Absorption Spectra of Light Ions in the Extreme Ultraviolet

Extract

We have used the method of two laser produced plasmas (Jannitti et al. 1984a) to measure the absorption spectra of the ions Be⁺⁺ (Jannitti et al. 1984b), Be⁺ (Jannitti et al. 1984c) and B⁺ in the grazing incidence and normal incidence region. Both discrete and continua transitions have been measured and values of the photoionization cross sections are derived.

The experimental set up referring to the normal incidence investigation is shown in Fig. 1. A laser beam of 10 J of energy and 15 ns (FWHM) duration is split in two parts and generates two plasmas: one on target T of high atomic number (Cu) used as a background continuum emitting source and a second on target A for producing the absorbing species to be studied. For the latter a sphero-cylindrical lens is used producing a focal spot 100 µm wide and up to 10 mm long. The continuum radiation produced on a target tilted 45° both with respect to the laser beam and to the axis of observation was collected by a toroidal mirror whose radii of curvature, R = 640 mm in the plane of incidence and ρ = 530 mm in the plane perpendicular to the former are such to compensate the astigmatism of the 2 m radius grating.