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From Quantum to Cosmos: Fundamental Physics Research in Space International Workshop, Washington, D.C. USA, May 22-24, 2006

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Technology Development for Fundamental Physics Missions in the context of the GP-B Lessons Learned

Robert L. ByerDepartment of Applied Physics

Stanford University

AbstractThe lessons learned from the GP-B experiment have implications for future fundamental physics missions in areas that range from operational and commissioning of a drag free science mission to details of technology associated with proof mass materials, patch effects on coatings, charge control, and data rates required for mission operations. Examples of future missions that require drag free control include STEP, LISA Pathfinder/ST-7 and LISA. In particular, LISA technology has been under development in both Europe and the United States with the goal of understanding the noise and sensitivity for drag fdree operation at 10^-15 m/sec^2, fully five orders of magnitude beyond the demonstrated sensitivity for the GP-B mission. Achievement of these technology goals in light of experience gained through GP-B will be discussed.

From Quantum to CosmosAirlie Center

Warrenton, VAMay 21- 24, 2006


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Contents

LISA and LIGO at the beginningLISA at the beginningLIGO current status

ST-7/GRS Program Technology Development for the LISA- PF

(descoped – May 2005)

GP-B; Lessons LearnedOrganization, Structure and ManagementTechnology Development, testing and modelingFlight operations and commissioning

Future conceptsBig Bang Observer The Universe; the Ultimate Laboratory


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LISA Concept

Peter Bender holding 4x4cm Au/Pt cube Schematic of LISA in 1988 Expected Launch date of 1998 (now >2015)

Laser power 1WLaser stability extremely highLaser reliability > 5 years

Gravitational waves opena new window on universe

Detect amplitude and phaseof gravitational waveswith sensitivity to detect backthe era of galaxy formation.


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LISA Mission – Pre-Phase A Study 1995

LISA - Laser InterferometerSpace Antenna

Phase A Study - 1995Joint mission NASA and ESA

3 satellites in solar orbit1 W laser - Nd:YAG NPRO

5 million km interferometer path 30 light seconds round trip delay

Scheduled for launch in 20151 year to station, 5 year mission

Will detect binaries in our galaxyWill detect massive Black Holes at

Cores of most galaxies


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LISA and LIGO Detection Bands

Kip Thorne,CalTech


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Probing the Region near Massive Black Holes

LISA will observe compact stars scattering near Massive Black Holes

Orbits of compact stars near Massive Black Holes will evolverapidly and emit gravitational

waves

The warping of space-time caused by a black hole spiraling into a massive black hole. Courtesy of K. Thorne,

Caltech

Stellar-mass black holes orbiting massive black holes provide precision tests of

gravitational theory in the high-field limit


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Ground-based Gravitational Wave Detectors

• LIGO, VIRGO, GEO, TAMA … ca. 2004– 4000m, 3000m, 2000m, 600m, 300m inteferometers built

to detect gravitational waves from compact objects


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LIGO Observatories

LIGO Hanford Observatory, WA

LIGO Livingston Observatory, LA

simplified optical layout


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Peter Fritschel, Commissioning Report,15 Aug 2005, LIGO # G050371

Best Strain Sensitivities for LIGO Interferometers S1 (2002) – S5 (2006)


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Peter Fritschel, Commissioning Report,15 Aug 2005, LIGO # G050371

Recent LIGO Sensitivity

S5 Performance - 14.5 Mpc


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Contents


ST-7/GRS Program Technology Development joint with LISA- PathFinder


GP-B; Lessons LearnedOrganization, Structure and ManagementTechnology Development, testing and modelingFlight operations and commissioning



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ST7/GRS Project Management Team

Scott WilliamsDevelopment Manager

Robert L. ByerPrincipal Investigator

Sasha BuchmanProject Manager

Dan DeBraProject Technologist

Dave KlingerManaging Director

Mac KeiserProject Scientist

Stanford University


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ST7/GRS Staff

John HansonSystems Engineering &Control Systems

Bill DavisMechanical Systems

Dave FernandesSoftware Manager

Dale GillTest Mass

Dave LaubenMeasurement

Systems

Rick BevanResource Manager

Dorrene RossPerformance Assurance(it was this or her cat)


