Comparative Study on the Uniform Energy Deposition Achievable via Optimized Plasmonic Nanoresonator Distributions

Plasmonic nanoresonators of core–shell composition and nanorod shape were optimized to tune their absorption cross-section maximum to the central wavelength of a short laser pulse. The number density distribution of randomly located nanoresonators along a laser pulse-length scaled target was numerically optimized to maximize the absorptance with the criterion of minimal absorption difference between neighboring layers illuminated by two counter-propagating laser pulses. Wide Gaussian number density distribution of core–shell nanoparticles and nanorods enabled to improve the absorptance with low standard deviation; however, the energy deposited until the overlap of the two laser pulses exhibited a considerable standard deviation. Successive adjustment resulted in narrower Gaussian number density distributions that made it possible to ensure almost uniform distribution of the deposited energy integrated until the maximal overlap of the two laser pulses. While for core–shell nanoparticles the standard deviation of absorptance could be preserved, for the nanorods it was compromised. Considering the larger and polarization independent absorption cross-section as well as the simultaneously achievable smaller standard deviation of absorptance and deposited energy distribution, the core–shell nanoparticles outperform the nanorods both in optimized and adjusted nanoresonator distributions. Exception is the standard deviation of deposited energy distribution considered for the complete layers that is smaller in the adjusted nanorod distribution. Optimization of both nanoresonator distributions has potential applications, where efficient and uniform energy deposition is crucial, including biomedical applications, phase transitions, and even fusion.

Improved One- and Multiple-Photon Excited Photoluminescence from Cd2+-Doped CsPbBr3 Perovskite NCs

Metal halide perovskite nanocrystals (NCs) attract much attention for light-emitting applications due to their exceptional optical properties. More recently, perovskite NCs have begun to be considered a promising material for nonlinear optical applications. Numerous strategies have recently been developed to improve the properties of metal halide perovskite NCs. Among them, B-site doping is one of the most promising ways to enhance their brightness and stability. However, there is a lack of study of the influence of B-site doping on the nonlinear optical properties of inorganic perovskite NCs. Here, we demonstrate that Cd2+ doping simultaneously improves both the linear (higher photoluminescence quantum yield, larger exciton binding energy, reduced trap states density, and faster radiative recombination) and nonlinear (higher two- and three-photon absorption cross-sections) optical properties of CsPbBr3 NCs. Cd2+ doping results in a two-photon absorption cross-section, reaching 2.6 × 106 Goeppert-Mayer (GM), which is among the highest reported for CsPbBr3 NCs.

Photosynthetic light harvesting and thylakoid organization in a CRISPR/Cas9 Arabidopsis thaliana LHCB1 knockout mutant.

Light absorbed by chlorophylls of photosystem II and I drives oxygenic photosynthesis. Light-harvesting complexes increase the absorption cross-section of these photosystems. Furthermore, these complexes play a central role in photoprotection by dissipating the excess of absorbed light energy in an inducible and regulated fashion. In higher plants, the main light-harvesting complex is the trimeric LHCII. In this work, we used CRISPR/Cas9 to knockout the five genes encoding LHCB1, which is the major component of the trimeric LHCII. In absence of LHCB1 the accumulation of the other LHCII isoforms was only slightly increased, thereby resulting in chlorophyll loss leading to a pale green phenotype and growth delay. Photosystem II absorption cross-section was smaller while photosystem I absorption cross-section was unaffected. This altered the chlorophyll repartition between the two photosystems, favoring photosystem I excitation. The equilibrium of the photosynthetic electron transport was partially maintained by a lower photosystem I over photosystem II reaction center ratio and by the dephosphorylation of LHCII and photosystem II. Loss of LHCB1 altered the thylakoid structure, with less membrane layers per grana stack and reduced grana width. Stable LHCB1 knock out lines allow characterizing the role of this protein in light harvesting and acclimation and pave the way for future in vivo mutational analyses of LHCII.

Traceable total ozone column retrievals from direct solar spectral irradiance measurements in the ultraviolet

Total column ozone (TCO) is commonly measured by Brewer and Dobson spectroradiometers. Both types of instruments are using four wavelengths in the ultraviolet radiation range to derive TCO. For the calibration and quality assurance of the measured TCO both instrument types require periodic field comparisons with a reference instrument. This study presents traceable TCO retrievals from direct solar spectral irradiance measurements with the portable UV reference instrument QASUME. TCO is retrieved by a spectral fitting technique derived by a minimal least square fit algorithm using spectral measurements in the wavelength range between 305 nm and 345 nm. The retrieval is based on an atmospheric model accounting for different atmospheric parameters such as effective ozone temperature, aerosol optical depth, Rayleigh scattering, SO2, ground air pressure, ozone absorption cross sections and top-of-atmosphere solar spectrum. Traceability means, that the QASUME instrument is fully characterized and calibrated in the laboratory to SI standards (International System of Units). The TCO retrieval method from this instrument is independent from any reference instrument and does not require periodic in situ field calibration. The results show that TCO from QASUME can be retrieved with a relative standard uncertainty of less than 0.8 %, when accounting for all possible uncertainties from the measurements and the retrieval model, such as different cross sections, different reference solar spectra, uncertainties from effective ozone temperature or other atmospheric parameters. The long-term comparison of QASUME TCO with a Brewer and a Dobson in Davos, Switzerland, reveals, that all three instruments are consistent within 1 % when using the ozone absorption cross section from the University of Bremen. From the results and method presented here, other absolute SI calibrated cost effective solar spectroradiometers, such as array spectroradiometers, may be applied for traceable TCO monitoring.

Absorption by stringy black holes

We investigate the absorption of planar massless scalar waves by a charged rotating stringy black hole, namely a Kerr–Sen black hole. We compute numerically the absorption cross section and compare our results with those of the Kerr–Newman black hole, a classical general relativity solution. In order to better compare both charged black holes, we define the ratio of the black hole charge to the extreme charge as Q. We conclude that Kerr–Sen and Kerr–Newman black holes have a similar absorption cross section, with the difference increasing for higher values of Q.