Surface plasmon-based detection for picosecond ultrasonics in planar gold-dielectric layer geometries

F Noll; N Krauß; V Gusev; T Dekorsy; M Hettich

doi:10.1016/j.pacs.2023.100464

Surface plasmon-based detection for picosecond ultrasonics in planar gold-dielectric layer geometries

Photoacoustics. 2023 Feb 23:30:100464. doi: 10.1016/j.pacs.2023.100464. eCollection 2023 Apr.

Authors

F Noll^{1

2}, N Krauß¹, V Gusev³, T Dekorsy^{1

4}, M Hettich^{1

2}

Affiliations

¹ Department of Physics, University of Konstanz, 78464 Konstanz, Germany.
² Research Center for Non-Destructive Testing GmbH (RECENDT), Altenbergerstr. 69, 4040 Linz, Austria.
³ Laboratoire d'Acoustique de l'Université du Mans (LAUM), UMR 6613, Institut d'Acoustique - Graduate School (IA-GS), CNRS, Le Mans Université, Av. O. Messiaen, 72085 Le Mans, France.
⁴ Institute of Technical Physics, German Aerospace Center, Pfaffenwaldring 38-40, 70569 Stuttgart, Germany.

Abstract

Longitudinal acoustic modes in planar thin gold films are excited and detected by a combination of ultrafast pump-probe photoacoustic spectroscopy and a surface plasmon resonance (SPR) technique. The resulting high sensitivity allows the detection of acoustic modes up to the 7th harmonic (258 GHz) with sub-pm amplitude sensing capabilities. This makes a comparison of damping times of individual modes possible. Further, the dynamics of the real and imaginary part of the dielectric function and the film's thickness variation are separated by using the dependence of the amplitudes of the acoustic modes on the detection angle and the surface plasmon resonance. We find that longitudinal acoustic modes in the gold films mainly affect the real part of the dielectric function and highlight the importance to consider thickness related effects in acousto-plasmonic sensing.

Keywords: ASOPS; ASOPS, Asynchronous optical sampling; Acousto-plasmonics; Attenuated Total Reflection (ATR); Coherent Acoustic Phonons; Picosecond ultrasonics; Surface plasmon resonance (SPR); Thin Films.