G. González

Suspensions thermal noise in the LIGO gravitational wave detector

We present a calculation of the maximum sensitivity achievable by the LIGO gravitational wave detector in construction, due to limiting thermal noise of its suspensions. We present a method to calculate thermal noise that allows the prediction of the suspension thermal noise in all of its six degrees of freedom, from the energy dissipation due to the elasticity of the suspension wires. We show how this approach encompasses and explains previous ways to approximate the thermal noise limit in gravitational wave detectors. We show how this approach can be extended to more complicated suspensions to be used in future LIGO detectors.

Quantum-limited optical phase detection at the 10-10-rad level

Interferometric detection of gravitational waves at a level of astrophysical interest is expected to require measurement of optical phase differences of < or = 10(-10) rad. A fundamental limit to the phase sensing is the statistics of photon detection--Poisson statistics for light in a coherent state. We have built a laboratory-scale interferometer to achieve and investigate the phase detection sensitivity required for the Laser Interferometer Gravitational-Wave Observatory. With 70 W of circulating power, we have obtained a phase sensitivity of 1.28 x 10(-10) rad/square root(Hz) at frequencies above 600 Hz, limited by quantum noise. Below 600 Hz, excess noise above the quantum limit is seen, and we present our investigations into the sources of this excess. Compared with the results of previous such experiments, the phase sensitivity over the full 100-Hz-10-kHz band of interest has been improved by factors of up to 100, with a factor-of-2.5 improvement in the quantum-limited level.

Development of a double pendulum for gravitational wave detectors

Seismic noise will be the dominant source of noise at low frequencies for ground based gravitational wave detectors, such as LIGO now under construction. Future interferometers installed at LIGO plan to use at least a double pendulum suspension for the test masses to help filter the seismic noise. We are constructing an apparatus to use as a test bed for double pendulum design. Some of the tests we plan to conduct include: dynamic ranges of actuators, and how to split control between the intermediate mass and lower test mass; measurements of seismic transfer functions; measurements of actuator and mechanical cross couplings; and measurements of the noise from sensors and actuators. All these properties will be studied as a function of mechanical design of the double pendulum.

Toward gravitational wave detection

An overview of some tools and techniques being developed for data conditioning (regression of instrumental and environmental artifacts from the data channel), detector design evaluation (modeling the science “reach” of alternative detector designs and configurations), noise simulations for mock data challenges and analysis system validation, and analyses for the detection of gravitational radiation from gamma-ray burst sources.

Angular noise in gravitational wave detectors

Angular fluctuations of suspended mirrors in gravitational wave interferometers are a source of noise both for the locking and the operation of the detectors. We describe here some of the sources of these fluctuations and methods for the estimation of their order of magnitude.