Polariton lasing in organic semiconductor microcavities

The absorption and emission of light is fundamental to both optoelectronics and biological processes. This process usually takes place in discreet jumps, in which an excited state electron emits a photon as it returns to its ground state, or a photon is absorbed to create an excited state electron. Our growing ability to manipulate light and matter however now allows a different possibility, in which the photon and exciton are ‘mixed’ together, forming a type of state called a cavity-polariton. Rather than being of simple academic interest, cavity polaritons are a fascinating test-bed for fundamental physics and can have potential applications in ultra-low threshold lasers, on-chip communications elements and new types of quantum-mechanical simulator devices.

Polaritons can be created in an optical structure in which a semiconductor is placed between two highly reflective mirrors. This structure traps photons into a series of discreet optical modes. Within the so-called ‘strong-coupling regime’ the photons trapped in the cavity can couple with the excited states of a semiconductor within the cavity and form the cavity-polaritons. In this project, you will develop strong-coupled optical cavities that contain a range of organic semiconductor thin films and assess their relative lasing threshold when optically pumped. You will explore a wide range of materials, including organic semiconductor dyes and perovskite nanocrystals with your objective being the fabrication of polariton lasers that operate at very low thresholds. You will also develop nanoscale lithographic techniques to laterally pattern the cavity structures, forming optical micro-pillars, which you will explore with high-resolution microscopy techniques. As part of the project, you will collaborate with our colleagues at the Universities of Southampton and St. Andrews as part of a multi-million pound ’Hybrid Polaritonics’ project. This is an experimental research project suitable for Physicists, Electronic Engineers or Physical Chemists who wish to build a career in the field of photonics and optoelectronics.