Title: Vibrational Spectroscopy and Optomechanical Interactions with Tip-enhanced Nanocavities
When: Thursday, June 05, 2025, 12:00
Place: Department of Theoretical Condensed Matter Physics, Faculty of Sciences, Module 5, Seminar Room (5th Floor)
Speaker: Philippe Roelli, CIC nanoGUNE BRTA, 20018 Donostia-San Sebastián, Spain.
Subwavelength nanocavities have been an essential tool for interrogating matter at the nanoscale and investigating fundamental processes that govern light-matter interactions. Particularly, in the field of spectroscopy, nanocavities have enabled access to optoelectronic properties of single molecules through various optical processes including Raman scattering, photoluminescence, coherent anti-Stokes Raman scattering and two-photon absorption. However, several challenges, such as (i) efficiently coupling incoming light to the nanocavities, and (ii) tuning the interaction between the molecules and nanocavities in operando, remain open. In this talk, I’ll present how field enhancements inside nanocavities across visible (VIS) and infrared (IR) regions of the electro-magnetic spectrum can be controlled via the scanning metallic tip of a s-SNOM microscope. Specifically, I’ll introduce the concept of tip-enhanced nanocavity and illustrate its potential with one first application: continuous-wave (CW) IR-to-VIS upconversion. Singularly, in our experiment, the nanomechanical positioning of the microscope’s tip controls the emergence of upconverted photons from the molecule-filled gap of a nanoparticle-on-mirror (NPoM) cavity. This first study highlights the versatility of tip-enhanced nanocavities and their potential for broader applications in nonlinear optics studies of diverse 2D materials and thin molecular films. More generally, by leveraging the coupling strength uniquely accessible to molecular vibrations in the mid-IR and the single-photon detection capabilities available in the visible range, our study points to new strategies for the observation of cavity QED phenomena in the few-molecules limit.
References
- P. Roelli, I. Pascual, I. Niehues, J. Aizpurua & R. Hillenbrand, accepted in Light: Science & Applications (2025)
- P. Roelli, H. Hu, E. Verhagen, S. Reich & C. Galland, Perspective article in ACS Photonics, 4486-4501 (2024)
- W. Chen, P. Roelli, et al., Science 374, 1264–1267 (2021).
