Bulletin of the American Physical Society
50th Annual Meeting of the Division of Plasma Physics
Volume 53, Number 14
Monday–Friday, November 17–21, 2008; Dallas, Texas
Session BO4: Laser Plasma Pulse Compression/Laboratory Astrophysics |
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Chair: Ilya Dodin, Princeton University Room: Reunion B |
Monday, November 17, 2008 9:45AM - 9:57AM |
BO4.00001: Numerical studies of nonlinear Raman amplification of laser pulses in plasma R.M.G.M. Trines, R. Bingham, P.A. Norreys, F. Fiuza, L.O. Silva, R.A. Cairns Raman amplification of a short probe pulse off a long pump in plasma is an attractive alternative to amplification in solids, as plasma can tolerate much higher intensities. Most theoretical and experimental studies conducted to date have employed moderate probe intensities ($< 10^{16}$ W/cm$^2$) and widths ($< 50$ micron). However, truly competitive intensities can only be reached if the amplification process is carried out at much higher probe intensities ($10^{17}-10^{18}$ W/cm$^2$) and widths ($1-10$ mm). In this regime, various nonlinear effects become important, such as Langmuir wave breaking, Raman forward scattering, self-focusing, filamentation, and gain narrowing. In addition, nonlinear saturation of various processes may limit the energy transfer efficiency from pump to probe. In this paper we present 1-D and 2-D numerical simulations of strongly nonlinear Raman and superradiant amplification. The influence of various nonlinear processes will be investigated and the consequence for these amplification schemes will be discussed. This work is supported by the STFC Accelerator Science and Technology Centre and the STFC Centre for Fundamental Physics. [Preview Abstract] |
Monday, November 17, 2008 9:57AM - 10:09AM |
BO4.00002: Backward Stimulated Raman Scattering from 30 fsec 200 TW pulses in laser wakefield acceleration experiments Y. Horovitz, T. Matsuoka, C. McGuffey, S.S. Bulanov, V. Chvykov, P. Drake, F. Dollar, C. Huntington, G. Kalintchenko, P. Rousseau, V. Yanovsky, A. Maksimchuk, K. Krushelnick Backward stimulated Raman scattering (B-SRS) is an important process in high energy laser-plasma experiments in the context of inertial confinement fusion. However this phenomenon has never previously been studied during the interaction of high power femtosecond pulses with plasmas. We have performed the first experiments in this regime and have measured the spectral shape and efficiency of backscattered SRS light during interactions with 30 fsec pulses with low density plasmas at powers up to 200 TW. The spectrum of the Raman backscattered light was observed to be extremely modulated. For lower power interactions in certain regimes a correlation with relativistic electron beam generation could also be observed. [Preview Abstract] |
Monday, November 17, 2008 10:09AM - 10:21AM |
BO4.00003: Progress in laser pulse amplification by stimulated Raman scattering in a plasma Y. Ping, R. Kirkwood, R. Rygg, S. Wilks, N. Meezan, O. Landen, N. Fisch, V. Malkin, E. Valeo, J. Wurtele, C. Niemann Amplification and compression of short laser pulses via Raman scattering in a plasma is a promising scheme for reaching ultrahigh laser powers beyond the limit of solid-state-based laser systems. We report the recent progress in the development of a plasma amplifier for a 1-5 ps seed and 1ns pump in a 3 mm plasma with the temperature and density needed for efficient compression of the pulse when the interaction length is increased (ie. Te $\sim $ 275 eV, ne $\sim $ 1 x 10$^{19}$ /cc, Kirkwood et. al, Phys. Plasmas 2007). A high-quality amplified pulse has been observed when the pump intensity is kept below 10$^{14}$ W/cm$^2$, while beam-spray onset is consistent with a few percent of the pump energy being above the filamentation threshold. A maximum output energy of 16mJ has been achieved. These results are being used to benchmark simulations and are critical for scaling up the Raman compression to large laser systems. [Preview Abstract] |
Monday, November 17, 2008 10:21AM - 10:33AM |
BO4.00004: Gamma Ray Sources using Imperfect Relativistic Mirrors Jos\'e Tito Mendonca, Antonio Serbeto In this work, the collective backscattering of intense laser radiation by energetic electron beams is considered. Exact solutions for the radiation field are obtained, for arbitrary electron pulse shapes and laser intensities. The electron beams act as imperfect nonlinear mirrors on the incident laser radiation. This collective backscattering process can lead to the development of new sources of ultra-short pulse radiation in the gamma-ray domain. Numerical examples show that, for plausible experimental conditions, intense pulses of gamma-rays, due to the double Doppler shift of the harmonics of the incident laser radiation, can be produced using the available technology, with durations less than one attosecond. [Preview Abstract] |
Monday, November 17, 2008 10:33AM - 10:45AM |
