Bulletin of the American Physical Society
60th Annual Meeting of the APS Division of Plasma Physics
Volume 63, Number 11
Monday–Friday, November 5–9, 2018; Portland, Oregon
Session JO8: Radiation from Plasmas and Laser-plasma Accelerators |
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Chair: Douglass Schumacher, Ohio State University Room: OCC C120-122 |
Tuesday, November 6, 2018 2:00PM - 2:12PM |
JO8.00001: Characteristics of the synchrotron-like X-ray source from laser-wakefield acceleration Yong Ma, Amina E Hussein, Oliver Finaly, Mattew J. V. Streeter, Brendan Kettle, Stephen J. D. Dann, Nancy Senabulya, Felicie Albert, Nicolas Bourgeois, Silvia Cipiccia, Isabel Gallardo González, Andrew Higginbotham, Dino Jaroszynski, Katerina Falk, Karl Michael Krushelnick, Nuno Lemos, Nelson Carreira Lopes, Olle Lundh, Stuart P D Mangles, Zulfikar Najmudin, Rajeev Pattathil, Michal Smid, Dan Symes, Ashwin Shahani, Alexander GR Thomas The synchrotron-like radiation source generated by laser wakefield accelerators due to electrons' oscillatory motion, known as "betatron'' X-rays, is a promising alternative to the synchrotron X-ray source owing to comparable photon energies and peak brightness but with much smaller facility size and cost. Such kind of radiation normally has a femtosecond ultrashort pulse duration, a few milliradians low divergence and a ~um source size. These properties guarantees its excellent performance in both high-temporal- and high-spatial-resolution imaging and also makes it a promising tool in probing ultrafast phenomena as well as pumping warm dense matters. We present here the generation of betatron X-ray source during the interaction of a 300 TW laser with density tailored plasma provided by a dual-stage 3D-printed gas-cell. We will discuss the dependence of betatron X-rays properties on plasma parameters and the electron beam properties. Preliminary results on X-ray phase contrast imaging of eutectic alloy microstructure will also be addressed. |
Tuesday, November 6, 2018 2:12PM - 2:24PM |
JO8.00002: Wakefield acceleration and betatron radiation driven by linearly polarized Laguerre-Gaussian orbital angular momentum laser pulses Andrew Longman, Carlos Salgado, Ghassan Zeraouli, Jon Imanol Apiñaniz, Jose Antonio Pérez-Hernández, Massimo De Marco, Calvin He, Giancarlo Gatti, Luca Volpe, Wendell T Hill, Robert Fedosejevs In this work, we report on the first results of wakefield accelerated electrons by ultra-intense linearly polarized Laguerre-Gaussian orbital angular momentum (OAM) modes. These modes, generated after compression in the VEGA2 200TW Titanium:Sapphire laser system at the Centro de Láseres Pulsados (CLPU) in Spain used new novel off-axis spiral phase mirrors to convert the flat top laser mode to high purity Laguerre-Gaussian LG10, LG20 and LG-10 beams with intensities of over 10^18Wcm-2. The difference in electron and betatron divergence, flux, and spectrum when compared to the standard TEM00 mode will be presented. Additionally, the generation of strong axial magnetic fields in these new interactions will be discussed. These results will be compared to simple analytic scaling models and simulations using the 3D PIC code EPOCH. |
Tuesday, November 6, 2018 2:24PM - 2:36PM |
