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|
Advanced LIGO News
Stray Light Controls will Enhance Detector Sensitivity
A gravitational wave interferometer contains numerous pieces of hardware that support the leading roles played by the main laser, vibration isolation, core optics and light sensors. Stray light controls (SLC) inside the vacuum constitute a key interferometer support system. SLC baffles come in different styles, but all provide a metal surface to block the passage of stray light and holes in the surface to allow the passage of intended light. Although the baffles lack the complexity of many other aLIGO components, their sizes and their locations in the vacuum create significant installation challenges.
The input path (laser to power-recycling optics), output path (beam splitter to detector output) and each long arm of a LIGO detector will contain one or more baffles. The input and output baffles are disks with either a single hole or several holes, depending on the number and positions of beams that must transit them. Installation of the baffle shown in the top photo requires the retraction of flexible beam tube bellows near a seam that joins a tube section to a vacuum chamber. After removing bolts at the seam, retraction of the bellows will open the seam, allowing the baffle to slip into the tube. Installation teams must preserve the clean state of the baffle during insertion, and must re-seal the vacuum to its previous integrity. Baffles for the long arms, known as arm cavity baffles (ACB's, left photo), don't fasten directly to the vacuum infrastructure. ACB's couple to the undersides (optical tables) of the vibration isolation platforms in LIGO's large vacuum chambers, adjacent to the mirror suspensions that hold the long-arm cavity optics. In one instance, a team hand-carried the large box-like ACB through roughly 20 meters of beam tube to reach the destination chamber near the beam splitter. ACB's contain a set of photodiodes, signals from which will assist with beam alignment and the locking of the long arms of a detector.
Stray light in a detector can act as a noise source for LIGO if not thoroughly supressed. Small amounts of stray light arise from scattering inside the vacuum. The purity of mirror substrates and coatings, the exclusion of particulates from the vacuum interior and the careful control of the laser beam profile and its dispersion serve to minimize the percentage of scattered light. As LIGO moves toward significantly higher input laser power in the advanced detectors, however, the amount of scattered light will increase. Stray light controls must ensure that this light can't propogate through the detector to disturb the beams that interact with sensing photodiodes.
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