When the ratio of these two signals is calculated, the peak shapes in the mass spectrum are improved significantly. Pulses of analyte and matrix ions from individual drops are measured simultaneously using the twin quadrupole ICP-MS with monodisperse dried microparticulate injection (MDMI). At modest Pb concentrations (500 ppm), a shoulder on the leading edge of the Li+ signal becomes apparent. Space charge effects are consistent with the disturbances seen.

  17. Generation of diluted magnetic semiconductor nanostructures by pulsed laser ablation in liquid

    NASA Astrophysics Data System (ADS)

    Savchuk, Ol. A.; Savchuk, A. I.; Stolyarchuk, I. D.; Tkachuk, P. M.; Garasym, V. I.

    2015-11-01

    Results of study of two members of diluted magnetic semiconductor (DMS) family, namely Cd1-xMnxTe and Zn1-xMnxO, which are in form of micro- and nanoparticles generated by pulsed laser ablation in liquid medium (PLAL), have been presented. The structural analysis using X-ray diffraction (XRD) of nanocrystals indicated that Mn has entered the AIIBVI lattice without changing the crystal structure and systematically substituted the A2+ ions in the lattice. Atomic force microscopy (AFM) gives information about surface morphology of the formed nanostructures. The scanning electron microscopy (SEM) clearly illustrates flower-like particles of Zn1-xMnxO, which consist of nanosheets and nanoleaves with average thickness about (5-8) nm. Obviously, these nanoobjects are responsible for the observed blue shift of the absorption edge in DMS nanostructures. In magneto-optical Faraday rotation spectra of both Cd1-xMnxTe and Zn1-xMnxO nanostructures there were exhibited peculiarities associated with s,p-d spin exchange interactions and confinement effect. It was observed almost linear dependence of the Faraday rotation as function of magnetic field strength for nanoparticles in contrast to the dependence with saturation in bulk case.

  18. High-speed laser ablation of metal with pico- and subpicosecond pulses

    NASA Astrophysics Data System (ADS)

    Mazhukin, V. I.; Demin, M. M.; Shapranov, A. V.

    2014-05-01

    The mechanism of the high-speed ablation of aluminum with pico- and subpicosecond (10-11-10-13 s) laser pulses is considered. Mathematical modeling based on the continuum non-equilibrium two-temperature (TTM) model revealed that in a relatively narrow range of fluence 0.25-0.7 J/cm2, the regime of mechanical fragmentation of the irradiated surface is realized. The maximum values of the lattice temperature for the specified range of fluence are 2100-3500 K. The removal of the material is mechanical due to the negative stresses in the rarefaction wave following the shock wave. Explicit tracking of temporal and spatial position of the melting front has allowed establishing its role in the generation of superheated metastable states in the solid phase and the propagation of the shock wave. The removed material with total thickness of 60-100 nm is a collection of separate plates with thickness from 1 nm to 55 nm.

  19. Room temperature ferromagnetism in liquid-phase pulsed laser ablation synthesized nanoparticles of nonmagnetic oxides

    SciTech Connect

    Singh, S. C. Gopal, R.; Kotnala, R. K.

    2015-08-14

    Intrinsic Room Temperature Ferromagnetism (RTF) has been observed in undoped/uncapped zinc oxide and titanium dioxide spherical nanoparticles (NPs) obtained by a purely green approach of liquid phase pulsed laser ablation of corresponding metal targets in pure water. Saturation magnetization values observed for zinc oxide (average size, 9 ± 1.2 nm) and titanium dioxide (average size, 4.4 ± 0.3 nm) NPs are 62.37 and 42.17 memu/g, respectively, which are several orders of magnitude larger than those of previous reports. In contrast to the previous works, no postprocessing treatments or surface modification is required to induce ferromagnetism in the case of present communication. The most important result, related to the field of intrinsic ferromagnetism in nonmagnetic materials, is the observation of size dependent ferromagnetism. Degree of ferromagnetism in titanium dioxide increases with the increase in particle size, while it is reverse for zinc oxide. Surface and volume defects play significant roles for the origin of RTF in zinc oxide and titanium dioxide NPs, respectively. Single ionized oxygen and neutral zinc vacancies in zinc oxide and oxygen and neutral/ionized titanium vacancies in titanium dioxide are considered as predominant defect centres responsible for observed ferromagnetism. It is expected that origin of ferromagnetism is a consequence of exchange interactions between localized electron spin moments resulting from point defects.

  20. Dynamics of laser ablation at the early stage during and after ultrashort pulse

    NASA Astrophysics Data System (ADS)

    Ilnitsky, D. K.; Khokhlov, V. A.; Zhakhovsky, V. V.; Petrov, Yu V.; Migdal, K. P.; Inogamov, N. A.

    2016-11-01

    Study of material flow in two-temperature states is needed for a fundamental understanding the physics of femtosecond laser ablation. To explore phenomena at a very early stage of laser action on a metallic target our in-house two-temperature hydrodynamics code is used here. The early stage covers duration of laser pulse with next first few picoseconds. We draw attention to the difference in behavior at this stage between the cases: (i) of an ultrathin film (thickness of order of skin depth d skin or less), (ii) thin films (thickness of a film is 4-7 of d skin for gold), and (iii) bulk targets (more than 10d skin for gold). We demonstrate that these differences follow from a competition among conductive cooling of laser excited electrons in a skin layer, electron-ion coupling, and hydrodynamics of unloading caused by excess of pressure of excited free electrons. Conductive cooling of the skin needs a heat sink, which is performed by the cold material outside the skin. Such sink is unavailable in the ultrathin films.

  1. Room temperature ferromagnetism in liquid-phase pulsed laser ablation synthesized nanoparticles of nonmagnetic oxides

    NASA Astrophysics Data System (ADS)

    Singh, S. C.; Kotnala, R. K.; Gopal, R.

    2015-08-01

    Intrinsic Room Temperature Ferromagnetism (RTF) has been observed in undoped/uncapped zinc oxide and titanium dioxide spherical nanoparticles (NPs) obtained by a purely green approach of liquid phase pulsed laser ablation of corresponding metal targets in pure water. Saturation magnetization values observed for zinc oxide (average size, 9 ± 1.2 nm) and titanium dioxide (average size, 4.4 ± 0.3 nm) NPs are 62.37 and 42.17 memu/g, respectively, which are several orders of magnitude larger than those of previous reports. In contrast to the previous works, no postprocessing treatments or surface modification is required to induce ferromagnetism in the case of present communication. The most important result, related to the field of intrinsic ferromagnetism in nonmagnetic materials, is the observation of size dependent ferromagnetism. Degree of ferromagnetism in titanium dioxide increases with the increase in particle size, while it is reverse for zinc oxide. Surface and volume defects play significant roles for the origin of RTF in zinc oxide and titanium dioxide NPs, respectively. Single ionized oxygen and neutral zinc vacancies in zinc oxide and oxygen and neutral/ionized titanium vacancies in titanium dioxide are considered as predominant defect centres responsible for observed ferromagnetism. It is expected that origin of ferromagnetism is a consequence of exchange interactions between localized electron spin moments resulting from point defects.

  2. Room-temperature deposition of nanocrystalline PbWO 4 thin films by pulsed laser ablation

    NASA Astrophysics Data System (ADS)

    Ryu, J. H.; Yoon, J.-W.; Shim, K. B.; Koshizaki, N.

    2006-07-01

    Pulsed laser ablation (PLA) was applied to synthesize nanocrystalline PbWO4 thin films onto glass substrates. The effects of Ar background gas pressure on phase evolution, microstructures and optical characteristics of PbWO4 thin films were investigated in detail. The PLA processes were carried out at room temperature without substrate heating or post-annealing treatment. XRD and HR-TEM results revealed that the PbWO4 thin films are composed of nanocrystalline and amorphous phases. Moreover, the films contained a high density of lattice defects such as twin boundaries and edge dislocations. The crystallite size and crystallinity increased, which were associated with a change in surface morphology as the Ar pressure increased. Reduced tungsten states W5+ or W4+ induced by oxygen vacancies were observed at 10 Pa and the atomic concentration of all constituent element was almost stoichiometric, especially the [Pb]/[W] ratio, which was nearly unity above 50 Pa. The optical energy band-gap was 3.03 eV at 50 Pa and increased to 3.35 eV at 100 Pa, which are narrower than the reported value (4.20 eV). This optical band-gap narrowing could be attributed to localized band-tail states and new energy levels induced by the amorphous structure and inherent lattice defects.

  3. Structural and optical properties of silicon nanoparticles prepared by pulsed laser ablation in hydrogen background gas

    NASA Astrophysics Data System (ADS)

    Makino, T.; Inada, M.; Yoshida, K.; Umezu, I.; Sugimura, A.

    We studied the structural and optical properties of silicon (Si) nanoparticles (np-Si) prepared by pulsed laser ablation (PLA) in hydrogen (H2) background gas. The mean diameter of the np-Si was estimated to be approximately 5 nm. The infrared absorption corresponding to Si-Hn (n=1,2,3) bonds was observed at around 2100 cm-1, and a Raman scattering peak corresponding to crystalline Si was observed at around 520 cm-1. These results indicate that nanoparticles are not an alloy of Si and hydrogen but Si nanocrystal covered by hydrogen or hydrogenated silicon. This means that surface passivated Si nanoparticles can be prepared by PLA in H2 gas. The band-gap energy of np-Si prepared in H2 gas (1.9 eV) was larger than that of np-Si prepared in He gas (1.6 eV) even though they are almost the same diameter. After decreasing the hydrogen content in np-Si by thermal annealing, the band-gap energy decreased, and reached the same energy level as np-Si prepared in He gas. Thus, the optical properties of np-Si were affected by the hydrogenation of the surface of np-Si.

  4. Influence of pulse duration on the plasma characteristics in high-power pulsed magnetron discharges

    SciTech Connect

    Konstantinidis, S.; Dauchot, J.P.; Ganciu, M.; Ricard, A.; Hecq, M.

    2006-01-01

    High-power pulsed magnetron discharges have drawn an increasing interest as an approach to produce highly ionized metallic vapor. In this paper we propose to study how the plasma composition and the deposition rate are influenced by the pulse duration. The plasma is studied by time-resolved optical emission and absorption spectroscopies and the deposition rate is controlled thanks to a quartz microbalance. The pulse length is varied between 2.5 and 20 {mu}s at 2 and 10 mTorr in pure argon. The sputtered material is titanium. For a constant discharge power, the deposition rate increases as the pulse length decreases. With 5 {mu}s pulse, for an average power of 300 W, the deposition rate is {approx}70% of the deposition rate obtained in direct current magnetron sputtering at the same power. The increase of deposition rate can be related to the sputtering regime. For long pulses, self-sputtering seems to occur as demonstrated by time-resolved optical emission diagnostic of the discharge. In contrary, the metallic vapor ionization rate, as determined by absorption measurements, diminishes as the pulses are shortened. Nevertheless, the ionization rate is in the range of 50% for 5 {mu}s pulses while it lies below 10% in the case of a classical continuous magnetron discharge.

  5. The interaction of intense subpicosecond laser pulses with underdense plasmas

    SciTech Connect

    Coverdale, Christine Ann

    1995-05-11

    Laser-plasma interactions have been of interest for many years not only from a basic physics standpoint, but also for their relevance to numerous applications. Advances in laser technology in recent years have resulted in compact laser systems capable of generating (psec), 1016 W/cm2 laser pulses. These lasers have provided a new regime in which to study laser-plasma interactions, a regime characterized by Lplasma ≥ 2LRayleigh > cτ. The goal of this dissertation is to experimentally characterize the interaction of a short pulse, high intensity laser with an underdense plasma (no ≤ 0.05ncr). Specifically, the parametric instability known as stimulated Raman scatter (SRS) is investigated to determine its behavior when driven by a short, intense laser pulse. Both the forward Raman scatter instability and backscattered Raman instability are studied. The coupled partial differential equations which describe the growth of SRS are reviewed and solved for typical experimental laser and plasma parameters. This solution shows the growth of the waves (electron plasma and scattered light) generated via stimulated Raman scatter. The dispersion relation is also derived and solved for experimentally accessible parameters. The solution of the dispersion relation is used to predict where (in k-space) and at what frequency (in ω-space) the instability will grow. Both the nonrelativistic and relativistic regimes of the instability are considered.

  6. A Nanosecond Pulsed Plasma Brush for Surface Decontamination

    NASA Astrophysics Data System (ADS)

    Neuber, Johanna; Malik, Muhammad; Song, Shutong; Jiang, Chunqi

    2015-11-01

    This work optimizes a non-thermal, atmospheric pressure plasma brush for surface decontamination. The generated plasma plumes with a maximum length of 2 cm are arranged in a 5 cm long, brush-like array. The plasma was generated in ambient air with <= 10 kV, 200 ns pulses at a repetition rate of 1.5 kHz. The energy per pulse and average power are in the range of 1-3 mJ and 0.5-1.5 W, respectively. Helium containing varying concentrations of water vapor was evaluated as the carrier gas and was fed into the plasma chamber at a rate varying between 1 to 7 SLPM. Optimization of the cold plasma brush for surface decontamination was tested in a study of the plasma inactivation of two common pathogens, Staphylococcus aureus and Acinetobacter baumannii. Laminate surfaces inoculated with over-night cultured bacteria were subject to the plasma treatment for varying water concentrations in He, flow rates and discharge voltages. It was found that increasing the water content of the feed gas greatly enhanced the bactericidal effect. Emission spectroscopy was performed to identify the reactive plasma species that contribute to this variation. Additional affiliation: Frank Reidy Research Center for Bioelectrics

  7. Portable laser ablation sampling device for elemental fingerprinting of objects outside the laboratory with laser ablation inductively coupled plasma mass spectrometry.

    PubMed

    Glaus, Reto; Koch, Joachim; Günther, Detlef

    2012-06-19

    Laser ablation-inductively coupled plasma mass spectrometry (LA-ICPMS) is a powerful method for elemental fingerprinting of solid samples in a quasi-nondestructive manner. In order to extend the field of application to objects outside the laboratory, a portable laser ablation sampling device was assembled using a diode pumped solid state laser and fiber-optics. The ablated materials were sampled on membrane filters and subsequently quantified by means of LA-ICPMS. The analytical performance of this approach was investigated for glass and gold reference materials. Accuracies of better than 20% were reached for most elements and typical limits of detection were found to be in the range of 0.01-1 μg/g. In summary, this approach combines spatially resolved sampling with the detection power of ICPMS and enables elemental fingerprinting of objects which cannot be transferred to the laboratory, e.g., archeological artifacts in museums.

  8. Transient plasma potential in pulsed dual frequency inductively coupled plasmas and effect of substrate biasing

    NASA Astrophysics Data System (ADS)

    Mishra, Anurag; Yeom, Geun Young

    2016-09-01

    An electron emitting probe in saturated floating potential mode has been used to investigate the temporal evolution of plasma potential and the effect of substrate RF biasing on it for pulsed dual frequency (2 MHz/13.56 MHz) inductively coupled plasma (ICP) source. The low frequency power (P2MHz) has been pulsed at 1 KHz and a duty ratio of 50%, while high frequency power (P13.56MHz) has been used in continuous mode. The substrate has been biased with a separate bias power at (P12.56MHz) Argon has been used as a discharge gas. During the ICP power pulsing, three distinct regions in a typical plasma potential profile, have been identified as `initial overshoot', pulse `on-phase' and pulse `off-phase'. It has been found out that the RF biasing of the substrate significantly modulates the temporal evolution of the plasma potential. During the initial overshoot, plasma potential decreases with increasing RF biasing of the substrate, however it increases with increasing substrate biasing for pulse `on-phase' and `off-phase'. An interesting structure in plasma potential profile has also been observed when the substrate bias is applied and its evolution depends upon the magnitude of bias power. The reason of the evolution of this structure may be the ambipolar diffusion of electron and its dependence on bias power.

