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Sample records for gas dynamic laser

  1. Radiant energy absorption studies for laser propulsion. [gas dynamics

    NASA Technical Reports Server (NTRS)

    Caledonia, G. E.; Wu, P. K. S.; Pirri, A. N.

    1975-01-01

    A study of the energy absorption mechanisms and fluid dynamic considerations for efficient conversion of high power laser radiation into a high velocity flow is presented. The objectives of the study are: (1) to determine the most effective absorption mechanisms for converting laser radiation into translational energy, and (2) to examine the requirements for transfer of the absorbed energy into a steady flow which is stable to disturbances in the absorption zone. A review of inverse Bremsstrahlung, molecular and particulate absorption mechanisms is considered and the steady flow and stability considerations for conversion of the laser power to a high velocity flow in a nozzle configuration is calculated. A quasi-one-dimensional flow through a nozzle was formulated under the assumptions of perfect gas.

  2. Closed-cycle gas dynamic laser design investigation

    NASA Technical Reports Server (NTRS)

    Ketch, G. W.; Young, W. E.

    1977-01-01

    A conceptual design study was made of a closed cycle gas-dynamic laser to provide definition of the major components in the laser loop. The system potential application is for long range power transmission by way of high power laser beams to provide satellite propulsion energy for orbit changing or station keeping. A parametric cycle optimization was conducted to establish the thermodynamic requirements for the system components. A conceptual design was conducted of the closed cycle system and the individual components to define physical characteristics and establish the system size and weight. Technology confirmation experimental demonstration programs were outlined to develop, evaluate, and demonstrate the technology base needed for this closed cycle GDL system.

  3. Gas Effect On Plasma Dynamics Of Laser Ablation Zinc Oxide

    NASA Astrophysics Data System (ADS)

    Abdelli-Messaci, S.; Kerdja, T.; Lafane, S.; Malek, S.

    2008-09-01

    In order to synthesis zinc oxide thin films and nanostructures, laser ablation of ZnO target into both vacuum and oxygen atmosphere was performed. The gas effect on the plume dynamics was studied for O2 pressures varied between 10-2 to 70 mbar. Plasma plume evolution was investigated by ICCD camera fast imaging. The plasma was created by a KrF excimer laser (λ = 248 nm, τ = 25 ns) at a fluence of 2 J/cm2. The light emitted by the plume was observed along the perpendicular to the ejection direction through a fast intensified charge-coupled device (ICCD). We have found that the plasma dynamics is very affected by the gas pressures. The photographs reveal the stratification of plasma into slow and fast components for 0.5 mbar O2 pressures and beyond. The photographs also show the apparition of hydrodynamic instabilities which are related to chemical reactions between the plasma and the surrounding gas for a certain range of pressures.

  4. Gas Effect On Plasma Dynamics Of Laser Ablation Zinc Oxide

    SciTech Connect

    Abdelli-Messaci, S.; Kerdja, T.; Lafane, S.; Malek, S.

    2008-09-23

    In order to synthesis zinc oxide thin films and nanostructures, laser ablation of ZnO target into both vacuum and oxygen atmosphere was performed. The gas effect on the plume dynamics was studied for O{sub 2} pressures varied between 10{sup -2} to 70 mbar. Plasma plume evolution was investigated by ICCD camera fast imaging. The plasma was created by a KrF excimer laser ({lambda} = 248 nm, {tau} = 25 ns) at a fluence of 2 J/cm{sup 2}. The light emitted by the plume was observed along the perpendicular to the ejection direction through a fast intensified charge-coupled device (ICCD). We have found that the plasma dynamics is very affected by the gas pressures. The photographs reveal the stratification of plasma into slow and fast components for 0.5 mbar O{sub 2} pressures and beyond. The photographs also show the apparition of hydrodynamic instabilities which are related to chemical reactions between the plasma and the surrounding gas for a certain range of pressures.

  5. Experimental Investigations of Laser Propulsion by Using Gas-Dynamic Laser

    NASA Astrophysics Data System (ADS)

    Rachuk, V. S.; Guterman, V. Yu.; Ivanov, A. V.; Rebrov, S. G.; Golikov, A. N.; Ponomarev, N. B.; Rezunkov, Yu. A.

    2006-05-01

    To launch vehicles with using of laser propulsion engines, promising direction is employing powerful Gas-dynamic Lasers (GDL) operating in a continuous mode. Russian enterprises have enough experience of creating such type of lasers. Experiments conducted with the continuous mode GDL on investigating of characteristics of Laser Propulsion (LP) at different schematics of operation processes in the LP are described in this article. The investigations are conducted by using the facility equipped with a CO2 GDL of a 10.6 μm wavelength.

  6. Numerical analysis of gas-dynamic instabilities during the laser drilling process

    NASA Astrophysics Data System (ADS)

    Khan, A. H.; O'Neill, W.; Tunna, L.; Sutcliffe, C. J.

    2006-08-01

    The use of high-pressure gas jets in the laser-drilling process has significant influence on the melt ejection mechanism. These jets are highly unstable and this directly relates to the gas pressure and the geometry of the hole being drilled. The evolution of gas-dynamic instabilities during the laser-drilling process was investigated numerically. A minimum length nozzle (MLN) with a 300 μm throat diameter was modelled at various gas pressures, with the gas jet impinging on a range of simulated holes with different aspect ratios. The simulations predict the formation of surface pressure fluctuations that have a broad spectrum due to both the turbulent nature of the jet and the blunt shock oscillation on the surface. The surface pressure variations and the blunt shock oscillation govern the gas dynamic conditions inside the hole, which strongly influence the melt ejection phenomena during the laser-drilling process.

  7. Numerical calculations of a high power CW CO2 gas-dynamic laser

    NASA Astrophysics Data System (ADS)

    Al-Hawat, Sharif; Al-Mutaib, Kheir

    2008-03-01

    Numerical solution of gas-dynamic laser equations in a gas mixture CO2:N2:H2O was carried out, using five-temperature-model (one translational and four vibrational temperatures) by a computational program written in FORTRAN. The spatial distributions of population inversion, gain and temperatures of the gas flow, in addition to the laser intensity and power extraction were studied inside the cavity, for certain initial conditions like pressure (p0=20 atm), temperature (T0= 1500 K), ratio of gases in the laser mixture (CO2:N2:H2O ≡ 10:85:5).

  8. Dynamics of Laser-Ablation Plume and Ambient Gas Visualized by Laser-Induced Fluorescence Imaging Spectroscopy

    NASA Astrophysics Data System (ADS)

    Sasaki, Koichi; Watarai, Hiroshi

    2006-04-01

    The dynamics of both a laser-ablation plume and ambient gas were studied by visualizing their density distributions by laser-induced fluorescence imaging spectroscopy. A deep dip was formed in the density distribution of the ambient gas. The depth of the dip was almost 100% immediately after irradiation of the ablation laser pulse. The size of the dip expanded with time. At a long delay time after the irradiation of the ablation laser pulse, the ambient gas returned to the dip and slowly filled it. The location of the dip corresponded to that of the plume ejected from the target. This means that the high pressure of the plume removed the ambient gas, and the plume and the ambient gas located exclusively. In addition, we observed the formation and propagation of a compressed layer around the dip.

  9. Diode laser absorption sensors for gas-dynamic and combustion flows

    NASA Technical Reports Server (NTRS)

    Allen, M. G.

    1998-01-01

    Recent advances in room-temperature, near-IR and visible diode laser sources for tele-communication, high-speed computer networks, and optical data storage applications are enabling a new generation of gas-dynamic and combustion-flow sensors based on laser absorption spectroscopy. In addition to conventional species concentration and density measurements, spectroscopic techniques for temperature, velocity, pressure and mass flux have been demonstrated in laboratory, industrial and technical flows. Combined with fibreoptic distribution networks and ultrasensitive detection strategies, compact and portable sensors are now appearing for a variety of applications. In many cases, the superior spectroscopic quality of the new laser sources compared with earlier cryogenic, mid-IR devices is allowing increased sensitivity of trace species measurements, high-precision spectroscopy of major gas constituents, and stable, autonomous measurement systems. The purpose of this article is to review recent progress in this field and suggest likely directions for future research and development. The various laser-source technologies are briefly reviewed as they relate to sensor applications. Basic theory for laser absorption measurements of gas-dynamic properties is reviewed and special detection strategies for the weak near-IR and visible absorption spectra are described. Typical sensor configurations are described and compared for various application scenarios, ranging from laboratory research to automated field and airborne packages. Recent applications of gas-dynamic sensors for air flows and fluxes of trace atmospheric species are presented. Applications of gas-dynamic and combustion sensors to research and development of high-speed flows aeropropulsion engines, and combustion emissions monitoring are presented in detail, along with emerging flow control systems based on these new sensors. Finally, technology in nonlinear frequency conversion, UV laser materials, room

  10. Gas dynamic effects on formation of carbon dimers in laser-produced plasmas

    NASA Astrophysics Data System (ADS)

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

    2011-09-01

    We investigated the effect of helium and nitrogen pressures on the dynamics of molecular species formation during laser ablation of carbon. For producing plasmas, planar carbon targets were irradiated with 1064 nm, 6 ns pulses from an Nd:yttrium aluminum garnet laser. The emission from excited C2 and CN molecules was studied using space resolved optical time-of-flight emission spectroscopy and spectrally resolved fast imaging. The intensity oscillations in C2 and CN monochromatic fast imaging and their emission space-time contours suggest that recombination is the major mechanism of C2 formation within the laser ablation carbon plumes in the presence of ambient gas.

  11. Random Vibration Tests for Prediction of Fatigue Life of Diffuser Structure for Gas Dynamic Laser

    NASA Astrophysics Data System (ADS)

    Maurer, O. F.; Banaszak, D. L.

    1980-01-01

    Static and dynamic strain measurements which were taken during test stand operations of the gas dynamic laser (GDL) for the AF Airborne Laser Laboratory indicated that higher than expected vibrational stress levels may possibly limit the fatigue life of the laser structure. Particularly the diffuser sidewall structure exhibited large amplitude random vibrations which were excited by the internal gas flow. The diffuser structure consists of two layers of brazed stainless steel, AISI-347, panels. Cooling ducts were milled into the outer face sheet. These in turn are backed by the inner face sheet. So called T-rail stiffeners silver-brazed to the outer face sheets add the required stiffness and divide the sidewall into smaller rectangular plate sections.

  12. Dynamics of a laser-produced silver plume in an oxygen background gas

    NASA Astrophysics Data System (ADS)

    Schou, Jorgen; Toftmann, Bo; Amoruso, Salvatore

    2004-09-01

    The expansion of a plasma plume in a background gas is a key problem for film deposition and laser ablation studies. Combined diagnostic measurements of deposition rates and ion time-of-flight (TOF) signals have been used to study the dynamics of a laser ablation plume in an oxygen gas. This study is similar to our previous work on an argon background gas and shows essentially the same trend. At an enhanced gas pressure, the angular distribution of collected ablated atoms becomes comparatively broad, while the total collected yield decreases strongly. The total collected yield exhibits three separate regimes with increasing pressure, a vacuum-like regime, a transition regime with increasing plume broadening and splitting of the ion signal, and at the highest pressures a diffusion-like regime with a broad angular distribution. In the high pressure regime, the expansion can be described by a simple model based on diffusion from a confined plume.

  13. Study of gas-fluidization dynamics with laser-polarized 129Xe.

    PubMed

    Wang, Ruopeng; Rosen, Matthew Scott; Candela, Donald; Mair, Ross William; Walsworth, Ronald Lee

    2005-02-01

    We report initial NMR studies of gas dynamics in a particle bed fluidized by laser-polarized xenon (129Xe) gas. We have made preliminary measurements of two important characteristics: gas exchange between the bubble and emulsion phases and the gas velocity distribution in the bed. We used T2* contrast to differentiate the bubble and emulsion phases by choosing solid particles with large magnetic susceptibility. Experimental tests demonstrated that this method was successful in eliminating 129Xe magnetization in the emulsion phase, which enabled us to observe the time dependence of the bubble magnetization. By employing the pulsed field gradient method, we also measured the gas velocity distribution within the bed. These results clearly show the onset of bubbling and can be used to deduce information about gas and particle motion in the fluidized bed. PMID:15833613

  14. Study of Gas-Fluidization Dynamics with Laser-Polarized 129Xe

    NASA Astrophysics Data System (ADS)

    Wang, R.; Rosen, M. S.; Candela, D.; Mair, R. W.; Walsworth, R. L.

    2004-07-01

    We report initial NMR studies of gas dynamics in a particle bed fluidized by laser-polarized xenon (129Xe) gas. We have made preliminary measurements of two important characteristics: gas exchange between the bubble and emulsion phases; and the gas velocity distribution in the bed. We used T2* contrast to differentiate the bubble and emulsion phases by choosing solid particles with large magnetic susceptibility, in order. Experimental tests demonstrated that this method was successful in eliminating 129Xe magnetization in the emulsion phase, which enabled us to observe the time-dependence of the bubble magnetization. By employing the pulsed field gradient method, we also measured the gas velocity distribution within the bed. These results clearly show the onset of bubbling and can be used to deduce information about gas and particle motion in the fluidized bed.

  15. Rapid estimation of characteristics of gas dynamic lasers

    NASA Technical Reports Server (NTRS)

    Murty, S. S. R.

    1974-01-01

    Sudden-freeze approximation is applied to the flow of a CO2-N2-He mixture in wedge-type nozzles. This approximation permits rapid estimation of the freezing temperature of the upper laser level as a function of the stagnation pressure and the nozzle geometry. The stagnation temperature and the composition of the mixture appear as parameters. Gain and power output may then be estimated and calculations are presented for two cases.

  16. Thermophysical and gas-dynamic characteristics of laser-induced gasplasma flows under femtosecond laser ablation of titanium in vacuum

    NASA Astrophysics Data System (ADS)

    Loktionov, E. Yu; Protasov, Yu S.; Protasov, Yu Yu

    2014-03-01

    We report the results of experimental investigation of thermophysical and gas-dynamic characteristics of the gas-plasma flows induced by ultrashort (45 - 60 fs) laser pulse irradiation (the radiation wavelength λ = 400, 800 nm) of a titanium target in vacuum (~5 × 10-4 mbar). The use of combined interferometric technique and complex experimental data processing allowed us to estimate the momentum coupling coefficient (Cm ~ 10-4 N W-1), the efficiency of laser energy conversion to the kinetic energy of the gas-plasma flow (65% - 85%), the spatiotemporal distributions of the particle density (ne = 1018 - 1020 cm-3) and velocity (langlevrangle=4 - 9 km s-1), the static (106 - 108 Pa) and total (107 - 1011 Pa) pressure and temperature (T=7 - 50 kK) in the flow. Our data are compared with published data obtained by other methods.

  17. Fragmentation dynamics of noble gas dimers in two-color intense laser fields

    NASA Astrophysics Data System (ADS)

    Magrakvelidze, M.; Wu, J.; Doerner, R.; Thumm, U.

    2013-05-01

    We studied the dissociation dynamics of noble gas dimer ions in two-color infrared intense laser fields by analyzing their fragment-kinetic-energy-release spectra as a function of the pump-probe delay. Our calculations predict a striking ``delay gap'' in the kinetic-energy-spectra for all noble gas dimers that was so far only measured for the Ar2 dimer. We identify this phenomenon as a frustrated dissociation mechanism. This mechanism requests different pump- and probe-pulse wavelengths and involves the pump pulse to both, singly ionize the neutral dimers and dipole-couple adiabatic states in the dimer ion. Supported by the US NSF and DOE.

  18. Ablation plume structure and dynamics in ambient gas observed by laser-induced fluorescence imaging spectroscopy

    NASA Astrophysics Data System (ADS)

    Miyabe, M.; Oba, M.; Iimura, H.; Akaoka, K.; Khumaeni, A.; Kato, M.; Wakaida, I.

    2015-08-01

    The dynamic behavior of an ablation plume in ambient gas has been investigated by laser-induced fluorescence imaging spectroscopy. The second harmonic beam from an Nd:YAG laser (0.5-6 J/cm2) was focused on a sintered oxide pellet or a metal chip of gadolinium. The produced plume was subsequently intersected with a sheet-shaped UV beam from a dye laser so that time-resolved fluorescence images were acquired with an intensified CCD camera at various delay times. The obtained cross-sectional images of the plume indicate that the ablated ground state atoms and ions of gadolinium accumulate in a hemispherical contact layer between the plume and the ambient gas, and a cavity containing a smaller density of ablated species is formed near the center of the plume. At earlier expansion stage, another luminous component also expands in the cavity so that it coalesces into the hemispherical layer. The splitting and coalescence for atomic plume occur later than those for ionic plume. Furthermore, the hemispherical layer of neutral atoms appears later than that of ions; however, the locations of the layers are nearly identical. This coincidence of the appearance locations of the layers strongly suggests that the neutral atoms in the hemispherical layer are produced as a consequence of three-body recombination of ions through collisions with gas atoms. The obtained knowledge regarding plume expansion dynamics and detailed plume structure is useful for optimizing the experimental conditions for ablation-based spectroscopic analysis.

  19. Gas phase dynamics of laser-generated nanoparticle populations and its application to nanomaterials fabrication

    NASA Astrophysics Data System (ADS)

    Bulut, Mevlut

    Naturally occurring materials often derive their outstanding properties from optimal anisotropic arrangements of nanoscale constituents. This requires a hierarchical organization of matter over several length scales, which is difficult to achieve in artificial materials made by conventional physical and chemical methods. This dissertation explores the combination of laser and aerosol processes as a novel approach to make thin film materials with a level of microscopic organization similar to that found in nature. Through a systematic investigation of the behavior of the gas-phase dynamics of nanoparticles generated by laser ablation of solid target materials in background gases and a study of the physical processes involved in gas-phase nanoparticle processing, a new instrument integrating a laser ablation source and an aerosol spectrometer was designed and implemented. Film deposition and nanoparticle deposition processes can be manipulated independently affording greater flexibility for materials fabrication than other laser methods. The integrated laser-aerosol method is very flexible and can be used in the synthesis of a variety of materials. In this dissertation it is applied to the deposition of nanocomposite thin films comprising tetrahedral amorphous carbon (ta-C) with embedded metal nanoparticles. The controlled incorporation of metal nanoparticles enables the modulation of the electrical conductivity of ta-C over four orders of magnitude without significantly or adversely affecting its mechanical properties.

  20. Effects of carrier gas dynamics on single wall carbon nanotube chiral distributions during laser vaporization synthesis.

    PubMed

    Landi, Brian J; Raffaelle, Ryne P

    2007-03-01

    We report on the utility of modifying the carrier gas dynamics during laser vaporization synthesis to alter the single wall carbon nanotube (SWNT) chiral distribution. SWNTs produced from an Alexandrite laser using conventional Ni/Co catalysts demonstrate marked differences in chiral distributions due to effects of helium gas and reactor chamber pressure, in comparison to conventional subambient pressures and argon gas. Optical absorption and Raman spectroscopies confirm that the SWNT diameter distribution decreases under higher pressure and with helium gas as opposed to argon. Fluorescence mapping of the raw soots in sodium dodecylbenzene sulfonate (SDBS)-D2O was used to estimate the relative (n, m)-SWNT content of the semiconducting types. A predominance of type II structures for each synthesis condition was observed. The distribution of SWNT chiral angles was observed to shift away from near-armchair configurations under higher pressure and with helium gas. These results illustrate the importance of gas type and pressure on the condensation/cooling rate, which allows for synthesis of specific SWNT chiral distributions. PMID:17450850

  1. Gas-dynamic explosion of water microparticles under action high-power femtosecond laser pulses

    NASA Astrophysics Data System (ADS)

    Zemlyanov, Alexander A.; Geints, Yuri E.; Apeksimov, Dmitrii V.

    2006-02-01

    Among the broad audience of problems of atmospheric nonlinear optics the important place is occupied with a problem about interaction of intensive laser radiation with water microparticles. Drops, being in a field of powerful light radiation, owing to effects of evaporation or explosion change the optical characteristics and influence on the optical properties of an environment. It results to that process and the distribution of intensive laser radiation in a particle is characterized by self-influence and is capable to change the internal power of a drop due to occurrence of areas of optical breakdown. In the report the model of destruction of water microparticles under action of supershort laser radiation is submitted. The physical contents of model is the effect of shock boiling up of a liquid at it gas-dynamic expansion from areas subject to optical breakdown.

  2. Laser studies of chemical dynamics at the gas-solid interface

    NASA Astrophysics Data System (ADS)

    Cavanagh, Richard R.; King, David S.

    The DOE funded research program Laser Studies of Chemical Dynamics at the Gas-Solid Interface has taken a detailed, microscopic view of molecules desorbed from surfaces in order to gain an understanding of energy flow and interaction potentials and how these control chemical reactivity at interfaces. Successful completion of these experiments required technical expertise both in surface science and laser-based molecular dynamics, a collaborative situation that exists in the NIST center for Atomic, Molecular and Optical Physics. During the three year period covered by this progress report, our goal was to use state-resolved techniques to examine a single chemisorption system in detail, and to observe how changes in the interaction potential or method of surface excitation are manifest in the desorption dynamics. The system chosen was NO/Pt(111). Studies were undertaken in which the effects on the NO-Pt interaction potential of coadsorbates--both weakly (CO) and strongly (NH(sub 3)) interacting-- could be examined. In addition, attempts were to be made to study non- equilibrium dynamics by using pulsed laser heating.

  3. Combined thermal and gas dynamics numerical model for laser ablation of carbon.

    PubMed

    Pathak, Kedar; Mullenix, Nathan; Povitsky, Alex

    2006-05-01

    One of the major methods of production of carbon nanotubes is the laser ablation process. In this process, a powerful nanosecond-scale laser beam illuminates a target. The resulting explosion produces a plume of rapidly expanding gaseous carbon with embedded metallic catalysts, on whose surfaces the nanotubes are formed. The time-scale of a single laser pulse is of the order of nanoseconds whereas the plume development and growth of nanotubes take up to several milliseconds. The synthesis process largely depends on the plume properties, i.e., on the temperature, pressure, and density of the expanding plume. In turn, the plume propagation depends on the ablation speed, pressure, and density. In the current study, a combined thermal and gas dynamics model is proposed, implemented and tested. The proposed model is based on combined conduction heat transfer within the solid target, carbon sublimation process described by equilibrium thermodynamics, and process of plume development described by continuous gas dynamics. The carbon sublimation model is based on Clausius-Clapeyron equation and conservation of energy for differential control volume. The parameters of the injected plume are defined by this thermal model. The validity of viscous and inviscid models of plume dynamics is discussed. The ability of finite-volume discretizations to capture the plume dynamics and its roll-up is compared for various numerical schemes. To evaluate the accuracy of numerical modeling of plume dynamics, we compare finite-volume discretization based on Relaxing TVD scheme with that based on the upwind scheme with Roe averaging at the cell interface and non-linear ENO scheme for second-order flux formulas. PMID:16792353

  4. Particle dynamics during nanoparticle synthesis by laser ablation in a background gas

    NASA Astrophysics Data System (ADS)

    Nakata, Yoshiki; Muramoto, Junichi; Okada, Tatsuo; Maeda, Mitsuo

    2002-02-01

    Particle dynamics during Si nanoparticle synthesis in a laser-ablation plume in different background gases were investigated by laser-spectroscopic imaging techniques. Two-dimensional laser induced fluorescence and ultraviolet Rayleigh scattering techniques were used to visualize the spatial distribution of the Si atoms and nanoparticles grown, respectively. We have developed a visualization technique called re-decomposition laser-induced fluorescence to observe small nanoparticles (hereafter called clusters) which are difficult to observe by the conventional imaging techniques. In this article, the whole process of nanoparticle synthesis in different background gases of He, Ne, Ar, N2 and O2 was investigated by these techniques. In He, Ne, Ar and N2 background gases at 10 Torr, the clustering of the Si atoms started 200, 250, 300 and 800 μs after ablation, respectively. The growth rate of the clusters in He background gas was much larger than that in the other gases. The spatial distributions of the Si nanoparticles were mushroom like in He, N2 and O2, and column like in Ne and Ar. It is thought that the difference in distribution was caused by differences in the flow characteristics of the background gases, which would imply that the viscosity of the background gas is one of the main governing parameters.

  5. Monte Carlo Simulation of Laser-Ablated Particle Splitting Dynamic in a Low Pressure Inert Gas

    NASA Astrophysics Data System (ADS)

    Ding, Xuecheng; Zhang, Zicai; Liang, Weihua; Chu, Lizhi; Deng, Zechao; Wang, Yinglong

    2016-06-01

    A Monte Carlo simulation method with an instantaneous density dependent mean-free-path of the ablated particles and the Ar gas is developed for investigating the transport dynamics of the laser-ablated particles in a low pressure inert gas. The ablated-particle density and velocity distributions are analyzed. The force distributions acting on the ablated particles are investigated. The influence of the substrate on the ablated-particle velocity distribution and the force distribution acting on the ablated particles are discussed. The Monte Carlo simulation results approximately agree with the experimental data at the pressure of 8 Pa to 17 Pa. This is helpful to investigate the gas phase nucleation and growth mechanism of nanoparticles. supported by the Natural Science Foundation of Hebei Province, China (No. A2015201166) and the Natural Science Foundation of Hebei University, China (No. 2013-252)

  6. Dissociation dynamics of noble-gas dimers in intense two-color IR laser fields

    NASA Astrophysics Data System (ADS)

    Magrakvelidze, M.; Thumm, U.

    2013-07-01

    We numerically model the dissociation dynamics of the noble-gas dimer ions He2+, Ne2+, Ar2+, Kr2+, and Xe2+ in ultrashort pump and probe laser pulses of different wavelengths. Our calculations reveal a distinguished “gap” in the kinetic energy spectra, observed experimentally for the Ar2 dimer [J. Wu , Phys. Rev. Lett.PRLTAO0031-900710.1103/PhysRevLett.110.033005 110, 033005 (2013)], for all noble-gas dimers for appropriate wavelength combinations. This striking phenomenon can be explained by the dissociation of dimer ions on dipole-coupled Born-Oppenheimer adiabatic potential curves. Comparing pump-probe-pulse-delay-dependent kinetic-energy-release spectra for different noble-gas dimer cations of increasing mass, we discuss increasingly prominent (i) fine-structure effects in and (ii) classical aspects of the nuclear vibrational motion.

  7. Ionization-induced dynamics of ultrashort laser pulses focused in a dense gas

    NASA Astrophysics Data System (ADS)

    Efimenko, E. S.; Kim, A. V.; Quiroga-Teixeiro, M.

    2009-10-01

    In the present paper we address several aspects of ionization-induced laser-gas interaction. First, we consider the ionization dynamics of an ultrashort laser pulse in the presence of additional electromagnetic perturbations, and show theoretically via dispersion relation analysis and numerically via 2D FDTD simulation that ionizationinduced scattering can occur even in the case of limited spatial and temporal scales and significantly affects pulse dynamics. Second, for the case of tight focusing of laser beam we show on the basis of numerical simulation that for 2D TE- and TM-polarized pulses there is a critical angle which delimits two qualitatively different regimes. For angles exceeding the critical one, the formed plasma distribution may become microstructured, otherwise the plasma structures are smooth. It is also shown than the critical angle and plasma-field dynamics depend significantly on pulse spectrum. Finally, we consider the impact of the electron collisions and Kerr nonlinearity and determine the boundaries within which the role of these effects is crucial.

  8. Probing laser induced metal vaporization by gas dynamics and liquid pool transport phenomena

    SciTech Connect

    DebRoy, T.; Basu, S.; Mundra, K. )

    1991-08-01

    During laser beam welding of many important engineering alloys, an appreciable amount of alloying element vaporization takes place from the weld pool surface. As a consequence, the composition of the solidified weld pool is often significantly different from that of the alloy being welded. Currently there is no comprehensive theoretical model to predict, from first principles, laser induced metal vaporization rates and the resulting weld pool composition changes. The weld pool heat transfer and fluid flow phenomena have been coupled with the velocity distribution functions of the gas molecules at various locations above the weld pool to determine the rates of the laser induced element vaporization for pure metals. The procedure allows for calculations of the condensation flux based on the equations of conservation of mass, momentum and energy in both the vapor and the liquid phases. Computed values of the rates of vaporization of pure metals were found to be in good agreement with the corresponding experimentally determined values. The synthesis of the principles of gas dynamics and weld pool transport phenomena can serve as a basis for weld metal composition control.

  9. Experimental investigation of the dynamics of laser-induced gas-plasma flows under femtosecond laser ablation of copper in vacuum

    NASA Astrophysics Data System (ADS)

    Loktionov, E. Yu.; Protasov, Yu. S.; Protasov, Yu. Yu.

    2013-11-01

    Thermophysical and gas-dynamic characteristics of gas-plasma flows induced by ultrashort laser pulses interacting with a thin-film copper target in vacuum were studied experimentally. Using combined laser interferometry and complex processing of experimental data, we estimated the momentum coupling coefficient and the efficiency of laser-energy conversion to kinetic energy, spatiotemporal distributions of the number density and velocities of particles, pressure, and temperature in the gas-plasma flow. We provide comparative analysis of presented data with those found in the literature, which were obtained by other methods.

  10. Molecular dynamics study of nanoparticle evolution in a background gas under laser ablation conditions

    NASA Astrophysics Data System (ADS)

    Gouriet, K.; Zhigilei, L. V.; Itina, T. E.

    2009-03-01

    Long-time evolution of nanoparticles produced by short laser interactions is investigated for different materials. To better understand the mechanisms of the nanoparticle formation at a microscopic level, we use molecular dynamics (MD) simulations to analyse the evolution of a cluster in the presence of a background gas with different parameters (density and temperature). In particular, we compare the simulation results obtained for materials with different interaction potentials (Morse, Lennard-Jones, and Embedded Atom Model). Attention is focused on the evaporation and condensation processes of a cluster with different size and initial temperature. As a result of the MD calculations, we determinate the influence of both cluster properties and background gas parameters on the nanoparticle evolution. The role of the interaction potential is discussed based on the results of the simulations.

  11. Dynamic processes in active medium of small diameter gas discharge lasers

    NASA Astrophysics Data System (ADS)

    Schishov, S. I.

    2008-03-01

    Review of electrodynamics properties for gas discharge lasers of small diameter has been completed with consideration of inertia typical for ionisation processes and transient nature of electron diffusion from unipolar to ambipolar. Procedure for calculation of transfer function and elements of equivalent electrical circuit for substitution of gas discharge laser discharge space.

  12. Propagation dynamics of femtosecond laser pulses in a hollow fiber filled with argon: constant gas pressure versus differential gas pressure

    NASA Astrophysics Data System (ADS)

    Nurhuda, Muhammad; Suda, Akira; Midorikawa, Katsumi; Hatayama, Masatoshi; Nagasaka, Keigo

    2003-09-01

    We investigate the dynamics of femtosecond laser pulses propagating in a hollow fiber filled with argon, through a full numerical solution of the nonlinear Schrödinger equation. The simulation results show that, if the intensity is low and no ionization takes place, the spatial profile of the beam does not change very much so that its propagation model may be simplified to a one-dimensional model. If the intensity is high and ionization takes place, the spatial dynamics as well as temporal dynamics become very complicated because of self-focusing and defocusing. It is found that, for the same value of the B integral, self-focusing inside a hollow fiber can be substantially suspended by a differential gas pressure technique, where the gas pressure is set to be a minimum at the entrance and then increased with the propagation distance. Numerical simulations show that using such a technique, the energy transmitted during propagation inside hollow fiber is significantly enhanced, and the spatial phase is also improved.

  13. Particle Dynamics in Neutral-Gas Confined Laser-Produced Plasmas

    NASA Astrophysics Data System (ADS)

    Kim, Yong W.

    2001-10-01

    Laser-produced plasma from a metallic target can be confined to higher plasma densities by immersing the target in an inert gas medium at increasingly high density. The plasma becomes Rayleigh-Taylor unstable, however, when the mass density of the neutral gas exceeds the plasma mass density substantially.[1] A new plasma diagnostic method is developed to help examine the early time development of the gas-plasma interfacial structure. A preliminary study based on plasma polarization spectroscopy is presented, in which the dynamics of atoms and ions are visualized in the presence of electromagnetic fields due to charge separation. The ambient gas pressure of argon is varied as active control in the low-pressure regime. Time-resolved multi-directional projections of an aluminum plasma are obtained in line and continuum emissions, polarization and spectral broadening including Doppler shifts. The electrostatic potential of the target is also followed. The results indicate a bifurcation of the phase-space distribution function and structural segmentation of the plasma into a thermalized core and a crown with highly aligned, energetic atoms and ions. Reconstruction of the plasma structure appears possible by generalization of the two new algorithms we have developed.[1,2] 1. Y.W. Kim and J.-C. Oh, Rev. Sci. Inst. 72, 948 (2001). 2. Y.W. Kim and C.D. Lloyd-Knight, Rev. Sci. Inst. 72, 944 (2001).

  14. Experimental and Numerical Analysis of Gas Dynamics in the Keyhole During Laser Metal Welding

    NASA Astrophysics Data System (ADS)

    Tenner, Felix; Brock, Christian; Gürtler, Franz-Josef; Klämpfl, Florian; Schmidt, Michael

    The keyhole is the crucial factor for an appropriate weld seam in laser metal welding. The stability of the keyhole is governed by multiple hydrodynamic effects such as melt flow, evaporation on the keyhole front, gas dynamics inside the evolving vapor plume and the resulting pressures from all these phenomena. Due to their elusive nature the measurement of pressures inside the keyhole is still an unresolved task. Here we show a quantification of the density of the metal vapor and the pressure inside the keyhole through measuring the keyhole opening geometry, the evaporation rate and the flow velocity inside the vapor plume. Furthermore, a comparison to a simulation model is shown. Our results are in accordance with theoretical approaches. In the future this results can support an increase of process understanding which eventually leads to a better control of the process in industry.

  15. Numerical analysis of supersonic gas-dynamic characteristic in laser cutting

    NASA Astrophysics Data System (ADS)

    Guo, Shaogang; Jun, Hu; Lei, Luo; Yao, Zhenqiang

    2009-01-01

    The influence of the processing parameters on the dynamic characteristic of supersonic impinging jet in laser cutting is studied numerically. The numerical modeling of a supersonic jet impinging on a plate with a hole is presented to analyze the gas jet-workpiece interaction. The model is able to make quantitative predictions of the effect of the standoff distance and exit Mach number on the mass flow rate and the axial thrust. The numerical results show that the suitable cutting range is slightly different for different exit Mach number, but the optimal cutting parameter for certain exit total pressure is nearly changeless. So the better cut quality and capacity can be obtained mainly by setting the suitable standoff distance for a certain nozzle pressure.

  16. Exploration of pulse timing for multiple laser hits within a combined heat transfer, phase change, and gas dynamics model for laser ablation

    NASA Astrophysics Data System (ADS)

    Mullenix, Nathan; Povitsky, Alex

    2007-05-01

    Laser ablation involves heat transfer, phase changes and/or chemical reactions, and gas dynamics. All three of these processes are tightly coupled with each other. A model has previously been developed to simulate the nanosecond scale laser ablation of carbon. This model has been extended to accommodate longer term simulations and multiple laser pulses. The effects of varying the timing of a second laser pulse by tens of nanoseconds are explored. It is shown that by changing this interval one can control the total mass ablated and the mass transfer rate.

  17. Dynamics of rare gas nanoclusters irradiated by short and intense laser pulses

    NASA Astrophysics Data System (ADS)

    Micheau, S.; Bonté, C.; Dorchies, F.; Fourment, C.; Harmand, M.; Jouin, H.; Peyrusse, O.; Pons, B.; Santos, J. J.

    2007-05-01

    We report on a joint experimental-theoretical effort to shed light on the dynamics of rare gas (Ar) nanoclusters irradiated by short and intense laser pulses. The experiments employ a streak camera coupled to a conical crystal to yield energy- and time-resolved X-ray spectra, in the keV range on picosecond scale. These spectra display ultrafast subpicosecond ionization dynamics, leading to highly charged states such as Ar 16+, and indicate that the duration of the energetic X-rays is less than the experimental 1.3 ps temporal resolution. The theoretical calculations rely on the well-known nanoplasma model, which has been improved to represent the collisional ionization processes that are of importance in nanoplasma dynamics. Allowance is made for high-order ionization transitions involving intermediate excited states. The simulations indicate significant populations of excited states of highly charged ions, in agreement with the experimental findings. Further, detailed collisional-radiative calculations indicate that the duration of the X-ray bursts is less than 100 fs.

  18. Experimental investigation of the structure and the dynamics of nanosecond laser-induced plasma in 1-atm argon ambient gas

    NASA Astrophysics Data System (ADS)

    Ma, Qianli; Motto-Ros, Vincent; Bai, Xueshi; Yu, Jin

    2013-11-01

    We have investigated the structure and the dynamics of the plasma induced on a metallic target in 1-atm argon ambient by a nanosecond laser pulse with irradiance in the range of 10 GW/cm2. The structure is revealed to be sensitively dependent on the laser wavelength. A layered structure of different species characterizes the plasma induced by ultraviolet 355 nm pulse, while an effective mixing between the ablation vapor and the shocked ambient gas is observed with infrared 1064 nm pulse. The absorption property of the shocked gas is found to be crucial for determining the structure of the plasma.

  19. Pressure wave charged repetitively pulsed gas laser

    DOEpatents

    Kulkarny, Vijay A.

    1982-01-01

    A repetitively pulsed gas laser in which a system of mechanical shutters bracketing the laser cavity manipulate pressure waves resulting from residual energy in the cavity gas following a lasing event so as to draw fresh gas into the cavity and effectively pump spent gas in a dynamic closed loop.

  20. Dynamics of dielectric barrier discharge in non-uniform gas composition investigated by laser spectroscopic measurements

    NASA Astrophysics Data System (ADS)

    Urabe, Keiichiro; Ito, Yosuke; Choi, Joon-Young; Sakai, Osamu; Tachibana, Kunihide

    2009-10-01

    It is well known that stable and glow dielectric barrier discharge (DBD) at atmospheric pressure is observed using helium gas and AC high voltage of kHz-order frequency. We have investigated the discharge mechanisms of DBDs from a view point of the spatiotemporal distributions of excited species measured by laser spectroscopic methods. In this presentation, we will show convincing arguments about the discharge model of the DBD especially having the non-uniformity of gas composition. As a DBD plasma source for atmospheric pressure processes, we have investigated an atmospheric pressure plasma jet (APPJ) using helium gas flow in ambient air, and this plasma source can be regarded as the DBD near the boundary interface of helium gas and ambient air. In this APPJ, we observed spatiotemporal distributions of excited species density inside the helium gas channel, using laser absorption spectroscopy and laser induced fluorescence, to measure the densities of helium metastable atom (2^3S1 state) and nitrogen ion (X^2σg^+ state) respectively. To study the influence of nitrogen gas contamination on the discharge profile of DBD, we have also applied CO2-laser heterodyne interferometry to measure the special distribution of electron density in parallel-plate DBD.

  1. Start-phase ionization dynamics in the laser plasma at low gas target densities

    NASA Astrophysics Data System (ADS)

    Belik, V. P.; Demidov, R. A.; Kalmykov, S. G.; Mozharov, A. M.; Petrenko, M. V.; Sasin, M. E.

    2013-12-01

    In Xe laser-produced-plasma sources of short-wave radiation, the laser-energy-to-EUV conversion efficiency (CE) proves substantially less than theoretical expectations. In the present work, a calculated estimate has been made which indicates that a long period of the primary ionization, lasting up to a moment when high-Z ions appear to emit short-wave photons, can be one of main causes for this. During that period the plasma remains low-ionized and absorbs weakly the laser energy. The estimate above has been experimentally confirmed with spectroscopic data and those on the effective ion charge derived from measured absorption of the laser radiation in the plasma. A preionization of the gas target with an ultraviolet (UV) excimer laser pulse is proposed as a method to accelerate the ionization process and consequently, to enhance CE.

  2. Ionization dynamics in the laser plasma in a low pressure gas target

    NASA Astrophysics Data System (ADS)

    Demidov, R. A.; Kalmykov, S. G.; Mozharov, A. M.; Petrenko, M. V.; Sasin, M. E.

    2012-11-01

    In Xe-laser-plasma short-wave-radiation sources, the laser-energy-to-EUV conversion efficiency (CE) turns out to be substantially lower than theoretical expectations. An estimation made in the present work is evidence of what a long period of the primary ionization, lasting up to a moment when high- Z ions appear to emit short-wave photons, can be considered as a main cause for the low CE values. During that period the plasma remains low-ionized and absorbs weakly the laser energy. Data deduced from laser light absorption measurements confirm the estimation above. A preionization of the gas target with the UV excimer laser pulse is proposed as a method to accelerate the ionization process.

  3. Three-dimensional-printed gas dynamic virtual nozzles for x-ray laser sample delivery.

    PubMed

    Nelson, Garrett; Kirian, Richard A; Weierstall, Uwe; Zatsepin, Nadia A; Faragó, Tomáš; Baumbach, Tilo; Wilde, Fabian; Niesler, Fabian B P; Zimmer, Benjamin; Ishigami, Izumi; Hikita, Masahide; Bajt, Saša; Yeh, Syun-Ru; Rousseau, Denis L; Chapman, Henry N; Spence, John C H; Heymann, Michael

    2016-05-30

    Reliable sample delivery is essential to biological imaging using X-ray Free Electron Lasers (XFELs). Continuous injection using the Gas Dynamic Virtual Nozzle (GDVN) has proven valuable, particularly for time-resolved studies. However, many important aspects of GDVN functionality have yet to be thoroughly understood and/or refined due to fabrication limitations. We report the application of 2-photon polymerization as a form of high-resolution 3D printing to fabricate high-fidelity GDVNs with submicron resolution. This technique allows rapid prototyping of a wide range of different types of nozzles from standard CAD drawings and optimization of crucial dimensions for optimal performance. Three nozzles were tested with pure water to determine general nozzle performance and reproducibility, with nearly reproducible off-axis jetting being the result. X-ray tomography and index matching were successfully used to evaluate the interior nozzle structures and identify the cause of off-axis jetting. Subsequent refinements to fabrication resulted in straight jetting. A performance test of printed nozzles at an XFEL provided high quality femtosecond diffraction patterns. PMID:27410079

  4. Laser-induced gas vortices.

    PubMed

    Steinitz, Uri; Prior, Yehiam; Averbukh, Ilya Sh

    2012-07-20

    Recently, several femtosecond-laser techniques have demonstrated molecular excitation to high rotational states with a preferred sense of rotation. We consider collisional relaxation in a dense gas of such unidirectionally rotating molecules, and suggest that due to angular momentum conservation, collisions lead to the generation of macroscopic vortex gas flows. This argument is supported using the Direct Simulation Monte Carlo method, followed by a computational gas-dynamic analysis. PMID:22861845

  5. Time- and Frequency-Dependent Imaging of Nuclear Dynamics in Laser-Excited Nobel-Gas Dimers

    NASA Astrophysics Data System (ADS)

    Magrakvelidze, M.; Kramer, A.; Bartschat, K.; Thumm, U.

    2014-05-01

    We study the nuclear dynamics of noble-gas dimer ions resolved in time using intense ultrashort pump in combination with delayed probe laser pulses. We compare our time-dependent numerical results with those from a complementary description of the same basic dynamics in the frequency domain. This alternative analysis is based on the Fourier transformation of the time- and internuclear-separation-dependent wavefunction probability density or, equivalently, the Fourier transformation of the delay-dependent kinetic-energy-release spectra. Specifically, for pump-laser excited diatomic molecules, it allows for the characterization of their nuclear motion in terms of coherently superimposed stationary vibrational states and the mapping of the laser-dressed nuclear potential curves, thereby supplementing the time-domain formulation, as we will demonstrate for the sequence He2+ to Xe2+ of dimer cations.

  6. Influence of gas-dynamic and energy parameters on form of laser cutting

    NASA Astrophysics Data System (ADS)

    Sudnik, W. A.; Pavele, L. A.

    2006-01-01

    A research on the laser cut formation by means of a physico-mathematical model and software is presented. The processes of energy absorption, chemical reactions, and vaporization in the film under the supersonic gas flow forces, accounting for the compression shocks along the front, are analyzed.

  7. Electron dynamics in strong laser pulse illumination of large rare gas clusters

    NASA Astrophysics Data System (ADS)

    Saalmann, U.; Rost, J. M.

    2005-11-01

    We analyze the dynamics of up to 105 electrons resulting from illuminating a xenon cluster with 9093 atoms with intense laser pulses of different length and peak intensity. Interesting details of electron motion are identified which can be probed with a time resolution of 100 attoseconds. Corresponding experiments would shed light on unexplored territory in complex electronic systems such as clusters and they would also permit to critically access the present theoretical description of this dynamics.

  8. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2014-04-01

    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.

  10. Dynamic mechanism of the velocity splitting of ablated particles produced by pulsed-laser deposition in an inert gas

    NASA Astrophysics Data System (ADS)

    Ding, X. C.; Wang, Y. L.; Chu, L. Z.; Deng, Z. C.; Liang, W. H.; Galalaldeen, I. I. A.; Fu, G. S.

    2011-12-01

    The transport dynamics of ablated particles produced by pulsed-laser deposition in an inert gas is investigated via the Monte Carlo simulation method. The splitting mechanism of ablated particles is discussed by tracking every ablated particle with their forces, velocities and locations. The force analysis demonstrates that whether the splitting appears or not is decided by the releasing way of the driving force acting on the ablated particles. The "average" drag force, which is related to the mass and radius of the ambient gas, determines the releasing way of the driving force. Our simulated results are approximately in agreement with the previous experimental data.

  11. Pulsed gas laser

    DOEpatents

    Anderson, Louis W.; Fitzsimmons, William A.

    1978-01-01

    A pulsed gas laser is constituted by Blumlein circuits wherein space metal plates function both as capacitors and transmission lines coupling high frequency oscillations to a gas filled laser tube. The tube itself is formed by spaced metal side walls which function as connections to the electrodes to provide for a high frequency, high voltage discharge in the tube to cause the gas to lase. Also shown is a spark gap switch having structural features permitting a long life.

  12. Gas dynamic effect in high energy fluid diode pumped alkali vapor laser

    NASA Astrophysics Data System (ADS)

    Xu, Yao; Li, Wenyu; Wang, Hongyan; Yang, Zining; Xu, Xiaojun

    2012-11-01

    In this paper, a simple one dimensional heated flow analysis model and 3-D finite volume method (FVM) is set to discuss the real gas dynamic effect in FDPAL. We found that huge amount of waste heat deposited in extreme compact volume size will notably affect active medium's local velocity, temperature and the density distribution along flow direction, and would accordingly affect pump beam's absorption and change optimized lasing conditions, hence, a comprehensive model incorporate gas dynamic effect should be built for DPAL's next stage development. We further proposed that expanding fluid channel may be a choice to increase optical thickness along pumping direction and alleviate this effect.

  13. Plasma species dynamics in a laser produced carbon plasma expanding in low pressure neutral gas background

    NASA Astrophysics Data System (ADS)

    Ruiz, H. M.; Guzmán, F.; Favre, M.; Bhuyan, H.; Chuaqui, H.; Wyndham, E.

    2012-06-01

    We present time and space resolved spectroscopic observations of a laser produced carbon plasma, in an argon background. An Nd:YAG laser pulse, 370 mJ, 3.5 ns, at 1.06 μm, with a fluence of 6.8 J/cm2, is used to produce a plasma from a solid graphite target, at a base pressure of 0.5 mTorr, and with 80 mTorr Argon background. The spectral emission in the visible is recorded with 15 ns time resolution. 20 ns time resolution plasma imagining, filtered at characteristic carbon species emission wavelengths, is used to study the dynamics of the expanding plasma. Two different fronts with ionic or molecular compositions are seen to detach from de laser target plasma.

  14. Effects of collision between two plumes on plume expansion dynamics during pulsed laser ablation in background gas

    NASA Astrophysics Data System (ADS)

    Umezu, Ikurou; Sakamoto, Naomichi; Fukuoka, Hiroshi; Yokoyama, Yasuhiro; Nobuzawa, Koichiro; Sugimura, Akira

    2013-03-01

    Si and Ge targets were simultaneously irradiated by individual two pulsed lasers, and two plumes from the targets were collided head-on with expectation to prepare hybrid nanoparticles. We investigate effects of He background gas pressure on plume collision dynamics. Three characteristic behaviors of plume expansion dynamics are observed at low, middle, and high background gas pressure regions. Interaction between the two atomic species during plume expansion was small and the effect of collision was hardly observed at a low background gas pressure, 130 Pa, while spatial evolution of the plume was suppressed at middle pressure, 270 Pa, due to collision of the two plumes. At high pressure, 2700 Pa, plume expansion is suppressed by background gas and the effect of a direct collision of two plumes was small. These results indicate that plume collision dynamics, which governs nanoparticle formation, and the mixture of Si and Ge species can be varied by background gas pressure. The deposit near the center of two targets was nanoparticles that were composed of Si and Ge.

  15. Deposition dynamics of droplet-free Si nanoparticles in Ar gas using laser ablation

    NASA Astrophysics Data System (ADS)

    Takeuchi, D.; Mizuta, T.; Makimura, T.; Yoshida, S.; Fujita, M.; Hata, K.; Shigekawa, H.; Murakami, K.

    2002-09-01

    Droplet-free deposition of Si nanoparticle films has been studied applying time-resolved imaging of Si nanoparticles formed by laser ablation of Si targets in Ar gas. We found that Si nanoparticles can be deposited not only on substrates facing to the targets but also on substrates placed beside the target. We further confirmed using a scanning tunneling microscope (STM), Si nanoparticles with sizes of 5-8 nm are deposited on substrates placed beside the target and using a scanning electron microscope (SEM) on the substrates, no droplets are observed.

  16. Ambient gas effects on the dynamics of laser-produced tin plume expansion

    NASA Astrophysics Data System (ADS)

    Harilal, S. S.; O'Shay, Beau; Tao, Yezheng; Tillack, Mark S.

    2006-04-01

    Controlling the debris from a laser-generated tin plume is one of the prime issues in the development of an extreme ultraviolet lithographic light source. An ambient gas that is transparent to 13.5 nm radiation can be used for controlling highly energetic particles from the tin plume. We employed a partial ambient argon pressure for decelerating various species in the tin plume. The kinetic energy distributions of tin species were analyzed at short and large distances using time and space resolved optical emission spectroscopy and a Faraday cup, respectively. A fast-gated intensified charged coupled device was used for understanding the hydrodynamics of the plume's expansion into argon ambient. Our results indicate that the tin ions can be effectively mitigated with a partial argon pressure ~65 mTorr. Apart from thermalization and deceleration of plume species, the addition of ambient gas leads to other events such as double peak formation in the temporal distributions and ambient plasma formation.

  17. High-power supersonic chemical lasers: gas-dynamic problems of operation of mobile systems with PRS

    NASA Astrophysics Data System (ADS)

    Boreysho, A. S.; Malkov, V. M.; Savin, A. V.

    2008-10-01

    Supersonic chemical lasers, such as HF /DF and COIL, have always been in the focus of special interest as the most powerful sources of continuous wave generation. Presently, autonomous mobile laser complexes (both air- and landbased) are being developed on the basis of SCL [1-3]. It is commonly accepted that SCL appeared, conditionally speaking, at the crossroads of a number of sciences: of physics - quantum electronics and physical kinetics; chemistry - combustion theory and chemical kinetics; classic optics - theory of resonators, aero-optics, and gas dynamics (there is a supersonic flow in the SCL channel). Due to this fact, all tasks and problems which could be resolved in the course of SCL development have complex character and could be considered as the next stage of complexity in comparison with the well known similar tasks which had been considered earlier. This is why they should be resolved anew with consideration of the specific aspects of the SCL processes. This is true for the gas-dynamic problems: new parameter areas, non-traditional channel geometry, consideration of new phenomena, etc.Supersonic chemical lasers, such as HF /DF and COIL, have always been in the focus of special interest as the most powerful sources of continuous wave generation. Presently, autonomous mobile laser complexes (both air- and landbased) are being developed on the basis of SCL [1-3]. It is commonly accepted that SCL appeared, conditionally speaking, at the crossroads of a number of sciences: of physics - quantum electronics and physical kinetics; chemistry - combustion theory and chemical kinetics; classic optics - theory of resonators, aero-optics, and gas dynamics (there is a supersonic flow in the SCL channel). Due to this fact, all tasks and problems which could be resolved in the course of SCL development have complex character and could be considered as the next stage of complexity in comparison with the well known similar tasks which had been considered earlier

  18. Polarization-phase dynamics in a four-frequency gas ring laser with elliptical polarization of counter-propagating waves

    NASA Astrophysics Data System (ADS)

    Svirina, L. P.

    2006-09-01

    Based on a developed and experimentally tested model, self-oscillatory lasing regimes have been studied for a Class A four-frequency gas ring laser with linear coupling of elliptically polarized counter-propagating waves. In the self-oscillatory regime, switching of the intensities, polarization states, and phase differences of the counter-propagating waves is observed, and also a polarization-phase dynamics effect involving displacement of the intensity switching point (with respect to detuning), due to the phase shift as a result of an ellipticity different from zero.

  19. A Newly Developed Large Diameter Diaphragmless Shock Tube for Studies on CO2-N2 Gas-Dynamic Laser

    NASA Astrophysics Data System (ADS)

    Rêgo, Israel Da Silveira; Sato, Kohnosuke; Miyoshi, Yoriaki; Ando, Taketora; Goto, Kentaro; Sakamoto, Mizuki; Kawasaki, Shoji; TRIAM Exp. Group

    A large diameter diaphragmless shock tube has been recently developed and designed to perform detailed studies of CO2-N2 gas-dynamic laser (GDL). This large diameter diaphragmless shock tube offers various advantages over the conventional shock tubes (diaphragm-type) as longer test times, higher degree of reproducibility of shock-tube data, and especially low-impurity operation condition. The latter advantage is experimentally demonstrated herein, which is very critical issue in the CO2-N2 GDL studies. A supersonic nozzle section was mounted at the end wall of the shock tube and instrumented for simultaneous measurement of laser output power and energy. The GDL action in a CO2-N2 mixture under low impurity condition has been obtained by using the large diameter diaphragmless shock tube for the first time.

  20. Influence of surrounding gas, composition and pressure on plasma plume dynamics of nanosecond pulsed laser-induced aluminum plasmas

    NASA Astrophysics Data System (ADS)

    Dawood, Mahmoud S.; Hamdan, Ahmad; Margot, Joëlle

    2015-10-01

    In this article, we present a comprehensive study of the plume dynamics of plasmas generated by laser ablation of an aluminum target. The effect of both ambient gas composition (helium, nitrogen or argon) and pressure (from ˜5 × 10-7 Torr up to atmosphere) is studied. The time- and space- resolved observation of the plasma plume are performed from spectrally integrated images using an intensified Charge Coupled Device (iCCD) camera. The iCCD images show that the ambient gas does not significantly influence the plume as long as the gas pressure is lower than 20 Torr and the time delay below 300 ns. However, for pressures higher than 20 Torr, the effect of the ambient gas becomes important, the shortest plasma plume length being observed when the gas mass species is highest. On the other hand, space- and time- resolved emission spectroscopy of aluminum ions at λ = 281.6 nm are used to determine the Time-Of-Flight (TOF) profiles. The effect of the ambient gas on the TOF profiles and therefore on the propagation velocity of Al ions is discussed. A correlation between the plasma plume expansion velocity deduced from the iCCD images and that estimated from the TOF profiles is presented. The observed differences are attributed mainly to the different physical mechanisms governing the two diagnostic techniques.

  1. Gas dynamic and time resolved imaging studies of single-wall carbon nanotubes growth in the laser ablation process

    NASA Astrophysics Data System (ADS)

    Sen, Rahul; Suzuki, S.; Kataura, H.; Achiba, Y.

    2001-10-01

    Single-wall carbon nanotubes (SWNTs) were synthesized by laser ablation of Ni-Co-graphite composite targets at 1200 °C under flowing argon. The effects of the temperature gradient near the target and the gas flow rate on the diameter distribution of SWNTs were studied in order to understand their growth dynamics. The diameter distribution of the SWNTs, analyzed by Raman spectroscopy, was dependent on the gas flow rate when there was a temperature gradient around the target. Time resolved scattering images from the ablated species at different flow rates indicated that velocities of backward moving species increased with increasing flow rate. These findings are used to estimate the time required for nucleation and the growth of SWNTs.

  2. Laser-driven rotational dynamics of gas-phase molecules: Control and applications

    NASA Astrophysics Data System (ADS)

    Ren, Xiaoming

    In this thesis, our work on developing new techniques to measure and enhance field-free molecular alignment and orientation is described. Non-resonant femtosecond laser pulses are used to align and orient rotationally-cold gas-phase molecules. The time-dependent Schrodinger equation is solved to simulate the experimental results. A single-shot kHz velocity map imaging (VMI) spectrometer is developed for characterizing 1D and 3D alignment. Stimulated by a novel metric for 3D alignment proposed by Makhija et al. [Phys. Rev. A 85,033425 (2012)], a multi-pulse scheme to improve 3D alignment is demonstrated experimentally on difluoro-iodobenzene molecules and the best field-free 3D alignment is achieved. A degenerate four wave mixing probe is developed to overcome limitations in VMI measurement; experiments on different types of molecules show good agreement with computational results. Highly aligned linear molecules are used for high harmonic generation experiments. Due to the high degree of alignment, fractional revivals, variation of revival structure with harmonic order and the shape resonance and Cooper minimum in the photoionization cross section of molecular nitrogen are all observed directly in experiment for the first time. Enhanced orientation from rotationally cold heteronuclear molecules is also demonstrated. We follow the theory developed by Zhang et al. [Phys. Rev. A 83, 043410 (2011)] and demonstrate experimentally for the first time that for rotationally cold carbon monoxide an aligning laser pulse followed by a two-color laser pulse can increase field-free orientation level by almost a factor of three compared to using just the two-color pulse.

  3. Rare earth gas laser

    DOEpatents

    Krupke, W.F.

    1975-10-31

    A high energy gas laser with light output in the infrared or visible region of the spectrum is described. Laser action is obtained by generating vapors of rare earth halides, particularly neodymium iodide or, to a lesser extent, neodymium bromide, and disposing the rare earth vapor medium in a resonant cavity at elevated temperatures; e.g., approximately 1200/sup 0/ to 1400/sup 0/K. A particularly preferred gaseous medium is one involving a complex of aluminum chloride and neodymium chloride, which exhibits tremendously enhanced vapor pressure compared to the rare earth halides per se, and provides comparable increases in stored energy densities.

  4. Optimization of gas dynamic and power parameters for continuous nuclear pumped laser

    NASA Astrophysics Data System (ADS)

    Korzenev, A. N.; Sizov, A. N.

    2008-01-01

    Optimization studies of optical and power performances of nuclear pumped lasers are performed. It is shown that the laser mix pump rate speed-up from 7 to 30 m/s and laser channel width reduction from 2 to 1 cm allows increasing the average specific energy input by the factor of 1.6 and narrowing the refraction factor measuring interval for 4 times.

  5. Effect of ambient gas on the expansion dynamics of plasma plume formed by laser blow off of thin film

    NASA Astrophysics Data System (ADS)

    George, Sony; Kumar, Ajai; Singh, R. K.; Nampoori, V. P. N.

    2010-03-01

    A study has been carried out to understand the influence of ambient gases on the dynamics of laser-blow-off plumes of multi-layered LiF-C thin film. Plume images at various time intervals ranging from 100 to 3000 ns have been recorded using an intensified CCD camera. Enhancement in the plume intensity and change in size and shape occurs on introducing ambient gases and these changes are highly dependent on the nature and composition of the ambient gas used. Velocity of the plume was found to be higher in helium ambient whereas intensity enhancement is greater in argon environment. The plume shapes have maximum size at 10-2 and 10-1 Torr of Ar and He pressures, respectively. As the background pressure increases further (>10-2 Torr: depending on the nature of gas), the plume gets compressed/focused in the lateral direction. Internal structure formation and turbulences are observed at higher pressures (>10-1 Torr) in both ambient gases.

  6. High Power Pulsed Gas Lasers

    NASA Astrophysics Data System (ADS)

    Witteman, W. J.

    1987-09-01

    Gas lasers have shown to be capable of delivering tens of terrawatt aspeak power or tens of kilowatt as average power. The efficiencies of most high power gas lasers are relatively high compared with other types of lasers. For instance molecular lasers, oscillating on low lying vibrational levels, and excimer lasers may have intrinsic efficiencies above 10%.The wavelengths of these gas lasers cover the range from the far infrared to the ultra-violet region, say from 12000 to 193 nm. The most important properties are the scalability, optical homogeneity of the excited medium, and the relatively low price per watt of output power. The disadvantages may be the large size of the systems and the relatively narrow line width with limited tunability compared with solid state systems producing the same peak power. High power gas lasers group into three main categories depending on the waste-heat handling capacity.

