Frequency Upconversion Turns IR Into Visible Light

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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