  9. Multiple Pulses from Plasma Jets onto Liquid Covered Tissue

    NASA Astrophysics Data System (ADS)

    Norberg, Seth; Tian, Wei; Johnsen, Eric; Kushner, Mark J.

    2014-10-01

    Atmospheric pressure plasma jets are being studied in the treatment of biological surfaces that are often covered by a thin layer of liquid. The plume of the plasma jet contains neutral radicals and charged species that solvate into the liquid and eventually form terminal species that reach the tissue below. The contribution of neutral and charged species to reactivity in the liquid is sensitive to whether the active plasma plume touches the liquid. In this paper, we discuss results from modeling the production of the aqueous species formed from the interaction of the plume of plasma jets over multiple pulses with the water layer, and the fluences of the species to the underlying tissue. The model used in this study, nonPDPSIM, solves transport equations for charged and neutral species and electron energy, Poisson's equation for the electric potential, and Navier-Stokes equations for the neutral gas flow. Radiation transport includes photoionization of O2 and H2O in the gas and liquid phases and photodissocation of H2Oaq in the liquid. Multiple pulses when the plasma plume touches and does not touch the liquid will be examined. Two regimes of hydrodynamics will be discussed - low repetition rates where the neutral radicals are blown away before the next discharge pulse, and high repetition rate when the plasma plume interacts with neutral radicals from previous pulses. The density of aqueous ions produced in the liquid layer is strongly dependent on whether the plasma effluent touches or does not touch the water surface. Work supported by DOE Office of Fusion Energy Science and NSF.

  10. Exponential frequency spectrum and Lorentzian pulses in magnetized plasmas

    SciTech Connect

    Pace, D. C.; Shi, M.; Maggs, J. E.; Morales, G. J.; Carter, T. A.

    2008-12-15

    Two different experiments involving pressure gradients across the confinement magnetic field in a large plasma column are found to exhibit a broadband turbulence that displays an exponential frequency spectrum for frequencies below the ion cyclotron frequency. The exponential feature has been traced to the presence of solitary pulses having a Lorentzian temporal signature. These pulses arise from nonlinear interactions of drift-Alfven waves driven by the pressure gradients. In both experiments the width of the pulses is narrowly distributed resulting in exponential spectra with a single characteristic time scale. The temporal width of the pulses is measured to be a fraction of a period of the drift-Alfven waves. The experiments are performed in the Large Plasma Device (LAPD-U) [W. Gekelman et al., Rev. Sci. Instrum. 62, 2875 (1991)] operated by the Basic Plasma Science Facility at the University of California, Los Angeles. One experiment involves a controlled, pure electron temperature gradient associated with a microscopic (6 mm gradient length) hot electron temperature filament created by the injection a small electron beam embedded in the center of a large, cold magnetized plasma. The other experiment is a macroscopic (3.5 cm gradient length) limiter-edge experiment in which a density gradient is established by inserting a metallic plate at the edge of the nominal plasma column of the LAPD-U. The temperature filament experiment permits a detailed study of the transition from coherent to turbulent behavior and the concomitant change from classical to anomalous transport. In the limiter experiment the turbulence sampled is always fully developed. The similarity of the results in the two experiments strongly suggests a universal feature of pressure-gradient driven turbulence in magnetized plasmas that results in nondiffusive cross-field transport. This may explain previous observations in helical confinement devices, research tokamaks, and arc plasmas.

  11. Design and fabrication of a 30 second pulsed plasma generator

    SciTech Connect

    Biagi, L.A.; Ehlers, K.W.; Lietzke, A.F.; Matuk, C.A.; Maruyama, Y.; Paterson, J.A.; Tanabe, J.T.

    1983-10-01

    The design and fabrication techniques for a large hybrid magnetic cusp plasma generator developed for 30 sec pulse length are described. Included are the magnetic cusp geometry features, water cooling characteristics, filament structures, and the high energy density actively cooled anode and electron dump employed.

  12. Characteristics of 2-heptanone decomposition using nanosecond pulsed discharge plasma

    NASA Astrophysics Data System (ADS)

    Nakase, Yuki; Fukuchi, Yuichi; Wang, Douyan; Namihira, Takao; Akiyama, Hidenori; Kumamoto University Collaboration

    2015-09-01

    Volatile organic compounds (VOC) evaporate at room temperature. VOCs typically consist of toluene, benzene and ethyl acetate, which are used in cosmetics, dry cleaning products and paints. Exposure to elevated levels of VOCs may cause headaches, dizziness and irritation to the eyes, nose, and throat; they may also cause environmental problems such as air pollution, acid rain and photochemical smog. As such, they require prompt removal. Nanosecond pulsed discharge is a kind of non-thermal plasma consisting of a streamer discharge. Several advantages of nanosecond pulsed discharge plasma have been demonstrated by studies of our research group, including low heat loss, highly energetic electron generation, and the production of highly active radicals. These advantages have shown ns pulsed discharge plasma capable of higher energy efficiency for processes, such as air purification, wastewater treatment and ozone generation. In this research, nanosecond pulsed discharge plasma was employed to treat 2-heptanone, which is a volatile organic compound type and presents several harmful effects. Characteristics of treatment dependent on applied voltage, gas flow rate and input energy density were investigated. Furthermore, byproducts generated by treatment were also investigated.

  13. Plasma relaxation mechanics of pulsed high power microwave surface flashover

    SciTech Connect

    Beeson, S.; Dickens, J.; Neuber, A.

    2013-09-15

    Microwave transmission and reflection characteristics of pulsed radio frequency field generated plasmas are elucidated for air, N{sub 2}, and He environments under pressure conditions ranging from 10 to 600 torr. The pulsed, low temperature plasma is generated along the atmospheric side of the dielectric boundary between the source (under vacuum) and the radiating environment with a thickness on the order of 5 mm and a cross sectional area just smaller than that of the waveguide. Utilizing custom multi-standard waveguide couplers and a continuous low power probing source, the scattering parameters were measured before, during, and after the high power microwave pulse with emphasis on the latter. From these scattering parameters, temporal electron density estimations (specifically the longitudinal integral of the density) were calculated using a 1D plane wave-excited model for analysis of the relaxation processes associated. These relaxation characteristics ultimately determine the maximum repetition rate for many pulsed electric field applications and thus are applicable to a much larger scope in the plasma community than just those related to high power microwaves. This manuscript discusses the diagnostic setup for acquiring the power measurements along with a detailed description of the kinematic and chemical behavior of the plasma as it decays down to its undisturbed state under various gas type and pressure conditions.

  14. A Novel Sterilization Method Using Pulsed Discharge Plasma

    NASA Astrophysics Data System (ADS)

    Wang, Xi-lu; Akira, Mizuno; Shijin, Katsura

    1998-01-01

    Pulsed discharge plasma(PDP) has been used to kill bacteria and the curves of the survival rate of bacteria against treatment time are obtained. Irreversible structural change in the cell membrane is caused by PDP and the cell is thus killed. The sterilization mechanism is analyzed.

  15. ICRF Heated Long-Pulse Plasma Discharges in LHD

    NASA Astrophysics Data System (ADS)

    Kumazawa, R.; Seki, T.; Mutoh, T.; Saito, K.; Watari, T.; Nakamura, Y.; Sakamoto, M.; Watanabe, T.; Kubo, S.; Shimozuma, T.; Yoshimura, Y.; Igami, H.; Takeiri, Y.; Oka, Y.; Tsumori, K.; Osakabe, M.; Ikeda, K.; Nagaoka, K.; Kaneko, O.; Miyazawa, J.; Morita, S.; Narihara, K.; Shoji, M.; Masuzaki, S.; Goto, M.; Morisaki, T.; Peterson, B. J.; Sato, K.; Tokuzawa, T.; Ashikawa, N.; Nishimura, K.; Funaba, H.; Chikaraishi, H.; Notake, T.; Torii, Y.; Okada, H.; Ichimura, M.; Higaki, H.; Takase, Y.; Kasahara, H.; Shimpo, F.; Nomura, G.; Takahashi, C.; Yokota, M.; Kato, A.; Zhao, Yanping; Yoon, J. S.; Kwak, J. G.; Yamada, H.; Kawahata, K.; Ohyabu, N.; Ida, K.; Nagayama, Y.; Noda, N.; Komori, A.; Sudo, S.; Motojima, O.; LHD Experimental Group

    2006-01-01

    A long-pulse plasma discharge for more than 30 min. was achieved on the Large Helical Device (LHD). A plasma of ne = 0.8× 1019 m-3 and Ti0 = 2.0 keV was sustained with PICH = 0.52 MW, PECH = 0.1 MW and averaged PNBI = 0.067 MW. Total injected heating energy was 1.3 GJ, which was a quarter of the prepared RF heating energy. One of the keys to the success of the experiment was a dispersion of the local plasma heat load to divertors, accomplished by shifting the magnetic axis inward and outward.

  16. Diagnostic du plasma d'ablation laser pour lacroissance de couches minces

    NASA Astrophysics Data System (ADS)

    Basillais, A.; Benzerga, R.; Le Menn, E.; Mathias, J.; Boulmer-Leborgne, C.; Perrière, J.

    2003-06-01

    Dans ce travail, nous nous sommes intéressés à la croissance de films de nitrure d'aluminium par ablation laser d'une cible d'aluminium assistée par un plasma d'azote créé par une décharge RF. Parallèlement, la spectroscopie d'émission a été largement utilisée pour le diagnostic de la plume plasma et du plasma de décharge RF afin de trouver des informations permettant de suivre le phénomène de croissance et qui seraient la signature d'un film de bonne stœchiométrie et qualité cristalline ou son contraire. Ainsi, l'étude de l'émission de la raie d'oxygène à 777nm dans le plasma d'ablation laser a permis d'expliquer le mécanisme de contamination des films par l'oxygène. De la même façon, nous nous sommes intéressés à l'émission de l'azote atomique dans la plume plasma et proche du substrat, dans la zone sombre où ces espèces participent directement à la croissance du film. Ainsi l'étude parallèle de l'influence des paramètres expérimentaux sur la qualité des films et sur la composition du plasma nous a permis d'optimiser le dispositif expérimental.

  17. Pulsed, atmospheric pressure plasma source for emission spectrometry

    DOEpatents

    Duan, Yixiang; Jin, Zhe; Su, Yongxuan

    2004-05-11

    A low-power, plasma source-based, portable molecular light emission generator/detector employing an atmospheric pressure pulsed-plasma for molecular fragmentation and excitation is described. The average power required for the operation of the plasma is between 0.02 W and 5 W. The features of the optical emission spectra obtained with the pulsed plasma source are significantly different from those obtained with direct current (dc) discharge higher power; for example, strong CH emission at 431.2 nm which is only weakly observed with dc plasma sources was observed, and the intense CN emission observed at 383-388 nm using dc plasma sources was weak in most cases. Strong CN emission was only observed using the present apparatus when compounds containing nitrogen, such as aniline were employed as samples. The present apparatus detects dimethylsulfoxide at 200 ppb using helium as the plasma gas by observing the emission band of the CH radical. When coupled with a gas chromatograph for separating components present in a sample to be analyzed, the present invention provides an apparatus for detecting the arrival of a particular component in the sample at the end of the chromatographic column and the identity thereof.

  18. Thrust Stand Measurements of a Conical Inductive Pulsed Plasma Thruster

    NASA Technical Reports Server (NTRS)

    Hallock, Ashley K.; Polzin, Kurt A.

    2012-01-01

    Inductive Pulsed Plasma Thrusters (iPPT) are spacecraft propulsion devices in which electrical energy is capacitively stored and then discharged through an inductive coil. The thruster is electrodeless, with a time-varying current in the coil interacting with a plasma covering the face of the coil to induce a plasma current. Propellant is accelerated and expelled at a high exhaust velocity (O(10 .. 100 km/s)) by the Lorentz body force arising from the interaction of the magnetic field and the induced plasma current. While this class of thruster mitigates the life-limiting issues associated with electrode erosion, inductive pulsed plasma thrusters can suffer from both high pulse energy requirements imposed by the voltage demands of inductive propellant ionization, and low propellant utilization efficiencies. A conical coil geometry may o er higher propellant utilization efficiency over that of a at inductive coil, however an increase in propellant utilization may be met with a decrease in axial electromagnetic acceleration, and in turn, a decrease in the total axially-directed kinetic energy imparted to the propellant.

  19. Effect of Pulsed Laser Ablation and Continuous Laser Heating on the Adhesion and Cohesion of Cold Sprayed Ti-6Al-4V Coatings

    NASA Astrophysics Data System (ADS)

    Perton, M.; Costil, S.; Wong, W.; Poirier, D.; Irissou, E.; Legoux, J.-G.; Blouin, A.; Yue, S.

    2012-12-01

    The individual and cumulative effects of in situ pulsed laser ablation and continuous laser pre-heating on adhesion and cohesion strength of cold sprayed Ti-6Al-4V coatings are investigated. Laser beams were coupled to a cold spray gun in order to ablate and pre-heat the substrate surface a few milliseconds prior to the impact of the spray particles. Cohesion and adhesion strength were evaluated by scratch test, standard ASTM C633 pull test and laser shock (LASAT) technique. The effects of laser ablation before and during cold spray operations were investigated. Results demonstrate that laser ablation of the substrate before cold spraying led to a smooth surface which improved adhesion strength. However, when laser ablation was maintained throughout the cold spray process, i.e., in between the coating layers, a reduction of cohesion and adhesion was observed. These negative effects were circumvented when laser ablation and laser pre-heating were combined.

  20. Plasma-mediated ablation for the management of obstructive sleep apnea

    NASA Astrophysics Data System (ADS)

    Puchalski, Robert; Shah, Udayan K.

    2000-05-01

    Plasma-mediated ablation (PMA) removes tissue by developing an electrically induced plasma layer between the instrument and target tissue. Charged particles within the plasma field then accelerate toward the tissue, breaking the molecular bonds within the top layer of tissue. Thermal damage to collateral tissue is minimal, resulting in the moniker, 'cold' ablation, for this method. Recently, instrumentation has been developed to permit application for soft tissue resection in Otolaryngology. Presentation of the theory, as well as the benefits and disadvantages associated with CoblationTM technology will be followed by examples of its use. A brief videotape will demonstrate the application of PMA for UPPP, tonsillectomy and nasal turbinate reduction. Preliminary experience from our institution, including eighteen children treated with tonsillectomy and followed for at least one month post-operatively, has provided an initial cohort for comparing the risks and benefits of the approach. The advantage of CoblationTM technology identified thus far, that of less thermal damage, is balanced against a decreased level of hemostasis (compared to MES) and an increased cost.

  1. 2-D Magnetohydrodynamic Modeling of A Pulsed Plasma Thruster

    NASA Technical Reports Server (NTRS)

    Thio, Y. C. Francis; Cassibry, J. T.; Wu, S. T.; Rodgers, Stephen L. (Technical Monitor)

    2002-01-01

    Experiments are being performed on the NASA Marshall Space Flight Center (MSFC) MK-1 pulsed plasma thruster. Data produced from the experiments provide an opportunity to further understand the plasma dynamics in these thrusters via detailed computational modeling. The detailed and accurate understanding of the plasma dynamics in these devices holds the key towards extending their capabilities in a number of applications, including their applications as high power (greater than 1 MW) thrusters, and their use for producing high-velocity, uniform plasma jets for experimental purposes. For this study, the 2-D MHD modeling code, MACH2, is used to provide detailed interpretation of the experimental data. At the same time, a 0-D physics model of the plasma initial phase is developed to guide our 2-D modeling studies.