  7. Gas-dynamic acceleration of laser-ablation plumes: Hyperthermal particle energies under thermal vaporization

    SciTech Connect

    Morozov, A. A.; Evtushenko, A. B.; Bulgakov, A. V.

    2015-02-02

    The expansion of a plume produced by low-fluence laser ablation of graphite in vacuum is investigated experimentally and by direct Monte Carlo simulations in an attempt to explain hyperthermal particle energies for thermally vaporized materials. We demonstrate that the translation energy of neutral particles, ∼2 times higher than classical expectations, is due to two effects, hydrodynamic plume acceleration into the forward direction and kinetic selection of fast particles in the on-axis region. Both effects depend on the collision number within the plume and on the particles internal degrees of freedom. The simulations allow ablation properties to be evaluated, such as ablation rate and surface temperature, based on time-of-flight measurements. Available experimental data on kinetic energies of various laser-produced particles are well described by the presented model.

  8. Gas-dynamic acceleration of laser-ablation plumes: Hyperthermal particle energies under thermal vaporization

    NASA Astrophysics Data System (ADS)

    Morozov, A. A.; Evtushenko, A. B.; Bulgakov, A. V.

    2015-02-01

    The expansion of a plume produced by low-fluence laser ablation of graphite in vacuum is investigated experimentally and by direct Monte Carlo simulations in an attempt to explain hyperthermal particle energies for thermally vaporized materials. We demonstrate that the translation energy of neutral particles, ˜2 times higher than classical expectations, is due to two effects, hydrodynamic plume acceleration into the forward direction and kinetic selection of fast particles in the on-axis region. Both effects depend on the collision number within the plume and on the particles internal degrees of freedom. The simulations allow ablation properties to be evaluated, such as ablation rate and surface temperature, based on time-of-flight measurements. Available experimental data on kinetic energies of various laser-produced particles are well described by the presented model.

  9. Dynamics of a femtosecond/picosecond laser-induced aluminum plasma out of thermodynamic equilibrium in a nitrogen background gas

    NASA Astrophysics Data System (ADS)

    Morel, Vincent; Bultel, Arnaud; Annaloro, Julien; Chambrelan, Cédric; Edouard, Guillaume; Grisolia, Christian

    2015-01-01

    Beyond the experimental studies, the assessment of the ability of ultra-short (femto or picosecond) laser pulses to provide correct estimates of the elemental composition of unknown samples using laser-induced breakdown spectroscopy requires the modeling of a typical situation. The present article deals with this modeling for aluminum in nitrogen. A spherical layer model is developed. The central aluminum plasma is produced by the ultra-short pulse. This plasma is described using our collisional-radiative model CoRaM-Al in an upgraded version involving 250 levels. Its expansion and relaxation take place in nitrogen, where the formation and the propagation of a shock wave are taken into account. In this shocked nitrogen layer, the equilibrium conditions are assumed. Mass, momentum and energy conservation equations written under an Eulerian form are used to correctly model the global dynamics. Energy losses are due to radiative recombination, thermal Bremsstrahlung and spontaneous emission. These elementary processes are implemented. The only input parameters are the pulse energy E0, the ablated mass M of the sample and the pressure p0 of the surrounding gas. The equilibrium composition involving N2, N, N2+, N+ and free electrons of the shocked nitrogen layer is calculated from the thermodynamic database of our collisional-radiative model CoRaM-N2. The conditions E0 = 10 mJ and M ≃ 10- 10 kg corresponding to a 532 nm laser pulse are chosen. The model assumes the initial equilibrium of the aluminum plasma produced by the laser pulse absorbed by the sample. Then, owing to the significant overpressure with respect to the background gas (p0 is assumed atmospheric), the surrounding gas starts to be compressed while the propagation of a shock wave takes place. The shock layer maximum pressure is obtained at approximately 20 ns. At this characteristic time, the nitrogen pressure is around 400 times the atmospheric pressure. A shock velocity of 7 km s- 1 is predicted. The

  10. Optical diagnostics of gas-dynamic flows using advanced laser measurement techniques

    NASA Technical Reports Server (NTRS)

    Gross, K. P.

    1985-01-01

    Using laser-induced fluorescence to probe nitrogen flows seeded with small amounts of nitric oxide, simultaneous measurements of all three thermodynamic scalar quantities temperature, density, and pressure, were demonstrated in a supersonic turbulent boundary layer. Instrumental uncertainty is 1% for temperature and 2% for density and pressure, making the techniques suitable for measurements of turbulent fluctuations. This technology is currently being transferred to an experimental program designed to use these optical techniques in conjunction with traditional methods to make measurements in turbulent flowfields that were not possible before. A detailed descritpion of the research progress and pertinent results are presented.

  11. Expansion dynamics of laser produced plasma

    SciTech Connect

    Doggett, B.; Lunney, J. G.

    2011-05-01

    We consider the applicability of the isentropic, adiabatic gas dynamical model of plume expansion for laser ablation in vacuum. We show that the model can be applied to ionized plumes and estimate the upper electron temperature limit on the applicability of the isentropic approximation. The model predictions are compared with Langmuir ion probe measurements and deposition profiles obtained for excimer laser ablation of silver.

  12. Dynamical modeling of laser ablation processes

    SciTech Connect

    Leboeuf, J.N.; Chen, K.R.; Donato, J.M.; Geohegan, D.B.; Liu, C.L.; Puretzky, A.A.; Wood, R.F.

    1995-09-01

    Several physics and computational approaches have been developed to globally characterize phenomena important for film growth by pulsed laser deposition of materials. These include thermal models of laser-solid target interactions that initiate the vapor plume; plume ionization and heating through laser absorption beyond local thermodynamic equilibrium mechanisms; gas dynamic, hydrodynamic, and collisional descriptions of plume transport; and molecular dynamics models of the interaction of plume particles with the deposition substrate. The complexity of the phenomena involved in the laser ablation process is matched by the diversity of the modeling task, which combines materials science, atomic physics, and plasma physics.

  13. LASER APPLICATIONS AND OTHER TOPICS IN QUANTUM ELECTRONICS: Gas-dynamic effects in the interaction of a motionless optical pulsating discharge with gas

    NASA Astrophysics Data System (ADS)

    Tishchenko, V. N.; Grachev, G. N.; Pavlov, A. A.; Smirnov, A. L.; Pavlov, A. A.; Golubev, M. P.

    2008-01-01

    The effect of energy removal from the combustion zone of a motionless optical pulsating discharge in the horizontal direction along the axis of a repetitively pulsed laser beam producing the discharge is discovered. The directivity diagram of a hot gas flow is formed during the action of hundreds of pulses. The effect is observed for short pulse durations, when the discharge efficiently generates shock waves. For long pulse durations, the heated gas propagates upward, as in a thermal source.

  14. Gas-dynamic perturbations in an electric-discharge repetitively pulsed DF laser and the role of He in their suppression

    NASA Astrophysics Data System (ADS)

    Evdokimov, P. A.; Sokolov, D. V.

    2015-11-01

    The gas-dynamic perturbations in a repetitively pulsed DF laser are studied using a Michelson interferometer. Based on the analysis of experimental data obtained in two experimental sets (working medium without buffer gas and with up to 90% of He), it is concluded that such phenomena as isentropic expansion of a thermal plug, gas heating by shock waves and resonance acoustic waves do not considerably decrease the upper limit of the pulse repetition rate below a value determined by the time of the thermal plug flush out of the discharge gap. It is suggested that this decrease for a DF laser with the SF6 - D2 working mixture is caused by the development of overheat instability due to an increased energy deposition into the near-electrode regions and to the formation of electrode shock waves. Addition of He to the active media of the DF laser changes the discharge structure and improves its homogeneity over the discharge gape cross section, thus eliminating the reason for the development of this instability. A signification dilution of the active medium of a DF laser with helium up to the atmospheric pressure allowed us to achieve the limiting discharge initiation frequencies with the active medium replacement ratio K ~ 1.

  15. Reliability factors in gas lasers

    NASA Astrophysics Data System (ADS)

    Malk, E. G.; Ramsay, I. A.

    1982-07-01

    Two types of gas lasers, the helium-neon laser and the sealed off, waveguide carbon dioxide laser, are discussed. The beneficial influence of hard seals on the HeNe laser is briefly described, and the resulting improved mean time between failures is described and discussed, showing a summary of lifetest data. Rejection percentages at 80 percent of the rated power in 18 months of elapsed time is determined to be 10 percent for one family of HeNe lasers and 7.6 percent for another family. An optical failure mode for HeNe lasers and the scientific investigation leading to its elimination are described. Finally, CO2 waveguide laser reliability is discussed in terms of the lifetime degradation factors involved in the operation of these lasers.

  16. Dynamic response of single crystalline copper subjected to quasi-isentropic laser and gas-gun driven loading

    NASA Astrophysics Data System (ADS)

    Meyers, M.; Jarmakani, H.; McNaney, J. M.; Schneider, M.; Nguyen, J. H.; Kad, B.

    2006-08-01

    Single crystalline copper was subjected to quasi-isentropic compression via gas-gun and laser loading at pressures between 18 GPa and 59 GPa. The deformation substructure was analyzed via transmission electron microscopy (TEM). Twins and laths were evident at the highest pressures, and stacking faults and dislocation cells in the intermediate and lowest pressures, respectively. The Preston-Tonks-Wallace (PTW) constitutive description was used to model the slip-twinning process in both cases.

  17. Dynamic response of single crystalline copper subjected to quasi-isentropic laser and gas-gun driven loading

    SciTech Connect

    Meyers, M; Jarmakani, H; McNaney, J; Schneider, M; Nguyen, J; Kad, B

    2006-05-22

    Single crystalline copper was subjected to quasi-isentropic compression via gas-gun and laser loading at pressures between 18 GPa and 59 GPa. The deformation substructure was analyzed via transmission electron microscopy (TEM). Twins and laths were evident at the highest pressures, and stacking faults and dislocation cells in the intermediate and lowest pressures, respectively. The Preston-Tonks-Wallace (PTW) constitutive description was used to model the slip-twinning process in both cases.

  18. High power gas laser amplifier

    DOEpatents

    Leland, Wallace T.; Stratton, Thomas F.

    1981-01-01

    A high power output CO.sub.2 gas laser amplifier having a number of sections, each comprising a plurality of annular pumping chambers spaced around the circumference of a vacuum chamber containing a cold cathode, gridded electron gun. The electron beam from the electron gun ionizes the gas lasing medium in the sections. An input laser beam is split into a plurality of annular beams, each passing through the sections comprising one pumping chamber.

  19. Electro-gas-dynamic CO lasers with combustion products: a new scientific direction to the creation of the industrial high-power lasers

    NASA Astrophysics Data System (ADS)

    Baranov, Igor M.

    1997-04-01

    An industrial high-power laser is a technical system to be characterized primarily by the efficiency. For a high-power laser system to become like an industrial one the efficiency must be more than 10%. As is well known a steam-engine has such an efficiency. In welding and in cutting thick materials to provide required power density in a spot for the device with long focus the value of output power of radiation must be no less than 100 kW at beam divergence 10-3 rad. At the present time there is a problem in concurrent fulfillment of the requirements on an output power, the divergence, and the efficiency as well as the requirements on the stability of output parameters, total resource of operation, the safety of operation, and the use of standard components. A line of attack on this problem is proposed by the present author through the use of continuous formation of a CO laser mixture by combustion of a chemical fuel and the use of atmospheric air as a buffer gas (up to 80%), which is cooled in supersonic nozzles followed by excitation in a radio-frequency (rf) electric discharge without an electron gun. A small-scale model system of electrogasdynamic CO laser was used by the present author and his colleagues to demonstrate for the first time the laser radiation was possible in a system with combustion products and air. A technical proposal for a multipurpose self-contained industrial cw high-power CO laser system is proposed. This laser system is based on standard electrical machinery with a gas-turbine drive without ejecting toxic CO into the atmosphere.

  20. Pump-probe studies of EUV and X-ray emission dynamics of laser-irradiated noble gas droplets

    NASA Astrophysics Data System (ADS)

    Parra, E.; McNaught, S. J.; Fan, J.; Milchberg, H. M.

    The interaction of high intensity 100-ps laser pulses with micron-sized noble gas (argon and krypton) droplets is experimentally investigated via a series of pump-probe experiments monitoring the delay-dependent X-ray and extreme ultraviolet (EUV) emission, and by imaging frequency-doubled probe light scattered from the interaction region. An understanding of the time scales for this interaction is important for optimization of EUV sources for next-generation lithography that utilizes laser-produced plasmas (LPP). Depending on the spectral region of interest, the type of emission, and the droplet characteristics, the effective emission lifetime was found to extend from a few hundred picoseconds to as long as several nanoseconds, in agreement with the expected plasma expansion, EUV excitation, and recombination emission time scales.

  1. Compact, high energy gas laser

    DOEpatents

    Rockwood, Stephen D.; Stapleton, Robert E.; Stratton, Thomas F.

    1976-08-03

    An electrically pumped gas laser amplifier unit having a disc-like configuration in which light propagation is radially outward from the axis rather than along the axis. The input optical energy is distributed over a much smaller area than the output optical energy, i.e., the amplified beam, while still preserving the simplicity of parallel electrodes for pumping the laser medium. The system may thus be driven by a comparatively low optical energy input, while at the same time, owing to the large output area, large energies may be extracted while maintaining the energy per unit area below the threshold of gas breakdown.

  2. Propagation dynamics of an ultrashort, high energy laser pulse via self-modulation in gas medium with atmospheric pressure for laser compression

    NASA Astrophysics Data System (ADS)

    Otsuka, Takamitsu; Kudo, Masashi; Sakai, Shohei; Higashiguchi, Takeshi; Yugami, Noboru; Yatagai, Toyohiko; Kodama, Ryosuke

    2010-08-01

    Self-compression of 20-mJ laser pulses has been demonstrated in a free-space argon-filled cell. A 130-fs pulse was compressed to less than 60 fs (full width at half maximum) with an output energy of 17 mj at an argon gas pressure of 25 kPa, corresponding to an input peak power of 3.65 times the self-focusing critical power through a single filament in a 10-mJ energy region.

  3. Low Voltage Gas Transport TE CO(2) Laser.

    PubMed

    Seguin, H J; Sedgwick, G

    1972-04-01

    The constructional and operational aspects of a low voltage transversely excited gas transport CO(2) laser are presented. This compact device incorporates a recirculating wind tunnel type geometry and possesses features of the gas dynamic, gas transport, and TEA lasers. The structure with an active length of 36 cm produced a cw power of approximately 200 W at an over-all system efficiency of 5% using a discharge potential of 1200 V. PMID:20119038

  4. Dynamics of vapor plume in transient keyhole during laser welding of stainless steel: Local evaporation, plume swing and gas entrapment into porosity

    NASA Astrophysics Data System (ADS)

    Pang, Shengyong; Chen, Xin; Shao, Xinyu; Gong, Shuili; Xiao, Jianzhong

    2016-07-01

    In order to better understand the local evaporation phenomena of keyhole wall, vapor plume swing above the keyhole and ambient gas entrapment into the porosity defects, the 3D time-dependent dynamics of the metallic vapor plume in a transient keyhole during fiber laser welding is numerically investigated. The vapor dynamical parameters, including the velocity and pressure, are successfully predicted and obtain good agreements with the experimental and literature data. It is found that the vapor plume flow inside the keyhole has complex multiple directions, and this various directions characteristic of the vapor plume is resulted from the dynamic evaporation phenomena with variable locations and orientations on the keyhole wall. The results also demonstrate that because of this dynamic local evaporation, the ejected vapor plume from the keyhole opening is usually in high frequency swinging. The results further indicate that the oscillation frequency of the plume swing angle is around 2.0-8.0 kHz, which is of the same order of magnitude with that of the keyhole depth (2.0-5.0 kHz). This consistency clearly shows that the swing of the ejected vapor plume is closely associated with the keyhole instability during laser welding. Furthermore, it is learned that there is usually a negative pressure region (several hundred Pa lower than the atmospheric pressure) of the vapor flow around the keyhole opening. This pressure could lead to a strong vortex flow near the rear keyhole wall, especially when the velocity of the ejected metallic vapor from the keyhole opening is high. Under the effect of this flow, the ambient gas is involved into the keyhole, and could finally be entrapped into the bubbles within a very short time (<0.2 ms) due to the complex flow inside the keyhole.

  5. Laser and gas centrifuge enrichment

    SciTech Connect

    Heinonen, Olli

    2014-05-09

    Principles of uranium isotope enrichment using various laser and gas centrifuge techniques are briefly discussed. Examples on production of high enriched uranium are given. Concerns regarding the possibility of using low end technologies to produce weapons grade uranium are explained. Based on current assessments commercial enrichment services are able to cover the global needs of enriched uranium in the foreseeable future.

  6. Laser and gas centrifuge enrichment

    NASA Astrophysics Data System (ADS)

    Heinonen, Olli

    2014-05-01

    Principles of uranium isotope enrichment using various laser and gas centrifuge techniques are briefly discussed. Examples on production of high enriched uranium are given. Concerns regarding the possibility of using low end technologies to produce weapons grade uranium are explained. Based on current assessments commercial enrichment services are able to cover the global needs of enriched uranium in the foreseeable future.

  7. Laser-induced gas-surface interactions

    NASA Astrophysics Data System (ADS)

    Chuang, T. J.

    Chemical reactions in homogeneous systems activated by laser radiation have been extensively investigated for more than a decade. The applications of lasers to promote gas-surface interactions have just been realized in recent years. The purpose of this paper is to examine the fundamental processes involved in laser-induced gas-surface chemical interactions. Specifically, the photon-enhanced adsorption, adsorbate-adsorbate and adsorbate-solid reactions, product formation and desorption processes are discussed in detail. The dynamic processes involved in photoexcitation of the electronic and vibrational states, the energy transfer and relaxation in competition with chemical interactions are considered. These include both single and multiple photon adsorption, and fundamental and overtone transitions in the excitation process, and inter- and intra-molecular energy transfer, and coupling with phonons, electron-hole pairs and surface plasmons in the energy relaxation process. Many current experimental and theoretical studies on the subject are reviewed and discussed with the goal of clarifying the relative importance of the surface interaction steps and relating the resulting concepts to the experimentally observed phenomena. Among the many gas-solid systems that have been investigated, there has been more extensive use of CO adsorbed on metals, and SF 6 and XeF 2 interactions with silicon as examples to illustrate the many facets of the electronically and vibrationally activated surface processes. Results on IR laser stimulated desorption of C 5H 5N and C 5D 5N molecules from various solid surfaces are also presented. It is clearly shown that rapid intermolecular energy exchange and molecule to surface energy transfer can have important effects on photodesorption cross sections and isotope selectivities. It is concluded that utilization of lasers in gas-surface studies not only can provide fundamental insight into the mechanism and dynamics involved in heterogeneous

  8. Role of ambient gas and laser fluence in governing the dynamics of the plasma plumes produced by laser blow off of LiF-C thin film

    NASA Astrophysics Data System (ADS)

    Singh, R. K.; Kumar, Ajai; Patel, B. G.; Subramanian, K. P.

    2007-05-01

    The time- and space-resolved emission profiles of Li mathsize="8pt">I and Li mathsize="8pt">II emission lines from the laser-blow-off plumes of a multilayered LiF-C thin film have been studied using spectroscopic technique. The evolution features were analyzed in different ambient environments ranging from high vacuum to 3mbars of argon pressures and at various fluences of the ablating laser. During the evolution of the plume, a transition region was found to exist between 4 and 6mm. Here, the plume dynamics changed from free expansion to collisional regime, where the plume experienced viscous force of the medium. The enhancement observed in neutral lines, in comparison with ionic lines, is explained in terms of the yield difference in electron impact excitation and ionization processes. Substantial difference in the arrival time distribution of the plume species was observed for Li mathsize="8pt">I and Li mathsize="8pt">II lines at high ambient pressures. Three expansion models are invoked to explain the evolution of the plume in different ambient conditions. The laser fluence was found to control the ratio of ions and neutrals.

  9. Gain dynamics in a pulsed laser amplifier on CO-He, CO-N{sub 2} and CO-O{sub 2} gas mixtures

    SciTech Connect

    Vetoshkin, S V; Ionin, Andrei A; Klimachev, Yu M; Kozlov, A Yu; Kotkov, A A; Rulev, O A; Seleznev, L V; Sinitsyn, D V

    2007-02-28

    Small-signal gain (SSG) dynamics G(t) in the active medium of a pulsed laser amplifier operating on the v+1{yields}vP(J) vibrational-rotational transitions of the CO molecule, including high (v > 15) vibrational transitions, is studied experimentally. It is demonstrated that as the vibrational number increases from 7 to 31, G changes with time slower, while G{sub max} decreases in this case by three times. It is found that at a fixed value of v the rate of the SSG rise increases with increasing the rotational number J > 6. It is shown that in oxygen-containing gas mixtures (CO:O{sub 2} = 1:19) the value of G{sub max} at low vibrational levels (for v < 13) can substantially exceed G{sub max} in mixtures containing nitrogen (CO:N{sub 2} = 1:19) instead of oxygen. It is found that the efficiency (47%) of a CO laser on mixtures with a high concentration of oxygen considerably exceeds the efficiency (30%) of a CO laser operating on a nitrogen-containing mixture. (active media)

  10. ACTIVE MEDIA: Gain dynamics in a pulsed laser amplifier on CO-He, CO-N2 and CO-O2 gas mixtures

    NASA Astrophysics Data System (ADS)

    Vetoshkin, S. V.; Ionin, Andrei A.; Klimachev, Yu M.; Kozlov, A. Yu; Kotkov, A. A.; Rulev, O. A.; Seleznev, L. V.; Sinitsyn, D. V.

    2007-02-01

    Small-signal gain (SSG) dynamics G(t) in the active medium of a pulsed laser amplifier operating on the v+1→vP(J) vibrational-rotational transitions of the CO molecule, including high (v > 15) vibrational transitions, is studied experimentally. It is demonstrated that as the vibrational number increases from 7 to 31, G changes with time slower, while Gmax decreases in this case by three times. It is found that at a fixed value of v the rate of the SSG rise increases with increasing the rotational number J > 6. It is shown that in oxygen-containing gas mixtures (CO:O2 = 1:19) the value of Gmax at low vibrational levels (for v < 13) can substantially exceed Gmax in mixtures containing nitrogen (CO:N2 = 1:19) instead of oxygen. It is found that the efficiency (47%) of a CO laser on mixtures with a high concentration of oxygen considerably exceeds the efficiency (30%) of a CO laser operating on a nitrogen-containing mixture.

  11. High-speed laser diagnostics for the study of flame dynamics in a lean premixed gas turbine model combustor

    NASA Astrophysics Data System (ADS)

    Boxx, Isaac; Arndt, Christoph M.; Carter, Campbell D.; Meier, Wolfgang

    2012-03-01

    A series of measurements was taken on two technically premixed, swirl-stabilized methane-air flames (at overall equivalence ratios of ϕ = 0.73 and 0.83) in an optically accessible gas turbine model combustor. The primary diagnostics used were combined planar laser-induced fluorescence of the OH radical and stereoscopic particle image velocimetry (PIV) with simultaneous repetition rates of 10 kHz and a measurement duration of 0.8 s. Also measured were acoustic pulsations and OH chemiluminescence. Analysis revealed strong local periodicity in the thermoacoustically self-excited (or ` noisy') flame (ϕ = 0.73) in the regions of the flow corresponding to the inner shear layer and the jet-inflow. This periodicity appears to be the result of a helical precessing vortex core (PVC) present in that region of the combustor. The PVC has a precession frequency double (at 570 Hz) that of the thermo-acoustic pulsation (at 288 Hz). A comparison of the various data sets and analysis techniques applied to each flame suggests a strong coupling between the PVC and the thermo-acoustic pulsation in the noisy flame. Measurements of the stable (` quiet') flame (ϕ = 0.83) revealed a global fluctuation in both velocity and heat-release around 364 Hz, but no clear evidence of a PVC.

  12. Infrared laser spectroscopic trace gas sensing

    NASA Astrophysics Data System (ADS)

    Sigrist, Markus

    2016-04-01

    Chemical sensing and analyses of gas samples by laser spectroscopic methods are attractive owing to several advantages such as high sensitivity and specificity, large dynamic range, multi-component capability, and lack of pretreatment or preconcentration procedures. The preferred wavelength range comprises the fundamental molecular absorption range in the mid-infared between 3 and 15 μm, whereas the near-infrared range covers the (10-100 times weaker) higher harmonics and combination bands. The availability of near-infrared and, particularly, of broadly tunable mid-infrared sources like external cavity quantum cascade lasers (EC-QCLs), interband cascade lasers (ICLs), difference frequency generation (DFG), optical parametric oscillators (OPOs), recent developments of diode-pumped lead salt semiconductor lasers, of supercontinuum sources or of frequency combs have eased the implementation of laser-based sensing devices. Sensitive techniques for molecular absorption measurements include multipass absorption, various configurations of cavity-enhanced techniques such as cavity ringdown (CRD), or of photoacoustic spectroscopy (PAS) including quartz-enhanced (QEPAS) or cantilever-enhanced (CEPAS) techniques. The application requirements finally determine the optimum selection of laser source and detection scheme. In this tutorial talk I shall discuss the basic principles, present various experimental setups and illustrate the performance of selected systems for chemical sensing of selected key atmospheric species. Applications include an early example of continuous vehicle emission measurements with a mobile CO2-laser PAS system [1]. The fast analysis of C1-C4 alkanes at sub-ppm concentrations in gas mixtures is of great interest for the petrochemical industry and was recently achieved with a new type of mid-infrared diode-pumped piezoelectrically tuned lead salt vertical external cavity surface emitting laser (VECSEL) [2]. Another example concerns measurements on short

  13. Mathematical modeling of gas-dynamic and radiative processes in experiments with the use of laser and heavy-ion beams

    NASA Astrophysics Data System (ADS)

    Vergunova, G. A.; Rozanov, V. B.; Denisov, O. B.; Orlov, N. Yu.; Rosmej, O. N.

    2013-09-01

    Results are presented from theoretical and experimental studies of gas-dynamic and radiative processes in the plasma that is planned to be used in future experiments on the stopping of fast heavy-ion beams. These experiments are aimed at measuring the enhanced (as compared to cold substance) plasma stopping power. To reliably interpret the experimental results, it is necessary to create a hydrodynamically stable homogeneous plasma with a uniform temperature and a lifetime exceeding the transit time of the heavy-ion beam (3-5 ns). The method for calculating plasma gas-dynamic characteristics with allowance for radiative heat transfer is described. The specific features of the so-called ion model of plasma, which is used to calculate plasma radiative characteristics, are discussed. The emission spectrum formed as a result of conversion of laser radiation into X-rays and the subsequent passing through a triacetate cellulose (C12H16O8) target is calculated. The simulated spectrum of transmitted radiation satisfactorily agrees with experimental data.

  14. Computational reacting gas dynamics

    NASA Technical Reports Server (NTRS)

    Lam, S. H.

    1993-01-01

    In the study of high speed flows at high altitudes, such as that encountered by re-entry spacecrafts, the interaction of chemical reactions and other non-equilibrium processes in the flow field with the gas dynamics is crucial. Generally speaking, problems of this level of complexity must resort to numerical methods for solutions, using sophisticated computational fluid dynamics (CFD) codes. The difficulties introduced by reacting gas dynamics can be classified into three distinct headings: (1) the usually inadequate knowledge of the reaction rate coefficients in the non-equilibrium reaction system; (2) the vastly larger number of unknowns involved in the computation and the expected stiffness of the equations; and (3) the interpretation of the detailed reacting CFD numerical results. The research performed accepts the premise that reacting flows of practical interest in the future will in general be too complex or 'untractable' for traditional analytical developments. The power of modern computers must be exploited. However, instead of focusing solely on the construction of numerical solutions of full-model equations, attention is also directed to the 'derivation' of the simplified model from the given full-model. In other words, the present research aims to utilize computations to do tasks which have traditionally been done by skilled theoreticians: to reduce an originally complex full-model system into an approximate but otherwise equivalent simplified model system. The tacit assumption is that once the appropriate simplified model is derived, the interpretation of the detailed numerical reacting CFD numerical results will become much easier. The approach of the research is called computational singular perturbation (CSP).

  15. Laser cross-flow gas system

    DOEpatents

    Duncan, David B.

    1992-01-01

    A method and laser apparatus are disclosed which provide for a cross-flow of gas near one end of a laser discharge tube. The cross-flow of gas causes a concentration gradient which affects diffusion of contaminants in the discharge tube towards the cross-flow of the gas, which contaminants are then withdrawn from the discharge tube.

  16. Spatial distribution of rare-earth ions and GaS4 tetrahedra in chalcogenide glasses studied via laser spectroscopy and ab initio molecular dynamics simulation

    NASA Astrophysics Data System (ADS)

    Lee, T. H.; Simdyankin, S. I.; Hegedus, J.; Heo, J.; Elliott, S. R.

    2010-03-01

    The spatial distribution of Nd3+ ions and GaS4 tetrahedral units in Nd-doped Ge-As-Ga-S glasses has been studied by laser spectroscopy and ab initio molecular dynamics (MD) simulations. A sharp increase in Nd3+ fluorescence intensities and lifetimes was observed with increasing Ga content, and attributed to the formation of tightly bound Nd3+ clusters in Ga-free glasses and the subsequent dissolution of such clusters upon Ga doping. A large modification in Nd3+ sites was also identified from low-temperature site-selective excitation spectra, suggesting preferential spatial correlations between Nd3+ and GaS4 tetrahedra even at low Ga-doping levels. MD simulations of these materials in the liquid state showed a tendency for Ga cluster formation as well as spatial correlations between Nd and Ga atoms consistent with the experimental results. On the basis of this result, a comprehensive structural model for Nd- and Ga-doped sulfide glasses is proposed.

  17. Inductive gas line for pulsed lasers

    DOEpatents

    Benett, William J.; Alger, Terry W.

    1985-01-01

    A gas laser having a metal inlet gas feed line assembly shaped as a coil, to function as an electrical inductance and therefore high impedance to pulses of electric current applied to electrodes at opposite ends of a discharge tube of a laser, for example. This eliminates a discharge path for the laser through the inlet gas feed line. A ferrite core extends through the coil to increase the inductance of the coil and provide better electric isolation. By elimination of any discharge breakdown through the gas supply, efficiency is increased and a significantly longer operating lifetime of the laser is provided.

  18. Inductive gas line for pulsed lasers

    DOEpatents

    Benett, W.J.; Alger, T.W.

    1982-09-29

    A gas laser having a metal inlet gas feed line assembly shaped as a coil, to function as an electrical inductance and therefore high impedance to pulses of electric current applied to electrodes at opposite ends of a discharge tube of a laser, for example. This eliminates a discharge path for the laser through the inlet gas feed line. A ferrite core extends through the coil to increase the inductance of the coil and provide better electric isolation. By elimination of any discharge breakdown through the gas supply, efficiency is increased and a significantly longer operating lifetime of the laser is provided.

  19. Nonlinear dynamics of additive pulse modelocked lasers

    SciTech Connect

    Sucha, G.; Bolton, S.R.; Chemla, D.S.

    1995-04-01

    Nonlinear dynamics have been studied in a number of modelocked laser systems, primarily in actively modelocked systems. However, less attention has been paid to the dynamics of passively modelocked laser systems. With the recent revolutionary advances in femtosecond modelocked laser technology, the understanding of instabilities and dynamics in passively modelocked lasers is an important issue. Here, the authors present experimental and numerical studies of the dynamics of an additive-pulse modelocked (APM) color-center laser.

  20. GAS LASERS FOR STRONG-FIELD APPLICATIONS.

    SciTech Connect

    POGORELSKY,I.V.

    2004-09-15

    Atomic-, molecular- and excimer-gas lasers employ variety of pumping schemes including electric discharge, optical, or chemical reactions and cover a broad spectral range from UV to far-IR. Several types of gas lasers can produce multi-kilojoule pulses and kilowatts of average power. Among them, excimer- and high-pressure molecular lasers have sufficient bandwidth for generating pico- and femtosecond pulses. Projects are underway and prospects are opening up to bring ultrafast gas laser technology to the front lines of advanced accelerator applications.

  1. Optical Filaments and Gas Dynamics in Air

    NASA Astrophysics Data System (ADS)

    Yeak, Jeremy

    Until now, the propagation dynamics of intense ultrashort laser pulses leading to optical filamentation in air has only been investigated in the frame of a dynamic balance between linear diffraction, Kerr self-focusing and plasma defocusing. This has led to the development of different theories surrounding the generation and persistence of optical filaments propagating over many Rayleigh lengths in air. These theories include wave-guiding model, moving focus model, dynamic spatial replenishment model and conical wave model. However, these models fail to capture the gas dynamics that arise from optical filaments interacting with air. In this work, we demonstrate that initial conditions are critical to the formation of optical filaments through the use of an aerodynamic window. Filament characteristics in air, such as spectral broadening, electrical conductivity and fluorescence, are measured and presented. Using these as diagnostic tools, we also show that the optical filamentation of ultrashort laser pulses can be enhanced at high repetition rates because of the thermal response of air, resulting from the interaction of each laser pulse with the modified atmospheric density distribution left behind by the preceding pulse. This is explained by the sudden deposition of energy by a filament in the air which generates a cylindrical shock wave, leaving behind a column of rarefied air. This low-density region persists for an extended period and can materially affect the propagation dynamics of an ensuing pulse that follows before the low-density region has relaxed sufficiently to ambient conditions. By further increasing the repetition rate, the onset of ionization is shifted downstream and the spectral continuum displays a stronger broadening on both sides of the original pulse spectrum. This gas dynamic interaction regime of filamentation can be utilized to enhance the length and spectral width of filaments for remote sensing and long range laser-induced high voltage

  2. Multiplex electric discharge gas laser system

    NASA Technical Reports Server (NTRS)

    Laudenslager, James B. (Inventor); Pacala, Thomas J. (Inventor)

    1987-01-01

    A multiple pulse electric discharge gas laser system is described in which a plurality of pulsed electric discharge gas lasers are supported in a common housing. Each laser is supplied with excitation pulses from a separate power supply. A controller, which may be a microprocessor, is connected to each power supply for controlling the application of excitation pulses to each laser so that the lasers can be fired simultaneously or in any desired sequence. The output light beams from the individual lasers may be combined or utilized independently, depending on the desired application. The individual lasers may include multiple pairs of discharge electrodes with a separate power supply connected across each electrode pair so that multiple light output beams can be generated from a single laser tube and combined or utilized separately.

  3. Gas-phase chemical dynamics

    SciTech Connect

    Weston, R.E. Jr.; Sears, T.J.; Preses, J.M.

    1993-12-01

    Research in this program is directed towards the spectroscopy of small free radicals and reactive molecules and the state-to-state dynamics of gas phase collision, energy transfer, and photodissociation phenomena. Work on several systems is summarized here.

  4. Selective IR multiphoton dissociation of molecules in a pulsed gas-dynamically cooled molecular flow interacting with a solid surface as an alternative to low-energy methods of molecular laser isotope separation

    NASA Astrophysics Data System (ADS)

    Makarov, G. N.; Petin, A. N.

    2016-03-01

    We report the results of studies on the isotope-selective infrared multiphoton dissociation (IR MFD) of SF6 and CF3I molecules in a pulsed, gas-dynamically cooled molecular flow interacting with a solid surface. The productivity of this method in the conditions of a specific experiment (by the example of SF6 molecules) is evaluated. A number of low-energy methods of molecular laser isotope separation based on the use of infrared lasers for selective excitation of molecules are analysed and their productivity is estimated. The methods are compared with those of selective dissociation of molecules in the flow interacting with a surface. The advantages of this method compared to the low-energy methods of molecular laser isotope separation and the IR MPD method in the unperturbed jets and flows are shown. It is concluded that this method could be a promising alternative to the low-energy methods of molecular laser isotope separation.

  5. Gas gun dynamics

    NASA Astrophysics Data System (ADS)

    Denny, Mark

    2013-09-01

    The mechanics and thermodynamics of one- and two-stage gas guns are developed. Very high projectile muzzle speed can be obtained by the two-stage version. The physics of simple gas guns, such as air rifles, is accessible to undergraduates and the same level of presentation is used here to understand more complex designs. Numerical solutions to the equations of motion are shown, along with insightful analytic approximations.

  6. Photodissociation dynamics of 2-chloro-6-nitrotoluene and nitrocyclopentane in gas phase: Laser-induced fluorescence detection of OH

    NASA Astrophysics Data System (ADS)

    Kawade, Monali N.; Saha, Ankur; Upadhyaya, Hari P.; Kumar, Awadhesh; Naik, Prakash D.

    2014-10-01

    Photodissociation of 2-chloro-6-nitrotoluene (ClNT) at 193, 248 and 266 nm and nitrocyclopentane (NCP) at 193 nm leads to the formation of OH, as detected by laser-induced fluorescence (LIF). The nascent OH produced from the photolysis of ClNT at all the wavelengths is vibrationally cold, with the Boltzmann type rotational state distributions. However, the nascent OH product from NCP is in the ground and vibrationally excited states with the measured average relative population in ν″ = 1 to that in ν″ = 0 of 0.12 ± 0.03, and these levels are characterized by rotational temperatures of 650 ± 180 K and 1570 ± 90 K, respectively. The translational energy partitioned in the OH fragment has been measured for photodissociation of both ClNT and NCP. On the basis of both the experimental results and the ground state molecular orbital (MO) calculations, a plausible mechanism for the OH formation has been proposed.

  7. On Predtechensky and Mayorov model for the plume expansion dynamics study into an ambient gas during thin film deposition by laser ablation

    NASA Astrophysics Data System (ADS)

    Lafane, S.; Kerdja, T.; Abdelli-Messaci, S.; Malek, S.; Kechouane, M.

    2013-01-01

    The plume expansion dynamics for the Sm1- x Nd x NiO3 thin films deposition by a KrF excimer laser into oxygen atmosphere has been investigated using fast imaging. The study was carried out at 0.2 and 0.3 mbar of oxygen pressure and for different laser fluences. The plasma plume dynamics was analysed in the framework of Predtechensky and Mayorov (PM) model. It was found that PM model gives a general description of the plume expansion by using parameters (laser fluence and oxygen pressure) that ensure a hemispherical expansion of the plume. The latter was discussed in the framework of the shock-wave model and the plume dimensions.

  8. SPECIAL ISSUE DEVOTED TO THE 25th ANNIVERSARY OF THE A.M. PROKHOROV GENERAL PHYSICS INSTITUTE: Femtosecond laser optical gas breakdown microplasma: the ionisation and postionisation dynamics

    NASA Astrophysics Data System (ADS)

    Bukin, V. V.; Garnov, S. V.; Malyutin, A. A.; Strelkov, V. V.

    2007-10-01

    The formation and evolution dynamics of the laser plasma produced in the microvolumes of gases (air, nitrogen, argon, and helium) upon their multiple ionisation by high-intensity (4×1016 W cm-2) tightly focused (to a region 1.7 μm in diameter) 400-nm, 100-fs second-harmonic pulses from a Ti:sapphire laser is studied. The spatiotemporal distribution profiles of the refractive index and electron microplasma density were recorded by ultrahigh-speed interferometry. The postionisation of a femtosecond laser plasma, i.e. the growth of the electron density known after the end of the exciting laser pulse, is detected for the first time. A theoretical model is proposed, which describes the mechanism of plasma postionisation by hot photoelectrons. The results of electron density calculations are in good agreement with experimental data.

  9. EFFECT OF LASER LIGHT ON MATTER. LASER PLASMAS: Boundary instability of an erosion laser plasma expanding into a background gas

    NASA Astrophysics Data System (ADS)

    Anisimov, V. N.; Grishina, V. G.; Derkach, O. N.; Kanevskiĭ, M. F.; Sebrant, A. Yu

    1993-12-01

    The stability of the contact region in the system consisting of an erosion plasma and a gas has been determined experimentally under conditions such that the length of the applied laser pulse is longer than the rise time of the instability, and the expansion of the erosion plume is accompanied by breakdown of the background gas. The evolution of perturbations of the plasma front following the introduction of initial perturbations with a fixed spatial period has been studied. It is possible to model the injection of plasma bunches into a low-pressure gas by studying the dynamics of the vaporization at moderate laser-light intensities, characteristic of technological applications.

  10. Nuclear pumped gas laser research

    NASA Technical Reports Server (NTRS)

    Thom, K.

    1976-01-01

    Nuclear pumping of lasers by fission-fragments from nuclear chain reactions is discussed. Application of the newly developed lasers to spacecraft propulsion or onboard power, to lunar bases for industrial processing, and to earth for utilization of power without pollution and hazards is envisioned. Emphasis is placed on the process by which the fission-fragement kinetic energy is converted into laser light.

  11. Gas Phase Molecular Dynamics

    SciTech Connect

    Hall, G.E.; Prrese, J.M.; Sears, T.J.; Weston, R.E.

    1999-05-21

    The goal of this research is the understanding of elementary chemical and physical processes important in the combustion of fossil fuels. Interest centers on reactions involving short-lived chemical intermediates and their properties. High-resolution high-sensitivity laser absorption methods are augmented by high temperature flow-tube reaction kinetics studies with mass spectrometric sampling. These experiments provide information on the energy levels, structures and reactivity of molecular flee radical species and, in turn, provide new tools for the study of energy flow and chemical bond cleavage in the radicals in chemical systems. The experimental work is supported by theoretical and computational work using time-dependent quantum wavepacket calculations that provide insights into energy flow between the vibrational modes of the molecule.

  12. Stochastic Quantum Gas Dynamics

    NASA Astrophysics Data System (ADS)

    Proukakis, Nick P.; Cockburn, Stuart P.

    2010-03-01

    We study the dynamics of weakly-interacting finite temperature Bose gases via the Stochastic Gross-Pitaevskii equation (SGPE). As a first step, we demonstrate [jointly with A. Negretti (Ulm, Germany) and C. Henkel (Potsdam, Germany)] that the SGPE provides a significantly better method for generating an equilibrium state than the number-conserving Bogoliubov method (except for low temperatures and small atom numbers). We then study [jointly with H. Nistazakis and D.J. Frantzeskakis (University of Athens, Greece), P.G.Kevrekidis (University of Massachusetts) and T.P. Horikis (University of Ioannina, Greece)] the dynamics of dark solitons in elongated finite temperature condensates. We demonstrate numerical shot-to-shot variations in soliton trajectories (S.P. Cockburn et al., arXiv:0909.1660.), finding individual long-lived trajectories as in experiments. In our simulations, these variations arise from fluctuations in the phase and density of the underlying medium. We provide a detailed statistical analysis, proposing regimes for the controlled experimental demonstration of this effect; we also discuss the extent to which simpler models can be used to mimic the features of ensemble-averaged stochastic trajectories.

  13. Rarefied gas dynamics using stochastic rotation dynamics

    NASA Astrophysics Data System (ADS)

    Tuzel, Erkan; Ihle, Thomas; Kroll, Daniel M.

    2003-03-01

    In the past two decades, Direct Simulation Monte Carlo (DSMC) has been the dominant predictive tool for rarefied gas dynamics. In the non-hydrodynamic regime, where continuum models fail, particle based methods have been used to model systems ranging from shuttle re-entry problems to mesoscopic flow in MEMS devices. A new method, namely stochastic rotation dynamics (SRD), which utilizes effective multiparticle collisions, will be described. It will be shown that it is possible to get the correct transport coefficients for Argon gas by tuning the collision parameters, namely the collision angle and collision probability. Simulation results comparing DSMC and SRD will be shown for equilibrium relaxation rates and Poiseuille flow. One important feature of SRD is that it coarse-grains the time scale, so that simulations in the transition regime are typically five to twenty times faster than for DSMC. Benchmarks as a function of Knudsen number will be given, and directions for further research will be discussed.

  14. Gain dynamics of a free-space nitrogen laser pumped by circularly polarized femtosecond laser pulses

    NASA Astrophysics Data System (ADS)

    Yao, Jinping; Xie, Hongqiang; Zeng, Bin; Chu, Wei; Li, Guihua; Ni, Jielei; Zhang, Haisu; Jing, Chenrui; Zhang, Chaojin; Xu, Huailiang; Cheng, Ya; Xu, Zhizhan

    2014-08-01

    We experimentally demonstrate ultrafast dynamic of generation of a strong 337-nm nitrogen laser by injecting an external seed pulse into a femtosecond laser filament pumped by a circularly polarized laser pulse. In the pump-probe scheme, it is revealed that the population inversion between the excited and ground states of N2 for the free-space 337-nm laser is firstly built up on the timescale of several picoseconds, followed by a relatively slow decay on the timescale of tens of picoseconds, depending on the nitrogen gas pressure. By measuring the intensities of 337-nm signal from nitrogen gas mixed with different concentrations of oxygen gas, it is also found that oxygen molecules have a significant quenching effect on the nitrogen laser signal. Our experimental observations agree with the picture of electron-impact excitation.

  15. Gain dynamics of a free-space nitrogen laser pumped by circularly polarized femtosecond laser pulses.

    PubMed

    Yao, Jinping; Xie, Hongqiang; Zeng, Bin; Chu, Wei; Li, Guihua; Ni, Jielei; Zhang, Haisu; Jing, Chenrui; Zhang, Chaojin; Xu, Huailiang; Cheng, Ya; Xu, Zhizhan

    2014-08-11

    We experimentally demonstrate ultrafast dynamic of generation of the 337-nm nitrogen laser by injecting an external seed pulse into a femtosecond laser filament pumped by a circularly polarized laser pulse. In the pump-probe scheme, it is revealed that the population inversion between the C(3)Π(u) and B(3)Π(g) states of N(2) for the free-space 337-nm laser is firstly built up on the timescale of several picoseconds, followed by a relatively slow decay on the timescale of tens of picoseconds, depending on the nitrogen gas pressure. By measuring the intensities of 337-nm signal from nitrogen gas mixed with different concentrations of oxygen gas, it is also found that oxygen molecules have a significant quenching effect on the nitrogen laser signal. Our experimental observations agree with the picture of electron-impact excitation. PMID:25320986

  16. Laser Additive Manufacturing of Gas Permeable Structures

    NASA Astrophysics Data System (ADS)

    Klahn, C.; Bechmann, F.; Hofmann, S.; Dinkel, M.; Emmelmann, C.

    Laser additive manufacturing offers a variety of new design possibilities. In mold making laser additive manufactured inserts with conformal cooling channels are already state of the art. Pneumatic ejectors for injection molds are a new application for laser additive manufacturing. The pneumatic ejectors require a durable gas permeable material. This material is produced by placing the scan vectors for the laser additive manufacturing process in a defined pattern. Trials with different plastics proofed the function and reliability of the pneumatic ejector concept in the injection molding cycle.

  17. High-Speed Multiplexed Spatiotemporally Resolved Measurements of Exhaust Gas Recirculation Dynamics in a Multi-Cylinder Engine Using Laser Absorption Spectroscopy.

    PubMed

    Yoo, Jihyung; Prikhodko, Vitaly; Parks, James E; Perfetto, Anthony; Geckler, Sam; Partridge, William P

    2016-04-01

    The need for more environmentally friendly and efficient energy conversion is of paramount importance in developing and designing next-generation internal combustion (IC) engines for transportation applications. One effective solution to reducing emissions of mono-nitrogen oxides (NOx) is exhaust gas recirculation (EGR), which has been widely implemented in modern vehicles. However, cylinder-to-cylinder and cycle-to-cycle variations in the charge-gas uniformity can be a major barrier to optimum EGR implementation on multi-cylinder engines, and can limit performance, stability, and efficiency. Precise knowledge and fine control over the EGR system is therefore crucial, particularly for optimizing advanced engine concepts such as reactivity controlled compression ignition (RCCI). An absorption-based laser diagnostic was developed to study spatiotemporal charge-gas distributions in an IC engine intake manifold in real-time. The laser was tuned to an absorption band of carbon dioxide (CO2), a standard exhaust-gas marker, near 2.7 µm. The sensor was capable of probing four separate measurement locations simultaneously, and independently analyzing EGR fraction at speeds of 5 kHz (1.2 crank-angle degree (CAD) at 1 k RPM) or faster with high accuracy. The probes were used to study spatiotemporal EGR non-uniformities in the intake manifold and ultimately promote the development of more efficient and higher performance engines. PMID:27091946

  18. High-Speed Multiplexed Spatiotemporally Resolved Measurements of Exhaust Gas Recirculation Dynamics in a Multi-Cylinder Engine Using Laser Absorption Spectroscopy

    DOE PAGESBeta

    Yoo, Jihyung; Prikhodko, Vitaly; Parks, James E.; Perfetto, Anthony; Geckler, Sam; Partridge, William P.

    2016-04-01

    The need for more environmentally friendly and efficient energy conversion is of paramount importance in developing and designing next-generation internal combustion (IC) engines for transportation applications. One effective solution to reducing emissions of mono-nitrogen oxides (NOx) is exhaust gas recirculation (EGR), which has been widely implemented in modern vehicles. However, cylinder-to-cylinder and cycle-to-cycle variations in the charge-gas uniformity can be a major barrier to optimum EGR implementation on multi-cylinder engines, and can limit performance, stability, and efficiency. Precise knowledge and fine control over the EGR system is thus crucial, particularly for optimizing advanced engine concepts such as reactivity controlled compressionmore » ignition (RCCI). An absorption-based laser diagnostic was developed to study spatiotemporal charge-gas distributions in an IC engine intake manifold in real-time. The laser was tuned to an absorption band of carbon dioxide (CO2), a standard exhaust-gas marker, near 2.7 µm. The sensor was capable of probing four separate measurement locations simultaneously, and independently analyzing EGR fraction at speeds of 5 kHz (1.2 crank-angle degree (CAD) at 1 k RPM) or faster with high accuracy. Lastly, the probes were used to study spatiotemporal EGR non-uniformities in the intake manifold and ultimately promote the development of more efficient and higher performance engines.« less

  19. Solar-pumped gas laser development

    NASA Technical Reports Server (NTRS)

    Wilson, J. W.

    1980-01-01

    A survey of gas properties through detailed kinetic models led to the identification of critical gas parameters for use in choosing appropriate gas combinations for solar pumped lasers. Broadband photoabsorption in the visible or near UV range is required to excite large volumes of gas and to insure good solar absorption efficiency. The photoexcitation density is independent of the absorption bandwidth. The state excited must be a metastable state which is not quenched by the parent gas. The emission bandwidth must be less than 10 A to insure lasing threshold over reasonable gain lengths. The system should show a high degree of chemical reversibility and an insensitivity to increasing temperature. Other properties such as good quantum efficiency and kinetic efficiency are also implied. Although photoexcitation of electronic vibrational transitions is considered as a possible system if the emission bands sufficiently narrow, it appears that photodissociation into atomic metastables is more likely to result in a successful solar pumped laser system.

  20. Widely tunable gas laser for remote sensing

    NASA Technical Reports Server (NTRS)

    Rothe, D. E.

    1988-01-01

    An advanced, highly efficient and reliable Rare-Gas Halide laser was developed. It employs the following: (1) novel prepulse techniques and impedance matching for efficient energy transfer; (2) magnetic switches for high reliability; (3) x-ray preionization for discharge uniformity and beam quality; and (4) an integrated gas flow loop for compactness. When operated as a XeCl laser, the unit produces 2 J per pulse with good beam uniformity. Optical pulse duration is 100 ns. Pulse repetition rate was tested up to 25 Hz. Efficiency is 3 percent.

  1. Shedding new light on gas dynamics

    NASA Technical Reports Server (NTRS)

    Mckenzie, Robert L.; Hanson, Ronald K.; Eckbreth, Alan C.

    1992-01-01

    Modern laser-spectroscopic techniques usually incorporate one or more laser beams and depend on their radiative interaction with some spectroscopic feature of the gas. Attention is given to laser absorption, laser-induced fluorescence, Rayleigh scattering, and Raman scattering. Consideration is given to UV Rayleigh scattering applied to aerodynamic flows to obtain images of a supersonic boundary layer that show instantaneous turbulent structures at a level of detail not achieved by any other practical method.

  2. Modeling of plume dynamics in laser ablation processes for thin film deposition of materials

    SciTech Connect

    Leboeuf, J.N.; Chen, K.R.; Donato, J.M.; Geohegan, D.B.; Liu, C.L.; Puretzky, A.A.; Wood, R.F.

    1995-12-31

    The transport dynamics of laser-ablated neutral/plasma plumes are of significant interest for film growth by pulsed-laser deposition of materials since the magnitude and kinetic energy of the species arriving at the deposition substrate are key processing parameters. Dynamical calculations of plume propagation in vacuum and in background gas have been performed using particle-in-cell hydrodynamics, continuum gas dynamics, and scattering models. Results from these calculations are presented and compared with experimental observations.

  3. Numerical investigation of the electron dynamic dependence on gas pressure in the breakdown of hydrogen by KrF laser radiation

    NASA Astrophysics Data System (ADS)

    Gamal, Yosr E. E.-D.; Elsayed, Khaled A.; Mahmoud, M. A.

    2012-10-01

    This paper presents a numerical investigation of the measurements that were carried out by Yagi et al. [12] to study the breakdown of molecular hydrogen induced by short laser of wavelength 248 nm and pulse duration 20 ns. The aim of the study is to give a detailed description of the physical processes which contributed to the breakdown of molecular hydrogen at focused intensities between 4×1012 W/cm2 and 8.0×1012 W/cm2 over gas pressure range extended from 150 to 7000 Torr. The applied computer simulation model is based on the numerical solution of the time dependent Boltzmann equation and a set of rate equations that describe the rate of change of the formed excited states population. The experimentally measured rate constants and cross-sections for the various physical processes involved in the model are used in the calculations. Provision is made for the electron impact ionization and photoionization of the excited states. The former process is incorporated parametrically in the calculation owing to the lack of quantitative description of this process. Computations are performed at each gas pressure. The calculated threshold intensities are found to be in good agreement with the experimentally measured ones, both showing a noticeable increase in the higher pressure region. Moreover, calculation of the electron energy distribution function (EEDF) and its parameters demonstrated the exact correlation between gas pressure and the physical processes responsible for determining the breakdown threshold intensity.

  4. Dynamically variable spot size laser system

    NASA Technical Reports Server (NTRS)

    Gradl, Paul R. (Inventor); Hurst, John F. (Inventor); Middleton, James R. (Inventor)

    2012-01-01

    A Dynamically Variable Spot Size (DVSS) laser system for bonding metal components includes an elongated housing containing a light entry aperture coupled to a laser beam transmission cable and a light exit aperture. A plurality of lenses contained within the housing focus a laser beam from the light entry aperture through the light exit aperture. The lenses may be dynamically adjusted to vary the spot size of the laser. A plurality of interoperable safety devices, including a manually depressible interlock switch, an internal proximity sensor, a remotely operated potentiometer, a remotely activated toggle and a power supply interlock, prevent activation of the laser and DVSS laser system if each safety device does not provide a closed circuit. The remotely operated potentiometer also provides continuous variability in laser energy output.

  5. Arthroscopic laser meniscectomy in a gas medium.

    PubMed

    Whipple, T L; Caspari, R B; Meyers, J F

    1985-01-01

    Laboratory investigations demonstrate the theoretical feasibility of utilizing CO2 laser energy for arthroscopic resection of the knee meniscus. Infrared light of 10.6 micron wavelength is sufficiently absorbed by fibrocartilage with byproducts of heat, water vapor, and a small residue of carbon ash. The remaining meniscus rim demonstrates viable chondrocytes in close proximity to the margin of resection, and gross collagen fiber architecture is preserved. The depth of penetration of the laser beam can be controlled by limiting the duration of exposure. Arthroscopic application of CO2 laser energy requires a gas medium. Carbon dioxide and nitrogen have proven to be satisfactory insufflation agents, with no lasting untoward effects noted in a clinical series of diagnostic arthroscopic procedures. The cost of laser generators and the lack of an ideal delivery system are limiting factors in clinical applications of this cutting mode for meniscectomy. PMID:3937537

  6. International Symposium on Gas Flow and Chemical Lasers, 8th, Madrid, Spain, Sept. 10-14, 1990, Proceedings

    SciTech Connect

    Orza, J.M.; Domingo, C.

    1991-01-01

    Papers are presented on current research developments and applications related to high-powered lasers. Recent advances in excimer laser technology, electron-beam-pumped excimer lasers, discharge technology for excimer lasers, and pulsed XeF lasers are examined. Consideration is given to short-wavelength lasers, chemical oxygen iodine lasers, and vibrational chemical lasers. Papers are presented on CO2, CO, N2O lasers, coupled CO2 lasers, laser induced perturbation in pulsed CO2 lasers, construction of sealed-off CO2 lasers, and computer modeling of discharge-excited CO gas flow. Topics discussed include gas-dynamic lasers, discharge and flow effects, matrix and laser optics and laser beam parameters. Laser-matter interactions, laser-induced surface plasma, plasma motion velocity along laser beams and thermocapillary effects are also discussed. Applications of laser technology are examined and high-speed laser welding, welding results, laser ablation, laser steel processing, and numerical modeling of laser-matter interaction in high-intensity laser applications are considered.

  7. Gas Dynamic Spray Technology Demonstration

    NASA Technical Reports Server (NTRS)

    Burford, Pattie Lewis

    2011-01-01

    Zinc primer systems are currently used across NASA and AFSPC for corrosion protection of steel. AFSPC and NASA have approved the use of Thermal Spray Coatings (TSCs) as an environmentally preferable alternative. TSCs are approved in NASA-STD-5008 and AFSPC and KSC is currently looking for additional applications in which TSC can be used. Gas Dynamic Spray (GDS, also known as Cold Spray) is being evaluated as a means of repairing TSCs and for areas such as corners and edges where TSCs do not work as well. Other applications could include spot repair/maintenance of steel on structures, facilities, and ground support equipment.

  8. Porosity formation and gas bubble retention in laser metal deposition

    NASA Astrophysics Data System (ADS)

    Ng, G. K. L.; Jarfors, A. E. W.; Bi, G.; Zheng, H. Y.

    2009-11-01

    One of the inherent problems associated with laser metal deposition using gas-assisted powder transfer is the formation of porosity, which can be detrimental to the mechanical properties of the bulk material. In this work, a comprehensive investigation of porosity is carried out using gas atomised Inconel 718 powder. In the analysis, a clear distinction is made between two types of porosity; namely lack of fusion and gas porosity. The results show that the two types of porosity are attributed by different factors. The gas porosity, which is more difficult to eliminate than the lack of fusion, can be as high as 0.7%. The study shows that the gas porosity is dependent on the process parameters and the melt pool dynamics. The flotation of entrapped gas bubbles was analysed, showing that in a stationary melt pool the gas would be retained by Marangoni-driven flow. The overall Marangoni-driven flow of the melt pool is in the order of five times higher than the flotation effect, and this is the reason why the melt pool geometry would tend to dominate the flow direction of the gas bubbles. Through optimisation, the gas porosity can be reduced to 0.037%.

  9. Subcycle engineering of laser filamentation in gas by harmonic seeding

    NASA Astrophysics Data System (ADS)

    Béjot, P.; Karras, G.; Billard, F.; Doussot, J.; Hertz, E.; Lavorel, B.; Faucher, O.

    2015-11-01

    Manipulating at will the propagation dynamics of high power laser pulses is a long-standing dream whose accomplishment would lead to the control of fascinating physical phenomena emerging from laser-matter interaction. The present work represents a significant step towards such a control by manipulating the nonlinear optical response of the gas medium. This is accomplished by shaping an intense laser pulse experiencing filamentation at the subcycle level with a relatively weak (≃1 % ) third-harmonic radiation. The control results from quantum interference between a single- and a two-color (mixing the fundamental frequency with its third-harmonic) ionization channel. This mechanism, which depends on the relative phase between the two electric fields, is responsible for wide refractive index modifications in relation with significant enhancement or suppression of the ionization rate. As a first application, we demonstrate the production and control of an axially modulated plasma channel.

  10. Modeling of dynamical processes in laser ablation

    SciTech Connect

    Leboeuf, J.N.; Chen, K.R.; Donato, J.M.; Geohegan, D.B.; Liu, C.L.; Puretzky, A.A.; Wood, R.F.

