| Abstract [eng] |
The aim of this work was to investigate how a low-energy prepulse affects the expansion dynamics of femtosecond laser-induced plasma and the X-ray emission yield. In the experiment, an iron target was irradiated using either a single femtosecond pulse or a pulsepair configuration, where a prepulse with an energy corresponding to approximately 12% of the main pulse energy was applied before the main pulse. The delay between the pulses was approximately 320 ps. The plasma evolution was recorded using femtosecond time-resolved optical shadowgraphy, while changes in the X-ray emission were evaluated by comparing the spectra obtained in the single-pulse and pulse-pair regimes. From the shadowgraphy images, the temporal evolution of the plasma height, width, geometrical anisotropy, and effective radius was determined. The effective radius dynamics were additionally described using a Sedov–Taylor-type hydrodynamic model. It was found that the pulse-pair regime increases the X-ray emission yield over the entire recorded energy range, with the strongest relative enhancement observed at higher photon energies. The shadowgraphy measurements showed that the prepulse affects different expansion directions unevenly: the plasma height changed only moderately, whereas the width parallel to the target surface increased more strongly. Using a Sedov–Taylor-type approximation, it was determined that, under the experimental conditions used in this work, the characteristic energy scale associated with hydrodynamic plasma expansion is approximately 2.7 times larger in the pulse-pair regime than in the single pulse case. The obtained results show that a relatively small prepulse energy can induce a disproportionately large change in both the hydrodynamic evolution of the plasma and the X-ray emission yield. |
