K. J. Witte

The asterix III pulsed high-power iodine laser

A system description and first results of the Asterix III high-power iodine laser built at IPP Garching are given. This laser is designed to yield an output energy of 1 kJ in about 1 ns. Until now pulses with output energies up to 300 J and pulse lengths ranging from 1 to 3 ns have been obtained.

Iodine laser oscillator in gain switch mode for ns pulses

Abstract An iodine laser oscillator is described, which delivers several mJ in ns-pulses. The oscillator is mode-locked by means of an acoustooptical modulator, the pulse duration varies with the iodine pressure. Apparent self-modelocking is due to saturation effects.

Advanced iodine laser concepts

The essential features of an advanced iodine laser are outlined. These are governed primarily by the proper choice of the stored inversion density of an amplifier and also by the means to enhance the energy extraction efficiency to values in excess of 50 percent. With these measures an amplifier chain with output energies in the kJ range and overall system efficiencies of almost 0.2 percent can be designed. This value is twice as high as that now achieved. As the laser-fusion experiments require a greater pulse duration variability than hitherto obtained, an oscillator pumped by an excimer laser is developed, allowing chain output pulse durations in the range from some 100 ps to several ns. The frequency conversion of iodine laser light by nonlinear interaction in crystals is also investigated.

An excimer laser pumped atomic iodine laser emitting pulses in the range of 2–12 ns☆

Abstract An iodine photodissociation laser is pumped with a laser pulse from a XeCl or a KrF laser. Single smooth laser pulses with a duration variable from 2.6 to 12 ns are emitted by the iodine laser. A pulse power of 0.5 MW is obtained with diffraction limited beam divergence.

Relativistic self-focusing of fs-laser pulses and their heating effect on the preformed plasma

Experiments in the context of fast ignition were carried out by focusing a 6-TW laser beam into a preformed plasma. An electron population with a quasi-temperature of 2 MeV was generated. The 2/spl omega/ self-emission image reveals a self-focused plasma channel formation, whereas X-ray pinhole photography shows a postheating of the preformed plasma.

Spectroscopy of plasmas at solid density generated by ultra-short laser pulses

Plasma close to solid density is generated by focusing a frequency doubled Ti-Sapphire laser delivering 150 fs high contrast pulses at an intensity of ≈1017 W/cm2 on solid flat targets. We will first discuss the mechanism of dense plasma production based on hydro code and PIC simulations and on measurements of the laser absorption and the energy transport into the dense target. Then we will present spectrally and temporally resolved measurements of aluminum K-shell spectra. Using a thin layer consisting of MgO or C on top of the Al we record Al K-shell spectra with strongly broadened and shifted lines. The analysis of the measured width and the red shift of the Ly-α line with its He-like satellites and of the He-β line with its Li-like satellites indicates the emission from a plasma at solid density with a temperature in the range 250 to 300 eV. The typical duration of the emission of these lines is ≈2 ps.

Time-resolved x-ray spectra from laser-generated high-density plasmas

We focused frequency doubled ultra short laser pulses on solid C, F, Na and Al targets, K-shell emission was systematically investigated by time resolved spectroscopy using a sub-ps streak camera. A large number of laser shots can be accumulated when triggering the camera with an Auston switch system at very high temporal precision. The system provides an outstanding time resolution of 1.7ps accumulating thousands of laser shots. The time duration of the He-(alpha) K-shell resonance lines was observed in the range of (2-4)ps and shows a decrease with the atomic number. The experimental results are well reproduced by hydro code simulations post processed with an atomic kinetics code.

Status of the Asterix IV iodine laser

After a description of the design and layout of the 2 kJ/5 TW single beam Asterix IV iodine laser the steps necessary for obtaining a laser beam intensity profile as homogeneous as possible are reported. These steps are: providing a homogeneous inversion density profile in the amplifiers by an appropriate flashlamp-reflector geometry and by compensating the edge enhancement caused by the image relaying system by suitable soft apertures. The paper concludes with a description of the results obtained by the laser system with the end-amplifier not in operation. The full system will become operational at the end of 1990.

Terawatt Iodine Laser

In this paper the high power iodine laser ASTERIX III is described. It is a single beam system designed to yield an output power in the 1 Terawatt range (energy about 1 kJ, pulse duration about or less than 1 ns). It will be used for plasma production with power densities on the target surface expected in the range between 1017 to 1018 W/cm2.

ON THE SECOND ORDER AUTOCORRELATION OF AN XUV ATTOSECOND PULSE TRAIN

Temporal widths of an attosecond (asec) XUV radiation pulse train, formed by the superposition of higher order harmonics, have been recently determined utilizing a 2nd order autocorrelation measurement. An assessment of the validity of the approach, for the broadband XUV radiation of asec pulses, is implemented through ab initio calculations modeling the spectral and temporal response of the two-XUV-photon He ionization detector employed. The measured width of the asec bursts is discussed in terms of the spectral phases of the individual harmonics, as well as in terms of the spatially modulated temporal width of the radiation, and is found in reasonable agreement with the expected duration.