LISA

http://www.esa.int/science/lisa October 3, 2005

LISALaser InterferometerSpace Antenna

Gravitational Physics ProgramTechnical implications

Jo van den BrandNIKHEF – Staff Meeting, January 2006

LISA

VIRGO & Lisa – Technical activities

Linear alignment of Virgo– Keep mirrors and input beam aligned

Monolithic suspension of Virgo mirrors – Reduce thermal noise

Recycling mirror for Virgo+– Improve mirror suspension

Lisa electronics– Drag-free control readout

LISA

Linear alignment of VIRGO interferometer

N

W

EOM

Phase modulation of input beam

Demodulation of photodiode signals at different output beams

– => longitudinal error signals

Quadrant diodes in output beams

– => Alignment information

– (differential wavefront sensing)

Anderson-Giordano technique

– 2 quadrant diodes after arm cavities

LISA

Can have 1 normal diode and 2 quadrant diodes at each output port

Detection

LISA

Linear alignment setup

LISA

Present Virgo noise budget

Control noise

LISA

Present situation

Frascati group is leaving Virgo

– Since 01/2006

Frascati’s responsibilities

– Original design of alignment system

– Strategy, optics, prototype experiments, …

– Design & realization of electronics

Problem

– Continue support for alignment electronics

– Make new modules / spare modules

– Continue development for new requirements

LISA

Developments

Present developments– More modules needed

– Installation of 9th quadrant diode (maybe 10th)

– Spares needed

– New Annecy local oscillator boards, compatible with alignment

– Phase shifters for standard photodiodes

Possible developments– Substitute Si diodes with InGaAs diodes

– Better quantum efficiency

– Lower bias voltage

– => higher power capability

lower noise

Reduction of electronics noise Better preamplifier: 5 pA/rtHz -> 1.6 pA/rtHz (?)

DC signals: pre-amplification / pre-shaping

– Fast quadrant centering system

– (Napoli is working on that)

– LA noise limits sensibility (especially at low frequencies)

LISA

QD electronics

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odul

ator

phas

e sh

ifte

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Quadrant diode box

Manpower estimate ~ 3FTEfrom electronics group

LISA

Virgo – local control of mirrors

Local control of mirrorsPresent accuracy about 1 micronFeedback systems induce noisePossible application for RASNIC

LISA

VIRGO Optical Scheme

Laser 20 W

Input Mode Cleaner (144 m)

Power

Recycling

3 km long Fabry-Perot

Cavities

Output Mode

Cleaner (4 cm)

LISA

Virgo – inside the central building

LISA

Mirror suspension

High quality fused silica mirrors

• 35 cm diameter, 10 cm thickness, 21 kg mass

• Substrate losses ~1 ppm

• Coating losses <5 ppm

• Surface deformation ~l/100

Superattenuators

Possible contributions:

Virgo+ will use monolythic suspension

Input-mode cleaner suspension

LISA

Fused silica fibers

Bonded to mirror

Reduce thermal noise

Needed for Virgo+

Realized by GEO600

Silicate (Hydroxy- Catalysis) Bonding

Weld

Monolithic suspension

LISA

Input mode cleaner

Mode cleaner cavity: filters laser noise, select TEM00 mode

refbeaminbeam outbeam

Input beam Transm. beam Refl. beam

LISA

LISA - drag free control

SRON Test equipment for position sensor read-

out electronics in on-ground tests of the satellite system

Simulation software modules of the position sensors, used in system simulations

TNO-TPD Test equipment of the Laser Optical Bench Decaging Mechanism (TBC)

Bradford Engineering Cold Gas propulsion (TBC)

LISA

LISA key technology

Test-mass position sensing: Capacitive sensing.

Drag-Free control.

FEEP micro-Newton thrusters. NIKHEF and SRON developASICS for electronic readoutof all LISA signalsLow noise, high resolution ADCsNIKHEF 2 – 3 ASIC designers+ 2 FTE support

LISA

Summary

Linear alignment of Virgo– 3 FTE electronics

Monolithic suspension of Virgo mirrors – 2 FTE EA

Recycling mirror for Virgo+– 2 FTE EA

Lisa electronics– 2 – 3 ASICS designers– 2 FTE support

LISA

Optimized alignment noise budget

Maximized powerOptimized mirror centering

(0.2 mm)

LISA

Scheme of LA electronics

ADC noisePreamp. noise

Shot noise

Low-pass filter

AC: Gain 200

DC: Gain 1

diff. sig.

non-diff.sig.

Non-optimal treatment of DC signalsdominated by ADC noise(but were not foreseen as error signals)

VMEQD box