Bulletin of the American Physical Society
63rd Annual Meeting of the APS Division of Plasma Physics
Volume 66, Number 13
Monday–Friday, November 8–12, 2021; Pittsburgh, PA
Session GO05: Coherent Radiation and Intense Laser-Driven X-ray SourcesOn Demand
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Chair: Ishay Pomerantz, Tel-Aviv University, Israel Room: Rooms 306-307 |
Tuesday, November 9, 2021 9:30AM - 9:42AM |
GO05.00001: Spatiotemporal Control of Laser Intensity Through Cross-Phase Modulation Tanner T Simpson, Dillon W Ramsey, Philip Franke, Dustin H Froula, John P Palastro Spatiotemporal pulse shaping provides control over the trajectory and range of an intensity peak. While this control can enhance laser-based applications, the optical configurations required for shaping the pulse can constrain the transverse or temporal profile, the orbital angular momentum (OAM), or the duration. Here we present a novel technique for spatiotemporal control that eliminates these constraints by using a "stencil" pulse to spatiotemporally structure a second, primary pulse through cross-phase modulation in a Kerr lens. The temporally shaped stencil pulse imparts a time-dependent focusing phase on to the primary pulse. This technique, the "flying focus X," allows the primary pulse to have any profile, OAM, or duration, expanding the flexibility of spatiotemporal pulse shaping for laser-based applications. As an example, simulations show that the flying focus X can deliver an arbitrary velocity, ultrashort intensity peak with OAM over distances much longer than a Rayleigh range. |
Tuesday, November 9, 2021 9:42AM - 9:54AM |
GO05.00002: High-power THz radiation generation during oblique-collision of two electron beams into a plasma Manoj Kumar, Teyoun Kang, Hyung Seon Song, Min Sup Hur The Langmuir waves excited by two counter-propagating electron beams via two-stream instability, collide to each other at an oblique angle, which forms a high level density modulation in the interaction region, where the both beam electrons are trapped. As a result, spatially-localized Langmuir wave-packets with large amplitude of longitudinal electric field are formed, which give rise to the bursts of electromagnetic radiation. Our two-dimensional particle-in-cell simulations for oblique-collision of low-density electron beams with different transverse profiles, show that a strong THz emission is obtained at second-harmonic of plasma frequency with a narrow spectral-width in vacuum, which is enhanced significantly compared to the head-on-collision1-2. The THz power-conversion efficiency is reached around ~ 0.0725, for the continuous injection of electron beams into the plasma, which makes it suitable for applications requiring high-power narrow-band THz radiation sources. |
Tuesday, November 9, 2021 9:54AM - 10:06AM |
GO05.00003: High-Power, High-Energy Laser-Plasma THz Generation with Joule- and Kilojoule-Class Lasers Gerrit Bruhaug, Hans Rinderknecht, Mingsheng Wei, Gilbert Collins, J. Ryan R Rygg, Yiwen E, Xi-Cheng Zhang, Kareem Garriga, Roger J Smith, Ales Necas, Kan Zhai |
Tuesday, November 9, 2021 10:06AM - 10:18AM |
GO05.00004: Phase matched plasma wakefield photon acceleration Ryan Sandberg, Alexander G Thomas We present Phase Matched Plasma Wakefield Photon Acceleration (PMPA), a scheme for dephasingless photon acceleration in a particle-beam-driven wake. Electromagnetic radiation seeing a decreasing plasma gradient shifts up in frequency. In PMPA, a laser pulse is situated in the wake of a relativistic electron bunch so that it sees a decreasing density gradient. Using a tapered density profile to keep witness laser pulse at the phase in the wake where the density is decreasing, simulations suggest that the frequency of the witness pulse can be shifted up by a factor of 5-10. |
Tuesday, November 9, 2021 10:18AM - 10:30AM |
