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Introduction

Nanometer- and micrometer-sized solid particles are distributed in the interstellar medium and play an important role for astrophysical processes such as star and planet formation. These particles show a rich chemistry and mineralogy as has been revealed by spectroscopic astronomical observations in the last decades. Many new observational data have been measured in the last years, e.g. by the Infrared Space Observatory in 1995-1998, and interpretation of these spectroscopic data is still in progress. This requires the comparison with data of ``analog materials'' delivered by spectroscopical laboratories. Various terrestrial analogs of cosmic solids have been studied in chemical and physical laboratories. However, many of these experiments neither took into account the specifics of cosmic dust materials (composition, lattice structure, processing, etc.), nor covered the wavelength intervals of the current astrophysical interests. Note also that these data are mainly in the form of graphics in papers, and free World Wide Web (WWW) resources on the optical constants are generally limited by several collections of refractive indices for a few materials. Since 1992, the Astrophysical Institute and University Observatory (AIU) Jena operates a Chemical and Spectroscopical Laboratory with the goal to study optical properties of analog materials of cosmic dust in the wavelength range from the ultraviolet to the far infrared. During this period, a compilation of optical constants (i.e. the complex refractive index $m=n+k\,i$ or the complex dielectric function $\varepsilon=m^2$) of such materials has been created. In collaboration with the Astronomical Institute of St.Petersburg University, this collection was expanded into an internet database that has been made available for the public in 1998 at http://www.astro.uni-jena.de/Users/database/entry.html or http://www.astro.spbu. ru/JPDOC/entry.html. In this paper we describe the current state and future of the database and give several examples of the data it contains and their possible applications.