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Recent Projects
Electron and Ion Dynamics of Warm Dense Matter
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Ultrafast and high intense laser and x-ray sources offer unique chance to create and diagnose warm dense matter (WDM), characterized by comparable thermal and Fermi energies, and ion-ion coupling parameters that exceed unity. As a convergence of plasma and condensed matter physics, it is of interest relevant to the fundamental significance in the phase transition and energy relaxation processes. In addition, electronic structure and related information in this regime is important to inertial confinement fusion, and wide range of astrophysical subjects such as the interior of large planets and cool stars. However, describing these state of matter associated with temperature of 1~10 eV and 0.1~10 times of solid density, are not obvious. Theoretically it is difficult by effects of electron degeneracy and strong correlation of ions, and experimentally it is needed to obtain single-state data of fast transient material. |
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We use femtosecond laser pulses which deposit energy isochorically into an inertially confined target on time scale faster than hydro expansion. Such high temperature, solid density matter has very high energy density (1~100 MJ/kg). Broadband x-ray pulse from the ALS is transmitted through the material and sent into spectrometer and ultrafast x-ray streak camera. It provides time resolved x-ray absorption spectra and information for the electronic structure of the warm dense matter at a well-defined density. This approach is depicted at the following.
Time resolved x-ray absorption of warm dense matter experiment at BL 6.0.2
Atomic, Molecular dynamics in intense EVU and soft x-ray
Atoms and Molecules have the bulk of their oscillator strength in the vacuum ultraviolet (VUV) and extreme ultraviolet (EUV) regions of the electromagnetic spectrum, yet most femtosecond spectroscopy has been technologically limited to the visible and infrared. We demonstrate time resolved photo-ionization measurement of excited molecules in the gas phase by combining different wavelengths from an intense high order harmonic source with variable delay. The developed techniques have broad applications for multi-photon studies with EVU and x-ray free electron lasers.
Following shows some characteristics of our high-order harmonic beamline based on multi-TW laser system.
- tunable soft x-ray peak power > 1 MW
- beam divergence < 1 mrad
- shot to shot fluctuations < 10%
- pulse length < 30 fs
- spatial and temporal coherence
- examine non-linear phenomena
High intensity High Order Harminocs (HHG) beamlines
Thomson Scattering of Shock Compressed Plasmas
Measurements of the conditions of compressed matter comprise a key scientific activity important for the investigation of many physical and chemical phenomena. At pressures above 1 Mbar, high-energy density physics conditions are accessed where phase transitions, quantum fluids, and conditions of Jovian planets. Higher pressure conditions above 100 Mbar have been predicted for inertial confinement fusion (ICF) experiments, where material density approaches ~ 1000 g/cc. In these regimes, direct and accurate measurements of thermodynamic and physical properties are of great interest to test dense plasma modeling and to address fundamental physics questions such as the equation of state and the structure of dense matter.
Quasimonoenergetic x-ray line radiation from powerful laser-produced plasma, such as Ly-alpha and He-alpha, and K-alpha radiations have been shown to fulfill the stringent requirements on photon numbers and bandwidth for spectrally resolved x-ray scattering measurement of such a dense matter in single shot experiments. This development has enabled quantitative in situ measurements of densities and temperatures with x-ray Thomson-scattering measurements.
(a) Schematics of experiment at OMEGA laser facility (b) X-ray image of target
Reference
Lee, et al., "X-Ray Thomson-Scattering Measurements of Density and Temperature in Shock-Compressed Beryllium" PRL 102, 115001 (2009).
Ultrafast Detector Development
To gain a fundamental understanding of chemical, physical and biological reactions, we needs to probe matter on timescales corresponding to vibrational periods of atoms (fs~ps) with spatial resolution close to inter-atomic dimensions (~ or < nm). The scientific achievements made in the field to date have intimately relied on the photon sources and detectors employed. This symbiotic relationship is certain to continue in the future. Thus detector and experiment optimization is of paramount importance.
The use of an x-ray streak camera to probe ultrafast phenomena on this time scale is currently undergoing intense development. A streak camera is a detector that resolves the intensity of a photon signal as a function of time and space. We have demonstrated a high resolution streak camera which would meets the demands on
- both spectral and temporal information
- linear temporal response with sub-ps resolution
- wide photon energy range (10eV~ 10keV)
Schematics illustrating streak camera operation principle.
Reference
Feng, et al., "An x-ray streak camera with high spatio-tempral resolution" APL 91, 134102 (2007).