Bulletin of the American Physical Society
62nd Annual Meeting of the APS Division of Plasma Physics
Volume 65, Number 11
Monday–Friday, November 9–13, 2020; Remote; Time Zone: Central Standard Time, USA
Session NO08: HED: Laser-Plasma InteractionsLive
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Chair: Jonathan Davies, LLE |
Wednesday, November 11, 2020 9:30AM - 9:42AM Live |
NO08.00001: Nonlinear Spatiotemporal Control of Laser Intensity T.T. Simpson, D. Ramsey, P. Franke, D.H. Froula, J.P. Palastro, N. Vafei-Najafabadi Spatiotemporal control of laser intensity has the potential to revolutionize or enable a wide range of laser-based applications that currently suffer from the poor flexibility offered by conventional optics. In particular, these optics limit the region of high intensity to the Rayleigh range while providing little to no control over its trajectory. Here, we introduce a novel technique for nonlinear spatiotemporal control, the ``self-flying-focus,'' that provides an arbitrary trajectory intensity peak that can be sustained for distances comparable to the focal length. The technique combines temporal pulse shaping with a lens-Kerr lens pair to customize the time and location at which each temporal slice comes to its nonlinear focus. As an example of its utility, simulations show that the self-flying-focus can form a highly uniform, meter-scale plasma suitable for advanced plasma-based accelerators. [Preview Abstract] |
Wednesday, November 11, 2020 9:42AM - 9:54AM Live |
NO08.00002: Slow and fast light in plasma C. Goyon, M. R. Edwards, T. Chapman, L. Divol, N. Lemos, G. J. Williams, D. A. Mariscal, D. P. Turnbull, A. M. Hansen, P. Michel Extreme manipulation of light's group velocity in optical media leads to ``fast'' and ``slow'' light, where pulses propagate superluminally or slow to an almost complete stop. Both phenomena have been found in a range of nonlinear optical media, including atomic gases, photorefractive crystals, and optical fibers. Plasmas are attractive for extreme non-linear optics as they tolerate fluences many orders of magnitude beyond the damage thresholds of traditional optical media, but high required powers and the complexity of the laser-produced plasma make precision control of group velocity difficult. We report the first experimental demonstration of slow and fast light in a plasma. We control the group velocity of light between 0.14c and -0.27c in a fully-ionized He/H2 plasma via optical wave mixing of an auxiliary pump laser and the manipulated probe beam, mediated by the wavelength-detuning-dependent ion-acoustic plasma response. Besides unveiling the potential of plasmas to generate slow and fast light at extreme fluences, these results might also impact inertial confinement fusion or high-energy density physics experiments, where complex wave-mixing processes between dozens of laser beams may impact the group velocities and temporal profiles of these beams. [Preview Abstract] |
Wednesday, November 11, 2020 9:54AM - 10:06AM Live |
NO08.00003: Applications of Electron Avalanche: Sensing Individual Electrons and Nonlinear Laser Self-Guiding D. Woodbury, R. M. Schwartz, E. Rockafellow, A. Goffin, H. M. Milchberg Electron avalanche ionization drives an exponential electron growth of electron density in background gases starting from a single electron seed, analogous single photon detection in a photomultiplier tube. Here we present two applications of electron avalanche driven by mid-IR and long-wave-IR (LWIR) lasers, which minimize the competing process of multiphoton ionization. In the first case, we used a picosecond mid-IR driver to experimentally measure ultralow electron densities from both radiation and femtosecond laser ionization over 14 orders of magnitude (from 10$^{\mathrm{3}}$ to 10$^{\mathrm{17}}$ cm$^{\mathrm{-3}})$. The picosecond pulse length limits electron diffusion to create discrete, countable breakdown sites around initial electron seeds, and thus enables highly accurate initial density measurements. For the second application, we discovered a new avalanche based mechanism for self-guided propagation of high power LWIR pulses in ambient air. We present a new simulation approach that incorporates the nonlinear response of an ensemble of spatially discrete and dynamic avalanche breakdown sites into a continuum propagation model, and demonstrate that avalanche ionization from aerosols leads to moderate intensity, long-range self-guiding of LWIR, few picosecond pulses in a large channel. [Preview Abstract] |
