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Dual Sphere Detectors

Dual Sphere Detectors. by Krishna Venkateswara. Contents. Introduction Review of noise sources in bar detectors Spherical detectors Dual sphere configuration Sensitivity in SQL Advantages/Drawbacks Dual cylinders and sensitivity Summary. Introduction.

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Dual Sphere Detectors

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  1. Dual Sphere Detectors by Krishna Venkateswara

  2. Contents • Introduction • Review of noise sources in bar detectors • Spherical detectors • Dual sphere configuration • Sensitivity in SQL • Advantages/Drawbacks • Dual cylinders and sensitivity • Summary

  3. Introduction • Proposed by M. Cerdonio, L. Conti et. al. in 2001 • Two nested spheres • Fabry-Perot cavity as motion sensor • Main advantages • Wide bandwidth • Spherical detector

  4. Bar detectors with resonant transducers Noise energy=Thermal + Amplifier + Back-action β = energy coupling factor τ= integration time A large β is needed to reduce thermal noise.

  5. Spherical Detectors • A sphere has a spherical symmetry and 5 degenerate quadrupole modes. • Uniform cross-section to GWs. • Can determine both source direction (, ) and wave polarization (h+, h). • Mount 6 radial transducers on truncated icosahedral configuration.  “Spherically symmetric” detection of the sphere (Johnson & Merkowitz, 1993)

  6. Dual sphere configuration • Inner sphere has quadrupole mode at f • Outer sphere at 2-3 times f • At frequencies in between, the two spheres are driven out of phase by GW • Noise sources: • Thermal noise • Back-action noise • Photon counting noise

  7. Response of the surface of a sphere to GW Noise spectral density for each sensor

  8. Total strain noise density

  9. Sensitivity at Standard Quantum Limit (SQL) Features • R = 0.95 m, and a = 0.57 m • Cross section proportional to ρvs5 • Molybdenum ρ = 10000 kg/m3 and vs= 6.2 km/s Q ~ 20 million at T ≤ 4 K Input light power of 7 W , Q/T ≥ 2·108 K-1

  10.  Beryllium ρ = 1900 kg/m3 and vs= 13 km/s, Q ? • Input light power of 12 W , Q/T ≥ 2·108 K-1 • Sapphire ρ = 4000 kg/m3 and vs= 10 km/s Q > 108 at T < 10 K

  11. Wideband Spherical detector High sensitivity (at SQL) Different frequency band Complicated design Sensor sensitivity difficult to realize Advantages/Drawbacks

  12. Dual Cylinders • Simpler design • Each mode contributes to noise while signal is mainly from Quadrupole mode selective readout • Low thermal noise from high frequency modes Xd = x1 – x2 + x3 – x4

  13. Readout and sensitivity • Required displacement sensitivity ~ 3 * 10-23 m/√Hz • Demonstrated sensitivity ~ 5 * 10-20 m/√Hz using • Optomechanical sensor. • Capacitive sensor using SQUID amplifiers.

  14. Summary • Offers advantage of spherical detection and wide bandwidth in an uncovered frequency band • Requires advanced suspension and complicated construction • Dual cylinder design gives up isotropic sensitivity but naturally supports ‘selective readout’ and simpler design • Both require advances in optical transducers.

  15. thank you!

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