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Optical constants


Collaboration with Instituto de Fisica Aplicada CSIC Madrid (J.I. Larruquert, J.A. Aznarez), Laboratorio Regionale IFN-CNR Luxor Padova (L. Poletto), Dipartimento di Elettronica Università di Pavia (M. Malvezzi)

The availability of optical constants n and k is a crucial aspect in the design of optical devices as interferential multilayer mirrors. Experimental data of the optical constants of most compounds and even several single elements are not available in important parts of the spectrum, such as lanthanides and rare earths in the EUV region. A Spanish-Italian collaborating group at BEAR beamline worked on the experimental determination of the optical constants of materials, mainly lanthanides and rare earths in the UV-Soft X range. The low absorption below O2,3, N4,5, and M4,5 absorption edges of lanthanides and rare earths turns them promising materials for the realization of multilayer mirrors.The experiments consisted mainly on the deposition in UHV of a thin film of the material under study onto a special substrate followed by the transmittance measurement of the film over a broad spectrum in situ in ultra high vacuum; several films of various thicknesses have been deposited. The transmittance as a function of film thickness is fitted for each wavelength and the fitting results in the direct determination of k at the given wave-length. The real part of the refractive index n has been obtained from k data using the Kramers-Kronig dispersion analysis. For this analysis, data on k, necessary in the whole spectral range, was measured from ~3 to 1,600 eV.

Extinction coefficient of promising materials in the EUV 50-105 nm spectral range

Typical setup for absorption measurements

Image of the sample: thin film deposited on a carbon film (10 nm)/ Ni grid (on the left). The glass witness sample allows to determine the film thickness by means of a θ 2θ reflectivity scan. 



Last Updated on Tuesday, 08 May 2012 15:32