Abstract
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 ultrashort laser driven plasma x-ray sources (LPXs) as an attractive supplement offer exceptional parameters to unleash ultrafast 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.