High average power, highly brilliant laser-produced plasma source for soft X-ray spectroscopy.

In this work, a novel laser-produced plasma source is presented which delivers pulsed broadband soft X-radiation in the range between 100 and 1200 eV. The source was designed in view of long operating hours, high stability, and cost effectiveness. It relies on a rotating and translating metal target and achieves high stability through an on-line monitoring device using a four quadrant extreme ultraviolet diode in a pinhole camera arrangement. The source can be operated with three different laser pulse durations and various target materials and is equipped with two beamlines for simultaneous experiments. Characterization measurements are presented with special emphasis on the source position and emission stability of the source. As a first application, a near edge X-ray absorption fine structure measurement on a thin polyimide foil shows the potential of the source for soft X-ray spectroscopy.

Real-time observation of interference between atomic one-electron and two-electron excitations.

We present results of real-time tracking of atomic two-electron dynamics in an autoionizing transient wave packet in krypton. A coherent superposition of two Fano resonances is excited with a femtosecond extreme-ultraviolet pulse. The evolution of the corresponding wave packet is subsequently probed with a delayed infrared pulse. In our specific case, we get access to the interference between one- and two-electron excitation channels in the launched wave packet, which is superimposed on its decay through autoionization. A simple model is able to account for the observed dynamical evolution of this wave packet.

Photoinjector drive laser of the FLASH FEL.

The upgraded photoinjector drive laser of the free-electron laser facility FLASH at DESY Hamburg is described in this paper. This laser produces trains of 800 and 2400 ultraviolet picosecond pulses at 1 MHz and 3 MHz repetition rate in the trains, respectively. The amplifying elements of the system are Nd:YLF-rods, which are pumped by fiber-coupled semiconductor diodes. Compared to the flashlamp-pumped photocathode laser previously used at FLASH, the new diode-pumped laser features a better reliability and a significantly improved stability of its pulse parameters.

Lateral movement of a laser-accelerated proton source on the target's rear surface.

The spatial dependence of proton acceleration at the rear surface of a target that is irradiated by high-contrast and ultraintense laser pulses is investigated. Lateral movement of the proton acceleration position at the rear surface is observed; this is tested by a two-pinhole measurement which results in the observation of protons with a narrow energy band. This drifting is only observed when relativistic-intensity laser pulses irradiate targets with a small preplasma at oblique incidence, as is confirmed by two-dimensional particle-in-cell simulations. This scenario of proton acceleration by the fast-moving sheath field leads to energy selection of the accelerated protons as a function of observing position.