Report on WG3 A European strategy for future detectors
M. Bonaldi1, V. Fafone3, R. Flaminio2-10, H. Lück5, M. Punturo6, K. Strain7,
G. Losurdo8, G. Frossati4, L. Gottardi4, G. Cagnoli8-9.
1
IFN, Trento, Italy
European Gravitational Observatory, Cascina, Italy
3
INFN Laboratori Nazionali di Frascati, Italy
4
Leiden University, The Netherlands
5
Max-Planck-Institut für Gravitationsphysik, AEI, Hannover, Germany
6
INFN, Perugia, Italy
7
University of Glasgow, Great Britain
8
INFN, Firenze, Italy
9
University of Glasgow, Glasgow, UK
10
LAPP/CNRS, Annecy, France
2
Coordinators: H. Lueck (University of Hannover) and M. Punturo (INFN, Perugia)
1. Introduction
Activities developed in continuation of what has been declared in the previous report (“Final
Remarks” section). The GEO and Virgo collaboration decided to join part of their efforts in a
common strategy to design advanced gravitational wave detectors. A WP3 meeting has been
devoted to this subject (Glasgow “GEO-Virgo” meeting) and an international workshop has
been organized by WP3 members in Perugia. Because of the importance of the discussed
items, it has been decided to enlarge the participation to the WP3 meetings as much as
possible, inviting WP1 and WP2 members and other experts to the meetings. The Auriga,
MiniGRAIL and ROG collaborations planned the medium and long term development of
resonant mass detectors technology. This subject was discussed in a dedicated WP3 meeting
(Glasgow “Auriga-ROG-MiniGRAIL” meeting), and in the Perugia international workshop,
and a common document on the future developments of resonant mass detectors was
submitted to the GWIC (Gravitational Wave International Committee).
2. Status of planned tasks
2.1 Evaluation of the proposed short term improvements
During each meeting, experts reported about technologies under development in the different
experiments. Starting from these reports a series of short term upgrades have been identified.
Obviously, since the topology and the status of the several detectors is different, the foreseen
upgrades are different.
Virgo+
For the Virgo detector the following improvements have been identified as short term
upgrades:
 Increase of the power circulating in the Fabry-Perot cavities by inserting a laser
amplifier in the injection system. This solution will permit to improve the sensitivity
of the detector in the “high” frequency range, without major changes in the
interferometer. The impact on the specification of the injection system is under
evaluation particularly taking the thermal lensing of the Faraday Isolator into account.
 Installation of a thermal compensation system. This should allow compensation of the
thermal lensing due to the larger power circulating in the interferometer and deposited
in the input mirrors. It would also permit a fine tuning of the reflectivity of the
recycling mirror.
 Improvement of the actuation system, through a lower noise driving electronics. With
the installation of a split path electronics, one for the locking and one for the control of
the interferometer, it will be possible to acquire lock exerting a large (noisy) force and
then maintain lock with a lower noise servo.
 Realization of a monolithic fused silica suspension for the Virgo main mirrors. This
would reduce the thermal noise of the suspension. Moreover the present mirrors made
in Herasil will be substituted with less lossy Suprasil substrates. This change will also
allow to take advantage from the more recent developments in coating technology thus
reducing both thermal noise and optical losses. The compliance with the stringent
cleanliness and safety requirements of Virgo must be still verified in a strongly
recommended engineering activity that should determine if this is really a short term
upgrade
In Figure 1 the expected sensitivity of Virgo+ is reported compared to the Virgo nominal
sensitivity. The sensitivity at low frequency of the detector should be limited by the
Newtonian noise. In Table 1 the detection distance for the Virgo+ detector is reported.
The Virgo+ upgrades have been submitted to the EGO council and to the INFN commission
n.2. The program has been approved and it has just started.
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10
(a) Virgo+ sensitivity
(b) Virgo+ (old mirr. th. noise model)
(c) Virgo+ without NN
(d) Nominal Virgo
(e) Newtonian Noise (CC)
-19
h(f) [1/sqrt(Hz)]
10
-20
10
(a)
-21
10
(c)
(d)
-22
10
(b)
(e)
-23
10
1
10
100
1000
10000
Frequency [Hz]
Figure 1 - Virgo+ sensitivity (a) compared to the Virgo one (d). The gravity gradient noise ("newtonian
noise") (e) limits at low frequency the expected sensitivity of the detector.
Event Rate/year
Range (Mpc)
NS - NS
0.025 - 10
114
NS – BH
10-3 – 15
230
BH – BH
3 10-2 – 90
584
SuperNovae
1
10
Table 1 - Detection distance and event rate in Virgo+ for different astronomical sources
GEO-HF
Similar to VIRGO the GEO600 detector will get several sequential upgrades in the timeframe
of 2007 to 2014 in order to provide scientifically useful data in the frequency range above 500
Hz to the GW detector network. The following upgrades are under discussion:
 The laser power currently available is 12 W at the output of the slave laser. This
power can be increased in a stepwise way by first inserting amplifier stages into the
beam path and later on switch to a different high power laser system. Within the
collaboration there are amplifier stages with a power of up to 50 W. A high power
laser system of 200 W is also available. The changes required for the input optic
stages are currently under investigation.