    1995-12-31

    Various physics and computational approaches have been developed to globally characterize phenomena important for film growth by pulsed-laser deposition of materials. These include thermal models of laser-solid target interactions that initiate the vapor plume, plume ionization and heating through laser absorption beyond local thermodynamic equilibrium mechanisms, hydrodynamic and collisional descriptions of plume transport, and molecular dynamics models of the interaction of plume particles with the deposition substrate.

  11. A gas-dynamical approach to radiation pressure acceleration

    NASA Astrophysics Data System (ADS)

    Schmidt, Peter; Boine-Frankenheim, Oliver

    2016-06-01

    The study of high intensity ion beams driven by high power pulsed lasers is an active field of research. Of particular interest is the radiation pressure acceleration, for which simulations predict narrow band ion energies up to GeV. We derive a laser-piston model by applying techniques for non-relativistic gas-dynamics. The model reveals a laser intensity limit, below which sufficient laser-piston acceleration is impossible. The relation between target thickness and piston velocity as a function of the laser pulse length yields an approximation for the permissible target thickness. We performed one-dimensional Particle-In-Cell simulations to confirm the predictions of the analytical model. These simulations also reveal the importance of electromagnetic energy transport. We find that this energy transport limits the achievable compression and rarefies the plasma.

  12. Dielectric ridge waveguide gas laser apparatus

    SciTech Connect

    DeMaria, A.J.; Bridges, W.

    1989-03-14

    A dielectric ridged waveguide flowing gas laser apparatus is described, comprising in combination; a dielectric substrate having a predetermined number of the grooves formed theron, the grooves extending along the longitudinal axis of the dielectric substrate, an electrically conductive member in parallel alignment with the grooved side of the dielectric substrate such that an air gasp is formed therebetween the air gap containing an active laser gas medium, electrically conductive strips disposed on the outside of the dielectric substrate forming electrodes, the conductive strips being aligned with the grooves and having the same length and width as the grooves, and an excitation source connected between the conductive member and the conductive strips, to provide lasing in the ridged waveguide.

  13. Laser plume dynamics during excimer laser nitriding of iron

    NASA Astrophysics Data System (ADS)

    Han, M.; Carpene, E.; Lieb, K. P.; Schaaf, Peter

    2003-11-01

    Laser nitriding of iron is an interesting phenomenon both in physics and industry. On the time scale of hundreds nanoseconds, high intensity (~108 W/cm2) pulsed excimer laser irradiation on iron in nitrogen atmosphere produced a thin iron nitride layer (thickness > 400 nm) with a mean nitrogen concentration exceeding 10 at which greatly improves the iron surface mechanical properties and the corrosion or erosion resistance. Laser plasma/plume plays a crucial role in the complicated interplay of the laser-plasma-metal system. Since the nitrogen pressure is one of the most important parameters determining the laser plume dynamics, a nitrogen pressure series ranging from 0.05 bar to 10 bar is conducted. The characteristic parameters of the nitrogen depth profile are extracted and their pressure dependence is qualitatively discussed. By isotopic experiments in 15N and natural nitrogen environment, the evolution of the nitrogen depth profile during laser nitriding process is successfully traced. Both of the experimental results suggested that a 1D laser supported combustion wave model is reasonable to describe the lasers plume dynamics.

  14. Gas dynamics in residual gas analyzer calibration

    SciTech Connect

    Santeler, D.J.

    1987-01-01

    Residual gas analyzers are used for measuring partial flow rates as well as for measuring partial pressures. The required calibration may also be obtained with either known flow rates or known pressures. The calibration and application procedures are straightforward when both are of the same type; however, substantial errors may occur if the two types are mixed. This report develops the basic equations required to convert between partial pressure calibrations and partial flow rate calibrations. It also discusses the question of fractionating and nonfractionating gas flow in various gas inlet and pumping systems.

  15. Gas dynamics of ethylene oxide during sterilization

    NASA Astrophysics Data System (ADS)

    Zhu, Z.; Matthews, I. P.; Wang, C.

    1999-07-01

    This article reports a case study of the dynamics of ethylene oxide gas during sterilization using a microwave spectrometer. A diffusion equation is used to describe the processes of gas penetration, gas sorption, and chemical reactions. The three processes, although mathematically related, may be solved separately under simplified assumptions. This permits the prediction of gas penetration and sorption as well as the effect of chemical reactions upon the gas concentration for loads of differing dimensions and densities.

  16. Gas laser with dual plasma mixing

    DOEpatents

    Pinnaduwage, L.A.

    1999-04-06

    A gas laser includes an enclosure forming a first chamber, a second chamber and a lasing chamber which communicates through a first opening to the first chamber and through a second opening to the second chamber. The lasing chamber has a pair of reflectors defining a Fabry-Perot cavity. Separate inlets enable different gases to be introduced into the first and second chambers. A first cathode within the first chamber is provided to produce positive ions which travel into the lasing chamber and a second cathode of a pin-hollow type within the second chamber is provided to produce negative ions which travel into the lasing chamber. A third inlet introduces a molecular gas into the lasing chamber, where the molecular gas becomes excited by the positive and negative ions and emits light which lases in the Fabry-Perot cavity. 2 figs.

  17. Gas laser with dual plasma mixing

    DOEpatents

    Pinnaduwage, Lal A.

    1999-01-01

    A gas laser includes an enclosure forming a first chamber, a second chamber and a lasing chamber which communicates through a first opening to the first chamber and through a second opening to the second chamber. The lasing chamber has a pair of reflectors defining a Fabry-Perot cavity. Separate inlets enable different gases to be introduced into the first and second chambers. A first cathode within the first chamber is provided to produce positive ions which travel into the lasing chamber and a second cathode of a pin-hollow type within the second chamber is provided to produce negative ions which travel into the lasing chamber. A third inlet introduces a molecular gas into the lasing chamber, where the molecular gas becomes excited by the positive and negative ions and emits light which lases in the Fabry-Perot cavity.

  18. A laser tracking dynamic robot metrology instrument

    NASA Technical Reports Server (NTRS)

    Parker, G. A.; Mayer, J. R. R.

    1989-01-01

    Research work over several years has resulted in the development of a laser tracking instrument capable of dynamic 3-D measurements of robot end-effector trajectories. The instrument characteristics and experiments to measure the static and dynamic performance of a robot in an industrial manufacturing environment are described. The use of this technology for space applications is examined.

  19. Collision dynamics of laser produced carbon plasma plumes

    NASA Astrophysics Data System (ADS)

    Favre, M.; Ruiz, H. M.; Cortés, D.; Merello, F.; Bhuyan, H.; Veloso, F.; Wyndham, E.

    2016-05-01

    We present preliminary experimental observations of the collision processes between two orthogonal laser produced plasmas in a low pressure neutral gas background. A Nd:YAG laser, 340 mJ, 3.5 ns, at 1.06 μm, operating at 10 Hz, is used in the experiments. The main laser beam is divided in two beams by a 50% beam splitter, and then focused over two rotating graphite targets, with characteristic fluence 3.5 J/cm2. Experiments are conducted in a range from a base pressure of 0.3 mTorr, up to 50 mTorr argon. The dynamics of the laser plasmas is characterized by time resolved and time integrated optical emission spectroscopy (OES), with 20 ns and 10 ms time resolution, and 50 ns time resolved plasma imaging of visible plasma emission. Clear effects of the neutral gas background on the postcollision plasma dynamics are identified. The overall dynamics of the post-collision plasma is found to be consistent with high collisionality of the carbon plasma plumes, which results in full stagnation on collisioning.

  20. Recent nuclear pumped laser results. [gas mixtures and laser plasmas

    NASA Technical Reports Server (NTRS)

    Miley, G. H.; Wells, W. E.; Akerman, M. A.; Anderson, J. H.

    1976-01-01

    Recent direct nuclear pumped laser research has concentrated on experiments with three gas mixtures (Ne-N2, He-Ne-O2, and He-Hg). One mixture has been made to lase and gain has been achieved with the other two. All three of these mixtures are discussed with particular attention paid to He-Hg. Of interest is the 6150-angstroms ion transition in Hg(+). The upper state of this transition is formed directly by charge transfer and by Penning ionization.

  1. High power gas laser - Applications and future developments

    NASA Technical Reports Server (NTRS)

    Hertzberg, A.

    1977-01-01

    Fast flow can be used to create the population inversion required for lasing action, or can be used to improve laser operation, for example by the removal of waste heat. It is pointed out that at the present time all lasers which are capable of continuous high-average power employ flow as an indispensable aspect of operation. High power laser systems are discussed, taking into account the gasdynamic laser, the HF supersonic diffusion laser, and electric discharge lasers. Aerodynamics and high power lasers are considered, giving attention to flow effects in high-power gas lasers, aerodynamic windows and beam manipulation, and the Venus machine. Applications of high-power laser technology reported are related to laser material working, the employment of the laser in controlled fusion machines, laser isotope separation and photochemistry, and laser power transmission.

  2. Gas laser in which the gas is excited by capacitor discharge

    SciTech Connect

    Lacour, B.; de Witte, O.; Maillet, M.; Vannier, C.

    1985-01-22

    A gas laser in which the gas is excited by laser discharge, said laser including two capacitors formed by two parallel metal plates between which two dielectric parts are spaced apart to form a passage which contains the laser gas. It further includes a transformer whose secondary winding is connected to the plates and whose primary winding is connected in series with a capacitor, means for charging and capacitor and a thyristor for discharging the capacitor in the primary winding. Application to exciting gas lasers in which the gas contains a dye stuff.

  3. Laser Gas Nitriding of Titanium and Titanium Alloys

    NASA Astrophysics Data System (ADS)

    Dai, J. J.; Hou, S. Q.

    Titanium and titanium alloys are widely used in many fields due to some of their characteristics such as light density, high strength, and excellent corrosion resistance. However, poor mechanical performances limit their practical applications. Laser gas nitriding is a promising method used to improve the surface properties of components. Recent developments on laser gas nitriding of titanium and titanium alloys are reviewed. The processing parameters have important effects on the resulting characteristics of titanium and titanium alloys. The resulting microstructure and properties of laser gas nitrided specimens are presented. The problems to be solved and the prospects in the field of laser gas nitriding of titanium and titanium alloys are discussed.

  4. Laser-driven nonlinear cluster dynamics

    SciTech Connect

    Fennel, Th.; Meiwes-Broer, K.-H.; Tiggesbaeumker, J.; Reinhard, P.-G.; Dinh, P. M.; Suraud, E.

    2010-04-15

    Laser excitation of nanometer-sized atomic and molecular clusters offers various opportunities to explore and control ultrafast many-particle dynamics. Whereas weak laser fields allow the analysis of photoionization, excited-state relaxation, and structural modifications on these finite quantum systems, large-amplitude collective electron motion and Coulomb explosion can be induced with intense laser pulses. This review provides an overview of key phenomena arising from laser-cluster interactions with focus on nonlinear optical excitations and discusses the underlying processes according to the current understanding. A general survey covers basic cluster properties and excitation mechanisms relevant for laser-driven cluster dynamics. Then, after an excursion in theoretical and experimental methods, results for single-photon and multiphoton excitations are reviewed with emphasis on signatures from time- and angular-resolved photoemission. A key issue of this review is the broad spectrum of phenomena arising from clusters exposed to strong fields, where the interaction with the laser pulse creates short-lived and dense nanoplasmas. The implications for technical developments such as the controlled generation of ion, electron, and radiation pulses will be addressed along with corresponding examples. Finally, future prospects of laser-cluster research as well as experimental and theoretical challenges are discussed.

  5. Laser-solid interaction and dynamics of the laser-ablated materials

    SciTech Connect

    Chen, K.R.; Leboeuf, J.N.; Geohegan, D.B.; Wood, R.F.; Donato, J.M.; Liu, C.L.; Puretzky, A.A.

    1995-07-01

    Rapid transformations through the liquid and vapor phases induced by laser-solid interactions are described by the authors` thermal model with the Clausius-Clapeyron equation to determine the vaporization temperature under different surface pressure condition. Hydrodynamic behavior of the vapor during and after ablation is described by gas dynamic equations. These two models are coupled. Modeling results show that lower background pressure results lower laser energy density threshold for vaporization. The ablation rate and the amount of materials removed are proportional to the laser energy density above its threshold. The authors also demonstrate a dynamic source effect that accelerates the unsteady expansion of laser-ablated material in the direction perpendicular to the solid. A dynamic partial ionization effect is studied as well. A self-similar theory shows that the maximum expansion velocity is proportional to c{sub s}{alpha}, where 1 {minus} {alpha} is the slope of the velocity profile. Numerical hydrodynamic modeling is in good agreement with the theory. With these effects, {alpha} is reduced. Therefore, the expansion front velocity is significantly higher than that from conventional models. The results are consistent with experiments. They further study how the plume propagates in high background gas condition. Under appropriate conditions, the plume is slowed down, separates with the background, is backward moving, and hits the solid surface. Then, it splits into two parts when it rebounds from the surface. The results from the modeling will be compared with experimental observations where possible.

  6. Gas-controlled dynamic vacuum insulation with gas gate

    DOEpatents

    Benson, David K.; Potter, Thomas F.

    1994-06-07

    Disclosed is a dynamic vacuum insulation comprising sidewalls enclosing an evacuated chamber and gas control means for releasing hydrogen gas into a chamber to increase gas molecule conduction of heat across the chamber and retrieving hydrogen gas from the chamber. The gas control means includes a metal hydride that absorbs and retains hydrogen gas at cooler temperatures and releases hydrogen gas at hotter temperatures; a hydride heating means for selectively heating the metal hydride to temperatures high enough to release hydrogen gas from the metal hydride; and gate means positioned between the metal hydride and the chamber for selectively allowing hydrogen to flow or not to flow between said metal hydride and said chamber.

  7. Gas-controlled dynamic vacuum insulation with gas gate

    DOEpatents

    Benson, D.K.; Potter, T.F.

    1994-06-07

    Disclosed is a dynamic vacuum insulation comprising sidewalls enclosing an evacuated chamber and gas control means for releasing hydrogen gas into a chamber to increase gas molecule conduction of heat across the chamber and retrieving hydrogen gas from the chamber. The gas control means includes a metal hydride that absorbs and retains hydrogen gas at cooler temperatures and releases hydrogen gas at hotter temperatures; a hydride heating means for selectively heating the metal hydride to temperatures high enough to release hydrogen gas from the metal hydride; and gate means positioned between the metal hydride and the chamber for selectively allowing hydrogen to flow or not to flow between said metal hydride and said chamber. 25 figs.

  8. Investigations of laser pumped gas cell atomic frequency standard

    NASA Technical Reports Server (NTRS)

    Volk, C. H.; Camparo, J. C.; Fueholz, R. P.

    1982-01-01

    The performance characteristics of a rubidium gas cell atomic frequency standard might be improved by replacing the standard rubidium discharge lamp with a single mode laser diode. Aspects of the laser pumped gas cell atomic clock studied include effects due to laser intensity, laser detuning, and the choice of the particular atomic absorption line. Results indicate that the performance of the gas cell clock may be improved by judicious choice of the operating parameters of the laser diode. The laser diode also proved to be a valuable tool in investigating the operation of the conventional gas cell clock. Results concerning linewidths, the light shift effect and the effect of isotopic spin exchange in the conventional gas cell clock are reported.

  9. Dynamics of Micro-Plasmas Generated in Noble Gases by Strong-Field Laser Pulses

    NASA Astrophysics Data System (ADS)

    Romanov, Dmitri A.; Compton, Ryan; Filin, Alex; Levis, Robert J.

    2010-03-01

    The ultrafast dynamics of micro-plasmas generated by an ˜80 fs laser pulse in noble gases has been investigated using four-wave mixing (FWM). The evolution patterns of the FWM signal are indicative of the gas species and ambient conditions. The signal is observed to reach higher intensity levels faster for Xe, with progressively lower scattering intensity and longer time dynamics for the noble gas series Xe, Kr, Ar, Ne, and He. The theoretical model for interpreting this temporal dynamics is based on initial tunnel ionization followed by electron impact ionization cooling. The model reproduces well the measured degree of ionization in atmospheric-pressure laser-induced plasmas and predicts quantitatively the intensity of four-wave mixing as a function of time for the series of five noble gases. The model also predicts the dynamics as a function of pump laser intensity and gas pressure. The findings open the way for effective control of micro-plasma dynamics.

  10. Stellar dynamics in gas: the role of gas damping

    NASA Astrophysics Data System (ADS)

    Leigh, Nathan W. C.; Mastrobuono-Battisti, Alessandra; Perets, Hagai B.; Böker, Torsten

    2014-06-01

    In this paper, we consider how gas damping affects the dynamical evolution of gas-embedded star clusters. Using a simple three-component (i.e. one gas and two stellar components) model, we compare the rates of mass segregation due to two-body relaxation, accretion from the interstellar medium, and gas dynamical friction in both the supersonic and subsonic regimes. Using observational data in the literature, we apply our analytic predictions to two different astrophysical environments, namely galactic nuclei and young open star clusters. Our analytic results are then tested using numerical simulations performed with the NBSymple code, modified by an additional deceleration term to model the damping effects of the gas. The results of our simulations are in reasonable agreement with our analytic predictions, and demonstrate that gas damping can significantly accelerate the rate of mass segregation. A stable state of approximate energy equilibrium cannot be achieved in our model if gas damping is present, even if Spitzer's Criterion is satisfied. This instability drives the continued dynamical decoupling and subsequent ejection (and/or collisions) of the more massive population. Unlike two-body relaxation, gas damping causes overall cluster contraction, reducing both the core and half-mass radii. If the cluster is mass segregated (and/or the gas density is highest at the cluster centre), the latter contracts faster than the former, accelerating the rate of core collapse.

  11. Measurement Of Ultrafast Ionisation From Intense Laser Interactions With Gas-Jets

    SciTech Connect

    Gizzi, Leonida A.; Galimberti, Marco; Giulietti, Antonio; Giulietti, Danilo; Koester, Petra; Labate, Luca; Tomassini, Paolo; Martin, Philippe; Ceccotti, Tiberio; De Oliveira, Pascal; Monot, Pascal

    2006-04-07

    Interaction of an intense, ultrashort laser pulse with a gas-jet target is investigated through femtosecond optical interferometry to study the dynamics of ionization of the gas. Experimental results are presented in which the propagation of the pulse in the gas and the consequent plasma formation is followed step by step with high temporal and spatial resolution. We demonstrate that, combining the phase shift with the measurable depletion of fringe visibility associated with the transient change of refractive index in the ionizing region and taking into account probe travel time can provide direct information on gas ionization dynamics.

  12. Collisional dynamics in a gas of molecular super-rotors.

    PubMed

    Khodorkovsky, Yuri; Steinitz, Uri; Hartmann, Jean-Michel; Averbukh, Ilya Sh

    2015-01-01

    Recently, femtosecond laser techniques have been developed that are capable of bringing gas molecules to extremely fast rotation in a very short time, while keeping their translational motion relatively slow. Here we study collisional equilibration dynamics of this new state of molecular gases. We show that the route to equilibrium starts with a metastable 'gyroscopic stage' in the course of which the molecules maintain their fast rotation and orientation of the angular momentum through many collisions. The inhibited rotational-translational relaxation is characterized by a persistent anisotropy in the molecular angular distribution, and is manifested in the optical birefringence and anisotropic diffusion in the gas. After a certain induction time, the 'gyroscopic stage' is abruptly terminated by an explosive rotational-translational energy exchange, leading the gas towards the final equilibrium. We illustrate our conclusions by direct molecular dynamics simulation of several gases of linear molecules. PMID:26160223

  13. Collisional dynamics in a gas of molecular super-rotors

    NASA Astrophysics Data System (ADS)

    Khodorkovsky, Yuri; Steinitz, Uri; Hartmann, Jean-Michel; Averbukh, Ilya Sh.

    2015-07-01

    Recently, femtosecond laser techniques have been developed that are capable of bringing gas molecules to extremely fast rotation in a very short time, while keeping their translational motion relatively slow. Here we study collisional equilibration dynamics of this new state of molecular gases. We show that the route to equilibrium starts with a metastable `gyroscopic stage' in the course of which the molecules maintain their fast rotation and orientation of the angular momentum through many collisions. The inhibited rotational-translational relaxation is characterized by a persistent anisotropy in the molecular angular distribution, and is manifested in the optical birefringence and anisotropic diffusion in the gas. After a certain induction time, the `gyroscopic stage' is abruptly terminated by an explosive rotational-translational energy exchange, leading the gas towards the final equilibrium. We illustrate our conclusions by direct molecular dynamics simulation of several gases of linear molecules.

  14. Advanced solar energy conversion. [solar pumped gas lasers

    NASA Technical Reports Server (NTRS)

    Lee, J. H.

    1981-01-01

    An atomic iodine laser, a candidate for the direct solar pumped lasers, was successfully excited with a 4 kW beam from a xenon arc solar simulator, thus proving the feasibility of the concept. The experimental set up and the laser output as functions of operating conditions are presented. The preliminary results of the iodine laser amplifier pumped with the HCP array to which a Q switch for giant pulse production was coupled are included. Two invention disclosures - a laser driven magnetohydrodynamic generator for conversion of laser energy to electricity and solar pumped gas lasers - are also included.

  15. Neutral gas dynamics in fireballs

    SciTech Connect

    Stenzel, R. L.; Ionita, C.; Schrittwieser, R.

    2011-06-01

    Fireballs are local discharge phenomena on positively biased electrodes in partially ionized plasmas. Electrons, energized at a double layer, heat neutral gas which expands. The gas pressure exceeds the plasma pressure, hence becomes important to the stability and transport in fireballs. The flow of gas moves the electrode and sensors similar to a mica pendulum. Flow speed and directions are measured. A fireball gun has been developed to partially collimate the flow of hot gas and heat objects in its path. New applications of fireballs are suggested.

  16. System for controlling the flow of gas into and out of a gas laser

    DOEpatents

    Alger, Terry; Uhlich, Dennis M.; Benett, William J.; Ault, Earl R.

    1994-01-01

    A modularized system for controlling the gas pressure within a copper vapor or like laser is described herein. This system includes a gas input assembly which serves to direct gas into the laser in a controlled manner in response to the pressure therein for maintaining the laser pressure at a particular value, for example 40 torr. The system also includes a gas output assembly including a vacuum pump and a capillary tube arrangement which operates within both a viscous flow region and a molecular flow region for drawing gas out of the laser in a controlled manner.

  17. Supersonic diode pumped alkali lasers: Computational fluid dynamics modeling

    NASA Astrophysics Data System (ADS)

    Rosenwaks, Salman; Yacoby, Eyal; Waichman, Karol; Sadot, Oren; Barmashenko, Boris D.

    2015-10-01

    We report on recent progress on our three-dimensional computational fluid dynamics (3D CFD) modeling of supersonic diode pumped alkali lasers (DPALs), taking into account fluid dynamics and kinetic processes in the lasing medium. For a supersonic Cs DPAL with laser section geometry and resonator parameters similar to those of the 1-kW flowing-gas subsonic Cs DPAL [A.V. Bogachev et al., Quantum Electron. 42, 95 (2012)] the maximum achievable output power, ~ 7 kW, is 25% higher than that achievable in the subsonic case. Comparison between semi-analytical and 3D CFD models for Cs shows that the latter predicts much higher maximum achievable output power than the former. Optimization of the laser parameters using 3D CFD modeling shows that very high power and optical-to-optical efficiency, 35 kW and 82%, respectively, can be achieved in a Cs supersonic device pumped by a collimated cylindrical (0.5 cm diameter) beam. Application of end- or transverse-pumping by collimated rectangular (large cross section ~ 2 - 4 cm2) beam makes it possible to obtain even higher output power, > 250 kW, for ~ 350 kW pumping power. The main processes limiting the power of Cs supersonic DPAL are saturation of the D2 transition and large ~ 40% losses of alkali atoms due to ionization, whereas the influence of gas heating is negligibly small. For supersonic K DPAL both gas heating and ionization effects are shown to be unimportant and the maximum achievable power, ~ 40 kW and 350 kW, for pumping by ~ 100 kW cylindrical and ~ 700 kW rectangular beam, respectively, are higher than those achievable in the Cs supersonic laser. The power achieved in the supersonic K DPAL is two times higher than for the subsonic version with the same resonator and K density at the gas inlet, the maximum optical-to-optical efficiency being 82%.

  18. Laser spectroscopy and dynamics of transient species

    SciTech Connect

    Clouthier, D.J.

    1993-12-01

    The goal of this program is to study the vibrational and electronic spectra and excited state dynamics of a number of transient sulfur and oxygen species. A variety of supersonic jet techniques, as well as high resolution FT-IR and intracavity dye laser spectroscopy, have been applied to these studies.

  19. Ablation dynamics in laser sclerotomy ab externo

    NASA Astrophysics Data System (ADS)

    Brinkmann, Ralf; Droege, Gerit; Mohrenstecher, Dirk; Scheu, M.; Birngruber, Reginald

    1996-01-01

    Laser sclerostomy ab externo with flashlamp excited mid-IR laser systems emitting in the 2-3 micrometer spectral range is in phase II clinical trials. Although acutely high success rates were achieved, the restenosis rate after several months is about 40%. Laser pulses of several hundreds of microseconds, known to induce thermo-mechanical explosive evaporation were used for this procedure. We investigated the ablation dynamics in tissue and the cavitation bubble dynamics in water by means of an Er:YAG laser system to estimate the extent of mechanical damage zones in the sclera and in the anterior chamber, which may contribute to the clinical failure. We found substantial mechanical tissue deformation during the ablation process caused by the cavitation effects. Stress waves up to several bar generated by explosive evaporization were measured. The fast mechanical stretching and collapsing of the scleral tissue induced by cavitation resulted in tissue dissection as could be proved by flash photography and histology. The observed high restenosis might be a result of a subsequent enhanced wound healing process. Early fistula occlusions due to iris adherences, observed in about 20% of the clinical cases may be attributed to intraocular trauma induced by vapor bubble expansion through the anterior chamber after scleral perforation. An automatic feedback system minimizing adverse effects by steering and terminating the laser process during scleral fistulization is demonstrated. Moreover, a new approach in laser sclerostomy ab externo is presented using a cw-IR laser diode system emitting at the 1.94 micrometer mid-IR water absorption peak. This system was used in vitro and showed smaller damage zones compared to the pulsed laser radiation.

  20. Ignition experiment design based on γ-pumping gas lasers

    NASA Astrophysics Data System (ADS)

    Bonyushkin, E. K.; Il'kaev, R. I.; Morovov, A. P.; Pavlovskii, A. I.; Lazhintsev, B. V.; Basov, N.; Gus'kov, S. Yu.; Rosanov, V. B.; Zmitrenko, N. V.

    1996-05-01

    Comparative analysis of gas lasers pumped by γ-radiation for ignition experiment is carried out. The possibilities of frequency-time pulse shaping are discussed for these kinds of laser drivers. New type of ICF target (LIGHT-target), which is able to provide an uniform deposition of laser driver energy is proposed as a target for ignition experiment.

  1. Plasma physics issues in gas discharge laser development

    SciTech Connect

    Garscadden, A. ); Kushner, M.J.; Eden, J.G. . Dept. of Electrical and Computer Engineering)

    1991-12-01

    In this paper an account is given of the interplay between partially ionized plasma physics and the development of gas discharge lasers. Gas discharge excitation has provided a wide array of laser devices extending from the soft X-ray region to the far infrared. The scaling of gas discharge lasers in power and energy also covers many orders of magnitude. The particular features of three regimes are discussed: short wavelength lasers (deep UV to soft X-ray); visible and near UV lasers; and infrared molecular gas lasers. The current status (Fall 1990) of these areas is reviewed, and an assessment is made of future research topics that are perceived to be important.

  2. Dynamics of the spectral behaviour of an ultrashort laser pulse in an argon-gas-filled capillary discharge-preformed plasma channel

    NASA Astrophysics Data System (ADS)

    Sakai, S.; Higashiguchi, T.; Yugami, N.; Bobrova, N.; Sentoku, Y.; Kodama, R.

    2013-11-01

    We have reported the argon plasma waveguide produced in an alumina (Al2O3) capillary discharge and used to guide ultrashort laser pulses at intensities of the order of 1016 W/cm2. A one-dimensional magnetohydrodynamic (MHD) code was used to evaluate the average degree of ionization of Ar in the preformed plasma channel. The spectrum of the propagated laser pulse in the Ar plasma waveguide was not modified and was well reproduced by a particle-in-cell (PIC) simulation under initial ion charge state of Ar3+ in the preformed plasma waveguide. The optimum timing for the laser pulse injection was around 150 ns after initiation of a discharge with a peak current of 200 A.

  3. Power supply for negative impedance gas discharge lasers

    SciTech Connect

    Bees, G.L.

    1987-12-29

    An adjustable constant current power supply for a negative impedance gas discharge laser is described comprising: means for providing constant output of current, means connected between the constant current providing means and the gas discharge laser for matching the current output of the constant current providing means with lasing requirements of the gas discharge laser, the constant current providing means providing electrical energy to pump the gas discharge laser; and means electrically connected to the constant current providing means for feeding a variable controlled voltage to the constant current providing means the variable voltage altering the constant output of current over a preselected range feedback circuit means for providing a control signal to the variably controlled voltage feeding means; such that output power of the gas discharge laser varies with the output of current from the current providing means.

  4. Precision and Fast Wavelength Tuning of a Dynamically Phase-Locked Widely-Tunable Laser

    NASA Technical Reports Server (NTRS)

    Numata, Kenji; Chen, Jeffrey R.; Wu, Stewart T.

    2012-01-01

    We report a precision and fast wavelength tuning technique demonstrated for a digital-supermode distributed Bragg reflector laser. The laser was dynamically offset-locked to a frequency-stabilized master laser using an optical phase-locked loop, enabling precision fast tuning to and from any frequencies within a 40-GHz tuning range. The offset frequency noise was suppressed to the statically offset-locked level in less than 40 s upon each frequency switch, allowing the laser to retain the absolute frequency stability of the master laser. This technique satisfies stringent requirements for gas sensing lidars and enables other applications that require such well-controlled precision fast tuning.

  5. Dynamics of strong-field laser-induced microplasma formation in noble gases

    NASA Astrophysics Data System (ADS)

    Romanov, D. A.; Compton, R.; Filin, A.; Levis, R. J.

    2010-03-01

    The ultrafast dynamics of microplasmas generated by femtosecond laser pulses in noble gases has been investigated using four-wave mixing (FWM). The time dependence of the FWM signal is observed to reach higher intensity levels faster for Xe, with progressively lower scattering intensity and longer time dynamics for the noble gas series Xe, Kr, Ar, Ne, and He. The temporal dynamics is interpreted in terms of a tunnel ionization and impact cooling mechanism. A formalism to interpret the observed phenomena is presented here with comparison to the measured laser intensity and gas pressure trends.

  6. Dynamic pulsing of a MOPA fiber laser

    NASA Astrophysics Data System (ADS)

    Romero, Rosa; Guerreiro, Paulo T.; Hendow, Sami T.; Salcedo, José R.

    2011-05-01

    Dynamic Pulsing is demonstrated using a pulsed MOPA fiber laser at 1064nm. The output of the MOPA laser is a pulsed profile consisting of a burst of closely spaced pulses. Tests were performed under several materials with pulse bursts ranging from 10ns to 1μs and operating from 500kHz down to single shot. In particular, percussion drilling in stainless steel is demonstrated showing improvements in quality and speed of the process. These profiles allow high flexibility and optimization of the process addressing the specificity of the end application. Dynamic Pulsing allows the same MOPA fiber laser to be used in diverse materials as well as different processes such us marking, drilling, scribing and engraving. The pulsed fiber laser used in this study is a MOPA-DY by Multiwave Photonics. It is based on a modulated seed laser followed by a series of fiber amplifiers and ending with an optically isolated collimator. This pulsed laser model has an output in such a way that each trigger produces a fast burst of pulses, with a repetition frequency within the burst of the order of tens of MHz. Within the burst it is possible to change the number of pulses, the individual pulse profile, burst pulse period and even to generate non-periodic burst pulse separations. The laser allows full freedom for all these combinations. The study here reported compares the impact of pulse peak power, number of pulses within a burst and the pulse burst period, on process quality (heat affected zone, debris, hole uniformity) and drilling yield.

  7. Plasma and laser kinetics and field emission from carbon nanotube fibers for an Advanced Noble Gas Laser (ANGL)

    NASA Astrophysics Data System (ADS)

    Moran, Paul J.; Lockwood, Nathaniel P.; Lange, Matthew A.; Hostutler, David A.; Guild, Eric M.; Guy, Matthew R.; McCord, John E.; Pitz, Greg A.

    2016-03-01

    A metastable argon laser operating at 912 nm has been demonstrated by optically pumping with a pulsed titanium sapphire laser to investigate the temporal dynamics of an Advanced Noble Gas Laser (ANGL). Metastable argon concentrations on the order of 1011 cm-3 were maintained with the use of a radio frequency (RF) capacitively coupled discharge. The end-pumped laser produced output powers under 2 mW of average power with pulse lengths on the order of 100 ns. A comparison between empirical results and a four level laser model using longitudinally average pump and inter-cavity intensities is made. An alternative, highly-efficient method of argon metastable production for ANGL was explored using carbon nanotube (CNT) fibers.

  8. Modeling dynamical geometry with lattice gas automata

    SciTech Connect

    Hasslacher, B.; Meyer, D.A.

    1998-06-27

    Conventional lattice gas automata consist of particles moving discretely on a fixed lattice. While such models have been quite successful for a variety of fluid flow problems, there are other systems, e.g., flow in a flexible membrane or chemical self-assembly, in which the geometry is dynamical and coupled to the particle flow. Systems of this type seem to call for lattice gas models with dynamical geometry. The authors construct such a model on one dimensional (periodic) lattices and describe some simulations illustrating its nonequilibrium dynamics.

  9. Comet Gas and Dust Dynamics Modeling

    NASA Technical Reports Server (NTRS)

    Von Allmen, Paul A.; Lee, Seungwon

    2010-01-01

    This software models the gas and dust dynamics of comet coma (the head region of a comet) in order to support the Microwave Instrument for Rosetta Orbiter (MIRO) project. MIRO will study the evolution of the comet 67P/Churyumov-Gerasimenko's coma system. The instrument will measure surface temperature, gas-production rates and relative abundances, and velocity and excitation temperatures of each species along with their spatial temporal variability. This software will use these measurements to improve the understanding of coma dynamics. The modeling tool solves the equation of motion of a dust particle, the energy balance equation of the dust particle, the continuity equation for the dust and gas flow, and the dust and gas mixture energy equation. By solving these equations numerically, the software calculates the temperature and velocity of gas and dust as a function of time for a given initial gas and dust production rate, and a dust characteristic parameter that measures the ability of a dust particle to adjust its velocity to the local gas velocity. The software is written in a modular manner, thereby allowing the addition of more dynamics equations as needed. All of the numerical algorithms are added in-house and no third-party libraries are used.

  10. Dual-wavelength quantum cascade laser for trace gas spectroscopy

    SciTech Connect

    Jágerská, J.; Tuzson, B.; Mangold, M.; Emmenegger, L.; Jouy, P.; Hugi, A.; Beck, M.; Faist, J.; Looser, H.

    2014-10-20

    We demonstrate a sequentially operating dual-wavelength quantum cascade laser with electrically separated laser sections, emitting single-mode at 5.25 and 6.25 μm. Based on a single waveguide ridge, this laser represents a considerable asset to optical sensing and trace gas spectroscopy, as it allows probing multiple gas species with spectrally distant absorption features using conventional optical setups without any beam combining optics. The laser capability was demonstrated in simultaneous NO and NO{sub 2} detection, reaching sub-ppb detection limits and selectivity comparable to conventional high-end spectroscopic systems.

  11. Laser-enhanced dynamics in molecular rate processes

    NASA Technical Reports Server (NTRS)

    George, T. F.; Zimmerman, I. H.; Devries, P. L.; Yuan, J.-M.; Lam, K.-S.; Bellum, J. C.; Lee, H.-W.; Slutsky, M. S.

    1978-01-01

    The present discussion deals with some theoretical aspects associated with the description of molecular rate processes in the presence of intense laser radiation, where the radiation actually interacts with the molecular dynamics. Whereas for weak and even moderately intense radiation, the absorption and stimulated emission of photons by a molecular system can be described by perturbative methods, for intense radiation, perturbation theory is usually not adequate. Limiting the analysis to the gas phase, an attempt is made to describe nonperturbative approaches applicable to the description of such processes (in the presence of intense laser radiation) as electronic energy transfer in molecular (in particular atom-atom) collisions; collision-induced ionization and emission; and unimolecular dissociation.

  12. Experimental evidence of antiphase population dynamics in lasers

    SciTech Connect

    Cabrera, Eduardo; Calderon, Oscar G.; Guerra, J.M.

    2005-10-15

    We report a direct experimental observation of antiphase oscillations in population dynamics in lasers. We show that these population oscillations are intrinsically related to the well-known antiphase polarization dynamics, i.e., the antiphase oscillations of two orthogonal polarization laser field states. We have used a class B Nd:YAG (yttrium aluminum garnet) laser.

  13. Computational modeling of intraocular gas dynamics.

    PubMed

    Noohi, P; Abdekhodaie, M J; Cheng, Y L

    2015-01-01

    The purpose of this study was to develop a computational model to simulate the dynamics of intraocular gas behavior in pneumatic retinopexy (PR) procedure. The presented model predicted intraocular gas volume at any time and determined the tolerance angle within which a patient can maneuver and still gas completely covers the tear(s). Computational fluid dynamics calculations were conducted to describe PR procedure. The geometrical model was constructed based on the rabbit and human eye dimensions. SF6 in the form of pure and diluted with air was considered as the injected gas. The presented results indicated that the composition of the injected gas affected the gas absorption rate and gas volume. After injection of pure SF6, the bubble expanded to 2.3 times of its initial volume during the first 23 h, but when diluted SF6 was used, no significant expansion was observed. Also, head positioning for the treatment of retinal tear influenced the rate of gas absorption. Moreover, the determined tolerance angle depended on the bubble and tear size. More bubble expansion and smaller retinal tear caused greater tolerance angle. For example, after 23 h, for the tear size of 2 mm the tolerance angle of using pure SF6 is 1.4 times more than that of using diluted SF6 with 80% air. Composition of the injected gas and conditions of the tear in PR may dramatically affect the gas absorption rate and gas volume. Quantifying these effects helps to predict the tolerance angle and improve treatment efficiency. PMID:26682529

  14. Computational modeling of intraocular gas dynamics

    NASA Astrophysics Data System (ADS)

    Noohi, P.; Abdekhodaie, M. J.; Cheng, Y. L.

    2015-12-01

    The purpose of this study was to develop a computational model to simulate the dynamics of intraocular gas behavior in pneumatic retinopexy (PR) procedure. The presented model predicted intraocular gas volume at any time and determined the tolerance angle within which a patient can maneuver and still gas completely covers the tear(s). Computational fluid dynamics calculations were conducted to describe PR procedure. The geometrical model was constructed based on the rabbit and human eye dimensions. SF6 in the form of pure and diluted with air was considered as the injected gas. The presented results indicated that the composition of the injected gas affected the gas absorption rate and gas volume. After injection of pure SF6, the bubble expanded to 2.3 times of its initial volume during the first 23 h, but when diluted SF6 was used, no significant expansion was observed. Also, head positioning for the treatment of retinal tear influenced the rate of gas absorption. Moreover, the determined tolerance angle depended on the bubble and tear size. More bubble expansion and smaller retinal tear caused greater tolerance angle. For example, after 23 h, for the tear size of 2 mm the tolerance angle of using pure SF6 is 1.4 times more than that of using diluted SF6 with 80% air. Composition of the injected gas and conditions of the tear in PR may dramatically affect the gas absorption rate and gas volume. Quantifying these effects helps to predict the tolerance angle and improve treatment efficiency.

  15. Modeling of ns and ps laser-induced soft X-ray sources using nitrogen gas puff target

    SciTech Connect

    Vrba, P.; Vrbova, M.; Zakharov, S. V.

    2014-07-15

    Gas puff laser plasma is studied as a source of water window radiation with 2.88 nm wavelength, corresponding to quantum transition 1s{sup 2} → 1s2p of helium-like nitrogen ions. Spatial development of plasma induced by Nd:YAG laser beam is simulated by 2D Radiation-Magneto-Hydro-Dynamic code Z*. The results for nitrogen gas layer (0.72 mm thickness, 1 bar pressure) and two different laser pulses (600 mJ/7 ns and 525 mJ/170 ps), corresponding to the experiments done in Laser Laboratory Gottingen are presented.

  16. High power lasers: Sources, laser-material interactions, high excitations, and fast dynamics in laser processing and industrial applications; Proceedings of the Meeting, The Hague, Netherlands, Mar. 31-Apr. 3, 1987

    NASA Technical Reports Server (NTRS)

    Kreutz, E. W. (Editor); Quenzer, Alain (Editor); Schuoecker, Dieter (Editor)

    1987-01-01

    The design and operation of high-power lasers for industrial applications are discussed in reviews and reports. Topics addressed include the status of optical technology in the Netherlands, laser design, the deposition of optical energy, laser diagnostics, nonmetal processing, and energy coupling and plasma formation. Consideration is given to laser-induced damage to materials, fluid and gas flow dynamics, metal processing, and manufacturing. Graphs, diagrams, micrographs, and photographs are provided.

  17. Investigation on RGB laser source applied to dynamic photoelastic experiment

    NASA Astrophysics Data System (ADS)

    Li, Songgang; Yang, Guobiao; Zeng, Weiming

    2014-06-01

    When the elastomer sustains the shock load or the blast load, its internal stress state of every point will change rapidly over time. Dynamic photoelasticity method is an experimental stress analysis method, which researches the dynamic stress and the stress wave propagation. Light source is one of very important device in dynamic photoelastic experiment system, and the RGB laser light source applied in dynamic photoelastic experiment system is innovative and evolutive to the system. RGB laser is synthesized by red laser, green laser and blue laser, either as a single wavelength laser light source, also as synthesized white laser light source. RGB laser as a light source for dynamic photoelastic experiment system, the colored isochromatic can be captured in dynamic photoelastic experiment, and even the black zero-level stripe can be collected, and the isoclinics can also be collected, which conducively analysis and study of transient stress and stress wave propagation. RGB laser is highly stable and continuous output, and its power can be adjusted. The three wavelengths laser can be synthesized by different power ratio. RGB laser light source used in dynamic photoelastic experiment has overcome a number of deficiencies and shortcomings of other light sources, and simplifies dynamic photoelastic experiment, which has achieved good results.

  18. Copper Gas Diffusers For Purging Line-Focus Laser Welds

    NASA Technical Reports Server (NTRS)

    Fonteyne, Steve L.; Hosking, Timothy J.; Shelley, D. Mark

    1996-01-01

    Modified flow diffusers built for inert-gas purging of welds made with 5-kW CO(2) lasers operating with line-focus optics in conduction mode instead of with point-focus optics in customary keyhole mode. Diffusers made of copper components brazed together, robust enough to withstand strong reflections of line-focused laser energy.

  19. Plume Dynamics of Laser-Produced Swine Muscle Tissue Plasma.

    PubMed

    Camacho, Joaquin J; Diaz, Luis; Marin-Roldan, Alicia; Moncayo, Samuel; Caceres, Jorge O

    2016-07-01

    We report on the plume dynamics of the plasma induced by laser ablation of a swine skeletal muscle tissue sample in different vacuum conditions. Pulses from a transversely excited atmospheric CO2 laser were focused onto a target sample and the induced plasma was allowed to expand in different air pressures. The expansion features were studied using fast photography of the overall visible emission by using a gated intensified charged coupled device. Free expansion and plume splitting were observed at different pressure levels. The expansion of the plasma plume front was analyzed using various expansion models and the velocity of the plume front was estimated. The effect of the number of accumulated laser shots on the crater volume at different ambient air pressures and an elemental analysis of the sample were performed using scanning electron microscopy coupled with energy dispersive X-ray spectroscopy (EDX) analysis. The surface morphology of the irradiated surface showed that increasing the pressure of the ambient gas decreased the ablated mass, or in other words it reduced significantly the laser-target coupling. PMID:27301327

  20. Gas dynamics in strong centrifugal fields

    SciTech Connect

    Bogovalov, S.V.; Kislov, V.A.; Tronin, I.V.

    2015-03-10

    Dynamics of waves generated by scopes in gas centrifuges (GC) for isotope separation is considered. The centrifugal acceleration in the GC reaches values of the order of 106g. The centrifugal and Coriolis forces modify essentially the conventional sound waves. Three families of the waves with different polarisation and dispersion exist in these conditions. Dynamics of the flow in the model GC Iguasu is investigated numerically. Comparison of the results of the numerical modelling of the wave dynamics with the analytical predictions is performed. New phenomena of the resonances in the GC is found. The resonances occur for the waves polarized along the rotational axis having the smallest dumping due to the viscosity.

  1. Laser speckle analysis of retinal vascular dynamics

    PubMed Central

    Neganova, Anastasiia Y; Postnov, Dmitry D; Jacobsen, Jens Christian B.; Sosnovtseva, Olga

    2016-01-01

    Studies of vascular responses are usually performed on isolated vessels or on single vessels in vivo. This allows for precise measurements of diameter or blood flow. However, dynamical responses of the whole microvascular network are difficult to access experimentally. We suggest to use full-field laser speckle imaging to evaluate vascular responses of the retinal network. Image segmentation and vessel recognition algorithms together with response mapping allow us to analyze diameter changes and blood flow responses in the intact retinal network upon systemic administration of the vasoconstrictor angiotensin II, the vasodilator acetylcholine or on the changing level of anesthesia in in vivo rat preparations.

  2. FIR line profiles as probes of warm gas dynamics

    NASA Astrophysics Data System (ADS)

    Betz, A. L.; Boreiko, R. T.

    Measurements of the shapes, velocities, and intensities of FIR lines all help to probe the dynamics, physical associations, and excitation conditions of warm gas in molecular clouds. With this in mind, we have observed the J=9-8, 12-11,14-13, and 16-15 lines of (12)CO and the 158 micron line of C II in a number of positions in 4 selected clouds. The data were obtained with a laser heterodyne spectrometer aboard NASA's Kuiper Airborne Observatory. Line measurements at 0.6 km/s resolution allow us to resolve the profiles completely, and thereby to distinguish between UV-and shock-heating mechanisms for the high-excitation gas. For CO, the high-J linewidths lie in the range of 4-20 km/s (FWHM), similar to those observed for low-J (J less than 4) transitions in these sources. This correspondence suggests that the hotter gas (T = 200-600 K) is dynamically linked to the quiescent gas component, perhaps by association with the UV-heated peripheries of the numerous cloud clumps. Much of the C II emission is thought to emanate from these cloud peripheries, but the line profiles generally do not match those seen in CO. None of the observed sources show any evidence in high-J (12)CO emission for shock-excitation (i.e., linewidths greater than 30 km/s).

  3. Laser absorption phenomena in flowing gas devices

    NASA Technical Reports Server (NTRS)

    Chapman, P. K.; Otis, J. H.

    1976-01-01

    A theoretical and experimental investigation is presented of inverse Bremsstrahlung absorption of CW CO2 laser radiation in flowing gases seeded with alkali metals. In order to motivate this development, some simple models are described of several space missions which could use laser powered rocket vehicles. Design considerations are given for a test call to be used with a welding laser, using a diamond window for admission of laser radiation at power levels in excess of 10 kW. A detailed analysis of absorption conditions in the test cell is included. The experimental apparatus and test setup are described and the results of experiments presented. Injection of alkali seedant and steady state absorption of the laser radiation were successfully demonstrated, but problems with the durability of the diamond windows at higher powers prevented operation of the test cell as an effective laser powered thruster.

  4. Collisional thulium vapour gas-discharge laser

    SciTech Connect

    Gerasimov, V A; Pavlinskii, A V

    2004-01-31

    A collisional laser on a system of atomic levels based on the principle proposed by Gould is built for the first time. The population of the upper laser level and relaxation of the lower level occur upon inelastic collisions of excited thulium atoms with helium atoms. The lower-level relaxation occurs in a reaction with an energy defect of > 13000 cm{sup -1}. (active media. lasers)

  5. [Laser Raman Spectroscopy and Its Application in Gas Hydrate Studies].

    PubMed

    Fu, Juan; Wu, Neng-you; Lu, Hai-long; Wu, Dai-dai; Su, Qiu-cheng

    2015-11-01

    Gas hydrates are important potential energy resources. Microstructural characterization of gas hydrate can provide information to study the mechanism of gas hydrate formation and to support the exploitation and application of gas hydrate technology. This article systemly introduces the basic principle of laser Raman spectroscopy and summarizes its application in gas hydrate studies. Based on Raman results, not only can the information about gas composition and structural type be deduced, but also the occupancies of large and small cages and even hydration number can be calculated from the relative intensities of Raman peaks. By using the in-situ analytical technology, laser Raman specstropy can be applied to characterize the formation and decomposition processes of gas hydrate at microscale, for example the enclathration and leaving of gas molecules into/from its cages, to monitor the changes in gas concentration and gas solubility during hydrate formation and decomposition, and to identify phase changes in the study system. Laser Raman in-situ analytical technology has also been used in determination of hydrate structure and understanding its changing process under the conditions of ultra high pressure. Deep-sea in-situ Raman spectrometer can be employed for the in-situ analysis of the structures of natural gas hydrate and their formation environment. Raman imaging technology can be applied to specify the characteristics of crystallization and gas distribution over hydrate surface. With the development of laser Raman technology and its combination with other instruments, it will become more powerful and play a more significant role in the microscopic study of gas hydrate. PMID:26978895

  6. Single shot dynamic ellipsometry mesaurements of laser-driven shock waves

    SciTech Connect

    Bolme, C. A.

    2007-12-12

    A technique has been developed to measure the time-resolved position of a laser-driven shock wave and the subsequent material flow. Ultrafast dynamic ellipsometry, using a chirped femtosecond laser pulse, probes picosecond material dynamics in a single shot by capitalizing on the refractive index changes in the shocked material. For transparent materials, the shock velocity, the particle velocity, and the shocked material's refractive index are extracted. Hugoniot data for poly(chlorotrifluoroethylene-co-vinylidene fluoride) (Kel-F 800) was obtained using ultrafast dynamic ellipsometry, and the data agrees well with previous data on macroscopic samples obtained in plate impact gas gun experiments.

  7. Molecular dynamics studies on nanoscale gas transport

    NASA Astrophysics Data System (ADS)

    Barisik, Murat

    Three-dimensional molecular dynamics (MD) simulations of nanoscale gas flows are studied to reveal surface effects. A smart wall model that drastically reduces the memory requirements of MD simulations for gas flows is introduced. The smart wall molecular dynamics (SWMD) represents three-dimensional FCC walls using only 74 wall Molecules. This structure is kept in the memory and utilized for each gas molecule surface collision. Using SWMD, fluid behavior within nano-scale confinements is studied for argon in dilute gas, dense gas, and liquid states. Equilibrium MD method is employed to resolve the density and stress variations within the static fluid. Normal stress calculations are based on the Irving-Kirkwood method, which divides the stress tensor into its kinetic and virial parts. The kinetic component recovers pressure based on the ideal gas law. The particle-particle virial increases with increased density, while the surface-particle virial develops due to the surface force field effects. Normal stresses within nano-scale confinements show anisotropy induced primarily by the surface force-field and local variations in the fluid density near the surfaces. For dilute and dense gas cases, surface-force field that extends typically 1nm from each wall induces anisotropic normal stress. For liquid case, this effect is further amplified by the density fluctuations that extend beyond the three field penetration region. Outside the wall force-field penetration and density fluctuation regions the normal stress becomes isotropic and recovers the thermodynamic pressure, provided that sufficiently large force cut-off distances are utilized in the computations. Next, non-equilibrium SWMD is utilized to investigate the surface-gas interaction effects on nanoscale shear-driven gas flows in the transition and free molecular flow regimes. For the specified surface properties and gas-surface pair interactions, density and stress profiles exhibit a universal behavior inside the

  8. Application of YAG laser welding to gas turbine components

    NASA Astrophysics Data System (ADS)

    Tsubota, Shuho; Mega, Masahiko; Takahashi, Koji; Uemura, Yoshitaka; Hirota, Norihide; Yamaguchi, Kengo

    2003-03-01

    An investigation to apply YAG laser welding to gas turbine components was carried out. The materials of gas turbine such as Ni base alloy are difficult to weld by conventional arc welding methods because of large heat affection. But laser welding can reduce heat input compared with conventional methods and keeps the good repeatability. The welding parameter survey was carried out to satisfy the designing requirements. The YAG laser welding under appropriate conditions enables to prevent welding defects such as HAZ cracks and improves the weld joints quality and performance. Tensile test and low cycle fatigue test were carried out. Tensile strength and fatigue life of laser weld joints are same or higher than that of conventional manual TIG weld joints. The Automatic YAG laser welding system was also developed and put into practical use.

  9. Planar Laser-Based QEPAS Trace Gas Sensor

    PubMed Central

    Ma, Yufei; He, Ying; Chen, Cheng; Yu, Xin; Zhang, Jingbo; Peng, Jiangbo; Sun, Rui; Tittel, Frank K.

    2016-01-01

    A novel quartz enhanced photoacoustic spectroscopy (QEPAS) trace gas detection scheme is reported in this paper. A cylindrical lens was employed for near-infrared laser focusing. The laser beam was shaped as a planar line laser between the gap of the quartz tuning fork (QTF) prongs. Compared with a spherical lens-based QEPAS sensor, the cylindrical lens-based QEPAS sensor has the advantages of easier laser beam alignment and a reduction of stringent stability requirements. Therefore, the reported approach is useful in long-term and continuous sensor operation. PMID:27367686

  10. Planar Laser-Based QEPAS Trace Gas Sensor.

    PubMed

    Ma, Yufei; He, Ying; Chen, Cheng; Yu, Xin; Zhang, Jingbo; Peng, Jiangbo; Sun, Rui; Tittel, Frank K

    2016-01-01

    A novel quartz enhanced photoacoustic spectroscopy (QEPAS) trace gas detection scheme is reported in this paper. A cylindrical lens was employed for near-infrared laser focusing. The laser beam was shaped as a planar line laser between the gap of the quartz tuning fork (QTF) prongs. Compared with a spherical lens-based QEPAS sensor, the cylindrical lens-based QEPAS sensor has the advantages of easier laser beam alignment and a reduction of stringent stability requirements. Therefore, the reported approach is useful in long-term and continuous sensor operation. PMID:27367686

  11. Multifrequency laser probing of CO-containing gas mixtures excited in a pulsed discharge

    SciTech Connect

    Ionin, Andrei A; Klimachev, Yu M; Kozlov, A Yu; Kotkov, A A; Rulev, O A; Seleznev, L V; Sinitsyn, D V

    2007-03-31

    The method of multifrequency laser probing is developed which can be used for diagnostics of the temperature and population of vibrational levels in gas mixtures containing CO molecules in excited vibrational states. The method is tested by studying the dynamics of the gas temperature and population of vibrational levels of the CO molecule in gas mixtures excited by a pulsed discharge. It is shown that the method provides the reduction of the gas temperature measurement error down to 3%. It is found that the population of lower vibrational levels in the CO-O{sub 2} mixture can exceed the population of levels in CO-He and CO-N{sub 2} laser mixtures by several times. (active media)

  12. Biomedical Investigations with Laser-Polarized Noble Gas Magnetic Resonance

    NASA Technical Reports Server (NTRS)

    Walsworth, Ronald L.

    2003-01-01

    We pursued advanced technology development of laser-polarized noble gas nuclear magnetic resonance (NMR) as a novel biomedical imaging tool for ground-based and eventually space-based application. This new multidisciplinary technology enables high-resolution gas-space magnetic resonance imaging (MRI)-e.g., of lung ventilation-as well as studies of tissue perfusion. In addition, laser-polarized noble gases (3He and 129Xe) do not require a large magnetic field for sensitive detection, opening the door to practical MRI at very low magnetic fields with an open, lightweight, and low-power device. We pursued two technology development specific aims: (1) development of low-field (less than 0.01 T) noble gas MRI of humans; and (2) development of functional MRI of the lung using laser-polarized noble gas and related techniques.

  13. LaRC results on nuclear pumped noble gas lasers

    NASA Technical Reports Server (NTRS)

    Deyoung, R. J.

    1979-01-01

    The recent experiment and theoretical results obtained for noble gas nuclear laser systems are presented. It is shown that the noble gas lasers are among the easiest systems to pump by nuclear excitation and as a result, all of the noble gases except He have lased under nuclear excitation. The noble gas systems are not ideal for high-power applications but they do give valuable insight into the operation and pumping mechanisms associated with nuclear lasers. At present, the Ar-Xe system is the best noble gas candidate for (U-235)F6 pumping. It appears that the quenching of Ar-Xe lasing is a result of the fluorine and not the uranium or fission fragments themselves. Thus, to achieve lasing with UF6, a fluorine compatible system must be found.

  14. Gas-component analysis of laser fusion targets.

    PubMed

    Schneggenburger, R G; Updegrove, W S; Nolen, R L

    1978-11-01

    A gas-chromatographic method for analyzing the fuel content of laser fusion targets has been developed. It provides information on isotope ratios in the fuel gas, percent of molecular species, and total pressure of fuel gas in individual targets to a limit of 0.2 ng DT. The method can also be used to quantify other gaseous components not active in the thermonuclear process (e.g., H2, He, etc.). PMID:18698997

  15. Dynamic and Structural Gas Turbine Engine Modeling

    NASA Technical Reports Server (NTRS)

    Turso, James A.

    2003-01-01

    Model the interactions between the structural dynamics and the performance dynamics of a gas turbine engine. Generally these two aspects are considered separate, unrelated phenomena and are studied independently. For diagnostic purposes, it is desirable to bring together as much information as possible, and that involves understanding how performance is affected by structural dynamics (if it is) and vice versa. This can involve the relationship between thrust response and the excitation of structural modes, for instance. The job will involve investigating and characterizing these dynamical relationships, generating a model that incorporates them, and suggesting and/or developing diagnostic and prognostic techniques that can be incorporated in a data fusion system. If no coupling is found, at the least a vibration model should be generated that can be used for diagnostics and prognostics related to blade loss, for instance.

  16. On dynamic gas ablation from spherical galaxies

    NASA Astrophysics Data System (ADS)

    Nepveu, M.

    1981-05-01

    Two-dimensional, time dependent gas dynamic calculations are presented on the transonic motion of galaxies through a cluster medium. Lea and De Young's (1976) calculations are extended to include violent behavior in the center. On time scales of 10 to the 8th yr, galaxies in clusters can already lose a significant fraction of their gaseous content (up to 50% has been found in the calculations). This dynamic ablation occurs through rarefaction rather than shock heating. Explosions in spherical galaxies become effective as mechanisms for gas removal only if the galaxy moves with respect to its surroundings. Speculations are made on stripping of spiral galaxies (moving head-on in a cluster); the Gunn and Gott (1972) stripping formula is put to doubt. A method is suggested to obtain information on the state of motion of field galaxies.

  17. Gas lasers pumped by runaway electrons preionized diffuse discharge

    NASA Astrophysics Data System (ADS)

    Panchenko, Alexei N.; Lomaev, Mikhail I.; Panchenko, Nikolai A.; Tarasenko, Victor F.; Suslov, Alexei I.

    2015-05-01

    It was shown that run-away electron preionized volume (diffuse) discharge (REP DD) can be used as an excitation source of gas mixtures at elevated pressures and can produce laser emission. We report experimental and simulated results of application of the REP DD for excitation of different active gas mixtures. Kinetic model of the REP DD in mixtures of nitrogen with SF6 is developed allowing predicting the radiation parameters of nitrogen laser at 337.1 nm. Peculiarities of the REP DD development in different gas mixtures are studied, as well. It was shown that the REP DD allows obtaining efficient lasing stimulated radiation in the IR, visible and UV spectral ranges. New operation mode of nitrogen laser is demonstrated under REP DD excitation. Laser action on N2, HF, and DF molecules was obtained with the efficiency close to the limiting value. Promising prospects of REP DD employment for exciting a series of gas lasers was demonstrated. It was established that the REP DD is most efficient for pumping lasers with the mixtures comprising electro-negative gases.

  18. Selfsimilar Spherical Compression Waves in Gas Dynamics

    NASA Astrophysics Data System (ADS)

    Meyer-ter-Vehn, J.; Schalk, C.

    1982-08-01

    A synopsis of different selfsimilar spherical compression waves is given pointing out their fundamental importance for the gas dynamics of inertial confinement fusion. Strong blast waves, various forms of isentropic compression waves, imploding shock waves and the solution for non-isentropic collapsing hollow spheres are included. A classification is given in terms of six singular points which characterise the different solutions and the relations between them. The presentation closely follows Guderley's original work on imploding shock waves

  19. Selfsimilar spherical compression waves in gas dynamics

    NASA Astrophysics Data System (ADS)

    Meyer-Ter-Vehn, J.; Schalk, C.

