Transcript LISA Interferometry TeV II Meeting Madison, Wi August 30th, 2006 Guido Mueller University of Florida [email protected].

LISA Interferometry
TeV II Meeting
Madison, Wi
August 30th, 2006
Guido Mueller
University of Florida
[email protected]
LISA
08/30/2006
Gravitational
Wave
Sources
1. Super-massive
Black Hole
mergers
Chandra: NGC6240
2. Extreme mass ratio
Inpirals (EMRIs)
3. Galactic Binaries
4. …
Credit: Tod Strohmayer (GSFC)
LISA vs. LIGO
08/30/2006
LISA: Joint NASA/ESA project
LIGO: NSF project
EMRIs
Advanced
LIGO
LISA Concept
08/30/2006
LISA Concept:
 3 Spacecraft in triangular
formation
 5 Gm distance betw. S/C
 Heliocentric Orbit
 Measure changes in
distance with
10pm/rtHz accuracy!
Movie
LISA
08/30/2006
Technical Challenges:
1. How to build a gravitational reference sensor?
Need a non-accelerated proof mass
acceleration < 3x10-15 m/s-2 / rHz
2. How to do pm-Interferometry over 5 Gm?
Interferometry Measurement System (IMS)
LISA Interferometry
08/30/2006
Goal:
Measure distances with
10 pm/rtHz accuracy
Basics:
Laser:
• Wavelength: 1mm
• Power: 1 W
Telescopes:
• f/1 - Cassegrain
• Diameter: 40cm
 Received power: ~100pW
The Main Problem
08/30/2006
The Orbit Problem:
Arm lengths change
by about 50.000 km
during 12 mts orbit
or by ~ 1m/s.
The Orbit Problem
08/30/2006
Arm lengths change
by about 50.000 km
during 12 mts orbit
or by ~ m/s.
 Doppler shifts
(~ MHz)
The Orbit Problem
08/30/2006
Arm lengths change
by about 50.000 km
during 12 mts orbit
or by ~ 1 m/s.
 Doppler shifts
(~ MHz)
 Unequal arm lengths
(frequency noise)
The Orbit Problem
08/30/2006
Arm lengths change
by about 50.000 km
during 12 mts orbit
or ~1 m/s.
Doppler shifts
(~ MHz)
 Unequal arm lengths
(frequency noise)
 Telescope
repointing
(pointing noise)
Very dynamic interferometer!
LISA Concept
08/30/2006
High Gain Antennas
uN-Thrusters
LISA Concept
08/30/2006
Optical Benches
Proof Mass Housing
Telescopes
Interferometry
08/30/2006
Main Components/Tasks:
1. Phasemeter
2. Laser Frequency Noise
3. Mechanical Noise
(Solution: Engineering)
Phasemeter
08/30/2006
Requirements:
• 2-20 MHz signal frequencies, changing by several MHz
• Frequency noise of 30Hz/Hz1/2 @ 1mHz
= 30000 cycl./Hz1/2 @ 1mHz
• need to be resolved with 10-5 cycles/Hz1/2 accuracy!
 Dynamic Range of 9 orders of magnitude.
The JPL Phasemeter
08/30/2006
Ai  t  sin  2 ft  i  t  
m
sin  2 ft  m  t 
cos  2 ft  m  t 
Input
Tracks the Phase of
RF signal with NCO
I
Q
Ao t 
r  t 
NCO
H f 
Feedback
I/Q demodulation with
tracking NCO
o  t 
The JPL Phasemeter
08/30/2006
Digitally tested dynamic range
requirement.
