Observation of X-ray fluorescence resulting from photoionization by a femtosecond laser-produced plasma X-ray source

We demonstrate the first observation of X-ray fluorescence resulting from inner-shell photoionization by a subpicosecond laser-produced plasma X-ray source. 8 keV electrons produced by a 100 fs laser at 3*10 16 W cm -2 intensity create K-shell vacancies in a Ti layer. This generates a 4.51 keV K alpha X-ray pulse which is used to photoionize a Ca sample. Fluorescence of Ca at 3.69 keV (K alpha ) and 4.01 keV (K beta ) is observed as a result of Ti K alpha photoionization.