Detecting mid-infrared light by molecular frequency upconversion in dual-wavelength nanoantennas

Abstract

Coherent interconversion of signals between optical and mechanical domains is enabled by optomechanical interactions. Extreme light-matter coupling produced by confining light to nanoscale mode volumes can then access single mid-infrared (MIR) photon sensitivity. Here we utilise the infrared absorption and Raman activity of molecular vibrations in plasmonic nanocavities to demonstrate frequency upconversion. We convert 𝝀 ~10 μm incoming light to visible via surface-enhanced Raman scattering (SERS) in doubly-resonant antennas that enhance upconversion by >10 10 . We show >200% amplification of the SERS antiStokes emission when a MIR pump is tuned to a molecular vibrational frequency, obtaining lowest detectable powers ~1 μW/μm 2 at room temperature. These results have potential for lowcost and large-scale infrared detectors and spectroscopic techniques, and bring singlemolecule sensing into the infrared.

Hybrid photonic-plasmonic cavity design for very large Purcell factors at telecom wavelengths

“…Building hybrid cavities that operate at telecom wavelengths does not only offers new perspectives in applications already existing in that spectral regime (optical communications, photonic biosensing, nonlinear signal processing) but could also enable the transfer of (near-)visible-regime applications (such as surfaceenhanced Raman spectroscopy [40] or optomechanicallydriven frequency conversion [38,41]) to a domain where a huge amount of high-quality instrumentation (tunable lasers, high speed photo-detectors, amplifiers) is available, whilst being implementable in silicon compatible chips.…”

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

“…temperature [1] (20-50 THz), we can identify molecular vibrations with SFG coefficients orders of magnitude larger than the one of the molecule (BPhT) used in the recent surface-enhanced upconversion experiments [3,4].…”

“…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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Integrated Molecular Optomechanics with Hybrid Dielectric–Metallic Resonators

“…Furthermore, with the correct description of coherence in the optomechanical interaction, new phenomena such as collective effects have been predicted, and within state of the art in plasmonic nano- and picocavities, one could envision promising applications such as coherent quantum state transfer and entanglement between photons and phonons − at high frequencies (1–100 THz), where no cooling is required. Very recent experimental works have already demonstrated mid-IR-to-visible transduction using this scheme. , …”