Equivalent Optical Setup
–
Digitally generated 3
independent, laser-like
x107noise
zoomsources such that,
Phase 0 + Phase 1 - Phase 2 = 0
dynamic range
~109 @ 5 mHz
Requirement
(Results from Daniel Shaddock, Brent Ware, Bob Spero, JPL)
Laser Frequency Noise
08/30/2006
Requirements:
• Frequency noise of 30Hz/Hz1/2 @ 1mHz (for Phase meter)
• Free running laser: ~ 1MHz/Hz1/2 @ 1mHz
• Everything below 30Hz/Hz1/2 reduces requirements
on Phase meter
Solution:
• Frequency stabilization
• Time Delay Interferometry
Frequency Stabilization
08/30/2006
1st Step: Stabilize to ultra-stable reference cavity:
• Baseline: ULE or Zerodur spacer ring cavity
Ground testing:
Two lasers independently stabilized
to two reference cavities:
– References: 2 Zerodur spacers with
optically contacted mirrors in ultrastable vacuum chamber
– Pound Drever Hall stabilization
scheme (Modulation/Demodulation)
Frequency Stabilization
08/30/2006
UF-results
Similar Results
with ULE spacers:
• AEI Hanover
• GSFC
Can we do better?
Rachel
Cruz
Arm Locking
08/30/2006
Basic Idea: Lock laser frequency to LISA arm
Far S/C:
Transponder
(phase locked
laser)
!
S(t) = (t-2t)-(t) = 0
 Transfer function is zero at Fourier
frequencies fN = N/2t
 Requires tailored feedback gain (~1/sqrt(f))
at and above f1 up to UGF
 High bandwidth, only limited gain
 Laser frequency noise suppressed
at all frequencies except at fN = N/2t
Arm Locking
08/30/2006
Different potential realizations:
Single
Round-trip arm length
f1  30mHz
Common
Difference between arms
f1  3Hz
Sagnac
Sagnac effect (rotation)
f1  20kHz
Arm Locking
08/30/2006
Sagnac:
Sagnac
• Allows high-gain,
low-bandwidth feedback loop
• Very simple design
Main disadvantage:
• No redundancy:
If one link malfunctions,
the Sagnac signal is gone
 Common arm locking is the baseline
Sagnac effect (rotation)
f1  20kHz
Arm Locking
08/30/2006
Stabilized “Reference”
Stabilized “Master”
Phase-locked
“Slave”
Interferometer
& arm-locking
Arm Locking
08/30/2006
GPL
p1
p2
+
-
2
+
-
pLO
S21
LO
+ -
+
-
S20 
 p1  p0   pLO

1  GAL 1  e  st

Compare to LISA:
p0
-+
S20
e  st
GAL
+
-
2 
p1  pLO
1  GAL 1  est


Arm Locking
08/30/2006
Latest Arm Locking experiment at UF
• currently limited by missing real time phasemeter
EPD using 25 MHz digitization rate, delay of 1.065ms or f1 = 939Hz
Arm Locking
08/30/2006
Latest Arm Locking experiment at UF
• currently limited by missing real time phasemeter
Out-of-loop
Primary beat note
demodulated to 10kHz
Phase of 10kHz
signal measured using
software phase meter.
Arm Locking
08/30/2006
Out-of-loop
Primary beat note
demodulated to 10kHz
Phase of 10kHz
signal measured using
software phase meter.
Ira Thorpe
Time Delay Interferometry
08/30/2006
Laser frequency stabilization
Time Delay Interferometry (TDI)
First Generation X-combination:
Sb(t) - Sg(t) - Sb(t- 2τg) + Sg(t- 2τb)
Requires to know the light
travel times betw. S/C
 Ranging with 30m accuracy
Synthetic equal arm
Interferometer!
TDI Experiment
08/30/2006
(Nearly) full scale LISA signal
Limited by Transponder Noise
TDI Experiment
Phase Noise [cycles/rt(Hz)]
08/30/2006
• Results currently
limited by PLL
performance
5 orders
suppression
Rachel
Cruz
Frequency [Hz]
Summary
08/30/2006
LISA Interferometry:
Requirements:
10 pm/rtHz in a dynamic 5 Gm interferometer
Key Technologies:
Phase meter
Laser frequency stabilization
– Reference Cavity
– Arm locking
Time Delay Interferometry
Summary
08/30/2006
ESA/EU:
NASA/US:
ESA/Estec
GSFC
Astrium, Germany
JPL
AEI Hanover
University of Florida
University Trento
JILA
University of Birmingham
Stanford
University of Glasgow
University of Washington
…
…
+ many data analysis and theory groups
Summary
08/30/2006
LISA:
Remaining Challenges:
– How to move the telescope w/o distorting the measurements?
