title: Photometric observations of a polychromatic laser guide star.
abstract: We report the photometric observation of a polychromatic laser guide star (PLGS) using the AVLIS laser at the Lawrence Livermore National Laboratory (LLNL). The process aims at providing a measurement of the tilt of the incoming wave front at a telescope induced by atmospheric turbulence. It relies on the two-photon coherent excitation of the 4D5/2 energy level of sodium atoms in the mesosphere. We used two laser beams at 589 and 569 nm, with a maximum total average output power of approximately 350 W. For the purpose of photometric calibration, a natural star was observed simultaneously through the same instrument as the PLGS at the focus of the LLNL 50-cm telescope. Photometric measurements of the 330-nm return flux confirm our previous theoretical studies that the PLGS process should allow us at a later stage to correct for the tilt at wavelengths as short as approximately 1 microm at good astronomical sites. They show also that, at saturation of two-photon coherent absorption in the mesosphere, the backscattered flux increases by a factor of approximately 2 when the pulse repetition rate decreases by a factor of 3 at constant average power. This unexpected behavior is briefly discussed.
authors.affiliation: Centre de Recherche Astronomique de Lyon/Observatoire de Lyon, France. foy@obs.univ-lyon1.fr
authors.forename: R
authors.initials: R
authors.lastname: Foy
authors.forename: M
authors.initials: M
authors.lastname: Tallon
authors.forename: I
authors.initials: I
authors.lastname: Tallon-Bosc
authors.forename: E
authors.initials: E
authors.lastname: Thiébaut
authors.forename: J
authors.initials: J
authors.lastname: Vaillant
authors.forename: F C
authors.initials: FC
authors.lastname: Foy
authors.forename: D
authors.initials: D
authors.lastname: Robert
authors.forename: H
authors.initials: H
authors.lastname: Friedman
authors.forename: F
authors.initials: F
authors.lastname: Biraben
authors.forename: G
authors.initials: G
authors.lastname: Grynberg
authors.forename: J P
authors.initials: JP
authors.lastname: Gex
authors.forename: A
authors.initials: A
authors.lastname: Mens
authors.forename: A
authors.initials: A
authors.lastname: Migus
authors.forename: J M
authors.initials: JM
authors.lastname: Weulersse
authors.forename: D J
authors.initials: DJ
authors.lastname: Butler