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GRS Mechanical Status

Subsystem Prototype Eng. Model Flight

Test Mass

Housing

Caging System

Chassis

Plunger Interface

Insulator

Guide

Solder Joint

Heater

Bellows

Insulator

Chassis Well

Solder ActuatorRev. 3.09/30/04


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GRS Electrical Status

Subsystem Prototype Eng Model Flight

Feedthroughs

Charge Management

Integrated Avionics

Readout Electronics


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Salient Features• Test mass noise < 2.8x10-14 m/s2/√Hz, 1 mHz

to 30 mHz

• Position measurement to < 3 nm/√Hz, 1 mHz to 30 mHz

• Accelerometer mode

• Validation of thruster performance

• Force noise diagnostics

• Validation of drag free environment models

Gravitational Reference Sensor Technologies• Test mass is 4-cm cube of Au coated Au/Pt alloy• Beryllia housing with plated Au electrodes• Vacuum system supporting 10-5 Pa EOL• Caging system capable of supporting launch loads and re-caging• Capacitive sensing system providing < 3 nm/√Hz measurement• Electrostatic forcing system providing 2x10-7 m/s2 peak

acceleration

Gravitational Reference Sensor (GRS)

GRS Overview

GRS Sensor Unit

EM Proof Mass

Housing Prototype


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Stanford University ST7/GRS Team April 2005

Stanford ST-7/GRS Team - April 2005

Descoped – May 2005


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The Stanford LISA Team - 2006

*Alex GohDan DeBra*Aaron Swank*Graham Allen*John ConklinNorna Robertson*Sei Higuchi

Not shownKe-Xun SunSasha BuchmanMac KeiserBob Byer

*graduate students

The Stanford LISA team

Fairbank’s Principle – Disaster compels Creative Thought.


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The Stanford LISA Lab

Graham Allen: Optical Sensing

Patrick LuGrating design and fabrication

John ConklinCenter of Mass MeasurementOptical shadow sensor

Aaron SwankMass distributionMoment of Inertia measurement

Ke-Xun Sun (staff)External Interferometry

Sun & Sei HiguchiLED UV charge management system

Technologies equally applicable to LISA configurationsPh. D Graduate Students heavily involved in LISA research

Sei HiguchiThermal control

Allex GohCharge modeling


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GRS Heritage

• Inertial Sensor based on Stanford experience withTRIAD (Stanford/APL, 1972, < 5x10-11 m/s2 RMS over 3 days)GP-B (Stanford, launched 4/ 04, < 2x10-12 m/s2/√Hz at 5x10-3 Hz )

• Earlier sensors used spherical test massesFewer degrees of freedom to control

• Proposed LISA sensor uses a faceted test massControl position of laser beam on test massAllows validation at picometer level– Test mass is 4-cm cube of Au/Pt alloy

Dense, to reduce motion in response to forcesLow magnetic susceptibility, used on TRIAD

• Charge ManagementCharge Management design derived from GP-BUV Source is GP-B flight spare.

GP-B Flight Gyroscope

TRIAD sensor- 1972


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The Drag Free Performance ChallengeImprove the State of the Art by 100,000

Disturbance Reduction

System

To Payload Processor

Drag Free Control Laws

NThrusters

Capacitive Sensor/Actuator

Vacuum Mgmt

Caging Mechanism

Charge Mgmt

Electronics

PM

GRS

Gravitational Reference Sensor

Disturbance Reduction

System

To Payload Processor



NThrusters

NThrusters

Capacitive Sensor/Actuator

Vacuum Mgmt

Caging Mechanism

Charge Mgmt

Electronics

PM

GRSGRS

Gravitational Reference Sensor

High Precision Reference • Inertial Anchor• Accelerometer• Gyroscope

10-15

10-14

10-13

10-12

10-11

10-10

10-9

10-8

10-7

10-4 10-3 10-2 10-1

Spec

ific

For

ce N

oise

(m

/s2 /¦H

z)

Frequency (Hz)

LISA

EX-5

GP-B

GRACE

TRIAD

DRSMinimum

Goal

TRIAD: 5x10-11 ms-2

RMS over 3 days

Microthrusters

SpacecraftProof Mass

Precision PositionMeasurement

Microthrusters

SpacecraftProof Mass

Precision PositionMeasurement


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Advanced DRS Concepts - Stanford

• Autonomous Gravitational Sensor – Separation from S/C

Interferometry– Measure PM position in housing– Use housing for interferometry

• Single proof mass (PM) per S/C• Non constraint GRS• Multiple stage disturbance isolation • Fiber utilization• Reflective Optics

Signal

LO

GRS with double sided grating forPM and interferometer reference


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Contents


ST-7/GRS Program Technology Development for LISA- PF


GP-B; Lessons LearnedOrganization, Structure and ManagementTechnology Development, testing and modelingFlight operations and commissioningDevelop and maintain a great team



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Technology Development for

LISA in the context of the

GP-B lessons learned

Stanford University

Orbit

GP-B Lessons Learned


ByerGroupGP-B Lessons Learned

• Operations and simulation are necessary. –Significant data rates are to be expected for LISA

– High fidelity simulation tools are needed to support operations planning and anomaly resolution for LISA.