– Do we need to measure these distortions and correct for them?
– How to align the spacecraft to acquire lock?
– Stable materials and components:
• Laser switch, Fiber launcher, Vacuum system, Discharging, PAA actuator,
…
Data Analysis challenges
– Galactic binaries create a GW “noise” floor
Does this sound different from other missions?
Summary
08/30/2006
LISA:
GRS:
– Will be flight tested in LTP around 2009/10
– LTP ground tests look very promising so far
Interferometry:
– Basic concepts of TDI, Arm-locking, clock noise removal are
well understood
– Experimental tests at component level are progressing very
well
– EPD unit enables detailed ground testing of TDI/AL
(Test as you fly, fly as you test)
Summary
08/30/2006
LISA:
Was considered a very challenging mission
No ground testing possible
No technology heritage for any of the major
technologies:
– GRS
– Interferometry
– Data Analysis
Arm Locking
08/30/2006
Out-of-loop
measurement of
primary beat note
using frequency
counter.
400x
Ira Thorpe
TDI Experiment
08/30/2006
Delayed
Prompt
Prompt-Delayed
First experimental
verification of TDI!
Rachel Cruz, Michael Hartman, UF
Electronic Phase Delay
08/30/2006
UF technique:
Laser Phase replaced by beat note phase
Beat note phase delayed electronically (EPD).
LISA photodiodes replaced by electronic mixers.
LISA
UF Simulator
Electronic Phase Delay
08/30/2006
System
Date
Hardware
Max. Signal
Freq.
Original
Summer
2004
200 kHz PCI
card
30 kHz
2
80s
Current
Summer
2005
Pentek
5 MHz
4
6s
Future
Fall
2006
Pentek w/
PMs & NCOs
20 MHz
4
35s*
# Chan. Max. Delay
*Depends on resolution & BW
Short LISA History
08/30/2006
Foundation paper in 1984 by Bender, Faller, Hall, Hils and Vincent
Concept developed through
–
Concept studies ‘84-’93
–
ESA Pre-Phase studies ‘93-’98 (cf., PPA2 document)
–
NASA Team-X study ‘98
–
ESA Industrial Phase A Study ‘98-’00 (cf., FTR and STS documents)
–
GSFC Project Office formed in ‘01, technology planning and development commenced.
–
We
entered
Phase
A
late
2004!
Flight demonstrations (LISA Pathfinder and ST-7) initiated in ‘00-’01
–
NASA Formulation Phase began Oct. ‘04
–
ESA Industrial Formulation Study begun at Astrium/Friedrichshafen Jan. ‘05, finished
Phase I in Oct. ‘05
Concept has not significantly changed since PPA2 in 1998.
Current focus
–
Architecture definition and refinement, design trade studies
–
Technology development
–
LISA Pathfinder and ST-7
Slide stolen from Robin ‘Tuck’ Stebbins LISA Symposium Talk
Mission Status
08/30/2006
• ST7 brings the least well-tested LISA instrumentation, DRS, to TRL
level 9
• Preparations for 2010 launch will already greatly enhance
-Experience in building flight models
-Experience in tightly-coupled NASA/ESA cooperation
• Results from 2010 launch will be in time to inform formulation
FY07
1
2
3
FY08
4
1
2
3
FY09
4
1
2
3
FY10
4
HW delivery
1
2
3
FY11
4
1
2
3
launch
ST-7
Phase C/D
Phase E
LISA
Phase A (survival)
Slide stolen from Colleen Hartman, LISA Symposium
Phase A
Phase B
4
Mission Status
08/30/2006
• Budget requirements have
necessitated Beyond Einstein
be sequential missions rather
than parallel efforts
Instead of two parallel lines
of sequential missions
• Funding wedge for first BE
mission start in 2009
We hear you …
• One of 3 will go first: LISA,
Con-X, JDEM
JDEM:
Additional competition!