GO05.00005: Optical Shock-Enhanced Self-Photon Acceleration Philip Franke, Dillon W Ramsey, Tanner T Simpson, Dustin H Froula, John P Palastro Broadband sources of coherent radiation find diverse utility across many scientific disciplines as experimental drivers and diagnostic tools. State-of-the-art supercontinuum sources, which primarily achieve spectral broadening through Kerr-induced self-phase modulation of ultrashort laser pulses, have been limited to wavelengths >100 nm. Extending broadband sources into the extreme ultraviolet (EUV, \lambda< 100 nm) would benefit several key applications. In principle, large spectral shifts can be obtained over short interaction lengths in a rapidly ionizing medium, but so far, photon acceleration from optical to EUV frequencies has met with limited success. Combining spatiotemporal and transverse intensity profile shaping of a short pulse laser can largely eliminate the adverse effects of diffraction, refraction, and dephasing in a photon accelerator. This structured flying focus drives a guiding plasma density profile that moves at a tunable focal velocity in a homogenous, partially ionized plasma, opening a new self-shocked photon acceleration regime. This regime is characterized by extreme self-steepening and spectral broadening of the laser light, culminating in the formation and collapse of an optical shock. We demonstrate this optical shock-enhanced self-photon acceleration in a structured flying-focus driven plasma, and show that multi-octave spectra extending well into the EUV (400 nm to 60 nm) can be generated over <100 \mum of interaction length. A simple short-pass filter can isolate coherent, high intensity (>1 x 1015 W/cm2), sub-fs pulses (<400 as) from the accelerator output, without the need for post-compression. |
Tuesday, November 9, 2021 10:30AM - 10:42AM |
GO05.00006: Generation of Terawatt Attosecond Pulses from Relativistic Transition Radiation Xinlu Xu, David Cesar, Sebastien Corde, Vitaly Yakimenko, Mark J Hogan, Chandrashekhar Joshi, Agostino Marinelli, Warren B Mori When a femtosecond duration and hundreds of kiloampere peak current electron beam traverses the vacuum and high-density plasma interface, a new process, that we call relativistic transition radiation (RTR), generates an intense ∼100 as pulse containing ∼1 terawatt power of coherent vacuum ultraviolet (VUV) radiation accompanied by several smaller femtosecond duration satellite pulses. This pulse inherits the radial polarization of the incident beam field and has a ring intensity distribution. This RTR is emitted when the beam density is comparable to the plasma density and the spot size much larger than the plasma skin depth. Physically, it arises from the return current or backward relativistic motion of electrons starting just inside the plasma that Doppler up shifts the emitted photons. The number of RTR pulses is determined by the number of groups of plasma electrons that originate at different depths within the first plasma wake period and emit coherently before phase mixing. |
Tuesday, November 9, 2021 10:42AM - 10:54AM |
GO05.00007: Low-Order Harmonics Emitted from Relativistic Plasma Mirrors Driven by Two-Color and Elliptically Polarized Lasers Nicholas M Fasano, Matthew R Edwards, Andreas M Giakas, Anatoly Morozov, Timothy Bennett, Julia M Mikhailova Plasma mirrors are created when high-power light is focused onto the surface of a solid target causing rapid ionization of the target's surface. They have been demonstrated as a practical optical component for numerous applications, including temporal contrast enhancement, spatial mode cleaning, specular reflection, and focusing of high-power lasers. In addition, plasma mirrors driven by relativistic intensities leads to the generation of coherent harmonic radiation with wavelengths spanning from the infrared to the soft x-ray regime. Previous experimental and theoretical works have used spatially and temporally structured light waveforms for controlling the relativistic plasma dynamics leading up to the emission of these harmonics, which in turn allows for controlling the properties of the emitted radiation. In this work, we characterize the low-order harmonics emitted from a plasma mirror that is relativistically driven by a two-color laser and an elliptically polarized laser. We present measurements of the conversion efficiency and the polarization state of the first three harmonics and compare the results with three-dimensional particle-in-cell simulations. |
Tuesday, November 9, 2021 10:54AM - 11:06AM |
