The Mirror That Makes History

Balancing Act

More than a year after detecting the first confirmed gravitational waves, researchers were busy at the Laser Interferometer Gravitational-wave Observatory (LIGO) in Livingston, La., upgrading the massive instrument. Building on lessons learned during that historic first run, they expect the improved detector will find more gravitational waves during the second observing run, which began Nov. 30.
LIGO detects gravitational waves by splitting a powerful infrared laser beam in two, then sending the beams at right angles through tunnels to mirrors 2.5 miles away. The beams are recombined upon return. A gravitational wave will warp space and briefly change the relative distance between the mirrors and photo detector situated near the LIGO control room. The difference is astonishingly small, just 1/10,000 of a proton’s diameter, but it can be detected if the mirrors are isolated from all external sources of vibration.

Discover photo editor Ernie Mastroianni visited the facility in November as physicists and engineers were calibrating equipment.

Super Vacuum

Massive stainless steel tubes, vacuum equipment, and seismic isolation gear are prepared for installation at the corner station of the Laser Interferometer Gravitational-wave Observatory (LIGO) detector in Hanford, Washington. The facility is a near twin of the Livingston detector.

To insure the beam’s integrity, the laser travels through sealed stainless steel tubes, 1.2 meters wide, that hold a vacuum to just one trillionth of earth’s atmosphere, eight times less than open space. This vacuum, says LIGO spokesman William Katzman, has been maintained since 1999. It is the largest sustained ultra-high vacuum in the world and is necessary to prevent any air currents from deflecting the laser’s path.

Mirror, Mirror

Inside a stainless steel chamber, LIGO technicians examine the surface of one of the test mass mirrors that will reflect infrared laser light to measure the effect of gravity waves. After installation, all air was vacuumed from this chamber.

In the Control Room

Astrophysicist Stuart Aston monitors external vibrations on the LIGO test mass mirrors during an engineering run in November 2016. Aston's job is to keep optical components isolated from external vibration, and he was not happy as he scanned the data from LIGO’s control room.

“The multi-stage suspensions provide incredible levels of isolation from ground motion,” said Aston, but it wasn’t happening on this day. Less than a half-mile away, a logging crew was plowing a path through the forest, creating massive ground vibrations and swamping the gear that normally nullifies the noise.

Aston was soon driving the 2.5-mile distance to the detector’s far end to fix the glitch.

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