Rencontres de Moriond – Gravitation, La Thuile 2015
Sensitivity improvement of a laser interferometer limited by
inelastic back-scattering, employing dual readout
Melanie Meinders1,2 and Roman Schnabel1,2
1Institut
für Gravitationsphysik der Leibniz Universität Hannover and
Max-Planck Institut für Gravitationsphysik (Albert-Einstein-Institut), Callinstraße 38, 30167 Hannover, Germany
2Institut für Laserphysik und Zentrum für Optische Quantentechnologien der Universität Hamburg,
Luruper Chaussee 149, 22761 Hamburg, Germany
Parasitic signals due to scattered light
Infrared stray light in GEO600
•
Stray light hits vibrating surfaces
⇒ phase modulation
•
Back-scattering into interferometer mode
⇒ spurious signal
Melanie Meinders, La Thuile 2015
[S. Hild, PhD Thesis (2006)]
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Parasitic signals due to scattered light
Infrared stray light in GEO600
•
Stray light hits vibrating surfaces
⇒ phase modulation
•
Back-scattering into interferometer mode
⇒ spurious signal
Melanie Meinders, La Thuile 2015
Advanced readout today
Quadrature of parasitic signals is arbitrary
⇒ Read out second quadrature
⇒ Model scatter signal and subtract it from
scientific measurement
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Experimental setup
• Laser source : NPRO, 2W @ 1064nm
• Signals at audioband frequencies,
shifted to MHz and demodulated
• 50/50 splitting ⇒ signal-to-shot-noise-ratio
decreased by factor of 2
• Detection with two balanced homodyne
detectors (BHD1&2)
Melanie Meinders, La Thuile 2015
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Injected GW-signal
Injection from sound file* : Simulation of an inspiral of a binary neutron star system with equal masses
* GW-sound: [S. A. Hughes et al., http://gmunu.mit.edu/sounds/comparable_sounds/comparable_sounds.html]
Melanie Meinders, La Thuile 2015
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Model for the scatter signal
Melanie Meinders, La Thuile 2015
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Model for the scatter signal
𝑠0
𝐴m , 𝑓m , 𝜑m
Consider the case:
𝑠 𝑡 = 𝑠0 + 𝐴m sin(2𝜋𝑓m 𝑡 + 𝜑m )
and 𝑠0 , 𝐴m , 𝑓m , 𝜑m = const.
Melanie Meinders, La Thuile 2015
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Model for the scatter signal
𝑠0
𝐴m , 𝑓m , 𝜑m
Consider the case:
Doppler shift:
𝑠 𝑡 = 𝑠0 + 𝐴m sin(2𝜋𝑓m 𝑡 + 𝜑m )
max
𝑓ds = 2𝜋
𝐴
𝑓
cos(2𝜋𝑓
𝑡
+
𝜑
)
with
𝑓
= 2𝜋𝐴m 𝑓m /𝜆
m
m
m
m
ds
𝜆
and 𝑠0 , 𝐴m , 𝑓m , 𝜑m = const.
𝐴m > 𝜆 2𝜋 ⇒ frequency up-conversion
Melanie Meinders, La Thuile 2015
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Model for the scatter signal
𝜑 𝑡 = 2𝜋
⋅𝑠 𝑡
𝜆
𝑠0
amplitude
𝑥sc 𝑡 = 𝐴𝑥 cos 𝜑(𝑡)
𝐴m , 𝑓m , 𝜑m
phase
&
𝑝sc 𝑡 = 𝐴𝑝 sin 𝜑(𝑡)
Consider the case:
Doppler shift:
𝑠 𝑡 = 𝑠0 + 𝐴m sin(2𝜋𝑓m 𝑡 + 𝜑m )
max
𝑓ds = 2𝜋
𝐴
𝑓
cos(2𝜋𝑓
𝑡
+
𝜑
)
with
𝑓
= 2𝜋𝐴m 𝑓m /𝜆
m
m
m
m
ds
𝜆
and 𝑠0 , 𝐴m , 𝑓m , 𝜑m = const.
