A high-density sub-micron liquid spray for laser driven radiation sources

A new and (simple) versatile high-density sub-micron liquid spray source has been developed and examined for use in laser–plasma interaction studies. Sub-micron sized water droplets were produced in a spray by hypersonic expansion of superheated water vapour through a nozzle into vacuum. Employing Mie scattering and transmission measurement of the spray, the size of individual droplets were determined to a diameter of d = (0.15 ± 0.01) µm. The droplet number density varied from (1.6 ± 0.5) × 10 11 up to (7.5 ± 0.7) × 10 10 droplets cm −3 depending on the position below the nozzle while the maximum mean atomic density was >10 18 atoms cm −3 . This water spray target system provides a six to eight times higher x-ray emission at photon energies below 10 keV compared to a single droplet (15 µm diameter) source where both were irradiated with ultrafast (35 fs) 20 TW Ti : Sa laser pulses.