Very high-resolution spectroscopy: the ESPRESSO optical design

Resolving power of spectrographs for large telescopes is generally limited by the maximum dimension of the dispersion gratings. To overcome this limit, innovative optical configurations have been designed, starting from the ideas proposed for CODEX. By properly combining pupil slicing and anamorphic magnification, a R similar to 63'000-210'000 spectrograph has been designed. Many different solutions were proposed during the early design phases, and a detailed trade off study has been carried out to improve efficiency, manufacturability, and reduce risks and costs of the preliminary designs. We present a full description of the optical design of the spectrograph after preliminary design review, together with expected performances.