Observation of ultrafast solid-density plasma dynamics using femtosecond X-ray pulses from a free-electron laser

The complex physics of the interaction between short pulse high intensity lasers and solids is so far hardly accessible by experiments. As a result of missing experimental capabilities to probe the complex electron dynamics and competing instabilities, this impedes the development of compact laser-based next generation secondary radiation sources, e.g. for tumor therapy [Bulanov2002,ledingham2007], laboratory-astrophysics [Remington1999,Bulanov2015], and fusion [Tabak2014]. At present, the fundamental plasma dynamics that occur at the nanometer and femtosecond scales during the laser-solid interaction can only be elucidated by simulations. Here we show experimentally that small angle X-ray scattering of femtosecond X-ray free-electron laser pulses facilitates new capabilities for direct in-situ characterization of intense short-pulse laser plasma interaction at solid density that allows simultaneous nanometer spatial and femtosecond temporal resolution, directly verifying numerical simulations of the electron density dynamics during the short pulse high intensity laser irradiation of a solid density target. For laser-driven grating targets, we measure the solid density plasma expansion and observe the generation of a transient grating structure in front of the pre-inscribed grating, due to plasma expansion, which is an hitherto unknown effect. We expect that our results will pave the way for novel time-resolved studies, guiding the development of future laser-driven particle and photon sources from solid targets

Observation of Ultrafast Solid-Density Plasma Dynamics Using Femtosecond X-Ray Pulses from a Free-Electron Laser

The complex physics of the interaction between short-pulse ultrahigh-intensity lasers and solids is so far difficult to access experimentally, and the development of compact laser-based next-generation secondary radiation sources, e.g., for tumor therapy, laboratory astrophysics, and fusion, is hindered by the lack of diagnostic capabilities to probe the complex electron dynamics and competing instabilities. At present, the fundamental plasma dynamics that occur at the nanometer and femtosecond scales during the laser-solid interaction can only be elucidated by simulations. Here we show experimentally that small-angle x-ray scattering of femtosecond x-ray free-electron laser pulses facilitates new capabilities for direct in situ characterization of intense short-pulse laser-plasma interactions at solid density that allows simultaneous nanometer spatial and femtosecond temporal resolution, directly verifying numerical simulations of the electron density dynamics during the short-pulse high-intensity laser irradiation of a solid density target. For laser-driven grating targets, we measure the solid density plasma expansion and observe the generation of a transient grating structure in front of the preinscribed grating, due to plasma expansion. The density maxima are interleaved, forming a double frequency grating in x-ray free-electron laser projection for a short time, which is a hitherto unknown effect. We expect that our results will pave the way for novel time-resolved studies, guiding the development of future laser-driven particle and photon sources from solid targets

The association between frailty and MRI features of cerebral small vessel disease

Abstract: Frailty is a common syndrome in older individuals that is associated with poor cognitive outcome. The underlying brain correlates of frailty are unclear. The aim of this study was to investigate the association between frailty and MRI features of cerebral small vessel disease in a group of non-demented older individuals. We included 170 participants who were classified as frail (n = 30), pre-frail (n = 85) or non-frail (n = 55). The association of frailty and white matter hyperintensity volume and shape features, lacunar infarcts and cerebral perfusion was investigated by regression analyses adjusted for age and sex. Frail and pre-frail participants were older, more often female and showed higher white matter hyperintensity volume (0.69 [95%-CI 0.08 to 1.31], p = 0.03 respectively 0.43 [95%-CI: 0.04 to 0.82], p = 0.03) compared to non-frail participants. Frail participants showed a non-significant trend, and pre-frail participants showed a more complex shape of white matter hyperintensities (concavity index: 0.04 [95%-CI: 0.03 to 0.08], p = 0.03; fractal dimensions: 0.07 [95%-CI: 0.00 to 0.15], p = 0.05) compared to non-frail participants. No between group differences were found in gray matter perfusion or in the presence of lacunar infarcts. In conclusion, increased white matter hyperintensity volume and a more complex white matter hyperintensity shape may be structural brain correlates of the frailty phenotype

Enhanced efficiency of multilayer organic light-emitting diodes with a low-refractive index hole-transport layer: An effect of improved outcoupling?

