In order to measure the photon flux of highly intense and extremely pulsed vacuum ultraviolet (VUV) and extreme ultraviolet (EUV) radiation in absolute terms, we have developed a gas-monitor detector which is based on the atomic photoionization of a rare gas at low particle density. The device is indestructible and almost transparent. By first pulse-resolved measurements of VUV free-electron laser radiation at the TESLA test facility in Hamburg, a peak power of more than 100 MW was detected. Moreover, the extended dynamic range of the detector allowed its accurate calibration using spectrally dispersed synchrotron radiation at much lower photon intensities.

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A method and apparatus have been developed for precise measurements of the ratios of total cross sections for electron-impact ionization and photoionization in rare gases based on the comparison of the total ion yields of the two ionization processes. Low uncertainties for the cross-section ratios are achieved above all by using a cryogenic electrical substitution radiometer as a primary detector standard in the soft-x-ray and vacuum ultraviolet spectral ranges in order to determine the impinging photon flux. On the basis of our measured cross-section ratios and well-known total photoionization cross sections we deduce absolute total electronimpact ionization cross sections of rare gases. As a result we present ratios of total electron-impact ionization cross sections to total photoionization cross sections and deduce total electron-impact ionization cross sections of neon in the energy range of electrons from 140 to 4000 eV and of photons from 100 to 1500 eV. Relative uncertainties as low as 1.3% for the cross-section ratios and 2.8% for the total electron-impact ionization cross sections have been achieved. A comparison of our cross-section data with published experimental and theoretical data is presented.

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Spectra from various target materials from a KrF-laser plasma source have been investigated in the Extreme UV spectral range between 12 and 17nm using an off-Rowland grazing-incidence spectrograph. The electron temperature Te and mean ionization stages Z have been measured to amount to Te = 80eV and Z = 10–12, respectively. Additional calibration and measurement of the spatial and temporal characteristics of the plasma has been done using a combination of a multilayer mirror and XUV diode or fiber image carrier system. The maximum yield at 13.5nm (2.4–3 × 1015 phot/srnm) has been observed for targets with atomic number Za = 32, 50, 73–75, of which the radiative transitions have been identified as 3p–3d, 4d–4f and 4f–5d transitions respectively. The corresponding maximum conversion efficiency at 13.5nm was 0.43% in a 1% bandwidth. An option for further optimization of the KrF laser plasma source for application in EUV lithography is discussed.