Laser Guide Stars

A laser guide star is beamed out the open dome of Lick Observatory atop Mt. Hamilton, east of San Jose, Ca., in the first ever test of a laser guide star combined with adaptive optics on a large astronomical telescope.  The laser reflects off the sodium layer in the upper atmosphere, at an altitude of 60 miles, thus creating a manmade guide star.   The star serves as a focal point for a computer-driven membrane-thin mirror with 127 individual actuators glued to the back of it - tiny plungers that can adjust minute portions of the mirror 50-100 times per second to counteract the effects of atmospheric turbulence.  In so doing, the system combines Hubble Space Telescope-like clarity with the power of large land-based telescopes to give astronomers their best view yet of the cosmos.

Credit: Bryan Quintard, Lawrence Livermore National Laboratory

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