1. 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

2. 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

3. 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

4. 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

5. 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

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

7. 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

8. 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

9. 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

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

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

12. 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

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

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

15. 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)

16. 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

17. Calculated response to modulated laser power