Determination of hot carrier energy distributions from inversion of ultrafast pump-probe reflectivity measurements

• Type of Material: Article
• Authors: Tal Heilpern, Argonne National Laboratory; Manoj Manjare, Emory University; Alexander O. Govorov, Ohio University; Gary P. Wiederrecht, Argonne National Laboratory; Stephen K. Gray, Argonne National Laboratory; Hayk Harutyunyan, Emory University
• Language: English
• Date: 2018-05-10
• Publisher: Nature Publishing Group: Nature Communications
• Publication Version: Final Published Version
• Copyright Statement: © The Author(s) 2018
• License: Creative Commons Attribution 4.0 International
• Final Published Version (URL): http://dx.doi.org/10.1038/s41467-018-04289-3
• Title of Journal or Parent Work: Nature Communications
• ISSN: 2041-1723
• Volume: 9
• Issue: 1
• Start Page: 1853
• End Page: 1853
• Grant/Funding Information: This work was performed, in part, at the Center for Nanoscale Materials, a U.S. Department of Energy Office of Science User Facility, and supported by the U.S. Department of Energy, Office of Science, under Contract No. DE-AC02-06CH11357. M.M. and H.H. acknowledge support from Emory University startup funds and NSF EFMA – 1741691.
• Keywords: Science & Technology; METAL NANOPARTICLES; GOLD; RELAXATION; LIMIT; NOBLE-METALS; THERMALIZATION; Science & Technology - Other Topics; Multidisciplinary Sciences; ELECTRON DYNAMICS; FIELD CONFINEMENT
• Research Categories: Physics, General

Abstract

Developing a fundamental understanding of ultrafast non-thermal processes in metallic nanosystems will lead to applications in photodetection, photochemistry and photonic circuitry. Typically, non-thermal and thermal carrier populations in plasmonic systems are inferred either by making assumptions about the functional form of the initial energy distribution or using indirect sensors like localized plasmon frequency shifts. Here we directly determine non-thermal and thermal distributions and dynamics in thin films by applying a double inversion procedure to optical pump-probe data that relates the reflectivity changes around Fermi energy to the changes in the dielectric function and in the single-electron energy band occupancies. When applied to normal incidence measurements our method uncovers the ultrafast excitation of a non-Fermi-Dirac distribution and its subsequent thermalization dynamics. Furthermore, when applied to the Kretschmann configuration, we show that the excitation of propagating plasmons leads to a broader energy distribution of electrons due to the enhanced Landau damping.