LISA Laser Interferometer Space Antenna Gravitational Physics Program

LISA Laser Interferometer Space Antenna Gravitational Physics Program Technical implications Jo van den Brand NIKHEF – Staff Meeting, January 2006 http: //www. esa. int/science/lisa LISA October 3, 2005

VIRGO & Lisa – Technical activities § Linear alignment of Virgo – § Monolithic suspension of Virgo mirrors – § Improve mirror suspension Lisa electronics – LISA Reduce thermal noise Recycling mirror for Virgo+ – § Keep mirrors and input beam aligned Drag-free control readout

Linear alignment of VIRGO interferometer § Phase modulation of input beam W § Demodulation of photodiode N signals at different output beams – => longitudinal error signals § Quadrant diodes in output beams – => Alignment information – (differential wavefront sensing) § Anderson-Giordano technique – EOM LISA 2 quadrant diodes after arm cavities

Detection Can have 1 normal diode and 2 quadrant diodes at each output port 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 LISA – Continue support for alignment electronics – Make new modules / spare modules – Continue development for new requirements

Developments § Present developments – More modules needed – Installation of 9 th quadrant diode (maybe 10 th) – Spares needed – New Annecy local oscillator boards, compatible with alignment – Phase shifters for standard photodiodes § Possible developments – Substitute Si diodes with In. Ga. As diodes – Better quantum efficiency – Lower bias voltage – => higher power capability Þ lower noise Þ Reduction of electronics noise Þ Better preamplifier: 5 p. A/rt. Hz -> 1. 6 p. A/rt. Hz (? ) Þ 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 Manpower estimate ~ 3 FTE from electronics group LISA phase shifter demodulator Quadrant diode box

Virgo – local control of mirrors Local control of mirrors Present accuracy about 1 micron Feedback systems induce noise Possible application for RASNIC LISA

VIRGO Optical Scheme Input Mode Cleaner (144 m) 3 km long Fabry-Perot Cavities Laser 20 W Power Recycling Output Mode Cleaner (4 cm) LISA

Virgo – inside the central building LISA

Mirror suspension High quality fused silica mirrors LISA • 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

Monolithic suspension § Fused silica fibers § Bonded to mirror § Reduce thermal noise § Needed for Virgo+ § Realized by GEO 600 Weld Silicate (Hydroxy. Catalysis) Bonding LISA

Input mode cleaner § Mode cleaner cavity: filters laser noise, select TEM 00 mode Input beam LISA Transm. beam Refl. beam

LISA - drag free control § § § § LISA 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 LISA § 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 + 2 FTE support

Summary § Linear alignment of Virgo – § Monolithic suspension of Virgo mirrors – § 2 FTE EA Lisa electronics – – LISA 2 FTE EA Recycling mirror for Virgo+ – § 3 FTE electronics 2 – 3 ASICS designers 2 FTE support

Optimized alignment noise budget Maximized power Optimized mirror centering (0. 2 mm) LISA

Scheme of LA electronics Low-pass filter AC: Gain 200 diff. sig. Shot noise Preamp. noise QD box non-diff. sig. DC: Gain 1 Non-optimal treatment of DC signals dominated by ADC noise (but were not foreseen as error signals) LISA VME ADC noise