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LIGO Livingston Observatory News
Four Kilometers of Light Experience Recombination in Livingston
Latest Construction News
In December, the staff here at the LIGO Livingston Observatory
achieved lock of the short Michelson interferometer
in the corner station. In January, this success was quickly followed by
the finding of the laser beam traveling down the Beam Tubes and hitting each of the suspension structures in the End Stations
right on target. Since then there has been a flurry of coordinated
activity on at least half a dozen fronts to bring the separate
subsystems of the interferometer close to a "state of beautiful
harmony."
Early in April, these efforts paid off in the first lock of a 4Km, optically recombined Fabry-Perot, Michelson interferometer.
At left: View along the four-kilometer Livingston Beam Tube
In this configuration, the infrared light from the Pre-stabilized
Laser passes through the Input Optics, growing to a three-inch
diameter before it hits the main interferometer. One-thirtieth of
that light is passed through a slightly cocked suspended optic.
It then hits the Beamsplitter (shown at right) which lets half of the light continue
west towards the X-Arm, and sends the other half south towards the
Y-Arm. Each of these "arms" consists of a slightly (three percent)
transmitting mirror in the corner station and a highly reflecting
mirror four-kilometer (or two and a half miles!) away in the end
stations.
Shown at right: Close-up of the Beamsplitter.
If all goes well, the light bounces up and down the "arm" a couple hundred times, constructively interfering with the fresh laser light still coming out of the laser. This keeps building up and up until, like a rain gutter in a storm, it levels off and spills out as much through the corner station mirror as it gets coming in from that direction. For such an unlikely set of events to actually occur, the distance between these 11-kg cylinders of glass, which are suspended by a single loop of steel guitar string (high E), has to be held constant to within less than a nanometer (close to one-hundred millionth of an inch). Plus, the beams spilling out of the X- and Y-arms must interfere in such a way as to constructively add up in the direction pointing back at the laser and just exactly cancel out at the appropriately named dark port, which is on the north side of the Beamsplitter.
Since its first lock, the interferometer has gone from locking for tens of seconds to tens of minutes. We are currently attacking it on several fronts to extend this duration into the "few hours" regime. Unfortunately, due mainly to the violent ground quaking induced by the construction activity for the new building, we are forced to lie in wait (sort of like our friend in the photo below) until around 7 PM, when we can continue this exciting work. The next step is to add in the power-recycling mirror, this being the last dancer in the choreography of the Livingston interferometer. But more on that in these pages soon!
Construction of the new building here at the Livingston Observatory is proceeding pretty much as planned. The steel columns for the addition are in place, and work is underway to construct the roof (shown at left, below). The weather has been exceptionally dry, and this has helped immensely in maintaining the construction on schedule.
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Above: At left, roof construction. Right, frame installation.
The fitting out of the storage building is progressing well also. The columns to support the second floor are in place. The opening for the roll-up door, which will provide access to the high bay area from the receiving bay, has been cut and the frame installed (shown above, at right.) The slanted floor for the auditorium seating can be seen in the foreground.