• Special BE NRC panel in
2008-9
From Colleen Hartman, LISA Symposium
Optical Bench
08/30/2006
Phase Meter 2
Phase Meter 1
Phase Meter 3
Fiber to/from
Second Bench
to/from far SC
from Laser
Bench
Optical Bench
08/30/2006
Phase Meter 1
Bench A:
PM1A: 1(t) - 2(t) + fibernoise
Fiber to/from
Second Bench
from Laser
Bench
Bench B:
PM1B: 1(t) - 2(t) - fibernoise
PM1A + PM1B = 2 [1(t) - 2(t)]
• Independent of fiber noise
• Used to phase lock local lasers
• Allows to compare both
Interferometer arms
Only works if OPL in fiber is independent of propagation direction!
[Like having a beam splitter in a
Michelson Interferometer
Optical Bench
08/30/2006
Polarization Sagnac Interferometer
for Optical Fiber Tests at UF
Fiber
Pol
l/4
Laser
l/2
l/4
BS
Pol
Parallel tests in Glasgow, Hanover
Optical Bench
08/30/2006
Phase Meter 2
Phase Meter 1
Phase Meter 3
Fiber to/from
Second Bench
to/from far SC
from Laser
Bench
PM 2 – PM 1 : Distance PM - SC
Optical Bench
08/30/2006
Phase Meter 2
Phase Meter 1
Phase Meter 3
Fiber to/from
Second Bench
to/from far SC
from Laser
Bench
PM 3: Distance SC – SC How?
Optical Bench
08/30/2006
Phase Meter 3 on S/C 2 and 3:
• Used to Phase lock local laser
PM 3A – PM 1A
To Laser frequency
actuator ]PLL
from Laser
Bench
Phase Meter 3
to/from far SC
LISA
08/30/2006
Master S/C
Slaved S/C
Slaved S/C
Optical Bench
08/30/2006
Phase Meter 3 on Master S/C 1:
Phase Meter 3
PM 1A – PM 3A
= 1(t)-1(t-2t1)+GW1
(~Unequal Arm MI)
from Laser
Bench
• Dominated by Laser frequency noise df :
~1000 cycl./rtHz noise
to/from far SC
Primary Hardware
08/30/2006
Key Features
-
4 Channels
-
14-bit ADC
-
16-bit DAC
-
1 GB SDRAM
-
100 MHz sampling
-
5 FPGAs
-
PowerPC processor
-
Ethernet, serial, VME
Primary Hardware
08/30/2006
Key Features
-
4 Channels
-
14-bit ADC
-
16-bit DAC
-
1 GB SDRAM
-
100 MHz sampling
-
5 FPGAs
-
PowerPC processor
-
Ethernet, serial, VME
Limited to 33Ms/s
Gravitational Waves
08/30/2006
NS/NS merger
(MNS ~ 3x1030kg ~ 1.4 MSun)
1. Smallest Distance: dmin ~ 20km (2xDiameter of NS)
2. Potential Energy: E = - GM2/d ~ 3x1046J
3. Newton: f (d=100km) ~ 100 Hz,
f (d=20km) ~ 1 kHz
4. Takes about 1s to get from 100km to 20km
5. During that second nearly half of the
Potential Energy is radiated away!
6. Assume binary is in the Virgo cluster (15 Mpc ~ 6x1024 m)
We receive about P=1..100mW/m2 from each binary!
Like full moon during a clear night!
Gravitational Waves
08/30/2006
We can see the moon, why haven’t we
seen Gravitational Waves yet?
GW-Amplitude: h=dL/L is
G/c4 = 10-45s2/kg m
Gravitational Waves
08/30/2006
We can see the moon, why haven’t we
seen Gravitational Waves yet?
GW-Amplitude: h=dL/L is
G/c4 = 10-45s2/kg m
Our example (f=400Hz):
Or 1am over 1km
LISA
08/30/2006
LISA will probe space and time
at the forming edges of black holes listening to the
sounds of vibrating spacetime:
– the booming roar of supermassive black holes merging
– the chorus of death cries from stars on close orbits around
black holes
– and the ripping noise of zipping singularities
Even the NASA-folks were a little excited about LISA
Unfortunately, LISA will be unmanned and not on Mars …
Copied from: Beyond Einstein: from the big bang to black holes
UF Benchtop
08/30/2006
Ground-based Simulator:
1. First Generation of Experiments
• Frequency-stabilized lasers
• Arm-locking
• Time Delay Interferometry (TDI)
2. Future Experiments
• Doppler shifts
• Clock noise, laser com.
