Investigating spectrograph design parameters with the Yale Doppler diagnostic facility

The detection of earth-like exoplanets with the Doppler technique requires extreme precision spectrographs stable over timescales of years. The precision requirement of 10 cm/s is equivalent to a relative uncertainty of 3x10 ^-10, and, with the typical dispersion of the Echelle spectrographs used for this purpose, translates to a shift of a few nanometers of the spectrum on the detector. Consequently, the instrument must be well understood and optimized in every component and detail. We describe the Yale Doppler diagnostic facility (YDDF), a dedicated bench mounted Echelle spectrograph in our lab at Yale University, which will be used to systematically study the influence of different components at this precision level. The spectrograph bench allows for a flexible optical configuration, high resolution and sampling, and wide spectral coverage. Further, we incorporated a turbulence and guiding simulator to realistically reproduce the situation at the telescope, enabling end-to-end tests of important parameters.