[1] The experiment LSO (Lightning and Sprite Observations) is dedicated to the optical study, from the International Space Station, of sprites occurring in the upper atmosphere above thunderstorms. The objectives were to study these phenomena and to validate a new measurement concept for future measurements of sprites from space at the nadir. The first measurements were performed in the frame of the flight of the French Astronaut Claudie Haigneré (mission Andromède) in October 2001. Observations were performed by two microcameras, one in the visible and near-infrared and the other equipped with a moderately wide band filter at 761 nm. This filter includes the most intense N 2 1P emission of the sprites and partly the oxygen absorption A band of the atmosphere. The light emissions from sprites occurring in the middle and upper atmosphere are then differentiated from the emissions from lightning, occurring more deeply in the atmosphere and then more absorbed. This paper presents the first observations of sprites from space at the nadir and statistics about the respective intensities of lightning and sprites emissions as observed with this experiment.
When high intensity (≥1019 W cm−2) laser light interacts with matter, multi-MeV electrons are produced. These electrons can be utilized to generate a MeV bremsstrahlung x-ray emission spectrum as they propagate into a high-Z solid target positioned behind the interaction area. The short duration (<10 ps) and the small diameter (<500 μm) of the x-ray pulse combined with the MeV x-ray spectrum offers an interesting alternative to conventional bremsstrahlung x-ray sources based on an electron accelerator used to radiograph dense, rapidly moving objects. In experiments at the Omega EP laser, a multi-MeV x-ray source is characterized consistently with number of independent diagnostics. An unfiltered x-ray dose of approximately 2 rad in air at 1 m and a source diameter of less than 350 μm are inferred. Radiography of a complex and high area density (up to 61 g/cm2) object is then performed with few hundred microns spatial resolution.
Multi-keV x-ray generation from low-density (27±7mg∕cm3) nanofiber-cotton targets composed of titanium dioxide has been investigated. The cotton targets were heated volumetrically and supersonically to a peak electron temperature of 2.3keV, which is optimal to yield Ti K-shell x rays. Considerable enhancement of conversion efficiency [(3.7±0.5)%] from incident laser energy into Ti K-shell x rays (4–6keV band) was attained in comparison with that [(1.4±0.9)%] for a planar Ti-foil target.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.