01/08/2003
Gravitational Waves:Gravitational Waves:
Generated by huge accelerated masses suchas black holes in a binary system
Predicted by Einstein, never detected
d
01/08/2003
Frequencies & AmplitudesFrequencies & Amplitudes
Chirp Mass:
Amplitude:
GW Frequency Upper limit:
h0 ~ 2x10-2010kpc
R
f
HzM
MNS
3/2
f < 3.2 kHz MNS
M
3rS
d
3/2
M=(M1M2)
(M1+M2)
3/5
1/5
M ~ MS f ~ 10 Hz – 3 kHz
M ~ 108MS f ~ 0.1 mHz – 100 mHz
01/08/2003
History of a big fat weddingHistory of a big fat wedding
measure masses
and spins of binary system
detect normal modes of
ringdown to identify final NS or BH.
observe strong-field spacetime dynamics, spin
flips and couplings…
01/08/2003
LISA: Joint NASA/ESA project
Advanced LIGO
LIGO: NSF project
GW-Detectors
01/08/2003
Asymmetric BinariesAsymmetric Binaries
Compact Star orbits MBH in center of galaxy
Gravitational waves measure the multipole moments of the central object
Tests No hair theorem(BH described by mass, spin, and charge)Survey of MBH population
01/08/2003
The MissionThe Mission
3 spacecraft constellation
S/C separated by 5x106km
Drag-free proof masses inside
each S/C
Earth-trailing solar orbit
5 year mission life
10pm/rHz-Sensitivity
Launch 2014
LISA
01/08/2003
Spacecraft
Problem 1: • Environment will push/pull S/C by several m • Free falling proof mass needs to be shielded
Problems 2:• Interferometry: pm-sensitivity over Gm distances
01/08/2003
The ChallengesThe Challenges
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 in LISA?
Interferometry Measurement System (IMS)
Post processing of data (subtract instrumental noise)
Signal extraction (subtract known signals)
01/08/2003
GRSGRS
The Proof Mass: • Gold Platinum alloy• Cube (4cm)• Will float inside S/C
Housing:• Electrodes for
• Position Read out• Position Control
• Option: Optical readout
Housing connected to Optical Bench and S/C
01/08/2003
GRSGRS
A few forces pushing the PM:
Electro-magnetic Forces:
Charges on PM and magnetic susceptibility couple to variable solar magnetic field
Self gravity from S/C:
S/C motion with respect to PM < 10nm/rHz
Gas pressure noise:
Gas hitting the PM from both sides: T < 10-4K/rHz
Thermal photon pressure:
Black Body Radiation from walls: T < 10-4K/rHz
…
01/08/2003
LISA Interferometry LISA Interferometry
Background:
LISA-Signal: Phase of a laser field
– Main detector: Phase meter
Phase meter signal dominated by frequency noise
– Laser frequency noise
– Clock noise
Non-stable working point
– Doppler shifts
– Arm flexing
01/08/2003
Laser frequency stabilizationLaser frequency stabilization
Current frequency noise at UF: 1 kHz/rHz @ 1mHz.
Goal of 30Hz/rHz was met at AEI-Hanover and GSFC.
Goal is still 9 orders of magnitude to high for a direct measurement!
Pre-frequency stabilization using ultra-stable reference cavities
01/08/2003
LISA-Lab at GSFC:
• Reached 30Hz/rHz (original LISA Req.)
Ira Thorpe, Rachel Parks,Jordan Camp,Paul McNamara,G.M.
fm = Hz
Laser Frequency Stab.
01/08/2003
LISA Interferometry LISA Interferometry
Key Technologies to reduce frequency noise (FN):
1. Time Delay Interferometry (TDI)
• Measure same FN at different times and locations
• Time shift data sets
• Form appropriate linear combinations which cancel FN
2. Arm Locking
• Use LISA Interferometer arms as frequency reference
• Lock laser frequency on LISA arms
Baseline: Combination of both to
cancel 9 orders of magnitude noise!
01/08/2003
Experimental challenge:
• How to simulate 5 Gm (16 s) distance between S/C?
Solution: Electronic Phase Delay (EPD)
• Delay only the laser phase (carrier frequency is meaningless)!
1. Beat laser against reference laser (Beat frequency < 25MHz)
2. Digitize Beat Signal
3. Store Beat signal for 16s
4. Regenerate Beat signal
• Transfer function same as LISA arm with LISA-like noise
AD
C DA
C
Memory Buffer Analog Input Analog Output
Anti-Aliasing Filter
Reconstruction Filter
sin[t+10(t)] sin[t-)+10(t-)]
LISA Benchtop at UF LISA Benchtop at UF
01/08/2003
S12(t) = 20(t-21)-10(t)
S21(t)
TDI test at UFTDI test at UF
S23(t)
S13(t)
S32(t)
S31(t)
S12(t)
01/08/2003
S12(t) –S12(t-213)-S13(t)+S13(t-212) ~ GW
S21(t)=0
TDI with Phase lock loopTDI with Phase lock loop
S23(t)
S13(t)
S32(t)
S31(t)=0
S12(t)
01/08/2003
ArmlockingArmlocking
Basic Idea: Lock laser frequency to LISA arm
Far S/C:Transponder(phase locked laser)
S(t) = (t-2)-(t) = 0!
Transfer function is zero at Fourier frequencies fN = N/2
Laser phase will change periodically with period of round trip time 2
Laser frequency noise suppressed at all frequencies except at fN = N/2
01/08/2003
S13(t) = GW
S21(t)=0
TDI with Arm lockingTDI with Arm locking
S23(t)
S13(t)
S32(t)
S31(t)=0
S12(t)=0
01/08/2003
First Arm locking experimentsFirst Arm locking experiments
First experimental tests of Arm locking with VCO at UF:
Start-up transients:Noise suppression:
• Only 500ms delay here instead of 32s in LISA• Laser phase changes with 500ms period
01/08/2003
Benchtop Experiment for LISABenchtop Experiment for LISA
Research Plan at UF:
Test TDI, data-reduction algorithms with realistic laser phase noise
Test arm locking with realistic laser phase noise
Add clock noise, bench motion, arm flexing, and Doppler shifts
Start Mock-up data challenges
Expand to two lasers per S/C
Full Interferometer test before 2010
Development of data reduction and data analysis tools
– Massive Downsampling
– Subtraction of 1000s of known and unknown galactic binaries
We will produce experimental data to test this
01/08/2003
The Crew at UFThe Crew at UF
Rachel CruzIra Thorpe
Alix Preston
RodDelgadillo
MichaelHartmann
ShawnMitryk
GabrielBoothe
DerekKennedy
FormerStudents:
GuidoMueller
Sergei Klimenko
DavidTanner
ShannonSankar
Kim LukasMueller
Movie