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We present ellipsometric measurements of the far-infrared dielectric responseof polycrystalline samples of the new pnictide superconductor RO0.82F0.18FeAs(R=Nd and Sm). We find evidence that the electronic properties are stronglyanisotropic such that the optical spectra are dominated by the weaklyconducting c-axis response similar as in the cuprate high-temperaturesuperconductors (HTSC). Accordingly, we obtain an upper limit of the c-axissuperconducting plasma frequency of $\omega_{{\rm pl},c}^{\rm SC}\leq 260\cm$which corresponds to a lower limit of the c-axis magnetic penetration depth of$\lambda_c\geq6\mum$ and an anisotropy of $\lambda_c/\lambda_{ab}\geq 30$ ascompared to $\lambda_{ab}=185$ nm from muon spin rotation [A. Drew {\it etal.}, arXiv:0805.1042]. Also in analogy to the cuprate HTSC, our spectraexhibit the signatures of a gap-like suppression of the conductivity in thesuperconducting state with a large gap magnitude of $2\Delta\approx300\cm$ (37meV) and a ratio of $2\Delta/k_{\rm B}\tc\approx8$ that is suggestive of strongcoupling.

Superconducting energy gap and c-axis plasma frequency of (Nd,Sm)O0.82F0.18FeAs superconductors from infrared ellipsometry