The authors report on an internal device modification for multilayerorganic light-emitting diodes(OLEDs) with enhanced efficiency that promises high compatibility with conventional manufacturing processes. By copolymerization of a hole-conducting monomer with a compound possessing a lower refractive index, a hole-transport layer with reduced optical density but slightly reduced hole-transport properties is formed. MultilayerOLEDs based on this reduced-index layer show a 25% increased efficiency compared to reference devices. The results are compared to optical simulations of the dipole emission from thin organic films. It is found that the efficiency improvement is only to some extent due to enhanced outcoupling resulting directly from the reduced refractive index but primarily due to a change of the width of the emission zone

New Crosslinkable Hole Conductors for Blue-Phosphorescent Organic Light-Emitting Diodes

Shedding a blue light: A series of oxetane-functionalized crosslinkable triphenylamine dimers (XTPDs) is investigated as the hole-transport layers in blue-phosphorescent polymer light-emitting diodes (see scheme). These devices have improved performance characteristics, and their luminous efficiencies depend on the HOMO energies of the XTPDs

Enhanced efficiency of multilayer organic light-emitting diodes with a low-refractive index hole-transport layer: An effect of improved outcoupling?

The authors report on an internal device modification for multilayerorganic light-emitting diodes(OLEDs) with enhanced efficiency that promises high compatibility with conventional manufacturing processes. By copolymerization of a hole-conducting monomer with a compound possessing a lower refractive index, a hole-transport layer with reduced optical density but slightly reduced hole-transport properties is formed. MultilayerOLEDs based on this reduced-index layer show a 25% increased efficiency compared to reference devices. The results are compared to optical simulations of the dipole emission from thin organic films. It is found that the efficiency improvement is only to some extent due to enhanced outcoupling resulting directly from the reduced refractive index but primarily due to a change of the width of the emission zone

Photoprogrammable organic light-emitting diodes

Enlightening the memory: The integration of a crosslinkable photochromic dithienylperfluorocyclopentene (DTE) into organic light-emitting diodes (OLED) allows for the individualization of the emissive area of the OLED device, for example, for signage applications. The operation principle is based on switching the injection barrier for holes (positive charge carriers). Very large ON/OFF ratios of up to 3000 for current as well as electroluminescence have been achieved

New Crosslinkable Hole Conductors for Blue-Phosphorescent Organic Light-Emitting Diodes

Shedding a blue light: A series of oxetane-functionalized crosslinkable triphenylamine dimers (XTPDs) is investigated as the hole-transport layers in blue-phosphorescent polymer light-emitting diodes (see scheme). These devices have improved performance characteristics, and their luminous efficiencies depend on the HOMO energies of the XTPDs

Highly color-stable solution-processed multilayer WOLEDs for lighting application

White organic and especially polymeric light emitting devices (WPLEDs) have received particular attention due to their potential to provide cost-effective and simply manufactured solid-state light sources. The largest acceptable variation of Commission Internationale de L'Eclairage (CIE) coordinates is typically specified as Δx,y < 0.01 for general illumination purposes and even down to Δx,y < 0.005 by the automotive industry. Over the last few years great progress has been made regarding color-stability of OLEDs. In the first publications large color shifts of about Δx,y = 0.2,0.1 were reported. Current publications present devices with CIE variations as small as Δx,y = 0.02,0.02 or better, even for polymeric OLEDs. Here, we present a highly color-stable white fluorescent multilayer OLED consisting of a two-layer (yellow EML/blue EML) stack. The devices show white emission with CIE values of 0.324,0.346. Because of their extremely well-balanced electron and hole distribution, these devices show nearly no change in their CIE values (± 0.009,0.006) between 100 and 10 000 nits. Brightness in that range can be obtained at low voltages (4–8 V), at the same time providing a high efficiency of 6 cd A−1. In addition, due to the broad spectral width of the emission the devices exhibit a color rendering index of 84. This value complies favourably with actual demands for ambient lighting. The extrapolated half-brightness lifetime at an initial brightness of 100 cd m−2 exceeds 1000 h. All systems include the crosslinking of each layer either photo-chemically or thermally to enable the solution-processed complex multilayer OLED-structures