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: Interferometer Sensing and Controls

This subsystem comprises the length sensing and control, the alignment sensing and control, and the overall controls coordination for the Advanced LIGO interferometer design. The most significant differences in the Advanced LIGO subsystem are the addition of the signal recycling mirror and the resulting requirements on its controls, the addition of an output mode cleaner in the output port, the implementation of homodyne, or DC, readout of the gravitational wave channel, and the use of stable optical cavities for the power and signal recycling cavities. In addition, a pre-lock length stabilization system is implemented to render the locking process faster and more predictable.

In Advanced LIGO, all of the detection will be performed in vacuum with photodetectors and auxiliary optics mounted on seismic isolation systems. This will avoid the influence of air currents and dust on the beam, and minimize the motion of the beam with respect to the photodiode. Alignment sensing and control (ASC) will be accomplished by wavefront sensing techniques similar to those employed in initial LIGO. ASC will play an important role in managing the potential instability in angle brought about by photon pressure if exerted away from the center of mass of the optic. The greater demands placed by optical powers and sensitivity are complemented by the improved seismic isolation in Advanced LIGO, leading to similar demands on the control loop gains. In general, the active isolation system and the multiple actuation points for the suspension provide an opportunity to optimize actuator authority in a way not possible with initial LIGO.

      Mode cleaner control screen

    Small ALS beam on laser table

Tip-tilt assembly and testing

      LLO DRMI 30-second lock

    Reflection and transmission from output mode cleaner

Locking the output mode cleaner

      HAM 1 controls breadboard

    RF wavefront sensors

Wavefront sensor quadrant photodiodes

      First Michelson lock at LLO

    HAM 6 payload

HAM 1 tip-tilt

      Output mode cleaner

    Output mode cleaner test bench

Output mode cleaner suspension

      Quad and transmission monitor

    ISC breadboard in HAM

ISC breadboard

      Quad demodulator chassis

    Quad photodiode with whitening preamp

Quad controls

Additional Controls Photos

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