Laser-Produced Plasmas as Radiometric Transfer-Standard Sources for the Vacuum-Ultraviolet and the Soft-X-ray Range

Laser-produced tungsten plasmas were investigated with respect to their suitability as radiometric transfer standard sources in the range between 7 nm and 100 nm. For plasma generation a Nd:YAG/glass laser system with λ = 1.064 μm, a pulse length of 17 ns and pulse energies between 100 mJ and 800 mJ was used in connection with a focusing system of 85 mm focal length. The spectral concentration of radiant intensity time-integrated over one plasma radiation pulse was measured with a relative uncertainty of 8% using the electron storage ring BESSY as a primary standard. Within this uncertainty the radiant emission was reproducible during several months, if one applied specific procedures that had been developed for setting the laser parameters and the focusing conditions. The maximum of emission was found at 16.5 nm. At this wavelength a 800 mJ laser pulse generates 3.5 × 10 14 photons nm -1 sr -1 . The results of this study let us expect that a small transportable radiation standard is practical, which is based on a low-cost, single-stage, Nd-laser system.