Transcript Slide 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
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
p phase
difference
Here the outer resonator is driven above resonance
and the inner resonator is driven below resonance
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
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
x1
X1
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
High order modes of a cylindrical
DUAL detector
Large interrogation area
ACTIVE SUBTASKS
•Noise evaluation of DUAL det.
with selective and wide area
detection
Main activity on
•Development of concaveconvex cavities at room temp.
•Development of the folded
Fabry-Perot cavity
•Development of a selective
readout scheme for wide area
capacitive transducers
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
An hollow cylinder can
work as a DUAL (mode)
detector
the internal diameter is
the length to be measured
for the detection
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
nrext/vs
quadrupolar
modes in red
rint/rext
Mechanical Amplifier
based on the elastic
deformation of monolithic
devices is well known in
mechanical engineering
3 Joints
90 mm
Gain=1/α
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
Optimal design with FEA
Mechanical amplifier for capacitive transducers
4 paired
joints
stable against the
attractive force of
the armatures of the
capacitive transducer
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)
M3
M4
M1
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)
M2
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
Simple cavity (2 mirrors)
10000
FFP 9 mirrors
Photothermal
Laser freq. displacement (Hz/W)
1000
100
10
Mechanical masses
1
0.1
0.01
Mechanical mirrors
0.1
1
10
100
Frequency (Hz)
1000
10000
10000
Laser freq. displacement (Hz/W)
Laser freq. displacement (Hz/W)
10000
100
10
Mechanical masses
Mechanical mirrors
1
0.1
0.01
0.1
1
FFP 17 mirrors
Photothermal
1000
100
Photothermal
1000
Mechanical masses
10
Mechanical mirrors
1
0.1
0.01
0.1
1
10
100
Frequency (Hz)
1000
10000
10
100
Frequency (Hz)
1000
10000