GO05.00008: High-harmonic pulses driven by a flying focus John P Palastro, Philip Franke, Dustin H Froula, Khanh Linh Nguyen, Dillon W Ramsey, Tanner T Simpson, Kathleen Weichman An intense laser pulse can accelerate a photoionized electron back into its parent ion unleashing a broad spectrum of high-harmonic radiation. Conventional techniques for driving coherent pulses of this radiation rely on a delicate balance of dispersion and geometry to achieve phase matching and minimize absorption. Here we discover that spatiotemporally shaped laser pulses enable a novel technique for driving high-harmonic pulses that allows the radiation to accumulate without precise phase matching or significant absorption. By travelling faster than the phase velocity of the radiation, the intensity peak of a spatiotemporally shaped pulse can ionize and drive electron collisions ahead of the existing phase fronts. This prevents the transfer of energy back to the laser pulse and eliminates single-photon absorption in the downstream medium, increasing the energy radiated into broadband, extreme ultraviolet pulses by orders of magnitude. |
Tuesday, November 9, 2021 11:06AM - 11:18AM |
GO05.00009: Nonlinear Thomson Scattering with Ponderomotive Control Dillon W Ramsey, Bernardo F Malaca, Antonino Di Piazza, Martin Formanek, Philip Franke, Dustin H Froula, Miguel Pardal, Tanner T Simpson, Jorge Vieira, Kathleen Weichman, John P Palastro In nonlinear Thomson scattering, a relativistic electron reflects and reradiates the photons of a laser pulse, converting optical light to x rays or beyond. While this extreme frequency conversion offers a promising source for probing high-energy-density materials and driving uncharted regimes of nonlinear quantum electrodynamics, conventional nonlinear Thomson scattering has inherent trade-offs in its scaling with laser intensity. Here we discover that the ponderomotive control afforded by spatiotemporal pulse shaping enables novel regimes of nonlinear Thomson scattering that substantially enhance the scaling of the radiated power, emission angle, and frequency with laser intensity. By appropriately setting the velocity of the intensity peak, a spatiotemporally shaped pulse can increase the power radiated by orders of magnitude. The enhanced scaling with laser intensity allows for operation at significantly lower electron energies and eliminates the need for a high-energy electron accelerator. |
Tuesday, November 9, 2021 11:18AM - 11:30AM Not Participating |
GO05.00010: Towards realizing free-electron lasing with the BELLA Center laser-plasma accelerator Jeroen van Tilborg, Sam Barber, Curtis Berger, Fumika Isono, Cameron R Geddes, Carl B Schroeder, Eric Esarey One of the promising applications of laser-plasma accelerators (LPAs) is the ability to produce electron beams of sufficient brightness to drive a free-electron laser (FEL). The BELLA Center has coupled a dedicated 100-TW-class laser system to a down-ramp-injector LPA, advanced electron beam transport line, and strong-focusing undulator, making advances towards an LPA-driven FEL. In this contribution we will present an update on observations on advanced transport concepts for the laser and electron beam, including active stabilization feedback on the high-power laser system, optimization of the LPA source, correlation studies on the laser-plasma accelerator produced electron beams, all in the context of control and transport of the electron beam to the undulator to drive FEL lasing. |
Tuesday, November 9, 2021 11:30AM - 11:42AM |
GO05.00011: Frequency redshift of seeded FEL radiation generated with a low-energy chirped electron beam Fumika Isono, Carl B Schroeder, Jeroen van Tilborg, Sam Barber, Eric Esarey One method to achieve coherent radiation in a free-electron laser (FEL) driven by a laser-plasma accelerator is to reduce the electron beam slice energy spread by stretching the beam in a chicane, producing a linear energy chirp. Seed radiation at the resonant wavelength propagating in an undulator with the energy-chirped beam may be coherently amplified. With such a linear-energy-chirped beam, it is observed in simulations using Genesis 1.3 that the peak frequency of the seeded FEL radiation redshifts linearly with the amount of electron beam chirp and the undulator propagation distance, and inversely with the undulator wavelength and electron energy. This observed FEL radiation redshifting is explained by the dispersion of the microbunching structures during propagation due to the energy chirp of the electron beam, and analysed using the coupled Maxwell-Vlasov equations. Implications for planned laser-plasma accelerator driven FEL experiments at the BELLA Center are discussed. |