    1982-05-01

    A synopsis of different selfsimilar spherical compression waves is given pointing out their fundamental importance for the gas dynamics of inertial confinement fusion. Strong blast waves, various forms of isentropic collapsing hollow spheres are included. A classification is given in terms of six singular points which characterize the different solutions and the relations between them. The presentation closely follows Guderley's original work on imploding shock waves.

  20. Effect of background gas pressure and laser pulse intensity on laser induced plasma radiation of copper samples

    NASA Astrophysics Data System (ADS)

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

    2010-04-01

    Study of laser induced plasma emission of Cu in one dimension is numerically carried out. Effects of different background gas pressure (He), 100, 500, and 760 torr, and laser pulse intensities, 0.5, 0.7, and 1 GW/cm2, on the plasma emission as well as ablation processes are investigated. Under a specified condition, heat conduction equation in the target accompanied with gas dynamic equations in the plume is solved simultaneously. The mentioned equations are coupled to each other through the Knudsen layer conditions and the energy and mass balances at the interface between the target and the vapor. The Bremsstrahlung radiation of plasma and the spectral emission of copper atoms are studied under various background gas pressure and laser pulse intensities. Furthermore, number density of He, Cu, and the electron, pressure, and temperature of the plume under various conditions are obtained. In the early time after laser pulse, plasma radiation is mainly due to the Bremsstrahlung radiation while after some 10 ns, the plasma radiation is dominated by spectral emission of Cu atoms. A similar uncoupling is observed spatially. The Bremsstrahlung emission is dominant near the sample surface while at farther points the spectral emission is the dominant one. By increase in the background pressure and also the pulse intensity, the dominancy of the spectral emission would occur later in time and farther in position.

  1. Dynamics Of Electronic Excitation Of Solids With Ultrashort Laser Pulse

    SciTech Connect

    Medvedev, Nikita; Rethfeld, Baerbel

    2010-10-08

    When ultrashort laser pulses irradiate a solid, photoabsorption by electrons in conduction band produces nonequilibrium highly energetic free electrons gas. We study the ionization and excitation of the electronic subsystem in a semiconductor and a metal (solid silicon and aluminum, respectively). The irradiating femtosecond laser pulse has a duration of 10 fs and a photon energy of h-bar {omega} = 38 eV. The classical Monte Carlo method is extended to take into account the electronic band structure and Pauli's principle for electrons excited to the conduction band. In the case of semiconductors this applies to the holes as well. Conduction band electrons and valence band holes induce secondary excitation and ionization processes which we simulate event by event. We discuss the transient electron dynamics with respect to the differences between semiconductors and metals. For metals the electronic distribution is split up into two branches: a low energy distribution as a slightly distorted Fermi-distribution and a long high energy tail. For the case of semiconductors it is split into two parts by the band gap. To thermalize, these excited electronic subsystems need longer times than the characteristic pulse duration. Therefore, the analysis of experimental data with femtosecond lasers must be based on non-equilibrium concepts.

  2. Dynamic Phenomena in Laser Cutting and Process Performance

    NASA Astrophysics Data System (ADS)

    Schuöcker, Dieter; Aichinger, Joachim; Majer, Richard

    Laser cutting of sheet metals is widely used all over the world since it combines high speed with excellent cutting quality. Nevertheless if the thickness of the work piece becomes relatively high, the roughness of the cut edges becomes quite coarse and also the formation of dross and slag is likely. The latter phenomena must obviously be related to dynamic processes that can be identified as fluctuations in the liquid body that forms at the current end of the cut due to absorption of laser radiation and where material removal takes place due to friction with a sharply focused gas jet. A detailed analysis of the liquid layer shows that viscosity and surface tension that have so far not been considered very often in the literature have a strong impact on the material removal mechanism which consists of the formation and separation of droplets formed at the bottom of the work piece, thus being essentially intermittent. The mathematical treatment of this model shows good coincidence with experimental data. It gives rise to the idea that a substantial reduction of surface tension could improve the material removal mechanism insofar as the intermittent ejection is transformed into a continuous ejection of melt flow thus considerably improving cutting speed and quality. These ideas have also led to a new patent for an improved laser cutting head.

  3. Food monitoring based on diode laser gas spectroscopy

    NASA Astrophysics Data System (ADS)

    Lewander, M.; Guan, Z. G.; Persson, L.; Olsson, A.; Svanberg, S.

    2008-11-01

    Food is frequently packed in a controlled environment of gas, in order to extend shelf life. It is of great importance to be able to monitor the status of the packed food to ensure quality. We demonstrate a technique to monitor the gas inside packages non-intrusively by using a laser spectroscopic method in scattering solid materials. The technique named GASMAS (GAs in Scattering Media Absorption Spectroscopy) is based on tunable diode laser absorption spectroscopy and relies on the fact that free gas inside solid materials absorbs much sharper spectrally than the bulk material. Results from time dependent measurements of molecular oxygen and water vapour in packages of minced meat, bake-off bread, and the headspace of a milk carton are presented. We show that the technique allows gas measurements inside the food through the package, and assessment of the integrity of the package.

  4. Laser photoacoustics for gas analysis and materials testing

    NASA Astrophysics Data System (ADS)

    Sigrist, Markus W.

    1995-07-01

    The application of laser photoacoustics to two different areas is discussed. First, laser-induced spallation and interferometric detection of transient surface displacements is proposed as a powerful noncontact tool for the investigation of adhesion properties of solid surface coatings. Results for nickel and plasma-sprayed ceramic coatings are presented. Delamination processes at the interface between substrate and coating could be detected with excellent spatial and temporal resolution and adhesion strengths in the 0.2 to 2 GPa range be determined. Second, laser photoacoustic spectroscopy is applied to trace gas monitoring. An automated mobile CO2$ laser photoacoustic system is employed for in situ air monitoring with parts per billion sensitivity in industrial, urban, and rural environments. An improvement in detection selectivity for multicomponent gas mixtures is achieved with a continuously tunable high- pressure CO2 laser with a narrow linewidth of 0.017 cm-1. A CO laser photoacoustic system previously used for the analysis of motor vehicle exhausts is now employed for studying dimerization phenomena in fatty acid vapors. Finally, emphasis is put on the development of widely tunable, narrow-band, mid-IR laser sources based on optical parametric oscillation or difference frequency generation employing tunable diode lasers and AgGaSe2 as nonlinear material.

  5. The study of gas species on THz generation from laser-induced air plasma

    NASA Astrophysics Data System (ADS)

    Zhao, Ji; Zhang, LiangLiang; Wu, YiJian; Wu, Tong; Yuan, Hui; Zhang, CunLin; Zhao, YueJin

    2015-08-01

    Intense Terahertz waves generated from air-induced plasma and serving as broadband THz source provide a promising broadband source for innovative technology. Terahertz generation in selected gases has attracted more and more researchers' interests in recent years. In this research, the THz emission from different atoms is described, such as nitrogen, argon and helium in Michelson. The THz radiation is detected by a Golay Cell equipped with a 6-mm-diameter diamond-inputting window. It can be seen in the first time that when the pump power lies at a stable level, the THz generation created by the femtosecond laser focusing on the nitrogen is higher than which focusing on the helium, and lower than that produced in the argon gas environment. We believe that the THz intensity is Ar > N > Ne because of its atomic mass, which is Ar > N > Ne as well. It is clear that the Gas molecular decides the release of free electrons ionized from ultra short femtosecond laser through the electronic dynamic analysis. The higher the gas mass is, the stronger the terahertz emission will be. We further explore the THz emission at the different laser power levels, and the experimental results can be commendably quadratic fitted. It can be inferred that THz emission under different gas medium environment still complies with the law of four-wave mixing (FWM) process and has nothing to do with the gas environment: the radiation energy is proportional to the quadratic of incident laser power.

  6. Efficient gas lasers pumped by generators with inductive energy storage

    NASA Astrophysics Data System (ADS)

    Tarasenko, Victor F.; Panchenko, Alexei N.; Tel'minov, Alexei E.

    2008-05-01

    Laser and discharge parameters in mixtures of rare gases with halogens driven by a pre-pulse-sustainer circuit technique are studied. Inductive energy storage with semiconductor opening switch was used for the high-voltage pre-pulse formation. It was shown that the pre-pulse with a high amplitude and short rise-time along with sharp increase of discharge current and uniform UV- and x-ray preionization allow to form long-lived stable discharge in halogen containing gas mixtures. Improvement of both pulse duration and output energy was achieved for XeCl-, XeF-, KrCl- and KrF excimer lasers. Maximal laser output was as high as 1 J at efficiency up to 4%. Increase both of the radiation power and laser pulse duration were achieved in N2-NF3 (SF6) and He-F2 (NF3) gas mixtures, as well.

  7. Biomedical Investigations with Laser-Polarized Noble Gas Magnetic Resonance

    NASA Technical Reports Server (NTRS)

    Walsworth, Ronald L.

    2001-01-01

    We are developing laser-polarized noble gas nuclear magnetic resonance (NMR) as a novel biomedical imaging tool for ground-based and eventually space-based application. This emerging multidisciplinary technology enables high-resolution gas-space magnetic resonance imaging (MRI) (e.g., of lung ventilation) as well as studies of tissue perfusion. In addition, laser-polarized noble gases (He-3 and Xe-129) do not require a large magnetic field for sensitive detection, opening the door to practical MRI at very low magnetic fields with an open, lightweight, and low-power device. We are pursuing two specific aims in this research. The first aim is to develop a low-field (< 0.01 T) instrument for noble gas MRI of humans, and the second aim is to develop functional MRI of the lung using laser-polarized Xe-129 and related techniques.

  8. Multimode-diode-pumped gas (alkali-vapor) laser

    SciTech Connect

    Page, R H; Beach, R J; Kanz, V K

    2005-08-22

    We report the first demonstration of a multimode-diode-pumped gas laser--Rb vapor operating on the 795 nm resonance transition. Peak output of {approx}1 Watt was obtained using a volume-Bragg-grating stabilized pump diode array. The laser's output radiance exceeded the pump radiance by a factor greater than 2000. Power scaling (by pumping with larger diode arrays) is therefore possible.

  9. Statistical properties of gas ring lasers with backscattering

    NASA Astrophysics Data System (ADS)

    Pesquera, L.; Blanco, R.; Rodriguez, M. A.

    1989-06-01

    The statistical properties of two-mode gas ring lasers with backscattering are studied using the exact steady probability density obtained by Christian and Mandel (1986). It is shown that the intensity of both modes grows with increasing pump power and that the intensity fluctuations of both modes die out significantly above threshold. It is concluded that the two modes obey laser statistics when the backscattering is symmetric.

  10. Dynamics of laser ablated colliding plumes

    SciTech Connect

    Gupta, Shyam L.; Pandey, Pramod K.; Thareja, Raj K.

    2013-01-15

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

  11. Trace gas monitoring with infrared laser-based detection schemes

    NASA Astrophysics Data System (ADS)

    Sigrist, M. W.; Bartlome, R.; Marinov, D.; Rey, J. M.; Vogler, D. E.; Wächter, H.

    2008-02-01

    The success of laser-based trace gas sensing techniques crucially depends on the availability and performance of tunable laser sources combined with appropriate detection schemes. Besides near-infrared diode lasers, continuously tunable midinfrared quantum cascade lasers and nonlinear optical laser sources are preferentially employed today. Detection schemes are based on sensitive absorption measurements and comprise direct absorption in multi-pass cells as well as photoacoustic and cavity ringdown techniques in various configurations. We illustrate the performance of several systems implemented in our laboratory. These include time-resolved multicomponent traffic emission measurements with a mobile CO2-laser photoacoustic system, a diode-laser based cavity ringdown device for measurements of impurities in industrial process control, isotope ratio measurements with a difference frequency (DFG) laser source combined with balanced path length detection, detection of methylamines for breath analysis with both a near-IR diode laser and a DFG source, and finally, acetone measurements with a heatable multipass cell intended for vapor phase studies on doping agents in urine samples.

  12. Laser Raman sensor for measurement of trace-hydrogen gas

    NASA Technical Reports Server (NTRS)

    Adler-Golden, Steven M.; Goldstein, Neil; Bien, Fritz; Matthew, Michael W.; Gersh, Michael E.; Cheng, Wai K.; Adams, Frederick W.

    1992-01-01

    A new optical hydrogen sensor based on spontaneous Raman scattering of laser light has been designed and constructed for rugged field use. It provides good sensitivity, rapid response, and the inherent Raman characteristics of linearity and background gas independence of the signal. Efficient light collection and discrimination by using fast optics and a bandpass interference filter compensate for the inefficiency of the Raman-scattering process. A multipass optical cavity with a Herriott-type configuration provides intense illumination from an air-cooled CW gas laser. The observed performance is in good agreement with the theoretical signal and noise level predictions.

  13. Novel diode laser-based sensors for gas sensing applications

    NASA Technical Reports Server (NTRS)

    Tittel, F. K.; Lancaster, D. G.; Richter, D.

    2000-01-01

    The development of compact spectroscopic gas sensors and their applications to environmental sensing will be described. These sensors employ mid-infrared difference-frequency generation (DFG) in periodically poled lithium niobate (PPLN) crystals pumped by two single-frequency solid state lasers such as diode lasers, diode-pumped solid state, and fiber lasers. Ultrasensitive, highly selective, and real-time measurements of several important atmospheric trace gases, including carbon monoxide, nitrous oxide, carbon dioxide, formaldehyde [correction of formaldehye], and methane, have been demonstrated.

  14. Ray tracing in nuclear-pumped flowing gas lasers

    SciTech Connect

    Mat'ev, V Yu

    2003-06-30

    The ray tracing in the resonators of a nuclear-pumped flowing gas lasers is considered. The refractive index profile of the medium in a direction perpendicular to the optical axis in such lasers can be considered parabolic, but the steepness of the parabola is quite nonuniform along the ray trace, and the resonator stability condition (the absolute value of the ray matrix trace for a single trip of the ray in the resonator is smaller than two) is not sufficient to confine the ray within the resonator after a large number of trips. (lasers)

  15. Theoretical and experimental studies of optically pumped molecular gas lasers

    NASA Astrophysics Data System (ADS)

    Ratanavis, Amarin

    Optically pumped molecular gas lasers based on vibrational-rotational transitions in the infrared spectral region were studied experimentally and theoretically. A model was developed to predict the performance of such lasers and explore their potentials for energy and power scaling. This rate equation model was applied to explore the performance of a second-overtone (pulsed) and a first-overtone (CW) pumped HBr laser. Experimental improvements concerning temperature spectral tuning and frequency stabilization of a Nd:YAG laser that pumped HBr were accomplished. Lasing at 4 microns was demonstrated from such a system. We identified acetylene and hydrogen cyanide as potential laser gases that can be pumped with lasers emitting in the attractive telecommunication C band region at about 1.5 microns. Estimations and fluorescence measurements suggest the possibility of lasing in the 3 micron region. Lasing was demonstrated for the first time with a 5 ns pump pulse from an optical parametric oscillator using traditional cavities. The first gas filled hollow fiber laser based on population inversion was demonstrated with C2H2 and emission in the 3 micron region was observed. An analytical model indicates the possibility of CW lasing with small Stokes shift in both C2H 2 and HCN.

  16. Laser Oil and Gas Well Drilling Demonstration Videos

    DOE Data Explorer

    ANL's Laser Applications Laboratory and collaborators are examining the feasibility of adapting high-power laser technology to drilling for gas and oil. The initial phase is designed to establish a scientific basis for developing a commercial laser drilling system and determine the level of gas industry interest in pursuing future research. Using lasers to bore a hole offers an entirely new approach to mechanical drilling. The novel drilling system would transfer light energy from lasers on the surface, down a borehole by a fiber optic bundle, to a series of lenses that would direct the laser light to the rock face. Researchers believe that state-of-the-art lasers have the potential to penetrate rock many times faster than conventional boring technologies - a huge benefit in reducing the high costs of operating a drill rig. Because the laser head does not contact the rock, there is no need to stop drilling to replace a mechanical bit. Moreover, researchers believe that lasers have the ability to melt the rock in a way that creates a ceramic sheath in the wellbore, eliminating the expense of buying and setting steel well casing. A laser system could also contain a variety of downhole sensors, including visual imaging systems that could communicate with the surface through the fiber optic cabling. Earlier studies have been promising, but there is still much to learn. One of the primary objectives of the new study will be to obtain much more precise measurements of the energy requirements needed to transmit light from surface lasers down a borehole with enough power to bore through rocks as much as 20,000 feet or more below the surface. Another objective will be to determine if sending the laser light in sharp pulses, rather than as a continuous stream, could further increase the rate of rock penetration. A third aspect will be to determine if lasers can be used in the presence of drilling fluids. In most wells, thick fluids called "drilling muds" are injected into

  17. Dynamics Of A Laser-Induced Plume Self-Similar Expansion

    SciTech Connect

    Bennaceur-Doumaz, D.; Djebli, M.

    2008-09-23

    The dynamics of a laser ablation plume during the first stage of its expansion, just after the termination of the laser pulse is modeled. First, we suppose the laser fluence range low enough to consider a neutral vapor. The expansion of the evaporated material is described by one-component fluid and one-dimensional Euler equations. The vapor is assumed to follow an ideal gas flow. For high energetic ions, the charge separation can be neglected and the hydrodynamics equations can be solved using self-similar formulation. The obtained ordinary differential equations are solved numerically. Secondly, the effect of ionization is investigated when the evaporated gas temperature is sufficiently high. In this case, Saha equation is included in the formulation of the model. We find a self-similar solution for a finite value of the similarity variable which depends on the laser ablation parameters.

  18. Molecular dynamic simulation of non-melt laser annealing process

    NASA Astrophysics Data System (ADS)

    Liren, Yan; Dai, Li; Wei, Zhang; Zhihong, Liu; Wei, Zhou; Quan, Wang

    2016-03-01

    Molecular dynamic simulation is performed to study the process of material annealing caused by a 266 nm pulsed laser. A micro-mechanism describing behaviors of silicon and impurity atoms during the laser annealing at a non-melt regime is proposed. After ion implantation, the surface of the Si wafer is acted by a high energy laser pulse, which loosens the material and partially frees both Si and impurity atoms. While the residual laser energy is absorbed by valence electrons, these atoms are recoiled and relocated to finally form a crystal. Energy-related movement behavior is observed by using the molecular dynamic method. The non-melt laser anneal appears to be quite sensitive to the energy density of the laser, as a small excess energy may causes a significant impurity diffusion. Such a result is also supported by our laser anneal experiment.

  19. Dynamics of intense laser propagation in underdense plasma: Polarization dependence

    SciTech Connect

    Singh, D. K.; Fiuza, F.; Silva, L. O.; Davies, J. R.; Sarri, G.

    2012-07-15

    We present a comprehensive numerical study of the dynamics of an intense laser pulse as it propagates through an underdense plasma in two and three dimensions. By varying the background plasma density and the polarization of the laser beam, significant differences are found in terms of energy transport and dissipation, in agreement with recently reported experimental results. Below the threshold for relativistic self-focusing, the plasma and laser dynamics are observed to be substantially insensitive to the initial laser polarization, since laser transport is dominated by ponderomotive effects. Above this threshold, relativistic effects become important, and laser energy is dissipated either by plasma heating (p-polarization) or by trapping of electromagnetic energy into plasma cavities (s-polarization) or by a combination of both (circular polarization). Besides the fundamental interest of this study, the results presented are relevant to applications such as plasma-based accelerators, x-ray lasers, and fast-ignition inertial confinement fusion.

  20. Low-field MRI of laser polarized noble gas.

    PubMed

    Tseng, C H; Wong, G P; Pomeroy, V R; Mair, R W; Hinton, D P; Hoffmann, D; Stoner, R E; Hersman, F W; Cory, D G; Walsworth, R L

    1998-10-26

    NMR images of laser polarized 3He gas were obtained at 21 G using a simple, homebuilt instrument. At such low fields magnetic resonance imaging (MRI) of thermally polarized samples (e.g., water) is not practical. Low-field noble gas MRI has novel scientific, engineering, and medical applications. Examples include portable systems for diagnosis of lung disease, as well as imaging of voids in porous media and within metallic systems. PMID:11543589

  1. Low-field MRI of laser polarized noble gas

    NASA Technical Reports Server (NTRS)

    Tseng, C. H.; Wong, G. P.; Pomeroy, V. R.; Mair, R. W.; Hinton, D. P.; Hoffmann, D.; Stoner, R. E.; Hersman, F. W.; Cory, D. G.; Walsworth, R. L.

    1998-01-01

    NMR images of laser polarized 3He gas were obtained at 21 G using a simple, homebuilt instrument. At such low fields magnetic resonance imaging (MRI) of thermally polarized samples (e.g., water) is not practical. Low-field noble gas MRI has novel scientific, engineering, and medical applications. Examples include portable systems for diagnosis of lung disease, as well as imaging of voids in porous media and within metallic systems.

  2. 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.

  3. Computing interface motion in compressible gas dynamics

    NASA Technical Reports Server (NTRS)

    Mulder, W.; Osher, S.; Sethan, James A.

    1992-01-01

    An analysis is conducted of the coupling of Osher and Sethian's (1988) 'Hamilton-Jacobi' level set formulation of the equations of motion for propagating interfaces to a system of conservation laws for compressible gas dynamics, giving attention to both the conservative and nonconservative differencing of the level set function. The capabilities of the method are illustrated in view of the results of numerical convergence studies of the compressible Rayleigh-Taylor and Kelvin-Helmholtz instabilities for air-air and air-helium boundaries.

  4. Two-mode dynamics in different semiconductor laser structures

    NASA Astrophysics Data System (ADS)

    Scirè, Alessandro; Sorel, Marc; Colet, Pere; Tessone, Claudio Juan; Mirasso, Claudio R.; San Miguel, Maxi

    2006-04-01

    We review three two-mode models for different semiconductor laser structures: Vertical-Cavity Surface-Emitting Lasers (VCSELs), Twin-Stripe Semiconductor-Lasers (TSSL), and Semiconductor Ring Lasers (SRL). The VCSELs model and TSSL model display rich dynamic behavior when a saturable absorber is embedded in the cavity. VCSELs with saturable absorber showed polarization chaos, which found applications in encoded communications; TSSLs with saturable absorber show coherent locked states as well as chaotic behavior; and SRLs show a complex two-mode dynamics giving rise to bidirectional operation, alternate oscillations and spontaneous symmetry breaking toward quasi-unidirectional bistable solutions, with potential applications to all-optical switching.

  5. Molecular Dynamics Simulations of Laser Powered Carbon Nanotube Gears

    NASA Technical Reports Server (NTRS)

    Srivastava, Deepak; Globus, Al; Han, Jie; Chancellor, Marisa K. (Technical Monitor)

    1997-01-01

    Dynamics of laser powered carbon nanotube gears is investigated by molecular dynamics simulations with Brenner's hydrocarbon potential. We find that when the frequency of the laser electric field is much less than the intrinsic frequency of the carbon nanotube, the tube exhibits an oscillatory pendulam behavior. However, a unidirectional rotation of the gear with oscillating frequency is observed under conditions of resonance between the laser field and intrinsic gear frequencies. The operating conditions for stable rotations of the nanotube gears, powered by laser electric fields are explored, in these simulations.

  6. Control of fluid dynamics by nanoparticles in laser melting

    NASA Astrophysics Data System (ADS)

    Ma, Chao; Chen, Lianyi; Xu, Jiaquan; Zhao, Jingzhou; Li, Xiaochun

    2015-03-01

    Effective control of fluid dynamics is of remarkable scientific and practical significance. It is hypothesized that nanoparticles could offer a novel means to control fluid dynamics. In this study, laser melting was used to investigate the feasibility of tuning fluid dynamics by nanoparticles and possibly breaking existing limits of conventional laser processing techniques. Alumina nanoparticles reinforced nickel samples, fabricated through electrocodeposition, were used for laser melting experiments. Since the melt pool surface is controlled by the fluid dynamics, surface topographies were carefully studied to reveal the nanoparticle effect on the fluid dynamics. Characterizations of surface topographies and microstructures of pure Ni and Ni/Al2O3 nanocomposite were carried out before and after laser melting. The surface roughness of the Ni/Al2O3 nanocomposite sample was reduced significantly by laser melting, which broke the existing limit of laser surface polishing of pure Ni. It is believed that the nanoparticles increased the viscosity of the molten metal, thereby enhancing the viscous damping of the capillary oscillations in the melt pool, to produce a much smoother surface. Moreover, the experimental study also revealed that the viscosity enhancement by the nanoparticles effectively suppressed the thermocapillary flows which would introduce artificial asperities on a surface. The experimental results suggest that nanoparticles are effective in controlling melt pool dynamics and overcoming the existing limits of laser processing. The new methodology, fluid dynamics control by nanoparticles, opens a new pathway to enrich liquid based processes for broad applications.

  7. Hypersonic gasdynamic laser system

    SciTech Connect

    Foreman, K.M.; Maciulaitis, A.

    1990-05-22

    This patent describes a visible, or near to mid infra-red, hypersonic gas dynamic laser system. It comprises: a hypersonic vehicle for carrying the hypersonic gas dynamic laser system, and also providing high energy ram air for thermodynamic excitation and supply of the laser gas; a laser cavity defined within the hypersonic vehicle and having a laser cavity inlet for the laser cavity formed by an opening in the hypersonic vehicle, such that ram air directed through the laser cavity opening supports gas dynamic lasing operations at wavelengths less than 10.6{mu} meters in the laser cavity; and an optical train for collecting the laser radiation from the laser cavity and directing it as a substantially collimated laser beam to an output aperture defined by an opening in the hypersonic vehicle to allow the laser beam to be directed against a target.

  8. The influence of shielding gas in hybrid LASER MIG welding

    NASA Astrophysics Data System (ADS)

    Tani, Giovanni; Campana, Giampaolo; Fortunato, Alessandro; Ascari, Alessandro

    2007-07-01

    Hybrid LASER-GMAW welding technique has been recently studied and developed in order to meet the needs of modern welding industries. The two sources involved in this process play, in fact, a complementary role: fast welding speed, deep bead penetration and high energy concentration can be achieved through the LASER beam, while gap bridgeability and cost-effectiveness are typical of the GMAW process. Particularly interesting, in this context, is the CO 2 LASER-MIG welding which differs from the Nd:YAG LASER-MIG technique for the high powers that can be exploited and for the good power/cost ratio of the process. This paper is a part of a wide study on the hybrid CO 2 LASER-MIG welding and investigates the influence of the shielding gas both on the stability of the process and on the dimensional characteristics of the weld bead. Two different parameters have been taken into consideration in order to develop this analysis: the shielding gas composition and the shielding gas flow. The experiment, performed on AISI 304 stainless steel plates, has been planned exploiting design of experiment techniques. The results have been analyzed through a statistical approach in order to determine the real influence of each parameter on the overall process.

  9. Lasers '92; Proceedings of the International Conference on Lasers and Applications, 15th, Houston, TX, Dec. 7-10, 1992

    NASA Technical Reports Server (NTRS)

    Wang, Charles P. (Editor)

    1993-01-01

    Papers from the conference are presented, and the topics covered include the following: x-ray lasers, excimer lasers, chemical lasers, high power lasers, blue-green lasers, dye lasers, solid state lasers, semiconductor lasers, gas and discharge lasers, carbon dioxide lasers, ultrafast phenomena, nonlinear optics, quantum optics, dynamic gratings and wave mixing, laser radar, lasers in medicine, optical filters and laser communication, optical techniques and instruments, laser material interaction, and industrial and manufacturing applications.

  10. Single-shot diffusion measurement in laser-polarized Gas

    NASA Technical Reports Server (NTRS)

    Peled, S.; Tseng, C. H.; Sodickson, A. A.; Mair, R. W.; Walsworth, R. L.; Cory, D. G.

    1999-01-01

    A single-shot pulsed gradient stimulated echo sequence is introduced to address the challenges of diffusion measurements of laser polarized 3He and 129Xe gas. Laser polarization enhances the NMR sensitivity of these noble gases by >10(3), but creates an unstable, nonthermal polarization that is not readily renewable. A new method is presented which permits parallel acquisition of the several measurements required to determine a diffusive attenuation curve. The NMR characterization of a sample's diffusion behavior can be accomplished in a single measurement, using only a single polarization step. As a demonstration, the diffusion coefficient of a sample of laser-polarized 129Xe gas is measured via this method. Copyright 1999 Academic Press.

  11. Solid-state power supply for gas lasers

    NASA Astrophysics Data System (ADS)

    Bertolini, A.; Beverini, N.; Carelli, G.; Francesconi, M.; Nannizzi, M.; Strumia, F.; Ioli, N.; Moretti, A.

    2004-08-01

    A novel pulsed power supply for gas lasers is presented. The device uses only solid state components and is based on a capacitor bank discharge. Fast switching of the discharge is triggered by an insulated gate bipolar transistor. The terminal section of the power supply is a transformer designed to match the reactive capacitance of a gas discharge. Strokes up to 30 kV and 30 mA are achieved across the secondary windings of this transformer. The power supply delivers high voltage pulses with a duration between 0.5 and 50 μs and a repetition rate up to some kHz. The power supply has been tested on a longitudinal discharge quasi-cw regime CO2 laser. Laser pulses were generated with a duration down to the microseconds region, a peak power exceeding some kilowatts, and a repetition rate ranging from 200 Hz to a few kHz.

  12. Long-Range Coulomb Effect in Intense Laser-Driven Photoelectron Dynamics

    NASA Astrophysics Data System (ADS)

    Quan, Wei; Hao, Xiaolei; Chen, Yongju; Yu, Shaogang; Xu, Songpo; Wang, Yanlan; Sun, Renping; Lai, Xuanyang; Wu, Chengyin; Gong, Qihuang; He, Xiantu; Liu, Xiaojun; Chen, Jing

    2016-06-01

    In strong field atomic physics community, long-range Coulomb interaction has for a long time been overlooked and its significant role in intense laser-driven photoelectron dynamics eluded experimental observations. Here we report an experimental investigation of the effect of long-range Coulomb potential on the dynamics of near-zero-momentum photoelectrons produced in photo-ionization process of noble gas atoms in intense midinfrared laser pulses. By exploring the dependence of photoelectron distributions near zero momentum on laser intensity and wavelength, we unambiguously demonstrate that the long-range tail of the Coulomb potential (i.e., up to several hundreds atomic units) plays an important role in determining the photoelectron dynamics after the pulse ends.

  13. Long-Range Coulomb Effect in Intense Laser-Driven Photoelectron Dynamics

    PubMed Central

    Quan, Wei; Hao, XiaoLei; Chen, YongJu; Yu, ShaoGang; Xu, SongPo; Wang, YanLan; Sun, RenPing; Lai, XuanYang; Wu, ChengYin; Gong, QiHuang; He, XianTu; Liu, XiaoJun; Chen, Jing

    2016-01-01

    In strong field atomic physics community, long-range Coulomb interaction has for a long time been overlooked and its significant role in intense laser-driven photoelectron dynamics eluded experimental observations. Here we report an experimental investigation of the effect of long-range Coulomb potential on the dynamics of near-zero-momentum photoelectrons produced in photo-ionization process of noble gas atoms in intense midinfrared laser pulses. By exploring the dependence of photoelectron distributions near zero momentum on laser intensity and wavelength, we unambiguously demonstrate that the long-range tail of the Coulomb potential (i.e., up to several hundreds atomic units) plays an important role in determining the photoelectron dynamics after the pulse ends. PMID:27256904

  14. Long-Range Coulomb Effect in Intense Laser-Driven Photoelectron Dynamics.

    PubMed

    Quan, Wei; Hao, XiaoLei; Chen, YongJu; Yu, ShaoGang; Xu, SongPo; Wang, YanLan; Sun, RenPing; Lai, XuanYang; Wu, ChengYin; Gong, QiHuang; He, XianTu; Liu, XiaoJun; Chen, Jing

    2016-01-01

    In strong field atomic physics community, long-range Coulomb interaction has for a long time been overlooked and its significant role in intense laser-driven photoelectron dynamics eluded experimental observations. Here we report an experimental investigation of the effect of long-range Coulomb potential on the dynamics of near-zero-momentum photoelectrons produced in photo-ionization process of noble gas atoms in intense midinfrared laser pulses. By exploring the dependence of photoelectron distributions near zero momentum on laser intensity and wavelength, we unambiguously demonstrate that the long-range tail of the Coulomb potential (i.e., up to several hundreds atomic units) plays an important role in determining the photoelectron dynamics after the pulse ends. PMID:27256904

  15. Fluid energy machines as circulating blowers for gas lasers - Special design and performance characteristics

    NASA Astrophysics Data System (ADS)

    Henning, Hans-Heinrich

    1989-09-01

    Lasers are broadly applied in the industrial world, where CO2-lasers are used for metal processing. Other applications include the high power gas laser used as blower to circulate the laser gases, noting that an increasing number of radial-blowers is now used on CO2-lasers instead of roots-blowers. The demand, design, and advantages of fluid energy machines as circulating (radial and axial) blowers for gas lasers are described, with emphasis on high performance characteristics.

  16. Atypical Applications for Gas-coupled Laser Acoustic Detection

    NASA Astrophysics Data System (ADS)

    Caron, J. N.; Kunapareddy, P.

    2014-06-01

    Gas-coupled laser acoustic detection (GCLAD) was primarily developed to sense laser-generated ultrasound in composite materials. In a typical setup, a laser beam is directed parallel to the material surface. Radiated ultrasound waves deflect or displace the probe beam resulting from changes in the air's index of refraction. A position-sensitive photodetector senses the beam movement, and produces a signal proportional to the ultrasound wave. In this paper, we discuss three applications of GCLAD that take advantage of the unique detection characteristics. Directivity patterns of ultrasound amplitude in water demonstrate the use of GCLAD as a directional hydrophone. We also demonstrate the sensing of waveforms from a gelatin. The gelatin mimics ultrasound propagation through skin tissues. Lastly, we show how GCLAD can be used as a line receiver for continuous laser generation of ultrasound. CLGU may enable ultrasound scanning at rates that are orders of magnitude faster than current methods.

  17. GAS-PHASE MOLECULAR DYNAMICS: VIBRATIONAL DYNAMICS OF POLYATOMIC MOLECULES

    SciTech Connect

    MUCKERMAN,J.T.

    1999-06-09

    The goal of this research is the understanding of elementary chemical and physical processes important in the combustion of fossil fuels. Interest centers on reactions and properties of short-lived chemical intermediates. High-resolution, high-sensitivity, laser absorption methods are augmented by high-temperature, flow-tube reaction kinetics studies with mass-spectrometric sampling. These experiments provide information on the energy levels, structures and reactivity of molecular free radical species and, in turn, provide new tools for the study of energy flow and chemical bond cleavage in radicals involved in chemical systems. The experimental work is supported by theoretical studies using time-dependent quantum wavepacket calculations, which provide insight into energy flow among the vibrational modes of polyatomic molecules and interference effects in multiple-surface dynamics.

  18. Gas-Phase Molecular Dynamics: Vibrational Dynamics of Polyatomic Molecules

    SciTech Connect

    Muckerman, J.T.

    1999-05-21

    The goal of this research is the understanding of elementary chemical and physical processes important in the combustion of fossil fuels. Interest centers on reactions and properties of short-lived chemical intermediates. High-resolution, high-sensitivity, laser absorption methods are augmented by high- temperature, flow-tube reaction kinetics studies with mass-spectrometic sampling. These experiments provide information on the energy levels, structures and reactivity of molecular free radical species and in turn, provide new tools for the study of energy flow and chemical bond cleavage in the radicals involved in chemical systems. The experimental work is supported by theoretical studies using time-dependent quantum wavepacket calculations, which provide insight into energy flow among the vibrational modes of polyatomic molecules and interference effects in multiple-surface dynamics.

  19. Pulsed laser linescanner for a backscatter absorption gas imaging system

    DOEpatents

    Kulp, Thomas J.; Reichardt, Thomas A.; Schmitt, Randal L.; Bambha, Ray P.

    2004-02-10

    An active (laser-illuminated) imaging system is described that is suitable for use in backscatter absorption gas imaging (BAGI). A BAGI imager operates by imaging a scene as it is illuminated with radiation that is absorbed by the gas to be detected. Gases become "visible" in the image when they attenuate the illumination creating a shadow in the image. This disclosure describes a BAGI imager that operates in a linescanned manner using a high repetition rate pulsed laser as its illumination source. The format of this system allows differential imaging, in which the scene is illuminated with light at least 2 wavelengths--one or more absorbed by the gas and one or more not absorbed. The system is designed to accomplish imaging in a manner that is insensitive to motion of the camera, so that it can be held in the hand of an operator or operated from a moving vehicle.

  20. Modeling of static and flowing-gas diode pumped alkali lasers

    NASA Astrophysics Data System (ADS)

    Barmashenko, Boris D.; Auslender, Ilya; Yacoby, Eyal; Waichman, Karol; Sadot, Oren; Rosenwaks, Salman

    2016-03-01

    Modeling of static and flowing-gas subsonic, transonic and supersonic Cs and K Ti:Sapphire and diode pumped alkali lasers (DPALs) is reported. A simple optical model applied to the static K and Cs lasers shows good agreement between the calculated and measured dependence of the laser power on the incident pump power. The model reproduces the observed threshold pump power in K DPAL which is much higher than that predicted by standard models of the DPAL. Scaling up flowing-gas DPALs to megawatt class power is studied using accurate three-dimensional computational fluid dynamics model, taking into account the effects of temperature rise and losses of alkali atoms due to ionization. Both the maximum achievable power and laser beam quality are estimated for Cs and K lasers. The performance of subsonic and, in particular, supersonic DPALs is compared with that of transonic, where supersonic nozzle and diffuser are spared and high power mechanical pump (needed for recovery of the gas total pressure which strongly drops in the diffuser), is not required for continuous closed cycle operation. For pumping by beams of the same rectangular cross section, comparison between end-pumping and transverse-pumping shows that the output power is not affected by the pump geometry, however, the intensity of the output laser beam in the case of transverse-pumped DPALs is strongly non-uniform in the laser beam cross section resulting in higher brightness and better beam quality in the far field for the end-pumping geometry where the intensity of the output beam is uniform.

  1. Alkali--rare gas photodissociation lasers: Applications to laser physics and atom-atom interactions

    NASA Astrophysics Data System (ADS)

    Hewitt, John Darby

    This dissertation describes several experiments in which alkali--rare gas laser systems are utilized as a simple platform with which to isolate and study atom-atom interactions and fundamental physical processes that are ill-understood or have never been investigated previously. Specifically, the minimum allowable energy separation between levels 2 and 3 in a three-level laser system has been investigated experimentally, as have two-photon absorption processes in atomic Rb and Cs.

  2. Gas Dynamics as a Tool for Description of Nondeterministic Particles

    NASA Astrophysics Data System (ADS)

    Rylov, Yuri A.

    2016-05-01

    Classical gas dynamic equations describe mean motion of stochastic gas molecules. The reason of this stochasticity is in teraction (collisions) between molecules. The wave function is the way to describe the gas dynamic equations Rylov (J. Math. Phys. 40 256-278 1999). If a gas molecules interact via some force field κ l , the gas dynamic equations have the form of the Klein-Gordon equation provided they are written in terms of the wave function. Among two possible approaches: (i) quantum mechanics (QM) as axiomatic conception and (ii) QM as a kind of gas dynamics the second approach is more preferable, because in the first approach the wave function looks as a strange axiomatic object, whereas in the second approach the wave function is a natural way of the gas dynamics description. Besides the second approach admits one to obtain a more complete description of stochastic particles.

  3. Nonequilibrium dynamics of laser-generated plasma channels

    NASA Astrophysics Data System (ADS)

    Petrova, Tz. B.; Ladouceur, H. D.; Baronavski, A. P.

    2008-05-01

    A time-dependent nonequilibrium kinetics model based upon the time-dependent electron Boltzmann equation coupled with an extensive air chemistry model accounting for gas heating and vibrational kinetics is developed. The model is applied to the temporal evolution of femtosecond laser-generated air plasma channels at atmospheric pressure in an external electric field. The plasma channel dynamics depend upon the initial free electron density, the initial electron energy of the plasma, and upon the externally applied electric field strength. The model predicts an electric breakdown field strength of 5-10kV/cm with a delay time of hundreds of nanoseconds when the electron density drops to the optimum value of ˜1012-1013cm-3. The experimentally observed breakdown field is ˜5.7kV/cm with a statistical breakdown delay time of ˜200ns. The reduction in the breakdown field strength in natural air from ˜30to5kV/cm is attributed to a combination of processes such as enhanced ionization due to relaxation of the initial electron energy distribution function toward a Maxwellian distribution, strong electron detachment, and gas heating. The calculated electron density decay of the laser-generated plasma channel in both pure nitrogen and dry air is in good agreement with the NRL experiments. The derived rate constant for recombination in dry air is bBair=3.9×10-8cm3s-1 and in pure nitrogen it is bBN2=4.4×10-8cm3s-1. The attachment rate coefficient in dry air is ηBair=7.5×106s-1.

  4. Dynamic phenomena and quality defects in laser cutting

    NASA Astrophysics Data System (ADS)

    Schuöcker, Dieter; Schuöcker, Georg

    2012-07-01

    Laser cutting of sheet metals is used all over the world by production companies since it combines high speed, excellent quality and economic advantages. Nevertheless certain limits exist for materials thickness and speed and also to quality of the cut edges that show eventually strong roughness and adherent material as dross and slag. In order to extend these limits and to approve especially cutting speed and quality of the cut edges the mechanism of laser cutting must be fully understood. As far as it concerns steady state cutting the phenomena contributed to the process with a thin liquid layer covering the momentary end of the cut kerf that serves for absorption of laser radiation and also for generation of reaction heat also for melting of the solid material and finally for the ejection of liquid material at the bottom of the work piece due to the friction with the process gas have been clarified a long time before. Also dynamic phenomena associated to reaction and to waves on the surface of the liquid body that all lead to a certain roughness have been described in the past. Nevertheless the phenomena taking place inside the liquid layer are not fully understood especially the influence of surface tension that is much higher than the pressure in the melt and would in principal inhibit any ejection of melt that is necessary for cutting. Therefore the authors carried out an analysis of the processes taking place in the liquid body that leads to a picture with a discontinuous ejection of melt and explains the formation of a rough surface structure and also of adherent material for the case of a rather thick workpiece (> 10mm).

  5. Coherence, chaos and communication: Exploring and applying nonlinear laser dynamics

    NASA Astrophysics Data System (ADS)

    Roy, Rajarshi

    2000-12-01

    Surprising conceptual connections between quite different physical systems are traced. Nonlinear dynamics is the common formalism that provides the basis for understanding many puzzling observations, including laser instabilities. Experiments in our laboratory to investigate coupled laser systems and communication with chaotic waveforms are described.

  6. Proposed method of rotary dynamic balancing by laser

    NASA Technical Reports Server (NTRS)

    Perkins, W. E.

    1967-01-01

    Laser method, where high energies of monochromatic light can be precisely collimated to perform welding and machining processes, is proposed for rotary dynamic balancing. The unbalance, as detected with the velocity pickup, would trigger the laser system which would emit high energy pulses directed at the heavy side of the component.

  7. A Kinetic Plasma-Pumped Rare Gas Laser

    NASA Astrophysics Data System (ADS)

    Parsey, Guy; Güçlü, Yaman; Verboncoeur, John; Christlieb, Andrew

    2015-09-01

    Extending from diode-pumped alkali vapor lasers (DPAL), Han and Heaven have shown that rare gas metastable states, np5 (n + 1) s[ 3 / 2 ] 2 , can operate as the base of a three-level laser with excition of the (n + 1) s --> (n + 1) p transitions. Though both the rare gas lasers (RGL) and DPALs can be excited with incoherent optical pumping, RGLs do not suffer from the highly reactive behavior of alkali metals. Since metastable populations are maintained via electric discharge, we propose using a tuned electron energy distribution function (EEDF) to modify RGL efficiencies and drive the population inversion. The EEDF is maintained by the discharge along with the introduction of electron sources. Using our kinetic global modeling framework (KGMf) and three gas systems (helium buffered argon and krypton along with pure argon), we first validate the intracavity intensity laser model and then generate gain and energy efficiency baselines for each system. Parameter scanning methods are then used to find optimized EEDFs and system parameters for metastable production, generation of a lasing population inversion, and increasing RGL operation efficiencies. Finally, we determine if an RGL can operate without optical pumping. Supported by AFOSR and a MSU Strategic Partnership Grant

  8. Short pulse dynamics in a linear cavity fiber laser

    NASA Astrophysics Data System (ADS)

    Razukov, Vadim A.; Melnikov, Leonid A.

    2016-04-01

    New suitable numerical scheme is proposed for simulation of dynamics of oppositely running pulses in a fiber laser with linear cavity. The proposed model allows to include various temporal and spatial effects which affect the laser dynamics. The pulse evolution in the fiber cavity with perfect reflectors at the fiber ends with accounting of fiber group velocity dispersion and self-phase modulation is demonstrated.

  9. Dynamics of laser-guided alternating current high voltage discharges

    NASA Astrophysics Data System (ADS)

    Daigle, J.-F.; Théberge, F.; Lassonde, P.; Kieffer, J.-C.; Fujii, T.; Fortin, J.; Châteauneuf, M.; Dubois, J.

    2013-10-01

    The dynamics of laser-guided alternating current high voltage discharges are characterized using a streak camera. Laser filaments were used to trigger and guide the discharges produced by a commercial Tesla coil. The streaking images revealed that the dynamics of the guided alternating current high voltage corona are different from that of a direct current source. The measured effective corona velocity and the absence of leader streamers confirmed that it evolves in a pure leader regime.

  10. Resonant holographic measurements of laser ablation plume expansion in vacuum and argon gas backgrounds

    SciTech Connect

    Lindley, R.A.

    1993-10-01

    This thesis discusses the following on resonant holographic measurements of laser ablation plume expansion: Introduction to laser ablation; applications of laser ablation; The study of plume expansion; holographic interferometry; resonant holographic interferometry; accounting for finite laser bandwidth; The solution for doppler broadening and finite bandwidth; the main optical table; the lumonics laser spot shape; developing and reconstructing the holograms; plume expansion in RF/Plasma Environments; Determining {lambda}{sub o}; resonant refraction effects; fringe shift interpretation; shot-to-shot consistency; laser ablation in vacuum and low pressure, inert, background gas; theoretically modeling plume expansion in vacuum and low pressure, inert, background gas; and laser ablation in higher pressure, inert, background gas.

  11. A Fast, Electromagnetically Driven Supersonic Gas Jet Target For Laser Wakefield Acceleration

    SciTech Connect

    Krishnan, Mahadevan; Wright, Jason; Ma, Timothy

    2009-01-22

    Laser-Wakefield acceleration (LWFA) promises electron accelerators with unprecedented electric field gradients. Gas jets and gas-filled capillary discharge waveguides are two primary targets of choice for LWFA. Present gas jets have lengths of only 2-4 mm at densities of 1-4x10{sup 19} /cm{sup 3}, sufficient for self-trapping and acceleration to energies up to {approx}150 MeV. While 3 cm capillary structures have been used to accelerate beams up to 1 GeV, gas jets require a well-collimated beam that is {>=}10 mm in length and <500 {mu}m in width, with a tunable gas density profile to optimize the LWFA process. This paper describes the design of an electromagnetically driven, fast supersonic gas valve that opens in <100 {mu}s, closes in <500 {mu}s and can operate at pressures beyond 1000 psia. The motion of the valve seat (flyer plate) is measured using a laser probe and compared with predictions of a model. The valve design is based on an optimization of many parameters: flyer plate mass and durability, driver bank speed and stored energy for high rep-rate (>10 Hz) operation, return spring non-linearity and materials selection for various components. Optimization of the valve dynamics and preliminary designs of the supersonic flow patterns are described.

  12. Nonequilibrium dynamics of an ultracold dipolar gas

    NASA Astrophysics Data System (ADS)

    Sykes, A. G.; Bohn, J. L.

    2015-01-01

    We study the relaxation and damping dynamics of an ultracold, but not quantum degenerate, gas consisting of dipolar particles. These simulations are performed using a direct simulation Monte Carlo method and employing the highly anisotropic differential cross section of dipoles in the Wigner threshold regime. We find that both cross-dimensional relaxation and damping of breathing modes occur at rates that are strongly dependent on the orientation of the dipole moments relative to the trap axis. The relaxation simulations are in excellent agreement with recent experimental results in erbium. The results direct our interest toward a less explored regime in dipolar gases where interactions are dominated by collision processes rather than mean-field interactions.

  13. Iterated upwind schemes for gas dynamics

    SciTech Connect

    Smolarkiewicz, Piotr K. Szmelter, Joanna

    2009-01-10

    A class of high-resolution schemes established in integration of anelastic equations is extended to fully compressible flows, and documented for unsteady (and steady) problems through a span of Mach numbers from zero to supersonic. The schemes stem from iterated upwind technology of the multidimensional positive definite advection transport algorithm (MPDATA). The derived algorithms employ standard and modified forms of the equations of gas dynamics for conservation of mass, momentum and either total or internal energy as well as potential temperature. Numerical examples from elementary wave propagation, through computational aerodynamics benchmarks, to atmospheric small- and large-amplitude acoustics with intricate wave-flow interactions verify the approach for both structured and unstructured meshes, and demonstrate its flexibility and robustness.

  14. Study of optimal gas pressure in optically pumped D IIO gas terahertz laser

    NASA Astrophysics Data System (ADS)

    He, Zhihong; Yao, Jianquan; Ren, Xia; Yang, Yang; Luo, Xizhang; Wang, Peng

    2008-03-01

    Heavy water vapor (D IIO gas) which owns special structure properties, can generate terahertz (THz) radiation by optically pumped technology, and its 385 μm wavelength radiation can be widely used. In this research, on the base of semi-classical density matrix theory, we set up a three-level energy system as its theoretical model, a TEA-CO II laser 9R (22) output line (λ=9.26 μm) acted as pumping source, D IIO gas molecules were operating medium, the expressions of pumping absorption coefficient G p and THz signal gain coefficient G s were deduced , It was shown that the gain of THz signal was related with the energy-level parameters of operating molecules and some operating parameters of the THz laser cavity, mainly including gas pressure, temperature etc.; By means of iteration method, the output power density of THz pulse signal was calculated numerically as its initial power density was known; Changing the parameter of gas pressure and keeping others steady, the relationship curve between the output power intensity (Is) of Tera-Hz pulse laser and the operating D IIO gas pressure (P) was obtained. The curve showed that the power intensity (Is) increased with gas pressure (P) in a certain range, but decreased when the pressure (P) exceeded some value because of the bottleneck effect, and there was an optimal gas pressure for the highest output power. We used a grating tuned TEA-CO II laser as pumping power and a sample tube of 97cm length as THz laser operating cavity to experiment. The results of theoretical calculation and experiment matched with each other.

  15. Gas bubble dynamics in soft materials.

    PubMed

    Solano-Altamirano, J M; Malcolm, John D; Goldman, Saul

    2015-01-01

    Epstein and Plesset's seminal work on the rate of gas bubble dissolution and growth in a simple liquid is generalized to render it applicable to a gas bubble embedded in a soft elastic solid. Both the underlying diffusion equation and the expression for the gas bubble pressure were modified to allow for the non-zero shear modulus of the medium. The extension of the diffusion equation results in a trivial shift (by an additive constant) in the value of the diffusion coefficient, and does not change the form of the rate equations. But the use of a generalized Young-Laplace equation for the bubble pressure resulted in significant differences on the dynamics of bubble dissolution and growth, relative to an inviscid liquid medium. Depending on whether the salient parameters (solute concentration, initial bubble radius, surface tension, and shear modulus) lead to bubble growth or dissolution, the effect of allowing for a non-zero shear modulus in the generalized Young-Laplace equation is to speed up the rate of bubble growth, or to reduce the rate of bubble dissolution, respectively. The relation to previous work on visco-elastic materials is discussed, as is the connection of this work to the problem of Decompression Sickness (specifically, "the bends"). Examples of tissues to which our expressions can be applied are provided. Also, a new phenomenon is predicted whereby, for some parameter values, a bubble can be metastable and persist for long times, or it may grow, when embedded in a homogeneous under-saturated soft elastic medium. PMID:25382720

  16. Gas bubble dynamics in soft materials

    NASA Astrophysics Data System (ADS)

    Solano-Altamirano, J. M.; Malcolm, John D.; Goldman, Saul

    Epstein and Plesset's seminal work on the rate of gas bubble dissolution and growth in a simple liquid is generalized to render it applicable to a gas bubble embedded in a soft elastic medium. Both the underlying diffusion equation and the expression for the gas bubble pressure were modified to allow for the non-zero shear modulus of the elastic medium. The extension of the diffusion equation results in a trivial shift (by an additive constant) in the value of the diffusion coefficient, and does not change the form of the rate equations. But the use of a Generalized Young-Laplace equation for the bubble pressure resulted in significant differences on the dynamics of bubble dissolution and growth, relative to a simple liquid medium. Depending on whether the salient parameters (solute concentration, initial bubble radius, surface tension, and shear modulus) lead to bubble growth or dissolution, the effect of allowing for a non-zero shear modulus in the Generalized Young-Laplace equation is to speed up the rate of bubble growth, or to reduce the rate of bubble dissolution, respectively. The relation to previous work on visco-elastic materials is discussed, as is the connection of this work to the problem of Decompression Sickness (specifically, "the bends"). Examples of tissues to which our expressions can be applied are provided. Also, a new phenomenon is predicted whereby, for some parameter values, a bubble can be metastable and persist for long times, or it may grow, when embedded in a homogeneous under-saturated soft elastic medium.

  17. Study of simulating dynamic polarization laser echo signal

    NASA Astrophysics Data System (ADS)

    Yang, Di; Liu, Qing; Zhan, Yong-hong; Zeng, Chang-e.

    2014-12-01

    In the test for the laser seeker in the hardware-in-loop simulation, acquiring the effect of polarization laser echo wave to optical stress polarization of the seeker and to the polarization guidance performance was not considered. A new method to generating the dynamic polarization laser echo signal was provided based on the scene model; furthermore, the method to adding the polarization characters to the energy scene was introduced. At last, the insufficient of the method to generating and simulating the dynamic polarization signal was analyzed.

  18. Immunity to Laser Power Variation in a DFB Diode Laser Based Optical Gas Sensor Using a Division Process

    PubMed Central

    Chang, Hengtai; Chang, Jun; Huang, Qingjie; Wang, Qiang; Tian, Changbin; Wei, Wei; Liu, Yuanyuan

    2015-01-01

    The division process used in a DFB diode laser-based optical gas sensor was studied to improve the immunity to laser power variation. Residual amplitude modulation (RAM) in wavelength modulation spectroscopy (WMS) detection was eliminated by intensity normalization using a division process. As a result the detected harmonic signals showed a significant improvement in line shape. For the first harmonic (1f) signal, Bias was improved from 38.7% to 1.2%; Baseline Difference was improved from 2.7% to 0.69% and Asymmetry was improved from 15.4% to 0.22%. For the second harmonic (2f) signal, the Asymmetry Coefficient was improved from 103% to 5.1%. Moreover the division process can further suppress the influence of unstable laser power. As a result, for the 1f signal, stable detection with a variation coefficient of 0.59% was obtained over a wide dynamic range (0.38–8.1 mW). For the 2f signal, stable detection with a variation coefficient of 0.53% was obtained from 0.64 mW to 8.27 mW. The test results showed a good agreement with the theoretical analysis and the proposed method has considerable potential application in gas sensing. PMID:25912353

  19. Dynamics of flashlamp pumping a Nd:Cr:GSGG laser

    NASA Astrophysics Data System (ADS)

    Pack, Michael V.; Miller, Paul A.; Shelton, Jason

    2008-08-01

    We investigate the inversion dynamics in Nd:Cr:GSGG laser rods as a function of pumping frequency in order to optimize Nd:Cr:GSGG Q switched lasers for rapid time to fire applications. By frequency filtering the pump light to the Nd:Cr:GSGG rod and measuring the florescence from the rod, we determine the dynamics for different excitation processes in the laser (i.e. direct excitation of the Nd ions or indirect excitation via Cr ions). We also measure the flashlamp pulse shape using various spectral filters This combination of measurements help us understand the processes contributing and limiting the efficiency of Nd:Cr:GSGG lasers when the lasers must fire on a short time scale.

  20. Laser-plasma interactions in large gas-filled hohlraums

    SciTech Connect

    Turner, R.E.; Powers, L.V.; Berger, R.L.

    1996-06-01

    Indirect-drive targets planned for the National Ignition Facility (NIF) laser consist of spherical fuel capsules enclosed in cylindrical Au hohlraums. Laser beams, arranged in cylindrical rings, heat the inside of the Au wall to produce x rays that in turn heat and implode the capsule to produce fusion conditions in the fuel. Detailed calculations show that adequate implosion symmetry can be maintained by filling the hohlraum interior with low-density, low-Z gases. The plasma produced from the heated gas provides sufficient pressure to keep the radiating Au surface from expanding excessively. As the laser heats this gas, the gas becomes a relatively uniform plasma with small gradients in velocity and density. Such long-scale-length plasmas can be ideal mediums for stimulated Brillouin Scattering (SBS). SBS can reflect a large fraction of the incident laser light before it is absorbed by the hohlraum; therefore, it is undesirable in an inertial confinement fusion target. To examine the importance of SBS in NIF targets, the authors used Nova to measure SBS from hohlraums with plasma conditions similar to those predicted for high-gain NIF targets. The plasmas differ from the more familiar exploding foil or solid targets as follows: they are hot (3 keV); they have high electron densities (n{sub e}=10{sup 21}cm{sup {minus}3}); and they are nearly stationary, confined within an Au cylinder, and uniform over large distances (>2 mm). These hohlraums have <3% peak SBS backscatter for an interaction beam with intensities of 1-4 x 10{sup 15} W/cm{sup 2}, a laser wavelength of 0.351{micro}m, f/4 or f/8 focusing optics, and a variety of beam smoothing implementations. Based on these conditions the authors conclude that SBS does not appear to be a problem for NIF targets.

  1. Nonlinear dynamics of quantum cascade lasers with optical feedback

    NASA Astrophysics Data System (ADS)

    Jumpertz, L.; Ferré, S.; Schires, K.; Carras, M.; Grillot, F.

    2015-01-01

    Quantum Cascade (QC) lasers are widely used in optical communications, high-resolution spectroscopy, imaging, and remote sensing due to their wide spectral range, going from mid-infrared to the terahertz regime. The dynamics of QClasers are dominated by their ultrafast carrier lifetime, typically of the order of a few picoseconds. The combination of optical nonlinearities and ultrafast dynamics is an interesting feature of QC-lasers, and investigating the dynamical properties of such lasers gives unprecedented insights into the underlying physics of the components, which is of interest for the next generation of QC devices. A particular feature of QC-lasers is the absence of relaxation oscillations, which is the consequence of the relatively short carrier lifetime compared to photon lifetime. Optical feedback (i.e. self-injection) is known to be a robust technique for stabilizing or synchronizing a free-running laser, however its effect on QC-lasers remains mostly unexplored. This work aims at discussing the dynamical properties of QC-lasers operating under optical feedback by employing a novel set of rate equations taking into account the upper and lower lasing levels, the bottom state as well as the gain stage's cascading. This work analyzes the static laser properties subject to optical feedback and provides a comparison with experiments. Spectral analysis reveals that QC-lasers undergo distinct feedback regimes depending on the phase and amplitude of the reinjected field, and that the coherence-collapse regime only appears in a very narrow range of operation, making such lasers much more stable than their interband counterparts.

  2. Plasma laser accelerator: longitudinal dynamics, the plasma/laser interaction, and a qualitative design

    SciTech Connect

    Ruth, R.D.; Chao, A.W.

    1982-04-01

    In this paper we present our studies on a plasma laser accelerator. First we look at the longitudinal dynamics and the trapping of particles in the potential well due to the longitudinal electric field in a plasma density wave. Next we study the plasma/laser interaction to obtain power requirements. Lastly, we qualitatively design a plasma/laser accelerator with parameters somewhat more modest than existing suggestions.