  2. An Experimental Study of a Pulsed Electromagnetic Plasma Accelerator

    NASA Technical Reports Server (NTRS)

    Thio, Y. C. Francis; Eskridge, Richard; Lee, Mike; Smith, James; Martin, Adam; Markusic, Tom E.; Cassibry, Jason T.; Rodgers, Stephen L. (Technical Monitor)

    2002-01-01

    Experiments are being performed on the NASA Marshall Space Flight Center (MSFC) pulsed electromagnetic plasma accelerator (PEPA-0). Data produced from the experiments provide an opportunity to further understand the plasma dynamics in these thrusters via detailed computational modeling. The detailed and accurate understanding of the plasma dynamics in these devices holds the key towards extending their capabilities in a number of applications, including their applications as high power (greater than 1 MW) thrusters, and their use for producing high-velocity, uniform plasma jets for experimental purposes. For this study, the 2-D MHD modeling code, MACH2, is used to provide detailed interpretation of the experimental data. At the same time, a 0-D physics model of the plasma initial phase is developed to guide our 2-D modeling studies.

  3. Pulsed Plasma Lubrication Device and Method

    NASA Technical Reports Server (NTRS)

    Hofer, Richard R. (Inventor); Bickler, Donald B. (Inventor); D'Agostino, Saverio A. (Inventor)

    2016-01-01

    Disclosed herein is a lubrication device comprising a solid lubricant disposed between and in contact with a first electrode and a second electrode dimensioned and arranged such that application of an electric potential between the first electrode and the second electrode sufficient to produce an electric arc between the first electrode and the second electrode to produce a plasma in an ambient atmosphere at an ambient pressure which vaporizes at least a portion of the solid lubricant to produce a vapor stream comprising the solid lubricant. Methods to lubricate a surface utilizing the lubrication device in-situ are also disclosed.

  4. Plume segregation observed in hydrogen and deuterium containing plasmas produced by laser ablation of carbon fiber tiles from a fusion reactor

    NASA Astrophysics Data System (ADS)

    Mercadier, L.; Hermann, J.; Grisolia, C.; Semerok, A.

    2010-08-01

    The plasma produced by the irradiation of a hydrogen and deuterium containing carbon fiber composite with infrared laser pulses of 4-ns pulse duration has been investigated. The experiments were carried out under argon at reduced pressure. Microscopic analyses of the irradiated sample surface were performed to measure the ablation depth. Time- and space-resolved optical emission spectroscopy was applied to characterize the evolution of spectral line emission as a function of time and distance from the surface. Particular attention was paid to the time-of-flight characteristics of the hydrogen and deuterium Balmer α spectral lines. According to the different atomic masses of both isotopes, the expansion of hydrogen into the low pressure argon atmosphere was found to be slightly faster than that of deuterium. The effect of plume segregation is pressure dependent and tends to increase the analytical signal of heavy atoms with respect to lighter ones during laser-induced breakdown spectroscopy.

  5. Preclinical investigations of articular cartilage ablation with femtosecond and pulsed infrared lasers as an alternative to microfracture surgery.

    PubMed

    Su, Erica; Sun, Hui; Juhasz, Tibor; Wong, Brian J F

    2014-09-01

    Microfracture surgery is a bone marrow stimulation technique for treating cartilage defects and injuriesin the knee. Current methods rely on surgical skill and instrumentation. This study investigates the potential useof laser technology as an alternate means to create the microfracture holes. Lasers investigated in this study include an erbium:YAG laser (λ = 2.94 μm), titanium:sapphire femtosecond laser system (λ = 1700 nm), and Nd:glass femtosecond laser (λ = 1053 nm). Bovine samples were ablated at fluences of 8 to 18 J∕cm2 with the erbium:YAG laser, at a power of 300 ± 15 mW with the titanium:sapphire femtosecond system, and at an energy of 3 μJ∕pulse with the Nd:glass laser. Samples were digitally photographed and histological sections were taken for analysis. The erbium:YAG laser is capable of fast and efficient ablation; specimen treated with fluences of 12 and 18 J∕cm2 experienced significant amounts of bone removal and minimal carbonization with saline hydration. The femtosecond laser systems successfully removed cartilage but not clinically significant amounts of bone. Precise tissue removal was possible but not to substantial depths due to limitations of the systems. With additional studies and development, the use of femtosecond laser systems to ablate bone may be achieved at clinically valuable ablation rates.

  6. Enhancing ablation efficiency in micro structuring using a deformable mirror for beam shaping of ultra-short laser pulses

    NASA Astrophysics Data System (ADS)

    Smarra, M.; Dickmann, K.

    2016-03-01

    Using ultra-short laser pulses for the generation of microstructures results in a high flexible tool for free form geometries in the micro range. Increasing laser power and repetition rates increase as well the demand of high flexible and efficient process strategies. To increase the ablation efficiency the optimal fluency can be determined, which is a material specific value. By varying the beam shape, the ablation efficiency can be enhanced. In this study a deformable mirror was used to vary the beam shape. This mirror is built by combining a piezo-electric ceramic and a mirror substrate. The ceramic is divided into several segments, which can be controlled independently. This results in a high flexible deformable mirror which influences the beam shape and can be used to vary the spot size or generate line geometries. The ablation efficiency and roughness of small generated cavities were analyzed in this study as well as the dimensions of the cavity. This can be used to optimize process strategies to combine high volume ablation and fine detail generation.

  7. Preclinical investigations of articular cartilage ablation with femtosecond and pulsed infrared lasers as an alternative to microfracture surgery

    PubMed Central

    Su, Erica; Sun, Hui; Juhasz, Tibor; Wong, Brian J. F.

    2014-01-01

    Abstract. Microfracture surgery is a bone marrow stimulation technique for treating cartilage defects and injuries in the knee. Current methods rely on surgical skill and instrumentation. This study investigates the potential use of laser technology as an alternate means to create the microfracture holes. Lasers investigated in this study include an erbium:YAG laser (λ=2.94  μm), titanium:sapphire femtosecond laser system (λ=1700  nm), and Nd:glass femtosecond laser (λ=1053  nm). Bovine samples were ablated at fluences of 8 to 18  J/cm2 with the erbium:YAG laser, at a power of 300±15  mW with the titanium:sapphire femtosecond system, and at an energy of 3  μJ/pulse with the Nd:glass laser. Samples were digitally photographed and histological sections were taken for analysis. The erbium:YAG laser is capable of fast and efficient ablation; specimen treated with fluences of 12 and 18  J/cm2 experienced significant amounts of bone removal and minimal carbonization with saline hydration. The femtosecond laser systems successfully removed cartilage but not clinically significant amounts of bone. Precise tissue removal was possible but not to substantial depths due to limitations of the systems. With additional studies and development, the use of femtosecond laser systems to ablate bone may be achieved at clinically valuable ablation rates. PMID:25200394

  8. Preclinical investigations of articular cartilage ablation with femtosecond and pulsed infrared lasers as an alternative to microfracture surgery

    NASA Astrophysics Data System (ADS)

    Su, Erica; Sun, Hui; Juhasz, Tibor; Wong, Brian J. F.

    2014-09-01

    Microfracture surgery is a bone marrow stimulation technique for treating cartilage defects and injuries in the knee. Current methods rely on surgical skill and instrumentation. This study investigates the potential use of laser technology as an alternate means to create the microfracture holes. Lasers investigated in this study include an erbium:YAG laser (λ=2.94 μm), titanium:sapphire femtosecond laser system (λ=1700 nm), and Nd:glass femtosecond laser (λ=1053 nm). Bovine samples were ablated at fluences of 8 to 18 J/cm2 with the erbium:YAG laser, at a power of 300±15 mW with the titanium:sapphire femtosecond system, and at an energy of 3 μJ/pulse with the Nd:glass laser. Samples were digitally photographed and histological sections were taken for analysis. The erbium:YAG laser is capable of fast and efficient ablation; specimen treated with fluences of 12 and 18 J/cm2 experienced significant amounts of bone removal and minimal carbonization with saline hydration. The femtosecond laser systems successfully removed cartilage but not clinically significant amounts of bone. Precise tissue removal was possible but not to substantial depths due to limitations of the systems. With additional studies and development, the use of femtosecond laser systems to ablate bone may be achieved at clinically valuable ablation rates.

  9. Patterning of graphene on silicon-on-insulator waveguides through laser ablation and plasma etching

    NASA Astrophysics Data System (ADS)

    Van Erps, Jürgen; Ciuk, Tymoteusz; Pasternak, Iwona; Krajewska, Aleksandra; Strupinski, Wlodek; Van Put, Steven; Van Steenberge, Geert; Baert, Kitty; Terryn, Herman; Thienpont, Hugo; Vermeulen, Nathalie

    2016-05-01

    We present the use of femtosecond laser ablation for the removal of monolayer graphene from silicon-on-insulator (SOI) waveguides, and the use of oxygen plasma etching through a metal mask to peel off graphene from the grating couplers attached to the waveguides. Through Raman spectroscopy and atomic force microscopy, we show that the removal of graphene is successful with minimal damage to the underlying SOI waveguides. Finally, we employ both removal techniques to measure the contribution of graphene to the loss of grating-coupled graphene-covered SOI waveguides using the cut-back method. This loss contribution is measured to be 0.132 dB/μm.

  10. Dynamics of spallation during femtosecond laser ablation studied by time-resolved reflectivity with double pump pulses

    SciTech Connect

    Kumada, Takayuki Otobe, Tomohito; Nishikino, Masaharu; Hasegawa, Noboru; Hayashi, Terutake

    2016-01-04

    The dynamics of photomechanical spallation during femtosecond laser ablation of fused silica was studied by time-resolved reflectivity with double pump pulses. Oscillation of reflectivity was caused by interference between the probe pulses reflected at the sample surface and the spallation layer, and was enhanced when the surface was irradiated with the second pump pulse within a time interval, Δτ, of several picoseconds after the first pump pulse. However, as Δτ was increased, the oscillation amplitude decreased with an exponential decay time of 10 ps. The oscillation disappeared when Δτ exceeded 20 ps. This result suggests that the formation time of the spallation layer is approximately 10 ps. A second pump pulse with Δτ shorter than 10 ps excites the bulk sample. The spallation layer that is photo-excited by the first and second pump pulses is separated afterward. In contrast, a pulse with Δτ longer than the formation time excites and breaks up the spallation layer that has already been separated from the bulk. The formation time of the spallation layer, as determined in this experiment, is attributed to the characteristic time of the mechanical equilibration corresponding to the thickness divided by the sound velocity of the photo-excited layer.

  11. Performance of an ablator for Space Shuttle inorbit repair in an arc-plasma airstream

    NASA Technical Reports Server (NTRS)

    Stewart, D. A.; Cuellar, M.; Flowers, O.

    1983-01-01

    An ablator patch material performed well in an arc plasma environment simulating nominal Earth entry conditions for the Space Shuttle. Ablation tests using vacuum molded cones provided data to optimize the formulation of a two part polymer system for application under space conditions. The blunt cones were made using a Teflon mold and a state of the art caulking gun. Char stability of formulations with various amounts of catalyst and diluent were investigated. The char was found to be unstable in formulations with low amounts of catalyst and high amounts of diluent. The best polymer system determined by these tests was evaluated using a half tile patch in a multiple High Temperature Reusable surface Insulation tile model. It was demonstrated that this ablator could be applied in a space environment using a state of the art caulking gun, would maintain the outer mold line of the thermal protection system during entry, and would keep the bond line temperature at the aluminum tile interface below the design limit.

  12. Development of Electrothermal Pulsed Plasma Thrusters for Osaka-Institute-of-Technology Electric-Rocket-Engine onboard Small Space Ship

    NASA Astrophysics Data System (ADS)

    Ishii, Yushuke; Yamamoto, Tsuyoshi; Yamada, Minetsugu; Tahara, Hirokazu

    2008-12-01

    The Project of Osaka-Institute-of-Technology Electric-Rocket-Engine onboard Small Space Ship (PROITERES) was started at Osaka Institute of Technology. In PROITERES, a 10-kg small satellite with electrothermal pulsed plasma thrusters (PPTs), named JOSHO, will be launched in 2010. The main mission is powered flight of small satellite by electric thruster itself. Electrothermal PPTs were studied with both experiments and numerical simulations. An electrothermal PPT with a side-fed propellant feeding mechanism achieved a total impulse of 3.6 Ns with a repetitive 10000-shot operation. An unsteady numerical simulation showed the existence of considerable amount of ablation delaying to the discharge. However, it was also shown that this phenomenon should not be regarded as the ``late time ablation'' for electrothermal PPTs.

  13. Development of Electrothermal Pulsed Plasma Thrusters for Osaka-Institute-of-Technology Electric-Rocket-Engine onboard Small Space Ship

    SciTech Connect

    Ishii, Yushuke; Yamamoto, Tsuyoshi; Yamada, Minetsugu; Tahara, Hirokazu

    2008-12-31

    The Project of Osaka-Institute-of-Technology Electric-Rocket-Engine onboard Small Space Ship (PROITERES) was started at Osaka Institute of Technology. In PROITERES, a 10-kg small satellite with electrothermal pulsed plasma thrusters (PPTs), named JOSHO, will be launched in 2010. The main mission is powered flight of small satellite by electric thruster itself. Electrothermal PPTs were studied with both experiments and numerical simulations. An electrothermal PPT with a side-fed propellant feeding mechanism achieved a total impulse of 3.6 Ns with a repetitive 10000-shot operation. An unsteady numerical simulation showed the existence of considerable amount of ablation delaying to the discharge. However, it was also shown that this phenomenon should not be regarded as the 'late time ablation' for electrothermal PPTs.

  14. Temporal and spectral analysis of laser induced plasma in the ablation process of flexible printed circuit board

    NASA Astrophysics Data System (ADS)

    Ryoo, Hoon C.; Kim, Seok; Hahn, Jae W.

    2008-02-01

    Flexible printed circuit board (FPCB), consisting of copper sheets laminated onto non conductive film substrates with multiple structures, are core elements in electronics with their flexibility and capability of high density 3 dimensional wiring characteristics. In laser applied FPCB processing, a better understanding of the ablation mechanism leads to precision control of the depth processing especially by monitoring of the material transition layer. For this purpose, here we investigate the temporal and spectral behavior of the plasma plum generated on the single sided structure of FPCB using the technique of laser induced breakdown spectroscopy (LIBS). Using KrF excimer laser, the characteristic spectral emission lines of C II swan band at the wavelength of 516.5 nm and neutral copper at the wavelength range from 510 nm to 522 nm are acquired under ambient pressure in the ablation process of polyimide film and copper coated layer respectively. From a time delay from 50 ns to 4.05 μs from the beginning of the laser pulse, the temporal profiles of the spectral intensity are obtained in steps of 200 ns, which have a tendency of exponential decrease on both C II and neutral copper. In particular, we concentrate our attention on the temporal intensity behavior of the Bremsstrahlung continuum emission that decides the proper set of detection time window, by which the monitoring sensitivity of LIBS is determined. Finally, using the information of the temporal analysis for each molecular, atomic, and continuum emission, the transition layer between polyimide and copper film is distinguished by their characteristic peak information.