BO4.00005: Electron Temperature Measurements in a Turbulent Laser Enhanced Laser Induced Plasma Delonia Wiggins, Charlemagne Akpovo, Chavis Raynor, Joseph Johnson Since it has been shown that, an additional laser can change the spectroscopy of the laser induced plasmas, we will impose on the plasma a strong continuous wave fiber laser signal with a high energy density. A Nd-YAG pulsed laser of wavelength 532 nm with a maximum energy of 450 mJ creates a plasma at a focal point in the path of a 1kW cw fiber laser beam of wavelength 1080 nm. The plasma is created in air and a test chamber filled with different gas mixtures at different pressures. The optical emissions from this turbulent plasma were captured with two fiber optic cables and transmitted first to two monochrometers and ultimately to an ICCD and an oscilloscope. From the emissions of the plasma, the spectra of both the ionized and neutral lines can be captured using the ICCD. Both spectra are influenced as the power of the cw fiber laser increases. We will determine the influence of the cw fiber laser's properties on the turbulent properties and the local electron temperature of the pulsed laser induced plasma along with the role which the cw fiber laser plays in the evolution of turbulent parameters in the system. [Preview Abstract] |
Monday, November 17, 2008 10:45AM - 10:57AM |
BO4.00006: Onset of the formation of ultra-intense single cycle laser pulses in plasmas Jorge Vieira, Frederico Fiuza, Luis Silva, Warren Mori The formation of ultra-intense single cycle few-fs laser pulses in plasmas is dominated by self-steepening. In this work the onset of self-steepening is examined using the photon-kinetic equations. Known results regarding the self-compression of long laser pulses are readily recovered and generalized. In the short pulse limit, the threshold, and initial rates for self-steepening are determined. Our results suggest that initially mildly relativistic plasma responses provide ideal conditions both for the on-set of self-steepening and also for ultra-short/intense laser pulse generation. In addition, it is shown that the on-set of longitudinal modulations occurs first, but at a slower rate than the transverse self-focusing. We present 3D PIC simulations illustrating the process, and find very good agreement between the model and 1D PIC simulations in OSIRIS. A physical picture of the process suggests that self-steepening is similar to longitudinal asymmetric self-focusing. [Preview Abstract] |
Monday, November 17, 2008 10:57AM - 11:09AM |
BO4.00007: Nonlinear Optical Studies and Acoustic Characterization of an Underwater Laser Plasma Acoustic Source M. Hornstein, T.G. Jones, A. Ting, D. Kapolka, J. McGhee, J. Haney, Z. Wilkes, D. Lindwall Utilizing nonlinear optical effects, an appropriately tailored laser pulse can propagate many meters underwater at moderate intensity, then quickly converge to an intense focus within a few centimeters at a controlled remote location. Laser-induced breakdown (LIB) at the focus creates an expanding plasma region, thereby generating an acoustic shock. We are investigating intense underwater laser propagation and LIB to develop a remote underwater laser acoustic source. Lens-focused acoustic generation near the water surface, approximating nonlinear optical compression, has been comprehensively characterized, including measurements of power spectrum, directivity, and distance dependence. Acoustic pulses with up to 189 dB have been generated using femtosecond laser pulses with up to 12 mJ. The optical nonlinear index of refraction of water has been experimentally measured. An experimental study of optical filament evolution in water will also be presented. [Preview Abstract] |
Monday, November 17, 2008 11:09AM - 11:21AM |
BO4.00008: Experimental investigation of short light pulse amplification using stimulated Brillouin backscattering Livia Lancia, Jean-Rapha\"el Marqu\`es, Julien Fuchs, Caterina Riconda, Ana Mancic, Patrizio Antici, Patrick Audebert, Motoaki Nakatsutsumi, Stefan Weber, Vladimir T. Tikhonchuk, Stefan Hueller, Jean-Claude Adam, Anne H\'eron Efficient light amplification using stimulated Brillouin backscattering (SBS) in the strongly coupled regime has been predicted by numerical simulations. We experimentally investigated this regime by coupling two counter-propagating short pulses (a pump beam [0.4-30 ps, $\sim$10$^{16}$ W.cm$^{-2}$] and a seed beam, [400 fs, $\sim $10$^{15}$ W.cm$^{-2}$]), both at a wavelength 1.057 $\mu$m, in a preformed plasma. Diagnostics included energy and spectra of the transmitted pump and seed, and of the backscattered pump, as well as the duration of the transmitted seed. The spatio-temporal coherence of the transmitted pump (without seed) has been detected in order to gain insight in the SBS mechanism in this regime. Detailed results will be presented as a function of the plasma density, the ion species composing the plasma, and the polarisations of the pump and seed. [Preview Abstract] |
Monday, November 17, 2008 11:21AM - 11:33AM |