  3. Effect of laser pulse energy on the laser ignition of compressed natural gas fueled engine

    NASA Astrophysics Data System (ADS)

    Srivastava, Dhananjay Kumar; Wintner, Ernst; Agarwal, Avinash Kumar

    2014-05-01

    Laser pulses of few a nanoseconds' duration are focused by an appropriate converging lens system, leading to breakdown of the medium (combustible gases), resulting in the formation of intense plasma. Plasma thus induced can be used to initiate the combustion of combustible air-fuel mixtures in a spark ignition engine provided the energy of the plasma spark is high enough. Laser ignition has several advantages over the conventional spark ignition system, especially in case of lean air-fuel mixture. In this study, laser ignition of compressed natural gas was investigated in a constant volume combustion chamber (CVCC) as well as in a single-cylinder engine. Flame kernel visualizations for different pulse energy of natural gas-air mixtures were carried out in the CVCC. The images of the development of early flame kernel stages and its growth with time were recorded by shadowgraphy technique. The effect of laser pulse energy on the engine combustion, performance, and emissions was investigated using different air-fuel mixtures. Increased peak cylinder pressure, higher rate of heat release, faster combustion, and increased combustion stability were observed for higher laser pulse energies. The effect of laser pulse energy on the engine-out emissions was also investigated in this study.

  4. Laser-based dynamic evaporation and surface shaping of fused silica with assist gases: a path to rimless laser machining

    NASA Astrophysics Data System (ADS)

    Elhadj, S.; Matthews, M. J.; Guss, G. M.; Bass, I. L.

    2013-12-01

    Evaporation and ablation are fundamental processes which drive laser-material processing performance. In applications where surface shape is important, control of the temperature field and the resulting spatially varying material response must be considered. For that purpose, assist gases are useful in, first, lowering treatment temperatures and, second, in changing interfacial and bulk chemistry to limit capillary-driven flow. Additionally, laser-matter coupling is influenced by pulse length as it determines the heat affected zone. Using infrared imaging of CO2 laser-heated fused silica and surface profile measurements, we derive temperature and time dependent pitting rates along with shapes for a range of gases that include hydrogen, nitrogen, air, and helium. In the range of 1,500-4,500 K, evaporation, flow, and densification are shown to contribute to the pit shape. Analysis reveals a strong and complex dependence of rim formation on heating time and gas chemistry, mostly by lowering treatment temperature. Under dynamic heating, chemicapillarity appears to help in lowering rim height, in spite of the reactants mass transport limitations. Results on this gas-assisted approach suggest the possibility for sub-nanometer "rimless" laser-based machining.

  5. Dynamic testing of NOVA laser switchyard tower

    SciTech Connect

    Weaver, H.J.; Pastrnak, J.W.; Fields, D.E.

    1984-06-01

    NOVA is the latest in a series of powerful laser systems designed to study the feasibility of initiating a controlled fusion reaction by concentrating several laser beams on a small fuel target. The laser components, turning mirrors and target chamber are all mounted on large steel frame structures. These structures were first analyzed via finite element models to access their seismic integrity as well as their overall vibrational stability. When construction was completed, a modal analysis was performed on the structures to verify and improve the finite element models. This report discusses the linking of the analytical and experimental studies for the NOVA switchyard tower structure.

  6. Picosecond lasers with the dynamical operation control

    NASA Astrophysics Data System (ADS)

    Mikheev, N. G.; Morozov, V. B.; Olenin, A. N.; Yakovlev, D. V.

    2016-04-01

    Numerical model for simulation of generation process in advanced pulse-periodic high-peak-power picosecond diode-pumped Nd:YAG and Nd:YLF lasers has been developed. The model adequately describes picosecond pulse formation governed by active and passive mode-locking, negative feedback and adjustable loss level in the oscillator cavity. Optical jitter of output pulses attributed to laser generation development from spontaneous noise level was evaluated using statistical analysis of calculation results. In the presented laser scheme, minimal jitter value on the level ~40 ps was estimated.

  7. Classical dynamics of free electromagnetic laser pulses

    NASA Astrophysics Data System (ADS)

    Goto, S.; Tucker, R. W.; Walton, T. J.

    2016-02-01

    We discuss a class of exact finite energy solutions to the vacuum source-free Maxwell field equations as models for multi- and single cycle laser pulses in classical interaction with relativistic charged test particles. These solutions are classified in terms of their chiral content based on their influence on particular charge configurations in space. Such solutions offer a computationally efficient parameterization of compact laser pulses used in laser-matter simulations and provide a potential means for experimentally bounding the fundamental length scale in the generalized electrodynamics of Bopp, Landé and Podolsky.

  8. Photochemical gas lasers and hybrid (solid/gas) blue-green femtosecond systems

    NASA Astrophysics Data System (ADS)

    Mikheev, L. D.; Tcheremiskine, V. I.; Uteza, O. P.; Sentis, M. L.

    2012-01-01

    The review summarizes milestones and major breakthrough results obtained in the course of the development of a photochemical method applied to optical excitation of gas lasers on electronic molecular transitions by radiation from such unconventional pump sources as high-temperature electrical discharges and strong shock waves in gas. It also describes principles and techniques applied in hybrid (solid/gas) high-intensity laser systems emitting in the blue-green spectral region, and discusses wavelength scaling of laser-matter interaction by the example of laser wake-field acceleration (LWFA), high-order harmonic generation (HHG) and “water window” soft X-ray lasers. One of the most significant results of the photochemical method development consists in emerging broad bandwidth lasers (XeF(C-A), Xe2Cl, and Kr2F) operating in the blue-green spectral range, which have potential for amplification of ultra-short (down to 10 fs) optical pulses towards the Petawatt peak power level. The main goal of this review is to argue that the active media of these lasers may provide a basis for the development of fs systems generating super-intense ultrashort laser pulses in the visible spectral range. Some specific hybrid schemes, comprising solid state front-ends and photodissociation XeF(C-A) power boosting amplifiers, are described. They are now under development at the Lasers Plasmas and Photonic Processes (LP3) Laboratory (Marseille, France), the P.N. Lebedev Physical Institute (Moscow, Russia) and the Institute of High-Current Electronics (Tomsk, Russia) with the aim of conducting proof-of-principle experiments. Some consequences of the visible-wavelength laser field interaction with matter are also surveyed to demonstrate advantages of short driver wavelength in the considered examples. One of the most important consequences is the possibility of coherent soft X-ray generation within the “water window” spectral range with the use of short wavelength driver pulses to

  9. IV-VI semiconductor lasers for gas phase biomarker detection

    NASA Astrophysics Data System (ADS)

    McCann, Patrick; Namjou, Khosrow; Roller, Chad; McMillen, Gina; Kamat, Pratyuma

    2007-09-01

    A promising absorption spectroscopy application for mid-IR lasers is exhaled breath analysis where sensitive, selective, and speedy measurement of small gas phase biomarker molecules can be used to diagnose disease and monitor therapies. Many molecules such as nitric oxide, ethane, formaldehyde, acetaldehyde, acetone, carbonyl sulfide, and carbon disulfide have been connected to diseases or conditions such as asthma, oxidative stress, breast cancer, lung cancer, diabetes, organ transplant rejection, and schizophrenia. Measuring these and other, yet to be discovered, biomarker molecules in exhaled breath with mid-IR lasers offers great potential for improving health care since such tests are non-invasive, real-time, and do not require expensive consumables or chemical reagents. Motivated by these potential benefits, mid-IR laser spectrometers equipped with presently available cryogenically-cooled IV-VI lasers mounted in compact Stirling coolers have been developed for clinical research applications. This paper will begin with a description of the development of mid-IR laser instruments and their use in the largest known exhaled breath clinical study ever performed. It will then shift to a description of recent work on the development of new IV-VI semiconductor quantum well materials and laser fabrication methods that offer the promise of low power consumption (i.e. efficient) continuous wave emission at room temperature. Taken together, the demonstration of compelling clinical applications with large market opportunities and the clear identification of a viable pathway to develop low cost mid-IR laser instrumentation can create a renewed focus for future research and development efforts within the mid-IR materials and devices area.

  10. Laser gas analyzers for studying kinetics of gas exchange between vegetation biosystems and atmosphere

    NASA Astrophysics Data System (ADS)

    Ageev, B. G.; Kapitanov, V. A.; Ponomarev, Yu. N.; Vasiliev, V. A.; Karapuzikov, A. I.; Sherstov, I. V.

    2006-11-01

    Specifications and examples of application of laser gas-analyzers of near- and mid-infrared ranges for diagnostics of greenhouse gases (CO II, C IIH 4, and CH 4) emission by vegetation biosystems both under standard conditions and under impacts of natural and anthropogenic stresses are considered in the report. The gas-analyzer complex includes: 1) gas-analyzer with a multipass absorption cell based on the frequency-tunable diode laser (1600-1650 nm) for measuring sub-background methane concentrations (<= 20 ppbV); 2) gas-analyzer based on the wave-guide CO II-laser equipped with the intracavity acoustic detector capable of fast frequency scanning in the 9 and 10 μm generation bands and having the ethylene-sensitivity better than 1 ppbV. The technology of measurements of gas emission by plant stripped leaves and coniferous needles is described and the measurements of CO II and CH 4 emissions are presented.

  11. Laser gas-analyzers for studying kinetics of gas-exchange between vegetation biosystems and atmosphere

    NASA Astrophysics Data System (ADS)

    Ageev, B. G.; Kapitanov, V. A.; Ponomarev, Yu. N.; Vasiliev, V. A.; Karapuzikov, A. I.; Sherstov, I. V.

    2006-12-01

    Specifications and examples of application of laser gas-analyzers of near- and mid-infrared ranges for diagnostics of greenhouse gases (C0 II, C IIH 4, and CH 4) emission by vegetation biosystems both under standard conditions and under impacts of natural and anthropogenic stresses are considered in the report. The gas-analyzer complex includes: 1) gas-analyzer with a multipass absorption cell based on the frequency-tunable diode laser (1600-1 650 nm) for measuring sub-background methane concentrations (<=20 ppbV); 2) gas-analyzer based on the wave-guide C0 II-laser equipped with the intracavity acoustic detector capable of fast frequency scanning in the 9 and 10 μm generation bands and having the ethylene-sensitivity better than 1 ppbV. The technology of measurements of gas emission by plant stripped leaves and coniferous needles is described and the measurements of CO II and CH 4 emissions are presented.

  12. Multicomponent gas analyzers based on tunable diode lasers

    SciTech Connect

    Stepanov, E.V.; Zyrianov, P.V.; Khusnutdinov, A.N.; Kouznetsov, A.I.; Ponurovskii, Y.Ya.

    1996-12-31

    A family of multicomponent gas analyzers based on tunable diode lasers (TDL) are presented including: an open optical path 3-component gas analyzer for monitoring atmosphere pollution; a 4-gas component analyzer with a multipass cell, a multichannel TDL system with multipass cell and MIR fiber optics delivery, and a multichannel TDL analyzer for breath content gas analysis. A4B6 tunable diode lasers of different spectral region from 4 to 12 micron were used in every channel of the analyzers to obtain atmospheric transmission spectra and to measure concentration of studied gases. Main gaseous atmospheric pollutants like CO, NO, NH{sub 3}, CH{sub 4}, SO{sub 2}, etc. and some of breath gases could be measured at ppb concentration level in real time with these systems depending on customers requirements. The analyzers are driven by IBM compatible PC. The first results on field monitoring tests as well as on their application to human exhalation content analysis and human exposure monitoring are presented.

  13. Effects of argon gas flow rate on laser-welding.

    PubMed

    Takayama, Yasuko; Nomoto, Rie; Nakajima, Hiroyuki; Ohkubo, Chikahiro

    2012-01-01

    The purpose of this study was to evaluate the effects of the rate of argon gas flow on joint strength in the laser-welding of cast metal plates and to measure the porosity. Two cast plates (Ti and Co-Cr alloy) of the same metal were abutted and welded together. The rates of argon gas flow were 0, 5 and 10 L/min for the Co-Cr alloy, and 5 and 10 L/min for the Ti. There was a significant difference in the ratio of porosity according to the rate of argon gas flow in the welded area. Argon shielding had no significant effect on the tensile strength of Co-Cr alloy. The 5 L/min specimens showed greater tensile strength than the 10 L/min specimens for Ti. Laser welding of the Co-Cr alloy was influenced very little by argon shielding. When the rate of argon gas flow was high, joint strength decreased for Ti. PMID:22447067

  14. The dynamics of compact laser pulses

    NASA Astrophysics Data System (ADS)

    Goto, S.; Tucker, R. W.; Walton, T. J.

    2016-07-01

    We discuss the use of a class of exact finite energy solutions to the vacuum source-free Maxwell equations as models for multi- and single cycle laser pulses in classical interaction with relativistic charged point particles. These compact solutions are classified in terms of their chiral content and their influence on particular charge configurations in space. The results of such classical interactions motivate a phenomenological quantum description of a propagating laser pulse in a medium in terms of an effective quantum Hamiltonian.

  15. Effect of gas flow swirling on coating deposition by the cold gas-dynamic spray method

    NASA Astrophysics Data System (ADS)

    Kiselev, S. P.; Kiselev, V. P.; Zaikovskii, V. N.

    2012-03-01

    The effect of gas flow swirling on the process of coating deposition onto a target by the cold gas-dynamic spray method is studied experimentally and numerically. Flow swirling is found to change the gas flow field and to reduce the gas flow rate under typical conditions of cold gas-dynamic spray. In a non-swirled flow, the shape of the deposited spot is similar to a sharp cone. In contrast, the deposited spot in a swirled flow is shaped as a crater without particles at the center of this crater. It is found that this effect is caused by centrifugal forces acting on particles in a swirled gas flow.

  16. A nonconservative scheme for isentropic gas dynamics

    SciTech Connect

    Chen, Gui-Qiang |; Liu, Jian-Guo

    1994-05-01

    In this paper, we construct a second-order nonconservative for the system of isentropic gas dynamics to capture the physical invariant regions for preventing negative density, to treat the vacuum singularity, and to control the local entropy from dramatically increasing near shock waves. The main difference in the construction of the scheme discussed here is that we use piecewise linear functions to approximate the Riemann invariants w and z instead of the physical variables {rho} and m. Our scheme is a natural extension of the schemes for scalar conservation laws and it can be numerical implemented easily because the system is diagonalized in this coordinate system. Another advantage of using Riemann invariants is that the Hessian matrix of any weak entropy has no singularity in the Riemann invariant plane w-z, whereas the Hessian matrices of the weak entropies have singularity at the vacuum points in the physical plane p-m. We prove that this scheme converges to an entropy solution for the Cauchy problem with L{sup {infinity}} initial data. By convergence here we mean that there is a subsequent convergence to a generalized solution satisfying the entrophy condition. As long as the entropy solution is unique, the whole sequence converges to a physical solution. This shows that this kind of scheme is quite reliable from theoretical view of point. In addition to being interested in the scheme itself, we wish to provide an approach to rigorously analyze nonconservative finite difference schemes.

  17. Quench dynamics of a superfluid Fermi gas

    SciTech Connect

    Warner, G.L.; Leggett, A.J.

    2005-04-01

    With an eye toward the interpretation of so-called 'cosmological' experiments performed on the low-temperature phases of {sup 3}He, in which regions of the superfluid are destroyed by local heating with neutron radiation, we have studied the behavior of a Fermi gas subjected to uniform variations of an attractive BCS interaction parameter {lambda}. In {sup 3}He, the quenches induced by the rapid cooling of the 'hot spots' back through the transition may lead to the formation of vortex loops via the Kibble-Zurek mechanism. A consideration of the free energy available in the quenched region for the production of such vortices reveals that the Kibble-Zurek scaling law gives at best a lower bound on the defect spacing. Further, for quenches that fall far outside the Ginzburg-Landau regime, the dynamics on the pair subspace, as initiated by quantum fluctuations, tends irreversibly to a self-driven steady state with a gap {delta}{sub {infinity}}={epsilon}{sub C}(e{sup 2/N(0){lambda}}-1){sup -1/2}. In weak coupling, this is only half the BCS gap, the extra energy being taken up by the residual collective motion of the pairs.

  18. Ionization heating in rare-gas clusters under intense XUV laser pulses

    SciTech Connect

    Arbeiter, Mathias; Fennel, Thomas

    2010-07-15

    The interaction of intense extreme ultraviolet (XUV) laser pulses ({lambda}=32 nm, I=10{sup 11}-10{sup 14} W/cm{sup 2}) with small rare-gas clusters (Ar{sub 147}) is studied by quasiclassical molecular dynamics simulations. Our analysis supports a very general picture of the charging and heating dynamics in finite samples under short-wavelength radiation that is of relevance for several applications of free-electron lasers. First, up to a certain photon flux, ionization proceeds as a series of direct photoemission events producing a jellium-like cluster potential and a characteristic plateau in the photoelectron spectrum as observed in Bostedt et al. [Phys. Rev. Lett. 100, 133401 (2008)]. Second, beyond the onset of photoelectron trapping, nanoplasma formation leads to evaporative electron emission with a characteristic thermal tail in the electron spectrum. A detailed analysis of this transition is presented. Third, in contrast to the behavior in the infrared or low vacuum ultraviolet range, the nanoplasma energy capture proceeds via ionization heating, i.e., inner photoionization of localized electrons, whereas collisional heating of conduction electrons is negligible up to high laser intensities. A direct consequence of the latter is a surprising evolution of the mean energy of emitted electrons as function of laser intensity.

  19. Plume dynamics and cluster formation in laser-ablated copper plasma in a magnetic field

    SciTech Connect

    Pandey, Pramod K.; Thareja, R. K.

    2011-04-01

    Laser-ablated copper plasma plume expanding in a nonuniform magnetic field and ambient gas is investigated to understand plume dynamics using optical emission spectroscopy and fast imaging of the plume. A peculiar oscillatory behavior of the plume observed in magnetic field is discussed. The appearance and enhancement of Cu{sub 2} (A-X) band in ambient gas and in the presence of magnetic field is reported. The presence of magnetic field favors the formation of copper clusters in the expanding plumes.

  20. Thermochemically Driven Gas-Dynamic Fracturing (TDGF)

    SciTech Connect

    Michael Goodwin

    2008-12-31

    This report concerns efforts to increase oil well productivity and efficiency via a method of heating the oil-bearing rock of the well, a technique known as Thermochemical Gas-Dynamic Fracturing (TGDF). The technique uses either a chemical reaction or a combustion event to raise the temperature of the rock of the well, thereby increasing oil velocity, and oil pumping rate. Such technology has shown promise for future application to both older wellheads and also new sites. The need for such technologies in the oil extraction field, along with the merits of the TGDF technology is examined in Chapter 1. The theoretical basis underpinning applications of TGDF is explained in Chapter 2. It is shown that productivity of depleted well can be increased by one order of magnitude after heating a reservoir region of radius 15-20 m around the well by 100 degrees 1-2 times per year. Two variants of thermal stimulation are considered: uniform heating and optimal temperature distribution in the formation region around the perforation zone. It is demonstrated that the well productivity attained by using equal amounts of thermal energy is higher by a factor of 3 to 4 in the case of optimal temperature distribution as compared to uniform distribution. Following this theoretical basis, two practical approaches to applying TDGF are considered. Chapter 3 looks at the use of chemical intiators to raise the rock temperature in the well via an exothermic chemical reaction. The requirements for such a delivery device are discussed, and several novel fuel-oxidizing mixtures (FOM) are investigated in conditions simulating those at oil-extracting depths. Such FOM mixtures, particularly ones containing nitric acid and a chemical initiator, are shown to dramatically increase the temperature of the oil-bearing rock, and thus the productivity of the well. Such tests are substantiated by preliminary fieldwork in Russian oil fields. A second, more cost effective approach to TGDF is considered in

  1. Probing Molecular Dynamics at Attosecond Resolution with Femtosecond Laser Pulses

    NASA Astrophysics Data System (ADS)

    Tong, X. M.; Zhao, Z. X.; Lin, C. D.

    2003-12-01

    The kinetic energy distribution of D+ ions resulting from the interaction of a femtosecond laser pulse with D2 molecules is calculated based on the rescattering model. From analyzing the molecular dynamics, it is shown that the recollision time between the ionized electron and the D+2 ion can be read from the D+ kinetic energy peaks to attosecond accuracy. We further suggest that a more precise reading of the clock can be achieved by using shorter fs laser pulses (about 15fs).

  2. Lattice dynamics of femtosecond laser-excited antimony

    NASA Astrophysics Data System (ADS)

    Abdel-Fattah, Mahmoud Hanafy; Bugayev, Aleksey; Elsayed-Ali, Hani E.

    2016-07-01

    Ultrafast electron diffraction is used to probe the lattice dynamics of femtosecond laser-excited antimony thin film. The temporal hierarchies of the intensity and position of diffraction orders are monitored. The femtosecond laser excitation of antimony film was found to lead to initial compression after the laser pulse, which gives way to tension vibrating at new equilibrium displacement. A damped harmonic oscillator model, in which the hot electron-blast force contributes to the driving force of oscillations in lattice spacing, is used to interpret the data. The electron-phonon energy-exchange rate and the electronic Grüneisen parameter were obtained.

  3. Modeling of dynamic effects of a low power laser beam

    NASA Technical Reports Server (NTRS)

    Lawrence, George N.; Scholl, Marija S.; Khatib, AL

    1988-01-01

    Methods of modeling some of the dynamic effects involved in laser beam propagation through the atmosphere are addressed with emphasis on the development of simple but accurate models which are readily implemented in a physical optics code. A space relay system with a ground based laser facility is considered as an example. The modeling of such characteristic phenomena as laser output distribution, flat and curved mirrors, diffraction propagation, atmospheric effects (aberration and wind shear), adaptive mirrors, jitter, and time integration of power on target, is discussed.

  4. Laser ablation dynamics in metals: The thermal regime

    SciTech Connect

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

    2012-07-02

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

  5. Imaging Ultra-fast Molecular Dynamics in Free Electron Laser Field

    NASA Astrophysics Data System (ADS)

    Zhang, Y. Z.; Jiang, Y. H.

    The free electron laser (FEL) provides the coherent, brilliant and ultrashort light pulse in short wavelength (extreme ultraviolet and X-ray) regimes, opening up possibilities to study ultra-fast molecular dynamics in photo-induced chemical reactions with new methodologies. In this chapter, we introduce the time-resolved pump-probe experiments on gas-phase targets with FEL facilities to image the nuclear and electronic motions in molecular reactions, which serve as a benchmark for further FEL applications like coherent diffraction imaging and coherent control of functional dynamics in complex molecular reactions.

  6. High power fiber lasers in geothermal, oil and gas

    NASA Astrophysics Data System (ADS)

    Zediker, Mark S.

    2014-03-01

    The subject of this paper is the requirements, design, fabrication, and testing of a prototype laser rock drilling system capable of penetrating even the hardest rocks found deep in the earth. The Oil and Gas industry still uses many of the technologies that were in use at the turn of the 19th century. The drilling industry started with a great innovation with the introduction of the tri-cone bit by Howard Hughes in 1908. Since then, the industry has modified and optimized drilling systems with incremental advancement in the ability to penetrate hard crystalline rock structures. Most oil producing reservoirs are located in or below relatively soft rock formations, however, with the growing need for energy, oil companies are now attempting to drill through very hard surface rock and deep ocean formations with limited success. This paper will discuss the types of laser suitable for this application, the requirements for putting lasers in the field, the technology needed to support this laser application and the test results of components developed specifically by Foro Energy for the drilling application.

  7. Ionization and dissociation dynamics of molecules in strong laser fields

    NASA Astrophysics Data System (ADS)

    Lai, Wei

    The fast advancement of ultrashort-pulsed high-intensity laser technology allows for generating an electric field equivalent to the Coulomb field inside an atom or a molecule (e.g., EC=5.14x109 V/cm at the 1s orbit radius a0=0.0529 nm of the hydrogen atom, which corresponds to an intensity of 3.54x1016 W/cm2). Atoms and molecules exposed in such a field will easily be ionized, as the external field is strong enough to remove the electrons from the core. This is usually referred to "strong field". Strong fields provide a new tool for studying the interaction of atoms and molecules with light in the nonlinear nonperturbative regime. During the past three decades, significant progress has been made in the strong field science. Today, most phenomena involving atoms in strong fields have been relatively well understood by the single-active-electron (SAE) approximation. However, the interpretation of these responses in molecules has encountered great difficulties. Not like atoms that only undergo excitation and ionization, various dissociation channels accompanying excitation and ionization can occur in molecules during the laser pulse interaction, which imparts further complexity to the study of molecules in strong fields. Previous studies have shown that molecules can behave significantly different from rare gas atoms in phenomena as simple as single and double ionization. Molecular dissociation following ionization also presents challenges in strong fields compared to what we have learned in the weak-field regime. This dissertation focuses on experimental studies on ionization and dissociation of some commonly-seen small molecules in strong laser fields. Previous work of molecules in strong fields will be briefly reviewed, particularly on some open questions about multiple dissociation channels, nonsequential double ionization, enhanced ionization and molecular alignment. The identification of various molecular dissociation channels by recent experimental technical

  8. Light intensity independence during dynamic laser speckle analysis

    NASA Astrophysics Data System (ADS)

    Reis, Renan Oliveira; Rabal, Hector J.; Braga, Roberto A.

    2016-05-01

    We explore some different normalizations of current dynamic laser speckle activity measures searching for their performance with respect to the illumination inhomogeneity of the samples. Inertia Moment and Average Value of Differences of the co-occurrence matrix are compared using a paint-drying case study on a uniform sample where attenuation in a portion of the illuminated area is introduced using a neutral density filter. In this way, all environmental conditions being equal but non-uniform illumination permits the comparison on a better approximation to objectivity. The results presented show that it is possible to mitigate the effects of the illumination in the activities measured by the dynamic laser speckle.

  9. Energy coupling and plume dynamics during high power laser heating of metals

    SciTech Connect

    Jeong, S. |

    1997-05-01

    High power laser heating of metals was studied utilizing experimental and numerical methods with an emphasis on the laser energy coupling with a target and on the dynamics of the laser generated vapor flow. Rigorous theoretical modeling of the heating, melting, and evaporation of metals due to laser radiation with a power density below the plasma shielding threshold was carried out. Experimentally, the probe beam deflection technique was utilized to measure the propagation of a laser induced shock wave. The effects of a cylindrical cavity in a metal surface on the laser energy coupling with a solid were investigated utilizing photothermal deflection measurements. A numerical calculation of target temperature and photothermal deflection was performed to compare with the measured results. Reflection of the heating laser beam inside the cavity was found to increase the photothermal deflection amplitude significantly and to enhance the overall energy coupling between a heating laser beam and a solid. Next, unsteady vaporization of metals due to nanosecond pulsed laser heating with an ambient gas at finite pressure was analyzed with a one dimensional thermal evaporation model for target heating and one dimensional compressible flow equations for inviscid fluid for the vapor flow. Lastly, the propagation of a shock wave during excimer laser heating of aluminum was measured with the probe beam deflection technique. The transit time of the shock wave was measured at the elevation of the probe beam above the target surface; these results were compared with the predicted behavior using ideal blast wave theory. The propagation of a gaseous material plume was also observed from the deflection of the probe beam at later times.

  10. Optical Spectroscopy Using Gas-Phase Femtosecond Laser Filamentation

    NASA Astrophysics Data System (ADS)

    Odhner, Johanan; Levis, Robert

    2014-04-01

    Femtosecond laser filamentation occurs as a dynamic balance between the self-focusing and plasma defocusing of a laser pulse to produce ultrashort radiation as brief as a few optical cycles. This unique source has many properties that make it attractive as a nonlinear optical tool for spectroscopy, such as propagation at high intensities over extended distances, self-shortening, white-light generation, and the formation of an underdense plasma. The plasma channel that constitutes a single filament and whose position in space can be controlled by its input parameters can span meters-long distances, whereas multifilamentation of a laser beam can be sustained up to hundreds of meters in the atmosphere. In this review, we briefly summarize the current understanding and use of laser filaments for spectroscopic investigations of molecules. A theoretical framework of filamentation is presented, along with recent experimental evidence supporting the established understanding of filamentation. Investigations carried out on vibrational and rotational spectroscopy, filament-induced breakdown, fluorescence spectroscopy, and backward lasing are discussed.

  11. Optical spectroscopy using gas-phase femtosecond laser filamentation.

    PubMed

    Odhner, Johanan; Levis, Robert

    2014-01-01

    Femtosecond laser filamentation occurs as a dynamic balance between the self-focusing and plasma defocusing of a laser pulse to produce ultrashort radiation as brief as a few optical cycles. This unique source has many properties that make it attractive as a nonlinear optical tool for spectroscopy, such as propagation at high intensities over extended distances, self-shortening, white-light generation, and the formation of an underdense plasma. The plasma channel that constitutes a single filament and whose position in space can be controlled by its input parameters can span meters-long distances, whereas multifilamentation of a laser beam can be sustained up to hundreds of meters in the atmosphere. In this review, we briefly summarize the current understanding and use of laser filaments for spectroscopic investigations of molecules. A theoretical framework of filamentation is presented, along with recent experimental evidence supporting the established understanding of filamentation. Investigations carried out on vibrational and rotational spectroscopy, filament-induced breakdown, fluorescence spectroscopy, and backward lasing are discussed. PMID:24423375

  12. Remote laser spectroscopy of oil and gas deposits

    NASA Astrophysics Data System (ADS)

    Zhevlakov, A. P.; Bespalov, V. G.; Elizarov, V. V.; Grishkanich, A. S.; Kascheev, S. V.; Makarov, E. A.; Bogoslovsky, S. A.; Il'inskiy, A. A.

    2014-06-01

    We developed a Raman lidar with ultraspectral resolution for automatic airborne monitoring of pipeline leaks and for oil and gas exploration. Test flights indicate that a sensitivity of 6 ppm for methane and 2 ppm for hydrogen sulfide has been reached for leakage detection. The lidar is based on the CARS method with a Ti:Sapphire pump laser and a frequencydoubled YLF:Nd probe beam whose frequency is displaced by a BBO crystal. In ground-based experiments, a detection level of 3 to 10 molecules has been reached.

  13. Decay of transverse acoustic waves in a pulsed gas laser

    SciTech Connect

    Kulkarny, V.A.

    1980-11-01

    The long-term characteristics of transverse acoustic waves in the cavity of a pulsed gaseous laser were studied by analyzing them in a straight duct configuration with nonlinear techniques used in sonic boom problems. A decaying sawtooth waveform containing a shockwave reverberated in the cavity transverse to the flow direction. In the asymptotic decay, the relative pressure perturbation of the wave varies as the 2/5 power of the product of the relative overpressure from the pulse and the speed of sound in the gas.

  14. Supersonic gas jets for laser-plasma experiments

    NASA Astrophysics Data System (ADS)

    Schmid, K.; Veisz, L.

    2012-05-01

    We present an in-depth analysis of De Laval nozzles, which are ideal for gas jet generation in a wide variety of experiments. Scaling behavior of parameters especially relevant to laser-plasma experiments as jet collimation, sharpness of the jet edges and Mach number of the resulting jet is studied and several scaling laws are given. Special attention is paid to the problem of the generation of microscopic supersonic jets with diameters as small as 150 μm. In this regime, boundary layers dominate the flow formation and have to be included in the analysis.

  15. Dynamic materials evaluation by confined plasma ablation and laser-generated shocks

    NASA Astrophysics Data System (ADS)

    Paisley, Dennis L.; Swift, D. C.; Forsman, A. C.; Kyrala, George A.; Johnson, Randall P.; Kopp, Roger A.; Hauer, Allan A.; Wark, Justin S.; Loveridge, A.; Allen, A. M.; Kalantar, Daniel H.

    2000-08-01

    Laser-generated shocks can and have been used to study their effects on single crystal materials during shock compression. While a crystal undergoes shock compression and release, the transient x- ray diffraction (TXD) of the Bragg and Laue signals is indicative of the change in the crystal lattice spacing. The lattice spacing directly relates to the strain in the crystal. From the dynamic lattice data, strain, strain rate, and/or phase change in a material may be determined. Confined ablation plasmas can efficiently launch a flyer plate for direct impact on a target material imparting a well-characterized shock input and generate kilobar to megabar pressure pulses over a wide range of pulse duration (= 20 ns). The laser-launched flyer plates are analogous to those launched by gas guns, but the smaller size provides an experimental method not easily accessible by larger gas gun experiments. With lasers, diagnostic equipment can be easily synchronized to study dynamic material parameters, i.e., single crystal shock dynamics, interfacial bond strengths of thin coatings, grain-interfaces, texture, and high strain rates (106 - 109 sec-1).

  16. Equation of state of a laser-cooled gas

    NASA Astrophysics Data System (ADS)

    Rodrigues, J. D.; Rodrigues, J. A.; Moreira, O. L.; Terças, H.; Mendonça, J. T.

    2016-02-01

    We experimentally determine the equation of state of a laser-cooled gas. By employing the Lane-Emden formalism, widely used in astrophysics, we derive the equilibrium atomic profiles in large magneto-optical traps where the thermodynamic effects are cast in a polytropic equation of state. The effects of multiple scattering of light are included, which results in a generalized Lane-Emden equation for the atomic profiles. A detailed experimental investigation reveals an excellent agreement with the model, with a twofold significance. On one hand, we can infer the details of the equation of state of the system, from an ideal gas to a correlated phase due to an effective electrical charge for the atoms, which is accurately described by a microscopical description of the effective electrostatic interaction. On the other hand, we are able map the effects of multiple scattering onto directly controllable experimental variables, which paves the way to subsequent experimental investigations of this collective interaction.

  17. Laser application in measuring the dynamic deformation of gear teeth

    NASA Astrophysics Data System (ADS)

    Gao, Qi; Wu, Zhao-Tong; Li, Jianfeng; Tian, Zhiren

    1996-10-01

    The paper shows how the laser measurement method may be applied in mechanical engineering. Double-exposure speckle photography is used to measure the dynamic deformation of spur gear tooth. A series of experiments of gears with different speed, load and accuracy have been done and double-exposure speckle patterns at different meshing positions have been shot. The dynamic information of spur gear tooth during the whole meshing procedure is obtained by means of automatic image processing.

  18. Laser-Induced Spatiotemporal Dynamics of Magnetic Films.

    PubMed

    Shen, Ka; Bauer, Gerrit E W

    2015-11-01

    We present a theory for the coherent magnetization dynamics induced by a focused ultrafast laser beam in magnetic films, taking into account nonthermal (inverse Faraday effect) and thermal (heating) actuation. The dynamic conversion between spin waves and phonons is induced by the magnetoelastic coupling that allows efficient propagation of angular momentum. The anisotropy of the magnetoelastic coupling renders characteristic angle dependences of the magnetization propagation that are strikingly different for thermal and nonthermal actuation. PMID:26588408

  19. Laser sources and techniques for spectroscopy and dynamics

    SciTech Connect

    Kung, A.H.

    1993-12-01

    This program focuses on the development of novel laser and spectroscopic techniques in the IR, UV, and VUV regions for studying combustion related molecular dynamics at the microscopic level. Laser spectroscopic techniques have proven to be extremely powerful in the investigation of molecular processes which require very high sensitivity and selectivity. The authors approach is to use quantum electronic and non-linear optical techniques to extend the spectral coverage and to enhance the optical power of ultrahigh resolution laser sources so as to obtain and analyze photoionization, fluorescence, and photoelectron spectra of jet-cooled free radicals and of reaction products resulting from unimolecular and bimolecular dissociations. New spectroscopic techniques are developed with these sources for the detection of optically thin and often short-lived species. Recent activities center on regenerative amplification of high resolution solid-state lasers, development of tunable high power mid-IR lasers and short-pulse UV/VUV tunable lasers, and development of a multipurpose high-order suppressor crossed molecular beam apparatus for use with synchrotron radiation sources. This program also provides scientific and technical support within the Chemical Sciences Division to the development of LBL`s Combustion Dynamics Initiative.

  20. Dynamic gas temperature measurement system, volume 1

    NASA Technical Reports Server (NTRS)

    Elmore, D. L.; Robinson, W. W.; Watkins, W. B.

    1983-01-01

    A gas temperature measurement system with compensated frequency response of 1 kHz and capability to operate in the exhaust of a gas turbine engine combustor was developed. A review of available technologies which could attain this objective was done. The most promising method was identified as a two wire thermocouple, with a compensation method based on the responses of the two different diameter thermocouples to the fluctuating gas temperature field. In a detailed design of the probe, transient conduction effects were identified as significant. A compensation scheme was derived to include the effects of gas convection and wire conduction. The two wire thermocouple concept was tested in a laboratory burner exhaust to temperatures of about 3000 F and in a gas turbine engine to combustor exhaust temperatures of about 2400 F. Uncompensated and compensated waveforms and compensation spectra are presented.

  1. Dynamics of a vertical cavity quantum cascade phonon laser structure

    PubMed Central

    Maryam, W.; Akimov, A. V.; Campion, R. P.; Kent, A. J.

    2013-01-01

    Driven primarily by scientific curiosity, but also by the potential applications of intense sources of coherent sound, researchers have targeted the phonon laser (saser) since the invention of the optical laser over 50 years ago. Here we fabricate a vertical cavity structure designed to operate as a saser oscillator device at a frequency of 325 GHz. It is based on a semiconductor superlattice gain medium, inside a multimode cavity between two acoustic Bragg reflectors. We measure the acoustic output of the device as a function of time after applying electrical pumping. The emission builds in intensity reaching a steady state on a timescale of order 0.1 μs. We show that the results are consistent with a model of the dynamics of a saser cavity exactly analogous to the models used for describing laser dynamics. We also obtain estimates for the gain coefficient, steady-state acoustic power output and efficiency of the device. PMID:23884078

  2. Quantum state resolved gas-surface reaction dynamics experiments: a tutorial review.

    PubMed

    Chadwick, Helen; Beck, Rainer D

    2016-07-01

    We present a tutorial review of our quantum state resolved experiments designed to study gas-surface reaction dynamics. The combination of a molecular beam, state specific reactant preparation by infrared laser pumping, and ultrahigh vacuum surface analysis techniques make it possible to study chemical reactivity at the gas-surface interface in unprecedented detail. We describe the experimental techniques used for state specific reactant preparation and for detection of surface bound reaction products developed in our laboratory. Using the example of the reaction of methane on Ni and Pt surfaces, we show how state resolved experiments uncovered clear evidence for vibrational mode specificity and bond selectivity, as well as steric effects in chemisorption reactions. The state resolved experimental data provides valuable benchmarks for comparison with theoretical models for gas-surface reactivity aiding in the development of a detailed microscopic understanding of chemical reactivity at the gas-surface interface. PMID:26235656

  3. Blue laser system for photo-dynamic therapy

    NASA Astrophysics Data System (ADS)

    Dabu, R.; Carstocea, B.; Blanaru, C.; Pacala, O.; Stratan, A.; Ursu, D.; Stegaru, F.

    2007-03-01

    A blue laser system for eye diseases (age related macular degeneration, sub-retinal neo-vascularisation in myopia and presumed ocular histoplasmosis syndrome - POHS) photo-dynamic therapy, based on riboflavin as photosensitive substance, has been developed. A CW diode laser at 445 nm wavelength was coupled through an opto-mechanical system to the viewing path of a bio-microscope. The laser beam power in the irradiated area is adjustable between 1 mW and 40 mW, in a spot of 3-5 mm diameter. The irradiation time can be programmed in the range of 1-19 minutes. Currently, the laser system is under clinic tests.

  4. Highly mobile laser ranging facilities of the Crustal Dynamics Project

    NASA Technical Reports Server (NTRS)

    Coates, R. J.

    1984-01-01

    Technical specifications, performance, and applications of the NASA transportable laser ranging systems (TLRS-1 and -2) for use in the Crustal Dynamics Program are described. TLRS-1 is truck-mounted, with the laser deployed through the roof. Interacting with the LAGEOS satellite, TLRS has a photoelectric receiver for gathering data on the roundtrip time of the laser beam for calculations of the range gate. The laser has a 0.1 nsec pulse at 3.5 mJ/pulse. Range is measured to within an error of 9 cm. The TLRS-2 version is configured for ease of air transport and modular breakdown and assembly. It has been activated on Easter Island. TLRS-3 and -4 are in development to serve as mobile units in South America and the Mediterranean area.

  5. Ultrafast laser-driven proton sources and dynamic proton imaging

    SciTech Connect

    Nickles, Peter V.; Schnuerer, Matthias; Sokollik, Thomas; Ter-Avetisyan, Sargis; Sandner, Wolfgang; Amin, Munib; Toncian, Toma; Willi, Oswald; Andreev, Alexander

    2008-07-15

    Ion bursts, accelerated by an ultrafast (40 fs) laser-assisted target normal sheath acceleration mechanism, can be adjusted so as to deliver a nearly pure proton beam. Such laser-driven proton bursts have predominantly a low transverse emittance and a broad kinetic spectrum suitable for continuous probing of the temporal evolution of spatially extended electric fields that arise after laser irradiation of thin foils. Fields with a strength of up to 10{sup 10} V/m were measured with a new streaklike proton deflectometry setup. The data show the temporal and spatial evolution of electric fields that are due to target charge-up and ion-front expansion following intense laser-target interaction at intensities of 10{sup 17}-10{sup 18} W/cm{sup 2}. Measurement of the field evolution is important to gain further insight into lateral electron-transport processes and the influence of field dynamics on ion beam properties.

  6. Dynamics of Fourier domain mode-locked lasers.

    PubMed

    Slepneva, S; Kelleher, B; O'Shaughnessy, B; Hegarty, S P; Vladimirov, A G; Huyet, G

    2013-08-12

    An analysis of the dynamical features in the output of a Fourier Domain Mode Locked laser is presented. An experimental study of the wavelength sweep-direction asymmetry in the output of such devices is undertaken. A mathematical model based on a set of delay differential equations is developed and shown to agree well with experiment. PMID:23938841

  7. SOLITONS: Dynamics of strong coupling formation between laser solitons

    NASA Astrophysics Data System (ADS)

    Rosanov, Nikolai N.; Fedorov, S. V.; Shatsev, A. N.

    2005-03-01

    The dynamics of the strong coupling formation between two solitons with the unit topological charge is studied in detail for a wide-aperture class A laser. The sequence of bifurcations of the vector field of energy fluxes in the transverse plane was demonstrated during the formation of a soliton complex.

  8. Gas analysis of human exhalation by tunable diode laser spectroscopy

    NASA Astrophysics Data System (ADS)

    Stepanov, Eugene V.; Moskalenko, Konstantin L.

    1993-02-01

    Results of the application of a tunable diode laser (TDL) to determining the trace gas components of human exhalation are presented. The analyzer is specially developed to measure both carbon oxides (CO and CO2) in expired air. A few results illuminating possible applications of TDLs in high-sensitivity medical diagnostics have been obtained. For nonsmokers, expired concentrations of CO are slightly higher than those in inhaled air. The specific surplus value seems to be independent of the ambient atmospheric CO content. The surplus CO content increases by more than an order of magnitude just after intensive exercises, e.g., jogging. For smokers, the pharmacokinetic of abundant CO removal from the organism could be investigated by this technique, which provides quick and reliable measurements of smoking status. Breath-holding synchronous measurements of CO and CO2 in exhalation demonstrate behavior that is different with breath-holding time. The method seems useful for the investigation of phenomena such as molecular pulmonary diffusion through the alveolar-capillary membrane and an organism's adaptation to oxygen shortage. Prospects for the development and application of diode laser spectroscopy to trace gas analysis in medicine are also discussed.

  9. Laser plasma plume structure and dynamics in the ambient air: The early stage of expansion

    NASA Astrophysics Data System (ADS)

    Cirisan, M.; Jouvard, J. M.; Lavisse, L.; Hallo, L.; Oltra, R.

    2011-05-01

    Laser ablation plasma plume expanding into the ambient atmosphere may be an efficient way to produce nanoparticles. From that reason it would be interesting to study the properties of these laser induced plasmas formed under conditions that are known to be favorable for nanoparticles production. In general, plume behavior can be described as a two-stage process: a "violent" plume expansion due to the absorption of the laser beam energy (during the laser pulse) followed by a fast adiabatic expansion in the ambient gas (after the end of the laser pulse). Plasma plume may last a few microseconds and may have densities 10-6 times lower than the solid densities at temperatures close to the ambient temperature. Expansion of the plasma plume induced by the impact of a nanosecond laser beam (λ = 1064 nm) on the surface of metallic samples in the open air has been investigated by means of fast photography. Spatio-temporal evolution of the plume at the early stage of its expansion (first 330 ns) has been recorded. Structure and dynamics of the plasma plume have been investigated and compared to numerical simulations obtained with a hydro-code, as well as some scaling laws. In addition, measurements using different sample materials (Al, Fe, and Ti) have been performed in order to analyze the influence of target material on plume expansion.

  10. Open Path Trace Gas Laser Sensors for UAV Deployment

    NASA Astrophysics Data System (ADS)

    Shadman, S.; Mchale, L.; Rose, C.; Yalin, A.

    2015-12-01

    Novel trace gas sensors based on open-path Cavity Ring-down Spectroscopy (CRDS) are being developed to enable remote and mobile deployments including on small unmanned aerial systems (UAS). Relative to established closed-path CRDS instruments, the use of open-path configurations allows removal of the bulky and power hungry vacuum and flow system, potentially enabling lightweight and low power instruments with high sensitivity. However, open path operation introduces new challenges including the need to maintain mirror cleanliness, mitigation of particle optical effects, and the need to measure spectral features that are relatively broad. The present submission details open-path CRDS instruments for ammonia and methane and their planned use in UAS studies. The ammonia sensor uses a quantum cascade laser at 10.3 mm in a configuration in which the laser frequency is continuously swept and a trigger circuit and acousto-optic modulator (AOM) extinguish the light when the laser is resonant with the cavity. Ring-down signals are measured with a two-stage thermoelectrically cooled MCT photodetector. The cavity mirrors have reflectivity of 0.9995 and a noise equivalent absorption of 1.5 ppb Hz-1/2 was demonstrated. A first version of the methane sensor operated at 1.7um with a telecom diode laser while the current version operates at 3.6 um with an interband cascade laser (stronger absorption). We have performed validation measurements against known standards for both sensors. Compact optical assemblies are being developed for UAS deployment. For example, the methane sensor head will have target mass of <4 kg and power draw <40 W. A compact single board computer and DAQ system is being designed for sensor control and signal processing with target mass <1 kg and power draw <10 W. The sensor size and power parameters are suitable for UAS deployment on both fixed wing and rotor style UAS. We plan to deploy the methane sensor to measure leakage and emission of methane from

  11. Calibrating Laser Gas Measurements by Use of Natural CO2

    NASA Technical Reports Server (NTRS)

    Webster, Chris

    2003-01-01

    An improved method of calibration has been devised for instruments that utilize tunable lasers to measure the absorption spectra of atmospheric gases in order to determine the relative abundances of the gases. In this method, CO2 in the atmosphere is used as a natural calibration standard. Unlike in one prior calibration method, it is not necessary to perform calibration measurements in advance of use of the instrument and to risk deterioration of accuracy with time during use. Unlike in another prior calibration method, it is not necessary to include a calibration gas standard (and the attendant additional hardware) in the instrument and to interrupt the acquisition of atmospheric data to perform calibration measurements. In the operation of an instrument of this type, the beam from a tunable diode laser or a tunable quantum-cascade laser is directed along a path through the atmosphere, the laser is made to scan in wavelength over an infrared spectral region that contains one or two absorption spectral lines of a gas of interest, and the transmission (and, thereby, the absorption) of the beam is measured. The concentration of the gas of interest can then be calculated from the observed depth of the absorption line(s), given the temperature, pressure, and path length. CO2 is nearly ideal as a natural calibration gas for the following reasons: CO2 has numerous rotation/vibration infrared spectral lines, many of which are near absorption lines of other gases. The concentration of CO2 relative to the concentrations of the major constituents of the atmosphere is well known and varies slowly and by a small enough amount to be considered constant for calibration in the present context. Hence, absorption-spectral measurements of the concentrations of gases of interest can be normalized to the concentrations of CO2. Because at least one CO2 calibration line is present in every spectral scan of the laser during absorption measurements, the atmospheric CO2 serves

  12. The Quantum Dynamics of a Dilute Gas in a 3D BCC Optical Lattice

    NASA Astrophysics Data System (ADS)

    Reichl, Linda; Boretz, Yingyue

    2015-03-01

    The classical and quantum dynamics of a dilute gas of rubidium atoms, in a 3D body-centered cubic optical lattice, is studied for a range of polarizations of the laser beams forming the lattice. The relative polarization of the lasers determines the the structure of the potential energy seen by the rubidium atoms. If three pairs of in-phase mutually perpendicular laser beams, with the same wavelength, form the lattice, only a limited range of possible couplings can be realized in the lab. We have determined the band structure of the BCC optical lattice for all theoretically possible couplings, and find that the band structure for lattices realizable in the lab, differs significantly from that expected for a BCC crystal. As coupling is increased, the lattice becomes increasingly chaotic and it becomes possible to produce band structure that has qualitative similarity to a BCC. Welch Foundation

  13. Dynamics of gas disks in triaxial galaxies

    SciTech Connect

    Steiman-Cameron, T.Y.

    1984-01-01

    Increasing evidence has accumulated since the mid 1970's arguing that many, if not all, undisturbed galaxies may have triaxial mass distributions. The steady state configurations (preferred planes) of gas disks in triaxial galaxies with static and rotating surface figures is determined. In addition, the evolution of a gas disk as it settles into the steady state is followed for both axisymmetric and triaxial galaxies. Observational tests are provided for triaxial galactic geometry and give more accurate measures of settling times than those previously published. The preferred planes for gas disks in static and tumbling triaxial galaxies are determined using an analytic method derived from celestial mechanics. The evolution of gas disks which are not in the steady state is followed using numerical methods.

  14. Dynamic Properties of Langmuir Films by Laser Light Scattering

    NASA Astrophysics Data System (ADS)

    Sanders, John Newell

    A technique and instrumentation for measuring visco-elastic properties of Langmuir film organic monolayers has been developed. This technique is used to characterize certain films used in the manufacture of Langmuir-Blodgett solid films. Furthermore a comparison of the dynamic viscous and elastic moduli determined by this technique is made with static values determined from the Pressure versus Area Isotherm. Briefly, a Langmuir film consists of amphiphilic organic molecules spread in a trough filled with pure water. The hydrophobic ends of the molecules trap them on the water surface. When spread at a dilute concentration the molecules exhibit two dimensional ideal gas behavior. By increasing the surface concentration one obtains two dimensional liquid and finally two dimensional solid behavior. The measurement is performed by electrodynamically driving the liquid surface with the electric field from a razor blade brought to within less than 1 mm of the surface. A sinusoidally varying electric field induces dipoles in the water subphase and generates waves at twice the driving frequency (Attractive dipoles are generated whether the field is positive or negative). The space propagation and damping of these waves is measured by laser light scattering. A focused laser beam incident on the surface is reflected at an angle due to the slope of the waves on the surface. By observing the movement of the beam the amplitude and phase of the oscillation with respect to the driving function may be determined (via a Lock-In amplifier) at various distances from the razor blade. One may directly profile the waves by translating the profiler, or one may observe the variation in amplitude and phase while scanning the frequency or surface pressure. In the latter cases one uses a known reference state to determine the wavelength and damping from the amplitude and phase change. This data is fit by a non-linear least squares curve fitting program to determine the wavelength and space

  15. A mathematical model of the dynamics of antitumor laser immunotherapy

    NASA Astrophysics Data System (ADS)

    Dawkins, Bryan A.; Laverty, Sean M.

    2014-02-01

    We use a mathematical model to describe and predict the population dynamics of tumor cells, immune cells, and other immune components in a host undergoing laser immunotherapy treatment against metastatic cancer. We incorporate key elements of the treatment into the model: a function describing the laser-induced primary tumor cell death and parameters capturing the role and strength of the primary immunoadjuvant, glycated chitosan. We focus on identifying conditions that ensure a successful treatment. In particular, we study the patient response (i.e., anti-tumor immune dynamics and treatment outcome) in two different but related mathematical models as we vary quantitative features of the immune system (supply, proliferation, death, and interaction rates). We compare immune dynamics of a `baseline' immune model against an `augmented' model (with additional cell types and antibodies) and in both, we find that using strong immunoadjuvants, like glycated chitosan, that enhance dendritic cell activity yields more promising patient outcomes.

  16. Exact and approximate gas dynamics using the tangent gas

    NASA Technical Reports Server (NTRS)

    Daripa, P. K.; Sirovich, L.

    1986-01-01

    For the determination of aerodynamic characteristics such as lift, drag, and moment coefficients, it is crucial to compute the properties of steady flow past an airfoil. This investigation provides a set of flow dependent grid systems and initial flowfield guesses which substantially improve convergence rates when applied to the Euler equations for flows past an airfoil. The basic equations are examined, taking into account nonlinear equations which are difficult to solve. A good approximation to these equations under certain conditions can be obtained by introducing the so-called 'tangent gas approximation' considered by Woods (1961), in which the isentropic relation between rho and p is replaced by a tangent to a curve. Attention is given to the solution procedure, the analysis (direct) problem, and a comparison of the tangent gas solution with the converged Euler solution.

  17. Dynamics of gas-fluidized granular rods.

    PubMed

    Daniels, L J; Park, Y; Lubensky, T C; Durian, D J

    2009-04-01

    We study a quasi-two-dimensional monolayer of granular rods fluidized by a spatially and temporally homogeneous upflow of air. By tracking the position and orientation of the particles, we characterize the dynamics of the system with sufficient resolution to observe ballistic motion at the shortest time scales. Particle anisotropy gives rise to dynamical anisotropy and superdiffusive dynamics parallel to the rod's long axis, causing the parallel and perpendicular mean-square displacements to become diffusive on different time scales. The distributions of free times and free paths between collisions deviate from exponential behavior, underscoring the nonthermal character of the particle motion. The dynamics show evidence of rotational-translational coupling similar to that of an anisotropic Brownian particle. We model rotational-translational coupling in the single-particle dynamics with a modified Langevin model using nonthermal noise sources. This suggests a phenomenological approach to thinking about collections of self-propelling particles in terms of enhanced memory effects. PMID:19518218

  18. Dynamics of gas-fluidized granular rods

    NASA Astrophysics Data System (ADS)

    Daniels, L. J.; Park, Y.; Lubensky, T. C.; Durian, D. J.

    2009-04-01

    We study a quasi-two-dimensional monolayer of granular rods fluidized by a spatially and temporally homogeneous upflow of air. By tracking the position and orientation of the particles, we characterize the dynamics of the system with sufficient resolution to observe ballistic motion at the shortest time scales. Particle anisotropy gives rise to dynamical anisotropy and superdiffusive dynamics parallel to the rod’s long axis, causing the parallel and perpendicular mean-square displacements to become diffusive on different time scales. The distributions of free times and free paths between collisions deviate from exponential behavior, underscoring the nonthermal character of the particle motion. The dynamics show evidence of rotational-translational coupling similar to that of an anisotropic Brownian particle. We model rotational-translational coupling in the single-particle dynamics with a modified Langevin model using nonthermal noise sources. This suggests a phenomenological approach to thinking about collections of self-propelling particles in terms of enhanced memory effects.

  19. Dynamic changes in PDMS surface morphology in femtosecond laser treatment.

    PubMed

    Moon, Heh-Young; Sidhu, Mehra S; Lee, Heung Soon; Jeoung, Sae Chae

    2015-07-27

    We have investigated the effect of the dynamics of crater size on the poly(dimethylsiloxane) (PDMS) surface morphology in fs-laser micro-processing. PDMS surface was processed with varying both inter-pulse interval and inter-spot distance between successive laser pulses. With keeping the interval of 5 ms crater shape is round even if the spot is overlapped in space. But decreasing the interval to 0.02 ms the shape of the crater is no longer round. Decreasing the inter-distance between the craters results in roughened surface morphology even at time intervals of 5 ms. Temporal dependence of single-shot fs-laser induced crater size was measured as a function of time delay. Within 0.1 ms after pulse irradiation with a fluence of 4.8 J/cm2 on PDMS surface the crater size has reached to its maximum values and then decreased with a time constant of about 0.3 ms. The surface morphology after fs-laser pulse irradiation is strongly dependent on not only inter-spot distance between successive laser pulse but also their inter-pulse intervals. By proposing a theoretical model on their dynamic features, we will try to explain the current observation in quantitatively. PMID:26367645

  20. Spectroscopic and Dynamic Applications of Laser - Interactions.

    NASA Astrophysics Data System (ADS)

    Quesada, Mark Alejandro

    1987-05-01

    Five different studies of laser-molecule interactions are conducted in this thesis. In part one, the first observation of Autler-Townes splitting of molecules is discussed and used to measure vibronic transition moments between excited electronic states. The effect was observed in the two-color, four -photon ionization of hydrogen via the resonant levels E,F(v = 6, J = 1) and D(v = 2, J = 2). Calculations gave good fits to the observed spectra yielding a vibronic transition moment of 2.0 +/- 0.5 a.u. between the above excited states. In part two, a method for extracting the alignment parameters of a molecular angular momentum distribution using laser-induced fluorescence is presented. The treatment is applicable to the common case of cylindrically symmetric orientation distributions in the high J-limit. Four different combinations of rotational branches in the LIF absorption emission process are examined. Computer algebra programs are used to generate simple analytical expressions which account for the influence of saturation on determining alignment parameters. In part three, the application of MPI-optogalvanic spectroscopy to the molecule 1,4-diazabicyclo (2.2.2) octane (DABCO) at various levels in a methane/air flame environment is described. The method employs a burner design that permits access to preheated and primary reaction zones of the flame for laser probing. Hot bands arising from two-photon resonant (X_1 ' to A_1') transitions are measured and the intramolecular vibrational potentials for the ground and first excited state are determined. In part four, DABCO's nu_ {13} torsional mode relaxation in a helium -DABCO and argon-DABCO supersonic jet, under low expansion conditions, is discussed. Modeling of the relaxation using the linear Landau-Teller relaxation equation is undertaken with various attempts to incorporate the effects of velocity slip. The relaxation rate is found to be independent of slip and the cross section dependent on the inverse of

  1. Diode laser arrays for dynamic infrared scene projection

    NASA Astrophysics Data System (ADS)

    Beasley, D. Brett; Cooper, John B.

    1993-08-01

    A novel concept for dynamic IR scene projection using IR diode lasers has been developed. This technology offers significant cost and performance advantages over other currently available projector technologies. Performance advantages include high dynamic range, multiple wavebands, and high frame rates. A projector system which utilizes a 16-element linear array has been developed and integrated into the millimeter wave/infrared (MMW/IR) hardware-in-the-loop (HWIL) facility at the US Army Missile Command's (USAMICOM's) Research, Development, and Engineering Center (RDEC). This projector has demonstrated dynamic range in excess of 105, apparent temperatures greater than 2500 degree(s)C, and nanosecond response times. Performance characteristics for this projector system are presented in the paper. Designs for projectors to test other IR sensor configurations, including FPAs, have been developed and are presented as well. The FPA design consists of a linear array of diode lasers scanned by a polygon mirror. This low-cost projector offers high resolution, high contrast 2-D scenes at up to 10 KHz frame rates. Simulation of active IR countermeasures is another promising application of diode laser projector systems. The diode laser is capable of simulating flares or virtually any IR jammer waveform.

  2. Dynamic detection of species concentration and distribution in pre-combustion gases by laser spectroscopy of infrared absorption

    NASA Astrophysics Data System (ADS)

    Mei, Anhua; Aung, Kendrick

    2005-08-01

    This paper describes the development of spectrum computation and analysis for a single model and untunable laser spectroscopy to detect the species concentration and space distribution in pre-combustion gases. Absorption spectroscopy using infrared laser diode provides a dynamic, non-instructive, and in situ way to determine the concentration and distribution of the mixture of fuel gas and O2 in the pre-combustion gas stream. For species, wavelength suitable for absorption spectroscopy is determined using the spectra distributions of the species provided in HITRAN database. Inverse method and Abel algorithm are employed separately to retrieve the concentration of species and calculate the distribution of the measured gas. The results of the paper provide the foundation to develop a dynamic diagnostic instrument to monitor the state of gaseous species in hostile environments such as various industrial combustion systems.

  3. Pulsed laser facilities operating from UV to IR at the Gas Laser Lab of the Lebedev Institute

    NASA Astrophysics Data System (ADS)

    Ionin, Andrei; Kholin, Igor; Vasil'Ev, Boris; Zvorykin, Vladimir

    2003-05-01

    Pulsed laser facilities developed at the Gas Lasers Lab of the Lebedev Physics Institute and their applications for different laser-matter interactions are discussed. The lasers operating from UV to mid-IR spectral region are as follows: e-beam pumped KrF laser (λ= 0.248 μm) with output energy 100 J; e-beam sustained discharge CO2(10.6 μm) and fundamental band CO (5-6 μm) lasers with output energy up to ~1 kJ; overtone CO laser (2.5-4.2 μm) with output energy ~ 50 J and N2O laser (10.9 μm) with output energy of 100 J; optically pumped NH3 laser (11-14 μm). Special attention is paid to an e-beam sustained discharge Ar-Xe laser (1.73 μm ~ 100 J) as a potential candidate for a laser-propulsion facility. The high energy laser facilities are used for interaction of laser radiation with polymer materials, metals, graphite, rocks, etc.

