Advanced LIGO subsystems
are the organizational units of the overall project. Follow the links below to view the mission and progress of each subsystem.

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Input Optics

Advanced LIGO News

Commissioning Update from Livingston

Now that LIGO has completed construction of the advanced L1 interferometer at LIGO's Livingston, Louisiana facility and has brought the detector to first lock, groups of commissioners are taking charge of the instrument to improve its sensitivity and stability. This commissioning path will continue into 2015 as the project moves toward the first data run of the advanced era.

Advanced LIGO observers will recall that installation of the full L1 Advanced LIGO interferometer reached completion in March 2014. As evacuation of the vacuum system continued through March, crews became able to operate increasingly larger subsets of the detector. This testing proceeded with remarkable rapidity, leading to "locking" or complete control over the lengths of the 4km instrument by end May 2014. LIGO's integrated testing -- bringing more and more of the complete system together and understanding and resolving problems of interactions between the various subsystems -- has generated significant improvements both in detector stability and in noise performance. The longest full interferometer lock to date has approached three hours; LIGO's measure of success for this part of the project was two hours. We are delighted with this performance. Additionally, commissioners have successfully enabled the strain readout which will eventually indicate the time-trace of the gravitational wave signal. If LIGO were to perform a data run with L1 now, the detector could acquire neutron star binary inspiral signals to a distance of more than 20 Mpc. This recent progress now makes the Livingtson instrument a more sensitive detector than initial or enhanced LIGO, and the most sensitive gravitational wave detector ever put into operation. The figure below shows commissioning progress over the few months of integrated testing on a plot of instrument sensitivity versus frequency.

[July progress]

Figure 1: The L1 DARM displacement spectrum from end July 2014 (click for a larger view). For comparison, the DARM spectrum from Enhanced LIGO (S6) is also shown. The recent curve was taken with 2W of input power, while the S6 curve had 14W of input power. The high frequency noises are similar despite this power difference, due to the change in detector frequency response between Initial and Advanced LIGO: the cavity pole has moved from 80 Hz up to 400 Hz. At 1 kHz and above the aLIGO curve shows some features of the digital down-sampling filter (the ripple and roll-off), and at all frequencies this calibration is preliminary. The inset box shows L1's reach for a 1.4-solar-mass inspiral. aLIGO at full sensitivity will reach ~180 Mpc, a range that will require about a factor of 10 improvement over current performance at high frequencies and about a factor of 1000 at low frequencies. There is work to do!

Based on this progress, the Advanced LIGO Project can declare success on L1 by meeting the two-hour requirement for full lock with control of all length degrees-of-freedom and an operational strain readout. This represents a huge step forward as LIGO moves from the construction project on L1 to the operations commissioning phase, in which the greater LIGO Scientific Collaboration (LSC) can enter the fray to help bring the instrument to readiness for a first observing run in 2015. Work will continue across all frequencies shown in the plot above to further lower the noise spectrum. In the high-frequency regime, more light power in the detector will yield better quantum noise limited performance. At low frequencies personnel will focus on control loop refinement and the chasing of electronics noise sources. At all frequencies LIGO will uncover and remove couplings to mechanical and acoustical excitations. The LSC detector characterization group is profiling the noise statistics of the data stream, performing studies of narrow-band line features in the spectrum, and helping to identify coupling paths that require attention.


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