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UBC Theses and Dissertations

Measuring the return flux from laser guide stars Gagné, Ronald C


For future extremely-large telescopes (ELT), operation at or near diffraction limited resolutions will be the norm, rather than the exception. Thus, adaptive optics systems and laser guide star facilities will be a critical component of the ELTs. The UBC Large Zenith Telescope (LZT) has conducted lidar observations to monitor the vertical distribution of sodium atoms with the goal of understanding both the abundance and evolution of sodium in the mesosphere to aid in both AO and laser guide star (LGS) return flux simulations. Access to the LZT's high resolution lidar experiment has lead to a joint collaboration between UBC, Thirty Meter Telescope (TMT), and the Technical Institute of Physics and Chemistry of the Chinese Academy of Sciences (TIPC), to conduct upgrades of at the LZT site for sodium laser characterization tests, specifically TIPC's prototype pulsed sodium laser. The additional facilities and instrumentation at the LZT site include: 1) a new building to be used as a laser room to house visiting groups' lasers, corresponding control equipment and power systems, 2) optical equipment (scanning Fabry-Pérot interferometer, fast photodiode sensor, and miscellaneous optical filters) to measure the characteristics of the laser spectral format and pulse-shapes of pulsed lasers, and finally, 3) the site is now capable of directly imaging both natural stars and the LGS sodium spot with a 30 cm Ritchey-Chrétien equipped with a SBIG CCD camera to help determine the e ciency of LGS lasers. This document describes the new ancillary equipment for sodium laser characterization tests as well as a successful campaign conducted in the summer of 2012 on the UBC lidar laser. The summer campaign measured the laser pulse profile and spectral profile as well as LGS sodium spot measurements. The combined measurements which subsequently lead to an estimated sodium column density ranging from 5.1 × 10¹³ atoms/m² to 1.1 × 10¹³ − 1.5 × 10¹³ atoms/m² depending on the number of laser spectral modes used in the model.

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