Room temperature polariton condensate using a biologically produced fluorescent protein

Organic materials offer attractive properties for solid-state lasers, including large oscillator strength, high exciton binding energy, spectral tunability, and compatibility with low-cost fabrication processes. However, despite impressive proof-of-principle demonstrations and dramatic improvements in performance, important fundamental limitations remain. Particular challenges are concentration quenching and bi-molecular exciton recombination, which limit the available gain under practical pumping conditions. For electrical pumping, there are further restrictions, including the low charge carrier mobility of most organic materials. Recently, it has been suggested that lasers operating in the regime of strong exciton-photon coupling may address some of these challenges.
Here, we will summarize key results from two collaborations that both look at unconventional nano-scale organic materials for solid-state lasers: Biologically produced fluorescent proteins and single-walled carbon nanotubes.
We found that the barrel-like molecular structure of fluorescent proteins prevents concentration-induced quenching of fluorescence and drastically reduces singlet-singlet annihilation at high exciton densities. This facilitates low-threshold lasing in various configurations and has recently enabled the realization of the first organic polariton laser that can be pumped in a quasi-continuous ns-regime.
In another collaboration, we have shown that the special photo-physical properties of polymer-sorted semiconducting single-walled carbon nanotubes render them well suited for strong light-matter coupling, possibly up to the ultra-strong coupling regime. Most recently, we found that the high charge carrier mobility and stability also enable efficient electrical generation of exciton polaritons. Using a light-emitting field-effect transistor geometry, we achieved current densities ~18,000 A/cm² while maintaining strong coupling conditions.