Pushing for Strong Duty Factors

LIGO's interferometers now display the benefits of recent performance improvements. The frequency spectrum shown below (click to enlarge) contains a snapshot of the current noise floor for the L1 and H1 interferometers. Note that both axes are marked in logarithmic scales. At frequences above several dozen cycles per second the H1 and L1 curves rest atop the solid curve, LIGO's design sensitivity.

Extraordinary control of the interferometers is required to maintain this level of sensitivity hour after hour and day after day. LIGO personnel continue to give careful attention to duty factor (or duty cycle), a statistic that reports the percentage of available time that the interferometers are locked and acquiring data. The image below (click to enlarge), taken from the LIGO Hanford electronic log, shows instrument performance from 8:00 PM PST on June 28 to 8:00 AM on June 29. The lower left panel, the state vector value, shows the operating states of H1 (red), L1 (green) and H2 (blue). A state vector value of 4 indicates data acquisition at high sensitivity. When the state vector is at 4, computer codes deliver a sensing range estimate (upper right) for a neutron star inspiral (astrophysical event). The vertical axis on the range plot is marked in MegaParsecs. 1 MPc is the equivalent of 3.26 million light years. The upper left panel displays frequency-banded outputs from several LHO seismometer channels. Seismic behavior shapes the interferometers' noise profiles at low frequencies. Finally, the lower right panel shows the strength of calibration signals that run continuously in the detectors. Duty factors over the twelve-hour period shown here are very good, with only one lock loss of appreciable length on one interferometer.