Enhanced light-matter interactions in laser systems incorporating metal-based optical confinement

The aim of plasmonics is to exploit the strong coupling between photons and collective electron oscillations in metals, so-called surface plasmon polaritons, which enable a strong confinement of the electromagnetic field to metal-dielectric interfaces. The interaction of confined optical states with electronic transitions within matter accelerates these otherwise slow light-matter interactions. This work’s purpose is to investigate accelerated light-matter interactions within plasmonic lasers, which arise due to optical confinement, and how these influence laser dynamics. In particular, this work focuses on the fabrication, demonstration and characterisation of plasmonic lasers. The devices investigated in this work consist of semiconductor nanowires made from zinc oxide (ZnO) placed in the proximity of a silver substrate. In this geometry the metal allows for strong optical confinement, whereas the semiconductor delivers the necessary gain to achieve lasing. Operating at room temperature, the emission from ZnO lies near the surface plasmon frequency, where confinement and loss become maximal, leading to accelerated spontaneous recombination, gain switching and gain recovery compared with conventional - photonic - ZnO nanowire lasers. To assess the lasing dynamics, in this work a novel double-pump spectroscopy technique is used, which exploits the non-linearity of the laser process to allow the investigation of accelerated light-matter interactions. This novel technique is necessary, as the speed of plasmonic devices is too fast for electrical detection, and the emission of single devices is too weak for non-linear spectroscopic techniques. Comparing photonic and plasmonic devices reveals contrasting dynamics between both, highlighting the benefits of plasmonic confinement, but also exposing an important limitation. Plasmonic devices could potentially be faster, but are ultimately limited by internal relaxation processes of the chosen gain medium. The findings of this work will improve the understanding of plasmonic lasers and their limitations, but also lead to improved knowledge of internal semiconductor processes.Open Acces