Coherent ultrafast X-ray sources and their applications

Summary: The project proposed here aims at the development of measurement techniques for the complete temporal characterization (chirp, temporal profile) of the attosecond pulses for the entire soft x-ray regime. The technique will also be extended to hard x-ray energies (>10 keV) and applied to the characterization of XFEL pulses with expected pulse durations from a few femtoseconds to a few hundred attoseconds. Abstract: The generation of ever shorter pulses is a key to exploring the dynamic behaviour of matter on ever shorter time scales. Recent developments have pushed the duration of laser pulses close to its natural limit, to the wave cycle, which lasts somewhat longer than one femtosecond (1 fs = 10-15 s) in the visible spectral range. Time- resolved measurements with these pulses are able to trace dynamics of molecular structure but fail to capture electronic processes occuring in atoms on an attosecond (1 as=10 -18 s) time scale. The generation of high-order harmonic radiation in the extreme ultraviolet and soft x-ray regime from atoms exposed to intense few- femtosecond-duration laser pulses comprising just a few wave cycles opened the way to the generation of isolated pulses shorter than 1 femtosecond in the soft x-ray regime. Recently there has also been a great deal of excitement about LINAC based x-ray sources. X-ray free electron lasers (XFEL) - in combination with precision bunch compression and filtering techniques - hold promise for generating sub-femtosecond hard x-ray pulses in the foreseeable future. First experiments in inner-shell atomic spectroscopy, carried out at the Photonics Institute of the Vienna University of Technology, opened up the era of attosecond-physics. The tools which have been used, attosecond XUV-pulses, represent the present state of the art, covering an energy range of 90 to 100 eV. Capturing a variety of inner-shell electronic processes in atoms as well as fast structure and electronic dynamics in biological molecules need higher energy radiation in the x-ray regime. The research mentioned in the summary will be implemented in collaboration with Jerome Hastings and coworkers at the Standford Linear Accelerator and will combine for the first time laser-based attosecond techniques with accelerator-base technologies for the generation and application of ultrashort high-brilliance x-ray pulses. The novel ultrafast techniques will reach out to previously inaccessible time domains and photon energy ranges and will be used for time-resolved spectroscopy of strongly-bound (inner-shell) electrons.