  4. Effects of xenon cover gas in CO/sub 2/ laser welding

    SciTech Connect

    Hendrix, T.L.

    1980-07-01

    Weld spatter in CO/sub 2/ laser welding is detrimental to miniature components. The effects of using xenon gas as an inert laser welding atmosphere to reduce weld spatter are discussed. The laser plume characteristics, weld penetration, and weld spatter are evaluated.

  5. Gas adsorption and accumulation on hydrophobic surfaces: Molecular dynamics simulations

    NASA Astrophysics Data System (ADS)

    Luo, Qing-Qun; Yang, Jie-Ming

    2015-09-01

    Molecular dynamics simulations show that the gas dissolved in water can be adsorbed at a hydrophobic interface and accumulates thereon. Initially, a water depletion layer appears on the hydrophobic interface. Gas molecules then enter the depletion layer and form a high-density gas-enriched layer. Finally, the gas-enriched layer accumulates to form a nanobubble. The radian of the nanobubble increases with time until equilibrium is reached. The equilibrium state arises through a Brenner-Lohse dynamic equilibrium mechanism, whereby the diffusive outflux is compensated by an influx near the contact line. Additionally, supersaturated gas also accumulates unsteadily in bulk water, since it can diffuse back into the water and is gradually adsorbed by a solid substrate. Project supported by the National Natural Science Foundation of China (Grant No. 21376161).

  6. Dynamically adjustable annular laser trapping based on axicons

    SciTech Connect

    Shao, Bing; Esener, Sadik C.; Nascimento, Jaclyn M.; Botvinick, Elliot L.; Berns, Michael W

    2006-09-01

    To study the chemotactic response of sperm to an egg and to characterize sperm motility, an annular laser trap based on axicons is designed, simulated with the ray-tracing tool, and implemented. The diameter of the trapping ring can be adjusted dynamically for a range of over 400 {mu}m by simply translating one axicon along the optical axis. Trapping experiments with microspheres and dog sperm demonstrate the feasibility of the system,and the power requirement agrees with theoretical expectation. This new type of laser trapping could provide a prototype of a parallel, objective, and quantitative tool for animal fertility and biotropism study.

  7. Dynamics of carrier recombination in a semiconductor laser structure

    SciTech Connect

    Dzhioev, R. I. Kavokin, K. V.; Kusrayev, Yu. G.; Poletaev, N. K.

    2015-11-15

    Carrier-recombination dynamics is studied by the method of optical orientation at room temperature in the active layer of a laser diode structure. The dependence of the degree of electron-spin orientation on the excitation density is attributed to saturation of the nonradiative-recombination channel. The time of electron capture at recombination centers is determined to be τ{sub e} = 5 × 10{sup –9} s. The temperature of nonequilibrium electrons heated by a He–Ne laser is estimated.

  8. Ultrafast dynamic ellipsometry and spectroscopy of laser shocked materials

    SciTech Connect

    Bolme, Cynthia A; Mc Grane, Shawn D; Dang, Nhan C; Whitley, Von H; Moore, David S.

    2011-01-20

    Ultrafast dynamic ellipsometry is used to measure the material motion and changes in the optical refractive index of laser shock compressed materials. This diagnostic has shown us that the ultrafast laser driven shocks are the same as shocks on longer timescales and larger length scales. We have added spectroscopic diagnostics of infrared absorption, ultra-violet - visible transient absorption, and femtosecond stimulated Raman scattering to begin probing the initiation chemistry that occurs in shock reactive materials. We have also used the femtosecond stimulated Raman scattering to measure the vibrational temperature of materials using the Stokes gain to anti-Stokes loss ratio.

  9. 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.

  10. Electron Dynamics in Nanostructures in Strong Laser Fields

    SciTech Connect

    Kling, Matthias

    2014-09-11

    The goal of our research was to gain deeper insight into the collective electron dynamics in nanosystems in strong, ultrashort laser fields. The laser field strengths will be strong enough to extract and accelerate electrons from the nanoparticles and to transiently modify the materials electronic properties. We aimed to observe, with sub-cycle resolution reaching the attosecond time domain, how collective electronic excitations in nanoparticles are formed, how the strong field influences the optical and electrical properties of the nanomaterial, and how the excitations in the presence of strong fields decay.

  11. Cold-atom dynamics in crossed-laser-beam waveguides

    SciTech Connect

    Torrontegui, E.; Muga, J. G.; Echanobe, J.; Ruschhaupt, A.; Guery-Odelin, D.

    2010-10-15

    We study the dynamics of neutral cold atoms in an L-shaped crossed-beam optical waveguide formed by two perpendicular red-detuned lasers of different intensities and a blue-detuned laser at the corner. The motion in one sense is optimized, and the motion in the other sense may be suppressed even if it is energetically allowed. Quantum and classical simulations are performed and give similar results. Complemented with a vibrational cooling process we find a range of parameters for which this setting works as a one-way device or 'atom diode'.

  12. Dark solitons in laser radiation build-up dynamics.

    PubMed

    Woodward, R I; Kelleher, E J R

    2016-03-01

    We reveal the existence of slowly decaying dark solitons in the radiation build-up dynamics of bright pulses in all-normal dispersion mode-locked fiber lasers, numerically modeled in the framework of a generalized nonlinear Schrödinger equation. The evolution of noise perturbations to quasistationary dark solitons is examined, and the significance of background shape and soliton-soliton collisions on the eventual soliton decay is established. We demonstrate the role of a restoring force in extending soliton interactions in conservative systems to include the effects of dissipation, as encountered in laser cavities, and generalize our observations to other nonlinear systems. PMID:27078358

  13. Measurement of ultrafast dynamics in the interaction of intense laser pulses with gases, atomic clusters, and plasmas

    NASA Astrophysics Data System (ADS)

    Kim, Ki-Yong

    2003-10-01

    We have investigated the time resolved dynamics of intense, ultrashort pulse laser interactions with gases, nanometer-size clusters, and plasma waveguides. To probe the ultrafast dynamics in these interactions, we developed a new femtosecond optical diagnostic, single-shot supercontinuum spectral interferometry (SSSI), which measures ultra-rapid transients induced by an intense laser pulse in the complex index of refraction. The measurement of the transient refractive index in intense laser-heated materials provides a direct view of how the laser-produced perturbation evolves in time and space. Our SSSI diagnostic is capable of ˜10 fs temporal resolution on a temporal window ˜1.5 ps long, along with ˜7 mum one-dimensional (1D) spatial resolution. SSSI was first applied to probe the ionization dynamics of helium gas under the irradiation of high intensity (˜1017 W/cm 2) laser pulses. It revealed a characteristic stepwise transition process He → He+ → He2+, in agreement with the optical field ionization model. This measurement was used as a test case to demonstrate that finite laser-target interaction lengths can strongly affect the interpretation of all measurements involving extraction of transient phases. The time-resolved explosion dynamics of intense (˜1015 W/cm2) laser-heated clusters was also studied with SSSI and additional ultrafast optical diagnostics. Here, the ultrafast processes are ionization and rapid cluster plasma explosion. The measurement strongly supports our laser-cluster interaction scenario in which laser-heated clusters explode layer-by-layer, and the laser is strongly coupled at critical density. For the cluster sizes and laser intensities of this experiment, the measured several hundred-femtosecond evolution timescale of laser-heated clusters can be understood in terms of plasma hydrodynamics. A major implication of our understanding of microscopic cluster dynamics was the prediction and observation of self-focusing in clustered

  14. 100-J UV laser for dynamic compression research

    NASA Astrophysics Data System (ADS)

    Zweiback, J.; Fochs, S. F.; Bromage, J.; Broege, D.; Cuffney, R.; Currier, Z.; Dorrer, C.; Ehrich, B.; Engler, J.; Guardalben, M.; Kephalos, N.; Marozas, J.; Roides, R.; Zuegel, J.

    2016-03-01

    A 100-J, 351-nm laser has been developed for the Dynamic Compression Sector located at the Advanced Photon Source. This laser will drive shocks in solid-state materials which will be probed by picosecond x-ray pulses available from the synchrotron source. The laser utilizes a state-of-the-art fiber front end providing pulse lengths up to 20 ns with pulse shapes tailored to optimize shock trajectories. A diode-pumped Nd:glass regenerative amplifier is followed by a four-pass, flash-lamp-pumped rod amplifier. The regenerative amplifier is designed to produce up to 20 mJ with high stability. The final amplifier uses a six-pass, 15-cm, Nd:glass disk amplifier based on an OMEGA laser design. A KDP Type-II/Type-II frequency tripler configuration converts the 1053-nm laser output to a wavelength of 351 nm and the ultraviolet beam is image relayed to the target chamber. Smoothing by Spectral Dispersion and polarization smoothing have been optimized to produce uniform shocks in the materials to be tested. Custom control software collects all diagnostic information and provides a central location for all aspects of laser operation.

  15. CFD assisted simulation of temperature distribution and laser power in pulsed and CW pumped static gas DPALs

    NASA Astrophysics Data System (ADS)

    Waichman, Karol; Barmashenko, Boris D.; Rosenwaks, Salman

    2015-10-01

    An analysis of radiation, kinetic and fluid dynamic processes in diode pumped alkali lasers (DPALs) is reported. The analysis is based on a three-dimensional, time-dependent computational fluid dynamics (3D CFD) model. The CFD code which solves the gas conservation equations includes effects of natural convection and temperature diffusion of the species in the DPAL mixture. The gas flow conservation equations are coupled to the equations for DPAL kinetics and to the Beer-Lambert equations for pump and laser beams propagation. The DPAL kinetic processes in the Cs/CH4 (K/He) gas mixtures considered involve the three low energy levels, (1) n2S1/2, (2) n2P3/2 and (3) n2P1/2 (where n=4,6 for K and Cs, respectively), three excited alkali states and two alkali ionic states. Using the CFD model, the gas flow pattern and spatial distributions of the pump and laser intensities in the resonator were calculated for end-pumped CW and pulsed Cs and K DPALs. The DPAL power and medium temperature were calculated as a function of pump power and pump pulse duration. The CFD model results were compared to experimental results of Cs and K DPALs.

  16. 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

  17. Monitoring interfacial dynamics by pulsed laser techniques

    SciTech Connect

    Richmond, G.L.

    1991-01-01

    Goal is to develop new optical methods for the study of dynamic processes at the electrode/electrolyte interface. In the past year, optical second harmonic generation was used for time resolved measurements of thallium electrodeposition on Cu(111). Other studies included the study of the photochemistry involved in a GaAs surface treatment known as photowashing, and the study of picosecond time resolved luminescence decays from GaAs in electrochemical environments (power dependent effects). 4 figs. (DLC)

  18. Long-range open-path greenhouse gas monitoring using mid-infrared laser dispersion spectroscopy

    NASA Astrophysics Data System (ADS)

    Daghestani, Nart; Brownsword, Richard; Weidmann, Damien

    2015-04-01

    Accurate and sensitive methods of monitoring greenhouse gas (GHG) emission over large areas has become a pressing need to deliver improved estimates of both human-made and natural GHG budgets. These needs relate to a variety of sectors including environmental monitoring, energy, oil and gas industry, waste management, biogenic emission characterization, and leak detection. To address the needs, long-distance open-path laser spectroscopy methods offer significant advantages in terms of temporal resolution, sensitivity, compactness and cost effectiveness. Path-integrated mixing ratio measurements stemming from long open-path laser spectrometers can provide emission mapping when combined with meteorological data and/or through tomographic approaches. Laser absorption spectroscopy is the predominant method of detecting gasses over long integrated path lengths. The development of dispersion spectrometers measuring tiny refractive index changes, rather than optical power transmission, may offer a set of specific advantages1. These include greater immunity to laser power fluctuations, greater dynamic range due to the linearity of dispersion, and ideally a zero baseline signal easing quantitative retrievals of path integrated mixing ratios. Chirped laser dispersion spectrometers (CLaDS) developed for the monitoring of atmospheric methane and carbon dioxide will be presented. Using quantum cascade laser as the source, a minimalistic and compact system operating at 7.8 μm has been developed and demonstrated for the monitoring of atmospheric methane over a 90 meter open path2. Through full instrument modelling and error propagation analysis, precision of 3 ppm.m.Hz-0.5 has been established (one sigma precision for atmospheric methane normalized over a 1 m path and 1 s measurement duration). The system was fully functional in the rain, sleet, and moderate fog. The physical model and system concept of CLaDS can be adapted to any greenhouse gas species. Currently we are

  19. LASERS: Emission dynamics of coupled Nd3+ : YAG lasers with a shared population inversion source

    NASA Astrophysics Data System (ADS)

    Kaptsov, L. N.; Yatskiv, A. M.

    1995-08-01

    A calculation is made of the frequency spectrum of relaxation oscillations of a cw Nd3+ : YAG laser with several lasing channels intersecting in the same active element. It is shown that the highest frequency of relaxation oscillations of isolated channels is virtually retained when these channels are coupled by population inversion, but the other frequencies are reduced. The results of these calculations are in agreement with measurements carried out on a double-beam laser. Experiments are reported on the transition of such a system to dynamic chaos. As in the case of a solid-state laser which emits multimode (in respect of the longitudinal index) radiation, near the frequencies of relaxation oscillations the transition of the investigated system to dynamic chaos follows the Ruelle—Takens—Newhouse scenario.

  20. Dynamic x-ray imaging of laser-driven nanoplasmas

    NASA Astrophysics Data System (ADS)

    Fennel, Thomas

    2016-05-01

    A major promise of current x-ray science at free electron lasers is the realization of unprecedented imaging capabilities for resolving the structure and ultrafast dynamics of matter with nanometer spatial and femtosecond temporal resolution or even below via single-shot x-ray diffraction. Laser-driven atomic clusters and nanoparticles provide an ideal platform for developing and demonstrating the required technology to extract the ultrafast transient spatiotemporal dynamics from the diffraction images. In this talk, the perspectives and challenges of dynamic x-ray imaging will be discussed using complete self-consistent microscopic electromagnetic simulations of IR pump x-ray probe imaging for the example of clusters. The results of the microscopic particle-in-cell simulations (MicPIC) enable the simulation-assisted reconstruction of corresponding experimental data. This capability is demonstrated by converting recently measured LCLS data into a ultrahigh resolution movie of laser-induced plasma expansion. Finally, routes towards reaching attosecond time resolution in the visualization of complex dynamical processes in matter by x-ray diffraction will be discussed.

  1. Dual-Beam Atom Laser Driven by Spinor Dynamics

    NASA Technical Reports Server (NTRS)

    Thompson, Robert; Lundblad, Nathan; Maleki, Lute; Aveline, David

    2007-01-01

    An atom laser now undergoing development simultaneously generates two pulsed beams of correlated Rb-87 atoms. (An atom laser is a source of atoms in beams characterized by coherent matter waves, analogous to a conventional laser, which is a source of coherent light waves.) The pumping mechanism of this atom laser is based on spinor dynamics in a Bose-Einstein condensate. By virtue of the angular-momentum conserving collisions that generate the two beams, the number of atoms in one beam is correlated with the number of atoms in the other beam. Such correlations are intimately linked to entanglement and squeezing in atomic ensembles, and atom lasers like this one could be used in exploring related aspects of Bose-Einstein condensates, and as components of future sensors relying on atom interferometry. In this atom-laser apparatus, a Bose-Einstein condensate of about 2 x 10(exp 6) Rb-87 atoms at a temperature of about 120 micro-K is first formed through all-optical means in a relatively weak singlebeam running-wave dipole trap that has been formed by focusing of a CO2-laser beam. By a technique that is established in the art, the trap is loaded from an ultrahigh-vacuum magnetooptical trap that is, itself, loaded via a cold atomic beam from an upstream two-dimensional magneto-optical trap that resides in a rubidium-vapor cell that is differentially pumped from an adjoining vacuum chamber, wherein are performed scientific observations of the beams ultimately generated by the atom laser.

  2. Multifractality and the effect of turbulence on the chaotic dynamics of a HeNe laser

    NASA Astrophysics Data System (ADS)

    Gulich, Damián.; Zunino, Luciano; Pérez, Darío.; Garavaglia, Mario

    2013-09-01

    We propose the use of multifractal detrended fluctuation analysis (MF-DFA) to measure the influence of atmospheric turbulence on the chaotic dynamics of a HeNe laser. Fit ranges for MF-DFA are obtained with goodness of linear fit (GoLF) criterion. The chaotic behavior is generated by means of a simple interferometric setup with a feedback to the cavity of the gas laser. Such dynamics have been studied in the past and modeled as a function of the feedback level. Different intensities of isotropic turbulence have been generated with a turbulator device, allowing a structure constant for the index of refraction of air adjustable by means of a temperature difference parameter in the unit. Considering the recent interest in message encryption with this kind of setups, the study of atmospheric turbulence effects plays a key role in the field of secure laser communication through the atmosphere. In principle, different intensities of turbulence may be interpreted as different levels of white noise on the original chaotic series. These results can be of utility for performance optimization in chaotic free-space laser communication systems.

  3. Gas emissions and slug dynamics at Stromboli

    NASA Astrophysics Data System (ADS)

    Pering, Tom D.; McGonigle, Andrew J. S.; James, Mike R.; Tamburello, Giancarlo; Aiuppa, Alessandro

    2016-04-01

    We present UV camera data for 200 strombolian and hornito degassing events at Stromboli during June and July 2014. This data was processed to calculate SO2 masses for each event. In addition to calculating SO2 masses of the slugs which generate these events we also observe periods of elevated flux following events, termed the gas coda, lasting ≈ 30 - 180 s, which we also calculate SO2masses for. This provided a range of explosive plus coda SO2 masses of ≈ 18 - 225 kg. In combination with 3D fluid numerical simulations of slug flow we begin to probe a possible generation mechanism for the observed gas codas. The simulations show that 'daughter bubbles' are produced from the base of ascending slugs, which result in gas mass loss rates from the slugs of between ≈ 1.2 - 14.2 kg s‑1. Nf, the dimensionless inverse viscosity number, can be used to characterise the form of a slug wake, and hence when mass loss through daughter bubble production may occur. However, the observed daughter bubble behaviour occurs at lower levels of Nf than predicted by previous mm- to cm-scale studies and suggests that extra physics (e.g. surface tension), beyond that included in Nf, may be needed to parameterise daughter bubble production. We suggest that daughter bubbles could play a role in modulating explosivity of strombolian eruptions as a potential causal mechanism for gas coda production.

  4. Resonance transition 795-nm Rubidium laser using 3He buffer gas

    SciTech Connect

    Wu, S S; Soules, T F; Page, R H; Mitchell, S C; Kanz, V K; Beach, R J

    2007-08-02

    We report the first demonstration of a 795-nm Rubidium resonance transition laser using a buffer gas consisting of pure {sup 3}He. This follows our recent demonstration of a hydrocarbon-free 795-nm Rubidium resonance laser which used naturally-occurring He as the buffer gas. Using He gas that is isotopically enriched with {sup 3}He yields enhanced mixing of the Rb fine-structure levels. This enables efficient lasing at reduced He buffer gas pressure, improving thermal management in high average power Rb lasers and enhancing the power scaling potential of such systems.

  5. Laser velocimetry measurements in a gas turbine research combustor

    NASA Technical Reports Server (NTRS)

    Driscoll, J. F.; Pelaccio, D. G.

    1979-01-01

    The effects of turbulence on the production of pollutant species in a gas-turbine research combustor are studied using laser diffraction velocimetry (LDV) techniques. Measurements that were made in the primary combustion zone include mean velocity, rms velocity fluctuations, velocity probability distributions, and autocorrelation functions. A unique combustor design provides relatively uniform flow conditions and independent control of drop size, equivalence ratio, inlet temperature, and combustor pressure. Parameters which characterize the nature of the spray combustion (i.e., whether single droplet or group combustion occurs), were determined from the LDV data. Turbulent diffusivity (eddy viscosity) reaches a value of 2930 sq cm/sec, corresponding to a convective integral length scale of 1.8 cm. The group combustion number, based on turbulent diffusivity, is measured to be 6.2

  6. Surface-Specific Laser Matter Interactions and Dynamics

    SciTech Connect

    Joly, Alan G.; Beck, Kenneth M.; Hess, Wayne P.

    2010-10-08

    Neutral magnesium atom desorption is induced using infrared and visible femtosecond laser pulses at energies well below the excitation threshold of the bulk material. We find that infrared femtosecond laser excitation of MgO nanocrystalline samples desorbs neutral Mg-atoms with hyperthermal kinetic energies ranging from 0.1 to 0.6 eV, while visible femtosecond excitation desorbs neutral Mg-atoms with thermal kinetic energies ranging from 0.01 to 0.1 eV. The hyperthermal kinetic energy distribution is similar to the distribution observed previously under nanosecond laser excitation in the ultraviolet. The hyperthermal kinetic energy distribution supports the contention that emission is induced predominantly by electron trapping at Mg corner surface sites. The results demonstrate that femtosecond photon pulses can serve as a powerful tool for probing desorption dynamics at surfaces.

  7. Greenhouse Gas Laser Imaging Tomography Experiment (GreenLITE)

    NASA Astrophysics Data System (ADS)

    Dobler, Jeremy; Blume, Nathan; Braun, Michael; Zaccheo, T. Scott; Pernini, Tim; Botos, Chris

    2016-06-01

    Exelis has recently developed a novel laser-based instrument to aid in the autonomous real-time monitoring and mapping of CO2 concentration over a two-dimensional area. The Greenhouse gas Laser Imaging Tomography Experiment (GreenLITE) instrument uses two transceivers and a series of retroreflectors to continuously measure the differential transmission over a number of overlapping lines of sight or "chords", forming a plane. By inverting the differential transmission measurements along with locally measured temperature (T), pressure (P) and relative humidity (RH) the average concentration of CO2 along each chord can be determined and, based on the overlap between chords, a 2D map of CO2 concentration over the measurement plane can be estimated. The GreenLITE system was deployed to the Zero Emissions Research and Technology (ZERT) center in Bozeman, Montana, in Aug-Sept 2014, where more than 200 hours of data were collected over a wide range of environmental conditions, while utilizing a controlled release of CO2 into a segmented underground pipe [1]. The system demonstrated the ability to identify persistent CO2 sources at the test facility and showed strong correlation with an independent measurement using a LI-COR based system. Here we describe the measurement approach, instrument design, and results from the deployment to the ZERT site.

  8. Heavy Gas Conversion of the NASA Langley Transonic Dynamics Tunnel

    NASA Technical Reports Server (NTRS)

    Corliss, James M.; Cole, Stanley, R.

    1998-01-01

    The heavy gas test medium has recently been changed in the Transonic Dynamics Tunnel (TDT) at the NASA Langley Research Center. A NASA Construction of Facilities project has converted the TDT heavy gas from dichlorodifluoromethane (R12) to 1,1,1,2 tetrafluoroethane (R134a). The facility s heavy gas processing system was extensively modified to implement the conversion to R134a. Additional system modifications have improved operator interfaces, hardware reliability, and quality of the research data. The facility modifications included improvements to the heavy gas compressor and piping, the cryogenic heavy gas reclamation system, and the heavy gas control room. A series of wind tunnel characterization and calibration tests are underway. Results of the flow characterization tests show the TDT operating envelope in R134a to be very similar to the previous operating envelope in R12.

  9. Electric-discharge gas laser based on a multisectional discharge gap

    SciTech Connect

    Lazhintsev, B V; Nor-Arevyan, V A

    2000-01-31

    An electric discharge laser with an electrode unit of novel design was developed. An electric discharge system was based on multisectional plate-like electrodes and an automatic UV preionisation that makes it possible to form a highly stable volume discharge. High-efficiency lasing in N{sub 2} and XeF lasers was achieved. A pulse repetition rate up to 200 Hz was realised in the N{sub 2} laser without recourse to gas circulation. (lasers)

  10. Frequency comb offset dynamics of SESAM modelocked thin disk lasers.

    PubMed

    Emaury, Florian; Diebold, Andreas; Klenner, Alexander; Saraceno, Clara J; Schilt, Stéphane; Südmeyer, Thomas; Keller, Ursula

    2015-08-24

    We present a detailed study of the carrier-envelope offset (CEO) frequency dynamics of SESAM modelocked thin disk lasers (TDLs) pumped by kW-class highly transverse multimode pump diodes with a typical M(2) value of 200-300, and give guidelines for future frequency stabilization of multi-100-W oscillators. We demonstrate CEO frequency detection with > 30 dB signal-to-noise ratio with a resolution bandwidth of 100 kHz from a SESAM modelocked Yb:YAG TDL delivering 140 W average output power with 748-fs pulses at 7-MHz pulse repetition rate. We compare with a low-power CEO frequency stabilized Yb:CALGO TDL delivering 2.1 W with 77-fs pulses at 65 MHz. For both lasers, we perform a complete noise characterization, measure the relevant transfer functions (TFs) and compare them to theoretical models. The measured TFs are used to determine the propagation of the pump noise step-by-step through the system components. From the noise propagation analysis, we identify the relative intensity noise (RIN) of the pump diode as the main contribution to the CEO frequency noise. The resulting noise levels are not excessive and do not prevent CEO frequency stabilization. More importantly, the laser cavity dynamics are shown to play an essential role in the CEO frequency dynamics. The cavity TFs of the two lasers are very different which explains why at this point a tight CEO frequency lock can be obtained with the Yb:CALGO TDL but not with the Yb:YAG TDL. For CEO stabilization laser cavities should exhibit high damping of the relaxation oscillations by nonlinear intra-cavity elements, for example by operating a SESAM in the roll-over regime. Therefore the optimum SESAM operation point is a trade-off between enough damping and avoiding multiple pulsing instabilities. Additional cavity components could be considered for supplementary damping independent of the SESAM operation point. PMID:26368160

  11. Dynamics of pulsed laser ablation in high-density carbon dioxide including supercritical fluid state

    NASA Astrophysics Data System (ADS)

    Urabe, Keiichiro; Kato, Toru; Stauss, Sven; Himeno, Shohei; Kato, Satoshi; Muneoka, Hitoshi; Baba, Motoyoshi; Suemoto, Tohru; Terashima, Kazuo

    2013-10-01

    To gain a better understanding of pulsed laser ablation (PLA) processes in high-density fluids, including gases, liquids, and supercritical fluids (SCFs), we have investigated the PLA dynamics in high-density carbon dioxide (CO2) using a time-resolved shadowgraph (SG) observation method. The SG images revealed that the PLA dynamics can be categorized into two domains that are separated by the gas-liquid coexistence curve and the Widom line, which forms a border between the gaslike and liquidlike domains of an SCF. Furthermore, a cavitation bubble observed in liquid CO2 near the critical point exhibited a particular characteristic: the formation of an inner bubble and an outer shell structure. The results indicate that the thermophysical properties of the reaction field generated by PLA can be dynamically tuned by controlling the solvent temperature and pressure, particularly near the critical point.

  12. Ultrafast dynamic ellipsometry and spectroscopy of laser shocked materials

    SciTech Connect

    Mcgrane, Shawn David; Bolme, Cindy B; Whitley, Von H; Moore, David S

    2010-01-01

    Shock waves create extreme states of matter with very high pressures, temperatures, and volumetric compressions, at an exceedingly rapid rate of change. We review how to use a beamsplitter and a note card to turn a typical chirp pulse amplified femtosecond laser system into an ultrafast shock dynamics machine. Open scientific questions that can be addressed with such an apparatus are described. We report on the development of several single shot time resolved diagnostics needed to answer these questions. These single shot diagnostics are expected to be broadly applicable to other types of laser ablation experiments. Experimental results measured from shocked material dynamics of several systems are detailed. Finally, we report on progress towards using transient absorption as a measure of electronic excitation and coherent Raman as a picosecond probe of temperature in shock compressed condensed matter.

  13. Temporal dynamics of storage ring free electron lasers

    NASA Astrophysics Data System (ADS)

    Couprie, M. E.; Hara, T.; Gontier, D.; Troussel, P.; Garzella, D.; Delboulbé, A.; Billardon, M.

    1996-02-01

    The growth and saturation of a storage ring free electron laser (SRFEL) is driven by the beam behavior, including bunch lengthening or coherent modes of longitudinal motion (the bunch length being related to the energy spread), detuning effects, and a modification of the bunch distribution by the FEL interaction; all of these phenomena are accumulated for various passes, leading to complex dynamical processes. The knowledge and understanding of the dynamics, together with the stability over time are essential for efficient use of SRFEL sources. This is illustrated with the Super-ACO FEL experiment, analyzed from growth from the positron bunch to laser saturation and induced positron beam modification. Stability analysis (jitter, shape, intensity) is then performed carefully. A longitudinal feedback system can significantly improve it. Information provided with a streak camera reveals the distribution of a single FEL micropulse or synchrotron radiation pulse without any averaging or sampling.

  14. Ultrafast Dynamic Ellipsometry And Spectroscopy Of Laser Shocked Materials

    SciTech Connect

    McGrane, S. D.; Bolme, C. A.; Whitley, V. H.; Moore, D. S.

    2010-10-08

    Shock waves create extreme states of matter with very high pressures, temperatures, and volumetric compressions, at an exceedingly rapid rate of change. We review how to use a beamsplitter and a note card to turn a typical chirp pulse amplified femtosecond laser system into an ultrafast shock dynamics machine. Open scientific questions that can be addressed with such an apparatus are described. We report on the development of several single shot time resolved diagnostics needed to answer these questions. These single shot diagnostics are expected to be broadly applicable to other types of laser ablation experiments. Experimental results measured from shocked material dynamics of several systems are detailed. Finally, we report on progress towards using transient absorption as a measure of electronic excitation and coherent Raman as a picosecond probe of temperature in shock compressed condensed matter.

  15. Applications of laser-induced gratings to spectroscopy and dynamics

    SciTech Connect

    Rohlfing, E.A.

    1993-12-01

    This program has traditionally emphasized two principal areas of research. The first is the spectroscopic characterization of large-amplitude motion on the ground-state potential surface of small, transient molecules. The second is the reactivity of carbonaceous clusters and its relevance to soot and fullerene formation in combustion. Motivated initially by the desire to find improved methods of obtaining stimulated emission pumping (SEP) spectra of transients, most of our recent work has centered on the use of laser-induced gratings or resonant four-wave mixing in free-jet expansions. These techniques show great promise for several chemical applications, including molecular spectroscopy and photodissociation dynamics. The author describes recent applications of two-color laser-induced grating spectroscopy (LIGS) to obtain background-free SEP spectra of transients and double resonance spectra of nonfluorescing species, and the use of photofragment transient gratings to probe photodissociation dynamics.

  16. Electron Dynamics in Intense Laser Fields: A Bohmian Mechanics Study

    NASA Astrophysics Data System (ADS)

    Jooya, Hossein Z.; Telnov, Dmitry A.; Chu, Shih-I.

    2016-05-01

    We study the electron quantum dynamics of atomic hydrogen under intense near infrared laser fields by means of the De Broglie-Bohm's framework of Bohmian mechanics. This method is used to study the mechanism of the multiple plateau generation and the cut-off extension, as the main characteristic features of high order harmonic generation spectrum. Electron multiple recollision dynamics under intense mid-infrared laser fields is also investigated. In this case, the resulting patterns in the high-order harmonic generation and the above-threshold ionization spectra are analyzed by comprehensive picture provided by Bohmian mechanics. The time evolution of individual trajectories is closely studied to address some of the major structural features of the photoelectron angular distributions. This work is partially supported by DOE.

  17. Deformable silicon membrane for dynamic linear laser beam diffuser

    NASA Astrophysics Data System (ADS)

    Masson, J.; Bich, A.; Herzig, H. P.; Bitterli, R.; Noell, W.; Scharf, T.; Voelkel, R.; Weible, K. J.; de Rooij, N. F.

    2010-02-01

    We present a dynamic laser beam shaper based on MEMS technology. We show a prototype of a dynamic diffuser made of single crystal silicon. A linearly deformable silicon micromembrane is used to diffuse a laser beam in one dimension. Resonance frequencies of the membrane can range from 1 kHz to 20 kHz. Mode shapes of the deformable mirror are excited using magnetic actuation. Diffusing angle can be tuned by adjusting the driving current in the membrane. We measured a diffusing angle of 1° for an applied current of 40 mA. The aluminum coated mirror can handle 140 W/cm2 of visible to infrared optical power. Application to smooth out interference pattern generated by a static diffuser is shown.

  18. Buffer gas effects on output power of a copper vapor laser

    NASA Astrophysics Data System (ADS)

    Behrouzinia, S.; Khorasani, K.; Farahmandjou, M.

    2016-05-01

    A copper vapor laser with an active medium length of 60 cm and bore of 16 mm was operated and optimized using different buffer gases to investigate the effect of pressure and gas flow rates on the laser output power. It was shown that a special interval of operational pressure and an optimum gas flow rate associated with the type of buffer gas were obtained.

  19. A study on shielding gas contamination in laser welding of non-ferrous alloys

    NASA Astrophysics Data System (ADS)

    Tani, G.; Ascari, A.; Campana, G.; Fortunato, A.

    2007-12-01

    Laser welding of non-ferrous alloys is a high-productivity and cost-effective joining technology, which gained an undoubted interest especially in aerospace, chemical and medical industry, where high strength and corrosion resistant mechanical parts are required. Unfortunately some of the most used non-ferrous alloys are highly reactive with respect to the components of the environmental atmosphere: oxygen, nitrogen, hydrogen and humidity. This reactivity leads to the formation of porosities and to oxides and nitrides inclusion, which are responsible for a decrease of ductility and strength in welded joints. According to this a good shielding technique of the weld pool is of primary importance in order to obtain sound beads and reliable manufacturings. This paper deals with the opportunity of simulating the shielding gas behavior by means of Computational Fluid Dynamics software in order to understand the relationship among the outlet position, the shielding gas type and its flow rate. A simulation activity was carried out in order to evaluate the behavior of shielding gas concentration surrounding the weld pool. The simulated welding environment was simplified without considering the presence and the effect of the plasma plume. The main results concern the shielding gas contamination prediction with respect to the distance from the beam-material interaction zone.

  20. Complete Characterization of Molecular Dynamics in Ultrashort Laser Fields

    SciTech Connect

    Feuerstein, B.; Ergler, Th.; Rudenko, A.; Zrost, K.; Schroeter, C. D.; Moshammer, R.; Ullrich, J.; Niederhausen, T.; Thumm, U.

    2007-10-12

    Reaction Microscope-based, complete, and time-resolved Coulomb explosion imaging of vibrating and dissociating D{sub 2}{sup +} molecules with femtosecond time-resolution allowed us to perform an internuclear distance (R-)dependent Fourier analysis of the corresponding wave packets. Calculations demonstrate that the obtained two-dimensional R-dependent frequency spectra enable the complete characterization of the wave packet dynamics and directly visualize the field-modified molecular potential curves in intense, ultrashort laser pulses.

  1. Cavitation bubble dynamics during thulium fiber laser lithotripsy

    NASA Astrophysics Data System (ADS)

    Hardy, Luke A.; Kennedy, Joshua D.; Wilson, Christopher R.; Irby, Pierce B.; Fried, Nathaniel M.

    2016-02-01

    The Thulium fiber laser (TFL) is being explored for lithotripsy. TFL parameters differ from standard Holmium:YAG laser in several ways, including smaller fiber delivery, more strongly absorbed wavelength, low pulse energy/high pulse rate operation, and more uniform temporal pulse structure. High speed imaging of cavitation bubbles was performed at 105,000 fps and 10 μm spatial resolution to determine influence of these laser parameters on bubble formation. TFL was operated at 1908 nm with pulse energies of 5-75 mJ, and pulse durations of 200-1000 μs, delivered through 100-μm-core fiber. Cavitation bubble dynamics using Holmium laser at 2100 nm with pulse energies of 200-1000 mJ and pulse duration of 350 μs was studied, for comparison. A single, 500 μs TFL pulse produced a bubble stream extending 1090 +/- 110 μm from fiber tip, and maximum bubble diameters averaged 590 +/- 20 μm (n=4). These observations are consistent with previous studies which reported TFL ablation stallout at working distances < 1.0 mm. TFL bubble dimensions were five times smaller than for Holmium laser due to lower pulse energy, higher water absorption coefficient, and smaller fiber diameter used.

  2. Dynamic thermal model of photovoltaic cell illuminated by laser beam

    NASA Astrophysics Data System (ADS)

    Liu, Xiaoguang; Hua, Wenshen; Guo, Tong

    2015-07-01

    Photovoltaic cell is one of the most important components of laser powered unmanned aerial vehicle. Illuminated by high power laser beam, photovoltaic cell temperature increases significantly, which leads to efficiency drop, or even physical damage. To avoid such situation, the temperature of photovoltaic cell must be predicted precisely. A dynamic thermal model of photovoltaic cell is established in this paper, and the relationships between photovoltaic cell temperature and laser power, wind speed, ambient temperature are also analyzed. Simulation result indicates that illuminated by a laser beam, the temperature of photovoltaic cell rises gradually and reach to a constant maximum value. There is an approximately linear rise in photovoltaic cell temperature as the laser flux gets higher. The higher wind speed is, the stronger forced convection is, and then the lower photovoltaic cell temperature is. But the relationship between photovoltaic cell temperature and wind speed is not linear. Photovoltaic cell temperature is proportional to the ambient temperature. For each increase of 1 degree of ambient temperature, there is approximate 1 degree increase in photovoltaic cell temperature. The result will provide fundamentals to take reasonable measures to control photovoltaic cell temperature.

  3. Gas-Monitor Detector for Intense and Pulsed VUV/EUV Free-Electron Laser Radiation

    NASA Astrophysics Data System (ADS)

    Sorokin, A. A.; Bobashev, S. V.; Feldhaus, J.; Gerth, Ch.; Gottwald, A.; Hahn, U.; Kroth, U.; Richter, M.; Shmaenok, L. A.; Steeg, B.; Tiedtke, K.; Treusch, R.

    2004-05-01

    In the framework of current developments of new powerful VUV and EUV radiation sources, like VUV free-electron-lasers or EUV plasma sources for 13-nm lithography, we developed a gas-monitor detector in order to measure the photon flux of highly intense and extremely pulsed VUV and EUV radiation in absolute terms. The device is based on atomic photoionization of a rare gas at low particle density. Therefore, it is free of degradation and almost transparent, which allows the detector to be used as a continuously working beam-intensity monitor. The extended dynamic range of the detector allowed its calibration with relative standard uncertainties of 4% in the Radiometry Laboratory of the Physikalisch-Technische Bundesanstalt at the electron-storage ring BESSY II in Berlin using spectrally dispersed synchrotron radiation at low photon intensities and its utilization for absolute photon flux measurements of high power sources. In the present contribution, we describe the design of the detector and its application for the characterization of VUV free-electron-laser radiation at the TESLA test facility in Hamburg. By first pulse resolved measurements, a peak power of more than 100 MW at a wavelength of 87 nm was detected.

  4. Numerical Studies of the Application of Shock Tube Technology for Cold Gas Dynamic Spray Process

    NASA Astrophysics Data System (ADS)

    Nickel, R.; Bobzin, K.; Lugscheider, E.; Parkot, D.; Varava, W.; Olivier, H.; Luo, X.

    2007-12-01

    A new method for a combustion-free spraying is studied fundamentally by modeling and simulation in comparison with first experiments. The article focuses on the numerical simulation of the gas-particle nozzle flow, which is generated by the shock reflection at the end wall section of a shock tube. To study the physical fundamentals of this process, at present only a single shot operation is considered. The particles are injected downstream of the nozzle throat into a supersonic nozzle flow. The measurements of the particle velocity made by a laser Doppler anemometry (LDA) set up show that the maximum velocity amounts to 1220 m/s for stainless steel particles of 15 μm diameter. The CFD-Code (Fluent) is first verified by a comparison with available numerical and experimental data for gas and gas-particle flow fields in a long Laval-nozzle. The good agreement implied the great potential of the new dynamic process concept for cold-gas coating applications. Then the flow fields in the short Laval nozzle designed and realized by the Shock Wave Laboratory (SWL) are investigated. The gas flow for experimentally obtained stagnation conditions is simulated. The gas-particle flow without and with the influence of the particles on the gas flow is calculated by the Surface Engineering Institute (IOT) and compared with experiments. The influence of the injection parameters on the particle velocities is investigated, as well.

  5. BUBBLE DYNAMICS AT GAS-EVOLVING ELECTRODES

    SciTech Connect

    Sides, Paul J.

    1980-12-01

    Nucleation of bubbles, their growth by diffusion of dissolved gas to the bubble surface and by coalescence, and their detachment from the electrode are all very fast phenomena; furthermore, electrolytically generated bubbles range in size from ten to a few hundred microns; therefore, magnification and high speed cinematography are required to observe bubbles and the phenomena of their growth on the electrode surface. Viewing the action from the front side (the surface on which the bubbles form) is complicated because the most important events occur close to the surface and are obscured by other bubbles passing between the camera and the electrode; therefore, oxygen was evolved on a transparent tin oxide "window" electrode and the events were viewed from the backside. The movies showed that coalescence of bubbles is very important for determining the size of bubbles and in the chain of transport processes; growth by diffusion and by coalescence proceeds in series and parallel; coalescing bubbles cause significant fluid motion close to the electrode; bubbles can leave and reattach; and bubbles evolve in a cycle of growth by diffusion and different modes of coalescence. An analytical solution for the primary potential and current distribution around a spherical bubble in contact with a plane electrode is presented. Zero at the contact point, the current density reaches only one percent of its undisturbed value at 30 percent of the radius from that point and goes through a shallow maximum two radii away. The solution obtained for spherical bubbles is shown to apply for the small bubbles of electrolytic processes. The incremental resistance in ohms caused by sparse arrays of bubbles is given by {Delta}R = 1.352 af/kS where f is the void fraction of gas in the bubble layer, a is the bubble layer thickness, k is the conductivity of gas free electrolyte, and S is the electrode area. A densely populated gas bubble layer on an electrode was modeled as a hexagonal array of

  6. Cellular automatons applied to gas dynamic problems

    NASA Astrophysics Data System (ADS)

    Long, Lyle N.; Coopersmith, Robert M.; McLachlan, B. G.

    1987-06-01

    This paper compares the results of a relatively new computational fluid dynamics method, cellular automatons, with experimental data and analytical results. This technique has been shown to qualitatively predict fluidlike behavior; however, there have been few published comparisons with experiment or other theories. Comparisons are made for a one-dimensional supersonic piston problem, Stokes first problem, and the flow past a normal flat plate. These comparisons are used to assess the ability of the method to accurately model fluid dynamic behavior and to point out its limitations. Reasonable results were obtained for all three test cases, but the fundamental limitations of cellular automatons are numerous. It may be misleading, at this time, to say that cellular automatons are a computationally efficient technique. Other methods, based on continuum or kinetic theory, would also be very efficient if as little of the physics were included.

  7. Cellular automatons applied to gas dynamic problems

    NASA Technical Reports Server (NTRS)

    Long, Lyle N.; Coopersmith, Robert M.; Mclachlan, B. G.

    1987-01-01

    This paper compares the results of a relatively new computational fluid dynamics method, cellular automatons, with experimental data and analytical results. This technique has been shown to qualitatively predict fluidlike behavior; however, there have been few published comparisons with experiment or other theories. Comparisons are made for a one-dimensional supersonic piston problem, Stokes first problem, and the flow past a normal flat plate. These comparisons are used to assess the ability of the method to accurately model fluid dynamic behavior and to point out its limitations. Reasonable results were obtained for all three test cases, but the fundamental limitations of cellular automatons are numerous. It may be misleading, at this time, to say that cellular automatons are a computationally efficient technique. Other methods, based on continuum or kinetic theory, would also be very efficient if as little of the physics were included.

  8. Waveguide CO2 laser gain: Dependence on gas kinetic and discharge properties

    NASA Technical Reports Server (NTRS)

    Cohen, S. C.

    1975-01-01

    Using a simple rate equation approach the gas kinetic and discharge properties of waveguide CO2 lasers were examined. The dependence was calculated of the population inversion and laser small signal gain on gas pressure, gas mixture, pumping rate (discharge current), tube bore diameter, and wall temperature. At higher pressures the gain is optimized by using more helium rich mixtures and smaller bore diameters. The dependence of laser tunability on the gas kinetic properties and cavity losses was determined, it was found that for loss cavities the laser tunability may substantially exceed the molecular fullwidth at half maximum. The more helium rich gas mixtures give greater tunability when cavity losses are small and less tunability when cavity losses are large. The role of the various gases in the waveguide CO2 laser is the same as that in conventional devices, by contrast with conventional lasers, the waveguide laser transition is homogeneously broadened. The dependence of gain on gas pressure and other kinetic and discharge properties differs substantially from that predicted by scaling results from conventional low pressure lasers.

  9. Dual exposure interferometry. [gas dynamics and flow visualization

    NASA Technical Reports Server (NTRS)

    Smeets, G.; George, A.

    1982-01-01

    The application of dual exposure differential interferometry to gas dynamics and flow visualization is discussed. A differential interferometer with Wallaston prisms can produce two complementary interference fringe systems, depending on the polarization of the incident light. If these two systems are superimposed on a film, with one exposure during a phenomenon, the other before or after, the phenomenon will appear on a uniform background. By regulating the interferometer to infinite fringe distance, a resolution limit of approximately lambda/500 can be obtained in the quantitative analysis of weak phase objects. This method was successfully applied to gas dynamic investigations.

  10. A dynamic model for power deposition in 3He lasers pumped by 3He(n,p) 3H reactions

    NASA Astrophysics Data System (ADS)

    Çetin, Füsun

    2004-07-01

    The coupled variation of power density with gas density in a nuclear-pumped laser, which is excited by 3He(n,p) 3H reaction products, is considered. In the literature, volumetric excitation by reaction products of 3He(n,p) 3H is only considered for the case in which gas density is uniform and does not change during the pumping. In this work, a time-dependent model describing the coupled fluid dynamic and particle transport behaviour of the gas has been developed. In modelling charge particle transport behaviour, a previously reported energy deposition model for a constant gas density is extended for a variable gas density by taking into account variations in the particle range, macroscopic cross sections and neutron flux depending on density field of the gas. The coupled equations, which are obtained by using the power deposition density expression obtained for variable gas density in the acoustically filtered equations of motion of the gas, are solved numerically. Spatial and temporal variations of power deposition density and gas density during the pumping pulse are determined for various operating pressures ranging from 0.5 to 10 atm. In the calculations, the characteristics of I.T.U TRIGA Mark-II Reactor are used and it is assumed that laser tube is placed in the centre of the reactor core. Obtained results are presented and examined.

  11. DIODE-LASER-BASED MEASUREMENTS OF HYDROGEN FLUORIDE GAS DURING CHEMICAL SUPPRESSION OF FIRES

    EPA Science Inventory

    Near-infrared tunable diode laser (NIR-TDL) spectroscopy is used to quantify HF gas produced during fire suppressant testing of Halon alternatives. Results of comparisons with other techniques for measuring HF gas concentrations are discussed. Measurements of HF gas produced in l...

  12. Laser absorption, power transfer, and radiation symmetry during the first shock of inertial confinement fusion gas-filled hohlraum experiments

    NASA Astrophysics Data System (ADS)

    Pak, A.; Dewald, E. L.; Landen, O. L.; Milovich, J.; Strozzi, D. J.; Berzak Hopkins, L. F.; Bradley, D. K.; Divol, L.; Ho, D. D.; MacKinnon, A. J.; Meezan, N. B.; Michel, P.; Moody, J. D.; Moore, A. S.; Schneider, M. B.; Town, R. P. J.; Hsing, W. W.; Edwards, M. J.

    2015-12-01

    Temporally resolved measurements of the hohlraum radiation flux asymmetry incident onto a bismuth coated surrogate capsule have been made over the first two nanoseconds of ignition relevant laser pulses. Specifically, we study the P2 asymmetry of the incoming flux as a function of cone fraction, defined as the inner-to-total laser beam power ratio, for a variety of hohlraums with different scales and gas fills. This work was performed to understand the relevance of recent experiments, conducted in new reduced-scale neopentane gas filled hohlraums, to full scale helium filled ignition targets. Experimental measurements, matched by 3D view factor calculations, are used to infer differences in symmetry, relative beam absorption, and cross beam energy transfer (CBET), employing an analytic model. Despite differences in hohlraum dimensions and gas fill, as well as in laser beam pointing and power, we find that laser absorption, CBET, and the cone fraction, at which a symmetric flux is achieved, are similar to within 25% between experiments conducted in the reduced and full scale hohlraums. This work demonstrates a close surrogacy in the dynamics during the first shock between reduced-scale and full scale implosion experiments and is an important step in enabling the increased rate of study for physics associated with inertial confinement fusion.

  13. Laser absorption, power transfer, and radiation symmetry during the first shock of inertial confinement fusion gas-filled hohlraum experiments

    SciTech Connect

    Pak, A.; Dewald, E. L.; Landen, O. L.; Milovich, J.; Strozzi, D. J.; Berzak Hopkins, L. F.; Bradley, D. K.; Divol, L.; Ho, D. D.; MacKinnon, A. J.; Meezan, N. B.; Michel, P.; Moody, J. D.; Moore, A. S.; Schneider, M. B.; Town, R. P. J.; Hsing, W. W.; Edwards, M. J.

    2015-12-15

    Temporally resolved measurements of the hohlraum radiation flux asymmetry incident onto a bismuth coated surrogate capsule have been made over the first two nanoseconds of ignition relevant laser pulses. Specifically, we study the P2 asymmetry of the incoming flux as a function of cone fraction, defined as the inner-to-total laser beam power ratio, for a variety of hohlraums with different scales and gas fills. This work was performed to understand the relevance of recent experiments, conducted in new reduced-scale neopentane gas filled hohlraums, to full scale helium filled ignition targets. Experimental measurements, matched by 3D view factor calculations, are used to infer differences in symmetry, relative beam absorption, and cross beam energy transfer (CBET), employing an analytic model. Despite differences in hohlraum dimensions and gas fill, as well as in laser beam pointing and power, we find that laser absorption, CBET, and the cone fraction, at which a symmetric flux is achieved, are similar to within 25% between experiments conducted in the reduced and full scale hohlraums. This work demonstrates a close surrogacy in the dynamics during the first shock between reduced-scale and full scale implosion experiments and is an important step in enabling the increased rate of study for physics associated with inertial confinement fusion.

  14. Laser Interferometer Space Antenna double black holes: dynamics in gaseous nuclear discs

    NASA Astrophysics Data System (ADS)

    Dotti, Massimo; Colpi, Monica; Haardt, Francesco

    2006-03-01

    We study the inspiral of double black holes, with masses in the Laser Interferometer Space Antenna (LISA) window of detectability, orbiting inside a massive circumnuclear, rotationally supported gaseous disc. Using high-resolution smoothed particle hydrodynamics simulations, we follow the black hole dynamics in the early phase when gas-dynamical friction acts on the black holes individually, and continue our simulation until they form a close binary. We find that in the early sinking the black holes lose memory of their initial orbital eccentricity if they corotate with the gaseous disc. As a consequence, the massive black holes bind forming a binary with a low eccentricity, consistent with zero within our numerical resolution limit. The cause of circularization resides in the rotation present in the gaseous background where dynamical friction operates. Circularization may hinder gravitational waves from taking over and leading the binary to coalescence. In the case of counter-rotating orbits, the initial eccentricity (if present) does not decrease, and the black holes may bind forming an eccentric binary. When dynamical friction has subsided, for equal mass black holes and regardless their initial eccentricity, angular momentum loss, driven by the gravitational torque exerted on the binary by surrounding gas, is nevertheless observable down to the smallest scale probed (~=1 pc). In the case of unequal masses, dynamical friction remains efficient down to our resolution limit, and there is no sign of formation of any ellipsoidal gas distribution that may further harden the binary. During inspiral, gravitational capture of gas by the black holes occurs mainly along circular orbits; eccentric orbits imply high relative velocities and weak gravitational focusing. Thus, the active galactic nucleus activity may be excited during the black hole pairing process and double active nuclei may form when circularization is completed, on distance scales of tens of parsecs.

  15. Laser altimetry reveals complex pattern of Greenland Ice Sheet dynamics.

    PubMed

    Csatho, Beata M; Schenk, Anton F; van der Veen, Cornelis J; Babonis, Gregory; Duncan, Kyle; Rezvanbehbahani, Soroush; van den Broeke, Michiel R; Simonsen, Sebastian B; Nagarajan, Sudhagar; van Angelen, Jan H

    2014-12-30

    We present a new record of ice thickness change, reconstructed at nearly 100,000 sites on the Greenland Ice Sheet (GrIS) from laser altimetry measurements spanning the period 1993-2012, partitioned into changes due to surface mass balance (SMB) and ice dynamics. We estimate a mean annual GrIS mass loss of 243 ± 18 Gt ⋅ y(-1), equivalent to 0.68 mm ⋅ y(-1) sea level rise (SLR) for 2003-2009. Dynamic thinning contributed 48%, with the largest rates occurring in 2004-2006, followed by a gradual decrease balanced by accelerating SMB loss. The spatial pattern of dynamic mass loss changed over this time as dynamic thinning rapidly decreased in southeast Greenland but slowly increased in the southwest, north, and northeast regions. Most outlet glaciers have been thinning during the last two decades, interrupted by episodes of decreasing thinning or even thickening. Dynamics of the major outlet glaciers dominated the mass loss from larger drainage basins, and simultaneous changes over distances up to 500 km are detected, indicating climate control. However, the intricate spatiotemporal pattern of dynamic thickness change suggests that, regardless of the forcing responsible for initial glacier acceleration and thinning, the response of individual glaciers is modulated by local conditions. Recent projections of dynamic contributions from the entire GrIS to SLR have been based on the extrapolation of four major outlet glaciers. Considering the observed complexity, we question how well these four glaciers represent all of Greenland's outlet glaciers. PMID:25512537

  16. Instrumentation of dynamic gas pulse loading system

    SciTech Connect

    Mohaupt, H.

    1992-04-14

    The overall goal of this work is to further develop and field test a system of stimulating oil and gas wells, which increases the effective radius of the well bore so that more oil can flow into it, by recording pressure during the gas generation phase in real time so that fractures can be induced more predictably in the producing formation. Task 1: Complete the laboratory studies currently underway with the prototype model of the instrumentation currently being studied. Task 2: Perform field tests of the model in the Taft/Bakersfield area, utilizing operations closest to the engineers working on the project, and optimize the unit for various conditions encountered there. Task 3: Perform field test of the model in DGPL jobs which are scheduled in the mid-continent area, and optimize the unit for downhole conditions encountered there. Task 4: Analyze and summarize the results achieved during the complete test series, documenting the steps for usage of downhole instrumentation in the field, and compile data specifying use of the technology by others. Task 5: Prepare final report for DOE, and include also a report on the field tests completed. Describe and estimate the probability of the technology being commercialized and in what time span. The project has made substantial technical progress, though we are running about a month behind schedule. Expenditures are in line with the schedule. Increased widespread interest in the use of DGPL stimulation has kept us very busy. The computer modeling and test instrumentation developed under this program is already being applied to commercial operations.

  17. Blast Dynamics in a Dissipative Gas

    NASA Astrophysics Data System (ADS)

    Barbier, M.; Villamaina, D.; Trizac, E.

    2015-11-01

    The blast caused by an intense explosion has been extensively studied in conservative fluids, where the Taylor-von Neumann-Sedov hydrodynamic solution is a prototypical example of self-similarity driven by conservation laws. In dissipative media, however, energy conservation is violated, yet a distinctive self-similar solution appears. It hinges on the decoupling of random and coherent motion permitted by a broad class of dissipative mechanisms. This enforces a peculiar layered structure in the shock, for which we derive the full hydrodynamic solution, validated by a microscopic approach based on molecular dynamics simulations. We predict and evidence a succession of temporal regimes, as well as a long-time corrugation instability, also self-similar, which disrupts the blast boundary. These generic results may apply from astrophysical systems to granular gases, and invite further cross-fertilization between microscopic and hydrodynamic approaches of shock waves.

  18. Blast Dynamics in a Dissipative Gas.

    PubMed

    Barbier, M; Villamaina, D; Trizac, E

    2015-11-20

    The blast caused by an intense explosion has been extensively studied in conservative fluids, where the Taylor-von Neumann-Sedov hydrodynamic solution is a prototypical example of self-similarity driven by conservation laws. In dissipative media, however, energy conservation is violated, yet a distinctive self-similar solution appears. It hinges on the decoupling of random and coherent motion permitted by a broad class of dissipative mechanisms. This enforces a peculiar layered structure in the shock, for which we derive the full hydrodynamic solution, validated by a microscopic approach based on molecular dynamics simulations. We predict and evidence a succession of temporal regimes, as well as a long-time corrugation instability, also self-similar, which disrupts the blast boundary. These generic results may apply from astrophysical systems to granular gases, and invite further cross-fertilization between microscopic and hydrodynamic approaches of shock waves. PMID:26636851

  19. Experimental Study of Gas Hydrate Dynamics

    NASA Astrophysics Data System (ADS)

    Fandino, O.; Ruffine, L.

    2011-12-01

    Important quantities of methane and other gases are trapped below the seafloor and in the permafrost by an ice-like solid, called gas hydrates or clathrate hydrates. The latter is formed when water is mixing with different gases at high pressures and low temperatures. Due to a their possible use as a source of energy [1] or the problematic related to flow assurance failure in pipelines [2] the understanding of their processes of formation/destabilisation of these structures becomes a goal for many laboratories research as well as industries. In this work we present an experimental study on the stochastic behaviour of hydrate formation from a bulk phase. The method used here for the experiments was to repeat several time the same hydrate formation procedure and to notice the different from one experiment to another. A variable-volume type high-pressure apparatus with two sapphire windows was used. This device, already presented by Ruffine et al.[3], allows us to perform both kinetics and phase equilibrium measurements. Three initial pressure conditions were considered here, 5.0 MPa, 7.5 MPa and 10.0 MPa. Hydrates have been formed, then allowed to dissociate by stepwise heating. The memory effect has also been investigated after complete dissociation. It turned out that, although the thermodynamics conditions of formation and/or destabilization were reproducible. An attempt to determine the influence of pressure on the nucleation induction time will be discussed. References 1. Sum, A. K.; Koh, C. A.; Sloan, E. D., Clathrate Hydrates: From Laboratory Science to Engineering Practice. Industrial & Engineering Chemistry Research 2009, 48, 7457-7465. 2. Sloan, E. D., A changing hydrate paradigm-from apprehension to avoidance to risk management. Fluid Phase Equilibria 2005, 228, 67-74. 3. Ruffine, L.; Donval, J. P.; Charlou, J. L.; Cremière, A.; Zehnder, B. H., Experimental study of gas hydrate formation and destabilisation using a novel high-pressure apparatus. Marine

  20. A set of measurement system for the dynamic laser scatter characteristics of target

    NASA Astrophysics Data System (ADS)

    Wei, Xiangquan; Huang, Jianming; Xiao, Yuzhi; Fan, Xiaoli

    2015-12-01

    It is an important measure to observe target by using laser sensor in the field of target detection. Exact and reliable dynamic laser scatter characteristics of observing target, can not only be used for the design and development of laser sensor as well as the research of algorithm for target capture, recognition and tracking, but also can offer reference bases for the test flow programming. A set of simulation, measurement system for the dynamic laser scatter characteristics of observing target is introduced in this paper. The simulation problem of dynamic laser scatter characteristics of observing target is solved, under the circumstance of laboratory with different azimuth angle and pitch angle of observation. The dynamic laser scatter characteristics of observing target can be obtained directly by such system, the test data can be used for the verification of the analyzing model for the laser scatter characteristics of observing target, and can also offer basis for the development of laser detecting sensor.

  1. Dynamics of laser induced metal nanoparticle and pattern formation

    SciTech Connect

    Peláez, R. J. Kuhn, T.; Rodríguez, C. E.; Afonso, C. N.

