A hit-and-run Giant Impact scenario

The formation of the Moon from the debris of a slow and grazing giant impact of a Mars-sized impactor on the proto-Earth (Cameron & Ward 1976, Canup & Asphaug 2001) is widely accepted today. We present an alternative scenario with a hit-and-run collision (Asphaug 2010) with a fractionally increased impact velocity and a steeper impact angle.Comment: 11 pages, 2 figures, in press in ICARUS note

Evidence for temperature-independent triplet diffusion in a ladder-type conjugated polymer

Journal ArticleWe study the temperature dependence of triplet formation and decay by considering the phosphorescence dynamics in a prototypical conjugated polymer matrix. The dynamics of triplet formation as a function of temperature are unraveled by applying an electric field during optical singlet generation and recording the phosphorescence quenching. The diffusivity of triplet excitons in conjugated polymers is shown to be independent of temperature up to 200 K. We propose a diffusion model that describes the relaxation dynamics of triplet excitons at all times through triplet-triplet annihilation and spin orbit coupling at static heavy atom sites

Low-threshold polymeric distributed feedback lasers with metallic contacts

Journal ArticleOptical losses in waveguides comprising metallic contacts are thought to be a major hurdle to the realization of organic laser diodes. We demonstrate here that careful tuning of the waveguide mode in flexible distributed feedback lasers can allow lasing action to occur in organic thin films in the presence of contacting electrodes with virtually no difference when compared to metal free devices. A metallic electrode is most suited as the bottom contact between the polymer and the substrate as it reduces mode leakage into the substrate and enhances modal gain. In contrast, a thin transparent electrode such as a metal oxide is preferable for the top electrode, where confinement is not a problem

Stimulated emission depletion of triplet excitons in a phosphorescent organic laser

Journal ArticleTriplet formation is investigated in an optically pumped polymer laser by detecting the phosphorescence emission after excitation. A clear correlation is observed between the onset of lasing and a saturation of phosphorescence intensity due to stimulated emission depletion of the singlet state and the resulting reduction in intersystem crossing. The results are consistent with intersystem crossing constituting the dominant triplet formation pathway in conjugated polymers. Excitation at different wavelengths has no effect on the triplet saturation behavior, which allows the authors to exclude singlet fission or breaking as the origin of triplet formation. The method constitutes an implementation of a highly nondegenerate excitonic switch

On the origin and composition of Theia: Constraints from new models of the Giant Impact

Knowing the isotopic composition of Theia, the proto-planet which collided with the Earth in the Giant Impact that formed the Moon, could provide interesting insights on the state of homogenization of the inner solar system at the late stages of terrestrial planet formation. We use the known isotopic and modeled chemical compositions of the bulk silicate mantles of Earth and Moon and combine them with different Giant Impact models, to calculate the possible ranges of isotopic composition of Theia in O, Si, Ti, Cr, Zr and W in each model. We compare these ranges to the isotopic composition of carbonaceous chondrites, Mars, and other solar system materials. In the absence of post-impact isotopic re-equilibration, the recently proposed high angular momentum models of the Giant Impact ("impact-fission", Cuk & Stewart, 2012; and "merger", Canup, 2012) allow - by a narrow margin - for a Theia similar to CI-chondrites, and Mars. The "hit-and-run" model (Reufer et al., 2012) allows for a Theia similar to enstatite-chondrites and other Earth-like materials. If the Earth and Moon inherited their different mantle FeO contents from the bulk mantles of the proto-Earth and Theia, the high angular momentum models cannot explain the observed difference. However, both the hit-and-run as well as the classical or "canonical" Giant Impact model naturally explain this difference as the consequence of a simple mixture of two mantles with different FeO. Therefore, the simplest way to reconcile the isotopic similarity, and FeO dissimilarity, of Earth and Moon is a Theia with an Earth-like isotopic composition and a higher (~20%) mantle FeO content.Comment: 53 Pages, 10 Figures, 1 Table, 3 Supplementary Table

Temperature-sensitive poly(N-Isopropyl-Acrylamide) microgel particles: A light scattering study

We present a light scattering study of aqueous suspensions of microgel particles consisting of poly(N-Isopropyl-Acrylamide) cross-linked gels. The solvent quality for the particles depends on temperature and thus allows tuning of the particle size. The particle synthesis parameters are chosen such that the resulting high surface charge of the particles prevents aggregation even in the maximally collapsed state. We present results on static and dynamic light scattering (SLS/DLS) for a highly diluted sample and for diffuse optical transmission on a more concentrated system. In the maximally collapsed state the scattering properties are well described by Mie theory for homogenous hard spheres. Upon swelling we find that a radially inhomogeneous density profile develop

Simulation of facet heating in high-power red lasers

A two-dimensional self-consistent laser model has been used for the simulation of the facet heating of red emitting AlGaInP lasers. It solves in the steady-state the complete semiconductor optoelectronic and thermal equations in the epitaxial and longitudinal directions and takes into account the population of different conduction band valleys. The model considers the possibility of two independent mechanisms contributing to the facet heating: recombination at surface traps and optical absorption at the facet. The simulation parameters have been calibrated by comparison with measurements of the temperature dependence of the threshold current and slope efficiency of broad-area lasers. Facet temperature has been measured by micro-Raman spectrometry in devices with standard and non absorbing mirrors evidencing an effective decrease of the facet heating due to the non absorbing mirrors. A good agreement between experimental values and calculations is obtained for both devices when a certain amount of surface traps and optical absorption is assumed. A simulation analysis of the effect of non absorbing mirrors in the reduction of facet heating in terms of temperature, carrier density, material gain and Shockly-Read-Hall recombination rate profiles is provided

Strong magnetic response of submicron Silicon particles in the infrared

High-permittivity dielectric particles with resonant magnetic properties are being explored as constitutive elements of new metamaterials and devices in the microwave regime. Magnetic properties of low-loss dielectric nanoparticles in the visible or infrared are not expected due to intrinsic low refractive index of optical materials in these regimes. Here we analyze the dipolar electric and magnetic response of loss-less dielectric spheres made of moderate permittivity materials. For low material refractive index there are no sharp resonances due to strong overlapping between different multipole contributions. However, we find that Silicon particles with refractive index 3.5 and radius approx. 200nm present a dipolar and strong magnetic resonant response in telecom and near-infrared frequencies, (i.e. at wavelengths approx. 1.2-2 micrometer). Moreover, the light scattered by these Si particles can be perfectly described by dipolar electric and magnetic fields, quadrupolar and higher order contributions being negligible.Comment: 10 pages, 5 figure