• GW-signals
Long Term Goal: Provide realistic data
streams with injected GW signals
The Mission
08/30/2006
Current Design of single tube:
GRS-Challenges
08/30/2006
A few (obvious) forces pushing the PM:
Lorentz Force:
Charged PM moving in variable solar magnetic field
– Charge Control (UV-light, continuous or every ~10-20h?)
Magnetic Force:
Magnetic Susceptibility couples to magnetic fields
– Gold Platinum Alloy:
cm ~ 0 (Problem: Grains in PM have variable cm)
Self-Gravity from S/C:
1kg mass 10cm from PM gives a gradient of 10-7m/s2/m
– S/C motion < 10nm/rHz (Design of S/C, mN-Thrusters)
GRS
08/30/2006
A few (not so obvious) forces pushing the PM:
Patch Fields:
Crystal Boundaries create voltage potentials
Gas pressure noise:
Gas hitting the PM from both sides
– mDa ~ PDT
requires DT < 10-4K/rHz and P < 10-8torr
Thermal photon pressure:
Black Body Radiation from walls
– mDa ~ DT
…
requires DT < 10-4K/rHz
Timing Error
08/30/2006
The delay time of the EPD, just as the optical
delay time of the LISA arm, will not fall exactly
at one of the sampling points of the data stream.
Define the timing error as:
Dt |t EPD t shift |
1
Dt max  t samp
2
Suppression Limit
08/30/2006
•The timing error
in the experiment
< Δτmax = ½ tsamp =
6.25 μsec
•Interpolation can
be used to reduce
the timing error
•Experimental
results appear to
hit another noise
source at ~5x10-5
cycles/rt(Hz)
Phase Noise [cycles/rt(Hz)]
S (t )  p (t )  p (t  Dt )
~
~
| Smin ( f ,Dt )| 2sin(fDt )| p ( f )|
Smin(f,Δτmax)
Exp. Timedelayed Comb.
Frequency [Hz]
Two-Arm Experiment
08/30/2006
Data Analysis Challenge
08/30/2006
The signals
– 3 Hz sampling of 18 beat signals
– Time Delay Interferometry (TDI) algorithms to remove laser and clock
frequency noise
– Auxiliary ‘sciencekeeping’ data (solve for PM motion)
More than 10,000 interfering GW signals.
Signals have to be
– Identified, separated, tracked, and subtracted from data stream
Source direction can be determined
– Frequency and amplitude modulation from orbital Doppler shifts
– Phase modulation from time-of-flight across antenna
LISA Benchtop
08/30/2006
Reference laser
Master laser
LISA Simulator with
1 Laser on each S/C.
LISA Benchtop
08/30/2006
S21(t)
S23(t)
Reference laser
S13(t)
S12(t)
S32(t)
Master laser
S31(t)
S12(t) = 20(t-t21)-10(t)
LISA Benchtop
08/30/2006
S21(t)=0
S23(t)
Reference laser
S13(t)
S12(t)
S32(t)
Master laser
S31(t)=0
S12(t) = 20(t-t21)-10(t)
LISA Benchtop
08/30/2006
Note: All optical path are common mode
 Insensitive to Optical path length changes!
LISA Benchtop
08/30/2006
LISA Benchtop
08/30/2006
PD
Current Setup:
• Cancels all optical path length changes.
• No GW-signals or Doppler shifts
PD
PZT
PD
PD
Future Setup:
• Split Optical Path
• Doppler shift can be added
in the EPD unit
• GW-signal can be added via PZT
• Sensitive to acoustic noise
• Will be moved in Vacuum
LISA Benchtop
08/30/2006
S21(t)=0
S23(t)
Reference laser
S13(t)
S12(t)
S32(t)
Master laser
S31(t)=0
• Common Arm-locking
• Sagnac Arm-locking
•…