The absolute quantum efficiency of two Philips XP2020Q photomultipliers and one Hamamatsu R2059 photomultiplier are measured in the VUV range for three wavelength values, (193, 201, and 253 nm). We used a deuterium lamp for which the absolute radiance has been calibrated; the wavelength range is selected by means of optical filters.

The optical thickness of dense plasma, created in linear flashtubes filled with noble gases, is measured over the wavelength range 466-780 nm using a CW laser beam. The electron density and temperature radial profiles of the plasma are determined by spectroscopic methods, infrared laser interferometry and local thermodynamic equilibrium equations. Knowing those profiles, the absorption coefficients and consequently the xi fb factors are deduced from optical thickness measurements. These factors are compared with theoretical values of Hofsaess (1978) and with previously published experimental results. The dependence of xi fb on the wavelength and the plasma parameters (electron density in the range 7*1017-1.7*1018 cm-3, temperature between 10900 and 17000 K) is discussed. The effect of the interparticle interaction on the absorption in the dense plasmas is only sensitive to the shift of the photoionization thresholds of atoms.

Plasma creation occurs when the frequency of a tunable dye laser is adjusted to the 589 nm D-doublet of the sodium atom. Occurrence and Stark broadening of emission lines in the fluorescence light are used as diagnostics. The time history of the electron density and temperature is inferred from these measurements. The peak electron density was found to be above 5 · 1016 cm−3 with a temperature lower than 1 eV.

Based on the direct determination of the enrichment factor by means of a new method suitable for the investigation of gases, the influence on this factor of the temperature and of the pumping of the separator, of the injected volume, and of the flow rate in the column has been investigated.