  15. Plasma Sheet Velocity Measurement Techniques for the Pulsed Plasma Thruster SIMP-LEX

    NASA Technical Reports Server (NTRS)

    Nawaz, Anuscheh; Lau, Matthew

    2011-01-01

    The velocity of the first plasma sheet was determined between the electrodes of a pulsed plasma thruster using three measurement techniques: time of flight probe, high speed camera and magnetic field probe. Further, for time of flight probe and magnetic field probe, it was possible to determine the velocity distribution along the electrodes, as the plasma sheet is accelerated. The results from all three techniques are shown, and are compared for one thruster geometry.

  16. Results of the qualification test campaign of a Pulsed Plasma Thruster for Cubesat Propulsion (PPTCUP)

    NASA Astrophysics Data System (ADS)

    Ciaralli, S.; Coletti, M.; Gabriel, S. B.

    2016-04-01

    Pulsed Plasma Thruster for Cubesat Propulsion (PPTCUP) is an ablative pulsed plasma thruster designed with the aim of providing translational and orbital control to Cubesat platforms. The qualification model presented in this paper has been developed by Mars Space Ltd, Clyde Space Ltd and the University of Southampton to produce a versatile "stand-alone" module that can be bolted on the Cubesat structure, allowing the orbital control along the X or Y-axis of the satellite. An extensive and complete test campaign to qualify the unit for space flight, which includes electromagnetic compatibility (EMC) characterization, thermal cycling and mechanical tests, has been performed according to the NASA GEVS procedures. PPTCUP is characterized by an averaged specific impulse of 655±58 s and a deliverable total impulse of 48.2±4.2 Ns. Finally, it has been found that the unit is compliant with the EMC requirements and can successfully withstand the thermal and mechanical loads typical of a Cubesat space mission.

  17. Electron acceleration in collisionless shocks and magnetic reconnection by laser-produced plasma ablation

    NASA Astrophysics Data System (ADS)

    Park, Jaehong; Spitkovksy, Anatoly; Fox, Will; Bhattacharjee, Amitava

    2016-10-01

    We perform particle-in-cell simulations of collisionless shocks and magnetic reconnection generated by ablated plasma expanding into a magnetized background plasma. We find: (1) The simulated proton radiography produces different morphology of the shock structure depending on the orientation of the magnetic field and can be used to identify a shock in the experiment. Electrons are accelerated by the whistler waves generated at oblique sites of the shock. (2) Forced collisionless magnetic reconnection is induced when the expanding plumes carry opposite magnetic polarities and interact with a background plasma. Electrons are accelerated at the reconnection X line and reveal a power-law distribution as the plasma beta is lowered, β = 0.08 . As the plasma beta is increased, β = 0.32 , the 1st order Fermi mechanism against the two plasma plumes contributes to the electron acceleration as well as the X line acceleration. Using 3-D simulations, we also explore the effect of 3-D instabilities (Weibel instability or drift-kink) on particle acceleration and magnetic field annihilation between the colliding magnetized plumes

  18. Plasma Catalysis of Methane Decomposition in Pulse Microwave Discharge

    NASA Astrophysics Data System (ADS)

    Potapkin, B.; Rusanov, V.; Jivotov, V.; Babaritski, A.; Potechin, S.; Etievant, C.

    1997-10-01

    Investigation of plasma catalysis effects in various chemical reactions, such as SO2 and hydrocarbons oxidation, ammonia and nitrogen oxides synthesis, has been of interest for many decades. Present work describes the first experimental observation and theoretical analysis of plasma catalysis effects in the case of endothermic methane decomposition into molecular hydrogen and carbon black. Process energy requirements are coverd mainly by low potential gas thermal energy while plasma is used for acceleration of chemical reactions via active species generation. The experiments were done as follows: (i) methane was preheated in a conventional heat exchanger up to about 40-65 ^oC where thermal methane decomposition is limited by process kinetics, (ii) methane was passed through a non-equilibrium pulse microwave discharge (9.04 GHz, pulse duration 1 μs). Experiments have shown a strong catalytic effect of plasma on methane decomposition. The degree of conversion after discharge increased drastically, despite gas cooling, because of heat absorption in the methane decomposition reaction. Theoretical analysis of process kinetics and energy balance gave clear evidence of the catalytic effect of plasma under experimental conditions. The estimated chain length was about 300. The possible mechanism of plasma catalysis, the ion-molecular chain Winchester mechanism, is proposed and described.

  19. Ultra-Intense Laser Pulse Propagation in Gas and Plasma

    SciTech Connect

    Antonsen, T. M.

    2004-10-26

    It is proposed here to continue their program in the development of theories and models capable of describing the varied phenomena expected to influence the propagation of ultra-intense, ultra-short laser pulses with particular emphasis on guided propagation. This program builds upon expertise already developed over the years through collaborations with the NSF funded experimental effort lead by Professor Howard Milchberg here at Maryland, and in addition the research group at the Ecole Polytechnique in France. As in the past, close coupling between theory and experiment will continue. The main effort of the proposed research will center on the development of computational models and analytic theories of intense laser pulse propagation and guiding structures. In particular, they will use their simulation code WAKE to study propagation in plasma channels, in dielectric capillaries and in gases where self focusing is important. At present this code simulates the two-dimensional propagation (radial coordinate, axial coordinate and time) of short pulses in gas/plasma media. The plasma is treated either as an ensemble of particles which respond to the ponderomotive force of the laser and the self consistent electric and magnetic fields created in the wake of pulse or as a fluid. the plasma particle motion is treated kinetically and relativistically allowing for study of intense pulses that result in complete cavitation of the plasma. The gas is treated as a nonlinear medium with rate equations describing the various stages of ionization. A number of important physics issues will be addressed during the program. These include (1) studies of propagation in plasma channels, (2) investigation of plasma channel nonuniformities caused by parametric excitation of channel modes, (3) propagation in dielectric capillaries including harmonic generation and ionization scattering, (4) self guided propagation in gas, (5) studies of the ionization scattering instability recently

  20. Simulations of Super Alfvenic Laser Ablation Experiments in the Large Plasma Device

    NASA Astrophysics Data System (ADS)

    Clark, Stephen Eric

    Hybrid plasma simulations, consisting of kinetic ions treated using standard Particle- In-Cell (PIC) techniques and an inertialess charge-neutralizing electron fluid, have been used to investigate the properties of collisionless shocks for a number of years. They agree well with sparse data obtained by flying through Earth's bow shock and have been used to model high energy explosions in the ionosphere. In this doctoral dissertation hybrid plasma simulation is used on much smaller scales to model collisionless shocks in a controlled laboratory setting. Initially a two-dimensional hybrid code from Los Alamos National Laboratory was used to find the best experimental parameters for shock formation, and interpret experimental data. It was demonstrated using the hybrid code that the experimental parameters needed to generate a shock in the laboratory are relaxed compared to previous work that was done. It was also shown that stronger shocks can be generated when running into a density gradient. Laboratory experiments at the University of California at Los Angeles using the high energy kJ-class Nd:Glass 1053 nm Raptor laser, and later the low energy yet high repetition rate 25 J Nd:Glass 1053 nm Peening laser have been performed in the Large Plasma Device (LAPD), which have provided some much needed data to benchmark the hybrid simulation method. The LAPD provides a repeatable, quiescent, ambient magnetized plasma to surround the exploding laser produced plasma that is ablated from a High Density Polyethylene (HDPE) target. The plasma density peaks in the machine at ni O(1013 cm-3 ), which is sufficiently dense to strongly couple energy and momentum from a laser ablated carbon plasma ejected from the HDPE target into the magnetized ambient plasma. It has been demonstrated that a sub-critical shock is formed in the LAPD using the high energy Raptor laser, though the data from this experiment is scant. Hybrid simulation was used as an analysis tool for the shock

  1. A Tesla-pulse forming line-plasma opening switch pulsed power generator

    NASA Astrophysics Data System (ADS)

    Novac, B. M.; Kumar, R.; Smith, I. R.

    2010-10-01

    A pulsed power generator based on a high-voltage Tesla transformer which charges a 3.85 Ω/55 ns water-filled pulse forming line to 300 kV has been developed at Loughborough University as a training tool for pulsed power students. The generator uses all forms of insulation specific to pulsed power technology, liquid (oil and water), gas (SF6), and magnetic insulation in vacuum, and a number of fast voltage and current sensors are implemented for diagnostic purposes. A miniature (centimeter-size) plasma opening switch has recently been coupled to the output of the pulse forming line, with the overall system comprising the first phase of a program aimed at the development of a novel repetitive, table-top generator capable of producing 15 GW pulses for high power microwave loads. Technical details of all the generator components and the main experimental results obtained during the program and demonstrations of their performance are presented in the paper, together with a description of the various diagnostic tools involved. In particular, it is shown that the miniature plasma opening switch is capable of reducing the rise time of the input current while significantly increasing the load power. Future plans are outlined in the conclusions.

  2. High-Energy Two-Stage Pulsed Plasma Thruster

    NASA Technical Reports Server (NTRS)

    Markusic, Tom

    2003-01-01

    A high-energy (28 kJ per pulse) two-stage pulsed plasma thruster (MSFC PPT-1) has been constructed and tested. The motivation of this project is to develop a high power (approximately 500 kW), high specific impulse (approximately 10000 s), highly efficient (greater than 50%) thruster for use as primary propulsion in a high power nuclear electric propulsion system. PPT-1 was designed to overcome four negative characteristics which have detracted from the utility of pulsed plasma thrusters: poor electrical efficiency, poor propellant utilization efficiency, electrode erosion, and reliability issues associated with the use of high speed gas valves and high current switches. Traditional PPTs have been plagued with poor efficiency because they have not been operated in a plasma regime that fully exploits the potential benefits of pulsed plasma acceleration by electromagnetic forces. PPTs have generally been used to accelerate low-density plasmas with long current pulses. Operation of thrusters in this plasma regime allows for the development of certain undesirable particle-kinetic effects, such as Hall effect-induced current sheet canting. PPT-1 was designed to propel a highly collisional, dense plasma that has more fluid-like properties and, hence, is more effectively pushed by a magnetic field. The high-density plasma loading into the second stage of the accelerator is achieved through the use of a dense plasma injector (first stage). The injector produces a thermal plasma, derived from a molten lithium propellant feed system, which is subsequently accelerated by the second stage using mega-amp level currents, which eject the plasma at a speed on the order of 100 kilometers per second. Traditional PPTs also suffer from dynamic efficiency losses associated with snowplow loading of distributed neutral propellant. The twostage scheme used in PPT-I allows the propellant to be loaded in a manner which more closely approximates the optimal slug loading. Lithium propellant

  3. [Study on optical emission spectroscopy of pulse corona methane plasma].

    PubMed

    Li, Jin-Ping; Dai, Bin; Fan, Ting

    2009-07-01

    From experiments of methane pulse corona plasma and plasma emission spectrometry, the emission spectra of methane ranging from 370 to 1 100 nm were recorded and marked with CCD (Charge Coupled Device) grating spectrometry. The ionization products of H, C+, CH, C, C2, C3, C4, C5 and hydrocarbon were confirmed through high purity methane (purity 99.99%) ionized by pulse high voltage of 100 kV and 100 Hz under normal temperature and normal pressure. Through analyzing the experimental emission spectrum of methane plasma, the ionization mechanism, i.e. methane gas was ionized into corona plasma by pulse high voltage, was analyzed and the ionization of free radical CHn (n = 3, 2, 1), carbon and hydrocarbons was given as well. Research results show that the dehydrogenation achieved a high level when methane molecules collide inelastically with high energy electrons, and the hydrogen atoms, hydrogen ions and methane free radicals were synthesized into alkenes, alkynes, alkanes and high polymer of carbon with further inelastic collision of high energy electrons. This experimental spectrum and mechanism analysis can be applied to the research on methane conversion.

  4. Small plasma focus as neutron pulsed source for nuclides identification

    SciTech Connect

    Milanese, M.; Moroso, R.; Barbaglia, M.; Niedbalski, J.; Mayer, R.; Castillo, F.

    2013-10-15

    In this paper, we present preliminary results on the feasibility of employing a low energy (2 kJ, 31 kV) plasma focus device as a portable source of pulsed neutron beams (2.45 MeV) generated by nuclear fusion reactions D-D, for the “in situ” analysis of substances by nuclear activation. This source has the relevant advantage of being pulsed at requirement, transportable, not permanently radioactive, without radioactive waste, cheap, among others. We prove the feasibility of using this source showing several spectra of the characteristic emission line for manganese, gold, lead, and silver.

  5. A Concept for Directly Coupled Pulsed Electromagnetic Acceleration of Plasmas

    NASA Technical Reports Server (NTRS)

    Thio, Y.C. Francis; Cassibry, Jason T.; Eskridge, Richard; Smith, James; Wu, S. T.; Rodgers, Stephen L. (Technical Monitor)

    2001-01-01

    Plasma jets with high momentum flux density are required for a variety of applications in propulsion research. Methods of producing these plasma jets are being investigated at NASA Marshall Space Flight Center. The experimental goal in the immediate future is to develop plasma accelerators which are capable of producing plasma jets with momentum flux density represented by velocities up to 200 km/s and ion density up to 10(exp 24) per cu m, with sufficient precision and reproducibility in their properties, and with sufficiently high efficiency. The jets must be sufficiently focused to allow them to be transported over several meters. A plasma accelerator concept is presented that might be able to meet these requirements. It is a self-switching, shaped coaxial pulsed plasma thruster, with focusing of the plasma flow by shaping muzzle current distribution as in plasma focus devices, and by mechanical tapering of the gun walls. Some 2-D MHD modeling in support of the conceptual design will be presented.

  6. Influence of binders on infrared laser ablation of powdered tungsten carbide pressed pellets in comparison with sintered tungsten carbide hardmetals studied by inductively coupled plasma atomic emission spectrometry

    NASA Astrophysics Data System (ADS)

    Holá, Markéta; Otruba, Vítězslav; Kanický, Viktor

    2006-05-01

    Laser ablation (LA) was studied as a sample introduction technique for the analysis of powdered and sintered tungsten carbides (WC/Co) by inductively coupled plasma optical emission spectrometry (ICP-OES). The possibility to work with powdered and compact materials with close chemical composition provided the opportunity to compare LA sampling of similar substances in different forms that require different preparation procedures. Powdered WC/Co precursors of sintered hardmetals were prepared for the ablation as pressed pellets with and without powdered silver as a binder, while sintered hardmetal blocks were embedded into a resin to obtain discs, which were then smoothed and polished. A Q-switched Nd:YAG laser operated at its fundamental wavelength of 1064 nm with a pulse frequency of 10 Hz and maximum pulse energy of 220 mJ was used. A single lens was used for the laser beam focusing. An ablation cell (14 cm 3) mounted on a PC-controlled XY-translator was connected to an ICP spectrometer Jobin Yvon 170 Ultrace (laterally viewed ICP, mono- and polychromator) using a 1.5-m tubing (4 mm i.d.). Ablation was performed in a circular motion (2 mm diameter). Close attention was paid to the study of the crater parametres depending on hardness, cohesion and Ag binder presence in WC/Co samples. The influence of the Co content on the depth and structure of the ablation craters of the binderless pellets was also studied. Linear calibration plots of Nb, Ta and Ti were obtained for cemented WC/Co samples, binderless and binder-containing pellets. Relative widths of uncertainty intervals about the centroids vary between ± 3% and ± 7%, and exceptionally reach a value above 10%. The lowest determinable quantities (LDQ) of Nb, Ta and Ti calculated from the calibration lines were less than 0.5% (m/m). To evaluate the possibility of quantitative elemental analysis by LA-ICP-OES, two real sintered WC/Co samples and two real samples of powdered WC/Co materials were analysed. The

  7. Observation of hydrodynamic processes of radiation-ablated plasma in a small hole

    SciTech Connect

    Li, Hang; Kuang, Longyu; Jiang, Shaoen Ding, Yongkun; Song, Tianming; Yang, Jiamin Zhu, Tuo; Lin, Zhiwei; Zheng, Jianhua; Zhang, Haiying; Yu, Ruizhen; Liu, Shenye; Hu, Guangyue; Zhao, Bin; Zheng, Jian

    2015-07-15

    In the hohlraum used in laser indirect-drive inertial confinement fusion experiments, hydrodynamic processes of radiation-ablated high-Z plasma have a great effect on laser injection efficiency, radiation uniformity, and diagnosis of hohlraum radiation field from diagnostic windows (DW). To study plasma filling in the DWs, a laser-irradiated Ti disk was used to generate 2–5 keV narrow energy band X-ray as the intense backlighter source, and laser-produced X-ray in a hohlraum with low-Z foam tamper was used to heat a small hole surrounded by gold wall with 150 μm in diameter and 100 μm deep. The hydrodynamic movement of the gold plasma in the small hole was measured by an X-ray framing camera and the results are analyzed. Quantitative measurement of the plasma areal density distribution and evolution in the small hole can be used to assess the effect of plasma filling on the diagnosis from the DWs.

