GeMS Laser and the
September Earthquake
The large earthquake that hit Cerro Pachón
in September 2015 put the complex GeMS
“sodium” laser totally out of alignment; the
quake also caused us to lose the first of three
GeMS runs scheduled in Semester 2015B.
Figure 3.
Gemini staff operating
Gemini North from Hilo.
outside the building to monitor sky conditions, precipitation, and summit-level fog
(Figures 1 and 2). Software enhancements
ensure that the dome will close automatically should the network link from Hilo go
down while the dome is open, and we then
encounter precipitation. In November, we
started trial operations from the base (Figure 3), with the help of members of the day
crew who stayed late in case of problems at
startup. After a month of trials, which resulted in a lot of useful feedback, we were ready
to “fly solo.”
From here on, if you come observing at
Gemini North (e.g., for a Classical or Priority Visitor run), you can expect more air to
breathe than you would have if observing at
the summit.
We’re now working on the plan to repeat this
operation at Gemini South. In the interests
of efficiency, we’ll “copy and paste” as much
as possible from what we did in the north.
However, as this remains one of the single
biggest projects ever undertaken at Gemini South, we don’t expect to relocate to its
base facility in La Serena until late in 2016.
See the article on Base Facility Operations in
the October 2015, and Year in Review issues
of GeminiFocus.
14
GeminiFocus
The GeMS laser works by generating two infrared laser beams at different wavelengths,
mixing and amplifying these in a nonlinear
crystal, and producing a signal at the sum
of the two input frequencies. The resulting
beam is then directed into beam-transfer
optics for launch onto the sky. There are
many delicate, micron-scale adjustments in
this system, and a magnitude 8.4 earthquake
within 100 kilometers of the telescope site
was more than sufficient to take the laser’s
alignment back to “square one.”
To fix the laser, we essentially had to start
from scratch. We adopted a systematic approach, implementing some enhancements
that will make for much quicker recovery,
especially should we suffer a recurrence
(which we all, of course, hope we will not).
By late November it became clear that we
would lose the second GeMS run; now we’re
certain that we will not be operating GeMS
in January either. We’re now focusing on
protecting the February run. Hopefully a
final concerted push will get us back to 30
Watts of light at the sodium wavelength
with the steady performance that had been
achieved before the earthquake.
Mirror Coatings North
and South
As reported in the previous issue of GeminiFocus, both Gemini telescopes were shut
down for maintenance in September and
October (North and South, respectively).
Both shutdowns involved mirror coating
— the secondary at Gemini North, and the
January 2016