Tuesday, November 9, 2021 11:42AM - 11:54AM |
GO05.00012: Efficient Electron Acceleration and MeV Photon Radiation in Relativistically Transparent Magnetic Filaments Hans Rinderknecht, Gerrit Bruhaug, Matthew Van Dusen-Gross, Mingsheng Wei, Kathleen Weichman, John P Palastro, Alexey Arefiev, Tao Wang, Alejandro Laso Garcia, Toma Toncian, Hernan J Quevedo, Todd Ditmire, Domenico Doria, Klaus Spohr, Jarrod Williams, Alex Haid In relativistically transparent interactions, lasers with intensity above 1020 W/cm2 drive relativistic current filaments with ultrastrong azimuthal magnetic fields in classically overdense plasmas. These magnetic fields trap electrons, which are directly accelerated by the laser pulse to hundreds of MeV and efficiently radiate MeV-scale photons by synchrotron radiation. We present scaling laws that describe the radiated photon energy and radiation efficiency of this process, and the results of initial experiments to test this phenomenon at the Texas Petawatt Laser (TPW). The analytical scaling laws are validated by 3-D particle-in-cell simulations in two regimes of focal radius. Radiation efficiency is predicted to exceed 10% for laser intensity above 6×1021 W/cm2. Experiments at TPW using moderate laser intensity (1021 W/cm2) demonstrate the predicted signatures of electron acceleration and x-ray radiation from a subset of microchannel targets filled with low-density CH foam. Optimization of this ultrafast photon source for applications in high-energy-density, nuclear, and high-field physics is discussed. |
Tuesday, November 9, 2021 11:54AM - 12:06PM |
GO05.00013: Superradiant x-ray emission in nonlinear plasma wakefields Miguel Pardal, Jorge Vieira, Ricardo A Fonseca Plasma accelerator based betatron radiation stands as a promising alternative towards a compact x-ray source. The production of temporally coherent betatron x-rays, however, is yet to be observed experimentally since it requires very high quality electron bunches in order to enable the onset of the microbunching instability. |
Tuesday, November 9, 2021 12:06PM - 12:18PM |
GO05.00014: Laser driven MeV photon source development at BELLA Center Tobias M Ostermayr, Hai-En Tsai, Robert E Jacob, Sahel Hakimi, Liona Fan-Chiang, Samuel Barber, Fumika Isono, Jeroen van Tilborg, Anthony J Gonsalves, Kei Nakamura, Csaba Toth, Carl B Schroeder, Cameron R Geddes, Eric Esarey Compact, narrow bandwidth, femtosecond-pulsed, MeV photon sources (MPS) could have important applications in nuclear nonproliferation, medicine, industrial computed tomography, and photo-nuclear spectroscopy. Our all-optical source produces MeV photons through Thomson scattering of a laser pulse off relativistic electron beams produced in a laser-plasma accelerator (LPA). The overall system is driven by two high power laser systems for driving the LPA and producing MeV photons. Both feature independent amplification and compression, as well as femtosecond-level temporal synchronization to enable high photon flux with controlled yield and bandwidth. Ongoing updates will provide advanced control of the spatial and temporal pulse shapes for further optimization. |
Tuesday, November 9, 2021 12:18PM - 12:30PM |
GO05.00015: Quadrupole focused LWFA electron beam driven bremsstrahlung gamma ray source Vigneshvar Senthilkumaran, Keegan Behm, David Bailie, Jonathan Warwick, Guillermo M Samarin, Anatoly M Maksimchuk, John Nees, Gianluca Sarri, Alec G.R. Thomas, Karl M Krushelnick, Amina E Hussein Laser wakefield accelerators (LWFA) generate low transverse emittance, ultrashort electron bunches, and produce synchrotron-like light sources. To mitigate the issue of electron beam blowup, quadrupoles are employed to introduce strong focusing and efficient transport of the LWFA electron beams. This research work incorporated focused LWFA electron beams using a triplet quadrupole system along with a lead converter to examine the generation of intense gamma beams. We will discuss the generation of gamma ray beams and emphasize its energy spectrum, energy transfer, number of photons, focusing geometry, and flux through the results obtained by the Monte Carlo simulation of focused LWFA electron beam hitting the copper stack with and without a bremsstrahlung converter. |
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