  8. Towards higher stability of resonant absorption measurements in pulsed plasmas

    SciTech Connect

    Britun, Nikolay; Michiels, Matthieu; Snyders, Rony

    2015-12-15

    Possible ways to increase the reliability of time-resolved particle density measurements in pulsed gaseous discharges using resonant absorption spectroscopy are proposed. A special synchronization, called “dynamic source triggering,” between a gated detector and two pulsed discharges, one representing the discharge of interest and another being used as a reference source, is developed. An internal digital delay generator in the intensified charge coupled device camera, used at the same time as a detector, is utilized for this purpose. According to the proposed scheme, the light pulses from the reference source follow the gates of detector, passing through the discharge of interest only when necessary. This allows for the utilization of short-pulse plasmas as reference sources, which is critical for time-resolved absorption analysis of strongly emitting pulsed discharges. In addition to dynamic source triggering, the reliability of absorption measurements can be further increased using simultaneous detection of spectra relevant for absorption method, which is also demonstrated in this work. The proposed methods are illustrated by the time-resolved measurements of the metal atom density in a high-power impulse magnetron sputtering (HiPIMS) discharge, using either a hollow cathode lamp or another HiPIMS discharge as a pulsed reference source.

  9. Antibacterial activity of silver nanoparticles obtained by pulsed laser ablation in pure water and in chloride solution

    PubMed Central

    Perito, Brunella; Giorgetti, Emilia; Marsili, Paolo

    2016-01-01

    Summary Silver nanoparticles (AgNPs) have increasingly gained importance as antibacterial agents with applications in several fields due to their strong, broad-range antimicrobial properties. AgNP synthesis by pulsed laser ablation in liquid (PLAL) permits the preparation of stable Ag colloids in pure solvents without capping or stabilizing agents, producing AgNPs more suitable for biomedical applications than those prepared with common, wet chemical preparation techniques. To date, only a few investigations into the antimicrobial effect of AgNPs produced by PLAL have been performed. These have mainly been performed by ablation in water with nanosecond pulse widths. We previously observed a strong surface-enhanced Raman scattering (SERS) signal from such AgNPs by “activating” the NP surface by the addition of a small quantity of LiCl to the colloid. Such surface effects could also influence the antimicrobial activity of the NPs. Their activity, on the other hand, could also be affected by other parameters linked to the ablation conditions, such as the pulse width. The antibacterial activity of AgNPs was evaluated for NPs obtained either by nanosecond (ns) or picosecond (ps) PLAL using a 1064 nm ablation wavelength, in pure water or in LiCl aqueous solution, with Escherichia coli and Bacillus subtilis as references for Gram-negative and Gram-positive bacteria, respectively. In all cases, AgNPs with an average diameter less than 10 nm were obtained, which has been shown in previous works to be the most effective size for bactericidal activity. The measured zeta-potential values were very negative, indicating excellent long-term colloidal stability. Antibacterial activity was observed against both microorganisms for the four AgNP formulations, but the ps-ablated nanoparticles were shown to more effectively inhibit the growth of both microorganisms. Moreover, LiCl modified AgNPs were the most effective, showing minimum inhibitory concentration (MIC) values in a

  10. Effect of Laser Wavelength and Ablator Material on Hot Electron Generation in High Power Laser Plasma Interaction at Shock Ignition High Intensity Conditions

    NASA Astrophysics Data System (ADS)

    Wei, M. S.; Alexander, N. B.; Krauland, C. M.; Zhang, S.; Beg, F. N.; Theobald, W.; Betti, R.

    2015-11-01

    Hot electrons with energies <100 keV have been found to augment ablation pressure leading to Gbar shocks in strong spherical shock experiments on OMEGA*. To study this potential benefit at shock ignition-relevant high intensities (~1016 W/cm2) , we have conducted an experiment using the high-energy OMEGA EP laser system to examine the effect of laser wavelength, intensity and ablator material on hot electron generation and energy coupling. Targets are multilayered planar foils consisting of Cu and Al layers with an ablator made of either plastic (CH) or lithium. The target is first irradiated by multi-kJ UV beams at low intensity to produce a long scalelength, hot plasma, as is the case in the shock ignition regime. Correspondingly, this is followed by the injection of the high intensity UV or IR main interaction pulse. The resultant energy, spectrum and angular distributions of the hot electrons are measured via their induced Cu fluorescence emission and the bremsstrahlung radiation. Details of the experiment and results will be presented. Work supported by the DOE/NNSA under Contract DE-NA0002730 (NLUF).

  11. Measurement of pulse pressure in plasma by crusher gauge

    SciTech Connect

    Kalachnikov, E.V.; Rogovtsev, P.N.

    1988-06-01

    Results are presented of pressure measurements in the plasma of a stabilized pinched discharge with axial blow through of the current channel by plasma using static and dynamic methods for crusher gauge calibration. Accuracies for maximum pressure measurements for both calibration methods are evaluated. The dynamic properties of the crusher gauge are taken into account experimentally in studying pulse forces and pressures in the 1-100 MPa range for times of 10/sup /minus/5/ to 10/sup /minus/3/ seconds. A piezoelectric method and device for dynamic calibration of the pressure gauges is described.

  12. Combined effects of pre-pulsing and target geometry on efficient EUV production from laser produced plasma experiments and modeling

    NASA Astrophysics Data System (ADS)

    Hassanein, A.; Sizyuk, T.; Sizyuk, V.; Harilal, S. S.

    2011-04-01

    Laser produced plasmas (LPP) is currently a promising source of an efficient extreme ultraviolet (EUV) photon source production for advanced lithography. Optimum laser pulse parameters with adjusted wavelength, energy, and duration for simple planar or spherical tin target can provide 2-3% conversion efficiency (CE) in laboratory experiments. These values are also in good agreement with modeling results. Additional effects such as targets with complex geometry and tin-doped targets using pre-pulsing of laser beams can significantly increase CE. Recent studies showed that such improvements in LPP system are due to reduction in laser energy losses by decreasing photons transmission (higher harmonic of Nd:YAG laser) or photons reflection (for CO2 laser). Optimization of target heating using pre-pulses or ablating low-density and nanoporous tin oxide can further improve LLP sources by creating more efficient plasma plumes and as a result increasing CE, the most important parameter for EUV sources. The second important challenge in developing LPP devices is to decrease fast ions and target debris to protect the optical collection system and increase its lifetime. We investigated the combined effects of pre-pulsing with various parameters and different target geometries on EUV conversion efficiency and on energetic ions production. The much higher reflectivity of CO2 laser from a tin target leads to two possible ways for system improvement using pre-pulses with shorter laser wavelengths or using more complex targets geometries with special grooves as developed previously by the authors.

  13. Quasi ?non-destructive? laser ablation-inductively coupled plasma-mass spectrometry fingerprinting of sapphires

    NASA Astrophysics Data System (ADS)

    Guillong, M.; Günther, D.

    2001-07-01

    A homogenized 193 nm excimer laser with a flat-top beam profile was used to study the capabilities of LA-ICP-MS for 'quasi' non-destructive fingerprinting and sourcing of sapphires from different locations. Sapphires contain 97-99% of Al 2O 3 (corundum), with the remainder composed of several trace elements, which can be used to distinguish the origin of these gemstones. The ablation behavior of sapphires, as well as the minimum quantity of sample removal that is required to determine these trace elements, was investigated. The optimum ablation conditions were a fluency of 6 J cm -2, a crater diameter of 120 μm, and a laser repetition rate of 10 Hz. The optimum time for the ablation was determined to be 2 s, equivalent to 20 laser pulses. The mean sample removal was 60 nm per pulse (approx. 3 ng per pulse). This allowed satisfactory trace element determination, and was found to cause the minimum amount of damage, while allowing for the fingerprinting of sapphires. More than 40 isotopes were measured using different spatial resolutions (20-120 μm) and eight elements were reproducibly detected in 25 sapphire samples from five different locations. The reproducibility of the trace element distribution is limited by the heterogeneity of the sample. The mean of five or more replicate analyses per sample was used. Calibration was carried out using NIST 612 glass reference material as external standard. The linear dynamic range of the ICP-MS (nine orders of magnitude) allowed the use of Al, the major element in sapphire, as an internal standard. The limits of detection for most of the light elements were in the μg g -1 range and were better for heavier elements (mass >85), being in the 0.1 μg g -1 range. The accuracy of the determinations was demonstrated by comparison with XRF analyses of the same set of samples. Using the quantitative analyses obtained using LA-ICP-MS, natural sapphires from five different origins were statistically classified using ternary plots and

  14. Overview of NASA's Pulsed Plasma Thruster Development Program

    NASA Technical Reports Server (NTRS)

    Pencil, Eric J.; Kamhawi, Hani; Arrington, Lynn A.

    2004-01-01

    NASA's Pulsed Plasma Thruster Program consists of flight demonstration experiments, base research, and development efforts being conducted through a combination of in-house work, contracts, and collaborative programs. The program receives sponsorship from Energetics Project, the New Millennium Program, and the Small Business Innovative Research Program. The Energetics Project sponsors basic and fundamental research to increase thruster life, improve thruster performance, and reduce system mass. The New Millennium Program sponsors the in-orbit operation of the Pulsed Plasma Thruster experiment on the Earth Observing 1 spacecraft. The Small Business Innovative Research Program sponsors the development of innovative diamond-film capacitors, piezoelectric ignitors, and advanced fuels. Programmatic background, recent technical accomplishments, and future activities for each programmatic element are provided.

  15. Investigation of plasma parameters in an active screen cage-pulsed dc plasma used for plasma nitriding

    NASA Astrophysics Data System (ADS)

    Naeem, M.; Khattak, Z. I.; Zaka-ul-Islam, M.; Shabir, S.; Khan, A. W.; Zakaullah, M.

    2014-11-01

    Active screen cage-pulsed dc plasmas are widely used in the material processing applications such as plasma nitriding, carburizing and nitrocarburizing. Specifically for plasma nitriding applications, a H2-N2 mixture is used. In this article, a study of the electron number density (ne), atomic nitrogen density ([N]), electron temperature ? and the excitation temperature ? is reported in the presence of an active screen cage-pulsed dc plasma. The ne and ? are determined here by a triple Langmuir probe, while [N] and ? are estimated by optical emission spectroscopy (OES). The two temperatures and their ratio ? are compared for different input parameters (such as applied power, gas pressure and H2 percentage). This study is useful in active screen cage plasma nitriding applications where only few plasma diagnostic measurements have been reported.

  16. Self-focusing of electromagnetic pulsed beams in collisional plasmas

    SciTech Connect

    Faisal, Mohammad; Verma, M. P.; Sodha, Mahendra Singh

    2008-10-15

    In this paper, the self-focusing of an electromagnetic pulsed beam in a collisional plasma has been investigated in the paraxial approximation, following the formalism developed by Akhmanov. The energy balance equation for electrons, the equation expressing the equality of pressure gradient (of electrons and ions) to the force due to space charge field, and the equation for the beam width parameter f (obtained by following Akhmanov's approach) have been simultaneously solved for given initial (z=0) time profile of the pulse to obtain f as a function of {xi} (cz/{omega}r{sub 0}{sup 2}) and t{sup '}=t-z/V{sub g}, where V{sub g} is the group velocity. Both Gaussian and sine time profiles of the pulse have been investigated.

  17. Propagation of intense laser pulse in cold underdense plasma

    SciTech Connect

    Chen, X.L.; Sudan, R.N.

    1994-10-05

    We have derived a simplified set of three dimensional equations for the propagation of an intense laser pulse in cold underdense plasma [Phys. Fluids, {bold B}5, 1336 (1993)]. A three dimensional code has recently been developed to study this set of equations. Here we report on some of the preliminary results from the 3-d code. {copyright} 1994 {ital American} {ital Institute} {ital of} {ital Physics}

  18. Advanced modeling techniques in application to plasma pulse treatment

    NASA Astrophysics Data System (ADS)

    Pashchenko, A. F.; Pashchenko, F. F.

    2016-06-01

    Different approaches considered for simulation of plasma pulse treatment process. The assumption of a significant non-linearity of processes in the treatment of oil wells has been confirmed. Method of functional transformations and fuzzy logic methods suggested for construction of a mathematical model. It is shown, that models, based on fuzzy logic are able to provide a satisfactory accuracy of simulation and prediction of non-linear processes observed.

  19. Progress Towards Plasma Pulse Compression of High Energy, Long Pulse Laser Beams

    SciTech Connect

    Kirkwood, R K; Ping, Y; Rygg, R; Wilks, S; Meezan, N; Niemann, C; Landen, O; Fisch, N; Malkin, V; Valeo, E; Wurtele, J

    2008-06-19

    Compression of laser pulses to < {approx} 1-10 ps duration using stimulated Raman scattering (SRS) in a plasma promises to provide unprecedented power and intensity for a variety of applications, by avoiding the limits to fluence and intensity that are needed to avoid damage to the solid state optics that are used in conventional approaches. In particular, the ability to compress pump beam pulses of {approx} ns duration will allow present facilities with 10's kJ to over a MJ of energy to produce ultra short pulses efficiently, advancing applications in; fusion by fast ignition, x-ray production of high energy density experiments, as well as laser driven particle accelerators. We will discuss a series of experiments to demonstrate the needed beam amplification rate, and focal spot quality in a < 3mm plasma with the properties needed for compression of these pulses (n{sub e} {approx} 10{sup 19}/cm{sup 3}, T{sub e} 200 to 300 eV) when the plasma is extended. The experiments use He plasmas produced with a 300 J, 1 ns, beam at the Jupiter Laser facility to amplify a counter-propagating, ultra-short pulse (USP) seed by a factor of 10x to 37x and study the dependence of the amplification, the associated non-linear wave response, and the resulting beam quality and energy, on the intensity of both seed and pump beam. In particular, a regime in which amplification of USP beams is achieved while maintaining a low angular divergence of the beam consistent with good focal spot quality will be discussed.

  20. AnGa{sub 2}O{sub 4} Thin-Film Phosphors Grown by Pulsed Laser Ablation

    SciTech Connect

    Lee, Y.E.; Rouleau, C.M.; Park, C.; Norton, D.P.

