Mid-infrared (MIR) light is difficult to detect efficiently, and without cooling the detectors, despite the extremely valuable information it carries about molecules in healthcare, environmental sensing, as well as molecular conformation. Measuring a few molecules using MIR spectroscopy is also challenging, because each absorbs only a tiny amount of light. All these can be dramatically improved by embedding them in metallic ‘plasmonic’ cavities at the nanoscale which confine the light and enhance these interactions.
Current work:
Enhanced detection of MIR light
By trapping light in the gap between a gold nanoparticle and a mirror, which contains a single layer of molecules, we have found ways to convert MIR light into easily detectable visible light. We pattern the mirror into disks which enhance trapping of MIR light of particular colours. The MIR light excites specific vibrations of the molecule, which then absorb red light and relax by emitting a photon (that sums their energies) in the blue. Our design given million-fold improved efficiency. [1]
Further enhancing MIR detection using MIRVAL
This detection is improved if we use molecules or materials that emit light in the nano-gap region. Then absorbing MIR light in their vibrations allows the pump laser to be absorbed, giving then photoluminescence (PL) which is easily detected. This is the basis of our new MIRVAL grant, as well as a prototype demonstrator since it can lead to MIR imaging detectors. [2]
MIR resonators for light using plasmonics
By assembling nanoparticles into 2D sheets with precision nanogaps ~0.9nm wide that are scaffolded by a rigid molecule, we produce materials which trap light strongly. The colour which is trapped can be tuned across the MIR region by simply stacking these sheets on top of each other. This dramatically enhances the absorption by vibrations of molecules in the gaps, enabling their detection. [3]
Ultrafast mid-infrared measurements of vibrations
Using advanced ultrashort pulsed lasers producing pulses only 10-12s, we can investigate the time dynamics of all the vibrational processes in these nanogaps, and how they are completely modified by the confinement.
Key papers:
- Detecting mid-infrared light by molecular frequency upconversion in dual-wavelength nanoantennas, Science (2021); DOI: 10.1126/science.abk2593
- Single-molecule mid-infrared spectroscopy and detection through vibrationally assisted luminescence, Nature Photonics (2023); DOI 10.1038/s41566-023-01263-4
- Giant mid-IR resonant coupling to molecular vibrations in sub-nm gaps of plasmonic multilayer metafilms, Nature: Light Sciences & App (2022); DOI: 10.1038/s41377-022-00943-0
Current people involved:
JJB, Rakesh Arul, Caleb Todd, Fiona Bell, Yeeun Roh