Coherent upconversion of terahertz and mid-infrared signals into visible light opens new horizons for spectroscopy, imaging, and sensing but represents a challenge for conventional nonlinear optics. Here, we used a plasmonic nanocavity hosting a few hundred molecules to demonstrate optomechanical transduction of submicrowatt continuous-wave signals from the mid-infrared (32 terahertz) onto the visible domain at ambient conditions. The incoming field resonantly drives a collective molecular vibration, which imprints a coherent modulation on a visible pump laser and results in upconverted Raman sidebands with subnatural linewidth. Our dual-band nanocavity offers an estimated 13 orders of magnitude enhancement in upconversion efficiency per molecule. Our results demonstrate that molecular cavity optomechanics is a flexible paradigm for frequency conversion leveraging tailorable molecular and plasmonic properties.

The Netherlands Organisation for Scientific Research (NWO)
Photonic Forces

Chen, W., Roelli, P., Hu, H., Verlekar, S., Amirtharaj, S. P., Barreda, A. I., … Galland, C. (2021). Continuous-wave frequency upconversion with a molecular optomechanical nanocavity. Science, 374(6572), 1264–1267. doi:10.1126/science.abk3106