LISA
Laser Interferometer Space AntennaGravitational Physics Program
Technical implications
Jo van den Brand
NIKHEF – Staff Meeting, January 2006
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
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
Can have 1 normal diode and 2 quadrant diodes at each output port
Detection
Linear alignment setup
Present Virgo noise budget
Control noise
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
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)
QD electronics
demodulator phase shifter
Quadrant diode box
Manpower estimate ~ 3FTE
from electronics group
Virgo – local control of mirrors
Local control of mirrors
Present accuracy about 1 micron
Feedback systems induce noise
Possible application for RASNIC
VIRGO Optical Scheme
Laser 20 W
Input Mode Cleaner (144 m)
Power Recycling
3 km long Fabry-Perot Cavities
Output Mode Cleaner (4 cm)
Virgo – inside the central building
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
Fused silica fibers
Bonded to mirror
Reduce thermal noise
Needed for Virgo+
Realized by GEO600
Silicate
(Hydroxy- Catalysis)
Weld
Monolithic suspension
Input mode cleaner
Mode cleaner cavity: filters laser noise, select TEM00 mode
refbeam
inbeam outbeam
Input beam Transm. beam Refl. beam
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 key technology
Test-mass position sensing:
Capacitive sensing.
Drag-Free control.
FEEP micro-Newton thrusters. NIKHEF and SRON develop ASICS for electronic readout of all LISA signals
Low noise, high resolution ADCs
NIKHEF 2 – 3 ASIC designers
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
–
