Single-molecule mid-infrared spectroscopy and detection through vibrationally assisted luminescence

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jats:titleAbstract</jats:title>jats:pRoom-temperature detection of molecular vibrations in the mid-infrared (MIR, jats:italicλ</jats:italic> = 3–30 µm) has numerous applications, including real-time gas sensing, medical imaging and quantum communication. However, existing technologies rely on cooled semiconductor detectors because of thermal noise limitations. One way to overcome this challenge is to upconvert the low-energy MIR photons into high-energy visible wavelengths (jats:italicλ</jats:italic> = 500–800 nm) where detection of single photons is easily achieved using silicon technologies. This process suffers from weak cross-sections and the MIR-to-visible wavelength mismatch, limiting its efficiency. Here we exploit molecular emitters possessing both MIR and visible transitions from molecular vibrations and electronic states, coupled through Franck–Condon factors. By assembling molecules into a plasmonic nanocavity resonant at both MIR and visible wavelengths, and optically pumping them below the electronic absorption band, we show transduction of MIR light. The upconverted signal is observed as enhanced visible luminescence. Combining Purcell-enhanced visible luminescence with enhanced rates of vibrational pumping gives transduction efficiencies of >10%. MIR frequency-dependent upconversion gives the vibrational signatures of molecules assembled in the nanocavity. Transient picocavity formation further confines MIR light down to the single-molecule level. This allows us to demonstrate single-molecule MIR detection and spectroscopy that is inaccessible to any previous detector.</jats:p>


Acknowledgements: This work was supported by the European Research Council (ERC) under Horizon 2020 research and innovation programme PICOFORCE (grant no. 883703), THOR (grant no. 829067), POSEIDON (grant no. 861950) and the Engineering and Physical Sciences Research Council (EPSRC; EP/L015978/1, EP/L027151/1, EP/S022953/1, EP/P029426/1 and EP/R020965/1) (to J.J.B.). Further funding was provided by the Royal Society (RGS\R1\231458) to R.C. R.C. also acknowledges support from Trinity College, University of Cambridge. R.A. acknowledges support from the Rutherford Foundation of the Royal Society Te Apārangi of New Zealand, and the Winton Programme for the Physics of Sustainability.

Funder: University of Cambridge; doi:

5102 Atomic, Molecular and Optical Physics, 51 Physical Sciences
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Nature Photonics
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Springer Science and Business Media LLC
Engineering and Physical Sciences Research Council (EP/L027151/1)
Engineering and Physical Sciences Research Council (EP/P029426/1)
European Commission Horizon 2020 (H2020) ERC (883703)
European Commission Horizon 2020 (H2020) Future and Emerging Technologies (FET) (829067)
European Commission Horizon 2020 (H2020) Research Infrastructures (RI) (861950)
Engineering and Physical Sciences Research Council (EP/L015978/1)
Engineering and Physical Sciences Research Council (EP/R020965/1)
Engineering and Physical Sciences Research Council (EP/S022953/1)