  We introduce the RISTRETTO instrument for ESO VLT, an evolution from the
original idea of connecting the SPHERE high-contrast facility to the ESPRESSO
spectrograph (Lovis et al 2017). RISTRETTO is an independent, AO-fed
spectrograph proposed as a visitor instrument, with the goal of detecting
nearby exoplanets in reflected light for the first time. RISTRETTO aims at
characterizing the atmospheres of Proxima b and several other exoplanets using
the technique of high-contrast, high-resolution spectroscopy. The instrument is
composed of two parts: a front-end to be installed on VLT UT4 providing a
two-stage adaptive optics system using the AOF facility with coronagraphic
capability and a 7-fiber IFU, and a diffraction-limited R=135,000 spectrograph
in the 620-840 nm range. We present the requirements and the preliminary design
of the instrument.
