arXiv subjects

Nicola J. Fairbairn

Publications and source records attributed to Nicola J. Fairbairn.

3 recordsLinked to original sources

arXiv2026

Hybrid biphoton spectrometer for time-resolved quantum spectroscopy across visible and near-infrared regions

Joint spectral measurements are a powerful tool for characterising biphoton spectral correlation, which is crucial for quantum information and communication technologies. In these applications, highly pure biphoton states are essential in any time- and frequency-mode, often obviating the need for time-resolved measurements. Conversely, spectroscopy utilising entangled photon pairs is gaining significant attention for its ability to unveil molecular dynamics, a field that critically demands time-resolved capabilities. Here, we introduce a methodology for capturing a biphoton spectrum that comprises visible and near-infrared photons, resulting in a highly non-degenerate joint spectrum. Our system employs two non-scanning spectrographs: a fibre spectrometer for near-infrared photons and a delay-line-anode single-photon imager for visible photons. We successfully measure the joint spectral intensity by leveraging a time-tagging acquisition strategy. Furthermore, our approach uniquely enables time-resolved joint spectral measurements with respect to the laser synchronisation against the hundreds-of-picosecond instrument response function. Our methodology could advance heralded fluorescence spectroscopy using biphoton sources to investigate temporal dynamics of complex biological, chemical, and physical systems.

quant-ph↗

arXiv2025

Highly efficient exciton-exciton annihilation in single conjugated polymer chains

The number of excitons that conjugated polymers can support at any one time underpins their optoelectronic performance in light emitting diodes and as laser gain media, as it sets a natural limit on exciton density. Here we have measured the time-resolved photon statistics of single chains of polyfluorene to extract the absolute number of independent emitting sites present and its time dependence. We find that after 100 ps each chain can only support 1 or 2 independent excitons, and that even at the earliest times this number rises only to 4, suggesting a high degree of electronic coupling between chromophores that facilitates efficient exciton-exciton annihilation. In circumstances where a low density of low-energy sites is present, annihilation between them still dominates. The results indicate that achieving high exciton densities in conjugated polymers is difficult, and in applications where it is desirable new strategies should be devised to control exciton-exciton annihilation.

physics.chem-ph↗

arXiv2022

Understanding the impact of heavy ions and tailoring the optical properties of large-area Monolayer WS2 using Focused Ion Beam

Focused ion beam (FIB) has been used as an effective tool for precise nanoscale fabrication. It has recently been employed to tailor defect engineering in functional nanomaterials such as two-dimensional transition metal dichalcogenides (TMDCs), providing desirable properties in TMDC-based optoelectronic devices. However, the damage caused by the FIB irradiation and milling process to these delicate atomically thin materials, especially in the extended area, has not yet been elaboratively characterised. Understanding the correlation between lateral ion beam effects and optical properties of 2D TMDCs is crucial in designing and fabricating high-performance optoelectronic devices. In this work, we investigate lateral damage in large-area monolayer WS2 caused by the gallium focused ion beam milling process. Three distinct zones away from the milling location are identified and characterised via steady-state photoluminescence (PL) and Raman spectroscopy. An unexpected bright ring-shaped emission around the milled location has been revealed by time-resolved PL spectroscopy with high spatial resolution. Our finding opens new avenues for tailoring the optical properties of TMDCs by charge and defect engineering via focused ion beam lithography. Furthermore, our study provides evidence that while some localised damage is inevitable, distant destruction can be eliminated by reducing the ion beam current. It paves the way for the use of FIB to create nanostructures in 2D TMDCs, as well as the design and realisation of optoelectrical devices on a wafer scale.

physics.app-ph↗