When strong fields interact with matter, non-linear effects occur which set a number of interesting processes in motion. Our work ranges from the study of the photoelectron spectra of atoms, diatomic molecules, very sharp metal needles or metal surfaces [1–3] to the emission of high-frequency radiation (‘high-harmonic generation’) from atoms, molecules and solids [4, 5]. To this end, we also investigate charge transport in insulators under the influence of strong laser fields [6]. To simulate these processes, we use semi-classical methods, solve the time-dependent Schrödinger equation, or model the systems using large software packages for time-dependent density functional theory calculations. All research in this field is carried out in close collaboration with experimental groups.

© Isabella Floss

Figure 1: The excitation of a dielectric by an external laser field gives rise to non-linear effects that lead to the emission of high-frequency radiation (‘high-harmonic generation’). Interference effects lead to the…

Figure 1: The excitation of a dielectric by an external laser field gives rise to non-linear effects that lead to the emission of high-frequency radiation (‘high-harmonic generation’). Interference effects lead to the cancellation or amplification of certain frequencies during propagation through the material (front: spectrum at the incident surface; rear: spectrum of the emitted radiation)

We are currently investigating the decoherence of conduction electrons excited by ultrashort pulses (Fig. 1, [7]) using a quantum Monte Carlo simulation that takes into account the interaction of the electrons with the crystal ("thermal bath") and between multiple excited electrons.

In another research project, we are investigating the emission of photoelectrons, which, for ultrashort laser pulses, depends on the precise shape of the field profile. Significant differences have been observed between crystalline and amorphous materials [3], and water surfaces have also been investigated.

[1] A. Suñer-Rubio, C. Lemell, R.Y. Bello, J. Burgdörfer, A. Palacios, F. Martín, Phys. Rev. Res. 6, L022066 (2024), opens an external URL in a new window.

[2] M. Krüger, C. Lemell, G. Wachter, J. Burgdörfer, P. Hommelhoff, J. Phys B 51, 172001 (2018), opens an external URL in a new window.

[3] D. Potamianos, M. Schnitzenbaumer, C. Lemell, P. Scigalla, F. Libisch, E. Schock-Schmidtke, M. Haimerl, C. Schröder, M. Schäffer, J.T. Küchle, J. Riemensberger, K. Eberle, Y. Cui, U. Kleineberg, J. Burgdörfer, J.V. Barth, P. Feulner, F. Allegretti, R. Kienberger, Science Adv. 10, eado0073 (2024), opens an external URL in a new window.

[4] M. Monfared, E. Irani, C. Lemell, J. Burgdörfer, Phys. Rev. A 106, 053108 (2022), opens an external URL in a new window.

[5] I. Floss, C. Lemell, K. Yabana, J. Burgdörfer, J. Phys.: Conf. Ser. 1412, 082007 (2020), opens an external URL in a new window.

[6] M. Ossiander, K. Golyari, K. Scharl, L. Lehnert, F. Siegrist, J.P. Bürger, D. Zimin, J.A. Gessner, M. Weidman, I. Floss, V. Smejkal, S. Donsa, C. Lemell, F. Libisch, N. Karpowicz, J. Burgdörfer, F. Krausz, M. Schultze, Nature Comm. 13, 1620 (2022), opens an external URL in a new window.

[7] I. Floss, C. Lemell, G. Wachter, V. Smejkal, S.A. Sato, X.-M. Tong, K. Yabana, and J. Burgdörfer, Phys. Rev. A 97, 011401(R) (2018), opens an external URL in a new window and I. Floss, C. Lemell, K. Yabana, and J. Burgdörfer, Phys. Rev. B 99, 224301 (2019), opens an external URL in a new window.