JO8.00003: Time-resolved x-ray absorption spectroscopy of warm dense matter with betatron x-ray radiation Felicie Albert, Benjamin Barbrel, Florian Condamine, Fabien Dorchies, Roger Wirth Falcone, Amalia fernandez, Luke Fletcher, Alan Fry, Eric Galtier, Eliseo Gamboa, Siegfried Glenzer, Eduardo Granados, Marion Harmand, Stefan P Hau-Riege, Philip Heimann, Paul Michael King, Dominik Kraus, Andrew Krygier, Nuno Lemos, Haeja Lee, Andy Mackinnon, Stuart P D Mangles, Tadashi Ogitsu, Yuan Ping, Bradley Pollock Betatron x-ray radiation, produced by relativistic electrons oscillating in a laser-wakefield accelerator, has been used to perform time-resolved x-ray absorption spectroscopy. We measured the evolution of the X-ray Absorption Near Edge Structure (XANES) signal, near the oxygen K-edge (535 eV), of an SiO2 sample excited with optical laser light. Experiments were performed at the LCLS, Matter under Extreme Conditions end station, with a 1 J, 40 fs laser system. The laser was split to produce betatron x-rays in a gas cell with an electron density of 1.5 x 1019 cm-3, and to irradiate the SiO2 sample with intensities around 1015 W/cm2. The delay between the two pulses was varied to measure the evolution of the XANES signal. Our experiment produced electron beams with energies up to 200 MeV and betatron x-rays with critical energies of a few keV. By using an ellipsoidal mirror to refocus the x-rays onto the SiO2 sample, as well as an imaging x-ray spectrometer with a variable line spacing grating, we were able to obtain a sub-picosecond resolution. |
Tuesday, November 6, 2018 2:36PM - 2:48PM |
JO8.00004: Ultrafast melting of Warm Dense Cu studied by x-ray spectroscopy Michal Smid, Jurjen Pieter Couperus, Isabel Gallardo Gonzalez, Martin Hansson, Jan Vorberger, Jonathan C Wood, Stuart P D Mangles, Olle Lundh, Arie Irman, Katerina Falk We present a study of ultrafast heating of Warm Dense Cu diagnosed by the means of x-ray absorption spectroscopy carried out at the Lund Laser Center and Draco laser at HZDR. A thin Cu foil was directly heated to few eV temperature by a 30-fs laser pulse and probed with variable delay by a laser-driven betatron radiation. This betatron radiation, emitted by laser wake field accelerated electrons, is an unique x-ray source with its ultrashort duration and broadband spectrum, therefore it is ideally suited for this type of measurements. The sample was studied via the X-ray Absorption Near Edge Spectroscopy (XANES) in region above the Cu K-edge at 8.9 keV. This method provides temporally-resolved information about both the ionic structure of the matter and its temperature during the process of ultrafast heating and melting of the material. We deployed a newly developed spectrometer with a highly reflective HOPG crystal in a geometry well suited for detection of low intensity signals with high spectral and angular resolution. |
Tuesday, November 6, 2018 2:48PM - 3:00PM |
JO8.00005: Simulations of X-ray free-electron-lasers driven by plasma-based acceleration Xinlu Xu, Thamine Dalichaouch, Shiyu Zhou, Fei Li, Weiming An, Mark J Hogan, Chandrashekhar Joshi, Warren B Mori Plasma-based acceleration can provide high-energy electrons in a very short distance, which can much shrink the size and reduce the cost of the transformative modern machine – X-ray free-electron-lasers. However there are many challenges needed to be overcome before plasma wakefields can generate electrons with the required beam quality (brightnesses and low energy spreads) inside the wake and before these beams can be transported from the plasma to the undulator without beam quality degradation. We will present our recent progress from particle-in-cell simulations and theory on this topic, including concepts for producing high energy beams with unprecedented normalized brightnesses using density down ramp injection in the three-dimensional nonlinear blowout regime, matching the beam out of the plasma using longitudinally tailored plasma profiles, and start-to-end simulations of such plasma wakefied accelerators driven X-ray free-electron-lasers.