• Surface physics of coatings are important. – Probable patch effects observed on GP-B. – Studies of spatial and temporal variations as well as impact of contamination are needed for LISA.

• Charge management is important. – Charge management was essential to establish GR-B operation. GP-B demonstrated concept and successful operations. – A larger dynamic range is needed for LISA.

• Simplify design and reduce coupled degrees of freedom.–Interacting multiple degrees of freedom and cross-coupling complicates operation concepts and instrument mode definitions.–LISA system must be designed for realistic operations.

• The noise tree is critical– Maintenance and test validation of noise budget parameters was critical to enable engineering decisions for GP-B. – Cross-coupling must be carefully modeled for LISA.

• Data Analysis• Ground Simulations

• Surface Coatings

• Charge management

LISA Technology

• Mod GRS – reduce X-talk & coupled DOF


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Low-g Inertial Sensor

Design and Test Facility

John MesterDavid Hipkins

William BenczeJohn W. Conklin

Stanford University

9 December 2005

GP-B Design and Hardware in the Loop Test Facility


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Simulator Facility in Action

• GP-B hardware in the loop simulator during flight unit testing:

– Functional verification

– Performance characterization

– Command sequence development and test

– Control algorithm development and tuning

– Dynamic modelling of proof mass sensor


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Hardware in the Loop Invaluable for Verification

• Hardware-in-the-loop verification– Fully integrated sensor-control-actuator

simulations, operating across payload/spacecraft interface

– Modular architecture

• Realistic simulation for ops training– Common development environment– High fidelity spacecraft bus and CPU– Integrated Mission Ops Center


ByerGroupExample: Initial Orbit Checkout

• Mission planning– Planned 6 weeks lasted 4 months

• The unexpected (> 100 anomalies)– Thruster failures– Rad induced MBEs (10 expected rate) – Computer reboots– Forward antenna degraded– Star sensor software difficulties

• Spacecraft commanding– 10,000 commands to spacecraft during IOC












LISA Technology



ByerGroupThe Patch Effect in LISA

• The patch effect refers to spatial variations in surface potential

• It can arise due to polycrystalline structure - potential varies with orientation

• It can be affected by presence of contaminants

• Patch fields are present on test mass and housing wall surfaces

• Interactions between patch fields cause forces that change with position, both in x and z directions - patch effect causes stiffness

• Combination of stiffness and residual relative motion of test mass and spacecraft produces an acceleration noise term

zx

d

test mass surface

housing wall surface


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Kelvin Probe

• The Kelvin probe measures contact potential difference (Vc) between a conducting

specimen and a vibrating probe tip

• It is a non-contact, non-destructive vibrating capacitor device

• A backing potential Vb electrically connects specimen and probe tip

• When Vb = -Vc, the circuit is balanced

• Null condition can be detected accurately• The Goddard probe is a custom-built UHV system with scanning capability

Kelvin’s original apparatusView of probe (diameter 3mm)

sitting above samples


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Materials StudiedDr. Norna Robertson (Stanford, Glasgow)

• Test mass: – Au/Pt with gold coating

• Housing walls:– substrate:

beryllia, alumina or titanium (for inserts)– coatings:

gold, diamond-like carbon (DLC), indium tin oxide, titanium carbide

+ various underlying layers chosen for adhesion, conductivity and smoothness

Example of samples ready for measurement in the Kelvin probe

Clockwise from top left: AuNb on alumina, DLC/Ti/Au/Nb on beryllia, DLC/Ti/Au/Ti on titanium, DLC/Ti/Au/Ti on alumina

Note: many of the samples were precision coated in-house at Stanford


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Spatial scan example

Gold-niobium on alumina (p-to-p 13 mV)


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Kelvin probe measurements: investigations of the patch effect with applications to ST-7 and LISAN A Robertson, J R Blackwood, S Buchman, R L Byer, J Camp, D Gill, J Hanson, S Williams and P ZhouClass. Quantum Grav. 23 No 7 (7 April 2006) 2665-2680

Conclusions to date

Spatial Variations: • Peak to peak ~6 mV to ~50 mV,

Standard deviation () ~1 mV to ~10 mV• Extrapolate to relevant spatial scale:

Multiply by factor of ~3 to ~7.5 (model dependent)

We conclude results meet 100 mV requirement assuming extrapolation valid • The data also revealed evidence of behavioral trends with pressure and

probable contamination effects which could affect the interpretation of the results

Temporal Variations:• In general lower ambient pressure decreased variation• Current accuracy of instrument (~1 mV) is limiting measurements at level

above that needed to test for LISA requirements






• Charge management is important. – Charge management was essential to establish GP-B operation. GP-B demonstrated concept and successful operations. – A larger dynamic range is needed for LISA.






