Advanced LIGO subsystems
are the organizational units of the overall project. Follow the links below to view the mission and progress of each subsystem.

Auxiliary Optics Core Optics
Data Acquisition Data and
Input Optics

Advanced LIGO News

Arm Length Stabilization Takes Shape

[psl_als]Arm length stabilization (ALS) refers to the LIGO detector subsytem that will bring the long detector arms to a controlled and quiet state, ready to integrate into a fully controlled interferometer in which the light resonates in all parts. New for Advanced LIGO, ALS has required extensive installation at the Livingston and Hanford sites. These installation activities are nearing completion at Hanford and will continue at Livingston into 2014 as LLO completes work at the detector end stations. The key parts of ALS include 1) An out-of-vacuum table at each end station on which a green laser will inject light into the vacuum; 2) An in-vacuum transmission monitor suspension at each end station that routes the green light through the neighboring end test mass (mirror - ETM) and toward the inner test mass (ITM) 4km away; 3) a set of optics in HAM 1, the vacuum chamber in the corner station that's next to the main laser enclosure, that will reflect each arriving long-arm green beam through a viewport and out of the vacuum onto (4) an optical table adjacent to HAM 1 that receives and processes the green beams from each arm; 5) Hardware on the main laser table (photo above) that directs a small portion of the main laser beam into HAM 1 where it's changed to green and compared to the green light from the arms, and 6) Equipment that directs another portion of the main beam into a pair of 4km optical fibers where it travels to each end station and serves to synchronize the green beam that was mentioned in (1).

[transmon]The in-vacuum ALS transmission monitor (shown on a test stand in the adjacent photo) fastens to the underside of the large-chamber vibration isolation platforms (ISI's) in the same manner as the nearby end test mass large optic suspensions -- a single ISI bears the load of both units. HAM 1's tip-tilt mirrors and other optical components don't require a level of vibration isolation that necessitates an ISI; their isolation specifications are a bit more relaxed. LIGO then chooses to deploy Initial LIGO passive vibration isolation stacks in HAM 1 of each detector (photo below right). HAM 1 represents the only re-use of HAM passive stacks in Advanced LIGO.

[passive stack]ALS exists to facilitate rapid and reliable locking of the advanced detectors. Once locked, the interferometers won't use the out-of-vacuum ALS photodiode signals. Better-isolated in-vacuum sensors will take over and provide the angle-sensing and length-sensing control signals needed to maintain the resonating detector on its high-sensitivity operating point.

      Cleaning a viewport on HAM 1

[HAM 1]
    HAM 1 optical table

  Beam diverters awaiting optics


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