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Tuesday, November 6, 2018 3:00PM - 3:12PM |
JO8.00006: The laser-plasma-accelerator-driven free electron laser project at the BELLA Center Jeroen van Tilborg, Samuel Barber, Fumika Isono, Carl Schroeder, Eric Esarey, James Rosenzweig, Nathan Majernik, Wim Leemans At LBNL's BELLA Center, we have established a new facility dedicated to driving incoherent and coherent undulator radiation by electron beams produced in a laser plasma accelerator (LPA). A dedicated 100-TW class 5Hz laser system is coupled to a mm-scale LPA, followed by state-of-the-art electron beam transport, phase-space manipulation, diagnostics, and a 4-meter-long undulator. The viability of a compact coherent undulator-based light source [the free electron laser (FEL)], operational in the soft X-ray regime, hinges on the ability of the LPA to produce sufficiently bright electron beams and maintain this quality during transport. Intrinsic mrad-scale divergence, %-level energy spread, and fluctuations in beam energy, make this a challenging task. In this presentation we will present our approach, including improved laser stability, robust down-ramp injection in the LPA, compact active plasma lens technology for compact transport, a chicane for slice energy spread reduction, and the strong-focusing VISA undulator for enhanced beam-radiation interaction. Both simulations and experimental results will be presented. |
Tuesday, November 6, 2018 3:12PM - 3:24PM |
JO8.00007: Control of tunable, quasi-monoenergetic electron beams from laser-plasma accelerators and their application for compact, narrow bandwidth Thomson photon sources H. -E. Tsai, C. G. R. Geddes, T. Ostermayr, G. Otero, T. Larrieu, J. Van Tilborg, S. K. Barber, F. Isono, R. Lehe, A. J. Gonsalves, K. Nakamura, Cs. Toth, C. B. B Schroeder, E. Esarey, W. P. Leemans We demonstrate precise control of a laser-plasma accelerator (LPA) using a shock-induced density down-ramp injector. Experiments systematically varied the shock injector profile, including the shock angle, up-ramp width, and acceleration length. These results establish that, by adjusting shock position, up-ramp, and angle, beam energy, energy spread, and pointing can be controlled. As a result, e-beam were highly tunable from 30 to 300 MeV with <10% energy spread, 1.5 mrad divergence and 0.35 mrad pointing fluctuation. Particle-in-cell (PIC) simulation characterized how variations in the shock profile impacted the injection process. This highly controllable LPA represents a suitable and compact beam source for the MeV Thomson photon experiments now being started on a newly constructed one hundred TW laser system. Set-up and initial experiments using this system will be presented. |
Tuesday, November 6, 2018 3:24PM - 3:36PM |
JO8.00008: Cherenkov radiation from a plasma John Palastro, Thomas M Antonsen, Arnaud Colaïtis, Russell Follett, David Turnbull, Jorge M Vieira, Dustin H Froula The dispersion of electromagnetic waves in a plasma has traditionally precluded the emission of Cherenkov radiation into the far field: the phase velocity of the radiation exceeds the speed of light in vacuum and therefore the speed of a conventional driver. The flying focus—a moving focal point resulting from a chirped laser pulse focused by a chromatic lens—provides an intensity peak that can travel at superluminal velocities. Theory and simulations show that a plasma ponderomotively excited by a flying focus pulse can emit far-field Cherenkov radiation at THz frequencies. |
Tuesday, November 6, 2018 3:36PM - 3:48PM |
JO8.00009: Electromagnetic wave frequency upconversion in dynamic media Kenan Qu, Qing Jia, Matthew R Edwards, Nathaniel J Fisch Frequency upconversion of an electromagnetic wave can occur in ionized plasma with decreasing electric permittivity and in split-ring resonator-structure metamaterials with decreasing magnetic permeability. This talk will present a general theory [1] to describe the evolution of the wave frequency, amplitude, and energy density in media with temporally decreasing refractive index. It is shown that upconversion of the wave frequency partitions the wave energy into both high- and low-frequency modes, and the efficiencies of frequency upconversion are comparable using decreased permittivity and decreased permeability. This method has important applications including generating coherent and chirped ultraviolet and x-ray pulses with independently tunable frequency and bandwidth [2].
