Discovery research · Current
Molecular holography
Fundamental research at the point where coherent Raman scattering meets plasmonic surfaces. The goal is to record a hologram in which every particle is identified by what it is made of, not by a label attached to it.
The physics
Driving a vibration, then watching it
In stimulated Raman spectroscopy two optical fields coherently drive a vibrational mode, while one of those fields — or in CARS a third — probes the coherent molecular vibration that results. Tune the frequency difference between the fields and you map out the vibrational spectrum of whatever is there.
The reason to bother is signal. Incoherent Raman scales linearly with the number of molecules. Coherent Raman scales quadratically. Combined with plasmonic enhancement at a nanostructured surface, that difference is worth roughly eight orders of magnitude in enhancement factor.
What we demonstrated first
Two proof-of-concept results came out of this lab:
- Coherent light emission from nanostructured particles, through stimulated Raman scattering at molecular vibrational frequencies.
- A hologram of gold nanoparticles, recorded and reconstructed.
We were the first group in the world to demonstrate CW stimulated SERS — surface-enhanced stimulated Raman scattering driven by continuous-wave sources rather than the pulsed lasers the technique had always required. The result was published in Faraday Discussions in 2017 and extended in Scientific Reports in 2019. Continuous-wave sources are cheaper, smaller and easier to keep aligned, which is what turns a demonstration into an instrument other people can build.
Modular stimulated Raman spectrometer
Pump–probe bench supporting pulsed and continuous-wave sources, with polarisation switching to turn stimulated emission on and off. Built by a graduate student in this lab.
Why not fluorescence?
Fluorescence labels bleach, and their emission lines are broad. Raman linewidths are an order of magnitude narrower or more.
That difference is the whole argument: narrow lines mean hundreds of chemically distinct particles can be told apart simultaneously in one volume, where fluorescence manages a handful.
Where this goes
Hundreds of particles, three dimensions, no labels
Put the two results together — coherent emission from plasmonic particles, and holographic reconstruction — and you get a technique that records the position of every particle in a millimetre-scale volume in three dimensions, and identifies each one by its vibrational fingerprint.
For live-cell biology that would mean watching hundreds of distinguishable molecular species move through a cell at once, without attaching anything to them that changes how they behave. That is the direction the programme is heading, and it is where a student with optics and computational reconstruction interests would land.
Selected publications from this area
Monfared, Shaffer, Gambhir and Hewitt, “Continuous-Wave Coherent Raman Spectroscopy via Plasmonic Enhancement,” Scientific Reports 9, 12092, 2019.
Lee and Hewitt, “First Demonstration of Surface Enhanced – Stimulated Raman Spectroscopy (SE-SRS) using low-power CW sources,” Faraday Discussions 205, 2017.
Lucas et al., “Aggregation of nanoparticles in endosomes and lysosomes produce Surface Enhanced Raman Spectroscopy,” Journal of Nanophotonics 9, 2015.
Related outputs
Everything this programme produced
The papers, the news and the recognition that came out of this area, each filtered to it.
The refereed papers behind this programme, filtered to molecular holography.
Including the first demonstration anywhere of CW stimulated SERS.
Press coverage of the lab’s research.
The instruments this work is carried out on.
Funded by
Who supports this work
The agencies, foundations and partners that fund the molecular holography programme.
Join us
Work on this
This programme suits students who want to build and align an optical bench themselves, and who are comfortable with the computational side of holographic reconstruction.