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 $\sim 10^2$, 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.
Highlights
Use of optical scattering for detection and measurement is a powerful and widespread approach underpinning techniques such as interferometric scattering microscopy [1], dynamic light scattering [2], and diffusing wave spectroscopy [3]
In order to further study the statistical properties of the enhancement factors, Monte Carlo simulations were performed for scattering of surface plasmon-polaritons (SPPs) propagating at a metal-dielectric interface by nanoparticles in the dielectric near the surface
We have presented a general formalism to describe multiple scattering-based enhancements to the field perturbation caused by adding an analyte particle into a random distribution of background scatterers
Summary
Use of optical scattering for detection and measurement is a powerful and widespread approach underpinning techniques such as interferometric scattering microscopy (iSCAT) [1], dynamic light scattering [2], and diffusing wave spectroscopy [3]. As sensitivity gains have been made, so sensing has moved from monitoring of bulk properties to detection of individual nanometer-sized analyte particles, such as virions and proteins [4] Such small dimensions mean particles only scatter weakly, presenting a major challenge. Through consideration of the role of scattering phase, propagation phase, and absorption we identify a nontrivial dependence of the mean enhancement on tunable properties of the scattering configuration This dependence is explored as a route to sensor optimisation in Sec. III C. As such the insights gained in this paper allow us to understand the interplay of absorption and multiple scattering upon addition of an analyte particle, and to guide future development of optimal random SPP sensors
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