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

Subsystem: Seismic Isolation

The seismic isolation subsystem consists of Internal Seismic Isolation (ISI) and Hydraulic External Pre-Isolators (HEPI). Seismic isolation serves to attenuate ground motion transmitted to the instrument both in the control band (frequencies below 10 Hz) and in the observation band (above 10 Hz). It also provides the capability to align and position optical payloads in the vacuum chambers. Significantly improved seismic isolation will be required for Advanced LIGO to realize the benefit from the reduction in thermal noise due to improvements in the suspension system. The Initial LIGO isolation system will undergo complete replacement (except for HEPI at LIGO Livingston, which was fast-tracked for Initial LIGO deployment). The comprehensive scale of the seismic isolation upgrade offers the opportunity to make a coordinated design to enhance both the isolation and controls aspects of the interferometer.

The root mean square (RMS) differential motion of the test masses while the interferometer is locked must be held to a small value (less than 10-14 m) for many reasons: to limit light fluctuations at the antisymmetric port and to limit cross coupling from laser noise sources, as examples. Similarly, the RMS velocity of the test mass must be small enough and the test mass control robust enough that the interferometer can acquire lock. This establishes the requirement on the design of the seismic isolation system in the frequency band from 1 to 10 Hz of approximately 10-11 m per rt Hz, and a reduction in the microseism band to several tenths of a micron per rt hertz.

      HAM ISI riser installation

    Livingston HAM 5

  Livingston BSC 1 ISI under wraps

      ISI test, high and low gain

    Livingston BSC 3 cartridge in the air

  Output Faraday isolator on a HAM ISI

      Counterweights in HAM 3

    Internal seismic isolation actuator

  HEPI installation on a BSC

      BSC ISI installation preparation

    HAM ISI installation

  HAM ISI installation

      HAM ISI Assembly at LLO

    Testing an ISI In-vacuum Sensor

  Installation of a HEPI Assembly

Additional Seismic Photos

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