In situ measurement of absorption in high-power interferometers by using beam diameter measurements

We present a simple technique to make in situ measurements of the absorption in the optics of high-power laser interferometers. The measurement is particularly useful to those commissioning large-scale high power optical systems

Implementation of barycentric resampling for continuous wave searches in gravitational wave data

We describe an efficient implementation of a coherent statistic for continuous gravitational wave searches from neutron stars. The algorithm works by transforming the data taken by a gravitational wave detector from a moving Earth bound frame to one that sits at the Solar System barycenter. Many practical difficulties arise in the implementation of this algorithm, some of which have not been discussed previously. These difficulties include constraints of small computer memory, discreteness of the data, losses due to interpolation and gaps in real data. This implementation is considerably more efficient than previous implementations of these kinds of searches on Laser Interferometer Gravitational Wave (LIGO) detector data.Comment: 10 pages, 3 figure

Analysis of spatial mode sensitivity of gravitational wave interferometer and targeted search for gravitational radiation from the Crab pulsar

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Physics, February 2008.Includes bibliographical references (p. 167-171).Over the last several years the Laser Interferometer Gravitational Wave Observatory (LIGO) has been making steady progress in improving the sensitivities of its three interferometers, two in Hanford, Washington, and one in Livingston, Louisiana. These interferometers have reached their target design sensitivities and have since been collecting data in their fifth science run for well over a year. On the way to increasing the sensitivities of the interferometers, difficulties with increasing the input laser power, due to unexpectedly high optical absorption, required the installation of a thermal compensation system. We describe a frequency resolving wavefront sensor, called the phase camera, which was used on the interferometer to examine the heating effects and corrections of the thermal compensation system. The phase camera was also used to help understand an output mode cleaner which was temporarily installed on the Hanford 4 km interferometer. Data from the operational detectors was used to carry out two continuous gravitational wave searches directed at isolated neutron stars. The first, targeted RX J1856.5-3754, now known to be outside the LIGO detection band, was used as a test of a new multi interferometer search code, and compared it to a well tested single interferometer search code and data analysis pipeline. The second search is a targeted search directed at the Crab pulsar, over a physically motivated parameter space, to complement existing narrow time domain searches. The parameter space was chosen based on computational constraints, expected final sensitivity, and possible frequency differences due to free precession and a simple two component model.(cont.) An upper limit on the strain of gravitational radiation from the Crab pulsar of 1.6 x 10-24 was found with 95% confidence over a frequency band of 6 x 10-3 Hz centered on twice the Crab pulsar's electromagnetic pulse frequency of 29.78 Hz. At the edges of the parameter space, this search is approximately 105 times more sensitive than the time domain searches. This is a preliminary result, presently under review by the LIGO Scientific Collaboration.by Joseph Betzwieser.Ph.D

advligorts: The Advanced LIGO Real-Time Digital Control and Data Acquisition System

The Advanced LIGO detectors are sophisticated opto-mechanical devices. At the core of their operation is feedback control. The Advanced LIGO project developed a custom digital control and data acquisition system to handle the unique needs of this new breed of astronomical detector. The advligorts is the software component of this system. This highly modular and extensible system has enabled the unprecedented performance of the LIGO instruments, and has been a vital component in the direct detection of gravitational waves

advligorts: The Advanced LIGO real-time digital control and data acquisition system

The Advanced LIGO detectors are sophisticated opto-mechanical devices. At the core of their operation is feedback control. The Advanced LIGO project developed a custom digital control and data acquisition system to handle the unique needs of this new breed of astronomical detector. The advligortsis the software component of this system. This highly modular and extensible system has enabled the unprecedented performance of the LIGO instruments, and has been a vital component in the direct detection of gravitational waves

Multi-color Cavity Metrology

Long baseline laser interferometers used for gravitational wave detection have proven to be very complicated to control. In order to have sufficient sensitivity to astrophysical gravitational waves, a set of multiple coupled optical cavities comprising the interferometer must be brought into resonance with the laser field. A set of multi-input, multi-output servos then lock these cavities into place via feedback control. This procedure, known as lock acquisition, has proven to be a vexing problem and has reduced greatly the reliability and duty factor of the past generation of laser interferometers. In this article, we describe a technique for bringing the interferometer from an uncontrolled state into resonance by using harmonically related external fields to provide a deterministic hierarchical control. This technique reduces the effect of the external seismic disturbances by four orders of magnitude and promises to greatly enhance the stability and reliability of the current generation of gravitational wave detector. The possibility for using multi-color techniques to overcome current quantum and thermal noise limits is also discussed

Improving the Robustness of the Advanced LIGO Detectors to Earthquakes

Teleseismic, or distant, earthquakes regularly disrupt the operation of ground–based gravitational wave detectors such as Advanced LIGO. Here, we present EQ mode, a new global control scheme, consisting of an automated sequence of optimized control filters that reduces and coordinates the motion of the seismic isolation platforms during earthquakes. This, in turn, suppresses the differential motion of the interferometer arms with respect to one another, resulting in a reduction of DARM signal at frequencies below 100 mHz. Our method greatly improved the interferometers\u27 capability to remain operational during earthquakes, with ground velocities up to 3.9 μm s−1 rms in the beam direction, setting a new record for both detectors. This sets a milestone in seismic controls of the Advanced LIGO detectors\u27 ability to manage high ground motion induced by earthquakes, opening a path for further robust operation in other extreme environmental conditions

First Demonstration of Electrostatic Damping of Parametric Instability at Advanced LIGO

Interferometric gravitational wave detectors operate with high optical power in their arms in order to achieve high shot-noise limited strain sensitivity. A significant limitation to increasing the optical power is the phenomenon of three-mode parametric instabilities, in which the laser field in the arm cavities is scattered into higher-order optical modes by acoustic modes of the cavity mirrors. The optical modes can further drive the acoustic modes via radiation pressure, potentially producing an exponential buildup. One proposed technique to stabilize parametric instability is active damping of acoustic modes. We report here the first demonstration of damping a parametrically unstable mode using active feedback forces on the cavity mirror. A 15 538 Hz mode that grew exponentially with a time constant of 182 sec was damped using electrostatic actuation, with a resulting decay time constant of 23 sec. An average control force of 0.03 nN was required to maintain the acoustic mode at its minimum amplitude