Yb:YAG Innoslab amplifier: efficient high repetition rate subpicosecond pumping system for optical parametric chirped pulse amplification.

We report on a Yb:YAG Innoslab laser amplifier system for generation of subpicsecond high energy pump pulses for optical parametric chirped pulse amplification (OPCPA) at high repetition rates. Pulse energies of up to 20 mJ (at 12.5 kHz) and repetition rates of up to 100 kHz were attained with pulse durations of 830 fs and average power in excess of 200 W.

Transverse-coherence properties of the free-electron-laser FLASH at DESY.

A general theoretical approach based on the decomposition of statistical fields into a sum of independently propagating transverse modes was used for the analysis of the coherence properties of the new free-electron laser source FLASH operated at 13.7 nm wavelength. The analysis shows that several transverse modes are contributing to the total radiation field of FLASH.

Observation of structural anisotropy and the onset of liquidlike motion during the nonthermal melting of InSb.

The melting dynamics of laser excited InSb have been studied with femtosecond x-ray diffraction. These measurements observe the delayed onset of diffusive atomic motion, signaling the appearance of liquidlike dynamics. They also demonstrate that the root-mean-squared displacement in the [111] direction increases faster than in the [110] direction after the first 500 fs.

Atomic-scale visualization of inertial dynamics.

The motion of atoms on interatomic potential energy surfaces is fundamental to the dynamics of liquids and solids. An accelerator-based source of femtosecond x-ray pulses allowed us to follow directly atomic displacements on an optically modified energy landscape, leading eventually to the transition from crystalline solid to disordered liquid. We show that, to first order in time, the dynamics are inertial, and we place constraints on the shape and curvature of the transition-state potential energy surface.