    2015-02-09

    Discontinuous metal films are converted into either almost round, isolated, and randomly distributed nanoparticles (NPs) or fringed patterns of alternate non transformed film and NPs by exposure to single pulses (20 ns pulse duration and 193 nm wavelength) of homogeneous or modulated laser beam intensity. The dynamics of NPs and pattern formation is studied by measuring in real time the transmission and reflectivity of the sample upon homogeneous beam exposure and the intensity of the diffraction orders 0 and 1 in transmission configuration upon modulated beam exposure. The results show that laser irradiation induces melting of the metal either completely or at regions around intensity maxima sites for homogeneous and modulated beam exposure, respectively, within ≤10 ns. The aggregation and/or coalescence of the initially irregular metal nanostructures is triggered upon melting and continues after solidification (estimated to occur at ≤80 ns) for more than 1 μs. The present results demonstrate that real time transmission rather than reflectivity measurements is a valuable and easy-to-use tool for following the dynamics of NPs and pattern formation. They provide insights on the heat-driven processes occurring both in liquid and solid phases and allow controlling in-situ the process through the fluence. They also evidence that there is negligible lateral heat release in discontinuous films upon laser irradiation.

  2. Dynamic tuning of lattice plasmon lasers with long coherence characteristics

    NASA Astrophysics Data System (ADS)

    Hoang, Thang; Yang, Ankun; Schatz, George; Odom, Teri; Mikkelsen, Maiken

    Here, we experimentally demonstrate dynamic tuning of an optically-pumped lattice plasmon laser based on arrays of gold nanoparticles and liquid gain materials [A. Yang, T.B. Hoang et al., Nature Communications 6, 6939 (2015)]. The structure consists of an array of 120 nm diameter gold disks with a height of 50 nm and 600 nm spacing. A liquid gain material composed of IR-140 dye molecules dissolved in a variety of organic solvents is placed on top of the disks and held in place by a thin glass coverslip. At a lasing wavelength of 860 nm, time-resolved measurements show a dramatic reduction of the decay time from 1 ns to less than 20 ps when the optical excitation power density increases from below to above the lasing threshold, indicating the transition from spontaneous to stimulated emission. By changing the dielectric environment surrounding the gold disks in real time, the lasing wavelength can be dynamically tuned over a 55 nm range. Finally, we will discuss recent experiments where we probe both the temporal and spatial coherence properties of the lattice plasmon laser. This advance of tunable plasmon lasers offer prospects to enhance and detect weak physical and chemical processes on the nanoscale in real time.

  3. Cloud-particle galactic gas dynamics and star formation

    NASA Technical Reports Server (NTRS)

    Roberts, W. W., Jr.

    1983-01-01

    Galactic gas dynamics, spiral structure, and star formation are discussed in relation to N-body computational studies based on a cloud-particle model of the interstellar medium. On the small scale, the interstellar medium is seen as cloud-dominated and supernova-perturbed. It is noted that the cloud-particle model simulates cloud-cloud collisions, the formation of stellar associations, and supernova explosions as dominant local processes. On the large scale, in response to a spiral galactic gravitational field, global density waves and galactic shocks develop having large-scale characteristics similar to those found in continuum gas dynamical studies. Both the system of gas clouds and the system of young stellar associations forming from the clouds figure in the global spiral structure. However, with the attributes of neither assuming a continuum of gas (as in continuum gas dynamical studies) or requiring a prescribed equation of state (such as the isothermal condition), the cloud-particle picture retains much of the detail lost in earlier work. By detail is meant the small-scale features and structures so important in understanding the local, turbulent state of the interstellar medium as well as the degree of raggedness often seen to be superposed on the global spiral structure.

  4. Dynamics of Laser-Driven Shock Waves in Solid Targets

    NASA Astrophysics Data System (ADS)

    Aglitskiy, Y.; Karasik, M.; Velikovich, A. L.; Serlin, V.; Weaver, J.; Schmitt, A. J.; Obenschain, S. P.; Grun, J.; Metzler, N.; Zalesak, S. T.; Gardner, J. H.; Oh, J.; Harding, E. C.

    2009-11-01

    Accurate shock timing is a key issue of both indirect- and direct-drive laser fusions. The experiments on the Nike laser at NRL presented here were made possible by improvements in the imaging capability of our monochromatic x-ray diagnostics based on Bragg reflection from spherically curved crystals. Side-on imaging implemented on Nike makes it possible to observe dynamics of the shock wave and ablation front in laser-driven solid targets. We can choose to observe a sequence of 2D images or a continuous time evolution of an image resolved in one spatial dimension. A sequence of 300 ps snapshots taken using vanadium backlighter at 5.2 keV reveals propagation of a shock wave in a solid plastic target. The shape of the shock wave reflects the intensity distribution in the Nike beam. The streak records with continuous time resolution show the x-t trajectory of a laser-driven shock wave in a 10% solid density DVB foam.

  5. Gas dynamical approach to study dust acoustic solitary waves

    SciTech Connect

    Maitra, Sarit; Roychoudhury, Rajkumar

    2005-06-15

    Dust acoustic nonlinear waves are studied using gas dynamical approach. The structure equation for dust fluid has been obtained using the conservation laws for mass flux and momentum. The role of dust sonic point for the formation of soliton has been discussed. Conditions for the existence of soliton have been derived in terms of collective Mach number, taking into account the dust charge variation.

  6. Developments towards in-gas-jet laser spectroscopy studies of actinium isotopes at LISOL

    NASA Astrophysics Data System (ADS)

    Raeder, S.; Bastin, B.; Block, M.; Creemers, P.; Delahaye, P.; Ferrer, R.; Fléchard, X.; Franchoo, S.; Ghys, L.; Gaffney, L. P.; Granados, C.; Heinke, R.; Hijazi, L.; Huyse, M.; Kron, T.; Kudryavtsev, Yu.; Laatiaoui, M.; Lecesne, N.; Luton, F.; Moore, I. D.; Martinez, Y.; Mogilevskiy, E.; Naubereit, P.; Piot, J.; Rothe, S.; Savajols, H.; Sels, S.; Sonnenschein, V.; Traykov, E.; Van Beveren, C.; Van den Bergh, P.; Van Duppen, P.; Wendt, K.; Zadvornaya, A.

    2016-06-01

    To study exotic nuclides at the borders of stability with laser ionization and spectroscopy techniques, highest efficiencies in combination with a high spectral resolution are required. These usually opposing requirements are reconciled by applying the in-gas-laser ionization and spectroscopy (IGLIS) technique in the supersonic gas jet produced by a de Laval nozzle installed at the exit of the stopping gas cell. Carrying out laser ionization in the low-temperature and low density supersonic gas jet eliminates pressure broadening, which will significantly improve the spectral resolution. This article presents the required modifications at the Leuven Isotope Separator On-Line (LISOL) facility that are needed for the first on-line studies of in-gas-jet laser spectroscopy. Different geometries for the gas outlet and extraction ion guides have been tested for their performance regarding the acceptance of laser ionized species as well as for their differential pumping capacities. The specifications and performance of the temporarily installed high repetition rate laser system, including a narrow bandwidth injection-locked Ti:sapphire laser, are discussed and first preliminary results on neutron-deficient actinium isotopes are presented indicating the high capability of this novel technique.

  7. In-gas-cell laser ion source for KEK isotope separation system

    NASA Astrophysics Data System (ADS)

    Mukai, M.; Hirayama, Y.; Jeong, S. C.; Imai, N.; Ishiyama, H.; Miyatake, H.; Oyaizu, M.; Watanabe, Y. X.; Kim, Y. H.

    2014-02-01

    The KEK isotope separation system (KISS) is an element-selective isotope separator under development at RIKEN. The in-gas-cell laser ion source is a critical component of the KISS, a gas cell filled with argon gas of 50 kPa enclosed in a vacuum chamber. In the gas cell, nuclear reaction products are stopped (i.e., thermalized and neutralized) and transported by a laminar flow of argon to the ionization region just upstream of the gas outlet, and thereby an element of interest among those reaction products is selectively ionized by two-color resonant laser irradiation. Recently, we succeeded to extract laser-ionized Fe ions by injecting an energetic Fe beam into the gas cell. Recent off- and on-line test results were presented and discussed.

  8. Laser Spectroscopy Based Multi-Gas Monitor Technology Demonstration

    NASA Technical Reports Server (NTRS)

    Mudgett, Paul D.; Pilgrim, Jeffrey S.

    2016-01-01

    The timing was right in the “evolution” of low power tunable diode laser spectroscopy (TDLS) to design a spacecraft cabin air monitor around technology being developed at a small company funded by SBIR grants. NASA Centers had been monitoring their progress hoping that certain key gaps in the long term gas monitoring development roadmap could be filled by TDLS. The first iteration of a monitor for multiple gases called the Multi-Gas Monitor (MGM) which measures oxygen, carbon dioxide, ammonia and water vapor, as well as temperature and pressure. In January 2013, the ISS Program being particularly interested in ammonia funded a technology demonstration of MGM. The project was a joint effort between Vista Photonics for the sensor, NASA-JSC for project management and laboratory calibration, and Nanoracks for the enclosure and payload certification/integration. Nanoracks was selected in order to use their new experimental infrastructure located in an EXPRESS rack in the JEM. The MGM enclosure has multiple power supply options including 5VDC USB interface to the Nanoracks Frame, 28VDC Express Rack power and internal rechargeable batteries. MGM was calibrated at NASA-JSC in July 2013, delivered to ISS on 37 Soyuz in November 2013 and was installed and activated in February 2014. MGM resided in the Nanoracks Frame making continuous measurements the majority of the time, but also spent a day in Node 3 on battery power, and a month in the US Lab Module on 28VDC power, as part of the demonstration. Data was downloaded via Nanoracks on roughly a weekly basis. Comparisons were made with data from the Major Constituents Analyzer (MCA) which draws and analyzes air from JEM and other modules several times per hour. A crewmember challenged the carbon dioxide channel by breathing into the intake upon startup, and challenged the ammonia channel later using a commercial ammonia inhalant. Many interesting phenomena in the cabin atmosphere were detected during the tech demo

  9. Gas dynamic simulations of galaxy formation

    NASA Technical Reports Server (NTRS)

    Evrard, August E.

    1993-01-01

    Results are presented from a simulation modeling the formation of a group of galaxies in a 'standard' cold, dark matter universe with delta = 1, h sub 0 = 50 km/(s(Mpc)), baryon fraction omega sub b = 0.1 and spectrum normalization sigma sub 8 = 0.6 (bias parameter b = 1.7). Initial conditions are generated within a periodic box with comoving length 16 Mpc in a manner constrained to produce a small cluster of total mass approximately 10 exp 14 solar mass. Two sets of 643 particles are used to model the dark matter and baryon fluids. Each gas particle represents 1.08 x 10 exp -8 solar mass, implying an L* galaxy is resolved by approximately 1000 particles. The system is evolved self-consistently in three dimensions using the combined N-body/hydrodynamic scheme P3MSPH up to a final redshift z = 1. Evolving to the present is prohibited by the fact that the mean density in the simulated volume is above critical and the entire volume would be going nonlinear beyond this point, We are currently analyzing another run with somewhat poorer mass resolution which was evolved to the present.

  10. Transverse demagnetization dynamics of a unitary Fermi gas.

    PubMed

    Bardon, A B; Beattie, S; Luciuk, C; Cairncross, W; Fine, D; Cheng, N S; Edge, G J A; Taylor, E; Zhang, S; Trotzky, S; Thywissen, J H

    2014-05-16

    Understanding the quantum dynamics of strongly interacting fermions is a problem relevant to diverse forms of matter, including high-temperature superconductors, neutron stars, and quark-gluon plasma. An appealing benchmark is offered by cold atomic gases in the unitary limit of strong interactions. Here, we study the dynamics of a transversely magnetized unitary Fermi gas in an inhomogeneous magnetic field. We observe the demagnetization of the gas, caused by diffusive spin transport. At low temperatures, the diffusion constant saturates to the conjectured quantum-mechanical lower bound ≃ ħ/m, where m is the particle mass. The development of pair correlations, indicating the transformation of the initially noninteracting gas toward a unitary spin mixture, is observed by measuring Tan's contact parameter. PMID:24833387

  11. Frequency conversion of radiation of IR molecular gas lasers in nonlinear crystals (A review)

    NASA Astrophysics Data System (ADS)

    Ionin, A. A.; Kinyaevskiy, I. O.; Klimachev, Yu. M.; Kotkov, A. A.

    2015-09-01

    The solution of problems related, e.g., to transport of laser radiation in the atmosphere requires availability of a broadband IR laser source operating in the transparency windows of the atmosphere. In this review, we present the results of an investigation of the properties of a hybrid laser system consisting of molecular gas pump lasers and a solid-state laser frequency converter based on nonlinear crystals. We demonstrate broadening and enrichment of spectrum of radiation of the pump laser by means of sum- and difference-frequency generation. In particular, by using a relatively simple laser system consisting of gas-discharge CO and CO2 lasers, radiation tunable over a large number of spectral lines in a broad range of wavelength from 2.5 to 16.6 µm (more than two and a half octaves), which includes two transparency windows of the atmosphere, is obtained. Thus, the possibility of exploring the IR spectral range by means of hybrid laser systems based on frequency conversion of radiation of molecular gas lasers is demonstrated.

  12. Laser-solid interaction and dynamics of laser-ablated materials

    SciTech Connect

    Chen, K.R.; Neboeuf, J.N.; Wood, R.F.; Geohegan, D.B.; Donato, J.M.; Liu, C.L.; Puretzky, A.A.

    1995-09-01

    An annealing model is extended to treat the vaporization process, and a hydrodynamic model describes the ablated material. We find that dynamic source and ionization effects accelerate the expansion front of the ablated plume with thermal vaporization temperature. The vaporization process and plume propagation in high background gas pressure are studied.

  13. Annular billiard dynamics in a circularly polarized strong laser field

    NASA Astrophysics Data System (ADS)

    Kamor, A.; Mauger, F.; Chandre, C.; Uzer, T.

    2012-01-01

    We analyze the dynamics of a valence electron of the buckminsterfullerene molecule (C60) subjected to a circularly polarized laser field by modeling it with the motion of a classical particle in an annular billiard. We show that the phase space of the billiard model gives rise to three distinct trajectories: “whispering gallery orbits,” which hit only the outer billiard wall; “daisy orbits,” which hit both billiard walls (while rotating solely clockwise or counterclockwise for all time); and orbits that only visit the downfield part of the billiard, as measured relative to the laser term. These trajectories, in general, maintain their distinct features, even as the intensity is increased from 1010 to 1014Wcm-2. We attribute this robust separation of phase space to the existence of twistless tori.

  14. Laser Actuation of Cantilevers for Picometre Amplitude Dynamic Force Microscopy

    PubMed Central

    Evans, Drew R.; Tayati, Ponlawat; An, Hongjie; Lam, Ping Koy; Craig, Vincent S. J.; Senden, Tim J.

    2014-01-01

    As nanoscale and molecular devices become reality, the ability to probe materials on these scales is increasing in importance. To address this, we have developed a dynamic force microscopy technique where the flexure of the microcantilever is excited using an intensity modulated laser beam to achieve modulation on the picoscale. The flexure arises from thermally induced bending through differential expansion and the conservation of momentum when the photons are reflected and absorbed by the cantilever. In this study, we investigated the photothermal and photon pressure responses of monolithic and layered cantilevers using a modulated laser in air and immersed in water. The developed photon actuation technique is applied to the stretching of single polymer chains. PMID:24993548

  15. Laser actuation of cantilevers for picometre amplitude dynamic force microscopy.

    PubMed

    Evans, Drew R; Tayati, Ponlawat; An, Hongjie; Lam, Ping Koy; Craig, Vincent S J; Senden, Tim J

    2014-01-01

    As nanoscale and molecular devices become reality, the ability to probe materials on these scales is increasing in importance. To address this, we have developed a dynamic force microscopy technique where the flexure of the microcantilever is excited using an intensity modulated laser beam to achieve modulation on the picoscale. The flexure arises from thermally induced bending through differential expansion and the conservation of momentum when the photons are reflected and absorbed by the cantilever. In this study, we investigated the photothermal and photon pressure responses of monolithic and layered cantilevers using a modulated laser in air and immersed in water. The developed photon actuation technique is applied to the stretching of single polymer chains. PMID:24993548

  16. Coherent control of quantum dynamics in laser kicked molecular rotors

    NASA Astrophysics Data System (ADS)

    Bitter, Martin; Milner, Valery

    2016-05-01

    We investigate experimentally the dynamics of true quantum kicked rotors - oxygen and nitrogen molecules subject to a sequence of more than 20 ultrashort laser pulses with peak intensities exceeding 1013 W/ cm2 per pulse. Using state-resolved rotational Raman spectroscopy, we show that the centrifugal distortion is the main obstacle in reaching high rotational states, as it results in the coherent oscillations of rotational population similar to Bloch oscillations in condensed matter. We demonstrate that the timing of the individual pulses can be optimized to partially mitigate the centrifugal limit and produce broader rotational wave packets with higher degrees of rotational coherence. Progress towards the experimental observation of Anderson localization in laser-kicked molecular rotors will be discussed.

  17. SHIELD: Neutral Gas Kinematics and Dynamics

    NASA Astrophysics Data System (ADS)

    McNichols, Andrew; Teich, Yaron; Cannon, John M.; SHIELD Team

    2016-01-01

    The "Survey of HI in Extremely Low-mass Dwarfs" (SHIELD) is a multiwavelength, legacy-class observational study of 12 low-mass dwarf galaxies discovered in Arecibo Legacy Fast ALFA (ALFALFA) survey data products. Here we present new results of detailed kinematic analyses of these systems using multi-configuration, high spatial (˜300 pc) and spectral (0.82 - 2.46 km s-1 ch-1) resolution HI observations from the Karl G. Jansky Very Large Array. For each source, we produce velocity fields and dispersion maps using different spatial and spectral resolution representations of the data in order to attempt derivation of an inclination-corrected rotation curve. While both two- and three-dimensional fitting techniques are employed, the comparable magnitudes of velocity dispersion and projected rotation result in degeneracies that prohibit unambiguous circular velocity solutions. We thus make multiple position-velocity cuts across each galaxy to determine the maximum circular rotation velocity (≤ 30 km-1 for the survey population). Baryonic masses are calculated using single-dish H I fluxes from Arecibo and stellar masses derived from HST and Spitzer imaging. Comparison is made with total dynamical masses estimated from the position-velocity analysis. The SHIELD galaxies are contextualized on the baryonic Tully-Fisher relation.Support for this work was provided by NSF grant AST-1211683 to JMC at Macalester College.

  18. GAS PHASE MOLECULAR DYNAMICS: HIGH-RESOLUTION SPECTROSCOPIC PROBES OF CHEMICAL DYNAMICS.

    SciTech Connect

    HALL, G.E.

    2006-05-30

    This research is carried out as part of the Gas Phase Molecular Dynamics group program in the Chemistry Department at Brookhaven National Laboratory. High-resolution spectroscopic tools are developed and applied to problems in chemical dynamics. Recent topics have included the state-resolved studies of collision-induced electronic energy transfer, dynamics of barrierless unimolecular reactions, and the kinetics and spectroscopy of transient species.

  19. Demonstration of a neonlike argon soft-x-ray laser with a picosecond-laser-irradiated gas puff target.

    PubMed

    Fiedorowicz, H; Bartnik, A; Dunn, J; Smith, R F; Hunter, J; Nilsen, J; Osterheld, A L; Shlyaptsev, V N

    2001-09-15

    We demonstrate a neonlike argon-ion x-ray laser, using a short-pulse laser-irradiated gas puff target. The gas puff target was formed by pulsed injection of gas from a high-pressure solenoid valve through a nozzle in the form of a narrow slit and irradiated with a combination of long, 600-ps and short, 6-ps high-power laser pulses with a total of 10 J of energy in a traveling-wave excitation scheme. Lasing was observed on the 3p (1)S(0)?3s (1)P(1) transition at 46.9 nm and the 3d (1)P(1)?3p (1)P(1) transition at 45.1 nm. A gain of 11 cm(-1) was measured on these transitions for targets up to 0.9 cm long. PMID:18049619

  20. Postquench dynamics and prethermalization in a resonant Bose gas

    NASA Astrophysics Data System (ADS)

    Yin, Xiao; Radzihovsky, Leo

    2016-03-01

    We explore the dynamics of a resonant Bose gas following its quench to a strongly interacting regime near a Feshbach resonance. For such deep quenches, we utilize a self-consistent dynamic field approximation and find that after an initial regime of many-body Rabi-type oscillations between the condensate and finite-momentum quasiparticle pairs, at long times, the gas reaches a prethermalized nonequilibrium steady state. We explore the resulting state through its broad stationary momentum distribution function, that exhibits a power-law high-momentum tail. We study the dynamics and steady-state form of the associated enhanced depletion, quench-rate-dependent excitation energy, Tan's contact, structure function, and radio-frequency spectroscopy. We find these predictions to be in a qualitative agreement with recent experiments.

  1. Laser acceleration of monoenergetic protons with a near-critical, optically-shaped gas target

    NASA Astrophysics Data System (ADS)

    Chen, Yu-Hsin; Helle, Michael; Ting, Antonio; Gordon, Daniel; Polyanskiy, Mikhail; Pogorelsky, Igor; Babzien, Marcus; Najmudin, Zulfikar

    2015-11-01

    Laser-based ion acceleration is studied using the intense terawatt CO2 laser pulse with a near-critical hydrogen gas target. The gas density profile is tailored by a hydrodynamic shock, which is launched by ablation of solid with a moderate-energy, nanosecond Nd:YAG laser pulse in the vicinity of the gas jet. A sharp density gradient is thus created near the edge of the gas column, resulting to ~ 6X local density enhancement up to several times of critical density within 100 micrometers before CO2 laser pulse arrives. With such density profile, we have observed quasi-monoenergetic proton beams with energies >1 MeV and good shot-to-shot reproducibility. In contrast, no protons were observed when the hydrodynamic shock is absent. Results from experiments and simulations will be presented. This work is supported by U.S. Department of Energy.

  2. Continuous and Pulsed THz generation with molecular gas lasers and photoconductive antennas gated by femtosecond pulses

    NASA Astrophysics Data System (ADS)

    Cruz, Flavio C.; Nogueira, T.; Costa, Leverson F. L.; Jarschel, Paulo F.; Frateschi, Newton C.; Viscovini, Ronaldo C.; Vieira, Bruno R. B.; Guevara, Victor M. B.; Pereira, Daniel

    2008-04-01

    We report THz generation based on two systems: 1) continuous-wave (cw) laser generation in molecular gas lasers, and 2) short pulse generation in photoconductive antennas, gated by femtosecond near-infrared Ti:sapphire lasers. With the first system, we have generated tens of monochromatic cw laser lines over the last years, extending roughly from 40 microns to several hundred microns. This is done by optical pumping of gas lasers based on polar molecules such as methanol and its isotopes. In the second system, under development, pulsed THz radiation is generated by a photoconductive antenna built in a semi-insulating GaAs substrate excited by femtosecond pulses from a near-infrared (800 nm) Ti:sapphire laser.

  3. A survey of laser and selected optical systems for remote measurement of pollutant gas concentrations

    NASA Technical Reports Server (NTRS)

    Grant, W. B.; Menzies, R. T.

    1983-01-01

    Applications of the Differential Absorption Lidar (DIAL) technique to the remote sensing of pollutant gases are surveyed. In the DIAl technique, the differential absorption of two laser beams reflected back to a receiver from a target determines the concentration of the gas being studied. The types of instruments available are considered in detail: dye lidar (to measure nitrogen dioxide, sulfur dioxide, and ozone); carbon dioxide laser (for ozone, ethylene, ammonia, and hydrazine), helium-neon laser (for methane); hydrogen fluoride laser (for HF); and tunable diode laser (for nitric oxide and carbon monoxide). DIAL instruments are compared with other optical remote sensors such as Fourier-transform infrared spectrometers, correlation spectrometers (COSPEC and GASPEC), and grating spectrometers; and criteria for the selection of an appropriate gas measuring system are suggested. Laser and other optical remote sensors are found to be cost effective in many cases, despite the fact that they are more costly than point-monitoring systems.

  4. Multiple-Diode-Laser Gas-Detection Spectrometer

    NASA Technical Reports Server (NTRS)

    Webster, Christopher R.; Beer, Reinhard; Sander, Stanley P.

    1988-01-01

    Small concentrations of selected gases measured automatically. Proposed multiple-laser-diode spectrometer part of system for measuring automatically concentrations of selected gases at part-per-billion level. Array of laser/photodetector pairs measure infrared absorption spectrum of atmosphere along probing laser beams. Adaptable to terrestrial uses as monitoring pollution or control of industrial processes.

  5. Optical velocimeters for moving surfaces using gas and semiconductor lasers

    NASA Astrophysics Data System (ADS)

    Belousov, P. Ya.; Dubnistshev, Yu. N.; Meledin, V. G.

    1990-10-01

    A differential arrangement using a laser for the measurement of the velocity of moving surfaces is discussed. Configurations of optical velocimeters with diffraction beam-splitters are shown not to be critical on the wavelength stability of a semiconductor laser. Laser meters measuring the velocity and length of rolled stock have been built on the basis of the devices considered.

  6. Laser-induced magnetization dynamics and reversal in ferrimagnetic alloys.

    PubMed

    Kirilyuk, Andrei; Kimel, Alexey V; Rasing, Theo

    2013-02-01

    This review discusses the recent studies of magnetization dynamics and the role of angular momentum in thin films of ferrimagnetic rare-earth-transition metal (RE-TM) alloys, e.g. GdFeCo, where both magnetization and angular momenta are temperature dependent. It has been experimentally demonstrated that the magnetization can be manipulated and even reversed by a single 40 fs laser pulse, without any applied magnetic field. This switching is found to follow a novel reversal pathway, that is shown however to depend crucially on the net angular momentum, reflecting the balance of the two opposite sublattices. In particular, optical excitation of ferrimagnetic GdFeCo on a time scale pertinent to the characteristic time of the exchange interaction between the RE and TM spins, i.e. on the time scale of tens of femtoseconds, pushes the spin dynamics into a yet unexplored regime, where the two exchange-coupled magnetic sublattices demonstrate substantially different dynamics. As a result, the reversal of spins appears to proceed via a novel transient state characterized by a ferromagnetic alignment of the Gd and Fe magnetic moments, despite their ground-state antiferromagnetic coupling.Thus, optical manipulation of magnetic order by femtosecond laser pulses has developed into an exciting and still expanding research field that keeps being fueled by a continuous stream of new and sometimes counterintuitive results. Considering the progress in the development of plasmonic antennas and compact ultrafast lasers, optical control of magnetic order may also potentially revolutionize data storage and information processing technologies. PMID:23377279

  7. Primary zone dynamics in a gas turbine combustor

    NASA Astrophysics Data System (ADS)

    Sullivan, J. P.; Barron, D.; Seal, M.; Morgan, D.; Murthy, S. N. B.

    1989-01-01

    Fluid mechanical investigations simulating the flow in the primary zone of a gas turbine combustor are presented using three generic test rigs: (1) rotating pipe yielding a swirling jet of air; (2) primary zone model with a single swirler and various primary jet configurations, operated with air; and (3) two rectangular models of a (stretched-out) annular combustor with five swirlers in the backwall and with various primary jet configurations, one operated with air and the other with water. Concentration measurements are obtained using laser sheet imaging techniques and velocity measurements using a laser Doppler velocimeter. The results show recirculation zones, intense mixing, instabilities of the interacting jets and the presence of large random vortical motions. The flowfields are shown to exhibit bimodal behavior, have asymmetries despite symmetrical geometry and inlet conditions and display strong jet/swirler and swirler/swirler interactions.

  8. Gas Dynamics during Thermal Remediation: Visualization, Quantification and Enhancement

    NASA Astrophysics Data System (ADS)

    Mumford, K. G.; Hegele, P. R.

    2014-12-01

    In situ thermal treatment (ISTT) technologies, such as electrical resistance heating (ERH) and thermal conductive heating (TCH), rely on the in situ production of a gas phase composed of steam and vaporized volatile organic compounds (VOCs). This gas phase must be captured, extracted, and processed in an aboveground treatment system to meet remediation objectives. When used to treat volatile non-aqueous phase liquids (NAPLs), gases can be created at temperatures below the boiling points of both the groundwater and the NAPL, in a process commonly referred to as co-boiling, and vaporized VOCs can condense if gases are transported to colder regions or are not captured before thermal treatment has stopped. As such, an understanding of gas formation, connection, and flow is important for the design and operation of ISTT technologies. A recent series of laboratory experiments focused on the visualization and quantification of gas dynamics during water boiling and NAPL-water co-boiling, and the investigation of potential NAPL redistribution. Experiments were conducted in a sand-packed glass-walled chamber (40 cm tall × 20 cm wide × 1 cm thick) heated by electrical resistance. Temperatures and electric currents were measured, and digital images were captured throughout the experiments to quantify gas saturations using light transmission techniques. Additional experiments also investigated the exsolution of dissolved gas as a technique to enhance gas production at lower temperatures. Results showed the development of disconnected and connected gas flow regimes, with disconnected flow occurring at early times and during co-boiling. Results also showed the potential for NAPL redistribution due to displacement by gas formed within pools, and due to condensation in colder regions. These results highlight the need to carefully consider gases in the design of ISTT heating and gas extraction systems to ensure remediation performance.

  9. Radiation intensity distribution in a nuclear-pumped gas-flow laser

    SciTech Connect

    Korzenev, A N; Limar', Yu M; Sizov, A N; Sinyanskii, A A

    2005-09-30

    It is shown experimentally that two lasing zones, displaced directly towards the entrance of the laser channel, are formed in gas-flow lasers pumped by the fission fragments of uranium nuclei. As the pump power is increased, these zones merge into a single zone that expands towards the exit section of the channel. The time dependence of the lasing power qualitatively repeats the shape of the exciting neutron pulse. (lasers)

  10. Gas hydrate dynamics in heterogeneous media - challenges for numerical modeling

    NASA Astrophysics Data System (ADS)

    Burwicz, Ewa; Ruepke, Lars; Wallmann, Klaus

    2013-04-01

    Gas hydrates are ice-like crystalline cage structures containing various greenhouse gases, such as methane or CO2, which are locked within their spatial structure. Gas hydrate distribution in oceanic settings is mainly controlled by three factors: 1) low temperature regimes, 2) high pressure regimes, and 3) presence of biodegradable organic matter. Due to their composition, hydrates are vulnerable to temperature, pressure, and, to a smaller degree, salinity changes. The occurrence of gas hydrates in marine sediments was discovered mainly along continental margins (slope and rise) where water depths exceed 400 m and the bottom water temperatures are small enough to sustain their presence. The amount of gas hydrates present in marine sediments on a global scale is still under debate. Several numerical models of a different complexity have been developed to estimate the potential amount of clathrates locked world-wide within marine sediments. The range of estimates starts from 500 Gt up to 57,000 Gt of methane carbon which implies a variation of several orders of magnitude. It has been already established that current climate changes are triggering some of the methane releases around the world. Prominent gas hydrate occurrence zones, such as Blake Ridge, can provide important information of the scale of potential hazards and help to predict a future impact of such events. Blake Ridge is a well investigated gas hydrate province containing a large amount of a locked methane gas. With the new numerical multiphase model we have been investigating 1) the potential risk of gas hydrate destabilization caused by several environmental factors (e.g. bottom water temperature rise, sea-level variations), 2) the effect of changing sedimentation regimes to the total amount of gas hydrate, 3) dynamics of hydrate formation in heterogeneous sediment layers, and 4) the impact of dynamic compaction on fluid and gas flow regimes. The model contains four phases (solid porous matrix, pore

  11. Monitoring interfacial dynamics by pulsed laser techniques: Annual report

    SciTech Connect

    Richmond, G.

    1987-01-01

    Several types of materials have been surveyed including thin film and layered semiconductors as well as a metal and semimetal. Second harmonic (SH) generation measurements on these materials were made using both nanosecond (Q-switched) and picosecond (mode-locked) pulsed Nd:YAG lasers with appropriate gated or photon counting detection. Initial studies were performed under steady state conditions in order to optimize the experiments for time-resolved studies. SHG were also extended to the time domain. A means of monitoring surface structure and reconstruction phenomena in-situ was developed. This discovery now opens a broad new area of dynamic interfacial measurements to be done in-situ.

  12. Interferometric technique for determining the energy deposition in gas-flow nuclear-pumped lasers

    SciTech Connect

    Pikulev, A A

    2001-06-30

    An interference technique is developed for determining the energy deposition in gas-flow lasers pumped by uranium fission fragments. It is shown that four types of interference patterns may be formed. Algorithms are presented for determining the type of interference and for enumerating the maxima in interference pattern. (lasers, active media)

  13. Intracavity Raman lasers

    SciTech Connect

    Band, Y.B.; Ackerhalt, J.R.; Krasinski, J.S.; Heller, D.F.

    1989-02-01

    Experimental and theoretical studies of intracavity Raman lasers are presented. Advantages of intracavity Raman lasers, particularly for low-emission cross section and broadly tunable vibronic gain media, are described. Experimental studies of a hydrogen gas Raman laser pumped inside the cavity of an alexandrite laser are presented. A theoretical model of the dynamics of a unidirectional intracavity Raman ring laser is developed and solved analytically. This model is adapted to simulate experiments.

  14. Numerical modeling of pulsed laser-material interaction and of laser plume dynamics

    SciTech Connect

    Zhao, Qiang; Shi, Yina

    2015-03-10

    We have developed two-dimensional Arbitrary Lagrangian Eulerian (ALE) code which is used to study the physical processes, the plasma absorption, the crater profile, and the temperature distribution on metallic target and below the surface. The ALE method overcomes problems with Lagrangian moving mesh distortion by mesh smoothing and conservative quantities remapping from Lagrangian mesh to smoothed one. A new second order accurate diffusion solver has been implemented for the thermal conduction and radiation transport on distorted mesh. The results of numerical simulation of pulsed laser ablation are presented. The influences of different processes, such as time evolution of the surface temperature, interspecies interactions (elastic collisions, recombination-dissociation reaction), interaction with an ambient gas are examined. The study presents particular interest for the analysis of experimental results obtained during pulsed laser ablation.

  15. Laser-Launched Flyer Plates and Direct Laser Shocks for Dynamic Material Property Measurements

    NASA Astrophysics Data System (ADS)

    Paisley, D. L.; Swift, D. C.; Johnson, R. P.; Kopp, R. A.; Kyrala, G. A.

    2002-07-01

    The Trident laser at Los Alamos was used to impart known and controlled shocks in various materials by launching flyer plates or by irradiating the sample directly. Materials investigated include copper, gold, NiTi, SS316, and other metals and alloys. Tensile spall strength, elastic-plastic transition, phase boundaries, and equation of state can be determined with small samples. Using thin samples (0.1 - 1.0 mm thick) as targets, high pressure gradients can be generated with relatively low pressures, resulting in high tensile strain rates (105 to 108 s-1). Free surface and interface velocities are recorded with point- and line-imaging VISARs. The flexible spatial and temporal pulse profiles of Trident, coupled with the use of laser-launched flyer plates, provides capabilities which complement experiments conducted using gas guns and tensile bars.

  16. Laser energy deposition and its dynamic uniformity for direct-drive capsules

    SciTech Connect

    Xu, Yan; Wu, SiZhong; Zheng, WuDi

    2015-04-15

    The total laser energy deposition of multi-laser-beam irradiation is not only associated with the dynamic behavior of capsule but also the time-dependent angular distribution of the energy deposition of each beam around its axis. The dynamic behavior of laser energy deposition does not linearly respond to the dynamic behavior of laser irradiation. The laser energy deposition uniformity determines the symmetry of implosion. The dynamic behavior of laser energy deposition non-uniformity in OMEGA for laser with square beam shape intensity profile is investigated. In the case of smaller laser spot, the initial non-uniformity caused by laser beam overlap is very high. The shell asymmetry caused by the high initial laser irradiation non-uniformity is estimated by the extent of distortion of shock front which is not as severe as expected before the shock driven by main pulse arrives. This suggests that the large initial non-uniformity due to smaller laser spot is one of the elements that seed disturbance before the main pulse. The rms of laser energy deposition during the main pulse remains above 2%. Since the intensity of main driving pulse usually is several times higher than that of picket pulses, the non-uniformity in main pulse period may jeopardize the symmetrical implosion. When dynamic behavior of capsule is considered, the influence of beam pointing error, the target positioning error, and beam-to-beam power unbalance is quite different for the case of static capsule.

  17. Multiple Point Dynamic Gas Density Measurements Using Molecular Rayleigh Scattering

    NASA Technical Reports Server (NTRS)

    Seasholtz, Richard; Panda, Jayanta

    1999-01-01

    A nonintrusive technique for measuring dynamic gas density properties is described. Molecular Rayleigh scattering is used to measure the time-history of gas density simultaneously at eight spatial locations at a 50 kHz sampling rate. The data are analyzed using the Welch method of modified periodograms to reduce measurement uncertainty. Cross-correlations, power spectral density functions, cross-spectral density functions, and coherence functions may be obtained from the data. The technique is demonstrated using low speed co-flowing jets with a heated inner jet.

  18. Carrier dynamics in femtosecond-laser-excited bismuth telluride

    NASA Astrophysics Data System (ADS)

    Wang, J. L.; Guo, L.; Ling, C.; Song, Y. M.; Xu, X. F.; Ni, Z. H.; Chen, Y. F.

    2016-04-01

    The carrier dynamics of B i2T e3 is studied using the femtosecond pump-probe technique. Three distinct processes, including free carrier absorption, band filling, and electron-hole recombination, are found to contribute to the reflectivity changes. The two-temperature model is used to describe the intraband energy relaxation process of carriers, and the Drude contribution well explains the intensity dependence of the peak values of the nonoscillatory component in the reflectivity signal. The combined effects of free carrier absorption and band filling result in a reflection minimum at about 2 ps after laser excitation. The nonzero background signal increases linearly with the pump fluence, which is attributed to the electron-hole recombination. Finally, our results provide an illustration of investigating the carrier dynamics in semiconductors from the ultrafast reflectivity spectra.

  19. Molecular dynamic studies on anisotropic explosion of laser irradiated Xe cluster

    SciTech Connect

    Mishra, Gaurav; Gupta, N. K.

    2012-09-15

    A three dimensional molecular dynamic model is used to investigate the dynamics of Xe clusters of various radii irradiated by laser of moderate intensities ({approx}10{sup 14}-10{sup 16}W/cm{sup 2}). The FWHM pulse duration of the laser is varied from few laser cycles to hundreds of femtosecond. For cluster of radius 50 A irradiated by a laser of 170 fs pulse duration, it is observed that ion yield is more along the direction of laser polarization than perpendicular to it. This trend reverses (more ions are emitted along the direction perpendicular to laser polarization than parallel to it) when laser pulses of few cycles are used. This reversal of anisotropy is explained on the basis of spatial shielding of ions due to the oscillating inner electron cloud along direction of laser electric field. The nature of anisotropy remains same with variations in laser intensity and cluster size.

  20. Red and infrared gas laser beam for therapy

    NASA Astrophysics Data System (ADS)

    Pascu, Mihail-Lucian; Ristici, Marin; Ristici, E.; Tivarus, Madalina-Elena

    2000-06-01

    For the low power laser therapy, the experiments show that better results are obtained when the laser beam is an overlapping of two radiations: one in the visible region of the spectrum and the other in IR region. Also, some experiments show that for good results in biostimulation it is important to have a high coherence length of laser beam; this is not the case of the laser diodes The He-Ne laser has the best coherence, being able to generate laser radiations in visible and IR. It has tow strong laser lines: 633 nm and 1.15 micrometers . Although their gains are about the same, the available power of the red radiation is 3-4 times higher because of its larger width, when they oscillate separately. Using special dichroic mirrors for simultaneous reflection of the both liens, the laser beam will consist of the two radiations, each of them having good coherence . A 420 mm active length, 1.8 mm inner diameter He-Ne laser tube and a special designed resonator has been developed. The mirrors reflect both radiations as follows: one reflects 99.9 percent and the other, the output mirror, reflects 98 percent. There is a competition between them because these lines have a common lower level. The output power of the laser beam as 6 mW for 633 nm and 4 mW for 1.15 micrometers , respectively.

  1. Dynamics and Synchronization of Semiconductor Lasers for Chaotic Optical Communications

    NASA Astrophysics Data System (ADS)

    Liu, Jia-Ming; Chen, How-Foo; Tang, Shuo

    The objective of this chapter is to provide a complete picture of the nonlinear dynamics and chaos synchronization of single-mode semiconductor lasers for chaotic optical communications. Basic concepts and theoretical framework are reviewed. Experimental results are presented to demonstrate the fundamental concepts. Numerical computations are employed for mapping the dynamical states and for illustrating certain detailed characteristics of the chaotic states. Three different semiconductor laser systems, namely, the optical injection system, the optical feedback system, and the optoelectronic feedback system, that are of most interest for high-bit-rate chaotic optical communications are considered. The optical injection system is a nonautonomous system that follows a period-doubling route to chaos. The optical feedback system is a phase-sensitive delayed-feedback autonomous system for which all three known routes, namely, period-doubling, quasiperiodicity, and intermittency, to chaos can be found. The optical feedback system is a phase-insensitive delayed-feedback autonomous system that follows a quasiperiodicity route to chaotic pulsing. Identical synchronization in unidirectionally coupled configurations is the focus of discussions for chaotic communications. For optical injection and optical feedback systems, the frequency, phase, and amplitude of the optical fields of both transmitter and receiver lasers are all locked in synchronism when complete synchronization is accomplished. For the optoelectronic feedback system, chaos synchronization involves neither the locking of the optical frequency nor the synchronization of the optical phase. For both optical feedback and optoelectronic feedback systems, where the transmitter is configured with a delayed feedback loop, anticipated and retarded synchronization can be observed as the difference between the feedback delay time and the propagation time from the transmitter laser to the receiver laser is varied. For a

  2. Development of a gas cell-based laser ion source for RIKEN PALIS

    NASA Astrophysics Data System (ADS)

    Sonoda, T.; Wada, M.; Tomita, H.; Sakamoto, C.; Takatsuka, T.; Noto, T.; Iimura, H.; Matsuo, Y.; Kubo, T.; Shinozuka, T.; Wakui, T.; Mita, H.; Naimi, S.; Furukawa, T.; Itou, Y.; Schury, P.; Miyatake, H.; Jeong, S.; Ishiyama, H.; Watanabe, Y.; Hirayama, Y.

    2013-04-01

    We developed a prototype laser ionization gas cell with a beam extraction system. This device is for use of PArasitic Laser Ion-Source (PALIS), which will be implemented into RIKEN's fragment separator, BigRIPS as a part of SLOWRI. Off-line resonant laser ionization for stable Co, Cu, Fe, Ni, Ti, Nb, Sn, In and Pd inside the gas cell, ion extraction and transport to the high-vacuum region via SPIG and QMS have been confirmed (Sonoda et al, Nucl Instrum Meth B 295:1, 2013).

  3. Experimental Investigation for 100-Joule-class TEA CO2 Laser and Gas Interaction

    NASA Astrophysics Data System (ADS)

    Dou, Zhiguo; Yao, Honglin; Wang, Jun; Wen, Ming; Wang, Peng; Yang, Jan; Li, Chong

    2006-05-01

    Impulse coupling coefficient Cm is one of the most important performance parameters in laser propulsion. Cm is the impulse increment of lightcraft that per joule laser beam energy acts on. The TEA CO2 laser, whose single pulse energy is 100-Joule-class and wavelength is 10.6μm, is adopted by experimental research. In experimental environment cabin, the parabolic lightcraft is fixed on impact pendulum. Using Air, N2, He, CO2, N2-He and N2-CO2, different Cm is obtained. Experimental results indicate that Cm of the mixed gas is improved through changing gas component ratio.

  4. Anisotropic dynamics in a shaken granular dimer gas experiment

    NASA Astrophysics Data System (ADS)

    Atwell, J.; Olafsen, J. S.

    2005-06-01

    The dynamics, velocity fluctuations, and particle-plate interactions for a two-dimensional granular gas of shaken, nonspherical particles are studied experimentally. The experiment consists of a horizontal plate that is vertically oscillated to drive the dynamics of macroscopic dimers, spherical pairs that are loosely connected by a rod that couple the interaction each of the spheres has with the shaking plate. The extended nature of the particles results in more than one energy-momentum transfer between the plate and each dimer per shaking cycle. This complex interaction results in anisotropic behavior for the dimer that is a function of the shaking parameters.

  5. Dynamics of femtosecond laser-induced melting of silver

    SciTech Connect

    Chan Wailun; Averback, Robert S.; Cahill, David G.; Lagoutchev, Alexei

    2008-12-01

    We use optical third-harmonic generation to measure the melting dynamics of silver following femtosecond laser excitation. The dynamics reveals an unusual two-step process that is associated with the extreme electronic temperatures and very short time and length scales. In the first, which lasts a few picoseconds, the electron and phonon systems begin to equilibrate, and a thin surface layer undergoes melting. Heat conduction during this period is strongly suppressed by electron scattering from d-band excitations. In the second stage, the surface region remains above the melting temperature for a surprisingly long time, 20-30 ps, with the melt front propagating into the bulk at a velocity of {approx_equal}350 m s{sup -1}. In this stage, the electron and phonon systems again fall out of equilibrium and conduction of heat away from the surface region is now limited by the weak electron-phonon (e-p) coupling. From our model calculation, we propose that the melt depths in noble metals irradiated by femtosecond lasers are limited to thicknesses on the order of two to three times of the optical-absorption depth of the light.

  6. PARTICLE-GAS DYNAMICS WITH ATHENA: METHOD AND CONVERGENCE

    SciTech Connect

    Bai Xuening; Stone, James M. E-mail: jstone@astro.princeton.ed

    2010-10-15

    The Athena magnetohydrodynamics code has been extended to integrate the motion of particles coupled with the gas via aerodynamic drag in order to study the dynamics of gas and solids in protoplanetary disks (PPDs) and the formation of planetesimals. Our particle-gas hybrid scheme is based on a second-order predictor-corrector method. Careful treatment of the momentum feedback on the gas guarantees exact conservation. The hybrid scheme is stable and convergent in most regimes relevant to PPDs. We describe a semi-implicit integrator generalized from the leap-frog approach. In the absence of drag force, it preserves the geometric properties of a particle orbit. We also present a fully implicit integrator that is unconditionally stable for all regimes of particle-gas coupling. Using our hybrid code, we study the numerical convergence of the nonlinear saturated state of the streaming instability. We find that gas flow properties are well converged with modest grid resolution (128 cells per pressure length {eta}r for dimensionless stopping time {tau} {sub s} = 0.1) and an equal number of particles and grid cells. On the other hand, particle clumping properties converge only at higher resolutions, and finer resolution leads to stronger clumping before convergence is reached. Finally, we find that the measurement of particle transport properties resulted from the streaming instability may be subject to error of about {+-}20%.

  7. Investigation of laser dynamics, modulation and control by means of intra-cavity time varying perturbation

    NASA Technical Reports Server (NTRS)

    Harris, S. E.; Siegman, A. E.; Kuizenga, D. J.; Kung, A. H.; Young, J. F.; Bekkers, G. W.; Bloom, D. M.; Newton, J. H.; Phillion, D. W.

    1975-01-01

    The generation of tunable visible, infrared, and ultraviolet light is examined, along with the control of this light by means of novel mode-locking and modulation techniques. Transient mode-locking of the Nd:YAG laser and generation of short tunable pulses in the visible and the alkali metal inert gas excimer laser systems were investigated. Techniques for frequency conversion of high power and high energy laser radiation are discussed, along with high average power blue and UV laser light sources.

  8. Supersymmetric formulation of polytropic gas dynamics and its invariant solutions

    SciTech Connect

    Grundland, A. M.; Hariton, A. J.

    2011-04-15

    In this paper, a supersymmetric extension of the polytropic gas dynamics equations is constructed through the use of a superspace involving two independent fermionic variables and two bosonic superfields. A superalgebra of symmetries of the proposed extended model is determined and a systematic classification of the one-dimensional subalgebras of this superalgebra is performed. Through the use of the symmetry reduction method, a number of invariant solutions of the supersymmetric polytropic gas dynamics equations are found. Several types of solutions are obtained including algebraic-type solutions and propagation waves (simple and double waves). Many of the obtained solutions involve arbitrary functions of one or two bosonic or fermionic variables. In the case where the arbitrary functions involve only the independent fermionic variables, the solutions are expressed in terms of Taylor expansions.

  9. The magnetic field of Mars - Implications from gas dynamic modeling

    NASA Technical Reports Server (NTRS)

    Russell, C. T.; Luhmann, J. G.; Spreiter, J. R.; Stahara, S. S.

    1984-01-01

    On January 21, 1972, the Mars 3 spacecraft observed a variation in the magnetic field during its periapsis passage over the dayside of Mars that was suggestive of entry into a Martian magnetosphere. Original data and trajectory of the spacecraft have been obtained (Dolginov, 1983) and an attempt is made to simulate the observed variation of the magnetic field by using a gas dynamic simulation. In the gas dynamic model a flow field is generated and this flow field is used to carry the interplanetary magnetic field through the Martian magnetosheath. The independence of the flow field and magnetic field calculation makes it possible to converge rapidly on an IMF orientation that would result in a magnetic variation similar to that observed by Mars 3. There appears to be no need to invoke an entry into a Martian magnetosphere to explain these observations.

  10. High spatial resolution measurements of ram accelerator gas dynamic phenomena

    NASA Technical Reports Server (NTRS)

    Hinkey, J. B.; Burnham, E. A.; Bruckner, A. P.

    1992-01-01

    High spatial resolution experimental tube wall pressure measurements of ram accelerator gas dynamic phenomena are presented. The projectile resembles the centerbody of a ramjet and travels supersonically through a tube filled with a combustible gaseous mixture, with the tube acting as the outer cowling. Pressure data are recorded as the projectile passes by sensors mounted in the tube wall at various locations along the tube. Data obtained by using a special highly instrumented section of tube has allowed the recording of gas dynamic phenomena with a spatial resolution on the order of one tenth the projectile length. High spatial resolution tube wall pressure data from the three regimes of propulsion studied to date (subdetonative, transdetonative, and superdetonative) are presented and reveal the 3D character of the flowfield induced by projectile fins and the canting of the projectile body relative to the tube wall. Also presented for comparison to the experimental data are calculations made with an inviscid, 3D CFD code.

  11. A minimum entropy principle in the gas dynamics equations

    NASA Technical Reports Server (NTRS)

    Tadmor, E.

    1986-01-01

    Let u(x bar,t) be a weak solution of the Euler equations, governing the inviscid polytropic gas dynamics; in addition, u(x bar, t) is assumed to respect the usual entropy conditions connected with the conservative Euler equations. We show that such entropy solutions of the gas dynamics equations satisfy a minimum entropy principle, namely, that the spatial minimum of their specific entropy, (Ess inf s(u(x,t)))/x, is an increasing function of time. This principle equally applies to discrete approximations of the Euler equations such as the Godunov-type and Lax-Friedrichs schemes. Our derivation of this minimum principle makes use of the fact that there is a family of generalized entrophy functions connected with the conservative Euler equations.

  12. Optically pumped alkali laser and amplifier using helium-3 buffer gas

    DOEpatents

    Beach, Raymond J.; Page, Ralph; Soules, Thomas; Stappaerts, Eddy; Wu, Sheldon Shao Quan

    2010-09-28

    In one embodiment, a laser oscillator is provided comprising an optical cavity, the optical cavity including a gain medium including an alkali vapor and a buffer gas, the buffer gas including .sup.3He gas, wherein if .sup.4He gas is also present in the buffer gas, the ratio of the concentration of the .sup.3He gas to the .sup.4He gas is greater than 1.37.times.10.sup.-6. Additionally, an optical excitation source is provided. Furthermore, the laser oscillator is capable of outputting radiation at a first frequency. In another embodiment, an apparatus is provided comprising a gain medium including an alkali vapor and a buffer gas including .sup.3He gas, wherein if .sup.4He gas is also present in the buffer gas, the ratio of the concentration of the .sup.3He gas to the .sup.4He gas is greater than 1.37.times.10.sup.-6. Other embodiments are also disclosed.

  13. DIODE LASER-BASED MEASUREMENTS OF HYDROGEN FLUORIDE GAS DURING CHEMICAL SUPPRESSION OF FIRES

    EPA Science Inventory

    Near-infrared tunable diode laser (NIR-TDL) spectroscopy is used to quantify hydrogen fluoride (HF) gas produced during fire-suppressant testing of Halon alternatives. Results of comparisons with other techniques for measuring HF gas concentrations are discussed. Measurements of ...

  14. Trace gas absorption spectroscopy using laser difference-frequency spectrometer for environmental application

    NASA Technical Reports Server (NTRS)

    Chen, W.; Cazier, F.; Boucher, D.; Tittel, F. K.; Davies, P. B.

    2001-01-01

    A widely tunable infrared spectrometer based on difference frequency generation (DFG) has been developed for organic trace gas detection by laser absorption spectroscopy. On-line measurements of concentration of various hydrocarbons, such as acetylene, benzene, and ethylene, were investigated using high-resolution DFG trace gas spectroscopy for highly sensitive detection.

  15. Merger Signatures in the Dynamics of Star-forming Gas

    NASA Astrophysics Data System (ADS)

    Hung, Chao-Ling; Hayward, Christopher C.; Smith, Howard A.; Ashby, Matthew L. N.; Lanz, Lauranne; Martínez-Galarza, Juan R.; Sanders, D. B.; Zezas, Andreas

    2016-01-01

    The recent advent of integral field spectrographs and millimeter interferometers has revealed the internal dynamics of many hundreds of star-forming galaxies. Spatially resolved kinematics have been used to determine the dynamical status of star-forming galaxies with ambiguous morphologies, and constrain the importance of galaxy interactions during the assembly of galaxies. However, measuring the importance of interactions or galaxy merger rates requires knowledge of the systematics in kinematic diagnostics and the visible time with merger indicators. We analyze the dynamics of star-forming gas in a set of binary merger hydrodynamic simulations with stellar mass ratios of 1:1 and 1:4. We find that the evolution of kinematic asymmetries traced by star-forming gas mirrors morphological asymmetries derived from mock optical images, in which both merger indicators show the largest deviation from isolated disks during strong interaction phases. Based on a series of simulations with various initial disk orientations, orbital parameters, gas fractions, and mass ratios, we find that the merger signatures are visible for ˜0.2-0.4 Gyr with kinematic merger indicators but can be approximately twice as long for equal-mass mergers of massive gas-rich disk galaxies designed to be analogs of z ˜ 2-3 submillimeter galaxies. Merger signatures are most apparent after the second passage and before the black holes coalescence, but in some cases they persist up to several hundred Myr after coalescence. About 20%-60% of the simulated galaxies are not identified as mergers during the strong interaction phase, implying that galaxies undergoing violent merging process do not necessarily exhibit highly asymmetric kinematics in their star-forming gas. The lack of identifiable merger signatures in this population can lead to an underestimation of merger abundances in star-forming galaxies, and including them in samples of star-forming disks may bias the measurements of disk properties such

  16. Gas-Phase Molecular Dynamics: High Resolution Spectroscopy and Collision Dynamics of Transient Species

    SciTech Connect

    Hall G. E.; Goncharov, V.

    2012-05-29

    This research is carried out as part of the Gas-Phase Molecular Dynamics program in the Chemistry Department at Brookhaven National Laboratory. Chemical intermediates in the elementary gas-phase reactions involved in combustion chemistry are investigated by high resolution spectroscopic tools. Production, reaction, and energy transfer processes are investigated by transient, double resonance, polarization and saturation spectroscopies, with an emphasis on technique development and connection with theory, as well as specific molecular properties.

  17. Gas-Phase Molecular Dynamics: High Resolution Spectroscopy and Collision Dynamics of Transient Species

    SciTech Connect

    Hall, G.E.

    2011-05-31

    This research is carried out as part of the Gas-Phase Molecular Dynamics program in the Chemistry Department at Brookhaven National Laboratory. Chemical intermediates in the elementary gas-phase reactions involved in combustion chemistry are investigated by high resolution spectroscopic tools. Production, reaction, and energy transfer processes are investigated by transient, double resonance, polarization and saturation spectroscopies, with an emphasis on technique development and connection with theory, as well as specific molecular properties.

  18. Reconstructive tomography in gas dynamics and plasma physics

    NASA Astrophysics Data System (ADS)

    Pikalov, Valerii Vladimirovich; Preobrazhenskii, Nikolai Georgievich

    The physics, mathematics, and principal applications of reconstructive tomography are examined with particular reference to problems in aerodynamics, gas dynamics, and plasma physics. The discussion covers fluoroscopic tomography and tomosynthesis, tomography with a priori constraints, mathematical formalisms of the linear tomography of asymmetric objects, theoretical principles of the linear tomography of two-dimensional objects, and algorithms of two-dimensional linear tomography. Some problems in three-dimensional linear tomography are also discussed.

  19. 3D printing of gas jet nozzles for laser-plasma accelerators

    NASA Astrophysics Data System (ADS)

    Döpp, A.; Guillaume, E.; Thaury, C.; Gautier, J.; Ta Phuoc, K.; Malka, V.

    2016-07-01

    Recent results on laser wakefield acceleration in tailored plasma channels have underlined the importance of controlling the density profile of the gas target. In particular, it was reported that the appropriate density tailoring can result in improved injection, acceleration, and collimation of laser-accelerated electron beams. To achieve such profiles, innovative target designs are required. For this purpose, we have reviewed the usage of additive layer manufacturing, commonly known as 3D printing, in order to produce gas jet nozzles. Notably we have compared the performance of two industry standard techniques, namely, selective laser sintering (SLS) and stereolithography (SLA). Furthermore we have used the common fused deposition modeling to reproduce basic gas jet designs and used SLA and SLS for more sophisticated nozzle designs. The nozzles are characterized interferometrically and used for electron acceleration experiments with the Salle Jaune terawatt laser at Laboratoire d'Optique Appliquée.

  20. 3D printing of gas jet nozzles for laser-plasma accelerators.

    PubMed

    Döpp, A; Guillaume, E; Thaury, C; Gautier, J; Ta Phuoc, K; Malka, V

    2016-07-01

    Recent results on laser wakefield acceleration in tailored plasma channels have underlined the importance of controlling the density profile of the gas target. In particular, it was reported that the appropriate density tailoring can result in improved injection, acceleration, and collimation of laser-accelerated electron beams. To achieve such profiles, innovative target designs are required. For this purpose, we have reviewed the usage of additive layer manufacturing, commonly known as 3D printing, in order to produce gas jet nozzles. Notably we have compared the performance of two industry standard techniques, namely, selective laser sintering (SLS) and stereolithography (SLA). Furthermore we have used the common fused deposition modeling to reproduce basic gas jet designs and used SLA and SLS for more sophisticated nozzle designs. The nozzles are characterized interferometrically and used for electron acceleration experiments with the Salle Jaune terawatt laser at Laboratoire d'Optique Appliquée. PMID:27475557

  1. Electron Density Measurements in UV-Preionized XeCl and CO2 Laser Gas Mixtures

    NASA Astrophysics Data System (ADS)

    Takagi, Shigeyuki; Sato, Saburo; Goto, Tatsumi

    1989-11-01

    A Langmuir probe technique has been used to measure electron densities and temperatures in UV-preionized XeCl excimer and CO2 laser gas mixtures in a laser tube. For this experiment, only pin electrodes (preionization sparks) were operated with no discharge between the main electrodes. The measured electron densities were about 108 cm-3 in both the excimer and CO2 laser gases, compared with 1010 cm-3 in pure He gas. The electron density was found to increase due to the proximity of the main electrodes. The coefficients of absorption for excimer and CO2 laser gas were obtained from the characteristics of the electron densities vs the distance from the UV source. Based on the absorption coefficient for XeCl, 0.9 cm-1 atm-1, we propose pin-electrode arrangements for spatially uniform preionization.

  2. Efficient gas lasers pumped by run-away electron preionized diffuse discharge

    NASA Astrophysics Data System (ADS)

    Panchenko, Alexei N.; Lomaev, Mikhail I.; Panchenko, Nikolai A.; Tarasenko, Victor F.; Suslov, Alexey I.

    2015-02-01

    It was shown that run-away electron preionized volume (diffuse) discharge (REP DD) can be used as an excitation source of active gas mixtures at elevated pressures and can produce laser emission. We report experimental and calculated results of application of the REP DD for excitation of different active gas mixtures. It was shown that the REP DD allows to obtain efficient lasing stimulated radiation in the IR, visible and UV spectral ranges. Kinetic model of the REP DD in mixtures of nitrogen with SF6 is developed allowing to predict the radiation parameters of nitrogen laser at 337.1 nm. Promising prospects of REP DD employment for exciting a series of gas lasers was demonstrated. Lasing was obtained on molecules N2, HF, and DF with the efficiency close to the limiting value. It was established that the REP DD is most efficient for pumping lasers with the mixtures comprising electro-negative gases.