𝐴m > 𝜆 2𝜋 ⇒ frequency up-conversion
Melanie Meinders, La Thuile 2015
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Generation of a scatter shoulder
𝐴m ≈ 5.2 𝜆 ⇒ 𝑓max ≈ 160Hz
𝑓m = 5Hz
Melanie Meinders, La Thuile 2015
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Scatter limited measurements
scatter shoulder
BHD1: x(t)
quadrature
marker
BHD2: p(t)
optical
shot-noise
𝐴m ≈ 5.2 𝜆 ⇒ 𝑓max ≈ 160Hz
𝑓m = 5Hz
𝑥 𝑡 = 𝑥GW 𝑡 + 𝑥sc (𝑡),
𝑥sc 𝑡 ∝ cos 𝜑(𝑡)
𝑝 𝑡 = 𝑝sc 𝑡 ∝ sin 𝜑(𝑡)
Melanie Meinders, La Thuile 2015
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Subtraction of the scatter shoulder
𝑝sc 𝑡 ∝ sin(𝜑0 + 2𝜋
𝐴m sin(2𝜋𝑓m 𝑡 + 𝜑m ))
𝜆
𝑥 𝑡 = 𝑥GW 𝑡 + 𝑥sc (𝑡),
Melanie Meinders, La Thuile 2015
𝑥sc 𝑡 ∝ cos 𝜑(𝑡)
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Subtraction of the scatter shoulder
𝑝sc 𝑡 ∝ sin(𝜑0 + 2𝜋
𝐴m sin(2𝜋𝑓m 𝑡 + 𝜑m ))
𝜆
𝑝sc 𝑡 ∝ sin 𝜑 𝑡 ⇒ 𝜑 𝑡 ⇒ 𝑥sc 𝑡 ∝ cos 𝜑(𝑡)
𝑥 𝑡 = 𝑥GW 𝑡 + 𝑥sc (𝑡),
Melanie Meinders, La Thuile 2015
𝑥sc 𝑡 ∝ cos 𝜑(𝑡)
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Subtraction of the scatter shoulder
𝑝sc 𝑡 ∝ sin(𝜑0 + 2𝜋
𝐴m sin(2𝜋𝑓m 𝑡 + 𝜑m ))
𝜆
𝑝sc 𝑡 ∝ sin 𝜑 𝑡 ⇒ 𝜑 𝑡 ⇒ 𝑥sc 𝑡 ∝ cos 𝜑(𝑡)
𝑥 𝑡 = 𝑥GW 𝑡 + 𝑥sc (𝑡),
𝑥sc 𝑡 ∝ cos 𝜑(𝑡)
𝑥 𝑡 − 𝑥sc (𝑡)
[http://arxiv.org/abs/1501.05219]
Melanie Meinders, La Thuile 2015
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Subtraction of the scatter shoulder
Comparison with a reference measurement
BHD1
scatter shoulder
quadrature
marker
GW-signal
optical
shot-noise
𝑥 𝑡 = 𝑥GW 𝑡 + 𝑥sc (𝑡),
𝑥sc 𝑡 ∝ cos 𝜑(𝑡)
𝑥 𝑡 − 𝑥sc (𝑡)
[http://arxiv.org/abs/1501.05219]
Melanie Meinders, La Thuile 2015
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Compatibility with squeezed light injection
vacuum
squeezed phase
~6dB
vacuum
•
•
squeezed amplitude
~6dB
Entanglement-enhanced readout with
simultaneous nonclassical noise suppression
of ~6dB in both orthogonal signal quadratures
Application as a sub-shot-noise veto-channel for
parasitic signals due to stray light
[Steinlechner et al., Nat. Phot. 7, 626-630 (2013)]
Melanie Meinders, La Thuile 2015
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Rencontres de Moriond – Gravitation, La Thuile 2015
Thank you for your attention!