LPHYS'26.    Plenary Speakers:

  1. Quantum Engineering of Strong Field Physics

    • Photo

      Thomas Brabec


      Department of Physics, University of Ottawa, Ottawa, ON, Canada
    Biography:

    Thomas Brabec received his PhD in 1992 and his Habilitation in 1997 from the Vienna University of Technology. Since 2002, he has been a Professor in the Department of Physics at the University of Ottawa and a Canada Research Chair in Ultrafast Photonics.

    His research expertise lies in ultrafast science, nonlinear optics, quantum and classical dynamics, and strong-field dynamics in gases and solids. He has authored more than 200 peer-reviewed publications in these areas, which have received broad international recognition.

    Abstract:

    Strong field physics started in atomic and molecular physics and extended over the past decade to material science. While atoms are isolated systems, in solids many-body effects due to the interaction with the environment have to be considered. As full many-body treatments are extremely challenging, this is usually done by defining an effective dephasing time T2 within the relaxation time approximation. However, the relaxation time approximation causes “dephasing ionization”, resulting in an unphysical enhancement of ionization by up to orders of magnitude. As such, a more sophisticated model is needed that ideally maintains simplicity and wide applicability of the relaxation time approximation.

    In the first part, such a (spin-boson) model will be introduced, based on a coupling between electron and a bosonic harmonic oscillator heat bath. The heat bath can accurately represent phonons, and collective electronic excitations, such as excitons, and plasmons. A parameters scan reveals that the unphysical aspects of dephasing ionization disappear; only in exotic materials with strong heat bath coupling novel ionization effects are predicted.

    In the second part, we recognize that light can also serve as a heat bath, with the advantage that nature and strength of the coupling can be controlled by pulse energy and photon distribution. Specifically, two-color experiments are discussed with a moderately intense classical laser pulse, and a perturbative quantum field, such as bright squeezed vacuum (BSV), acting as a “quantum heat bath”. Very moderate BSV fields are found to enhance ionization and HHG by orders of magnitude, thus allowing control of fundamental strong field processes. The lower required intensities remedy a key weakness of strong laser fields; that they distort the very processes they are meant to measure.

    In the last part, the quantum properties of harmonic radiation generated by a superposition of classical and perturbative quantum fields are discussed. The central idea is to transfer quantum properties from the perturbative quantum field to the harmonic pulse, thus shifting the generation of quantum pulses from the infrared into the XUV. We show how the entanglement between quantum beam and harmonics can be harnessed to create a variety of non-classical states commonly used in quantum information science, such as high purity single photon states, Schrödinger cat states, and photon added squeezed vacuum states. This opens a path towards engineering the quantum properties of ultrashort high harmonics.

  2. High-power Single-Frequency Multimode Fiber Laser Amplifiers

    • Photo

      Hui Cao


      Department of Applied Physics, Yale University, New Haven, CT, USA
    Biography:

    Hui Cao is the John C. Malone Professor of Applied Physics, a Professor of Physics, and a Professor of Electrical Engineering at Yale University. She received her Ph.D. degree in Applied Physics from Stanford University in 1997. Prior to joining the Yale faculty in 2008, she was on the faculty of Northwestern University for ten years.

    Her technical interests and activities are in the areas of mesoscopic physics, complex photonic materials and devices, nanophotonics, and biophotonics. Cao is a Fellow of IEEE, AAAS, APS, and OSA, and an elected member of the National Academy of Sciences and the American Academy of Arts and Sciences.

    Abstract:

    High-power fibre lasers are powerful tools used in science, industry, and defence. A major roadblock for further power scaling of single-frequency fibre laser amplifiers is stimulated Brillouin scattering. Efforts have been made to mitigate this nonlinear process, but these were mostly limited to single-mode or few-mode fibre amplifiers, which have good beam quality.

    Recently, we explored a highly multimode fibre amplifier in which stimulated Brillouin scattering was greatly suppressed due to a reduction of light intensity in a large fibre core and a broadening of the Brillouin scattering spectrum by multimode excitation. By applying a spatial wavefront-shaping technique to the input light of a nonlinear amplifier, the output beam was focused to a diffraction-limited spot.

    Our multimode fibre amplifier can operate at high power with high efficiency and narrow linewidth, which ensures high coherence. Optical wavefront shaping enables coherent control of multimode laser amplification, with potential applications in coherent beam combining, large-scale interferometry, and directed energy delivery.