Time Resolved Investigation of Coherent Surface Phonon Polaritons*

The sub-wavelength confinement and enhanced electric field created by plasmons render accessible precise sensing and strong coupling at room temperature. [1, 2] However, the high frequency and short lifetime of plasmons inhibit the full potential of this technology and substitutes with longer lifetime and that can be studied in the time domain are being sought-after. [3] Here, we propose and demonstrate an experimental approach using femtosecond pump-probe spectroscopy allowing the time-domain study of surface phonon polaritons. We first build a theoretical framework for the generation and detection of these modes that we verify experimentally. By comparing experiments and Finite Difference Time Domain simulations we highlight that dark and bright modes are simultaneously generated. Thanks to this time-domain method, we then investigate mode dependent decay and energy transfer to the environment. Our observations open the way to deeper investigations of the role of coherence in the rich polariton physics.

[1] Maier, S. A. Plasmonics: Fundamentals and Applications (Springer, 2007).
[2] Törmä, P. & Barnes, W. L. Strong, Rep. Prog. Phys. 78, 013901 (2015).
[3] R. Hillenbrand, T. Taubner & F. Keilmann, Nature 418, 159 (2002).