AbstractThe investigation of beam-plasma interaction processes requires the development of plasma parameter diagnostic methods with high temporal and spatial resolution. The basic plasma parameters to be controlled when measuring the ion energy losses in ionized gases are the areal density of free electrons, the degree of ionization and the heavy element impurities during the electrical discharge in hydrogen. We present the relevant experimental results obtained by means of time-resolved, two-wavelength Mach-Zehnder interferometry based on HeNe (λ = 0.63 μm) and HeCd (λ = 0.44 μm) lasers. Optical emission line spectroscopy allowed us to follow the behaviour of the impurity concentrations with a high temporal resolution. Both methods have been used for diagnostic tests of a hydrogen plasma target.