UNCONVENTIONAL LIGHT SOURCES

Super-resolution refers to a powerful set of techniques that overcome the diffraction limit. Some of these techniques are based on the concept of image reconstruction by spatially sparse sampling. Here, we introduce the concept of super-resolution spectroscopy based on sparse sampling in the frequency domain, and show that this can be naturally achieved using a random laser source. In its chaotic regime, the emission spectrum of a random laser features sharp spikes at uncorrelated frequencies that are sparsely distributed over the emission bandwidth. These narrow lasing modes probe stochastically the spectral response of a sample, allowing it to be reconstructed with a resolution exceeding that of the spectrometer.

The special organization of BChls determines the formation of bright (superradiant) states with giant transition dipole moments, enabling energy super-transfer through the antenna complex and finally onto the RC. This is thought to be one of the main factors which allows such complexes to reach an energy transfer efficiency close to 100%, i.e., almost every absorbed photon results in charge separation at the RC.

RANDOM LASERS

Random lasers are laser sources that use a disordered gain medium, with no external cavity. The term random lasing refers to the fact that its modes are disordered in nature. The physics behind random lasing is quite rich. For instance, the number of modes is typically huge and a large amount of modes can be overlapping both in space and frequency. This leads to strong mode coupling and a broad parameter regime in which the output is chaotic. For each random laser shot, only a few modes actually reach the threshold, leading to the typical random laser emission spectrum that consists of a few narrow spikes well separated from each other. In the chaotic regime of operation, the emission spectrum of each random laser pulse is also completely uncorrelated with the previous pulse. Overall, these properties make random lasers an ideal class of source for sparse sampling in the frequency domain and super-resolution spectroscopy, speckle free imaging.

BIO-MIMETIC

SOLAR LASER

All photosynthetic systems use antenna complexes, a network of chlorophyll (Chl) molecules, to absorb sunlight and transport the excitations, resulting from photon absorption, to a special pigment-protein complex (the reaction center, RC), where charge separation occurs, a process which drives the subsequent photosynthetic steps. Photosynthetic antenna complexes thus play the role of sub-wavelength “nanoscopic lenses” able to concentrate sunlight to a specific location via exciton transfer. The key idea of our project is of exploiting natural and artificial antnennae for light harvesting applications.

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Main publications:

Boschetti, A., Taschin, A., Bartolini, P. et al. Spectral super-resolution spectroscopy using a random laser. Nat. Photonics 14, 177–182 (2020).
Boschetti, A., et al. Perspectives and recent advances in super-resolution spectroscopy: Stochastic and disordered-based approaches. Applied Physics Letters 120.25 (2022).
Valzelli, Alessia, et al. Large scale simulations of photosynthetic antenna systems: interplay of cooperativity and disorder.

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