BO4.00009: Laboratory simulation of photoionized plasma among astronomical compact objects Shinsuke Fujioka, Norimasa Yamamoto, Feilu Wang, David Salzmann, Yutong Li, Yong-Joo Rhee, Hiroaki Nishimura, Hideaki Takabe, Kunioki Mima X-ray line emission with several-keV of photon energy was observed from photoionized accreting clouds, for example CYGNUS X-3 and VELA X-1, those are exposed by hard x-ray continuum from the compact objects, such as neutron stars, black holes, or white dwarfs, although accreting clouds are thermally cold. The x-ray continuum-induced line emission gives a good insight to the accreting clouds. We will present a novel laboratory simulation of the photoionized plasma under well-characterized conditions by using high-power laser facility. Blackbody radiator with 500-eV of temperature, as a miniature of a hot compact object, was created.Silicon (Si) plasma with 30-eV of electron temperature was produced in the vicinity of the 0.5-keV blackbody radiator. Line emissions of lithium- and helium-like Si ions was clearly observed around 2-keV of photon-energy from the thermally cold Si plasma, this result is hardly interpreted without consideration of the photoionization. Atomic kinetics code reveals importance of inner-shell ionization directly caused by incoming hard x-rays. [Preview Abstract] |
Monday, November 17, 2008 11:33AM - 11:45AM |
BO4.00010: Shock-Clump Interaction Studies in the Laboratory B.E. Blue, C.A. Back, J.F. Hund, J.M. Foster, P.A. Rosen, R.J.R. Williams, B.H. Wilde, M. Douglas, R. Carver, J. Palmer, P. Hartigan, J.F. Hansen Large-scale directional outflows of supersonic plasma are driven by a wide variety of objects in the universe such as young stars, compact binaries, and supernovae. Typical models of the outflows assume simplistic geometries; however, images of most outflows show a much more complex structure that consists of multiple clumps and shocks with a variety of sizes. To bridge the gap between the complex system in space and the simplified models, controlled scaled experiments were performed to elucidate the physics of a shock progressing through a clumpy medium. This talk will present experiments on the Omega Laser in which a shock impacts density discontinuities in order to understand the perturbed shock structure as well as the evolution of the discontinuity in a localized area of a clumpy medium. We have obtained high-resolution radiographs that detail the temporal evolution of the shock and density discontinuity. [Preview Abstract] |
Monday, November 17, 2008 11:45AM - 11:57AM |
BO4.00011: Collimation of laboratory plasma jets studied with soft x-ray laser interferometry Michael Purvis, Jonathan Grava, Jorge Filevich, Jorge Rocca, James Dunn, Stephen Moon, Vyacheslav Shlyaptsev The collimation of dense laboratory plasma jets created by laser irradiation of triangular grooves on Al, Cu, and Mo targets at I = 1 x 10 $^{12}$ W/cm$^{2}$ was studied combining 2-D electron density maps produced by soft x-ray interferometry and simulations. The jet is initiated by accelerated plasma from the vertex and is augmented by the sequential arrival of wall material along the symmetry plane, where it collides and is re-directed outward. The collimation of the jets is observed to significantly increase with the target's atomic number. The code HYDRA reveals that increased radiation cooling early in the plasma evolution and inertial effects are responsible for the increased collimation of the high Z jets. Work supported by the NNSA SSAA program through DOE Grant {\#} DE-FG52-060NA26152 and the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. [Preview Abstract] |
Monday, November 17, 2008 11:57AM - 12:09PM |
BO4.00012: Radiation Induced Wall-Shocks as Diagnostic Features F.W. Doss, R.P. Drake, H.F. Robey, C.C. Kuranz Shock tube experiments in which heating ahead of the shock is present, by radiation transfer or other mechanisms, can exhibit heating and ablation of the tube material, driving an inwardly directed radial shock, which we call a wall-shock. Both the wall-shock and its interaction with the experiment's primary shock can be observed. From this interaction, various parameters related to shock speeds and temperatures may be inferred. Because wall-shocks may also be driven by laser preheat, they appear not only in experiments containing strongly radiating shocks, but in other laser driven shock experiments. We present several examples of wall shocks obtained in multiple experimental settings and observed by x-ray radiography, computational support generated from the radiation hydrodynamics code HYDRA, and work detailing how shock parameters may be estimated from wall-shock observations. [Preview Abstract] |
Monday, November 17, 2008 12:09PM - 12:21PM |
BO4.00013: Episodic ``Magnetic Tower'' Plasma Jets in a Laboratory Experiment Sergey Lebedev, F.A. Suzuki-Vidal, A. Ciardi, S.N. Bland, G. Hall, J.P. Chittenden, A. Harvey-Thomson, A. Marocchino, A. Frank, E. Blackman, T. Ray, C. Stehle We will present experimental results on formation of supersonic radiatively cooled plasma jets driven by the pressure of the toroidal magnetic field. The experimental configuration allows generation of several episodes of the ``magnetic tower'' jet eruptions. The subsequent magnetic bubbles have higher propagation velocities and are catching up the previously ejected, producing shocks. These experiments suggest that periodic formation of magnetic tower jets in the astrophysical situations could be responsible for some of the variability of the astrophysical jets. The experiments are scalable to astrophysical flows in that critical dimensionless numbers such as the plasma collisionality, the plasma beta and the magnetic Reynolds number are all in the astrophysically appropriate ranges. [Preview Abstract] |
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