59 research outputs found
A radiometer for stochastic gravitational waves
The LIGO Scientific Collaboration recently reported a new upper limit on an
isotropic stochastic background of gravitational waves obtained based on the
data from the 3rd LIGO science Run (S3). Now I present a new method for
obtaining directional upper limits that the LIGO Scientific Collaboration
intends to use for future LIGO science runs and that essentially implements a
gravitational wave radiometer.Comment: 6 pages, 2 figure
On choosing the start time of binary black hole ringdown
The final stage of a binary black hole merger is ringdown, in which the
system is described by a Kerr black hole with quasinormal mode perturbations.
It is far from straightforward to identify the time at which the ringdown
begins. Yet determining this time is important for precision tests of the
general theory of relativity that compare an observed signal with quasinormal
mode descriptions of the ringdown, such as tests of the no-hair theorem. We
present an algorithmic method to analyze the choice of ringdown start time in
the observed waveform. This method is based on determining how close the strong
field is to a Kerr black hole (Kerrness). Using numerical relativity
simulations, we characterize the Kerrness of the strong-field region close to
the black hole using a set of local, gauge-invariant geometric and algebraic
conditions that measure local isometry to Kerr. We produce a map that
associates each time in the gravitational waveform with a value of each of
these Kerrness measures; this map is produced by following outgoing null
characteristics from the strong and near-field regions to the wave zone. We
perform this analysis on a numerical relativity simulation with parameters
consistent with GW150914- the first gravitational wave detection. We find that
the choice of ringdown start time of after merger used in the
GW150914 study to test general relativity corresponds to a high dimensionless
perturbation amplitude of in the strong-field
region. This suggests that in higher signal-to-noise detections, one would need
to start analyzing the signal at a later time for studies that depend on the
validity of black hole perturbation theory.Comment: 23+4 pages, 22 figure
Sensing Optical Cavity Mismatch with a Mode-converter and Quadrant Photodiode
We present a new technique for sensing optical cavity mode mismatch and alignment by using a cylindrical lens mode converting telescope, radio-frequency quadrant photodiodes, and a heterodyne detection scheme. The telescope allows the conversion of the Laguerre-Gauss bullseye mode (LG01) into the 45° rotated Hermite-Gauss (“pringle”) mode (HG11), which can be easily measured with quadrant photodiodes. We show that we can convert to the HG basis optically, measure mode mismatched and alignment signals using widely produced radio-frequency quadrant photodiodes, and obtain a feedback error signal with heterodyne detection
A two-carrier scheme: evading the 3dB quantum penalty of heterodyne readout in gravitational-wave detectors
Precision measurements using traditional heterodyne readout suffer a 3dB
quantum noise penalty compared with homodyne readout. The extra noise is caused
by the quantum fluctuations in the image vacuum. We propose a two-carrier
gravitational-wave detector design that evades the 3dB quantum penalty of
heterodyne readout. We further propose a new way of realising
frequency-dependent squeezing utilising two-mode squeezing in our scheme. It
naturally achieves more precise audio frequency signal measurements with radio
frequency squeezing. In addition, the detector is compatible with other quantum
nondemolition techniques
New class of optical beams for large baseline interferometric gravitational wave detectors
A folded resonant Fabry-Perot cavity has the potential to significantly reduce the impact of coating thermal noise on the performance of kilometer scale gravitational wave detectors. When constructed using only spherical mirror surfaces it is possible to utilize the extremely robust TEM₀₀ mode optical mode. In this paper we investigate the potential thermal noise improvements that can be achieved for third generation gravitational wave detectors using realistic constraints. Comparing the previously proposed beam configurations such as e.g. higher order Laguerre-Gauss modes, we find that similar or better thermal noise improvement factors can be achieved, while avoiding degeneracy issues associated with those beams.Stefan W. Ballmer, David J. Ottawa
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