The concept of making a laser guided adaptive optics telescope was first published in the open literature in late 1985 (R. Foy and A. Labeyrie, Astronomy & Astrophysics, vol. 152, pg. L29, November 1985), and by the time the journal reached the University of Hawaii it was already early in 1986. Immediately upon seeing this paper, I decided to begin experimental work with laser guide stars. First I identified who might have a laser that could be tuned to the 589 nm sodium resonance line. This turned out to be any group doing LIDAR work. Then I began to telephone potential collaborators. One LIDAR group stood out above the rest, a group headed by Prof. Chester Gardner in the Department of Electrical and Computer Engineering at the University of Illinois Urbana-Champaign. Gardner's group was well-suited for this work because (1) they had an excellent reputation, (2) they had a working 589 nm sodium wavelength laser that could make the sodium laser guide star, and (3) they were accustomed to mounting campaigns at remote sites.
After a visit to Champaign-Urbana in the spring of 1986 to cement the collaboration, I applied for telescope time through normal channels at the University of Hawaii's Institute for Astronomy to conduct the first laser guide star test. The project was scheduled for early January, 1987. Three people came to Hawaii from central Illinois for this work: Prof. Chester Gardner and two graduate students, Dan Senft and Kevin Kwon. The aim of the experiment was to make images of the sodium return signal. Astronomers had to begin the process of learning how to make images of real laser return signals. (The LIDAR community was accustomed to projecting and detecting the sodium laser beam, but they made little attempt to produce a concentrated beam -- one that would look like a star -- and they only detected the signal photometrically with time-gated single-channel detectors, rather than imaging the return laser guide star signal.)
For this experiment the plan involved installing the University of Illinois' sodium
laser in the dome of a small 0.6-m telescope located adjacent to the larger
University of Hawaii 2.2-m telescope. The laser would be projected into the sky
through the small telescope and then images would be recorded with the 2.2-m telescope.
The view of the illuminated sodium layer from the 2.2-m telescope would be a
narrow line because the beam was being transmitted from the 0.6-m telescope located
approximately 50 meters away. The
two telescopes are shown below as they looked during the January 1987 observing
run. The 2.2-m telescope (on the left) has the 500x500 CCD camera mounted at
the Cassegrain focus. One corner of the sodium laser system can be seen in the
lower right corner of the 0.6-m telescope picture.
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The picture below is an outside shot showing the two telescope domes. The small dome
on the right housed the 0.6-m telescope and the large dome to the left houses the
2.2-m telescope. January snow can be seen on the ground.
The 0.6-m telescope is no longer on Mauna Kea. It was removed in the 1990's
to make way for the construction of the Gemini North 8.2-m telescope. The
Gemini North telescope has an ambitious plan to install a
sodium laser guide star system for multi-conjugate adaptive optics work, particularly
appropriate because their telescope occupies the site of the first sodium laser
guide star experiment on Mauna Kea. The nearby Keck 10-m Telescope also has
a program underway to create a sodium laser guided system.
The image below shows one of several long integrations taken on the night of
January 21, 1987 with the 500x500 CCD camera. As expected, the image of the
sodium layer shows a narrow central bright line of emission where the laser
beam sliced through the 8 km to 10 km thick layer of sodium
that is suspended some 95 km above the surface of the Earth. The width of the bright
narrow line (at the center of the oval extended light distribution) shows
the approximate diameter this laser guide star would have if it had been
viewed as an end-on pencil. This processed image was produced from the
original data and analyzed by yet another University of Illinois graduate student, Byron
Welsh.
The work described here was published in the journal Nature (L. Thompson and C. Gardner 1987 Nature vol. 328, pg. 229 Experiments on laser Guide Stars at Mauna Kea Observatory for Adaptive Optics in Astronomy). This paper in Nature caused quite a stir in the U.S. Military adaptive optics community which, as it turned out, had conducted several similar experiments of its own prior to 1987 to test the laser guide star concept. These experiments had been classified as Top Secret. The Thompson and Gardner experimental work -- plus engineering design calculations by Thompson, Gardner, and Gardner's students showing the feasibility of building laser guided systems -- considerably accelerated the process of getting the very extensive but secret work of the U.S. Military declassified. The military work was made public 4 years and 4 months after the Mauna Kea sodium laser guide star experiment described here.