Tue Hansen

ANGLE-RESOLVED ENERGY DISTRIBUTIONS OF LASER ABLATED SILVER IONS IN VACUUM

The energy distributions of ions ablated from silver in vacuum have been measured in situ for pulsed laser irradiation at 355 nm. We have determined the energy spectra for directions ranging from 5° to 75° with respect to the normal in the intensity range from 100 to 400 MW/cm2. At the highest intensity and for angles close to the normal, the highest ion energy measured exceeds 500 eV. However, the energy distributions are shifted strongly towards low energies with increasing angle.

Repetitive ultrafast melting of InSb as an x-ray timing diagnostic

We have demonstrated the possibility of using repetitive ultrafast melting of InSb as a timing diagnostic in connection with visible-light pump∕x-ray probe measurements at high-repetition-rate x-ray facilities. Although the sample was molten and regrown approximately 1×106 times, a distinct reduction in time-resolved x-ray reflectivity could be observed using a streak camera with a time resolution of 2.5ps. The time-resolved x-ray reflectivity displayed this distinct decrease despite the fact that the average reflectivity of the sample had fallen to approximately 50% of its original value due to accumulated damage from the prolonged laser exposure. The topography of the laser-exposed sample was mapped using an optical microscope, a stylus profilometer, photoelectron microscopy, and a scanning tunneling microscope. Although the surface of the sample is not flat following prolonged exposure at laser fluences above 15mJ∕cm2, the atomic scale structure regrows, and thus, regenerates the sample on a nanosecond...

Ion time-of-flight study of laser ablation of silver in low pressure gases

Abstract The dynamics of ions from a laser-ablated silver target in low pressure background atmospheres have been investigated in a simple geometry using an electrical probe. A simple scattering picture for the first transmitted peak of the observed plume splitting has been used to calculate cross sections of the ablated silver ions in oxygen (σ{O2}=4.8×10−16 cm2) and in argon (σ{Ar}=6.7×10−16 cm2). The dynamics of the blast wave is well described by blast wave theory.

Evolution of the plasma parameters in the expanding laser ablation plume of silver

The angular and radial variation of the ion density and electron temperature in the plasma plume produced by laser ablation of silver at fluences of 0.8-1.3 J cm -2 at 355 nm have been studied using a time-resolving Langmuir probe. The angular dependence of the electron temperature and the magnitude of the ion flux, at the time when the ion flux is maximised, agree with the predictions of the self-similar isentropic model of the plasma expansion by Anisimov et al.

Coherent Phonon Control

Trains of ultrashort laser pulses have been used to generate and to coherently control acoustic phonons in bulk InSb. The coherent acoustic phonons have been probed via time-resolved x-ray diffraction. The authors show that phonons of a particular frequency can either be enhanced or canceled. They have carried out simulations to understand the size of the effects and the levels of cancellation. (c) 2007 American Institute of Physics.

Status of the MAX IV light source project

The MAX IV light source project is presented. The MAX IV light source will consist of three low emittance storage rings and a 3 GeV injector linac. The three storage rings will be operated at 700 MeV, 1.5 GeV, and 3.0 GeV, which make it possible to cover a large spectral range from IR to hard X-rays with high brilliance undulator radiation from insertion devices optimised for each storage ring. The preparation of the injector linac to serve as a short pulse source and the major sub-systems of the facility are also presented.

Opportunities and challenges using short-pulse x-ray sources

Free-electron lasers will change the way we carry out time-resolved X-ray experiments. At present date, we use laser-produced plasma sources or synchrotron radiation. Laser-produced plasma sources have short pulses, but unfortunately large pulse-to-pulse fluctuations and large divergence. Synchrotron radiation from third generation source provide collimated and stable beams, but unfortunately long pulses. This means that either the time-resolution is limited to 100 ps or rather complex set-ups involving slicing or streak cameras are needed. Hard X-ray free-electron lasers will combine the best properties of present-day sources and increase the number of photons by many orders of magnitude. Already today, a precursor to the free-electron lasers has been built at Stanford Linear Accelerator Centre (SLAC). The Sub-Picosecond Photon Source (SPPS) has already shown the opportunities and challenges of using short-pulse X-ray sources. (Less)