Abstract

The evolution of chirped pulse amplification into the 20-fs regime has allowed the production of multiterawatt pulses at repetition rates of 10 to 50 Hz, or nearly 4 orders of magnitude higher than similar peak-power, nanosecond-duration, Nd:glass lasers. The combination of high peak power and repetition rate makes these systems ideal for producing very high fluxes of ultrafast x-rays from relativistic laser/matter interactions. Such x-ray pulses, which can in principle have durations of significantly less than a picosecond, are ideal probe sources studying solid state and chemical dynamics on an ultrafast timescale. Two approaches with respect to probing dynamics with laser-produced, ultrafast x-rays will be outlined; namely time-resolved x-ray diffraction and time-resolved x-ray absorption spectroscopy. The former is a global technique in that information about the position of all atoms in the sample is obtained. Results from a test study of laser illumination of GaAs indicate that it is possible to observe lattice displacements with milli-angstrom spatial resolution and picosecond temporal resolution with ultrafast x-ray diffraction. Time resolved x-ray absorption spectroscopy can be used to monitor local changes in the electronic environment of specific atoms in a large ensemble via changes in absorption fine structure or via energy shifts of inner shell absorption edges. This presentation will review both techniques and outline considerations for ideal laser systems, improved x-ray generation and experimental geometries.

© 1998 IEEE