Wednesday, November 11, 2020 10:06AM - 10:18AM Live |
NO08.00004: The Role of Polarization in Relativistic High Harmonic Generation Nicholas Beier, Yarin Heffes, Hunter Allison, Matthew Stanfield, Yasmeen Musthafa, Sahel Hakimi, Amina Hussein, Franklin Dollar Relativistic laser-solid interactions are capable of driving numerous sources, including attosecond x-rays from relativistic high harmonic generation. The interaction is highly sensitive to numerous parameters of the laser matter interactions, such as plasma density profile, laser contrast, wavelength, and angle of incidence. We perform a robust investigation on the role of polarization and selection rules for overdense, highly-relativistic, laser-matter interactions. We show that the spectrum produced has underlying features which are dependent on various aspects of the fundamental polarization state. This work is supported by NSF under Grant No. PHY-1753165, DMR-1548924, DGE-1633631, and CHE-0840513. [Preview Abstract] |
Wednesday, November 11, 2020 10:18AM - 10:30AM Live |
NO08.00005: Few-cycle Relativistic Laser-Plasma Interactions at Kilohertz Repetition Rates Matthew Stanfield, Hunter Allison, Nicholas Beier, Yasmeen Musthafa, Sahel Hakimi, Amina Hussein, Franklin Dollar Relativistic few cycle laser pulses enable applications in high field physics, such as high harmonic generation or laser wakefield acceleration. We demonstrate efficient pulse compression of an output of a 36 fs laser pulse at 800 nm to 7 fs at the kilohertz repetition rate. Characterization of the on-target intensity shows that the overall wavefront is preserved, such that intensity is increased by $>$4. With proper dispersion correction optics, intensities of 10$^{19}$ to 10$^{20}$ Wcm$^{-2}$ can be achieved. Numerical modeling is also presented for the pulse compression and the corresponding few cycle relativistic interaction. This work is supported by NSF under Grant No. DGE-1633631, DMR-1548924, PHY-1753165, and CHE-0840513. [Preview Abstract] |
Wednesday, November 11, 2020 10:30AM - 10:42AM Live |
NO08.00006: Monochromatic K$\alpha $ imaging for beam monitoring of an XFEL and a high-power femtosecond laser H. Sawada, J. Trzaska, C.B. Curry, M. Gauthier, L.B. Fletcher, S. Jiang, H.J. Lee, E.C. Galtier, E. Cunninghum, G. Dyer, T.S. Daykin, L. Chen, C. Salinas, G.D. Glenn, M. Frost, S.H. Glenzer, Y. Ping, A.J. Kemp, Y. Sentoku The spatial overlap of an X-ray Free Electron Laser (XFEL) and a high-power femtosecond laser must be ensured in order to study the plasma condition of a laser-irradiated region in time-resolved pump-probe experiments. In an experiment at the Matter in Extreme Conditions (MEC) end-station of the Linac Coherent Light Source, we applied monochromatic x-ray imaging for determining positions of the beam-target interaction by measuring XFEL- and laser-induced K$\alpha $ x rays with a spherical crystal imager (SCI). A thin titanium foil was irradiated by a MEC's 25-TW femtosecond laser, while a 7.0 keV XFEL beam was used to probe an isochorically heated plasma. Measured 4.51 keV Ti K$\alpha $ x rays produced by various sizes of the XFEL pulses penetrating through the foil were ranged from $\sim $80 $\mu $m in diameter down to 20x40 $\mu $m$^{\mathrm{2}}$. The laser-induced K$\alpha $ spots were measured to be between 40 and 80 $\mu $m FWHM in diameter. Successful beam overlapping was observed on \textasciitilde 58{\%} of all two-beam shots for 10 $\mu $m thick samples. Results reveal that imprecise target positioning is a major cause of large beam offsets. Details of the experiment and results including a correlation between SCI and x-ray Thomson Scattering signals will be discussed. This material is based upon work supported by the National Science Foundation under Grant No. 1707357. [Preview Abstract] |