  3. Effects of superficial gas velocity on process dynamics in bioreactors

    NASA Astrophysics Data System (ADS)

    Devi, T. T.; Kumar, B.

    2014-06-01

    Present work analyzes the flow hydrodynamics and mass transfer mechanisms in double Rushton and CD-6 impeller on wide range (0.0075-0.25 m/s) of superficial gas velocity ( v g) in a gas-liquid phase bioreactor by employing computational fluid dynamics (CFD) technique. The volume averaged velocity magnitude and dissipation rate are found higher with increasing superficial gas velocity. Higher relative power draw ( P g/ P 0) is predicted in CD-6 than the Rushton impeller but no significant difference in volume averaged mass transfer coefficient ( k L a) observed between these two types of impeller. The ratio of power draw with mass transfer coefficient has been found higher in CD-6 impeller (25-50 %) than the Rushton impeller.

  4. Modeling of neutral gas dynamics in high-density plasmas

    NASA Astrophysics Data System (ADS)

    Canupp, Patrick Wellington

    This thesis describes a physical model of chemically reactive neutral gas flow and discusses numerical solutions of this model for the flow in an inductively coupled plasma etch reactor. To obtain these solutions, this research develops an efficient, implicit numerical method. As a result of the enhanced numerical stability of the scheme, large time steps advance the solution from initial conditions to a final steady state in fewer iterations and with less computational expense than simpler explicit methods. This method would incorporate suitably as a module in currently existing large scale plasma simulation tools. In order to demonstrate the accuracy of the numerical technique, this thesis presents results from two simulations of flows that possess theoretical solutions. The first case is the inviscid flow of a gas through a converging nozzle. A comparison of the numerical solution to isentropic flow theory shows that the numerical technique capably captures the essential flow features of this environment. The second case is the Couette flow of a gas between two parallel plates. The simulation results compare well with the exact solution for this flow. After establishing the accuracy of the numerical technique, this thesis discusses results for the flow of chemically reactive gases in a chlorine plasma etch reactor. This research examines the influence of the plasma on the neutral gas and the dynamics exhibited by the neutral gas in the reactor. This research finds that the neutral gas temperature strongly depends on the rate at which inelastic, electron-impact dissociation reactions occur and on atomic chlorine wall recombination rates. Additionally, the neutral gas Aow in the reactor includes a significant mass flux of etch product from the wafer surface. Resolution of these effects is useful for neutral gas simulation. Finally, this thesis demonstrates that continuum fluid models provide reasonable accuracy for these low pressure reactor flows due to the fact

  5. Laser gas assisted treatment of AISI H12 tool steel and corrosion properties

    NASA Astrophysics Data System (ADS)

    Yilbas, B. S.; Toor, Ihsan-ul-Haq; Malik, Jahanzaib; Patel, F.

    2014-03-01

    Laser gas assisted treatment of AISI H12 tool steel surface is carried out and the electrochemical response of the laser treated surface is investigated. Morphological and metallurgical changes in the treated layer are examined using a scanning electron microscope, energy dispersive spectroscopy, and X-ray diffraction. Potentiodynamic polarization tests are carried out for untreated and laser treated specimen in 0.2 M NaCl solution at room temperature. It is found that the laser treated AISI H12 workpiece surfaces exhibit higher corrosion resistance as compared to untreated specimen as confirmed by lower corrosion rate, higher pitting potential, and lower passive current density.

  6. Channel Formation in Long Laser Pulse Interaction with a Helium Gas Jet

    SciTech Connect

    Malka, V.; De Wispelaere, E.; Amiranoff, F.; Baton, S.; Bonadio, R.; Coulaud, C.; Haroutunian, R.; Modena, A.; Puissant, D.; Stenz, C.; Hueller, S.; Casanova, M.

    1997-10-01

    Experimental realization of an electron density channel created by a low intensity laser in a helium gas jet is presented. The long (2.5mm) plasma channel is fully ionized and thus prevents undesirable refraction effects for propagation and guiding of a subsequent high intensity laser pulse. The channel parameters are easily controlled and well suited for laser guiding. The radial plasma expansion and the temperature evolution have been measured and compared to hydrodynamic simulations which show that the plasma expansion is governed by a thermal wave during the laser pulse. {copyright} {ital 1997} {ital The American Physical Society}

  7. Universal Loss Dynamics in a Unitary Bose Gas

    NASA Astrophysics Data System (ADS)

    Eismann, Ulrich; Khaykovich, Lev; Laurent, Sébastien; Ferrier-Barbut, Igor; Rem, Benno S.; Grier, Andrew T.; Delehaye, Marion; Chevy, Frédéric; Salomon, Christophe; Ha, Li-Chung; Chin, Cheng

    2016-04-01

    The low-temperature unitary Bose gas is a fundamental paradigm in few-body and many-body physics, attracting wide theoretical and experimental interest. Here, we present experiments performed with unitary 133Cs and 7Li atoms in two different setups, which enable quantitative comparison of the three-body recombination rate in the low-temperature domain. We develop a theoretical model that describes the dynamic competition between two-body evaporation and three-body recombination in a harmonically trapped unitary atomic gas above the condensation temperature. We identify a universal "magic" trap depth where, within some parameter range, evaporative cooling is balanced by recombination heating and the gas temperature stays constant. Our model is developed for the usual three-dimensional evaporation regime as well as the two-dimensional evaporation case, and it fully supports our experimental findings. Combined 133Cs and 7Li experimental data allow investigations of loss dynamics over 2 orders of magnitude in temperature and 4 orders of magnitude in three-body loss rate. We confirm the 1 /T2 temperature universality law. In particular, we measure, for the first time, the Efimov inelasticity parameter η*=0.098 (7 ) for the 47.8-G d -wave Feshbach resonance in 133Cs. Our result supports the universal loss dynamics of trapped unitary Bose gases up to a single parameter η*.

  8. Dynamic gas bearing turbine technology in hydrogen plants

    NASA Astrophysics Data System (ADS)

    Ohlig, Klaus; Bischoff, Stefan

    2012-06-01

    Dynamic Gas Bearing Turbines - although applied for helium refrigerators and liquefiers for decades - experienced limitations for hydrogen applications due to restrictions in axial bearing capacity. With a new design concept for gas bearing turbines developed in 2004, axial bearing capacity was significantly improved enabling the transfer of this technology to hydrogen liquefiers. Prior to roll-out of the technology to industrial plants, the turbine bearing technology passed numerous tests in R&D test benches and subsequently proved industrial scale demonstration at Linde Gas' hydrogen liquefier in Leuna, Germany. Since its installation, this turbine has gathered more than 16,000 successful operating hours and has outperformed its oil bearing brother in terms of performance, maintainability as well as reliability. The present paper is based on Linde Kryotechnik AG's paper published in the proceedings of the CEC 2009 concerning the application of Dynamic Gas Bearing Turbines in hydrogen applications. In contrast to the former paper, this publication focuses on the steps towards final market launch and more specifically on the financial benefits of this turbine technology, both in terms of capital investment as well as operating expenses.

  9. Dynamic Absorption Model for Off-Gas Separation

    SciTech Connect

    Veronica J. Rutledge

    2011-07-01

    Modeling and simulations will aid in the future design of U.S. advanced reprocessing plants for the recovery and recycle of actinides in used nuclear fuel. The specific fuel cycle separation process discussed in this report is the off-gas treatment system. The off-gas separation consists of a series of scrubbers and adsorption beds to capture constituents of interest. Dynamic models are being developed to simulate each unit operation involved so each unit operation can be used as a stand-alone model and in series with multiple others. Currently, a rate based, dynamic absorption model is being developed in gPROMS software. Inputs include liquid and gas stream constituents, column properties, liquid and gas phase reactions, number of stages, and inlet conditions. It simulates multiple component absorption with countercurrent flow and accounts for absorption by mass transfer and chemical reaction. The assumption of each stage being a discrete well-mixed entity was made. Therefore, the model is solved stagewise. The simulation outputs component concentrations in both phases as a function of time from which the rate of absorption is determined. Temperature of both phases is output as a function of time also. The model will be used able to be used as a standalone model in addition to in series with other off-gas separation unit operations. The current model is being generated based on NOx absorption; however, a future goal is to develop a CO2 specific model. The model will have the capability to be modified for additional absorption systems. The off-gas models, both adsorption and absorption, will be made available via the server or web for evaluation by customers.

  10. A comparison of the physics of Gas Tungsten Arc Welding (GTAW), Electron Beam Welding (EBW), and Laser Beam Welding (LBW)

    NASA Technical Reports Server (NTRS)

    Nunes, A. C., Jr.

    1985-01-01

    The physics governing the applicability and limitations of gas tungsten arc (GTA), electron beam (EB), and laser beam (LB) welding are compared. An appendix on the selection of laser welding systems is included.

  11. Study on elucidation of bactericidal effects induced by laser beam irradiation Measurement of dynamic stress on laser irradiated surface

    NASA Astrophysics Data System (ADS)

    Furumoto, Tatsuaki; Kasai, Atsushi; Tachiya, Hiroshi; Hosokawa, Akira; Ueda, Takashi

    2010-09-01

    In dental treatment, many types of laser beams have been used for various surgical treatments, and the influences of laser beam irradiation on bactericidal effect have been investigated. However, most of the work has been performed by irradiating to an agar plate with the colony of bacteria, and very few studies have been reported on the physical mechanism of bactericidal effects induced by laser beam irradiation. This paper deals with the measurement of dynamic stress induced in extracted human enamel by irradiation with Nd:YAG laser beams. Laser beams can be delivered to the enamel surface through a quartz optical fiber. Dynamic stress induced in the specimen using elastic wave propagation in a cylindrical long bar made of aluminum alloy is measured. Laser induced stress intensity is evaluated from dynamic strain measured by small semiconductor strain gauges. Carbon powder and titanium dioxide powder were applied to the human enamel surface as absorbents. Additionally, the phenomenon of laser beam irradiation to the human enamel surface was observed with an ultrahigh speed video camera. Results showed that a plasma was generated on the enamel surface during laser beam irradiation, and the melted tissues were scattered in the vertical direction against the enamel surface with a mushroom-like wave. Averaged scattering velocity of the melted tissues was 25.2 m/s. Induced dynamic stress on the enamel surface increased with increasing laser energy in each absorbent. Induced dynamic stresses with titanium dioxide powder were superior to those with carbon powder. Induced dynamic stress was related to volume of prepared cavity, and induced stress for the removal of unit volume of human enamel was 0.03 Pa/mm 3.

  12. Dynamic characterization of an industrial burner in working conditions by laser Doppler vibrometry

    NASA Astrophysics Data System (ADS)

    Paone, Nicola; Revel, Gian M.

    1998-06-01

    The paper presents the application of a laser Doppler vibrometer in order to characterize the dynamic behavior of a burner during normal working conditions. The burner is a 1:4 scale model of a real CH4 industrial burner for gas turbines, with a 120 kW power. A first series of test has been performed in order to determine the resonance frequencies of burner components, in such a way as to correlate the results achieved in working conditions with the characteristics of the structure. In a second series of tests the burner has been tested in exercise, firstly with only a cold jet of air flowing from the nozzle, then in real working conditions. In each test both vibration and acoustic measurements have been performed, in order to find correlation between combustion noise and structural vibrations. The laser Doppler vibrometer has been chosen to carry out measurements on the burner because of its capability of 'remotely' and non-intrusively determine vibrations. In order to assess the accuracy of vibrometer measurements through the flame, a theoretical model previously developed by the authors has been employed, which describes the interactions between laser interferometer and refractive index variations induced by the flame, in such a way as to estimate interfering and modifying inputs of the measurements system.

  13. Measurement of ammonia skin gas using a mid-infrared Pb-salt tunable diode laser

    NASA Astrophysics Data System (ADS)

    Clasp, Trocia N.; Kaimal, Sindhu; Reeve, Scott W.; Burns, William A.

    2010-04-01

    The concentration of Ammonia excreted through human skin has recently been measured using a gas chromatograph equipped with a flame ionization detector (GC-FID) by a group from Nagoya, Japan. These emissions, referred to as ammonia skin gas, were determined to be 1.7+/-.4 ng/cm3 for healthy subjects in the study. To achieve greater molecule specificity, sensitivity, as well as add a real time capability, we are investigating the potential of a mid IR laser spectrometer, consisting of a Pb-salt diode laser coupled with a low volume 75 meter Herriott gas sample cell, to perform real time ammonia diagnostic measurements. Here we will present a series of preliminary ammonia skin gas measurements obtained with this mid IR laser system.

  14. High pressure gas laser technology for atmospheric remote sensing

    NASA Technical Reports Server (NTRS)

    Javan, A.

    1980-01-01

    The development of a fixed frequency chirp-free and highly stable intense pulsed laser made for Doppler wind velocity measurements with accurate ranging is described. Energy extraction from a high pressure CO2 laser at a tunable single mode frequency is also examined.

  15. Reinjection of transmitted laser light into laser-produced plasma for efficient laser ignition.

    PubMed

    Endo, Takuma; Takenaka, Yuhei; Sako, Yoshiyuki; Honda, Tomohisa; Johzaki, Tomoyuki; Namba, Shinichi

    2016-02-10

    For improving the laser absorption efficiency in laser ignition, the transmitted laser light was returned to the laser-produced plasma by using a corner cube. In the experiments, the transmitted light was reinjected into the plasma at different times. The laser absorption efficiency was found to be substantially improved when the transmitted light was reinjected into the plasma after adequate plasma expansion. Furthermore, through visualization experiments on gas-dynamics phenomena, it was found that the reinjection of the transmitted light affected not only the laser absorption efficiency but also the gas dynamics after breakdown, and thereby the initial flame kernel development. PMID:26906388

  16. Natural Hydrofracturing, Dynamic Permeability, and Gas recovery (Invited)

    NASA Astrophysics Data System (ADS)

    Cathles, L. M.

    2013-12-01

    Hydrofracturing has suddenly transformed the hydrocarbon industry, turning even quite recent supply projections upside down. The miracle is that it can work so well. It will take time to understand the processes which allow oil and gas to be so effectively recovered from extremely impermeable carbonate and shale formations. Two factors seem particularly important: First, nature has already gas-fractured the shales during hydrocarbon generation. In the case of the Marcellus, the maturation process left the residual organic matter a froth of very small (2-5 nm) connected gas pockets, which drained into larger (perhaps now closed) fractures, and then into the surrounding formations where they produced joints. Second, the organic surfaces tend to be gas-wet and hydrophobic, whereas the silicate surfaces in the shale tend to be the reverse (hydrophilic and gas-phobic). The fluid phase interactions are thus complicated. The talk will briefly review these aspects of the complex hydrofracturing environment, and then explore whether the dynamic permeability produced when the hydrocarbons were expelled could be retained or recovered during a second, human, hydrofracturing.

  17. Computational simulation of hematocrit effects on arterial gas embolism dynamics

    PubMed Central

    Mukundakrishnan, Karthik; Ayyaswamy, Portonovo S.; Eckmann, David M.

    2012-01-01

    Background Recent computational investigations have shed light into the various hydrodynamic mechanisms at play during arterial gas embolism that may result in endothelial cell (EC) injury. Other recent studies have suggested that variations in hematocrit level may play an important role in determining the severity of neurological complications due to decompression sickness associated with gas embolism. Methods Towards developing a comprehensive picture, we have computationally modeled the effect of hematocrit variations on the motion of a nearly occluding gas bubble in arterial blood vessels of various sizes. The computational methodology is based on an axisymmetric finite difference immersed boundary numerical method to precisely track the blood-bubble dynamics of the interface. Hematocrit variations are taken to be in the range 0.2–0.6. The chosen blood vessel sizes correspond to small arteries, and small and large arterioles in normal humans. Results Relevant hydrodynamic interactions between the gas bubble and EC-lined vessel lumen have been characterized and quantified as a function of hematocrit levels. In particular, the variations in shear stress, spatial and temporal shear stress gradients, and the gap between bubble and vascular endothelium surfaces that contribute to EC injury have been computed. Discussion The results suggest that in small arteries, the deleterious hydrodynamic effects of the gas embolism on EC-lined cell wall are significantly amplified as the hematocrit levels increase. However, such pronounced variations with hematocrit levels are not observed in the arterioles. PMID:22303587

  18. Emission features and expansion dynamics of nanosecond laser ablation plumes at different ambient pressures

    SciTech Connect

    Farid, N.; Harilal, S. S. Hassanein, A.; Ding, H.

    2014-01-21

    The influence of ambient pressure on the spectral emission features and expansion dynamics of a plasma plume generated on a metal target has been investigated. The plasma plumes were generated by irradiating Cu targets using 6 ns, 1064 nm pulses from a Q-switched Nd:YAG laser. The emission and expansion dynamics of the plasma plumes were studied by varying air ambient pressure levels ranging from vacuum to atmospheric pressure. The ambient pressure levels were found to affect both the line intensities and broadening along with the signal to background and signal to noise ratios and the optimum pressure conditions for analytical applications were evaluated. The characteristic plume parameters were estimated using emission spectroscopy means and noticed that the excitation temperature peaked ∼300 Torr, while the electron density showed a maximum ∼100 Torr. Fast-gated images showed a complex interaction between the plume and background air leading to changes in the plume geometry with pressure as well as time. Surface morphology of irradiated surface showed that the pressure of the ambient gas affects the laser-target coupling significantly.

  19. Theoretical and experimental study of elliptical Gaussian-mode size dynamics in ring lasers

    SciTech Connect

    Bretenaker, F.; Le Floch, A.; Tache, J.P. )

    1990-04-01

    In the framework of the {ital ABCD} ray matrix formalism, a theoretical model is proposed to describe the fundamental TEM{sub 00} elliptical Gaussian-mode size variations due to frequency-dependent lenslike effects in ring lasers. Two different mode size dynamics are predicted in the sagittal and tangential planes of the planar ring cavity, leading to the existence of different critical geometries in each plane, i.e., geometries for which the tangential or sagittal mode size at a given point becomes independent of the focal length. The frequency-dependent diffraction losses associated with these mode size variations predict rather complex asymmetries in the output power profiles in usual ring lasers, even in the case of a single-isotope gas mixture. Moreover, a fully critical geometry'' is predicted for which sagittal and tangential critical geometries occur simultaneously, making the two mode sizes independent of the lenses. A first type of experiment confirms the existence of the sagittal and tangential double dynamics and the role played by resonant diffraction thanks to the diffracted-light-spectroscopy technique. A second type of experiment proves the existence of the fully critical geometry. The theoretical predictions are in very good agreement with the experimental results.

  20. Heat Transfer And Vapor Dynamics Induced By Nanosecond Laser Ablation Of Titanium Target

    SciTech Connect

    Hamadi, F.; Amara, E. H.; Mezaoui, D.

    2008-09-23

    A numerical modelling describing a pulsed nanosecond laser interaction with a titanium target is presented, resulting in the study of the plume expansion in vacuum or in background gas, using the species transport model available in Fluent computational fluid dynamics code. The heat transfers in the solid target and the molten material are modeled using an enthalpy formulation for the solid-liquid phase changing. The effect of laser fluences is investigated, and results are presented as a function of time. Moreover, the plasma or the vapour dynamics is calculated by solving a set of Navier-Stokes equations. The plasma absorption by inverse Bremsstrahlung, the ionization states and the density profiles of the Titanium ions and electrons in the plume are interactively included in the Fluent calculation process by the mean of User Defined Functions (UDFs) used in order to take into account the specificity of our problem. The ionization is computed by solving the Saha-Eggert equation assuming local thermodynamic equilibrium (LTE) conditions.

  1. Detection of trace concentrations of helium and argon in gas mixtures by laser-induced breakdown spectroscopy

    NASA Astrophysics Data System (ADS)

    McNaghten, E. D.; Parkes, A. M.; Griffiths, B. C.; Whitehouse, A. I.; Palanco, S.

    2009-10-01

    We report what we believe to be the first demonstration of the detection of trace quantities of helium and argon in binary and ternary gas mixtures with nitrogen by laser-induced breakdown spectroscopy (LIBS). Although significant quenching of helium transitions due to collisional deactivation of excited species was observed, it was found that losses in analytical sensitivity could be minimized by increasing the laser irradiance and decreasing the pressure at which the analyses were performed. In consequence, limits of detection of parts-per-million and tens of parts-per-million and linear dynamic ranges of several orders of magnitude in analyte concentration were obtained. The results of this study suggest that LIBS may have potential applications in the detection of other noble gases at trace concentrations.

  2. Gas-Phase Molecular Dynamics: Theoretical Studies in Spectroscopy and Chemical Dynamics

    SciTech Connect

    Yu, H.G.; Muckerman, J.T.

    2010-06-01

    The goal of this program is the development and application of computational methods for studying chemical reaction dynamics and molecular spectroscopy in the gas phase. We are interested in developing rigorous quantum dynamics algorithms for small polyatomic systems and in implementing approximate approaches for complex ones. Particular focus is on the dynamics and kinetics of chemical reactions and on the rovibrational spectra of species involved in combustion processes. This research also explores the potential energy surfaces of these systems of interest using state-of-the-art quantum chemistry methods.

  3. Gas-Phase Molecular Dynamics: Theoretical Studies In Spectroscopy and Chemical Dynamics

    SciTech Connect

    Yu H. G.; Muckerman, J.T.

    2012-05-29

    The main goal of this program is the development and application of computational methods for studying chemical reaction dynamics and molecular spectroscopy in the gas phase. We are interested in developing rigorous quantum dynamics algorithms for small polyatomic systems and in implementing approximate approaches for complex ones. Particular focus is on the dynamics and kinetics of chemical reactions and on the rovibrational spectra of species involved in combustion processes. This research also explores the potential energy surfaces of these systems of interest using state-of-the-art quantum chemistry methods, and extends them to understand some important properties of materials in condensed phases and interstellar medium as well as in combustion environments.

  4. A comparison of gas temperatures measured by ultraviolet laser scattering in atmospheric plasma sources

    NASA Astrophysics Data System (ADS)

    Sommers, Bradley S.; Adams, Steven F.

    2015-12-01

    A laser scattering system utilizing an ultraviolet laser with a triple grating spectrometer has been assembled in order to measure gas temperature in atmospheric plasma sources. Such laser scattering interactions offer a non-invasive technique for investigating atmospheric microplasma sources, which have potential applications in remote optical sensing, materials processing, and environmental decontamination. This particular system is unique in that it utilizes a ultraviolet laser line (266 nm), which increases the cross section for Rayleigh and Raman scattering by a factor of 16 in comparison to the more common 532 nm laser operating in the visible range. In this work, the laser scattering system is used to directly compare the rotational gas temperature (T r) and gas kinetic temperature (T g) in two different atmospheric plasma sources [1]: a direct current plasma jet operating on nitrogen and [2] a conventional pin-pin glow microdischarge in air. Results show agreement between T r and T g both in the low temperature afterglow of the plasma jet (300-700 K) and the hot center of the atmospheric glow (1500-2000 K). These observations lend credence to the common assumption of rotational relaxation in atmospheric plasmas and validate the ultraviolet laser diagnostic for future application in atmospheric microplasma sources.

  5. Design of gas circulation system in the high power fast axial flow CO2 laser

    NASA Astrophysics Data System (ADS)

    Huang, Hongyan; Wang, Youqing; Li, Qing; Jia, Xinting

    2009-08-01

    Increasing the output power of the fast axial flow CO2 laser requires a proportional growth of the mass flow with the laser power for convective cooling of the active laser medium. The previous research on high power CO2 laser was mostly focused on gas discharge. However, little attention was focused on the gas circulation system, which is also an essential technology to ensure the long time stable work of the high power fast axial flow CO2 laser. Based on the analysis of the characteristics of the 7 KW fast axial flow CO2 laser, expounded the important role of the gas circulation system, and then analyzed the parameters, the structure and the design of the system. After that, this paper compared various types of blowers and heat exchangers, chose magnetic levitation radial turbine blower and rectangle finned heat exchanger, in light of the prominent performance and compact structure. Further more, this paper also supplied the methods of the blower and heat exchanger selection and design. The results indicate that the magnetic levitation radial turbine blower and rectangle finned heat exchanger which have been chosen are suitable to the 7 kW fast axial flow CO2 laser.

  6. LASER TRIGGERED GAS SWITCHES UTILIZING BEAM TRANSPORT THROUGH 1 MO-cm DEIONIZED WATER.

    SciTech Connect

    Woodworth, Joseph Ray; Lehr, Jane; Blickem, James R.; Wallace, Zachariah R.; Anaya, Victor Jr; Corley, John P; Lott, John; Hodge, Keith; Zameroski, Nathan D.

    2005-11-01

    We report on the successful attempts to trigger high voltage pressurized gas switches by utilizing beam transport through 1 MO-cm deionized water. The wavelength of the laser radiation was 532 nm. We have investigated Nd: YAG laser triggering of a 6 MV, SF6 insulated gas switch for a range of laser and switch parameters. Laser wavelength of 532 nm with nominal pulse lengths of 10 ns full width half maximum (FWHM) were used to trigger the switch. The laser beam was transported through 67 cm-long cell of 1 MO-cm deionized water constructed with anti reflection UV grade fused silica windows. The laser beam was then focused to form a breakdown arc in the gas between switch electrodes. Less than 10 ns jitter in the operation of the switch was obtained for laser pulse energies of between 80-110 mJ. Breakdown arcs more than 35 mm-long were produced by using a 70 cm focusing optic.

  7. Indirect Gas Species Monitoring Using Tunable Diode Lasers

    DOEpatents

    Von Drasek, William A.; Saucedo, Victor M.

    2005-02-22

    A method for indirect gas species monitoring based on measurements of selected gas species is disclosed. In situ absorption measurements of combustion species are used for process control and optimization. The gas species accessible by near or mid-IR techniques are limited to species that absorb in this spectral region. The absorption strength is selected to be strong enough for the required sensitivity and is selected to be isolated from neighboring absorption transitions. By coupling the gas measurement with a software sensor gas, species not accessible from the near or mid-IR absorption measurement can be predicted.

  8. The development of a pulsed laser imaging system for natural gas leak detection

    NASA Astrophysics Data System (ADS)

    Kulp, Thomas J.

    The detection of gas leaks represents a critical operation performed regularly by the gas industry to maintain the integrity and safety of its vast network of piping, both above and below the ground. We are developing a technology that allows the real-time imaging of gas plumes in a television format. Termed backscatter absorption gas imaging (BAGI), the technique operates by illuminating a scene with infrared laser radiation having a wavelength that is absorbed by the gas to be detected (in this case, methane). Backscattered laser radiation is used to create a video image of the scene. If a leak of the target gas is present in the field-of-view of the camera, it attenuates a portion of the backscatter and creates a dark cloud in the video picture. The specific purpose of this project is to investigate a new method of accomplishing BAGI using a pulsed laser source. The pulsed laser imager under development in this project is expected to have a range (greater than or equal to 40 m) and sensitivity (less than 10 ppm-m) that will surpass the respective attributes of a scanned continuous wave laser imager. The pulsed system will operate by flooding (rather than scanning) the imaged scene with pulses of laser radiation. Imaging will be accomplished using a focal-plane array camera that operates in a snapshot format. The higher power of the pulsed laser source and the more effective collection optics of the focal-plane array-based receiver will allow the performance enhancements to be achieved.

  9. Gas-Phase Lasers - a Historical Perspective in Relation to the GEC

    NASA Astrophysics Data System (ADS)

    Hays, Gerry

    1997-10-01

    Understanding of gas-phase lasers inevitably involves an expertise in many of the specialties of the GEC community - especially homogenous and heterogeneous kinetics, collision cross-sections, gas breakdown physics and fundamental swarm parameters. The GEC community decided early in the evolution of gas-phase lasers to include papers on this topic and the result was many years of contributions to the evolution of and improvement in our understanding of this important class of lasers. Many of the ground-breaking results in gas laser technology were presented at the GEC over the last 3 decades as the traditional rare-gas atomic physics and low-temperature plasma groups turned their attention to parameters of interest to the laser modelers and experimenters. This paper will trace the development of this field, especially as it pertained to the GEC. Some of the key results will be highlighted, together with some of the unpublished trivia and anecdotal incidents in order to capture the flavor of the rapid developments in the early days. The talk will include speculation as to the direction this field is taking, and some suggestions as to opportunities. This work supported by the United States Department of Energy under Contract DE-AC04-94AL85000. Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed-Martin Company, for the United States Department of Energy.

  10. Laser-induced breakdown spectroscopy for in-cylinder equivalence ratio measurements in laser-ignited natural gas engines.

    PubMed

    Joshi, Sachin; Olsen, Daniel B; Dumitrescu, Cosmin; Puzinauskas, Paulius V; Yalin, Azer P

    2009-05-01

    In this contribution we present the first demonstration of simultaneous use of laser sparks for engine ignition and laser-induced breakdown spectroscopy (LIBS) measurements of in-cylinder equivalence ratios. A 1064 nm neodynium yttrium aluminum garnet (Nd:YAG) laser beam is used with an optical spark plug to ignite a single cylinder natural gas engine. The optical emission from the combustion initiating laser spark is collected through the optical spark plug and cycle-by-cycle spectra are analyzed for H(alpha)(656 nm), O(777 nm), and N(742 nm, 744 nm, and 746 nm) neutral atomic lines. The line area ratios of H(alpha)/O(777), H(alpha)/N(746), and H(alpha)/N(tot) (where N(tot) is the sum of areas of the aforementioned N lines) are correlated with equivalence ratios measured by a wide band universal exhaust gas oxygen (UEGO) sensor. Experiments are performed for input laser energy levels of 21 mJ and 26 mJ, compression ratios of 9 and 11, and equivalence ratios between 0.6 and 0.95. The results show a linear correlation (R(2) > 0.99) of line intensity ratio with equivalence ratio, thereby suggesting an engine diagnostic method for cylinder resolved equivalence ratio measurements. PMID:19470212

  11. Dynamic response of shear thickening fluid under laser induced shock

    SciTech Connect

    Wu, Xianqian Yin, Qiuyun; Huang, Chenguang; Zhong, Fachun

    2015-02-16

    The dynamic response of the 57 vol./vol. % dense spherical silica particle-polyethylene glycol suspension at high pressure was investigated through short pulsed laser induced shock experiments. The measured back free surface velocities by a photonic Doppler velocimetry showed that the shock and the particle velocities decreased while the shock wave transmitted in the shear thickening fluid (STF), from which an equation of state for the STF was obtained. In addition, the peak stress decreased and the absorbed energy increased rapidly with increasing the thickness for a thin layer of the STF, which should be attributed to the impact-jammed behavior through compression of particle matrix, the deformation or crack of the hard-sphere particles, and the volume compression of the particles and the polyethylene glycol.

  12. Lattice gas simulations of dynamical geometry in two dimensions

    NASA Astrophysics Data System (ADS)

    Klales, Anna; Cianci, Donato; Needell, Zachary; Meyer, David A.; Love, Peter J.

    2010-10-01

    We present a hydrodynamic lattice gas model for two-dimensional flows on curved surfaces with dynamical geometry. This model is an extension to two dimensions of the dynamical geometry lattice gas model previously studied in one dimension. We expand upon a variation of the two-dimensional flat space Frisch-Hasslacher-Pomeau (FHP) model created by Frisch [Phys. Rev. Lett.PRLTAO0031-9007 56, 1505 (1986)]10.1103/PhysRevLett.56.1505 and independently by Wolfram, and modified by Boghosian [Philos. Trans. R. Soc. London, Ser. A 360, 333 (2002)]10.1098/rsta.2001.0933. We define a hydrodynamic lattice gas model on an arbitrary triangulation whose flat space limit is the FHP model. Rules that change the geometry are constructed using the Pachner moves, which alter the triangulation but not the topology. We present results on the growth of the number of triangles as a function of time. Simulations show that the number of triangles grows with time as t1/3 , in agreement with a mean-field prediction. We also present preliminary results on the distribution of curvature for a typical triangulation in these simulations.

  13. Lattice gas simulations of dynamical geometry in two dimensions.

    PubMed

    Klales, Anna; Cianci, Donato; Needell, Zachary; Meyer, David A; Love, Peter J

    2010-10-01

    We present a hydrodynamic lattice gas model for two-dimensional flows on curved surfaces with dynamical geometry. This model is an extension to two dimensions of the dynamical geometry lattice gas model previously studied in one dimension. We expand upon a variation of the two-dimensional flat space Frisch-Hasslacher-Pomeau (FHP) model created by Frisch [Phys. Rev. Lett. 56, 1505 (1986)] and independently by Wolfram, and modified by Boghosian [Philos. Trans. R. Soc. London, Ser. A 360, 333 (2002)]. We define a hydrodynamic lattice gas model on an arbitrary triangulation whose flat space limit is the FHP model. Rules that change the geometry are constructed using the Pachner moves, which alter the triangulation but not the topology. We present results on the growth of the number of triangles as a function of time. Simulations show that the number of triangles grows with time as t(1/3), in agreement with a mean-field prediction. We also present preliminary results on the distribution of curvature for a typical triangulation in these simulations. PMID:21230410

  14. Dynamics of pulsed expansion of polyatomic gas cloud: Internal-translational energy transfer contribution

    SciTech Connect

    Morozov, A. A.

    2007-08-15

    Polyatomic gas cloud expansion under pulsed laser evaporation is studied on the basis of one-dimensional direct Monte Carlo simulation. The effect of rotational-translational (RT) and vibrational-translational (VT) energy transfer on dynamics of the cloud expansion is considered. Efficiency of VT energy transfer dependence on the amount of evaporated matter is discussed. To analyze VT energy transfer impact, the number of collisions per molecule during the expansion is calculated. The data are generally in good agreement with available analytical and numerical predictions. Dependencies of the effective number of vibrational degrees of freedom on the number of vibrationally inelastic collisions are obtained and generalized. The importance of the consideration of energy transfer from the internal degrees of freedom to the translational ones is illustrated by an example of pulsed laser evaporation of polytetrafluoroethylene (PTFE). Based on the obtained regularities, analysis of experimental data on pulsed laser evaporation of aniline is performed. The calculated aniline vibrational temperature correlates well with the experimentally measured one.

  15. Apply high-power fiber laser in oil/gas wells drilling

    NASA Astrophysics Data System (ADS)

    Jiang, Houman; Guo, Shaofeng; Chen, Minsun; Wang, Wenliang

    2015-05-01

    The concept of using lasers to drill through rock has been discussed in the oil and gas industries since the development of the high-power laser. To evaluate the possibility of fielding a laser drilling system, two laser-related problems have to be investigated. The first is the irradiation effects of laser upon rocks; the second is the effects in laser transmission from the source to the rock deep in the well. This transmission includes two stages: the first stage is the transmission inside a fiber, which is packaged in a cable and has about the same length with the well depth; the second stage refers to the transmission process when the laser leaves the fiber and some transforming optics and transmits to the rock surface, during which the well conditions may impose tough restrictions. In this paper, experiment results of laser irradiation upon siliceous sandstone and granite are reported, and the fiber transmission loss is simulated, considering the main absorbing or scattering mechanisms inside fiber. And the laser transmission from the fiber end to the rock surface, in my view, may impose great challenge on the laser drilling technology.

  16. Prepulse effect on intense femtosecond laser pulse propagation in gas

    SciTech Connect

    Giulietti, Antonio; Tomassini, Paolo; Galimberti, Marco; Giulietti, Danilo; Gizzi, Leonida A.; Koester, Petra; Labate, Luca; Ceccotti, Tiberio; D'Oliveira, Pascal; Auguste, Thierry; Monot, Pascal; Martin, Philippe

    2006-09-15

    The propagation of an ultrashort laser pulse can be affected by the light reaching the medium before the pulse. This can cause a serious drawback to possible applications. The propagation in He of an intense 60-fs pulse delivered by a Ti:sapphire laser in the chirped pulse amplification (CPA) mode has been investigated in conditions of interest for laser-plasma acceleration of electrons. The effects of both nanosecond amplified spontaneous emission and picosecond pedestals have been clearly identified. There is evidence that such effects are basically of refractive nature and that they are not detrimental for the propagation of a CPA pulse focused to moderately relativistic intensity. The observations are fully consistent with numerical simulations and can contribute to the search of a stable regime for laser acceleration.

  17. Characterization of a novel double-gas-jet laser plasma EUV source

    NASA Astrophysics Data System (ADS)

    de Bruijn, Rene; Bartnik, Andrzej; Fledderus, H. F.; Fiedorowicz, Henryk; Hegeman, Petra; Constantinescu, Raluca C.; Bijkerk, Fred

    2000-07-01

    A novel laser plasma EUV source geometry based on a (pulsed) double gas jet system has been characterized for utilization in EUV Lithography. The use of a secondary annular jet of a buffer gas in conjunction with the primary jet of target gas provides a considerable gain in EUV yield of an order of magnitude. The best CE data at 12.8 nm were obtained using xenon as target gas and hydrogen as buffer gas. The plasma source was driven using a short-wavelength KrF laser (0.9 J, 27 ns). Conversion efficiencies (CE) and EUV pulse shapes have been measured using calibrated Mo/Si multilayer mirrors and filtered junction diodes. A pinhole camera, equipped with a back illuminated CCD camera, was used to determine the plasma size in a wavelength range from 6 - 16 nm.

  18. Interferometric and schlieren characterization of the plasmas and shock wave dynamics during laser-triggered discharge in atmospheric air

    SciTech Connect

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

    2014-08-15

    This paper describes our efforts to reveal the underlying physics of laser-triggered discharges in atmospheric air using a Mach-Zehnder interferometer and schlieren photography. Unlike the hemispherical shock waves that are produced by laser ablation, bell-like morphologies are observed during laser-triggered discharges. Phase shifts are recovered from the interferograms at a time of 1000 ns by the 2D fast Fourier transform method, and then the values of the refractive index are deduced using the Abel inversion. An abundance of free electrons is expected near the cathode surface. The schlieren photographs visualize the formation of stagnation layers at ∼600 ns in the interaction zones of the laser- and discharge-produced plasmas. Multiple reflected waves are observed at later times with the development of shock wave propagations. Estimations using the Taylor-Sedov self-similar solution indicated that approximately 45.8% and 51.9% of the laser and electrical energies are transferred into the gas flow motions, respectively. Finally, numerical simulations were performed, which successfully reproduced the main features of the experimental observations, and provided valuable insights into the plasma and shock wave dynamics during the laser-triggered discharge.

  19. Excitation and dissociation of molecules by femtosecond IR laser radiation in the gas phase and on dielectric surfaces

    SciTech Connect

    Kompanets, V O; Laptev, Vladimir B; Makarov, Aleksandr A; Pigulskii, S V; Ryabov, Evgenii A; Chekalin, Sergei V

    2013-04-30

    This paper presents an overview of early studies and new experimental data on the effect of near-IR (0.8-1.8 {mu}m) and mid-IR (3.3-5.8 {mu}m) intense femtosecond (130-350 fs) laser pulses on polyatomic molecules in the gas phase and on the surface of substrates. We examine the vibrational dynamics of nine molecules containing a C=O chromophore group, which are initiated by resonance femtosecond IR laser radiation at a wavelength of {approx}5 {mu}m, and report measured characteristic times of intramolecular vibrational redistribution. The characteristic time of molecules containing a single C=O group lies in the range 2.4-20 ps and that of the Fe(CO){sub 5} and Cr(CO){sub 6} molecules lies in the nanosecond range ({approx}1.0 and {approx}1.5 ns, respectively). Carbon structures have been observed for the first time to result from the decomposition of (CF{sub 3}){sub 2}CCO molecules on the surface of metal fluorides under the effect of femtosecond IR laser radiation in the wavelength range 3.3-5.4 {mu}m with no gas-phase decomposition of the molecules. (extreme light fields and their applications)

  20. Instrumentation of Dynamic Gas Pulse Loading system. Final technical report

    SciTech Connect

    Mohaupt, H.

    1993-07-31

    The Dynamic Gas Pulse Loading (DGPL) process is an hydraulic fracturing method which uses CO{sub 2} and CO gas as a working fluid instead of a liquid. The DGPL system can be used to generate fractures for horizontal and vertical oil and gas well completions in both open hole and perforated casing. The DGPL system provides a cost effective tool for repairing near well bore permeability damage caused by inappropriate chemical treatment, migrating fines and paraffins, or slotted liners blocked by sand. Because the gas is generated from a solid propellant material by chemical reaction, no heavy equipment is required. Tremendous pump rates can be obtained. Peak pressures are naturally localized at the tool position by the tamping effect of well fluids. Thus many of the leakage and sealing problems which plague static hydrofrac processes ore completely avoided. DGPL may be effectively used before acid treatment to provide fresh pathways for the acid to reach the formation. The smaller tools may be positioned by wireline, though most Stressfrac tools are tubing conveyed.

  1. Investigating the dynamics of laser induced sparks in atmospheric helium using Rayleigh and Thomson scattering

    SciTech Connect

    Nedanovska, E.; Nersisyan, G.; Lewis, C. L. S.; Riley, D.; Graham, W. G.; Morgan, T. J.; Hüwel, L.; Murakami, T.

    2015-01-07

    We have used optical Rayleigh and Thomson scattering to investigate the expansion dynamics of laser induced plasma in atmospheric helium and to map its electron parameters both in time and space. The plasma is created using 9 ns duration, 140 mJ pulses from a Nd:YAG laser operating at 1064 nm, focused with a 10 cm focal length lens, and probed with 7 ns, 80 mJ, and 532 nm Nd:YAG laser pulses. Between 0.4 μs and 22.5 μs after breakdown, the electron density decreases from 3.3 × 10{sup 17 }cm{sup −3} to 9 × 10{sup 13 }cm{sup −3}, while the temperature drops from 3.2 eV to 0.1 eV. Spatially resolved Thomson scattering data recorded up to 17.5 μs reveal that during this time the laser induced plasma expands at a rate given by R ∼ t{sup 0.4} consistent with a non-radiative spherical blast wave. This data also indicate the development of a toroidal structure in the lateral profile of both electron temperature and density. Rayleigh scattering data show that the gas density decreases in the center of the expanding plasma with a central scattering peak reemerging after about 12 μs. We have utilized a zero dimensional kinetic global model to identify the dominant particle species versus delay time and this indicates that metastable helium and the He{sub 2}{sup +} molecular ion play an important role.

  2. Investigating the dynamics of laser induced sparks in atmospheric helium using Rayleigh and Thomson scattering

    NASA Astrophysics Data System (ADS)

    Nedanovska, E.; Nersisyan, G.; Morgan, T. J.; Hüwel, L.; Murakami, T.; Lewis, C. L. S.; Riley, D.; Graham, W. G.

    2015-01-01

    We have used optical Rayleigh and Thomson scattering to investigate the expansion dynamics of laser induced plasma in atmospheric helium and to map its electron parameters both in time and space. The plasma is created using 9 ns duration, 140 mJ pulses from a Nd:YAG laser operating at 1064 nm, focused with a 10 cm focal length lens, and probed with 7 ns, 80 mJ, and 532 nm Nd:YAG laser pulses. Between 0.4 μs and 22.5 μs after breakdown, the electron density decreases from 3.3 × 1017 cm-3 to 9 × 1013 cm-3, while the temperature drops from 3.2 eV to 0.1 eV. Spatially resolved Thomson scattering data recorded up to 17.5 μs reveal that during this time the laser induced plasma expands at a rate given by R ˜ t0.4 consistent with a non-radiative spherical blast wave. This data also indicate the development of a toroidal structure in the lateral profile of both electron temperature and density. Rayleigh scattering data show that the gas density decreases in the center of the expanding plasma with a central scattering peak reemerging after about 12 μs. We have utilized a zero dimensional kinetic global model to identify the dominant particle species versus delay time and this indicates that metastable helium and the He2+ molecular ion play an important role.

  3. A Diode Laser Study of the Catalytic Oxidation Dynamics of Acetaldehyde on Polycrystalline Platinum

    NASA Astrophysics Data System (ADS)

    Edington, Sean Coleman

    The catalytic oxidation of acetaldehyde on platinum was studied using a flow reactor equipped with a tunable diode laser absorption spectrometer and a quadrupole mass spectrometer. Reaction mixtures containing this molecule in varying proportion with oxygen and with argon as a carrier gas were flowed over a polycrystalline platinum mesh, which was resistively heated to different temperatures between 700 and 1000 K. The products of these reactions were monitored using mass spectrometry and the state-resolved spectra of CO 2 produced were collected using high-resolution tunable diode laser absorption spectroscopy. These data were analyzed to yield information about the dynamics of the reaction. Results indicate that production of CO and CO2 by this reaction proceeds via two distinct pathways. Acetaldehyde adsorbed on the surface decomposes to acetyl, which in turn decomposes CO and CHx. The adsorbed CO so prepared desorbs to yield the bulk of CO generated across all reaction conditions and also yields CO2 with a relatively deactivated asymmetric stretching mode under conditions of high temperature and low oxygen coverage. The acetyl-derived CHx dehydrogenates to yield surface carbon and H adatoms. Total oxidation of this surface carbon is the primary source of CO2 produced under all reaction conditions except those mentioned previously and is found to yield products with a preferentially excited asymmetric stretch. Combination of the CHx-derived H adatoms with surface oxygen drives the production of water by this reaction. During the course of the work described here, two notable improvements were made to our experimental apparatus. The first of these was the modification of the data acquisition process to significantly improve the signal-to-noise ratio achievable by our laser spectrometer with no increase in data collection time. The second was the development of data analysis software which significantly improved the efficiency and thoroughness of the process by

  4. FUNDAMENTAL STUDIES OF IGNITION PROCESSES IN LARGE NATURAL GAS ENGINES USING LASER SPARK IGNITION

    SciTech Connect

    Azer Yalin; Morgan Defoort; Bryan Willson

    2005-01-01

    The current report details project progress made during the first quarterly reporting period of the DOE sponsored project ''Fundamental studies of ignition processes in large natural gas engines using laser spark ignition''. The goal of the overall research effort is to develop a laser ignition system for natural gas engines, with a particular focus on using fiber optic delivery methods. In this report we present our successful demonstration of spark formation using fiber delivery made possible though the use of novel coated hollow fibers. We present results of (high power) experimental characterizations of light propagation using hollow fibers using both a high power research grade laser as well as a more compact laser. Finally, we present initial designs of the system we are developing for future on-engine testing using the hollow fibers.

  5. On the minimization of the prime power consumption of a coupling-modulated gas laser transmitter

    NASA Technical Reports Server (NTRS)

    Degnan, J. J.

    1973-01-01

    The prime power requirements of a coupling-modulated gas laser transmitter are presented. The latter consists of a gas discharge tube and electro-optic modulator inside a laser resonator. In performing the calculations, the laser discharge length and the modulator voltage are simultaneously varied so that the transmitted power remains constant. In this way, tradeoffs can be made between the prime power supplied individually to the discharge tube and to the modulator driver to obtain a transmitter configuration which minimizes the total prime power consumption. An analytical expression is derived which describes the effects of information bandwidth and transmitter output power on the prime power requirements. Specific numerical results are obtained for a CO2 laser transmitter based on presently available experimental data.

  6. Dynamic design of gas sorption J-T refrigerator

    NASA Technical Reports Server (NTRS)

    Chan, C. K.

    1986-01-01

    A long-life Joule-Thomson refrigerator which is heat powered, involves no sealing, and has few mechanical parts is desirable for long-term sensor cooling in space. In the gas-sorption J-T refrigerator, cooling is achieved by gas sorption (either adsorption or absorption) processes. Currently, a modular, single-stage refrigerator is being designed and built to be operated at 20 K. The design was analyzed using a dynamic model, which is described here. The model includes the kinetics of the compressors and the heat switches, the heat transfer of the pre-coolers and the heat exchangers, the on/off ratio of the check valves, and the impedance of the J-T valve. The cooling power, the cycle time, and the operating conditions were obtained in terms of the power input, the heat sink temperature, and the J-T impedance.

  7. Urban multitarget tracking via gas-kinetic dynamics models

    NASA Astrophysics Data System (ADS)

    Mahler, Ronald

    2013-05-01

    Multitarget tracking in urban environments presents a major theoretical and practical challenge. A recently suggested approach is that of modeling traffic dynamics using the fluid-kinetic methods of traffic-flow theory (TFT). I propose use of the newer, more general, gas-kinetic (GK) approach to TFT. In GK, traffic flow is modeled as a one- or two-dimensional constrained gas. The paper demonstrates the following. (1) The foundational concept in GK--the "phase-space density"--is the same thing as the probability hypothesis density (PHD) of multitarget tracking theory. (2) The theoretically best-that-one-can do approach to TFT-based tracking is a PHD filter. (3) Better performance can be obtained by augmenting this PHD filter as a cardinalized PHD (CPHD) filter. A simple example is presented to illustrate how PHD/CPHD filters can be integrated with conventional macroscopic, mesoscopic, and microscopic TFT.

  8. The in-gas-jet laser ion source: Resonance ionization spectroscopy of radioactive atoms in supersonic gas jets

    NASA Astrophysics Data System (ADS)

    Kudryavtsev, Yu.; Ferrer, R.; Huyse, M.; Van den Bergh, P.; Van Duppen, P.

    2013-02-01

    New approaches to perform efficient and selective step-wise resonance ionization spectroscopy (RIS) of radioactive atoms in different types of supersonic gas jets are proposed. This novel application results in a major expansion of the in-gas laser ionization and spectroscopy (IGLIS) method developed at KU Leuven. Implementation of resonance ionization in the supersonic gas jet allows to increase the spectral resolution by one order of magnitude in comparison with the currently performed in-gas-cell ionization spectroscopy. Properties of supersonic beams, obtained from the de Laval-, the spike-, and the free jet nozzles that are important for the reduction of the spectral line broadening mechanisms in cold and low density environments are discussed. Requirements for the laser radiation and for the vacuum pumping system are also examined. Finally, first results of high-resolution spectroscopy in the supersonic free jet are presented for the 327.4 nm 3d104s 2S1/2→ 3d104p 2P1/2 transition in the stable 63Cu isotope using an amplified single mode laser radiation.

  9. Gas nanobubbles and aqueous nanostructures: the crucial role of dynamization.

    PubMed

    Demangeat, Jean-Louis

    2015-04-01

    Nanobubbles (NBs) have been a subject of intensive research over the past decade. Their peculiar characteristics, including extremely low buoyancy, longevity, enhanced solubility of oxygen in water, zeta potentials and burst during collapse, have led to many applications in the industrial, biological and medical fields. NBs may form spontaneously from dissolved gas but the process is greatly enhanced by gas supersaturation and mechanical actions such as dynamization. Therefore, the formation of NBs during the preparation of homeopathic dilutions under atmospheric pressure cannot be ignored. I suggested in 2009 the involvement of NBs in nanometric superstructures revealed in high dilutions using NMR relaxation. These superstructures seemed to increase in size with dilution, well into the ultramolecular range (>12c). I report here new experiments that confirm the involvement of NBs and prove the crucial role of dynamization to create superstructures specific to the solute. A second dynamization was shown to enhance or regenerate these superstructures. I postulate that superstructures result from a nucleation process of NBs around the solute, with shells of highly organized water (with ions and silicates if any) which protect the solute against out-diffusion and behave as nucleation centres for further dilution steps. The sampling tip may play an active role by catching the superstructures and thus carry the encaged solute across the dilution range, possibly up to the ultramolecular range. The superstructures were not observed at low dilution, probably because of a destructuring of the solvent by the solute and/or of an inadequate gas/solute ratio. PMID:25869975

  10. Ultrafast electron diffraction from laser-aligned molecules in the gas phase

    NASA Astrophysics Data System (ADS)

    Yang, Jie

    Ultrafast electron diffraction has emerged since the end of last century, and has become an increasingly important tool for revealing great details of molecular dynamics. In comparison to spectroscopic techniques, ultrafast electron diffraction directly probes time-resolved structure of target molecules, and therefore can potentially provide "molecular movies" of the reactions being studied. These molecular movies are critical for understanding and ultimately controlling the energy conversion pathways and efficiencies of photochemical processes. In this dissertation, I have focused on ultrafast electron diffraction from gas-phase molecules, and have investigated several long-standing challenges that have been preventing researchers from being able to achieve 3-D molecular movies of photochemical reactions. The first challenge is to resolve the full 3-D structure for molecules in the gas phase. The random orientation of molecules in the gas phase smears out the diffraction signal, which results in only 1-D structural information being accessible. The second challenge lies in temporal resolution. In order to resolve coherent nuclear motions on their natural time scale, a temporal resolution of ˜200 femtosecond or better is required. However, due to experimental limitations the shortest temporal resolution that had been achieved was only a few picoseconds in early 2000, by Zewail group from Caltech. The first challenge is tackled by laser-alignment. In the first half of the dissertation, I approach this method both theoretically and experimentally, and demonstrate that by using a short laser pulse to transiently align target molecules in space, 3-D molecular structure can be reconstructed ab-initio from diffraction patterns. The second half of the dissertation presents two experiments, both of which are important steps toward imaging coherent nuclear motions in real time during photochemical reactions. The first experiment simultaneously resolves molecular alignment

  11. Electron beam method and apparatus for obtaining uniform discharges in electrically pumped gas lasers

    DOEpatents

    Fenstermacher, Charles A.; Boyer, Keith

    1986-01-01

    A method and apparatus for obtaining uniform, high-energy, large-volume electrical discharges in the lasing medium of a gas laser whereby a high-energy electron beam is used as an external ionization source to ionize substantially the entire volume of the lasing medium which is then readily pumped by means of an applied potential less than the breakdown voltage of the medium. The method and apparatus are particularly useful in CO.sub.2 laser systems.

  12. Laser desorption fast gas chromatography-mass spectrometry in supersonic molecular beams.

    PubMed

    Shahar, T; Dagan, S; Amirav, A

    1998-06-01

    A novel method for fast analysis is presented. It is based on laser desorption injection followed by fast gas chromatography-mass spectrometry (GC-MS) in supersonic molecular beams. The sample was placed in an open air or purged laser desorption compartment, held at atmospheric pressure and near room temperature conditions. Desorption was performed with a XeCl Excimer pulsed laser with pulse energy of typically 3 mJ on the surface. About 20 pulses at 50 Hz were applied for sample injection, resulting in about 0.4 s injection time and one or a few micrograms sample vapor or small particles. The laser desorbed sample was further thermally vaporized at a heated frit glass filter located at the fast GC inlet. Ultrafast GC separation and quantification was achieved with a 50-cm-long megabore column operated with a high carrier gas flow rate of up to 240 mL/min. The high carrier gas flow rate provided effective and efficient entrainment of the laser desorbed species in the sweeping gas. Following the fast GC separation, the sample was analyzed by mass spectrometry in supersonic molecular beams. Both electron ionization and hyperthermal surface ionization were employed for enhanced selectivity and sensitivity. Typical laser desorption analysis time was under 10 s. The laser desorption fast GC-MS was studied and demonstrated with the following sample/matrices combinations, all without sample preparation or extraction: (a) traces of dioctylphthalate plasticizer oil on stainless steel surface and the efficiency of its cleaning; (b) the detection of methylparathion and aldicarb pesticides on orange leaves; (c) water surface analysis for the presence of methylparathion pesticide; (d) caffeine analysis in regular and decaffeinated coffee powder; (e) paracetamol and codeine drug analysis in pain relieving drug tablets; (f) caffeine trace analysis in raw urine; (g) blood analysis for the presence of 1 ppm lidocaine drug. The features and advantages of the laser desorption fast GC

  13. Lateral expansion of a laser-supported detonation wave in a gas.

    NASA Technical Reports Server (NTRS)

    Howe, J. T.

    1972-01-01

    A model satisfying the conditions in the burnt (ionized) and ambient undisturbed gases is presented for the two-dimensional case of the absorption wave resulting from the interaction of a laser beam with the plasma it generates in the gas through which the beam propagates. The flowfield of the rarefaction wave resulting from the laser-supported detonation is discussed, along with the computed shock and flow deflection angles.

  14. Rapid Adiabatic Passage in a Rb gas with intense Frequency Chirped Laser Light

    NASA Astrophysics Data System (ADS)

    Kaufman, Brian; Grogan, Tanner; Paltoo, Tracy; Wright, Matthew

    We will discuss our progress toward using intense frequency chirped laser light to control the excitation of atoms in a room-temperature gas cell. We illuminate 87Rb atoms with a 1 GHz in 8 ns frequency chirped pulse of laser light covering the 5S1/2 F =1 --> 5P3/2 and explore the saturation behavior as intensity increases. We estimate that we are exciting over 90% of the atoms over 1 mm2.

  15. Accurate boundary conditions for exterior problems in gas dynamics

    NASA Technical Reports Server (NTRS)

    Hagstrom, Thomas; Hariharan, S. I.

    1988-01-01

    The numerical solution of exterior problems is typically accomplished by introducing an artificial, far field boundary and solving the equations on a truncated domain. For hyperbolic systems, boundary conditions at this boundary are often derived by imposing a principle of no reflection. However, waves with spherical symmetry in gas dynamics satisfy equations where incoming and outgoing Riemann variables are coupled. This suggests that natural reflections may be important. A reflecting boundary condition is proposed based on an asymptotic solution of the far field equations. Nonlinear energy estimates are obtained for the truncated problem and numerical experiments presented to validate the theory.

  16. Accurate boundary conditions for exterior problems in gas dynamics

    NASA Technical Reports Server (NTRS)

    Hagstrom, Thomas; Hariharan, S. I.

    1988-01-01

    The numerical solution of exterior problems is typically accomplished by introducing an artificial, far-field boundary and solving the equations on a truncated domain. For hyperbolic systems, boundary conditions at this boundary are often derived by imposing a principle of no reflection. However, waves with spherical symmetry in gas dynamics satisfy equations where incoming and outgoing Riemann variables are coupled. This suggests that natural reflections may be important. A reflecting boundary condition is proposed based on an asymptotic solution of the far-field equations. Nonlinear energy estimates are obtained for the truncated problem and numerical experiments presented to validate the theory.

  17. Gas Dynamics and Magnetic Fields in Infrared Dark Clouds

    NASA Astrophysics Data System (ADS)

    Pillai, T.

    2016-05-01

    Almost two decades ago, the discovery of a handful of Infrared Dark Clouds (IRDCs) heralded a new avenue for exploring the elusive early phases of massive star formation (Egan et al. 1998). Since then tremendous progress has been made in our understanding of these clouds. It is now well established that IRDCs are ubiquitous and harbor a broad spectrum of star forming stages. Thus studies of star formation and IRDCs are intricately tied together. I summarize some of the recent progress in understanding the magnetic field structure and gas dynamics in IRDCs in the context of high-mass star formation formation.

  18. Gas dynamics of a supersonic radial jet. Part I

    NASA Astrophysics Data System (ADS)

    Kosarev, V. F.; Klinkov, S. V.; Zaikovskii, V. N.; Kundasev, S. G.

    2015-11-01

    The gas dynamics of a supersonic radial jet was studied under conditions close to cold spraying. The jet visualization was performed for exhaustion into submerged space with atmospheric pressure and jet impingement to a target. For the cases of swirled and unswirled supersonic radial jets, the pressure profiles measured by a Pitot tube were taken for different distances from the nozzle outlet and for different widths of supersonic part δ ex = 0.5-2 mm and for prechamber pressure in the range p 0 = 1-2.5 MPa.

  19. Adaptive mesh refinement for 1-dimensional gas dynamics

    SciTech Connect

    Hedstrom, G.; Rodrigue, G.; Berger, M.; Oliger, J.

    1982-01-01

    We consider the solution of the one-dimensional equation of gas-dynamics. Accurate numerical solutions are difficult to obtain on a given spatial mesh because of the existence of physical regions where components of the exact solution are either discontinuous or have large gradient changes. Numerical methods treat these phenomena in a variety of ways. In this paper, the method of adaptive mesh refinement is used. A thorough description of this method for general hyperbolic systems is given elsewhere and only properties of the method pertinent to the system are elaborated.

  20. Improved low concentration gas detection system based on intracavity fiber laser

    NASA Astrophysics Data System (ADS)

    Zhang, Hongxia; Liu, Kun; Jia, Dagong; Xu, Tianhua; Liu, Tiegen; Peng, Gangding; Jing, Wencai; Zhang, Yimo

    2011-02-01

    The improvement of a low concentration gas detection system based on the intracavity fiber laser is proposed in this paper. The sensitivity of the system is deduced based on Lambert-Beer law. The optimized system was established with the gas cell made elaborately. In order to apply the wavelength sweeping technique, the fiber Bragg grating reflector was substituted by the wavelength independent Faraday rotation reflector. The sensitivity of the system for acetylene detection is reduced to less than 100 ppm by using the average of three absorption spectra. The acetylene detection coefficients of variation with different concentrations are measured. The gas measurement system is validated to detect low concentration gas effectively.