Ross C. Schofield

Fluorescence lifetime imaging microscopy (FLIM) is a powerful technique to map molecular environments independently of fluorophore density and excitation intensity. Despite its success, FLIM can be slow for long-lived and weak fluorescence. Here, we introduce full-field dual modulation FLIM (FDM-FLIM) for imaging weak and long-lived emitters. By modulating the excitation and emission and projecting the signal directly onto a camera, FDM-FLIM extracts lifetimes without frequency-domain phase retrieval. We demonstrate this for Er/Yb upconversion nanoparticles near plasmonic nanostructures, where Purcell-enhanced emission leads to spatially varying lifetimes that are otherwise obscured by nanoparticle-density variations, indicating that FDM-FLIM is a robust and accessible approach for full-field and hyperspectral lifetime imaging.

We report the measurement of thermal photon statistics from a semiconductor photon Bose-Einstein condensate operating just above the condensation threshold. We identify a regime where coherent, single-mode emission occurs while still demonstrating significant photon bunching. Taking advantage of the photon bunching, along with the continuous-wave operation and high photon flux, we demonstrate optical range sensing using a photon Bose-Einstein condensate. We characterize the precision of the range measurement and analyze the dependence on the condensate’s pump power and resulting coherence properties.

Photon condensation in semiconductor microcavities is a transformative technique for engineering quantum states of light at room temperature by tailoring strong but incoherent light-matter interactions. While continuous-wave and electrical pumping offer exceptional prospects for miniaturized quantum photonic technologies, harnessing these requires conceptual advances in understanding non-equilibrium light-matter dynamics in semiconductors. We resolve this challenge through an ab initio quantum kinetic theory capturing how Coulomb interactions of optically excited carriers and phonon scattering mediate photon thermalization and condensation in semiconductors. Our microscopic model shows that at high carrier densities, thermalization is dominated by carrier–carrier Coulomb scattering, in clear contrast to the rovibrational relaxation that governs dye-based photon condensates. The theory predicts a rich nonequilibrium phase diagram with thermal, Bose-condensed, multimode, and lasing phases, quantitatively in agreement with recent experiments. Crucially, we identify how cavity detuning controls transitions between equilibrium and gain-dominated regimes, enabling tailored design of coherent light sources. This work thus provides the foundation for semiconductor-based quantum photonic devices operating beyond conventional laser paradigms.

Plasmonic nanostructures enable efficient light-to-chemical energy conversion by concentrating optical energy into nanoscale volumes. A key mechanism in this process is chemical interface damping (CID), where surface plasmons are damped by adsorbed molecules, enabling the transfer of charge to adsorbed molecules. Here, we investigate the relationship between CID and adsorbate-induced changes in dc electrical resistivity for four molecular adsorbates on gold surfaces. Our results reveal two distinct CID regimes. On one hand, CID takes place via direct resonant electronic transitions to the lowest unoccupied molecular orbital. This mechanism is dependent on plasmon energy. In the second regime, plasmon damping takes place through inelastic electron scattering at the metal-molecule interface. This regime shows a weaker dependency on plasmon energy. This mechanism also leads to adsorbate-induced changes in dc resistivity. These findings provide previously unidentified insights into the microscopic origins of plasmon damping and offer a unified framework for understanding metal-adsorbate energy transfer.

Here we report the measurement of thermal photon statistics from a semiconductor photon Bose-Einstein condensate operating just above the condensation threshold. We identify a regime where coherent, single mode emission occurs while still demonstrating significant photon bunching. Taking advantage of the photon bunching, along with the continuous-wave operation and high photon flux, we demonstrate optical range sensing using a photon Bose-Einstein condensate. We characterise the precision of the range measurement and analyse the dependence on the condensate's pump power and resulting coherence properties.

Surface lattice resonance (SLR) lasers, where the gain is supplied by a thin-film active material and the feedback comes from multiple scattering by plasmonic nanoparticles, have shown both low threshold lasing and tunability of the angular and spectral emission at room temperature. However, typically used materials such as organic dyes and QD films suffer from photodegradation, which hampers practical applications. Here, we demonstrate photostable single-mode lasing of SLR modes sustained in an epitaxial solid-state InP slab waveguide. The nanoparticle array is weakly coupled to the optical modes, which decreases the scattering losses and hence the experimental lasing threshold is as low as 94.99 ± 0.82 μJ cm² pulse^-1. The nanoparticle periodicity defines the lasing wavelength and enables tunable emission wavelengths over a 70 nm spectral range. Combining plasmonic nanoparticles with an epitaxial solid-state gain medium paves the way for large-area on-chip integrated SLR lasers for applications, including optical communication, optical computing, sensing, and LiDAR.

We investigate repeatable and reliable tuning of single organic molecule fluorescence by applying strain via a piezoelectric substrate.

The indistinguishability of successively generated photons from a single quantum emitter is most commonly measured using two-photon interference at a beam splitter. Whilst for sources excited in the pulsed regime the measured bunching of photons reflects the full wave-packet indistinguishability of the emitted photons, for continuous wave (cw) excitation, the inevitable dependence on detector timing resolution and driving strength obscures the underlying photon interference process. Here we derive a method to extract full photon wave-packet indistinguishability from cw measurements by considering the relevant correlation functions. The equivalence of both methods is experimentally verified through a comparison of cw and pulsed excitation measurements on an archetypal source of photons, a single molecule.