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LIGO Livingston Observatory NewsLocking the Arms at Livingston
Scouts Do Good Deed for LIGO!
Construction Starts Up Again in Livingston
This month, the LIGO Livingston Observatory achieved two new milestones in our progress toward a full and completely functional laser interferometer. We demonstrated "locking" of the 4-km long Fabry-Perot cavities that constitute each arm of the interferometer. We first locked the X-arm, the arm in line with the input laser beam, by misaligning the recycling mirror so that the beam traversed it and the beam splitter without resonating in the recycling cavity. The input test mass along the X-arm and the end test mass four kilometers away were aligned to make an optically resonant cavity. We locked the arm by pushing on either the input or end test masses to maintain the overall length of the cavity within a few hundredths of a wavelength of the laser (1.06 microns). After adjusting the alignment servo controls, we were able to see a nicely shaped beam spot coming out of the end of the arm. (A little light leaks through the end mirror by design so that we can monitor the stored light in the cavity.)
Above: The figure shows the light that is transmitted out the end mass of the X-arm of the Fabry-Perot cavity. The transmitted light level increases when the cavity is in lock and there is a lot of stored light within the cavity. Two brief stretches are visible in the figure where the light level falls to a low level, indicating that the cavity is out of lock. These are apparent at the left and right sides of the figure. The red and green traces indicate the maximum and minimum values of the transmitted light and the gray trace is the average level. We are now trying to understand the fluctuations between the minimum and maximum values observed during lock.
We repeated this procedure on the Y-arm. Using the experience gained locking the X-arm, we were able to lock the Y-arm almost immediately once we put light in the cavity. This involved an extra optic because the light reflected off the beam splitter before entering the Fabry-Perot cavity. We are now using the data obtained from locking the cavities to investigate the sources of noise in the laser, the environmental and seismic noise, and the controls which align the interferometer mirrors and condition the light.
Our next step is to recombine the two beams to form a Michelson interferometer with Fabry-Perot arms. Stay "tuned" for further developments!
Last January 27, the Livingston Parish Cub Scout Pack 80 and Boy Scout Troop 156 planted 1000 cypress seedlings on the grounds of the LIGO Livingston Observatory. Approximately 40 boys and their parents arrived at 7 am on a drizzly Saturday morning to plant the trees, and by about 10:30 am, all 1000 were planted!
This is the second year in a row that the observatory has had cypress seedlings planted, and the second time that Scout Troop 156 has planted them. Louisiana state makes the seedlings available through the state-sponsored cypress re-forestation program. Each year the program distributes over 300,000 cypress seedlings statewide to be planted as part of re-forestation and erosion control projects. Since cypress roots spread out along the surface of the earth, and "love to get their feet wet" they are excellent for erosion control. Control of the soil motion along the borrow pits paralleling the 2.5 mile long arms of the interferometer is of particular concern for us, so we found this partnering with the state forestry department and the local Boy Scout and Cub Scout organizations to be wonderfully advantageous for everyone.
The trees were planted along the west arm (the X-arm) of the interferometer starting at the mid station and working out in either direction. In about 15 years, this area should be beautiful. We plan to continue this program in the future, creating a legacy for LIGO which should be a wonderful resource in the years to come.
After a 2.5 mile hike back to the observatory corner station, the boys and their parents enjoyed hot dogs on the grill, chips, and sodas! They'll all be back for an evening tour of LIGO later this spring.
During the early construction phase of LIGO, the sizes of the buildings were reduced to conserve funds. The savings were kept in the project's contingency fund to help deal with risks. Now that detector construction is nearly complete, we are more confident that we can restore some of the building space and features, and apply our latest understanding of how we use our observatory site. So we are adding space and functions to our storage facility.
The refurbished storage building, when combined with the new addition, will function as an integrated on-site facility designed to assemble, test and accept advanced instruments and equipment required for an enhanced LIGO Observatory. It will provide the space to house the receiving, shipping and inspection functions, as well as a future laboratory, an office expansion, a machine shop and a storage area. It also includes an auditorium with an entry lobby and display area that can incorporate the possibility of an adjacent future outreach center.
The photo at left shows the location where this new construction is taking place. The new addition will be erected to the left of the storage building and house the 40 foot by 80 foot high-bay area (the same size as the end-station high-bays).
Then, the photo at right is a view from inside the storage building. It shows the "pit" and "stage" for the new auditorium. It's hard to believe, but this is where the presentations and festivities of the LIGO inauguration were held.