stefan hild, andreas freise, simon chelkowski university of birmingham gwadw, elba, may 2008 virtual...
TRANSCRIPT
Stefan Hild, Andreas Freise, Simon Chelkowski
University of Birmingham
GWADW, ELBA, May 2008
Virtual Interferometry for future GW detectors
Stefan Hild ELBA GWADW, May 2008 Slide 2
Virtual interferometry (the Idea) Inspiration from time-delay interferometry
3rd generation detectors are likely to consist of several individual instruments (Triangle …)
Optical and/or electronical combination of the several outputs of the individual instruments might allow to do nice things: Null streams ? Displacement noise free interferometry ? Frequency noise rejection ? … many more … (hopefully ?)
This is a huge multi-dimensional playground.
Stefan Hild ELBA GWADW, May 2008 Slide 3
Virtual interferometry (the Idea) Inspiration from time-delay interferometry
3rd generation detectors are like to consists of several individual instruments (Triangle…)
Optical and/or electronical combination of the several outputs of the individual instruments might allow to do nice things: Null streams ? Displacement noise free interferometry ? Frequency noise rejection ? … many more … (hopefully ?)
This is a huge multi-dimensional playground.
Stefan Hild ELBA GWADW, May 2008 Slide 4
The 3rd Generation Holy Grail:Displacement noise free interferometry (DNFI)
If you get DNFI to work: you can reduce many limiting noise sources.
Example: 2nd Generation noise limits
Stefan Hild ELBA GWADW, May 2008 Slide 5
Starting point: DNFI a la Tarabrin:LIGO-P070109-00Z arXiv:0804.3955v1
Seems to be an interesting concept since it uses a standard Fabry-Perot cavity.
Modified version of the paper on the arXiv (end of April 2008)
Stefan Hild ELBA GWADW, May 2008 Slide 6
DNFI ala Tarabrin:
Using a double pumped (2 Laser of different polarisation) detuned Fabry Perot cavity
Read out at both ends of the cavity by 8 photo diodes (4 homodyne detectors)
Assumption: All auxiliary optics sit on isolated platforms (no relativ movement of the components on the platforms)
Setup shown in the paper:
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Stefan Hild ELBA GWADW, May 2008 Slide 7
DNFI ala Tarabrin:
Experimentalapproch of the setup:
Setup shown in the paper:
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Stefan Hild ELBA GWADW, May 2008 Slide 8
Intuitive understanding of DNFI ala Tarabrin (1)
Using simple Finesse simulations
GW and mirror displacement can be distinguished in the signals
Disp. M_a Disp. M_b GW
S1 - scaled(S2) gives a GW channel ‘free’ of M_a displacement
In phase
Out of phase
Stefan Hild ELBA GWADW, May 2008 Slide 9
What can we learn?Simple picture of a detuned cavity:
From the input side GW and end mirror displacement look identical
However, displacement of the input mirror looks different than GW (due to direct reflection)
Stefan Hild ELBA GWADW, May 2008 Slide 10
Intuitive understanding of DNFI ala Tarabrin (2)
Disp. M_a Disp. M_b GW
S3 - scaled(S4) gives a GW channel ‘free’ of M_b displacement In phase
Out of phase
Now using the signals from LASER-B.
Stefan Hild ELBA GWADW, May 2008 Slide 11
Creation DNFI channel for Tarabrin setup
Building a linear combination it is possible to create DNFI channel. We can suppress mirror displacement for frequencies below the
detuning of the cavity.
DNFI-channel = k1*S1 + k2*S2 + k3*S3 + k4*S4
Stefan Hild ELBA GWADW, May 2008 Slide 12
Problems of the Tarabrin Concept
Detuning reduces power buildup inside the cavity
Frequency noise (no common mode rejection)
Displacement noise of optics on the Platforms (Homodyne detectors)
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Stefan Hild ELBA GWADW, May 2008 Slide 13
Going forward with the Tarabrin Concept ??
Detuning reduces power buildup inside the cavity
Frequency noise (no common mode rejection)
Displacement noise of optics on the Platforms (Homodyne detectors)
Perhaps one can use more powerful lasers or larger power recycling factors ?
Combine 2 cavities to form a Michelson interferometer
Replace the homodyne detectors by the conventional beam splitter of the Michelson interferometer
Stefan Hild ELBA GWADW, May 2008 Slide 14
Our Playground … Single Michelson IFO with
douple pumped arm cavities.
3 Laser: all slightly different frequency (few GHz).
4 Photo detectors. PD1 only sees Laser1 PD2 only sees Laser2 PD3 only sees Laser3 PD123 sees an optical mix of all
lasers
2 Output mode cleaners.
Arm length of 3km.
Cavity detuning of a few kHz.
Stefan Hild ELBA GWADW, May 2008 Slide 15
Signal Transfer functions
Using a linear combination of PD1, PD2 and PD3 we can remove displacement of IX and IY. (as expected)
But we have no chance to remove EY and EX. (as expected)
To remove EX and EY we probably need sensing at the end of the arms (in reflection of EY and EX).
Stefan Hild ELBA GWADW, May 2008 Slide 16
Extending our Playground … A triangle of 3 Michelson IFOs
with arm cavities.
Each test mass is part of two Michelson IFOs.
3 Laser: all slightly different frequency (few GHz).
12 Photo detectors.
6 Output mode cleaners.
Arm length of 3km.
Cavity detuning of a few kHz
Stefan Hild ELBA GWADW, May 2008 Slide 17
Signal TFs of single Michelson
Now we can subtract IX, IY, EX and EY. One Michelson (made of X and Y arm) ‘displacement
noise free’ !!
Stefan Hild ELBA GWADW, May 2008 Slide 18
Displacement noise free Michelson interferometer
One Michelson (made of X and Y arm) ‘displacement noise free’ !!
DNFI-channel = k1*PD1 + k2*PD2 + k3*PD3 + k4*PDb2 + k5*PDc3
BUT this result is cheating… (for two reasons)
Displacement noise suppressioninside the detection (audio) band
Stefan Hild ELBA GWADW, May 2008 Slide 19
How we were cheating…
If any displacement or GW signal is present in the Z-arm this will couple into PDb2 and PDc3.
PD2 and PD3 will be contaminated by laser frequency noise (no common mode rejection)
DNFI-channel = k1*PD1 + k2*PD2 + k3*PD3 + k4*PDb2 + k5*PDc3
Stefan Hild ELBA GWADW, May 2008 Slide 21
Summary Virtual interferometry might be highly beneficial for 3rd
Generation GW detectors
Holy Grail = Realize Displacement noise free interferometry that combines: Noise suppression at (sub)audio band frequencies Keep the common mode rejection of frequency noise Using feasible geometries
The Tarabrin-Concept might be useful.
We presented some first and very preliminary analyses, but this needs to be continued.