    1999-04-05

    The growth and properties of undoped and Mn-doped ZnGa{sub 2}O{sub 4} thin-film phosphors on (100) MgO and glass substrates using pulsed laser ablation were investigated. Blue-white and green emission were observed for as-deposited undoped and Mn-doped films, respectively. Luminescent properties as well as crystallinity were considerably affected by processing conditions and film stoichiometry. Films with enhanced luminescent characteristics were obtained on single crystal substrates without post-annealing.

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

    NASA Astrophysics Data System (ADS)

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

    2009-06-01

    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 μs (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 μs 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 μm) 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.

  2. Plasma Parameter of a Capillary Discharge-Produced Plasma Channel to Guide an Ultrashort Laser Pulse

    SciTech Connect

    Higashiguchi, Takeshi; Terauchi, Hiromitsu; Bai, Jin-xiang; Yugami, Noboru

    2009-01-22

    We have observed the optical guiding of a 100-fs laser pulse with the laser intensity in the range of 10{sup 16} W/cm{sup 2} using a 1.5-cm long capillary discharge-produced plasma channel for compact electron acceleration applications. The optical pulse propagation using the plasma channel is achieved with the electron densities of 10{sup 17}-10{sup 18} cm{sup -3} and the electron temperatures of 0.5-4 eV at a discharge time delay of around 150 ns and a discharge current of 500 A with a pulse duration of 100-150 ns. An energy spectrum of the accelerated electrons from a laser-plasma acceleration scheme showed a peak at 1.3 MeV with a maximum energy tail of 1.6 MeV.

  3. Laser-induced breakdown spectroscopy for on-line control of selective removal of cobalt binder from tungsten carbide hardmetal by pulsed UV laser surface ablation

    NASA Astrophysics Data System (ADS)

    Li, Tiejun; Lou, Qihong; Wei, Yunrong; Huang, Feng; Dong, Jingxing; Liu, Jingru

    2001-09-01

    Laser-induced breakdown spectroscopy (LIBS) was successfully used in on-line control of selective removal of cobalt from tungsten carbide hardmetal by pulsed UV laser surface ablation. The dependence of LIBS on number of laser shots was investigated at different laser fluences. The optimal laser fluence of 2.5 J/cm 2 suited for selective removal of cobalt from surface layer of hardmetal was confirmed. The result sample was also subject to different post-examinations to evaluate the feasibility of the application of LIBS in this laser ablation process. It was demonstrated that, monitoring of the emission intensity of cobalt lines could be used as a control parameter for selective removal of cobalt from surface layer of hardmetal by pulsed UV laser. The on-line implementation of the spectroscopic technique LIBS to the surface-ablation process provided important information about the optimal-ablation parameters.

  4. Experimental investigation and 3D-simulation of the ablated morphology of titanium surface using femtosecond laser pulses

    NASA Astrophysics Data System (ADS)

    Liu, Dong; Chen, Chuansong; Man, Baoyuan; Meng, Xue; Sun, Yanna; Li, Feifei

    2015-12-01

    The femtosecond laser ablated morphology on titanium surface is investigated theoretically and experimentally. A three dimensional two temperature model (3D-TTM) is used to simulate the surface morphology of titanium sample which is irradiated by femtosecond laser pulses. The electron heat capacity and electron-phonon coupling coefficient of titanium (transition metal) are complex temperature dependent, so the two parameters are corrected based on the theory of electron density of states (DOS). The model is solved by the finite difference time domain (FDTD) method. The 3D temperature field near the target surface is achieved. The radius and depth of the ablated crater are obtained based on the temperature field. The evolutions of the crate's radius and depth with laser fluence are discussed and compared with the experimental results. It is found that the back-flow of the molten material and the deposition of the material vapor should be responsible for the little discrepancy between the simulated and experimental results. The present work makes a better understanding of the thermodynamic process of femtosecond laser ablating metal and meanwhile provides an effective method tool to predict the micro manufacturing process on metals with femtosecond laser.

  5. Growth of GaAs “nano ice cream cones” by dual wavelength pulsed laser ablation

    NASA Astrophysics Data System (ADS)

    Schamp, C. T.; Jesser, W. A.; Shivaram, B. S.

    2007-05-01

    Harmonic generation crystals inherently offer the possibility of using multiple wavelengths of light in a single laser pulse. In the present experiment, the fundamental (1064 nm) and second harmonic (532 nm) wavelengths from an Nd:YAG laser are focused together on GaAs and GaSb targets for ablation. Incident energy densities up to about 45 J/cm 2 at 10 Hz with substrate temperatures between 25 and 600 °C for durations of about 60 s have been used in an ambient gas pressure of about 10 -6 Torr. The ablated material was collected on electron-transparent amorphous carbon films for TEM analysis. Apart from a high density of isolated nanocrystals, the most common morphology observed consists of a crystalline GaAs cone-like structure in contact with a sphere of liquid Ga, resembling an "ice cream cone", typically 50-100 nm in length. For all of the heterostuctures of this type, the liquid/solid/vacuum triple junction is found to correspond to the widest point on the cone. These heterostructures likely form by preferential evaporation of As from molten GaAs drops ablated from the target. The resulting morphology minimizes the interfacial and surface energies of the liquid Ga and solid GaAs.

  6. Specific features of single-pulse femtosecond laser micron and submicron ablation of a thin silver film coated with a micron-thick photoresist layer

    SciTech Connect

    Zayarnyi, D A; Ionin, A A; Kudryashov, S I; Makarov, S V; Rudenko, A A; Drozdova, E A; Odinokov, S B

    2015-05-31

    Specific features of ablation of a thin silver film with a 1-μm-thick layer of a highly transparent photoresist and the same film without a photoresist layer under single tightly focused femtosecond laser pulses in the visible range (515 nm) are experimentally investigated. Interference effects of internal modification of the photoresist layer, its spallation ablation from the film surface and formation of through hollow submicron channels in the resist without its spallation but with ablation of the silver film lying under the resist are found and discussed. (extreme light fields and their applications)

  7. In situ diagnosis of pulsed UV laser surface ablation of tungsten carbide hardmetal by using laser-induced optical emission spectroscopy

    NASA Astrophysics Data System (ADS)

    Li, Tiejun; Lou, Qihong; Wei, Yunrong; Huang, Feng; Dong, Jingxing; Liu, Jingru

    2001-12-01

    Surface ablation of cobalt cemented tungsten carbide hardmetal with pulsed UV laser has been in situ diagnosed by using the technique of laser-induced optical emission spectroscopy. The dependence of emission intensity of cobalt lines on number of laser shots was investigated at laser fluence of 2.5 J/cm 2. As a comparison, the reliance of emission intensity of cobalt lines as a function of laser pulse number by using pure cobalt as ablation sample was also studied at the same laser condition. It was found that for surface ablation of tungsten carbide hardmetal at laser fluence of 2.5 J/cm 2, the intensities of cobalt lines fell off dramatically in the first 300 consecutive laser shots and then slowed down to a low stable level with even more shots. For surface ablation of pure cobalt at the same laser condition, the intensities of cobalt lines remained constant more or less even after 500 laser shots and then reduced very slowly with even more shots. It was concluded that selective evaporation of cobalt at this laser fluence should be responsible for the dramatic fall-off of cobalt lines with laser shots accumulation for surface ablation of tungsten carbide hardmetal. In contrast, for surface ablation of pure cobalt, the slow reduction of cobalt lines with pulse number accumulation should be due to the formation of laser-induced crater effect.

  8. Experimental Simulation of Meteorite Ablation during Earth Entry using a Plasma Wind Tunnel

    NASA Astrophysics Data System (ADS)

    Loehle, Stefan; Zander, Fabian; Hermann, Tobias; Eberhart, Martin; Meindl, Arne; Oefele, Rainer; Vaubaillon, Jeremie; Colas, Francois; Vernazza, Pierre; Drouard, Alexis; Gattacceca, Jerome

    2017-03-01

    Three different types of rocks were tested in a high enthalpy air plasma flow. Two terrestrial rocks, basalt and argillite, and an ordinary chondrite, with a 10 mm diameter cylindrical shape were tested in order to observe decomposition, potential fragmentation, and spectral signature. The goal was to simulate meteoroid ablation to interpret meteor observation and compare these observations with ground based measurements. The test flow with a local mass-specific enthalpy of 70 MJ kg‑1 results in a surface heat flux at the meteorite fragment surface of approximately 16 MW m‑2. The stagnation pressure is 24 hPa, which corresponds to a flight condition in the upper atmosphere around 80 km assuming an entry velocity of 10 km s‑1. Five different diagnostic methods were applied simultaneously to characterize the meteorite fragmentation and destruction in the ground test: short exposure photography, regular video, high-speed imaging with 10 kHz frame rate, thermography, and Echelle emission spectroscopy. This is the first time that comprehensive testing of various meteorite fragments under the same flow condition was conducted. The data sets indeed show typical meteorite ablation behavior. The cylindrically shaped fragments melt and evaporate within about 4 s. The spectral data allow the identification of the material from the spectra which is of particular importance for future spectroscopic meteor observations. For the tested ordinary chondrite sample a comparison to an observed meteor spectra shows good agreement. The present data show that this testing methodology reproduces the ablation phenomena of meteoritic material alongside the corresponding spectral signatures.

  9. Visible-light spectroscopy of pulsed-power plasmas (invited)

    NASA Astrophysics Data System (ADS)

    Arad, R.; Clark, R. E. H.; Dadusc, G.; Davara, G.; Duvall, R. E.; Fisher, A.; Fisher, V.; Foord, M. E.; Fruchtman, A.; Gregorian, L.; Krasik, Ya.; Litwin, C.; Maron, Y.; Perelmutter, L.; Sarfaty, M.; Sarid, E.; Shkolnikova, S.; Shpitalnik, R.; Troyansky, L.; Weingarten, A.

    1992-10-01

    We describe the investigations of the plasma behavior in three pulsed-power systems: a magnetically insulated ion diode, and plasma opening switch, and a gas-puffed Z pinch. Recently developed spectroscopic diagnostic techniques allow for measurements with relatively high spectral, temporal, and spatial resolutions. The particle velocity and density distributions within a few tens of microns from the dielectric-anode surface are observed using laser spectroscopy. Fluctuating electric fields in the plasma are inferred from anisotropic Stark broadening. For the plasma opening switch experiment, a novel gaseous plasma source was developed which is mounted inside the high-voltage inner conductor. The properties of this source, together with spectroscopic observations of the electron density and particle velocities of the injected plasma, are described. Emission line intensities during the switch operation are discussed. In the Z-pinch experiment, spectral emission-line profiles of various charge-state ions are studied during the implosion phase. Radial velocity distributions are observed from the line Doppler shifts and widths.

  10. Numerical Modeling and Testing of an Inductively-Driven and High-Energy Pulsed Plasma Thrusters

    NASA Technical Reports Server (NTRS)

    Parma, Brian

    2004-01-01

    Pulsed Plasma Thrusters (PPTs) are advanced electric space propulsion devices that are characterized by simplicity and robustness. They suffer, however, from low thrust efficiencies. This summer, two approaches to improve the thrust efficiency of PPTs will be investigated through both numerical modeling and experimental testing. The first approach, an inductively-driven PPT, uses a double-ignition circuit to fire two PPTs in succession. This effectively changes the PPTs configuration from an LRC circuit to an LR circuit. The LR circuit is expected to provide better impedance matching and improving the efficiency of the energy transfer to the plasma. An added benefit of the LR circuit is an exponential decay of the current, whereas a traditional PPT s under damped LRC circuit experiences the characteristic "ringing" of its current. The exponential decay may provide improved lifetime and sustained electromagnetic acceleration. The second approach, a high-energy PPT, is a traditional PPT with a variable size capacitor bank. This PPT will be simulated and tested at energy levels between 100 and 450 joules in order to investigate the relationship between efficiency and energy level. Arbitrary Coordinate Hydromagnetic (MACH2) code is used. The MACH2 code, designed by the Center for Plasma Theory and Computation at the Air Force Research Laboratory, has been used to gain insight into a variety of plasma problems, including electric plasma thrusters. The goals for this summer include numerical predictions of performance for both the inductively-driven PPT and high-energy PFT, experimental validation of the numerical models, and numerical optimization of the designs. These goals will be met through numerical and experimental investigation of the PPTs current waveforms, mass loss (or ablation), and impulse bit characteristics.

  11. Time-resolved microscopy reveals the driving mechanism of particle formation during ultrashort pulse laser ablation of dentin-like ivory.

    PubMed

    Domke, Matthias; Gavrilova, Anna; Rapp, Stephan; Frentzen, Matthias; Meister, Joerg; Huber, Heinz P

    2015-07-01

    In dental health care, the application of ultrashort laser pulses enables dental tissue ablation free from thermal side effects, such as melting and cracking. However, these laser types create undesired micro- and nanoparticles, which might cause a health risk for the patient or surgeon. The aim of this study was to investigate the driving mechanisms of micro- and nanoparticle formation during ultrashort pulse laser ablation of dental tissue. Time-resolved microscopy was chosen to observe the ablation dynamics of mammoth ivory after irradiation with 660 fs laser pulses. The results suggest that nanoparticles might arise in the excited region. The thermal expansion of the excited material induces high pressure in the surrounding bulk tissue, generating a pressure wave. The rarefaction wave behind this pressure wave causes spallation, leading to ejection of microparticles.

  12. Time-resolved microscopy reveals the driving mechanism of particle formation during ultrashort pulse laser ablation of dentin-like ivory

    NASA Astrophysics Data System (ADS)

    Domke, Matthias; Gavrilova, Anna; Rapp, Stephan; Frentzen, Matthias; Meister, Joerg; Huber, Heinz P.

    2015-07-01

    In dental health care, the application of ultrashort laser pulses enables dental tissue ablation free from thermal side effects, such as melting and cracking. However, these laser types create undesired micro- and nanoparticles, which might cause a health risk for the patient or surgeon. The aim of this study was to investigate the driving mechanisms of micro- and nanoparticle formation during ultrashort pulse laser ablation of dental tissue. Time-resolved microscopy was chosen to observe the ablation dynamics of mammoth ivory after irradiation with 660 fs laser pulses. The results suggest that nanoparticles might arise in the excited region. The thermal expansion of the excited material induces high pressure in the surrounding bulk tissue, generating a pressure wave. The rarefaction wave behind this pressure wave causes spallation, leading to ejection of microparticles.

  13. Downstream plasma transport and metal ionization in a high-powered pulsed-plasma magnetron

    NASA Astrophysics Data System (ADS)

    Meng, Liang; Yu, He; Szott, Matthew M.; McLain, Jake T.; Ruzic, David N.

    2014-06-01

    Downstream plasma transport and ionization processes in a high-powered pulsed-plasma magnetron were studied. The temporal evolution and spatial distribution of electron density (ne) and temperature (Te) were characterized with a 3D scanning triple Langmuir probe. Plasma expanded from the racetrack region into the downstream region, where a high ne peak was formed some time into the pulse-off period. The expansion speed and directionality towards the substrate increased with a stronger magnetic field (B), largely as a consequence of a larger potential drop in the bulk plasma region during a relatively slower sheath formation. The fraction of Cu ions in the deposition flux was measured on the substrate using a gridded energy analyzer. It increased with higher pulse voltage. With increased B field from 200 to 800 Gauss above racetrack, ne increased but the Cu ion fraction decreased from 42% to 16%. A comprehensive model was built, including the diffusion of as-sputtered Cu flux, the Cu ionization in the entire plasma region using the mapped ne and Te data, and ion extraction efficiency based on the measured plasma potential (Vp) distribution. The calculations matched the measurements and indicated the main causes of lower Cu ion fractions in stronger B fields to be the lower Te and inefficient ion extraction in a larger pre-sheath potential.

