Conference Agenda

Strong coupling with light has emerged as a powerful tool for modifying the properties of optical materials. Typical systems are based on a fluorescent layer embedded in a single optical cavity, whereby the excitonic emission is converted into a polarized, energy-tunable and dispersive polariton emission. There, excitons and photons coexist in the same volume and therefore any change in the emission properties of the excitonic material comes at the expense of simultaneously modifying the photonic environment where excitons reside, i.e., layer thickness and refractive index. Here, we demonstrate remote control over the intensity and total decay rate of the fluorescent layer by adding an extra purely photonic cavity strongly coupled to the first one. By modifying the resonant condition of the extra cavity, we reduce the total decay rate and suppress the fluorescence intensity of the fluorescent layer without explicitly affecting the first cavity. Such modification of the optical properties of the layer is the consequence of a resonant configuration that spatially segregates photons and excitons into different cavities.

Thanks to their excellent photoluminescence quantum yields, their facile and low-cost production, and their processing versatility, CsPbBr3 perovskite nanocrystals (NCs) stand out as excellent candidates to implement light-emitting devices. Elucidating their stimulated emission mechanisms is fundamental to achieve much more efficient and versatile perovskite lasers. In particular, two questions remain open: why the Amplified Spontaneous Emission (ASE) band is significantly shifted from the fluorescence one, and why the former seems to suddenly emerge from, and coexist with, the latter. These characteristic features have led to a debate, which is not settled yet, on which is the mechanism behind the ASE band shift. In this communication, we try to settle this debate and address these questions through experimental ASE measurements combined with numerical simulations. We show that the ASE behaviour in CsPbBr3 NCs thin films stems from a combination of reabsorption, excited state absorption, excitation of differently polarized waveguide modes, and the coexistence of short- and long-lived localized single excitons. The results in this work help understanding the stimulated emission mechanisms in perovskites and provide insightful information on research avenues to increase the efficiency of the light-emitting devices based on these materials.

Year by year, the importance of plastic nanostructures in photonics is increasing. Indeed, polymers represent an interesting alternative to more traditional metal oxides, being easily processable and allowing for light, free-standing and flexible structures. In the field of energy efficiency and sustainability, we bring in two positive examples of the use of plastic photonic crystals: sensing and thermal shielding. In sensing they allow for easy detection of analytes, such as the byproducts of food degradation; a colour change identifies the spoilage, with possible application of these plastic sensors in smart packaging applications. On the other hand, they can be of interest for thermal shielding applications. Indeed, they can be engineered as thin, transparent films able to reduce indoor heating by sunlight and in turn the energy consumption related to the use of air conditioning.

A Tm:LiYF4 laser operating on the 3H4 → 3H5 transition is integrated into a high-power diode-pumped Nd:ASL laser for intracavity upconversion pumping at 1.05 µm. This architecture leads to a record-high output power at 2.3 µm ever extracted from any upconversion pumped Thulium laser. The continuous-wave Tm-laser yields 1.81 W at 2.3 μm at 32 W of laser-diode pump power at 0.8 µm, rivalling direct diode pumping. The intracavity pumping mitigates weak absorption inherent to the upconversion pumping scheme and disperses the deposited heat over two laser crystals. This laser design minimizes heating of the Tm-crystal and enhances the tolerance to Tm3+ excited-state absorption, being promising for high-power 2.3-µm solid-state lasers based on thulium ions.

We report on an original chaotic dynamic behaviour of a passively Q-switched 2.3-µm Thulium laser operating on the 3H4 → 3H5 transition. The experiment employs a Tm:LiYF4 laser crystal within various laser cavity configurations, involving optional additional cascade laser operation on the 3F4 → 3H6 transition at 1.9 µm. The saturable absorber employed is Cr2+:ZnSe, which is exclusively saturated by the 2.3 µm laser emission. A precise analysis of the Q-switching dynamics shows a pronounced inclination of the cascade laser scheme towards chaotic operation. To investigate the origins of chaos, we originally monitor the metastable 3F4 level population using cascade laser operation at 1.9 µm, which proves to be a crucial underlying parameter for explaining the observed instabilities. This analysis allows for explaining the specific dynamics of the Q-switched 2.3 µm Tm-laser intrinsically linked to Tm3+-doped materials. A very atypical route to chaos for a Q-switched laser is demonstrated involving type I intermittencies. The obtained results are of great interest for studying the premises of chaos in pulsed solid-state lasers.