LISA Technology



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Discharge of Gyro #1

Typical charging rates ~ 0.1 mV/day

GP-B Charge Management - Rotor Electric Charge

UV lamps and switches assembly

Ti Steering Electrode


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UV LED vs. Mercury Lamp

UV LED – TO-39 can packaging– Fiber output with ST connector– Reduced weight– Power saving – Reduced heat generation, easy

thermal management near GRS

GP-B CMS in Flight- 2 Hg Lamps- Weight: 3.5 kg- Electrical Power 7~12 W

(1 lamp on, 5 W for lamp, 5 W TEC cooler)


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Positive and Negative AC Charge Transfer

UV LED and bias voltage modulated at 1 kHz – Out of GW Signal Band


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UV LED Charge Management System Have Potential Significant Scientific Pay Off

Direct Replacement ofMercury Lamp with UV LED ---

Save electrical power ~15 W per spacecraft

• The power can be used to increase laser power by 2x--– Enhance sensitivity by 41%, – Increase event rate and

detection volume by a factor of 282%.

– Significant astrophysical observational pay off

-2E-13

0

2E-13

4E-13

6E-13

8E-13

1E-12

1.2E-12

1.4E-12

1.6E-12

1.8E-12

-4 -3 -2 -1 0 1 2 3 4

Forward Bais Voltage (V)

Dis

char

ge

Rat

e (A

/uW

)

Hg Lamp (254nm) UV LED (257nm)

Comparable Discharge Rates For First UV LED Experiment












LISA Technology



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LISA Interferometer Space Antenna


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LISA Interferometer Basics

• Transponder technique– Incoming beam locked to local laser– Overcomes low power from far spacecraft

• Gravitational signal– Phase difference of arms measures–

• Correction of common phase shifts due to optics fixed to S/C

– Reflected signals from back of test masses

• Time Delayed Interferometry (TDI) – Frequency noise correction by signal average of arms– 12 interference beat signals measure as function of time

• In/Out beams at each optical system (6) @ Out/adjacent Out (6)

– Combinations of TDI• Gravitational signal without laser frequency noise• Instrument noise without gravitational signal 40 pm Hz-1/2 from 10-4 Hz to 10-1 Hz


ByerGroupLISA Two-Mass Configuration

Proof Mass

ProofMass

To and from Remote Spacecraft

Waveplate

Transmissive optics

Sensitive path

• Elaborated interferometer structure• Interlinked scheme for re-correlation• Long sensitive path• Coupling throughout the system• dn/dT problem in transmissive optics

• Alignment coupling


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Modular GRS Architecture Presented at LISA 5th Symposium July 2004

Outgoing Laser Beam

Proof Mass

Large gap

GRS Housing

Optical ReadoutBeam

Telescope

Incoming Laser Beam

Details shown next slide

• Single proof mass

• Modularized, stand-alone GRS

• GW detection optics external to GRS

• External laser beam not directly shining on test mass

• Internal optical sensing for higher precision

• Large gap for better disturbance reduction

• True 3-dim drag-free architecture

• Determine the geometric center and center of mass

Sun, Allen, Buchman, DeBra, Byer, CQG (22) 2005 S287-S296

Modular GRS Concept


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Modular GRS Compact, Reflective Optical Sensing Configuration

Double Sided Grating not transparent low known expansion interferometer mirror

Outside GRS Housing Grating at 1064 nm or 532nmfor polarization separated transmission and heterodyne detection

Inside GRS Housing: Grating at 1534

nm or shorter wavelengths for reflective resonant optical readout

Proof Mass

External laser interferometer

HousingInternal optical sensor(Graham Allen’s Lab)Microwatts of laser power

Grating


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Modular GRS Simplifies Control

DOFs Comparison Table

Mission &

DOF Counts

GP-B LISA MGRS

One SC

Displacement

6 9 3+3

Angular 3 9 3

Telescope 1 1

Total DOF 19 3+7

Total Fleet DOF 9 57 (3+7)x3

Control Matrix Dimension

9x9 57x57 30x30

Time to setup experiment

~

4 mo.

>

4 mo

• Transfer matrix contains diagonal blocks thanks to non-direct illumination

• Self calibration mechanism reduces command flow


ByerGroupLessons Learned

GP-B Lessons Learned– Surface physics of

coatings are important. – The noise tree is critical. – Detailed operations

planning augmented by hardware simulation is necessary.

