The production of extreme UV (EUV) radiation is a high-interest topic nowadays because of a series of potential applications [1]: high-resolution microscopy, e.g. for imaging in biology; micromachining of electromechanic or optical devices at submicrometer scale; radiobiological installations able to deliver high doses in a short time with a good spatial resolution; and, lastly, as a tool for future lithography allowing one to manufacture above-Gigabit capacity integrated circuits. More precisely, considerable efforts have been devoted during more than one decade to the elaboration of sources operating at 13.5 nm, this standard arising from the availability of high-reflectivity (~ 0.7) Mo/Si multilayer mirrors. In this range, usual X-ray tubes are not optimized and synchrotron sources, though very bright, only bring a costly alternative.

Several production schemes have been proposed, based either on discharge-produced plasmas or on laser-produced plasmas. A review of the various foreseen devices is available in the literature [2]. Various analyses [3] single out xenon and tin as promising sources. However the spectroscopy of these elements, ionized about 10 times in the relevant temperature region (around 25 eV), is rather complex: presence of several charge states, of one or more open subshells such as 4p or 4d, of complex configurations with several excited electrons. Therefore it is important in a first stage to describe accurately the involved atomic physics. Then the thermodynamic properties of such plasmas deserve a certain attention: indeed the density of such media is not always high enough so that the collisions ensure local thermodynamic equilibrium (LTE). At last it is useful to study the radiative transfer properties related to physical parameters such as emissivity and opacity: such quantities are important in several fields of physics, such as astrophysics or laser-target interaction.

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