[1] K. Qu, Q. Jia, M. R. Edwards, and N. J. Fisch, arXiv:1804.07358 (2018); [2]M. R. Edwards, K. Qu, Q. Jia, J. M. Mikhailova, and N. J. Fisch, Phys. Plasmas, 5, 053102, (2018). |
Tuesday, November 6, 2018 3:48PM - 4:00PM |
JO8.00010: Dipole THz radiation from a single cluster irradiated by high intensity and short pulse laser Daiki Kawahito, Masaki Hashida, Shuji Sakabe, Yasuhiko Sentoku THz radiation from laser produced plasmas has been studied as an application for strong energy and compact radiation sources. Among them, high intensity THz radiation had been experimentally observed from cluster media. However, the detailed mechanism of THz radiation from the cluster has not yet been clarified theoretically. Thus, it is difficult to optimize the THz radiation by changing the laser intensity and the size of the cluster. From the results of PIC simulation, we found that THz radiation results from the electron oscillation around a cluster driven by the laser ponderomotive force which pushes the electrons to the laser direction. After the laser irradiation, electrons oscillate by the electrostatic force from the cluster core and radiate the dipole electromagnetic field. The oscillation frequency, which corresponds to the radiation frequency, decreases to THz regime due to the decrease of the cluster density with the Coulomb expansion. We found that high emission is realized when the cluster density is kept above the cutoff density during the laser-plasma interaction. These results indicate the key process for describing the THz radiation from multi-body cluster media in the experimental system. |
Tuesday, November 6, 2018 4:00PM - 4:12PM |
JO8.00011: Strong Radiation Emission from Plasma Dipole Oscillation Min Sup Hur, Teyoun Kang, Bernhard Ersfeld, Dino Jaroszynski, Kenan Qu, Nathaniel J Fisch The plasma oscillation and Langmuir wave are usually regarded as non-radiating, because their electrostatic, curl-free nature of the electric field prohibits its coupling with the electromagnetic wave in plasma. However, in a non-uniform plasma, the plasma oscillation can take on a non-zero component of the curl of the electric field, leading to the emission of electromagnetic radiation by mechanisms of mode conversion or travelling wave antennae. These mechanisms, in non-uniform plasmas, inevitably yield broadband emission spectra. In contrast, we conceived a novel method of obtaining quasi-narrowband radiation from a localized plasma dipole oscillation, which is generated by colliding, detuned laser pulses in plasma. The radiation exhibits a quasi-narrowband peak around the plasma frequency, typically a few THz, which should yield diverse novel applications where strong terahertz fields are required for pump-probe studies of materials. Furthermore, we show that the field emitted from a plasma oscillation immersed in uniform plasma can transport its energy through the uniform plasma over a large distance without significant decay, in contradiction with the common wisdom of radiation cut-off in ambient plasma. The new discovery may be pertinent to solar radio bursts. |
Tuesday, November 6, 2018 4:12PM - 4:24PM |
JO8.00012: Dynamics of energy deposition of highly relativistic laser pulses in aligned nanowire arrays Adam F Moreau, Reed C Hollinger, Maria Gabriela Capeluto, Shoujun Wang, Yong Wang, Alex P Rockwood, Vural Kaymak, Alexander Pukhov, Alden H Curtis, Chase N Calvi, Vyacheslav N Shlyaptsev, Jorge Juan Rocca The ultrahigh energy density matter regime can be reached by irradiating arrays of vertically aligned nanowires with ultrahigh contrast fs laser pulses of relativistic intensities and joule-level energy [Ref 1,2]. The laser pulses penetrate deep into the array volumetrically heating the near solid density nanowire targets to multi-keV temperatures. As the wires explode a super-critical plasma fills the inter-wire gaps preventing further optical light from efficiently coupling into the volumetric plasma. Here we present the first results of the energy deposition dynamics into aligned Ni nanowires arrays at intensities up to 2 x 1021 Wcm-2 based on monitoring the x-ray emission and He-like ions line intensities. At these highly relativistic intensities the gaps in arrays of 100 nm diameter wires with average density 7% or 24 % solid density are measured to remain open for >100 fs. Knowledge of the gap closure dynamics will allow for optimal design of nanowire targets to match the pulse width and intensity of a given laser driver.
