Continuous-wave frequency upconversion with a molecular optomechanical nanocavity

Abstract

Optomechanical upconversion Molecules have rich signatures in their spectra at infrared wavelengths and are typically accessed with dedicated spectroscopic instrumentation. Chen et al . and Xomalis et al . report optomechanical frequency upconversion from the mid-infrared to the visible domain using molecular vibrations coupled to a plasmonic nanocavity at ambient conditions (see the Perspective by Gordon). Using different nanoantenna designs, one with a nanoparticle-on-resonator and the other with nanoparticle-in-groove, both approaches show the ability to upconvert the mid-infrared vibrations of the molecules in the nanocavity to visible light wavelengths. The effect could be used to simplify infrared spectroscopy, possibly with single-molecule sensitivity. —ISO

Molecular Vibration Explorer: an online database and toolbox for surface-enhanced frequency conversion, infrared and Raman spectroscopy

“…In the situation where the polarizations are defined by a plasmonic nanostructure and a specific orientation of the molecule is expected [3], the MVE toolbox permits to investigate the orientation dependence of the IR absorption, Raman and SFG signals. Figure 2 illustrates, for the case of cross-polarized local fields (IR field along y, Raman in/out fields along x), the changes in the different processes' magnitudes as function of the molecule orientation.…”

“…Thanks to the prediction of orientation dependence the MVE toolbox may help to optically assess the orientation of self-assembled monolayers within metallic structures [20] in a similar way as it could be de- termined in TERS experiments [21]. The MVE toolbox will also be useful in designing nanostructures and molecular layers maximizing the conversion efficiency of the SFG process for frequency conversion applications [1,3].…”

“…[1] for its interest in IR detector applications. We highlight BPhT with a grey circle, the only molecule ever used to date in a continuous wave SFG experiment [3]. Two other molecules with significantly higher calculated SFG efficiencies are highlighted in yellow and green.…”

“…IR absoprtion and Raman scattering can also be leveraged together in a process called vibrational sum- * z.koczor-benda@ucl.ac.uk frequency generation [3], which has proven useful for time-resolved studies of vibrational properties and dynamics of molecules at interfaces [8][9][10], such as in the context of catalysis. Moreover, recent proposals and experiments inspired by the field of cavity optomechanics [1,11] have translated this technique into a potential technology for frequency upconversion from the THz and IR domain into the visible domain [3,4]. Another related and emerging research field is that of vibrational polaritons [12][13][14], which aims in particular at remotely controlling chemical properties and reaction rates through strong coupling of vibrational modes with electromagnetic vacuum fluctuations.…”

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We present Molecular Vibration Explorer, a freely accessible online database and interactive tool for exploring vibrational spectra and tensorial light-vibration coupling strengths of a large collection of thiolated molecules. The 'Gold' version of the database gathers the results from density functional theory calculations on 2'800 commercially available thiol compounds linked to a gold atom, with the main motivation to screen the best molecules for THz and mid-infrared to visible upconversion [1][2][3][4]. Additionally, the 'Thiol' version of the database contains results for 1'900 unbound thiolated compounds.

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