  14. DURIP - Acquisition of an Inductively-Coupled Plasma Mass Spectrometer with Laser Ablation Source for Surface Characterization

    DTIC Science & Technology

    2010-12-24

    allows low interference which reduces common polyatomic interferences on As, Se, Cr, V and Fe, thus achieving lower detection limits in the plasma...Formerly Varian) 820 ICP-MS Ion Optics Soft Landed Hf on Si SEM Image of ablation track 178Hf LA-ICP-MS transient signals showing spatially resolved Hf on surface (left) and in defects (right)

  15. Burning DT Plasmas with Ultrafast Soft X-Ray Pulses

    NASA Astrophysics Data System (ADS)

    Hu, S. X.; Goncharov, V. N.; Skupsky, S.

    2012-10-01

    Fast ignition with narrowband, coherent ultrafast soft x-ray pulsesfootnotetextS. X. Hu, V. N. Goncharov, and S. Skupsky, ``Burning Plasmas with Ultrashort Soft-X-Ray Flashing,'' to be published in Physics of Plasmas. has been investigated for cryogenic deuterium--tritium (DT) plasma conditions achieved on the OMEGA Laser System. In contrast to using hard x-rays (hν = 3 to 6 keV) proposed in the original x-ray fast-ignition proposal, we find that soft x-ray sources with hν 500-eV photons can be more suitable for igniting the dense DT plasmas. Two-dimensional radiation--hydrodynamics simulations have identified the breakeven conditions for realizing such a ``hybrid'' ignition scheme (direct-drive compression with soft x-ray heating) with 50-μm-offset targets: an ˜10-ps soft x-ray pulse (hν 500 eV) with a total energy of 500 to 1000 J to be focused into a 10-μm spot size. A variety of x-ray pulse parameters have also been investigated for optimization. It is noted that an order of magnitude increase in neutron yield has been predicted even with x-ray energy as low as ˜50 J. Scaling this idea to a 1-MJ large-scale NIF target, a gain above ˜30 can be reached with the same soft x-ray pulse at 1.65-kJ energy. Even though such energetic x-ray sources do not currently exist, we hope that the proposed ignition scheme may stimulate efforts on generating powerful soft x-ray sources in future. This work was supported by the U.S. Department of Energy Office of Inertial Confinement Fusion under Cooperative Agreement No. DE-FC52-08NA28302.

  16. Spark ablation-inductively coupled plasma spectrometry for analysis of geologic materials

    USGS Publications Warehouse

    Golightly, D.W.; Montaser, A.; Smith, B.L.; Dorrzapf, A.F.

    1989-01-01

    Spark ablation-inductively coupled plasma (SA-ICP) spectrometry is applied to the measurement of hafnium-zirconium ratios in zircons and to the determination of cerium, cobalt, iron, lead, nickel and phosphorus in ferromanganese nodules. Six operating parameters used for the high-voltage spark and argon-ICP combination are established by sequential simplex optimization of both signal-to-background ratio and signal-to-noise ratio. The time-dependences of the atomic emission signals of analytes and matrix elements ablated from a finely pulverized sample embedded in a pressed disk of copper demonstrate selective sampling by the spark. Concentration ratios of hafnium to zirconium in zircons are measured with a precision of 4% (relative standard deviation, RSD). For ferromanganese nodules, spectral measurements based on intensity ratios of analyte line to the Mn(II) 257.610 nm line provide precisions of analysis in the range from 7 to 14% RSD. The accuracy of analysis depends on use of standard additions of the reference material USGS Nod P-1, and an independent measurement of the Mn concentration. ?? 1989.

  17. Vibration testing based on impulse response excited by pulsed-laser ablation: Measurement of frequency response function with detection-free input

    NASA Astrophysics Data System (ADS)

    Hosoya, Naoki; Kajiwara, Itsuro; Hosokawa, Takahiko

    2012-03-01

    We have developed a non-contact vibration-measurement system that is based on impulse excitation by laser ablation (i.e. laser excitation) to measure the high-frequency-vibration characteristics of objects. The proposed method makes it possible to analyse the frequency response function just by measuring the output (acceleration response) of a test object excited by pulsed-laser ablation. This technique does not require detection of the input force. Firstly, using a rigid block, the pulsed-laser-ablation force is calibrated via Newton's second law. Secondly, an experiment is conducted in which an object whose natural frequency lies in the high-frequency domain is excited by pulsed-laser ablation. The complex frequency spectrum obtained by Fourier transform of the measured response is then divided by the estimated pulsed-laser-ablation force. Finally, because of the error involved in the trigger position of the response with respect to the impulse arrival time, the phase of the complex Fourier transform is modified by accounting for the response dead time. The result is the frequency response function of the object. The effectiveness of the proposed method is demonstrated by a vibration test of an aluminium block.

  18. Structuring by field enhancement of glass, Ag, Au, and Co thin films using short pulse laser ablation

    SciTech Connect

    Ulmeanu, M.; Zamfirescu, M.; Rusen, L.; Luculescu, C.; Moldovan, A.; Stratan, A.; Dabu, R.

    2009-12-01

    Single pulse laser ablation of glass, Ag, Au, and Co thin films was experimentally investigated with a laser pulse width of 400 ps at a wavelength of 532 nm both in the far and near fields. In the far-field regime, the electromagnetic field results from a focused laser beam, while the near-field regime is realized by a combination of the focused laser beam incident on a spherical colloidal particle. For the near-field experiments we have used polystyrene colloidal particles of 700 nm diameter self-assembled or spin coated on top of the surfaces. Laser fluences applied are in the range of 0.01-10 J/cm{sup 2}. The diameter and the morphologies of the ablated holes were investigated by optical microscopy, profilometry, scanning electron microscopy, and atomic force microscopy. The dependence of the shape of the holes reflects the fluence regime and the thermophysical properties, i.e., melting temperature and thermal diffusivity of the surfaces involved in the experiments. We give quantitative data about the fluence threshold, diameter, and depth ablation dependence for the far and near fields and discuss their values with respect to the enhancement factor of the intensity of the electromagnetic field due to the use of the colloidal particles. Theoretical estimations of the intensity enhancement were done using the finite-difference time-domain method by using the RSOFT software. The application of near fields allows structuring of the surfaces with structure dimension in the order of 100 nm and even below.

  19. Selective ablation of atherosclerotic lesions with less thermal damage by controlling the pulse structure of a quantum cascade laser in the 5.7-µm wavelength range

    NASA Astrophysics Data System (ADS)

    Hashimura, Keisuke; Ishii, Katsunori; Awazu, Kunio

    2016-04-01

    Cholesteryl esters are the main components of atherosclerotic plaques, and they have an absorption peak at the wavelength of 5.75 µm. To realize less-invasive ablation of the atherosclerotic plaques using a quasi-continuous wave (quasi-CW) quantum cascade laser (QCL), the thermal effects on normal vessels must be reduced. In this study, we attempted to reduce the thermal effects by controlling the pulse structure. The irradiation effects on rabbit atherosclerotic aortas using macro pulse irradiation (irradiation of pulses at intervals) and conventional quasi-CW irradiation were compared. The macro pulse width and the macro pulse interval were determined based on the thermal relaxation time of atherosclerotic and normal aortas in the oscillation wavelength of the QCL. The ablation depth increased and the coagulation width decreased using macro pulse irradiation. Moreover, difference in ablation depth between the atherosclerotic and normal rabbit aortas using macro pulse irradiation was confirmed. Therefore, the QCL in the 5.7-µm wavelength range with controlling the pulse structure was effective for less-invasive laser angioplasty.

  20. Modeling of long term behavior of ablation plumes produced with ultrashort laser pulses

    SciTech Connect

    Feit, M D; Komashko, A M; Rubenchik, A M

    2000-02-10

    Expansion of ablation plumes created by intense ultrashort lasers is determined by various complicated physical processes which have very different spatial and time scales. Since complete simulation by one model is practically impossible, the authors suggest using two models describing initial and final stages that can be matched at an intermediate time. The proposed modeling procedure connects laser parameters to plume properties far away from the ablation spot. Laser material interaction and beginning of the expansion are simulated with a one-dimensional hydrodynamics code and the final stage is modeled using an analytical solution for an expanding three-dimensional ellipsoidal gas cloud.

  1. Pulsed laser ablation and deposition of bioactive glass as coating material for biomedical applications

    NASA Astrophysics Data System (ADS)

    D'Alessio, L.; Teghil, R.; Zaccagnino, M.; Zaccardo, I.; Ferro, D.; Marotta, V.

    1999-01-01

    A study of the laser ablation and deposition, on Ti-Al substrates, of a biologically active glass (Bioglass®) suitable for bone implants is reported. The analysis of the gaseous phase by emission spectroscopy and the characterisation of the films from a compositional and morphological point of view have been carried out. The mean chemical composition of the deposits obtained from Bioglass ablation is very close to the target composition and the morphology indicates that different mechanisms of material ejection are present.

  2. Pulsed Power Aspects of the NIF Plasma Electrode Pockels Cell

    SciTech Connect

    Arnold, P A; Ollis, C W; Hinz, A F; Barbosa, F; Fulkerson, E S

    2005-06-09

    The Plasma Electrode Pockels Cell (PEPC) embodies technology essential to the National Ignition Facility (NIF). Together with a thin-film polarizer, PEPC functions as an optical switch for the main amplifier cavity, allowing optical pulses to be trapped, and then released, and enabling NIF to take advantage of the attendant gain and cost-savings. Details of the genesis, development, and prototyping of the PEPC are well documented. After moving from its laboratory setting to the NIF facility, PEPC--via its performance during the two-year NIF Early Light (NEL) campaign and its ongoing operation during facility build-out--has proven to be a fully functional system. When complete, NIF will accommodate 192 beams, capable of delivering 1.8 MJ to a fusion target. Forty-eight Plasma Electrode Pockels--driven by nearly 300 high-power, high-voltage pulse generators--will support this complement of beams. As deployed, PEPC is a complex association of state-of-the-art optics; low-voltage and high-voltage electronics; and mechanical, gas, and vacuum subsystems--all under computer control. In this paper, we briefly describe each of these elements, but focus on the pulse power aspects of the PEPC system.

  3. Determination of elemental content off rocks by laser ablation inductively coupled plasma mass spectrometry

    USGS Publications Warehouse

    Lichte, F.E.

    1995-01-01

    A new method of analysis for rocks and soils is presented using laser ablation inductively coupled plasma mass spectrometry. It is based on a lithium borate fusion and the free-running mode of a Nd/YAG laser. An Ar/N2 sample gas improves sensitivity 7 ?? for most elements. Sixty-three elements are characterized for the fusion, and 49 elements can be quantified. Internal standards and isotopic spikes ensure accurate results. Limits of detection are 0.01 ??g/g for many trace elements. Accuracy approaches 5% for all elements. A new quality assurance procedure is presented that uses fundamental parameters to test relative response factors for the calibration.

  4. Online monitoring of nanoparticles formed during nanosecond laser ablation

    NASA Astrophysics Data System (ADS)

    Nováková, Hana; Holá, Markéta; Vojtíšek-Lom, Michal; Ondráček, Jakub; Kanický, Viktor

    2016-11-01

    The particle size distribution of dry aerosol originating from laser ablation of glass material was monitored simultaneously with Laser Ablation - Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS) analysis and two aerosol spectrometers - Fast Mobility Particle Sizer (FMPS) and Aerodynamic Particle Sizer (APS). The unique combination of LA-ICP-MS and FMPS offers the possibility of measuring the particle size distribution every 1 s of the ablation process in the size range of 5.6-560 nm. APS extends the information about particle concentration in the size range 0.54-17 μm. Online monitoring of the dry aerosol was performed for two ablation modes (spot and line with a duration of 80 s) with a 193 nm excimer laser system, using the glass reference material NIST 610 as a sample. Different sizes of laser spot for spot ablation and different scan speeds for line ablation were tested. It was found that the FMPS device is capable of detecting changes in particle size distribution at the first pulses of spot laser ablation and is suitable for laser ablation control simultaneously with LA-ICP-MS analysis. The studied parameters of laser ablation have an influence on the resulting particle size distribution. The line mode of laser ablation produces larger particles during the whole ablation process, while spot ablation produces larger particles only at the beginning, during the ablation of the intact layer of the ablated material. Moreover, spot ablation produces more primary nano-particles (in ultrafine mode size range < 100 nm) than line ablation. This effect is most probably caused by a reduced amount of large particles released from the spot ablation crater. The larger particles scavenge the ultrafine particles during the line ablation mode.

  5. Spatial and temporal studies of laser ablated ZnO plasma

    SciTech Connect

    Joshy, N. V.; Saji, K. J.; Jayaraj, M. K.

    2008-09-01

    Gallium doped zinc oxide was ablated using the third harmonics of Nd:YAG laser at various laser fluences and nitrous oxide ambient gas pressures. Optical emission spectroscopic technique was used to determine the plasma parameters. Spatial variation of electron number density (N{sub e}) was determined along the direction normal to the target surface. The electron density obtained was of the order of 10{sup 17} cm{sup -3}, for the laser fluence in the range of 1.27-6.35 J cm{sup -2}. The influence of the substrate temperature on the plasma plume was studied by keeping an Al{sub 2}O{sub 3} (alumina) substrate at a distance of 5 cm distance from the target at various temperatures. The increase in the substrate temperature enhanced the electron number density and intensity of spectral emissions of various species in the plume. The time of flight transients of specific emissions from the plume were recorded. The velocity of neutral gallium decreased from 6.45 to 3.87 km/s at 4 mm distance from the target when the ambient gas pressure was increased from 0.0001 to 0.1 mbar. The velocities of the species increased considerably with an increase in laser fluences. ZnO thin films were deposited on alumina substrates. The plasma plume kinematics were used to corroborate the nature of thin film deposition.

  6. Significance of ambient conditions in uranium absorption and emission features of laser ablation plasmas

    SciTech Connect

    Skrodzki, P. J.; Shah, N. P.; Taylor, N.; Hartig, K. C.; LaHaye, N. L.; Brumfield, B. E.; Jovanovic, I.; Phillips, M. C.; Harilal, S. S.

    2016-11-01

    This study employs laser ablation (LA) to investigate mechanisms for U optical signal variation under various environmental conditions during laser absorption spectroscopy (LAS) and optical emission spectroscopy (OES). Potential explored mechanisms for signal quenching related to ambient conditions include plasma chemistry (e.g., uranium oxide formation), ambient gas confinement effects, and other collisional interactions between plasma constituents and the ambient gas. LA-LAS studies show that the persistence of the U ground state population is significantly reduced in the presence of air ambient compared to nitrogen. LA-OES results yield congested spectra from which the U I 356.18 nm transition is prominent and serves as the basis for signal tracking. LA-OES signal and persistence vary negligibly between the test gases (air and N2), unlike the LA-LAS results. The plume hydrodynamic features and plume fundamental properties showed similar results in both air and nitrogen ambient. Investigation of U oxide formation in the laser-produced plasma suggests that low U concentration in a sample hinders consistent detection of UO molecular spectra.

  7. Significance of ambient conditions in uranium absorption and emission features of laser ablation plasmas

    NASA Astrophysics Data System (ADS)

    Skrodzki, P. J.; Shah, N. P.; Taylor, N.; Hartig, K. C.; LaHaye, N. L.; Brumfield, B. E.; Jovanovic, I.; Phillips, M. C.; Harilal, S. S.

