Abstract
One of the most significant limits to the sensitivity of current, and future, long-baseline interferometric gravitational wave detectors is thermal displacement noise of the test masses and their suspensions. This paper reports results of analytical and experimental studies of the limits to thermal noise performance of cryogenic silicon test mass suspensions set by two constraints on suspension fibre dimensions: the minimum dimensions required to allow conductive cooling for extracting incident laser beam heat deposited in the mirrors; and the minimum dimensions of fibres (set by their tensile strength) which can support test masses of the size envisaged for use in future detectors. We report experimental studies of breaking strength of silicon ribbons, and resulting design implications for the feasibility of suspension designs for future gravitational wave detectors using silicon suspension fibres. We analyse the implication of this study for thermal noise performance of cryogenically cooled silicon suspensions.
Highlights
Long baseline interferometers are used to search for gravitational waves from astronomical sources by sensing the relative displacements of mirrors suspended as pendulums to isolate the test mass mirrors from the effects of seismic noise at the ends of perpendicular interferometer arms [1]
This paper presents analysis of silicon suspension performance focusing on two of these additional factors that will have a significant bearing on the fibre dimensions—namely extraction of heat injected by the main interferometer laser beam; and the tensile strength of silicon
Silicon is a promising alternative material for future upgrades to existing gravitational wave detectors, and third generation detectors running at cryogenic temperatures in order to reduce thermal displacement noise
Summary
Long baseline interferometers are used to search for gravitational waves from astronomical sources by sensing the relative displacements of mirrors suspended as pendulums to isolate the test mass mirrors from the effects of seismic noise at the ends of perpendicular interferometer arms [1]. Mechanical dissipation in the pendulum suspensions gives rise to thermal displacement noise [2], x(ω), which may be usefully approximated to [3, 4]: x(ω) =. At detection band frequencies of ∼10–200 Hz, displacement sensitivities are limited by thermal motion of the test masses and their suspension elements. To minimise x(ω) over the detection band, current detector mirror suspensions are fabricated from ultra low mechanical loss materials. The material of choice is fused silica, which has significantly lower loss than metal wires at room temperature allowing low levels of suspension thermal noise [6,7,8,9,10,11,12,13,14]. Future sensitivity improvements to these detectors may require moving away from fused silica as a test mass suspension material
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