Oxford Centre for High Energy Density Science (OxCHEDS)

Abstract:

We present collective Thomson scattering with soft x-ray free electron laser radiation as a method to track the evolution of warm dense matter plasmas with ∼200 fs time resolution. In a pump-probe scheme an 800 nm laser heats a 20 ∼m hydrogen droplet to the plasma state. After a variable time delay in the order of ps the plasma is probed by an x-ray ultra violet (XUV) pulse which scatters from the target and is recorded spectrally. Alternatively, in a self-Thomson scattering experiment, a single XUV pulse heats the target while a portion of its photons are being scattered probing the target. From such inelastic x-ray scattering spectra free electron temperature and density can be inferred giving insight on relaxation time scales in plasmas as well as the equation of state. We prove the feasibility of this method in the XUV range utilizing the free electron laser facility in Hamburg, FLASH. We recorded Thomson scattering spectra for hydrogen plasma, both in the self-scattering and in the pump-probe mode using optical laser heating. © 2009 SPIE-.

Abstract:

The temporal resolution of existing streak cameras are limited by electron transit time dispersion. Here we present a state-of-art design compensating this to achieve a breakthrough of 100fs time resolution. ©2009 IEEE.

Abstract:

The energy transport in cone-guided low- Z targets has been studied for laser intensities on target of 2.5× 1020 W cm-2. Extreme ultraviolet (XUV) imaging and transverse optical shadowgraphy of the rear surfaces of slab and cone-slab targets show that the cone geometry strongly influences the observed transport patterns. The XUV intensity showed an average spot size of 65±10 μm for slab targets. The cone slabs showed a reduced spot size of 44±10 μm. The shadowgraphy for the aforementioned shots demonstrate the same behavior. The transverse size of the expansion pattern was 357±32 μm for the slabs and reduced to 210±30 μm. A transport model was constructed which showed that the change in transport pattern is due to suppression of refluxing electrons in the material surrounding the cone. © 2009 The American Physical Society.