LISA Benchtop Experiment

at UF

mueller@phys.ufl.edu

Guido Mueller University of Florida

21st July 2005

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