par Ahmed Ghalgaoui
Department of Physics, Dortmund University
Mardi 4 février, 11h – Amphithéâtre de l’ISMO
The advent of intense, subpicosecond laser pulses at terahertz (THz) frequencies has revolutionized THz spectroscopy, enabling detailed investigations of physical, chemical, and biological systems. These advancements have also paved the way for time-resolved measurements, where THz pulses probe the dynamic response following optical excitation.
Even under non-resonant conditions, intense THz pulses can trigger highly nonlinear phenomena. For instance, THz electric fields can accelerate valence electrons into the conduction band, enhancing conductivity in semiconductors [1,2]. At even higher field strengths, tunneling can drive electrons directly from the valence to the conduction band [3,4].
Unlike near-infrared or visible excitation, which often leads to incoherent dynamics and significant entropy transfer, strong THz fields can drive systems into nonlinear regimes, enabling coherent dynamics with minimal entropy increase. In this seminar, I will delve into the origins of THz emission in noncentrosymmetric materials [5] and examine how intense THz pulses can trigger nonlinear processes in condensed matter systems. These processes include interband tunneling, symmetry breaking in solids [6], and their extension to liquid phases. In the liquid phase, I will explore how the interplay between intermolecular interactions and strong THz fields allows for the manipulation of charge dynamics and dielectric properties in aqueous systems [7-9].
[1] D. Nicoletti and A. Cavalleri, Nonlinear light–matter interaction at terahertz frequencies. Adv. Opt. Photon., 8, 401 (2016).
[2] P. Salén, M. Basini, J. Helbing, M. Krasilikov, A. Y. Nikitin, G. Shamuilov, Z. Tibai, V. Zhunerchyk and V. Goryahko, Matter manipulation with extreme terahertz light: Progress in the enabling THz technology. Phys. Rep. 836, 1 (2019).
[3] W. Kuehn, P. Gaal, K. Reimann, M. Woerner, T. Elsaesser, R. Hey, Terahertz-induced interband tunneling of electrons in GaAs. Phys. Rev. B 82, 075204 (2010).
[4]H. Hirori, K. Shinokita, M. Shirai, et al., Extraordinary carrier multiplication gated by a picosecond electric field pulse. Nat Commun 2, 594 (2011).
[5] A. Ghalgaoui, K. Reimann, M. Woerner, T. Elsaesser et al., Resonant second-order nonlinear terahertz response of gallium arsenide. Phys. Rev. Lett. 121, 266602 (2018).
[6] M. Runge, A. Ghalgaoui, I. G. Vallejo, F. Thiemann et al., Ultrafast carrier dynamics and symmetry reduction in bismuth by nonperturbative optical excitation in the terahertz range. Phys. Rev. B 107, 245140 (2023).
[7] A. Ghalgaoui, L.-M- Koll, B. Schütte, K. Reimann et al., Field-induced tunneling ionization and terahertz-driven electron dynamics in liquid water. J. Phys. Chem. Lett. 18, 7717 (2020).
[8] A. Ghalgaoui, B. P. Fingerhut, K. Reimann, M. Woerner, T. Elsaesser, Terahertz polaron oscillations of electrons solvated in liquid water, Phys. Rev. Lett. 126, 097401 (2021).
[9] P. Singh, J. Zhang, A. Ghalgaoui, K. Reimann, B. P. Fingerhut et al., Coherent polaron dynamics of electrons solvated in polar liquids. PNAS Nexus, 1,1-8 (2022).