Single layers of MgF 2 and LaF 3 were deposited upon superpolished fused-silica and CaF 2 substrates by ion-beam sputtering ͑IBS͒ as well as by boat and electron beam ͑e-beam͒ evaporation and were characterized by a variety of complementary analytical techniques. Besides undergoing photometric and ellipsometric inspection, the samples were investigated at 193 and 633 nm by an optical scatter measurement facility. The structural properties were assessed with atomic-force microscopy, x-ray diffraction, TEM techniques that involved conventional thinning methods for the layers. For measurement of mechanical stress in the coatings, special silicon substrates were coated and analyzed. The dispersion behavior of both deposition materials, which was determined on the basis of various independent photometric measurements and data reduction techniques, is in good agreement with that published in the literature and with the bulk properties of the materials. The refractive indices of the MgF 2 coatings ranged from 1.415 to 1.440 for the wavelength of the ArF excimer laser ͑193 nm͒ and from 1.435 to 1.465 for the wavelength of the F 2 excimer laser ͑157 nm͒. For single layers of LaF 3 the refractive indices extended from 1.67 to 1.70 at 193 nm to ϳ1.80 at 157 nm. The IBS process achieves the best homogeneity and the lowest surface roughness values ͑close to 1 nm rms ͒ of the processes compared in the joint experiment. In contrast to MgF 2 boat and e-beam evaporated coatings, which exhibit tensile mechanical stress ranging from 300 to 400 MPa, IBS coatings exhibit high compressive stress of as much as 910 MPa. A similar tendency was found for coating stress in LaF 3 single layers. Experimental results are discussed with respect to the microstructural and compositional properties as well as to the surface topography of the coatings.

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We present recent results obtained by the European Free Electron Laser (FEL) project at the ELETTRA storage ring. Coherent and tunable light was produced in the ultraviolet down to below 190 nm, the shortest lasing wavelength obtained so far with a FEL oscillator. The performance of the FEL is described, together with a series of technical solutions that have been adopted on it. These solutions increase its validity as a source for applications, and demonstrate the potential of FEL oscillators to become sources with features in the vacuum ultraviolet

The determination of optical parameters of thin films from experimental data is a typical task in the field of optical-coating technology. The optical characterization of a single layer deposited on a substrate with known optical parameters is widely used for this purpose. Results of optical characterization are dependent on not only the choice of the thin-film model but also on the quality of experimental data. The theoretical results presented highlight the effect of systematic errors in measurement data on the determination of thin-film parameters. Application of these theoretical results is illustrated by the analysis of experimental data for magnesium fluoride thin films.

Working with wavelengths shorter than the deep ultraviolet involves the development of dedicated optics for free-electron lasers with devoted coating techniques and characterizations. High-performance deep-ultraviolet optics are specially developed to create low-loss, high-reflectivity dielectric mirrors with long lifetimes in harsh synchrotron radiation environments. In February 2001, lasing at 189.7 nm, the shortest wavelength obtained so far with free-electron-laser oscillators, was obtained at the European Free-electron-laser project at ELETTRA Synchrotron Light Laboratory, Trieste, Italy. In July 2001, 330-mW extracted power at 250 nm was measured with optimized transmission mirrors. Research and development of coatings correlated to lasing performance are reported.