Dresden 2020 – scientific programme
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MA: Fachverband Magnetismus
MA 21: Ultrafast Magnetization II
MA 21.4: Talk
Tuesday, March 17, 2020, 10:15–10:30, HSZ 101
Strain generation via two-photon absorbtion in Bi:YIG visualized with UXRD — •Steffen Peer Zeuschner1,2, Jan-Etienne Pudell1, Alexander von Reppert1, Marwan Deb1, Elena Popova3, Niels Keller3, Matthias Rössle2, Marc Herzog1, and Matias Bargheer1,2 — 1Institut für Physik und Astronomie, Universität Potsdam, 14476 Potsdam, Germany — 2Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, Wilhelm-Conrad-Roentgen Campus, BESSY II, 12489 Berlin, Germany — 3Groupe d'Etude de la Matiére Condensée (GEMaC), CNRS UMR 8635, Université Paris-Saclay, 78035 Versailles, France
By ultrafast X-ray diffraction (UXRD) we quantify the strain from coherent and incoherent phonons generated by one- and two-photon absorption in bismuth-doped yttrium iron garnet (Bi:YIG). This ferrimagnetic insulator is a workhorse for laser-induced spin dynamics that may be excited indirectly via phonons. We identify the two-photon absorption by the quadratic fluence dependence of the transient strain and confirm a short lifetime of the intermediate state via the inverse proportional dependence on the pump-pulse duration. From this, we estimate the two-photon absorption coefficient at 800nm using the linear relation between strain and absorbed energy density. For below band gap excitation, large fluences of about 100 mJ/cm2 and a pulse duration of 120 fs lead to considerable strain amplitudes of 0.1% which are driven exclusively by two-photon absorption.