Extremely fast processes happening on sub picosecond time scale can be captured by the well-known pump-probe scheme using ultrashort x-ray pulses as shutter. XFELs and femtosecond slicing beam lines on synchrotrons together-with ultra-short laser driven plasma x-ray sources (LPXs) as an attractive supplement offer exceptional parameters to unleash ultra-fast phenomenon. As pump-probe techniques based on the compact LPXs attract attention being jitter free, more precise knowledge of their emission duration, determining the measurement temporal resolution, became indispensable. We report here, for the first time, x-ray pulse duration from LPX using NIR pump x-ray probe cross-correlation method. The underlying mechanism is ultrafast relaxation of femtosecond laser-induced non-thermal electrons generated on the surface of transition metals. The emission duration of x-ray pulse is estimated by the evolution of transmission (110 ±6 fs) and fluorescence signals (129 ± 19 fs) and found in good agreement with the theoretical prediction of ≤100 fs for LPXs.
Ultrafast X-ray absorption spectroscopy (UXAS) offers the opportunity to investigate function-structure relationships of
complex organic molecules or biological functional subunits without the need of crystallization. Of special interest from
the viewpoint of structural biology is the region of K-edges of transition metals between 5 and 10 keV. Regardless of
successful application of time-resolved diffraction techniques to investigations of crystal dynamics using synchrotron
and laboratory based sources there are only very few examples for application of UXAS to revealing the structural
dynamics in biomolecular systems. This is mainly caused by the lack of broadband ultrafast x-ray sources as well as of
appropriate optics adapted to these sources. Due to the long-data-recording time in UXAS experiments the sample
integrity is mainly determined by the average power of the pump pulses inducing the structural changes. Using a fixed
energy of the pump pulse the latter one is determined by the repetition rate of the pump laser. In this paper we discuss the
prospects of UXAS comparing fs laser plasma sources with different repetition rates in combination with tailor-made
optics based on highly annealed pyrolytic graphite (HAPG).