61 research outputs found
A 6D interferometric inertial isolation system
We present a novel inertial-isolation scheme based on six degree-of-freedom
(6D) interferometric sensing of a single reference mass. It is capable of
reducing inertial motion by more than two orders of magnitude at 100\,mHz
compared with what is achievable with state-of-the-art seismometers. This will
enable substantial improvements in the low-frequency sensitivity of
gravitational-wave detectors. The scheme is inherently two-stage, the reference
mass is softly suspended within the platform to be isolated, which is itself
suspended from the ground. The platform is held constant relative to the
reference mass and this closed-loop control effectively transfers the low
acceleration-noise of the reference mass to the platform. A high loop gain also
reduces non-linear couplings and dynamic range requirements in the
soft-suspension mechanics and the interferometric sensing
Broadband sensitivity enhancement of detuned dual-recycled Michelson interferometers with EPR entanglement
We demonstrate the applicability of the EPR entanglement squeezing scheme for
enhancing the shot-noise-limited sensitivity of a detuned dual-recycled
Michelson interferometers. In particular, this scheme is applied to the
GEO\,600 interferometer. The effect of losses throughout the interferometer,
arm length asymmetries, and imperfect separation of the signal and idler beams
are considered
Fundamental Limitations of Cavity-assisted Atom Interferometry
Atom interferometers employing optical cavities to enhance the beam splitter
pulses promise significant advances in science and technology, notably for
future gravitational wave detectors. Long cavities, on the scale of hundreds of
meters, have been proposed in experiments aiming to observe gravitational waves
with frequencies below 1 Hz, where laser interferometers, such as LIGO, have
poor sensitivity. Alternatively, short cavities have also been proposed for
enhancing the sensitivity of more portable atom interferometers. We explore the
fundamental limitations of two-mirror cavities for atomic beam splitting, and
establish upper bounds on the temperature of the atomic ensemble as a function
of cavity length and three design parameters: the cavity g-factor, the
bandwidth, and the optical suppression factor of the first and second order
spatial modes. A lower bound to the cavity bandwidth is found which avoids
elongation of the interaction time and maximizes power enhancement. An upper
limit to cavity length is found for symmetric two-mirror cavities, restricting
the practicality of long baseline detectors. For shorter cavities, an upper
limit on the beam size was derived from the geometrical stability of the
cavity. These findings aim to aid the design of current and future
cavity-assisted atom interferometers.Comment: 11 pages, 12 figure
Feasibility of near-unstable cavities for future gravitational wave detectors
Near-unstable cavities have been proposed as an enabling technology for
future gravitational wave detectors, as their compact structure and large beam
spots can reduce the coating thermal noise of the interferometer. We present a
tabletop experiment investigating the behaviour of an optical cavity as it is
parametrically pushed to geometrical instability. We report on the observed
degeneracies of the cavity's eigenmodes as the cavity becomes unstable and the
resonance conditions become hyper-sensitive to mirror surface imperfections. A
simple model of the cavity and precise measurements of the resonant frequencies
allow us to characterize the stability of the cavity and give an estimate of
the mirror astigmatism. The significance of these results for gravitational
wave detectors is discussed, and avenues for further research are suggested.Comment: 11 pages, 8 figure
Thermal modelling of Advanced LIGO test masses
High-reflectivity fused silica mirrors are at the epicentre of current
advanced gravitational wave detectors. In these detectors, the mirrors interact
with high power laser beams. As a result of finite absorption in the high
reflectivity coatings the mirrors suffer from a variety of thermal effects that
impact on the detectors performance. We propose a model of the Advanced LIGO
mirrors that introduces an empirical term to account for the radiative heat
transfer between the mirror and its surroundings. The mechanical mode frequency
is used as a probe for the overall temperature of the mirror. The thermal
transient after power build-up in the optical cavities is used to refine and
test the model. The model provides a coating absorption estimate of 1.5 to 2.0
ppm and estimates that 0.3 to 1.3 ppm of the circulating light is scattered on
to the ring heater.Comment: 14 pages, 9 figure
Particle swarming of sensor correction filters
Reducing the impact of seismic activity on the motion of suspended optics is essential for the operation of ground-based gravitational wave detectors. During periods of increased seismic activity, low-frequency ground translation and tilt cause the Advanced LIGO observatories to lose 'lock', reducing their duty cycles. This paper applies modern global-optimisation algorithms to aid in the design of the 'sensor correction' filter, used in the control of the active platforms. It is shown that a particle swarm algorithm that minimises a cost-function approximating the differential root mean squared velocity between platforms can produce control filters that perform better across most frequencies in the control bandwidth than those currently installed. These tests were conducted using training data from the LIGO Hanford Observatory seismic instruments and simulations of the Horizontal Access Module Internal Seismic Isolation platforms. These results show that new methods of producing control filters are ready for use at LIGO. The filters were implemented at LIGO's Hanford Observatory, and use the resulting data to refine the cost function. © 2020 IOP Publishing Ltd Printed in the U
Sensing and control in dual-recycling laser interferometer gravitational-wave detectors
We introduce length-sensing and control schemes for the dual-recycled cavity-enhanced Michelson interferometer configuration proposed for the Advanced Laser Interferometer Gravitational Wave Observatory (LIGO). We discuss the principles of this scheme and show methods that allow sensing and control signals to be derived. Experimental verification was carried out in three benchtop experiments that are introduced. We present the implications of the results from these experiments for Advanced LIGO and other future interferometric gravitational-wave detectors
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