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 Computing Systems
Facilities Modifications	Input Optics
Interferometer Control	Pre-Stabilized Laser
Seismic Isolation	Suspensions

Advanced LIGO News

One-Arm Test Yields Encouraging Results

November 2012

LIGO Hanford's one-arm test closed in September 2012 with its primary goals successfully completed and with a storehouse of results that will guide future installation and commissioning. The LIGO commissioning team tasked with the test obtained a substantial list of outcomes, some highlights of which included the following.

• At the outset of the test, the team launched a green laser beam into the H1 detector's vacuum system at the Y end station, through a set of transmission monitor optics (photo above), through the end test mass (mirror - ETM; photo below) and on its way to the inner test mass (ITM) four kilometers away. The landing of the beam on the ITM and, soon after, it's subsequent resonance in the 4km arm cavity verified the soundness of the optical path along the arm.
• At the close of the test commissioners were locking the arm on resonance for periods of up to twelve hours (interrupted by daytime installation activities), evidence of the first-order stability of the optics and their controls. Initial LIGO usually required months of commissioning to bring the cavities into lock for long periods.
• Vibration isolation and auxiliary systems performed satisfactorily in this initial shakedown. The hydraulic external pre-isolator (HEPI), the in-chamber internal seismic isolation (ISI) and the multi-stage optics suspensions behaved as expected. The thermal compensation system (ring heaters around the ITM and ETM) operated within its noise specifications. The optical lever angular control system met its long-term drift specification.

The one-arm test didn't exercise some of these systems to their fullest degree and plenty of additional commissioning lies ahead. The ITM and ETM hang in four-stage suspensions that provide noise cancellation at each stage (adjacent photo), but only a subset of the controls were deployed to stabilize the mirrors. The green laser light injected at the end station wasn't synchronized to the main (infrared) laser in the corner station as will be the case for future tests. Instead, a spare infrared laser and reference cavity in the corner station sent light through a 4km optical fiber to the end station, where it was converted to green. Noise on the light from the reference system and the optical fiber was visible at higher frequencies throughout the test. Seismic noise clearly manifested itself at frequencies below 1 Hz; a more complete mitigation effort will include additional feedback that becomes available when the full arm length stabilization controls enter the mix over the next year.

Hanford will next undertake a half-interferometer test on the Y arm (HIFO-Y) that will include all of the one-arm components plus the main laser, the suspended mode cleaner and the power recycling optics that lie between the laser and the beam splitter. Installation of these items is currently underway; watch for news of HIFO-Y in the summer of 2013.

aLIGO News Archive

August 2016 -- LIGO Reports O1 Results

June 2016 -- Another Black Hole Merger

Feburary 2016 -- First Gravitational Wave Detection

November 2015 -- O1 Progress Report

August 2015 -- Final Preparations for the O1 Run

February 2015 -- Hanford's H1 Achieves Two-Hour Lock

July 2014 -- Livingston Commissioning Progress

June 2014 -- Livingston Locks the L1 Interferometer

December 2013 -- Livingston Installs End Station Payloads

September 2013 -- Half-interferometer Test Closes

June 2013 -- DRMI Test at Livingston

May 2013 -- Arm Length Stabilization

November 2012 -- One-arm Test at Hanford

September 2012 -- LIGO Begins Locking Optical Cavities

August 2012 -- Installation of Stray Light Controls

July 2012 -- Small Optic Suspenions Enter L1

April 2012 -- First Cartridges Enter the Vacuum

November 2011 -- Glass Fiber Suspensions in Production

October 2011 -- Continued Suspension Development

July 2011 -- Hanford's H2 Becomes a 4K

May 2011 -- LLO Laser Installation Completed

March 2011 -- Input and Output Tubes Undergo Removal

February 2011 -- New Laser Enclosure Takes Shape

December 2010 -- Initial LIGO Comes Out of the Vacuum

October 2010 -- S6 Yields to Advanced LIGO

September 2010 -- Ear Bonding on Large Optics

May 2010 -- Monolithic Suspension Progress

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• Last modified Oct 24, 2016
• For information about LIGO, contact info(at)ligo.caltech.edu
• LIGO is supported by the National Science Foundation. Any opinions, findings, conclusions or recommendations expressed here are those of the author(s) and do not necessarily reflect the views of the National Science Foundation