Pierced mirrors in ultrastable spectrographs

Pierced mirrors are used in high resolution and ultrastable spectrographs to feed guiding cameras and to improve the target stability. This paper describes the concept, design, manufacture, test and integration of ESPRESSO pierced mirrors which are part of the Fiber Link subsystem. ESPRESSO is a spectrograph located in the Coude Laboratory of VLT that can be feed by the light of any VLT telescope. Similar mirrors will be used in the Fiber Link subsystem of NIRSP spectrograph which is an Infrared spectrograph for the 3.6 m telescope of the Silla Observatory.