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GWADW / Elba 23.05.2011
Laser systems for LISA
and its precursor mission LISA Pathfinder
Michael Tröbs
Max-Planck-Institut für Gravitationsphysik und Universität Hannover
1
GWADW / Elba 23.05.2011
Lasers for LISA Pathfinder
AEI Hannover
2
•
•
GWADW / Elba 23.05.2011
LISA Pathfinder optical metrology system
AEI Hannover
3
GWADW / Elba 23.05.2011
LISA Pathfinder interferometry concept
AEI Hannover
4
Heinzel et al. CQG vol. 20 pp. S153 (2003)
GWADW / Elba 23.05.2011
LISA Pathfinder interferometry concept
AEI Hannover
stableunstable
GWADW / Elba 23.05.2011
LISA Pathfinder Interferometry concept
AEI Hannover
6
reference
interferometer
measurement
interferometer
Wand et al. CQG vol. 23 pp. S159 (2006)
GWADW / Elba 23.05.2011
LISA Pathfinder hardware implementation
AEI Hannover
7
stable
Laser Laser modulator Optical bench
unstable
GWADW / Elba 23.05.2011
LISA Pathfinder optical bench PFM
AEI Hannover
8
GWADW / Elba 23.05.2011
LISA Pathfinder optical bench PFM
AEI Hannover
9
GWADW / Elba 23.05.2011
Laser system for LISA Pathfinder
AEI Hannover
10
GWADW / Elba 23.05.2011
Reference laser unit FM free-running noise
AEI Hannover
11
Frequency noise Relative power noise
GWADW / Elba 23.05.2011
Laser frequency stabilization
AEI Hannover
12
GWADW / Elba 23.05.2011
Laser power stabilisation
AEI Hannover
13
GWADW / Elba 23.05.2011
Optical pathlength difference stabilisation
AEI Hannover
14
reference
interferometer
measurement
interferometer
Pathlength
changes
common-mode
in reference and
measurement
interferometers
Common-mode noise suppression only works down to nm/√Hz
GWADW / Elba 23.05.2011
Optial pathlength difference stabilisation
AEI Hannover
15
Wand et al. CQG
vol. 23 pp. S159 (2006)
GWADW / Elba 23.05.2011
Optical pathlength difference stabilisation
AEI Hannover
16Wand et al. CQG vol. 23 pp. S159 (2006)
GWADW / Elba 23.05.2011
AEI Hannover
17
GWADW / Elba 23.05.2011
LISA laser
AEI Hannover
18
√
GWADW / Elba 23.05.2011
LISA laser system components
AEI Hannover
19
GWADW / Elba 23.05.2011
Seed lasers for LISA
AEI Hannover
20Tröbs et al. JOSAB 26 pp. 1137 (2009)
GWADW / Elba 23.05.2011
Ultra Stable Oscillator (USO) phase noise
Phase noise of on-board
clocks (USOs) is too high!
Therefore low noise in
clock tone transfer chain required
Baseline design concept: measure
phase noise for later cancellation.
GWADW / Elba 23.05.2011
USO clock tone transfer chain
2 GHz
GWADW / Elba 23.05.2011
USO phase noise measurement
GWADW / Elba 23.05.2011
Requirements
Phase read-out:
Ancillary Modulation Error:
LISA frequency band:
GWADW / Elba 23.05.2011
EOM phase fidelity
AEI Hannover
25
Barke et al. Appl Phys B (2010) 98: 33–39
GWADW / Elba 23.05.2011
Phase characteristics of optical amplifiers
Potential sources of differential phase noise in amplifiers
Lc
fEOM2
• nonlinear dispersion and
laser frequency changes
• first measurements show
tiny effect
• should be negligible in LISA
GWADW / Elba 23.05.2011
Phase characteristics of optical amplifiers
Optical amplifiers under test
Core-pumped amplifier
Two identical stages
Pumping directly the core of a
single-mode fiber
2 x 0.4 m active fiber
1 W output power
Cladding-pumped amplifier
Single stage
Pumping in the multi-mode
cladding
3 m active fiber
1 W output power
Amplifiers supplied by Laser Zentrum Hannover e. V.
GWADW / Elba 23.05.2011
Phase characteristics of optical amplifiers
Optical amplifiers under test
Core-pumped amplifier
Two identical stages
Pumping directly the core of a
single-mode fiber
2 x 0.4 m active fiber
1 W output power
Cladding-pumped amplifier
Single stage
Pumping in the multi-mode
cladding
3 m active fiber
1 W output power
Amplifiers supplied by Laser Zentrum Hannover e. V.
GWADW / Elba 23.05.2011
Phase characteristics of optical amplifiers
Measurement setup
GWADW / Elba 23.05.2011
Phase characteristics of optical amplifiers
Differential phase noise of amplifiers
1 W output power
Within LISA requirement 2 GHz sideband frequency
Tröbs et al. JPCS (2010) 208: 012042
GWADW / Elba 23.05.2011
Summary
AEI Hannover
31
GWADW / Elba 23.05.2011
Thank you
AEI Hannover
32LISA Pathfinder in acoustic test chamber at ESA
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