Bio-inspired natural sunlight-pumped lasers

Abstract

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 an improvement of several orders of magnitude over existing comparable technologies: state-of-the-art solar pumped lasers operate above 1000 suns (corresponding to 1000 times the natural sunlight power). 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, by exploiting a highly symmetric arrangement of molecules organized in a hierarchy of energy scales, exhibit a very large internal efficiency in harvesting photons from a power source as dilute as natural sunlight. Specifically, we consider substituting the reaction center of photosynthetic complexes in purple bacteria (Rhodobacter Sphaeroides) with 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.

Efficient light harvesting and photon sensing via engineered cooperative effects

“…A similar idea has been successfully employed by some of the authors of this paper in Ref. [33] where a bio-inspired sunlight-pumped laser has been proposed.…”

“…This mechanism has been also discusses and exploited in Ref. [33] by some of the Authors of this manuscript. As a final remark, let us note that exploiting thermal relaxation to suppress re-emission requires a detailed knowledge of the system-bath coupling and bath structure, while the mechanism proposed by us in the main text is more direct and does not depend on the details of the system-bath coupling to be effective.…”

“…where n S ≈ 0.04 is the Bose occupation of the Sun photons at the excitation energy ω 0 and at the Sun temperature (6000 K) and f S = 5.4 × 10 −6 accounts for the Sunto-Earth distance [33]. Specifically, under sunlight illumination each eigenstate acquires absorption and stimulated emission rates, B α = f S n S γ| p Eα | 2 , with f S representing the solid angle of the Sun as seen on Earth,…”

Efficient light harvesting and photon sensing via engineered cooperative effects

“…This shows that several paths are available to suppress re-emission, and red-shifting the central core absorber energy can also be very effective in suppressing re-emission. This mechanism has also been discussed and exploited in reference [39] by some of the authors of this manuscript. As a final remark, let us note that exploiting thermal relaxation to suppress re-emission requires detailed knowledge of the system-bath coupling and bath structure, while the mechanism proposed by us in this manuscript is more direct and does not depend on the details of the system-bath coupling to be effective.…”

“…where n S ≈ 0.04 is the Bose occupation of the Sun photons at the excitation energy ω 0 and at the Sun temperature (6000 K) and f S = 5.4 × 10 −6 accounts for the Sun-to-Earth distance [39]. Specifically, under sunlight illumination each eigenstate acquires absorption and stimulated emission rates,…”