T3 DEVELOPMENT OF SELECTIVE READOUT SCHEMES AIM: selection of the normal modes of vibration which carry gravitational signal by means of a suitable design of the test masses and the displacement transducers PARTICIPANTS CNR Istituto di Fotonica e Nanotecnologie (IFN) - Trento CNRS Laboratoire Kastler-Brossel (LKB) - Paris INFN (LENS - Florence, LNL – Legnaro, Genova) Paolo Falferi IFN - Trento 2nd ILIAS-GW Meeting, October 24th – 25th, Palma de Mallorca

DUAL DETECTORS Dual Main Concept Measurement of differential deformations of two nested massive resonators Wideband selective transducers NO resonant bandwidth limit and NO thermal noise contribution from light resonant transducer

Important feature: p phase difference between the modes of internal and external resonators Here the outer resonator is driven above resonance and the inner resonator is driven below resonance

BY MEANS OF A SUITABLE TEST MASS DESIGN SELECTION BY MEANS OF A SUITABLE TEST MASS DESIGN With a suitable design of the test masses it is possible to filter out the modes that do not carry information about the gravitational wave signal QUADRUPOLAR MODES

BY MEANS OF A SUITABLE ARRANGEMENT OF THE READOUTS SELECTION BY MEANS OF A SUITABLE ARRANGEMENT OF THE READOUTS X1 X4 X3 X2 2D quadrupolar filter: X = x1+x2-x3-x4

Example of Thermal and BA noise reduction using selective readout X = x1+x2-x3-x4 X1 X4 X3 X2

SELECTION BY MEANS OF LARGE AREA TRANSDUCERS Local effects have to be considered in the design of the transducer Brownian noise (thermal noise of high order modes) Thermodynamic noise Photothermal noise Small interrogation region means large fluctuations Average over high order modes Large interrogation area High order modes of a cylindrical DUAL detector

Noise evaluation of DUAL det. with selective and wide area detection ACTIVE SUBTASKS Noise evaluation of DUAL det. with selective and wide area detection Development of concave-convex cavities at room temp. Development of the folded Fabry-Perot cavity Development of a selective readout scheme for wide area capacitive transducers Main activity on

An hollow cylinder can work as a DUAL (mode) detector Noise Evaluation Of A DUAL Detector The DUAL concept which works between two modes of two different bodies can work also between two modes of the SAME body the internal diameter is the length to be measured for the detection An hollow cylinder can work as a DUAL (mode) detector the deformation of the inner surface has “opposite sign” for the first and the second quadrupolar mode

+ = The p phase difference concept still holds First quad. mode Second quad. mode + = Frequency DUAL stands for DUAL mode !

A mode selection by means of a suitable test mass design is needed quadrupolar modes in red nrext/vs rint/rext

Mechanical Amplifier Gain=1/α based on the elastic deformation of monolithic devices is well known in mechanical engineering Goals for the mechanical amplifier for DUAL: Broadband (up to 5.0 kHz) Displacement gain factor 1/ ≥ 10 First internal resonance out of the working band Negligible intrinsic thermal noise 3 Joints 90 mm Gain=1/α Optimal design with FEA

Mechanical amplifier for capacitive transducers stable against the attractive force of the armatures of the capacitive transducer 4 paired joints

Two-stage mechanical amplifier In this configuration Gain=10 on 5 kHz bandwidth with SiC Gain=10 on 3 kHz bandwidth with Al

Folded Fabry-Perot (FFP) M1 M2 M3 M4 D F. Marin, L. Conti, M. De Rosa: “A folded Fabry-Perot cavity for optical sensing in gravitational wave detectors”, Phys. Lett. A 309, 15 (2003) Signal:  N Brownian noise:  N Radiation pressure:  N·F (constant) Displacement noise:  1/F  N Linewidth ( bandwidth):  1/(N·F) (constant)

Prototype of FFP fabricated Two parallel rows of mirrors on independent oscillating masses, with resonance frequencies of 1 kHz and 2 kHz Three possible configurations: 2 (simple FP), 9, 17 mirrors The response of the cavity length to a modulation of the intracavity power will be measured: photo-thermal effect mechanical response from the masses mirror surface deformation

Calculated response to modulated laser power