status of the glasgow sagnac speedmeter experiment€¦ · high laser powers so that michelson...
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Sebastian Steinlechner for the Glasgow Sagnac Speed Meter Team
LVC Meeting Pasadena, March 2015
LIGO-DCC: G1500358
Status of the Glasgow Sagnac Speed Meter Experiment
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What is the Sagnac Speed Meter Experiment?
The Glasgow Sagnac Speed Meter experiment is an ERC funded project with
three major goals:
1. Create an ultra-low noise speed meter testbed which is dominated by radiation
pressure noise
2. Demonstrate the back-action noise cancellation of the Sagnac topology
3. Explore speed meter technology for future GW detectors, such as ET
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How will we reach these goals?
LVC Pasadena, 2015 3
• Show that Sagnac
configuration can beat the
equivalent Michelson
configuration
• Need low-mass optics and
high laser powers so that
Michelson would be
backaction-noise limited
• Aim for 2-3x better
sensitivity between 100Hz
and 1kHz
• Assume Michelson is
understood well enough
– Won’t actually build it
– Go straight for Sagnac
S. Steinlechner
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Conceptual approach
• In-vacuum operation, passive
multi-stage seismic pre-isolation
• Triangular arm cavities with
monolithically suspended mirrors
• One gram ITMs, 100g ETMs
4 LVC Pasadena, 2015 S. Steinlechner
Target displacement sensitivity:
better than 10-18 m/√Hz at 1kHz
• Approx. 2.8m cavity round trip length,
20ppm – 30ppm loss per round trip
• Approx. 1kW of intra-cavity power
• Large laser beam spots to reduce
coating Brownian thermal noise
• In vacuum suspended balanced
homodyne detector
ITM ETMs
BHD
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Work ongoing on all fronts
LVC Pasadena, 2015 5 S. Steinlechner
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Quantum-noise modelling
• Model influence of imperfections on
QRPN reduction
• Analytical model based on two-photon
transfer matrix S. Danilishin et al.: Quantum noise of non-ideal
Sagnac speed meter interferometer with
asymmetries, arXiv:1412.0931, accepted by NJP
• Asymmetries cause Michelson-like
behaviour, reintroducing back-action
noise
• Can now simulate and reproduce the QN
behaviour in Finesse and Optickle models
LVC Pasadena, 2015 6 S. Steinlechner
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Results from quantum-noise modelling
• Lossless Sagnac has 1/𝑓
slope at low frequencies
• Even small loss values
introduce Michelson-type
1/𝑓2 slope again
• Important quantity here is
𝑇𝐿𝑜𝑠𝑠/𝑇𝐼𝑇𝑀
• We will have 𝑇𝐼𝑇𝑀 ≈700ppm, so can’t afford
much more than
𝑇𝐿𝑜𝑠𝑠 ≈ 30ppm
• For Einstein Telescope,
𝑇𝐼𝑇𝑀 will be on the few-
percent level, makes loss
requirements much more
lenient
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Reducing arm-cavity finesse?
• It’s the small arm-cavity bandwidth that makes our experiment
susceptible to small loss
• Could we reduce ITM reflectivity and “just use more laser power”?
• Turns out there is an optimal ratio of power to cavity linewidth
• Decreasing linewidth by x10 needs x104 more laser power
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More results from quantum-noise modelling
• Beam-splitter
imbalance again
gives Michelson-
like QN
• This time, 1/𝑓
slope from
decreasing Sagnac
signal transfer
combines with
1/𝑓2 RPN curve to
give 1/𝑓3
• Need beam-
splitter balanced
to within 0.1%
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Bridge installation
• Bridge structure on top of seismic
isolation stack rigidly connects
breadboards inside the two vacuum
tanks for LF stability
• Filled with Silastic rubber compound to
dampen resonances
• Test assembly worked, but…
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Cleanliness issues
• RGA spectrum shows lots of long-chained hydrocarbons
• Probably residue from cutting fluid? (Anyone good at analysing RGA data?)
• Breadboards will get baked, hopefully removing the issue
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Work on suspensions
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Work on suspensions
LVC Pasadena, 2015 13 S. Steinlechner
Auxiliary suspensions
• Input beam
steering
• Small Sagnac
• Double pendulum
• No vertical stage
• Compact design
• Coil actuation on
upper mass
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Work on suspensions
LVC Pasadena, 2015 14 S. Steinlechner
ETM suspensions
• 100g mirror
mass
• AEI prototype
design
• Triple
pendulum
• Monolithic last
stage
• Fast ESD
actuation
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Work on suspensions
LVC Pasadena, 2015 15 S. Steinlechner
1g suspensions
• Similar to 100g
suspensions, but
scaled down
• Work in progress ?
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Parts for auxiliary suspensions arrived
From design to reality
LVC Pasadena, 2015 16 S. Steinlechner
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Auxiliary suspensions assembly
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One-gram suspensions
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• Extensive modelling underway
• Investigating and optimising parameters such as
– Mirror size and geometry
– Suspension options (number of fibres, attachment points)
– Fibre diameter and length
• Identified possible parameter
set giving us 100Hz to 1kHz
window
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Meet the Scientists
LVC Pasadena, 2015 19 S. Steinlechner
Daniela Pascucci
Stefan Danilishin
Sebastian Steinlechner
Stefan Hild
Andreas Gläfke
Christian Gräf
Jennifer Wright
Alasdair Houston
Jan-Simon Hennig
Russell Jones
Sean Leavey
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LVC Pasadena, 2015 S. Steinlechner 20
Thanks for listening!