80-µs pulsewidth from a circulation-free diode-pumped liquid organic laser limited by thermal blooming.

Continuous-wave laser emission is challenging to obtain in organic lasers, whether in the solid or liquid form, a limitation caused by long-lived triplet states and by thermal effects. In liquid dye lasers, both issues can be fixed by rapidly flowing the dye, which is technically complex and prevents those lasers to be further miniaturized or easily integrated. Here we address the issue of the maximal pulsewidth that can be obtained in liquid dye lasers in the absence of any dye flow, in a compact and cost-effective diode-pumped laser system. Pulses as long as 80 µs have been obtained, thanks to the combination of a hemispherical resonator design, almost insensitive to thermal-lens effects, and an intentional mismatch between pump and cavity spatial modes. The limitation in pulse duration is shown to be entirely due to thermal blooming, and more specifically to diffraction losses brought by the spherical aberration of the thermal lens.

UV photobleaching of carbon nanodots investigated by in situ optical methods.

Carbon dots are a family of optically-active nanoparticles displaying a combination of useful properties that make them attractive for many applications in photonics and photochemistry. Despite the initial claims of high photostability of carbon dots even under prolonged illuminations, several recent studies have evidenced their photobleaching (PB) under UV light, detrimental for some applications. A study of the mechanism and dynamics of carbon dot PB can be considered a useful route to gather relevant information on the underlying photophysics of these nanoparticles, which is still widely debated. Here we report a study of the PB of carbon dots under UV light, conducted through optical experiments under well-controlled illumination conditions. In particular, the use of a laser as an irradiation source allows a precise control of the irradiated volume, and provides accurate estimates and control of the administered energy. Besides, our setup allows spectroscopic measurements to be carried out in situ at the irradiated site, thus allowing us to investigate in real time the progress of photobleaching effects through a time-resolved approach. Therefore, our experiments allow the precise kinetics of the undergoing PB process to be captured which is found to be significantly affected by disorder and photoselection effects. Furthermore, our study discloses several pieces of information on the nature of the main blue chromophore absorbing at 340 nm and emitting at 430 nm, and on its PB mechanism. We propose that the emissive units consist in small molecular-like chromophores adsorbed on carbon dot surfaces and are in a dynamical equilibrium with free diffusing molecules in solution. Their photobleaching proceeds in two distinct steps: in the first phase, linear absorption of UV photons rapidly converts the molecular surface chromophores into a non-emissive form, likely through an isomerization, causing the disappearance of the fluorescence properties but almost no changes in the optical absorption spectra. At higher fluences, a complete destruction of the optically-active centers is observed, which completely wipes out all the absorption features of surface chromophores and only leaves a fully carbonized, yet non-fluorescent, dot core.

Land cover and forest connectivity alter the interactions among host, pathogen and skin microbiome.

Deforestation has detrimental consequences on biodiversity, affecting species interactions at multiple scales. The associations among vertebrates, pathogens and their commensal/symbiotic microbial communities (i.e. microbiomes) have important downstream effects for biodiversity conservation, yet we know little about how deforestation contributes to changes in host microbial diversity and pathogen abundance. Here, we tested the effects of landcover, forest connectivity and infection by the chytrid fungus Batrachochytrium dendrobatidis (Bd) on amphibian skin bacterial diversity along deforestation gradients in Brazilian landscapes. If disturbance to natural habitat alters skin microbiomes as it does in vertebrate host communities, then we would expect higher host bacterial diversity in natural forest habitats. Bd infection loads are also often higher in these closed-canopy forests, which may in turn impact skin-associated bacterial communities. We found that forest corridors shaped composition of host skin microbiomes; high forest connectivity predicted greater similarity of skin bacterial communities among host populations. In addition, we found that host skin bacterial diversity and Bd loads increased towards natural vegetation. Because symbiotic bacteria can potentially buffer hosts from Bd infection, we also evaluated the bi-directional microbiome-Bd link but failed to find a significant effect of skin bacterial diversity reducing Bd infections. Although weak, we found support for Bd increasing bacterial diversity and/or for core bacteria dominance reducing Bd loads. Our research incorporates a critical element in the study of host microbiomes by linking environmental heterogeneity of landscapes to the host-pathogen-microbiome triangle.