– Interacting multiple degrees of freedom and cross-coupling complicates instrument operations.

– Charge management is essential to establish GRS operation.

ST-7 Lessons Learned– Further test mass

technology development is needed.

– Combining control and measurement electronics is hard.

– Caging of soft faceted AuPt test mass without surface damage is difficult.

– Vacuum requirements complicate GRS design.

– Requirements constrain housing design.


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When we achieve our goals, what will LISA be able to “see”?

• No limits!– LISA will be able to see supermassive

black hole mergers back to the beginning of the universe (if they are there)

Most powerful events in the universe!Release a billion times more energy in a minute than our sun does in its lifetime!

How many are predicted?

As many as 10 supermassive black hole mergers observable per year (Maybe lots more!?)

LISA will probe the ultimate limits of mass, energy, & gravity!


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John ConklinGraduate student Aero-Astro GP-B/LISA


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time

?What is the Origin of the Universe?

What role did Quantum Gravity play in the birth of the Universe?

The fabric of Space & Time: Was Einstein right?

How did Black Holes form in the early Universe?;Are Gamma Ray Bursts related to Black Holes?

What is Dark Matter? Does Dark Energy really exist?

How did Galaxies form? Which came first, Black Holes or Galaxies?

How does our star work? Is Life in our galaxy unique?

What is the future fate of the Universe?

Exploration of the Universe -The BIG questions

The Universe is our ultimate Laboratory!


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LISA Orbits

Three spacecraft in triangular formation; separated by 5 million km

Spacecraft have constant solar illumination

Formation trails Earth by 20°; approximately constant arm-lengths

1 AU = 1.5x108 km


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LISA - Massive Black Holes Binaries

• Precision tests of dynamical non-linear gravity

• The role of massive black holes in galaxy evolution

• Fraction of galactic mergers forming massive black holes•Timing of the earliest massive black hole mergers?

Answers to basic questions in physics and astrophysics

Chandra image of NGC6240 a super massive black hole binary

Merging galaxies NGC4038 and NGC4039. by Hubble Space Telescope. Courtesy of B. Whitmore,

Space Telescope Science Institute & NASA


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Laser Source for LISA Flight

Block diagram of the MOFA laser system

Laser Oscillator(NPRO orFiber laser)

Fiber Amplifier

Reliable Pump Diode Modules

Output Filter and Collimator

WDM

MOFA configuration - NPRO or fiber laser oscillator

- All Fiber configuration preferred (No open gap requiring alignment rigidity)

- Fiber amplifier with multi-pump modules for redundancy and fail/operate reliability

- Frequency & Intensity stability should meet LISA requirements

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- Fiber laser

- 136 W fiber amplifier

- Laser stabilization

- Noise reduction

- Fail/Operate laser


ByerGroupSecond Harmonic 532 nm Laser for LISA

LISA sensitivity comparison using 1W 1064 nm laser (upper curve) , 2W 1064 nm laser (middle curve) and 2W 532 nm SHG source (lower curve).

Hzmcm30

m105

W3.0

nm10641110~

2

9

2

1

0

2

3

12

D

L

Px

Shorter wavelength- Scales as 1.5, more

effective than simply raising power

- Gain in shot noise limited region

- Two colors for LISA, enhanced efficiency

- Iodine hyperfine transition for laser stabilization


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Big Bang Observatory BBO

Arms are 50,000 km

2009 ST-7 2015 LISA2025 BBO


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Stochastic gravitational wave backgroundStochastic gravitational wave background

•Detect by cross-correlating interferometer outputs in pairs• Hanford - Livingston, Hanford - Hanford

•Good sensitivity requires:• GW > 2D (detector baseline)• f < 40 Hz for L - H pair

• Initial LIGO limiting sensitivity: 10-6

Analog from cosmic microwave background -- WMAP 2003

The integral of [1/f•GW(f)] over all frequencies corresponds to the

fractional energy density in gravitational waves in the

Universe

d(ln f ) GW ( f )0

GW

critical


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Aaron Swank


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Sei Higuchi


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Spacecraft

Two optical assemblies– Proof mass and sensors– 30 cm telescope– Interferometry: 20 pm/√Hz– 1 W, 1.06 µ Nd:YAG lasers

Drag-free control– Positioning to 10 nm/√Hz– Attitude to 3 nrad/√Hz


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Payload


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LISA Systems

Test mass Optical bench

Y tube

PayloadSpacecraft Propulsion module

Launchconfiguration

byer group from quantum to cosmos: fundamental physics research in space international workshop,...

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