    2016-11-01

    This study employs laser ablation (LA) to investigate mechanisms for U optical signal variation under various environmental conditions during laser absorption spectroscopy (LAS) and optical emission spectroscopy (OES). Potential mechanisms explored for signal quenching related to ambient conditions include plasma chemistry (e.g., uranium oxide formation), ambient gas confinement effects, and other collisional interactions between plasma constituents and the ambient gas. LA-LAS studies show that the persistence of the U ground state population is significantly reduced in the presence of air ambient compared to nitrogen. LA-OES yields congested spectra from which the U I 356.18 nm transition is prominent and serves as the basis for signal tracking. LA-OES signal and persistence vary negligibly between the test gases (air and N2), unlike the LA-LAS results. The plume hydrodynamic features and plume fundamental properties showed similar results in both air and nitrogen ambient. Investigation of U oxide formation in the laser-produced plasma suggests that low U concentration in a sample hinders consistent detection of UO molecular spectra.

  8. Understanding plume splitting of laser ablated plasma: A view from ion distribution dynamics

    SciTech Connect

    Wu, Jian; Li, Xingwen; Wei, Wenfu; Jia, Shenli; Qiu, Aici

    2013-11-15

    Plume splitting in low-pressure ambient air was understood in view of ion distribution dynamics from the laser ablated Al plasma (1064 nm 0.57 J/mm{sup 2}) by combining fast photography and spatially resolved spectroscopy. In the beginning, the spectral lines were mainly from the Al III ion. Then, the Bragg peak in stopping power of the ambient gas to Al III could be the dominant reason for the enhanced emission from the fast moving part, and the recombination of Al III to Al I-II ions near the target surface was response to the radiations from the slow moving/stationary part. As the ambient gas pressure increased, stopping distances of the Al III decreased, and radiation from the air ions became pronounced. The laser shadowgraph image at 1100 Pa indicated that the shock wave front located between the fast moving and slow moving parts. Electron densities of the fast moving plasma, which peaked at the plasma front, were on the order of 10{sup 16} cm{sup −3}, and the electron temperatures were 2–3 eV.

  9. Observation of amplification of a 1ps pulse by SRS of a 1 ns pulse in a plasma with conditions relevant to pulse compression

    SciTech Connect

    Kirkwood, R K; Dewald, E; Wilks, S C; Meezan, N; Niemann, C; Berger, R L; Landen, O L; Wurtele, J; Charman, A E; Lindberg, R; Fisch, N J; Malkin, V M

    2006-05-24

    The compression of a laser pulse by amplification of an ultra short pulse beam Which seeds the stimulated Raman scatter of the first beam has been long been discussed in the context of solid and gas media. We investigate the possibility of using intersecting beams in a plasma to compress nanosecond pulses to picosecond duration by scattering from driven electron waves. Recent theoretical studies have shown the possibility of efficient compression With large amplitude, non-linear Langmuir waves driven either by SRS or non-resonantly. We describe experiments in which a plasma suitable for pulse compression is created , and amplification of an ultra short pulse beam is demonstrated.

  10. Development of a short pulsed solid propellant plasma thruster

    NASA Technical Reports Server (NTRS)

    Guman, W. J.

    1974-01-01

    The experimental results are summarized that were obtained in the development of a Teflon solid propellant pulsed plasma thruster. The feasibility was established of storing and feeding solid propellant in the form of an open circular loop into an operational thruster. This technique was verified to be practical by feeding over 20 inches of Teflon into a micro-thruster over an accumulated life test of 1858 hours. High energy density capacitors were evaluated under vacuum conditions when the capacitor is coupled directly to a plasma thruster. Numerous early capacitor failures were encountered. It was concluded that essentially all of the failures encountered in a vacuum environment are due to an internal electrical breakdown that will occur inside a capacitor that is not truly hermetically sealed. A steady input power significantly in excess of 130 watts can safely be tolerated if heat conduction can be provided to a sink whose temperature is about 16 C. A vacuum life test of the capacitor bank was carried out while discharging into a milli-lb. (milli-Newton) type pulsed plasma thruster. More than 1500 hours of vacuum testing of this milli-Newton type system has been accumulated without any capacitor problems. Recommendations are made for future capacitor designs.

  11. Dynamics of a pulsed inductively coupled oxygen plasma

    NASA Astrophysics Data System (ADS)

    Zaka-ul-Islam, Mujahid

    2016-11-01

    Inductively coupled plasma system (ICPs) is extensively used for a wide range of nanofabrication applications. The ICPs operated in a pulsed or power modulated mode has shown several advantages compared to the continuous discharge. In this work, the plasma dynamics in a planar coil pulsed inductively coupled plasma system (ICPs) operated in oxygen has been investigated, using phase and space resolved optical emission spectroscopy. It is well-known that the ICPs operates in two distinct operational modes as a function of power known as E and H modes, generated dominantly by capacitive and inductive couplings, respectively. The measurements show that the discharge ignites due a capacitive coupling (in the E-mode) and later transits to the H-mode as a function of time. The inductive coupling, however, starts during the E-mode along with capacitive coupling. The relative contribution of inductive coupling increases until the discharge reaches the E-H transition where the growth rate of inductive coupling becomes much faster. It is found that the time to reach E-H transition decreases with the pressure. At the E-H transition, the total emission has a spike-like feature (i.e., it first achieves a peak emission which later decreases and finally settles to a lower value). The 2D images of the discharge show that at the time of peak total-emission, the discharge structure is sharp and bright, which later decreases in brightness and becomes diffusive.

  12. Ultrashort-pulse propagation through free-carrier plasmas

    SciTech Connect

    Gulley, Jeremy R.; Dennis, W. M.

    2010-03-15

    The past decade has seen frequent use of a modified nonlinear Schroedinger equation to describe ultrashort pulse propagation in materials where free-carrier plasmas are present. The optical contribution from the resulting free-current densities in this equation is often described using a classical Drude model. However, the ultimate form of this contribution in the modified nonlinear Schroedinger equation is somewhat inconsistent in the literature. We clarify this ambiguity by deriving the modified nonlinear Schroedinger equation from the classical wave equation containing a free-current density contribution. The Drude model is then used to obtain an expression for the complex free-carrier current density envelope with temporal dispersion corrections for ultrashort laser pulses. These temporal dispersion corrections to the current-density term differ, to our knowledge, from all other models in the literature in that they depend more sensitively on the value of the Drude free-carrier collision time. These corrections reduce to the current models in the literature for limiting cases. Theoretical analysis and computer simulations show that these differences can significantly affect the dynamic interactions of plasma absorption and plasma defocusing for materials with free-carrier collision times on the order of one optical cycle (or less) of the applied field.

  13. Comparison of pulsed corona plasma and pulsed electric fields for the decontamination of water containing Legionella pneumophila as model organism.

    PubMed

    Banaschik, Robert; Burchhardt, Gerhard; Zocher, Katja; Hammerschmidt, Sven; Kolb, Juergen F; Weltmann, Klaus-Dieter

    2016-12-01

    Pulsed corona plasma and pulsed electric fields were assessed for their capacity to kill Legionella pneumophila in water. Electrical parameters such as in particular dissipated energy were equal for both treatments. This was accomplished by changing the polarity of the applied high voltage pulses in a coaxial electrode geometry resulting in the generation of corona plasma or an electric field. For corona plasma, generated by high voltage pulses with peak voltages of +80kV, Legionella were completely killed, corresponding to a log-reduction of 5.4 (CFU/ml) after a treatment time of 12.5min. For the application of pulsed electric fields from peak voltages of -80kV a survival of log 2.54 (CFU/ml) was still detectable after this treatment time. Scanning electron microscopy images of L. pneumophila showed rupture of cells after plasma treatment. In contrast, the morphology of bacteria seems to be intact after application of pulsed electric fields. The more efficient killing for the same energy input observed for pulsed corona plasma is likely due to induced chemical processes and the generation of reactive species as indicated by the evolution of hydrogen peroxide. This suggests that the higher efficacy and efficiency of pulsed corona plasma is primarily associated with the combined effect of the applied electric fields and the promoted reaction chemistry.

  14. Experimental and modelling investigations into the laser ablation with picosecond pulses at second harmonics

    NASA Astrophysics Data System (ADS)

    Boerner, Paul; Zandonadi, Germana; Eberle, Gregory; Wegener, Konrad

    2015-03-01

    Ablation threshold experiments on various materials are carried out using a picosecond laser generating second harmonic radiation in air at atmospheric pressure. Various materials are investigated which vary according to their different electronic band gap structure and include: silicon, fine grain polycrystalline diamond, copper, steel and tungsten carbide. Through the use of scanning electron microscopy and 3D confocal microscopy, the crater depth and diameter are determined and a correlation is found. The ablation thresholds are given for the aforementioned materials and compared with recent literature results. Picosecond laser-material interactions are modelled using the two-temperature model, simulated and compared with experimental results for metallic materials. An extension of the two-temperature model to semiconducting and insulating materials is discussed. This alternative model uses multiple rate equations to describe the transient free electron density. Additionally, a set of coupled ordinary differential equations describes the processes of multiphoton excitation, inverse bremsstrahlung, and collisional excitation. The resulting electron density distribution can be used as an input for an electron density dependent twotemperature model. This multiple rate equation model is a generic and fast model, which provides important information like ablation threshold, ablation depth and optical properties.

  15. Short intense laser pulse collapse in near-critical plasma.

    PubMed

    Sylla, F; Flacco, A; Kahaly, S; Veltcheva, M; Lifschitz, A; Malka, V; d'Humières, E; Andriyash, I; Tikhonchuk, V

    2013-02-22

    It is observed that the interaction of an intense ultrashort laser pulse with a near-critical gas jet results in the pulse collapse and the deposition of a significant fraction of the energy. This deposition happens in a small and well-localized volume in the rising part of the gas jet, where the electrons are efficiently accelerated and heated. A collisionless plasma expansion over ~ 150 μm at a subrelativistic velocity (~ c/3) has been optically monitored in time and space, and attributed to the quasistatic field ionization of the gas associated with the hot electron current. Numerical simulations in good agreement with the observations suggest the acceleration in the collapse region of relativistic electrons, along with the excitation of a sizable magnetic dipole that sustains the electron current over several picoseconds.

  16. Simultaneous spatial and temporal focusing of femtosecond pulses: A new paradigm for material processing and tissue ablation

    NASA Astrophysics Data System (ADS)

    Block, Erica K.

    Femtosecond lasers are now prolific in many disciplines. While the mechanisms of femtosecond-material interactions are widely understood, femtosecond lasers as industrial and medical tools still have shortcomings. Currently conventional state of the art platforms are unable to support low numerical aperture (NA) beams (that provide large focal volumes and long working distances) without sacrificing axial precision. Furthermore inline (refractive) delivery systems that are necessary for industrial and clinical medical applications are currently hindered by nonlinear effects when delivering femtosecond pulses with tens of microJoule pulse energies and greater. In this thesis Simultaneous Space Time Focusing (SSTF) is presented as a new paradigm to move the field of femtosecond micromachining significantly forward. With this system we have delivered microjoule femtosecond pulses with low numerical aperture geometries (<0.05 NA) with characteristics that are significantly improved compared to standard focusing paradigms. Nonlinear effects that would normally result in focal plane shifts and focal spot distortion are mitigated when SSTF is employed. As a result, it is shown that SSTF will enable surgical implementations that are presently inhibited. Initial ablation experiments of ocular tissue show unprecedented performance with this technique. Implementation of SSTF, in the past, has been overly complicated. Multiple compressors and diffraction gratings resulted in low throughput efficiency. In the second part of this thesis we have focused on significantly streamlining the SSTF design into a flexible, single grating, integrated SSTF/chirped-pulse amplification system with an inline (refractive) delivery system to move towards industrial and clinical medical applications. For the first time this design also allows for variation of the beam aspect ratio of an SSTF beam, and thus the degree of pulse-front tilt at focus, while maintaining a net zero-dispersion system

  17. Dynamics and interactions of pulsed laser generated plasma bubbles in dusty plasma liquids

    SciTech Connect

    Chu Hongyu; Liao Chenting; I Lin

    2005-10-31

    The plasma bubble with dust particle depletion can be generated by a nano-second laser pulse focused on one of the dust particles suspended in a strongly coupled dusty plasma liquid. The bubble dynamics at different time scales, including the initial forming and later traveling stages are investigated. In the first stage, dust particles are pushed outward by the outward ion flow associated with the plume generated by the more intensed plasma. The bubble then travels downward at a speed about 60 mm/s associated with a surrounding dipole-like dust flow field. Two bubbles can also be simultaneously generated at different locations by separated laser pulses to study their interactions. Strong coupling is observed between two vertical bubbles. However, two horizontal bubbles are weakly coupled. The possible mechanism is discussed.

  18. Surface damage of W exposed to combined stationary D plasma and ELMs-like pulsed plasma

    NASA Astrophysics Data System (ADS)

    Jia, Y. Z.; Liu, W.; Xu, B.; Qu, S. L.; Morgan, T. W.

    2017-04-01

    The surface damage of W under D plasma and ELMs-like transient heat loads was studied by combined stationary and pulsed D plasma. Low-flux transient heat loads will promote blister formation due to the gas expansion inside the blisters. On the contrary, high-flux transient heat loads will mitigate blistering due to the high surface temperature. Therefore, blistering on W surface first increased and then decreased with the increasing transient heat loads. The promotion effect of pulsed plasma on blistering is more obvious on [001] and [110] surfaces than on [111] surface, and the orientation dependence of blisters was mitigated by the transient heat loads. Surface modification induced by transient heat loads only formed on [001] and [110] surfaces, but did not form on [111] surface. The orientation dependence of surface modification was mainly due to the slipping system of dislocations.

  19. Double-pulse induced harmonic generation in laser-produced plasmas

    NASA Astrophysics Data System (ADS)

    Ganeev, Rashid A.; Suzuki, Masayuki; Yoneya, Shin; Kuroda, Hiroto

    2015-12-01

    We report the studies of the metals, non-metals, powders, and nanoparticles as the targets for laser ablation induced high-order harmonic generation of ultrashort pulses using the double-pulse technique. The proposed technique demonstrates the attractiveness as the method for the studies of the high-order nonlinear optical properties of various materials. The comparative analysis of the harmonic generation using different targets showed that the species allowing easier ablation (powders, nanoparticles) produce stronger harmonic yield in the extreme ultraviolet range.

  20. Humidity sensors applicative characteristics of granularized and porous Bi2O3 thin films prepared by oxygen plasma-assisted pulsed laser deposition

    NASA Astrophysics Data System (ADS)

    Tudorache, Florin; Petrila, Iulian; Condurache-Bota, Simona; Constantinescu, Catalin; Praisler, Mirela

    2015-01-01

    Pulsed laser ablation of pure bismuth targets in a plasma discharge followed by thermal treatment as preparation method for humidity high-sensitive bismuth trioxide thin films deposited onto Si/Pt substrates were analyzed. Several thin films were deposited at different substrate temperatures during the pulsed laser deposition namely between 300 °C and 600 °C. Near to the electrical investigation, the structure and the morphology of the films as keys features for water adsorption are thoroughly investigated and correlated with their sensitivity as humidity sensors. Thus, it has been found that strong granularized Bi2O3 thin films obtained through oxygen plasma-assisted pulsed laser deposition onto Si/Pt substrate at 500 °C provide the most interesting humidity sensing characteristics.