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Tuesday, November 6, 2018 4:24PM - 4:36PM |
JO8.00013: Au L shell emission from nanowire arrays irradiated at highly relativistic intensities Reed C Hollinger, Adam F Moreau, Maria Gabriela Capeluto, Yong Wang, Shoujun Wang, Alex P Rockwood, Alden H Curtis, Chase N Calvi, Vural Kaymak, Alexander Pukhov, Vyacheslav N Shlyaptsev, Jorge Juan Rocca Irradiating ordered nanostructure arrays with high contrast, femtosecond laser pulses at relativistic intensities allows for a unique combination of nearly complete optical absorption and light penetration much deeper than the typical optical penetration depth. This results in the volumetric heating of near solid density plasmas to multi keV temperatures up to several micron in depth [1]. Here we present the first results of Au nanowires volumetrically heated with highly relativistic femtosecond pulses with intensities up to 4x1021 Wcm-2. Time integrated x-ray spectra show strong line emission from the L shell of Au with sufficient resolution to identify different charge states up to Ne-like Au (Au+69). The increased volume of this plasma hampers the hydrodynamic expansion time while the large electron density contributes to a faster radiative cooling time, creating a more efficient x-ray source than solid density targets [2]. Experimental results will be presented and compared to the result of detailed particle in cell simulations.
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Tuesday, November 6, 2018 4:36PM - 4:48PM |
JO8.00014: A bright laser-driven X-ray and particle source based on micro-structured silicon targets Markus Roth, Nico W. Neumann, Leonard N.K. Döhl, Jonathan Jarrett, Christopher Baird, Tina Ebert, Robert Heathcote, Markus Hesse, Aasia Hughes, Paul McKenna, David Neely, Dean Rusby, Christopher Spindloe, Gabriel Schauman, Alexandra Tebartz, Nigel Woolsey We report on the first use of micro-structured targets with highly light absorbing properties in high power laser-plasma science. Spectral and spatial investigation of reflectance, X-ray generation, electron and ion acceleration in the experiment demonstrate the performance of the novel, robust targets. Using high contrast lasers on micro-structured silicon targets we demonstrate a significant increase in electron, ion and X-ray yield compared to flat foil targets. The micro-structured surface decreases reflection losses from the interaction area significantly, while an increased brilliance in X-ray radiation is measured. In addition, while a boost in the particle flux is observed, the mean ion and electron temperatures are comparable between the two target types. Employing the strong performance of the source we present here, the impact of further investigations of micro-structured silicon targets to the field of versatile and powerful laser-driven particle and X-ray sources is motivated. |
Tuesday, November 6, 2018 4:48PM - 5:00PM |
JO8.00015: Photon Acceleration in the Ionization Front of a Flying Focus Andrew Howard, David Turnbull, Andrew Davies, Dustin H. Froula, John Palastro A high-intensity laser pulse propagating through a medium triggers an ionization front that can frequency upshift and accelerate the photons of a secondary pulse. Dramatic frequency shifts, for instance from the optical to extreme UV, require that the photons remain in the ionization front over an extended distance. Traditionally, however, several effects have limited the interaction distance: the accelerated photons quickly outpace the ionization front, and the ionizing pulse diffracts or refracts from the plasma. The “flying focus”—a moving focal point resulting from a chirped laser pulse focused by a chromatic lens—overcomes these limitations. A flying focus pulse can drive a counter-propagating ionization front that travels at the speed of light in vacuum over a distance much greater than the Rayleigh range. Here we present photon kinetics simulations demonstrating photon acceleration in such a front. |
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