Wednesday, November 11, 2020 10:42AM - 10:54AM Live |
NO08.00007: Radiation from a particle with constant velocity and time-varying charge, with applications to ultrashort pulsed laser filament microwave emission E. L. Ruden, J. A. Elle, A. C. Englesbe, A. P. Lucero, A. Schmitt-Sody, J. E. Wymer A charged particle with constant velocity and time-varying charge $Q\left( t\right) $ resulting from charge-exchange with an otherwise stationary medium emits electromagnetic radiation despite lack of acceleration of the particle itself. This occurs regardless of whether the particle is real, such as a heavy ion traversing an electron stripper, or the electromagnetic equivalent, such as when charge equals the time integral of a short current pulse caused by an ultrashort pulse laser (USPL) wave packet after it has self-focused via the Kerr effect. The pulse width of the radiation is the time interval over which $Q\left( t\right) $ varies times $\left( 1-\beta \cos \theta \right) $, assuming the particle dimensions are negligible relative to $\beta c$ times this pulse width. Here, $\beta $ is the particle speed relative to the speed of light in the medium $c$, and $\theta $ is the emission angle relative to the direction of motion. The violation of this assumption for small $\theta $ for $\beta \approx 1$, such as occurs for USPL filamentation in a gas, provides the basis for estimating the time scale of the current pulse, a parameter of great interest for understanding its physical mechanism. [Preview Abstract] |
Wednesday, November 11, 2020 10:54AM - 11:06AM Live |
NO08.00008: Scaling of laser-driven proton and electron acceleration as a function of pulse duration in the multi-ps regime Raspberry Simpson, Graeme Gordon Scott, Dean Rusby, Paul King, Elizabeth Simpson Grace, G. Jackson Williams, Derek Mariscal, Tammy Ma A new class of multi-kilojoule, multi-picosecond short-pulse lasers such as NIF-ARC, OMEGA-EP, LMJ-PETAL and LFEX-GEKKO, enable exciting opportunities to produce high-brightness, high-energy laser-driven particle sources for applications in high-energy-density science. Recent results on this type of platform have demonstrated enhanced accelerated proton energies and electron temperatures when compared to established scaling laws. Motivated by these results, this work examines laser-driven proton and electron acceleration in the multi-picosecond regime ($>$1ps) at laser intensities of 10$^{17}$ - 10$^{19}$ W/cm$^2$. A detailed scaling study was performed on the TITAN laser at the Jupiter Laser Facility and found that the accelerated electrons and maximum proton energies exceeded the ponderomotive scaling in the multi-picosecond regime. The results are consistent with the accelerating sheath field being established a population of super-ponderomotive electrons. A new analytical scaling is presented to reflect this enhancement of the accelerated particle characteristics. [Preview Abstract] |
Wednesday, November 11, 2020 11:06AM - 11:18AM Live |
NO08.00009: Absorption of Intense Short Laser Pulses in Nanowire Arrays Andreas Kemp, Scott Wilks, Gary Grim, Riccardo Tommasini, Ginevra Cochran, Jaebum Park We study the absorption of intense short laser pulses in arrays of carbon nanowires attached to solid substrates; in particular, we are interested in sub-100fs pulses with several Joules of energy, as well as multi-picosecond, multi-kiloJoule pulses. In both cases, we find that laser absorption of nanowire targets exceeds that of flat targets even if preceded by density gradients. Performing two- and three-dimensional particle-in-cell simulations, we focus on laser absorption physics, particle acceleration during the formation of nanoscale z-pinches, and on applications like the optimization of this target platform for nuclear physics experiments [Kemp et al, Nat.Comm. 10:4156 (2019)] and compact, fast neutron sources. [Preview Abstract] |
Wednesday, November 11, 2020 11:18AM - 11:30AM Live |
