Fig. 1. (a) General scheme of the experimental setup. (b) Central cross-section of the nozzle. (c) Coordinates of the focal spot position.

Fig. 2. (a), (b) X-ray emission spectra and (c)–(e) corresponding electron measurement results detected in -direction (laser propagation axis) for the following experimental conditions: inlet gas pressure – , laser energy – , laser beam is focused at the center of Ar gas jet, perpendicularly to gas flow -axis at the distance from nozzle outlet (a), (c), (d) and (b), (e) .

Fig. 3. X-ray emission spectra of Ar plasma depend on – laser focusing point displacement from nozzle outlet , measured at fixed parameters: inlet Ar gas pressure – , laser energy on target – , laser pulse duration – , laser contrast – in diagnostic direction (a) , (b)  and (c) . Note that, the X-ray intensity on axis of ordinates is given in absolute values.

Fig. 4. (a) Dependence of the X-ray emission registered in the -direction on (the distance from the nozzle outlet to the laser focusing point). Simulated spectra obtained by the radiational–collisional code PrismSpect for different electron temperatures , fixed atomic densities and the hot electrons fraction of 0.1% with the temperature are shown by the red lines. (b) X-ray yield per laser shot of photons with the energy of versus distance from the nozzle throat for diagnostic directions , and . (c) Results of hydrodynamic calculations for the gas jet density profile for the slit nozzle MS05-10-166^[24] and different .

Fig. 5. Dependence of Ar plasma X-ray emission spectra on the laser pulse energy . The X-ray emission was observed in (a) -direction, (b) -direction and (c) -direction. The X-ray emission spectra have been measured under the following experimental conditions: entry pressure of the Ar gas jet – , the distance from nozzle outlet to laser focus position – , laser pulse duration – , laser pulse contrast – .

Fig. 6. (a) The comparison of the Ar plasma X-ray emission spectra measured for two different laser pulse energies and and kinetic modeling carried out with the PrismSpect. The calculations have been done for the fixed parameters: the ion density of the Ar gas jet – , fraction 0.1% of hot electrons with . (b) Yield of X-ray photons with the energies versus the incident laser pulse energy.

Fig. 7. (a) X-ray emission spectra of Ar plasma; (b) X-ray photons yield – at the energy range versus the laser pulse duration – ; (c) X-ray photons yield – in the energy range versus entry Ar gas pressure – , observed for the laser focusing position for diagnostic directions , and toward the axis of the laser propagation direction.