The Polychromatic Laser Guide Star aims at providing for the tilt measurement from a LGS without any natural guide star. Thus it allows adaptive optics to provide us with a full sky coverage. This is critical in particular to extend adaptive optics to the visible range, where isoplanatism is so small that the probability is negligible to find a natural star to measure the tilt. We report new results obtained within the framework of the Polychromatic LGS programme ELP-OA. Natural stars have been used to mimic the PLGS, in order to check the feasibility of using the difference in the tilt at two wavelengths to derive the tilt itself. We report results from the ATTILA experiment obtained at the 1.52 m telescope at Observatoire de Haute-Provence. Tilts derived from the differential tilts are compared with direct tilt measurements. The accuracy of the measurements is currently ≈ 1.5 Airy disk rms at 550 nm. These results prove the feasibility of the Polychromatic Laser Guide Star programme ELP-OA. New algorithms based on inverse problems under development within our programme would lead to smaller error bars by 1 magnitude, as soon as they will run fast enough. We describe the ELP-OA demonstrator which we are setting up at the same telescope, with a special emphasis on the optimization of the excitation process, which definitely has to rely on the two-photon excitation of sodium atoms in the mesosphere. We will describe the implementation at the telescope, including the projector device, the focal instrumentation and the NdYAG pumped dye lasers.

Resume. The correction of the tilt for adaptive optics devices from the only laser guide star can be done with the polychromatic laser guide star. We report the progress of the first demonstrator of the implementation of this concept, at Observatoire de Haute-Provence. We review the last steps of the feasibility studies, the optimization of the laser parameters, and the studies of the implementation at the OHP 1.52m telescope, including the beam propagation to the lasers room to the mesosphere and the algorithms for tip-tilt measurements.

The camera described in this paper has been specifically designed for the TAROT-1 project [1] (in this paper we describe the main parameters of the TAROT camera, its design and current status). The primary objective of the “Télescope à Action Rapide pour les Objets Transitoires” (Rapid Action Telescope for Transient Objects — hereafter TAROT) is the search for cosmic Gamma-Ray Burst (GRB) optical prompt counterparts. As this was demonstrated in the case of GRB 990123 [2], optical emission may be emitted both during the GRB itself, and as a delayed, decaying afterglow. TAROT-1 is a 25-cm, 2×2 deg. Field of view, fully automated telescope, able to point to any location in the sky and start exposure in less than 3 seconds (typically 1-2 sec). The main technical parameters of TAROT are summarised in table 1, while figure 1 displays a diagram of the present commercial camera from Apogee Corp., based on the Kodak KAF 1300 CCD chip. Additional scientific objectives of TAROT-1 are the detection of exoplanets using the transit method; the detection of relatively close supernovae; the follow-up of high-energy transient sources, and more generally the study of variable and transient sources; GRB source positions are sent to TAROT via the GRB co-ordinate network [3]. This software system sends timely positions to the observers, using a socket connection in the case of TAROT. The positions of interest originate from the CGRO/BATSE and as of January 2000 from the HETE-II experiments. The time elapsed from the beginning of the burst to the reception of the GRB source co-ordinates is about 5 seconds for both satellites.