Klaus Eidmann

Route to intense single attosecond pulses

A feasibility study is presented for the generation of single attosecond pulses using harmonics produced by planar targets irradiated at high intensities. The investigation focuses on the interaction of a few-optical cycles, carrier-envelope phase controlled, near-infrared laser pulse with an overdense plasma. The results obtained using an one-dimensional particle-in-cell code indicate that at laser intensities of 1020 W cm−2 a single sub-fs pulse can be generated in the 20–70 eV spectral range with an efficiency of a few per cent and with 10−3 to 10−4 for higher photon energies.

Conversion of laser light into soft x rays. Part I: Dimensional analysis

The conversion of laser light into soft x rays by irradiation of a high‐Z material is theoretically investigated for open, planar geometry. The material may be subdivided into a hot, low‐density conversion layer, optically thin for the x rays, and a dense, optically thick reemission zone. The two layers are coupled through radiation only. Dimensional analysis yields asymptotic expressions for the x‐ray conversion efficiency and the reemission coefficient and hence for the total converted flux from the target.

Opacity Studies of Iron in the 15-30eV Temperature Range

Absorption of the 2p-3d transitions of iron has been measured using point projection spectroscopy. Thin C tamped Fe foils were heated around 20 eV by X-rays generated in gold spherical hohlraums irradiated by the high-power laser ASTERIX IV. Absorption of Fe V to Fe X has been observed in the spectral vicinity of 730 eV (17 A). The Ag backlighter source and absorbed spectra were recorded on the same shot by a TlAP crystal spectrograph. The experimental spectra have been reproduced by the two superconfiguration local thermodynamic equilibrium codes SCO and STA. Detailed statistical calculations of the different ionic structures have also been performed with the Spin Orbit Split Arrays method, allowing the determination of ion populations. The electron temperature and average ionization obtained by fitting the experiment with the different calculations were compared with radiative hydrodynamic simulations.

Threshold of the 2ωpe instability in a laser produced plasma

Abstract 3 2 ωL emission from various plane targets irradiated by a 20 J, 5 ns neodymium laser pulse has been investigated. The onset of 3 2 ωL emission and an increase in intensity by five orders of magnitude is observed at a laser intensity of ≌2×1013W cm-2, the threshold intensity predicted for excitation of the 2ωpe instability.

Conversion of laser light into soft x rays. Part II: Numerical results

The conversion of laser light into soft x rays during interaction of intense laser light with a planar gold target was investigated numerically with the help of the multi code [Comput. Phys. Commun. 49, 475 (1988)]. It solves one‐dimensional hydrodynamics including flux‐limited electron heat conduction, multigroup radiation diffusion, and steady‐state nonlocal thermodynamic equilibrium radiation physics. The influence of various parameters such as the laser intensity, wavelength, and pulse duration on the conversion efficiency of laser light into x rays was studied. Particular emphasis was placed on comparing the numerical results with the model presented in the preceding paper (Part I) [Phys. Fluids B 2, 199 (1990)]. According to this model the radiating plasma can be divided into a conversion layer and a reemission zone. Its essential features are confirmed by the numerical results.

K-shell spectra from hot dense aluminum layers buried in carbon and heated by ultrashort laser pulses

Ultrashort laser pulses allow for the generation of hot plasmas near solid state densities. For this purpose a Ti:Sapphire laser was used, which delivers after frequency doubling, pulses of high contrast with an energy of about 60mJ and a duration of 150fs at 395nm. The typical intensity on the target was a few 1017W/cm2. To achieve a high degree of uniformity we used targets consisting of a 25nm thin Al tracer layer buried at different depths up to 400nm in solid carbon. Time-integrated Al K-shell spectra are presented. Characteristic features of the spectra are significant high-order satellite line emission, strong line broadening and a center-of-mass line shift to the red, which was observed in transitions from principal quantum number n=2 or 3 to 1. Accurate measurement of the shift was made possible by using the cold Si Kα line as an absolute wavelength calibration. In addition to time-integrated measurements, we used an ultrafast X-ray streak camera to obtain time and spectrally resolved spectra. Typical durations of the Lyα and Heα lines are in the range 2–4 ps. The experimental results are compared with a time-dependent model, which combines hydrodynamic simulations, time-dependent atomic kinetics, detailed spectral line shapes including line shifts, and radiation transport.

Comparative study of time-resolved K-shell spectra from aluminum plasmas generated by ultrashort laser pulses at 395 and 790 nm

A comparative study of temporally and spectrally resolved K-shell emission from aluminum targets heated with 150 fs Ti:sapphire laser pulses at 790 and 395 nm is presented at an intensity of 5×1017 W/cm2. Whereas at 395 nm spectrally broad intense plasma lines and a weak Kα line with durations (full width at half maximum) of 1–2 ps are observed, the spectrum at 790 nm shows weak narrow plasma lines and an intense Kα line with durations of 3–5 ps.

Conical x-ray crystal spectrometer for time integrated and time resolved measurements

We present a new x-ray spectrometer setup based on a conically curved mica crystal in the von Hamos configuration. An x-ray sensitive charge coupled device or streak camera can be easily coupled in a perpendicular orientation to the spectrally resolved x-ray line focus. Shifting the crystal along its axis of symmetry allows one to change the dispersion and the signal flux density on the detector. A large spectral range at high resolution and adjustable signal intensity is accessible with this setup.

Effect of plasma peak density on energetic proton emission in ultrashort high-intensity laser-foil interactions

The influence of plasma peak density on energetic proton emission from the rear side of a foil irradiated by a 70-fs intense laser pulse at normal incidence has been studied. When the plasma peak density of the foil is overdense, forward energetic proton emission is dominant and attributed to rear surface acceleration. Along with the plasma peak density changed from overdense to underdense, a transition of proton acceleration from the forward to the radial direction is observed, and in the latter case energetic protons are emitted radially and slightly forward.

Generation of picosecond hard-x-ray pulses in a femtosecond-laser-driven x-ray diode

The temporal characteristics of ultrashort hard-x-ray pulses generated in a femtosecond-laser-driven x-ray diode are investigated for what is believed to be the first time. Copper Kalpha x-ray pulses with a duration of a few picoseconds are measured with a jitter-free x-ray streak camera.