LPHYS'20.    Plenary Speakers:

  1. Terahertz Pulses Generated by Classical or Relativistic Laser-Matter Interaction

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      Luc Bergé

      Alternative Energies and Atomic Energy Commission (CEA), Arpajon, France

    Terahertz pulses are very popular because of their numerous applications, for example, in security screening, medical imaging, time-domain spectroscopy and remote detection [1]. Located between microwaves and optical waves in the electromagnetic spectrum, terahertz waves can now be exploited in molecular spectroscopy from plasma emitters produced by femtosecond laser pulses ionizing gases such as air.

    At classical (non-relativistic) laser intensities, gas plasmas created by two-color optical pulses supply suitable emitters free of any damage. Electrons are tunnel ionized by the asymmetric light field usually composed of a fundamental wavelength and its second harmonic [2]. The resulting “photocurrent” polarized in the laser direction generates an ultrabroadband terahertz radiation, which finds direct applications in the coherent spectroscopy of complex molecules [3]. At relativistic intensities, plasma waves trigger a strong longitudinal field used in laser-wakefield acceleration. Accelerated electrons crossing the plasma-vacuum interface then emit coherent transition radiation operating in the terahertz band [4], which may be optimized by, e.g., increasing the laser wavelength [5].

    This talk will review the different physical mechanisms involved in the terahertz emission by laser-gas and laser-solid interaction at classical or relativistic intensity. Recent results on the plasma-based terahertz spectroscopy of solid materials will be presented in the context of the project ALTESSE. The last part of the talk will discuss new perspectives in the production of ultra-intense terahertz pulses from electron and ion acceleration in relativistic plasmas.

    1. [1] M Tonouchi, Nat. Photon. 1, 9691 (2007)
    2. [2] K-Y Kim, A J Taylor, J H Glownia, and G Rodriguez, Nat. Photonics 2, 605 (2008)
    3. [3] L Bergé, K Kaltenecker, S Engelbrecht, A Nguyen, S Skupin, L Merlat, B Fischer, B Zhou, I Thiele, and P U Jepsen, Europhys. Lett. 126, 24001 (2019)
    4. [4] J Déchard, A Debayle, X Davoine, L Gremillet, and L Bergé, Phys. Rev. Lett. 120, 144801 (2018)
    5. [5] J Déchard, X Davoine, and L Bergé, Phys. Rev. Lett. 123, 264801 (2019)
  2. Shaping Coherent XUV Beams for Controlled Attosecond Pulse Propagation


    Attosecond pulses are currently often emitted via high order harmonic generation in gases. These ultrashort pulses can be controlled in terms of bandwidth, chirp and pulse duration. They are a key tool to track ultrafast dynamics such as electronic relaxation or even state-dependent attosecond delays at ionization by measuring how the dephasing due to ionization evolves with the probed state. Most of these studies rely on spatially averaged measurements over the light/matter interaction volume. It generally assumes that in experiments, all XUV frequency components have the same spatial properties or that measuring an averaged dephasing in the spectral domain is sufficient to extract the full dynamics in the temporal domain.

    The spatial properties of these ultrashort XUV beams can nevertheless be complex [1-4]. In particular, it has been observed that the harmonic beams exhibit wavefronts with a radius of curvature that changes significantly with the harmonic order [5] and that several harmonic can have very different spatial profiles [6]. This implies that all refocused harmonics are not automatically overlapped into an experimental target, thus implying that the XUV bandwidth can be very space dependent. This impacts the temporal profile of attosecond pulses that evolves during propagation. As a consequence, controlling attosecond pulse propagation remains challenging.

    During this talk, I will present work on spatial shaping of coherent XUV beams via wavefront shaping and present a model that predicts the XUV beam profile and allow controlling attosecond pulse propagation. This work showed that separating spatially the XUV foci is a way to achieve XUV spectral filtering with high efficiency [7] and that spatially shaping the fundamental beam is a powerful way to generate XUV beams with controlled properties.

    1. [1] A Dubrouil, O Hort, F Catoire, D Descamps, S Petit, E Mével, V V Strelkov, and E Constant, Nat. Commun. 5, 4637 (2014)
    2. [2] F Catoire, A Ferré, O Hort, A Dubrouil, L Quintard, D Descamps, S Petit, F Burgy, E Mével, Y Mairesse, and E Constant, Phys. Rev. A 94, 063401 (2016)
    3. [3] E Frumker, G G Paulus, H Niikura, A Naumov, D M Villeneuve, and P B Corkum, Opt. Express 20, 13870 (2012)
    4. [4] L Quintard, V Strelkov, J Vabek, O Hort, A Dubrouil, D Descamps, F Burgy, C Péjot, E Mével, F Catoire, and E Constant, Sci. Adv. 5, eaau7175 (2019)
    5. [5] K Veyrinas, C Valentin, D Descamps, C Péjot, F Burgy, F Catoire, E Constant, and E Mével, arXiv:1912.12707 (2019)
    6. [6] H Wikmark, C Guo, J Vogelsang, P W Smorenburg, H Coudert-Alteirac, J Lahl, J Peschel, P Rudawski, H Dacasa, S Carlström, S Maclot, M B Gaarde, P Johnsson, C L Arnold, and A L'Huillier, P Natl. Acad. Sci. USA 116, 4779 (2019)
    7. [7] M Nisoli, E Priori, G Sansone, S Stagira, G Cerullo, S De Silvestri, C Altucci, R Bruzzese, C de Lisio, P Villoresi, L Poletto, M Pascolini, and G Tondello, Phys. Rev. Lett. 88, 033902 (2002)
  3. Instabilities to Extremes – Real Time Measurements in Nonlinear Fibre and Laser Systems


    Real-time ultrafast measurement techniques have revolutionized the study of instabilities in optics and have revealed new parallels with similar processes in wider areas of physics. For example, considering the particular case of nonlinear pulse propagation in optical fiber, it has been possible to develop an analogy between noise-induced modulation instability and soliton localization, with the emergence of giant rogue waves on the ocean. And in the case of instabilities in mode-locked lasers, it is now possible to directly study a wide range of nonlinear dynamical processes never before observed such as soliton emergence from noise, soliton molecule growth and decay, soliton explosions, and chaos. This talk will review a selection of recent results in this area, considering implications both for fundamental studies of nonlinear dynamics, as well as for practical laser development.

  4. Squeezing and Random Number Generation on a Chip

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      Alexander L Gaeta

      Department of Applied Physics and Applied Mathematics, Columbia University, New York, NY, USA

    Chip-based nonlinear photonics has shown to be a powerful platform for demonstrating nonlinear optical processes such as supercontinuum generation, four-wave mixing, and Kerr-comb generation. I will discuss our recent results showing that these processes can be expanded to produce squeezed states of light and random number generation in microresonators.

  5. Heat and Hall Transport in Strongly Interacting Quantum Gases

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      Martin Zwierlein

      Massachusetts Institute of Technology, Cambridge, MA, USA

    Understanding transport in the strongly interacting quantum matter is one of the greatest challenges of many-body physics. Homogeneous samples of ultracold atomic gases provide a remarkable opportunity to study transport down to the single-atom level. However, while particle and spin transport is rather readily accessible, the transport of heat and momentum, as well as transport in the presence of gauge fields, requires the development of novel tools and techniques. I will present our recent direct observation of heat transport in strongly interacting Fermi gases using local thermometry, as well as novel measurements of Hall viscosity in a quantum gas under rotation.