optomechanical devices for improving the sensitivity of gravitational wave detectors chunnong zhao...
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Optomechanical Devices for Improving the Sensitivity of Gravitational Wave Detectors
Chunnong Zhaofor Australian International Gravitational wave Research centreUniversity of Western Australia
The University of Western Australia
Outline
• Gravitational wave detectors and quantum noise limits• Squeezed vacuum injection, and white-light cavity for
improving the sensitivity• Optomechanical filters for achieving frequency-
dependent squeezing and white-light cavity• Thermal noise issue, noise-free optical dilution and
mechanical resonator design• Summary
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Fabry-Perot Cavity
Fabry-Perot Cavity
Beam Splitter
Power Recycling Cavity
Signal Recycling Mirror
Nd:YAG laserl = 1064nm
Gravitational wave detector
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Quantum noise limited sensitivity
Conventional detector
Frequency-dependent squeezed vacuum injection
Phase-squeezed vacuum injection
White-light cavity
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Demonstration of squeezed vacuum injection on LIGO detector H1
Nature Photonics, 7, p 613-619, (2013)
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Frequency-dependent squeezing injection
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The filter cavity requirements:• Low optical loss• Low linewidth ~100Hz• Tuneable for optimization
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Frequency-dependent squeezed vacuum
• A lossless cavity is an ideal unity gain filter, and a ideal frequency-dependent squeezing angle rotator.
• The corner frequency of the rotator is the corner frequency of the cavity.
• For Advanced LIGO type detector, the corner frequency should be ~100Hz.
• To optimize a detuned interferometer detector, more than 2 filter cavities with optimized detuning and linewidth are required.
• These requirements lead to the alternative choice of active optomechanical filters.
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Frequency-dependent squeezing injection
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• Optomechanical filter cavity can have very narrow linewidth • and be tuneable by tuning the pump light
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Narrow-band optomechanical filters
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Narrow-band optomechanical filters
J. Qin, et al., PRA 89, 041802(R) (2014)
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Narrow-band optomechanical filters
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Narrow-band optomechanical filters
Classical noise ellipse angle rotation
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White-light cavity
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Negative dispersion medium
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White-light cavity
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• ITM and SEM form a cavitythat is transparent to the GW signal• Optomechanical cavity provide negative dispersion
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Negative dispersion and white-light cavity
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Negative dispesion and white-light cavity
Negative dispersion cavity response:
Normal cavity round-trip phase lag:
Phase cancelation requirement:
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Negative dispersion
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Negative dispersion
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Negative dispersion
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Negative dispersion
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Thermal noise
• The thermal noise of the mechanical resonator will be detrimental to all the benefits mentioned above.
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1010~
mQ
T
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Optical dilution
Mechanical frequency shift from 12Hz -> 1kHz
The problem: quantum radiation pressure noise and instability (negative damping)
T. Corbitt, et al, PRL 99, 160801 (2007)
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Optical dilution
Quantum destructive interference cancels the noise and damping
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Optical dilution
Frequency Shift from 6.2 kHz to 145 kHzQ-factor increased 50-fold.
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Cat-flap resonators
Cat-flap resonatorOptical dilution of a cat-flap resonator
The intrinsic (gravity-free) frequency of the silicon nitride cat-flap is ~20Hz while for the graphene we expect 0.2 Hz. Since both should be able to be diluted to 200kHz we have typical dilution factors of ~108 (SiN) and ~1012 for graphene.
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Cat-flap resonator
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Optical dilution
Partial reflective mirror
Cat-flap mirror
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Summary
• Optomechanical filters can potentially be used to improve the GW detector quantum noise limited sensitivity
• Thermal noise is the critical issue to the application • The noise-free optical dilution with careful designed
mechanical resonator is one of the solutions.
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