  Even though sunlight is by far the most abundant renewable energy source
available to humanity, its dilute and variable nature has kept efficient ways
to collect, store, and distribute this energy tantalisingly out of reach.
Turning the incoherent energy supply provided by the Sun into a coherent laser
beam would overcome several of the practical limitations inherent in using
sunlight as a source of clean energy: laser beams travel nearly losslessly over
large distances, and they are effective at driving chemical reactions which
convert sunlight into chemical energy. Here we propose a bio-inspired blueprint
for a novel type of laser with the aim of upgrading unconcentrated natural
sunlight into a coherent laser beam. Our proposed design constitutes a novel
and different path towards sunlight-pumped lasers. In order to achieve lasing
with the extremely dilute power provided by natural sunlight, we here propose a
laser medium comprised of molecular aggregates inspired by the architecture of
natural photosynthetic complexes. Such complexes exhibit a very large internal
efficiency in harvesting photons from a power source as dilute as natural
sunlight. Specifically, we consider a hybrid structure, where photosynthetic
complexes in purple bacteria (Rhodobacter sphaeroides) surround a suitably
engineered molecular dimer composed of two strongly coupled chromophores. We
show that if pumped by the surrounding photosynthetic complex, which
efficiently collects and concentrates solar energy, the core dimer structure
can reach population inversion, and reach the lasing threshold under natural
sunlight. The design principles proposed here will also pave the way for
developing other bio-inspired quantum devices.
