He-Ne laser and speckle
He-Ne laser and speckle
Gibbous moon
Gibbous moon
Water droplet
Water droplet
Electron tree
Fractal electron tree or Lichtenberg figure
Oscilloscope trace
Oscilloscope trace
Soap bubble colour fringes
Soap bubble colour fringes

About us

We are a theoretical research group forming part of the Photonics Division located at the Blackett Laboratory of Imperial College London. The group is lead by Dr. Matthew R. Foreman who currently holds a Royal Society University Research Fellowship.

Our research focuses on optical and plasmonic sensing, polarisation sensitive imaging, disordered media and electromagnetic theory. More information on some of our past and present projects can be found by visiting our Research pages.

Recent news

OSA Optical Sensors and Sensing Congress

21 Jul 2021: Joel will be presenting his recent work on tracking single particles using random scattering at the OSA Optical Sensors and Sensing Congress tomorrow as part of the Nanophotonics and Plasmonics Biosensors III session. If you are attending then check out his talk!

Theory of multiple scattering enhanced particle sensing - paper published

19 Jul 2021: Our recent theoretical article on enhancing single particle detection using multiple scattering has just been published in ACS Photonics.

MDPI Sensors Editorial Board

11 Jun 2021: Matthew has been invited to become a Editor for the Sensing and Imaging Section of the MDPI Sensors journal.

Recent publications

J. Berk and M. R. Foreman, "Role of Multiple Scattering in Single Particle Perturbations in Absorbing Random Media" Phys. Rev. Research in press (2006).

Abstract : Speckle patterns produced by disordered scattering systems exhibit a sensitivity to addition of individual particles which can be used for sensing applications. Using a coupled dipole model we investigate how multiple scattering can enhance field perturbations arising in such random scattering based sensors. Three distinct families of multiple scattering paths are shown to contribute and the corresponding complex enhancement factors derived. Probability distributions of individual enhancement factors over the complex plane are characterised numerically within the context of surface plasmon polariton scattering in which absorption is shown to play an important role. We show that enhancements become more strongly dependent on individual scatterer properties when absorption losses are larger, however, amplitude enhancements ~10^2, comparable to low loss surface plasmons, are achievable through sensor optimisation. Approximate analytic expressions for the complex mean enhancements are also found, which agree well with simulations when loop contributions are negligible.

J. Berk and M. R. Foreman, "Theory of Multiple Scattering Enhanced Single Particle Plasmonic Sensing" ACS Photon. in press, doi: 10.1021/acsphotonics.1c00725 (2006).

Abstract : Methods to increase the light scattered from small particles can help improve the sensitivity of many sensing techniques. Here, we investigate the role multiple scattering plays in perturbing the scattered signal when a particle is added to a random scattering environment. Three enhancement factors, parametrising the effect of different classes of multiple scattering trajectories on the field perturbation, are introduced and their mean amplitudes explored numerically in the context of surface plasmon polariton scattering. We demonstrate that there exists an optimum scatterer density at which the sensitivity enhancement is maximised, with factors on the order of 10^2 achievable. Dependence of the enhancement factors on scatterer properties are also studied.

F. Azeem, L. S. Trainor, P. A. Devane, D. S. Norman, A. Rueda, N. J. Lambert, M. Kumari, M. R. Foreman, H. G. L. Schwefel, "Dielectric perturbations: anomalous resonance frequency shifts in optical resonators" Opt. Lett. 46, 2477-2480 (2006).

Abstract : Small perturbations in the dielectric environment around a high quality whispering gallery mode resonator usually lead to a frequency shift of the resonator modes directly proportional to the polarizability of the perturbation. Here, we report experimental observations of strong frequency shifts that can be opposite and even exceed the contribution of the perturbations polarizability. The mode frequencies of a lithium niobate whispering gallery mode resonator are shifted using substrates of refractive indices ranging from 1.50 to 4.22. Both blue- and red-shifts are observed, as well as an increase in mode linewidth, when substrates are moved into the evanescent field of the whispering gallery mode. We compare the experimental results to a theoretical model by Foreman et al. and provide an additional intuitive explanation based on the Goos-Hänchen shift for the optical domain.

Funding

Our research is supported by generous funding from:

EPSRC
The Royal Society
Microsoft Research