Molecules have complex signatures in their spectra at infrared wavelengths, typically accessed using specialized spectroscopic equipment. Researchers discovered optomechanical frequency upconversion at ambient conditions from the mid-infrared to the visible domain using molecular vibrations coupled to a plasmonic nanocavity.
Both approaches demonstrate the ability to upconvert the mid-infrared vibrations of the molecules in the nanocavity to visible light wavelengths using different nanoantenna designs, one with a nanoparticle-on-resonator and the other with a nanoparticle-in-groove. The effect could simplify infrared spectroscopy with single-molecule sensitivity.
Coherent frequency upconversion of terahertz and mid-infrared signals into visible light opens up new possibilities for spectroscopy, imaging, and sensing but poses a challenge to traditional nonlinear optics. The researchers demonstrated optomechanical transduction of submicrowatt continuous-wave signals from the mid-infrared (32 terahertz) domain onto the visible domain at ambient conditions using a plasmonic nanocavity hosting a few hundred molecules.
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