Download Optomechanical Devices for Improving the Sensitivity

Optomechanical Devices for Improving the
Sensitivity of Gravitational Wave Detectors
Chunnong Zhao
for Australian International Gravitational wave
Research centre
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 frequencydependent squeezing and white-light cavity
• Thermal noise issue, noise-free optical dilution and
mechanical resonator design
• Summary
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Gravitational wave detector
Fabry-Perot Cavity
Power
Recycling Cavity
Nd:YAG laser
l = 1064nm
Beam Splitter
Fabry-Perot Cavity
Signal
Recycling Mirror
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Quantum noise limited sensitivity
Conventional detector
Phase-squeezed
vacuum injection
Frequency-dependent
squeezed vacuum injection
White-light cavity
4
Demonstration of squeezed vacuum injection on LIGO detector H1
Nature Photonics, 7, p 613-619, (2013)
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Frequency-dependent squeezing injection
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 frequencydependent 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
• 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
Negative dispersion
medium

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White-light cavity
• 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.
T
10
~ 10
Qm
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Optical dilution
Mechanical frequency shift
from 12Hz -> 1kHz
T. Corbitt, et al, PRL 99, 160801 (2007)
The problem: quantum radiation pressure
noise and instability (negative damping)
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Optical dilution
Quantum destructive interference cancels the noise and
damping
23
Optical dilution
Frequency Shift from 6.2 kHz to 145 kHz
Q-factor increased 50-fold.
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Cat-flap resonators
Optical dilution of a cat-flap resonator
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
Cat-flap mirror
Partial reflective
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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