Abstract. -The fibre-fed echelle spectrograph of Observatoire de Haute-Provence, ELODIE, is presented. This instrument has been in operation since the end of 1993 on the 1.93 m telescope. ELODIE is designed as an updated version of the cross-correlation spectrometer CORAVEL, to perform very accurate radial velocity measurements such as needed in the search, by Doppler shift, for brown-dwarfs or giant planets orbiting around nearby stars. In one single exposure a spectrum at a resolution of 42000 (λ/∆λ) ranging from 3906Å to 6811Å is recorded on a 1024×1024 CCD. This performance is achieved by using a tan θ = 4 echelle grating and a combination of a prism and a grism as cross-disperser. An automatic on-line data treatment reduces all the ELODIE echelle spectra and computes cross-correlation functions. The instrument design and the data reduction algorithms are described in this paper. The efficiency and accuracy of the instrument and its long term instrumental stability allow us to measure radial velocities with an accuracy better than 15 m s −1 for stars up to 9th magnitude in less than 30 minutes exposure time. Observations of 16th magnitude stars are also possible to measure velocities at about 1 km s −1 accuracy. For classic spectroscopic studies (S/N >100) 9th magnitude stars can be observed in one hour exposure time.

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We describe the principle of the polychromatic laser guide star(LGS) to recover the tilt information in imaging through the atmosphere. Observations using the A\TLIS laser at the Lawrence Livermore National Lab. are discussed in terms of returned flux in the ultraviolet. The major items of the programriie ELP-OA, starting now in France, are briefly reviewed, as well as the organisation of theLGS R&D in Europe. Finally the conclusion outlines the possible improvements of the polychromatic LGS to allows us to reasonably implement it at large astronomical telescopes.

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