NO08.00010: Laser-produced pair plasma in a magnetic mirror Gennady Fiksel, H. Chen, M.R. Edwards, J. von der Linded, T.A. Link, J. Peebles, L. Willingale Confinement of laser-produced positron-electron pair plasma in a magnetic mirror was studied on the Omega EP facility of the Laboratory for Laser Energetics (LLE) of the University of Rochester, NY. The plasma was produced by interaction of a high-intensity, 800~J, 10~ps laser beam with a 1mm-thick Au target. Two MIFEDS current generators discharged a 30~kA, 0.5~ms current pulse through two 4-loop magnetic coils. The coils, each with an inner diameter of 10~mm, were separated by 15~mm creating a magnetic mirror configuration with a mirror field of 15~T and a mirror ratio of 2.5. The particle losses and their energy spectra were measured by several magnetic particle energy analyzers situated around the target. To optimize the positron confinement, a parallel campaign on increasing the yield of low-energy positrons was conducted. The positron energy spectra were varied by manipulating the sheath electric field at the back of positron target using a secondary plasma produced by a 1~ns laser beam. The experimental results and their comparison to simulations will be presented. This work is supported the U.S. Department of Energy by LLNS, LLC, under Contract No. DE-AC52-07NA27344 under LDRD 20-LW-021. LLNL-ABS-811921. [Preview Abstract] |
Wednesday, November 11, 2020 11:30AM - 11:42AM Live |
NO08.00011: Laser Plasma Interactions in Cone Targets with Focusing Geometry Scott Wilks, A. Kemp, G. Cochran, J. Williams, S. Kerr, A. Mackinnon, A. MacPhee, D. Rusby, F. Albert, A. Pak, J. Bude, C. Siders, W. Keller, H. Chen, T. Lanier, N. Lemos, K. Miller, W. Mori Compound Parabolic Concentrator targets[1] have proven to be effective at generating relativistic electron energies well in excess of those observed when the same high energy, low intensity, long focal length laser pulses are shot onto foils. Details of the laser-plasma interaction are complex and change during these long ($\approx 10$ picosecond) pulses, making it difficult to optimize coupling the laser energy to the electrons in a systematic and predictable way. Plasma physics issues associated with this target and results of 3D PIC and radiation hydrodynamics simulations will be presented with an emphasis on determining how the laser energy couples to hot electrons. Specifically, we examine how the relative contributions of the laser plasma interaction in the underdense plasma and the laser intensity enhancement due to the focusing geometry of the cone contribute to the observed hot electron energy distributions. [1] MacPhee, et al., Optica Vol. 7, Issue 2, pp. 129-130 (2020) [Preview Abstract] |
Wednesday, November 11, 2020 11:42AM - 11:54AM Live |
NO08.00012: Time evolution of transient plasma states from nanowire arrays irradiated at relativistic intensities O.S. Humphries, P. Allan, C.R.D. Brown, L.M.R. Hobbs, S.F. James, M.G. Ramsay, B. Williams, D.J. Hoarty, M.P. Hill, S.M. Vinko Understanding the evolution of extreme states of matter driven by relativistic laser-plasma interactions is a fundamental problem in high-field physics. This is especially true for nanostructured targets, where hydrodynamic effects play a key role within the ultra-fast time scale of laser absorption. Nanowire array targets are of particular interest as they provide an efficient means to access the ultra-high-energy-density regime due to their increased optical absorption, and have been shown to act as very efficient x-ray emission sources. I will present analysis of time-resolved x-ray emission spectroscopy from petawatt-irradiated Nickel nanowire arrays, used to characterise the conditions achieved when scaling the performance of nanowire targets to relativistic intensities. A full time evolution of the plasma conditions is extracted from the experimental data, and shows good agreement with the physical interaction picture developed by prior computational studies. [Preview Abstract] |
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