Albert Einstein Institute
Max Planck Institute for Gravitational Physics and
Leibniz Universität Hannover
Michael Tröbs, Christina Bogan, Simon Barke, Gerrit Kühn,
Jens Reiche, Gerhard Heinzel, Karsten Danzmann
We gratefully acknowledge support by the German Aerospace Center (DLR) (50OQ0601, 50OQ1301) and thank the
German Research Foundation for funding the Cluster of Excellence QUEST
(Centre for Quantum Engineering and Space-Time Research).
Breadboard laser for LISA 10 years ago
 NPRO 1.2 W output power, 30 Hz/rtHz, fiber-coupled
pump module
2
LISA laser concept today
 Master oscillator fiber amplifier
 Developments ongoing at
 Lusospace / LZH
 GSFC
 Hardware with flight heritage
LTP RLU FM
Amplifier for laser com. terminal
3
LISA laser concept today
 Phase modulator between seed laser and amplifier for
 Clock noise transfer
 Ranging
 Data communication
4
LISA laser concept today
 Phase modulator between seed laser and amplifier for
 Clock noise transfer
 Ranging
 Data communication
4
USO clock tone transfer chain
5
USO clock tone transfer chain
2.4 GHz
5
USO phase noise measurement
6
Requirements – phase fidelity
Phase read-out:
Ancillary Modulation Error:
LISA frequency band:
1 cycle 1 pm 1 µcycle 6 µrad
Δ𝜙1 pm ≤
∙
≅
≅
1064 nm
Hz
Hz
Hz
2.4 GHz 6 µrad
𝑓
Δ𝜙AME ≤ Δ𝜙1 pm ∙ EOM ≅
∙
𝑓het
24 MHz
Hz
2.8 mHz
Δ𝜙AME′ (𝑓) ≤ 0.6 ∙ 1 +
𝑓
4
mrad
Hz
7
Requirements – EOM frequency
 Shot noise limit of both sideband-sideband beats
combined: 93.2 pm/ Hz
Δ𝜙𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐
 For Δ𝜙1 pm ≤
1 pm
Hz

𝑓
𝑓het
= Δ𝜙𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐 ∙
𝑓EOM
het ≤1/100
𝑓
EOM
8
Requirements – EOM frequency
 Shot noise limit of both sideband-sideband beats
combined: 93.2 pm/ Hz
Δ𝜙𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐
 For Δ𝜙1 pm ≤
1 pm
Hz

𝑓
2.4 GHz
𝑓het
= Δ𝜙𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐 ∙
𝑓EOM
het ≤1/100
𝑓
EOM
8
Sources of differential phase noise in amplifiers
• amplifier length changes ΔL
due to
• changes in ambient
temperature
• pump power changes
• seed power changes
• nonlinear dispersion and
laser frequency changes
2π ⋅ f EOM
∆ϕ =
⋅ ∆L
c
• combined effect measured
• ΔL≤12 µm/√Hz
• Effect measured for passive
fiber and found to be
negligible
9
5 W flight-representative amplifier by Tesat tested
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Tesat amplifier results
 Seeded by LISA-like signal (narrowband carrier + two sidebands with
17% power each)
 No sign of SBS visible in backscattered signal (was monitored live)
Tesat amplifier results
•
•
Relative power noise (RIN) was measured at 2.2 W output power
RIN compatible with LISA requirements
EOM phase fidelity
 Phase fidelity of waveguide EOM fulfills LISA requirements
Barke et al. Appl Phys B (2010) 98: 33–39
 Space-qualified version available
13
Breadboard amplifier phase fidelity
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Breadboard amplifier phase fidelity
15
Measurement principle
+1.6 kHz
16
Setup to measure phase noise introduced by fiber amplifier
 Breadboards, modular setup, and electronics in rack ensure transportability
 room temperature fluctuations  passive thermal isolation
 power dependent phase shift in mixers  active amplitude stabilizations
17
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Setup in the lab - overview
electronics
Optical
measurements
Computer
console
18
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Setup in the lab - lasers
Master
laser
Fibers
delivering
light to
measurement
breadboard
slave
laser
assembled and functional, path to measure phase noise introduced by EOM exists
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Setup in the lab – phase measurement
Fibers to
photodiodes
Fibers from
laser
Device under
test
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Setup in the lab - electronics
Laser driver
Amplitude
stabilizations
Offset phase lock
Signal generators
Spectrum analyzer
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Setup in the lab - electronics
Laser driver
Computer console
Power supply
AD converter
Anti-aliasing filter
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Sensitivity of test setup
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Sensitivity of test setup
Not reliably reproducible.
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Summary
 Laser system with flight
heritage available
 Transportable test setup is
in place*
 Next measurement windows are
 end June – mid July
 end August – mid October
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for your Attention
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