 GEO600 uses two sequential mode cleaners to spatially clean the laser light before
sending it into the interferometer. With enhanced laser light power the finesse of the
mode cleaners needs to be reduced in order to reduce radiation pressure effects and
avoid problems associated with thermal lensing. This can either be done by rotating
the polarization inside the mode cleaners by 90 degrees or by exchanging the mode
cleaner mirrors. Both alternatives are being investigated.
 The high circulating light power causes a thermal lens inside the beam splitter. Due to
the extraordinarily low absorption of the GEO600 beam splitter, which has been
measured to be below 0.25 ppm/cm, the light power inside the Power-Recycling
cavity of GEO600 can be enhanced to about 40 kW before the thermal lensing yields
an unstable cavity. With enhanced laser power this problem becomes more severe.
Thermal compensation of this lens by irradiating the beam splitter with an auxiliary
heater beam can reduce this effect. With optimized thermal compensation the power
may be enhanced to levels of about 100kW at the beam splitter improving the shot
noise limited sensitivity by a factor of 4.
 Further reduction of the shot noise can be achieved by injecting squeezed light into
the interferometer via the output port. This technique, currently under development
in the laboratories in Hannover, has already been demonstrated there at a table-top
dual recycled interferometer and can be implemented towards the end of the
timeframe mentioned above.
 Depending on the bandwidth of the source to be observed with GEO HF shaping the
response of the Signal Recycling cavity to a narrower bandwidth would allow a
further reduction of the shot noise within the resonance bandwidth of the signal
recycling cavity. An exchange of the main optics of GEO600, i.e. the folding mirrors,
the inboard (end) mirrors and the beam splitter is an option for decreasing the thermal
noise in the frequency range around 1 kHz. Especially mechanical losses that occur in
the coating of the mirrors cause thermal noise in this frequency range. There are
promising developments that may allow to reduce these losses in a few years time.
This will depend on the availability of additional funding, not yet approved.
Figure 2 shows the possible sensitivity curve for GEO HF for a circulating light power of
about 100 kW, an effective squeezing factor of 6dB and 700 Hz bandwidth of the Signal
Recycling cavity. For the total noise budget it is assumed that coating losses can be improved
by about a factor of four in comparison to current conservative estimates. Radiation pressure
effects which play a role at frequencies below a few hundred Hz have been neglected.
h(f) [1/sqrt(Hz)]
.
10
-21
10
-22
10
-23
10
-24
shot
thermorefractive
coating
substrate
suspension
seismic
total
10
2
10
3
Frequency [Hz]
Figure 2 - GEO HF possible sensitivity
The real contributions of thermal noise can still not be predicted as some of the important
material parameters are not yet well known. Effort is underway to obtain more complete
material data.
As all thermal noise contributions roll off towards higher frequencies the peak sensitivity can
be improved at the costs of signal bandwidth by increasing the reflectivity of the Signal
Recycling mirror. A reduction of the bandwidth by a factor of two would allow to reach a
sensitivity below 10-23/sqrt(Hz) at frequencies above a few kHz. This is the frequency range
where gravitational waves originating from a variety of neutron star modes are expected.
Which scenario will give the best scientific return is currently under investigation and will to
a large extend depend on the thermal noise that will be observed in GEO600..

Resonant bar detectors: AURIGA, EXPLORER and NAUTILUS
The currently operating resonant bar detectors (Auriga and the ROG detectors Explorer and
Nautilus) will be upgraded in the time frame 2006-2007. The target is to maintain their
sensitivity comparable (in their 100 Hz detector bandwidth) with the sensitivity of the best
operating interferometers and to give useful information on occurring astrophysical events
during the planned future joint observation with interferometric detectors. These upgrades
will be scheduled in order to keep always at least two detectors in data taking.
The planned upgrades are :
The implementation of more sensitive readouts and more efficient electromechanical
transducers on EXPLORER, AURIGA and NAUTILUS . A further improvement can be
obtained by cooling AURIGA and NAUTILUS to ultracryogenic temperature. 100 mK, like
in the first run, is a reasonable target. The 100 mK curves in Figure are obtained by assuming
that Q- factors do not depend on temperature, and that electrical noise and mechanical noise
scale with T. As regards the electrical noise, the scaling of the thermal noise in a high Q
resonator at ultracryogenic temperature has already been demonstrated. Finally, the SQUID
noise is assumed to saturate at a temperature of 200 mK, as observed in separate bench tests.
In the same time, one may try to reduce the electrical noise by increasing the transducer bias
field.
Figure 3 - AURIGA sensitivity: theoretical prediction by three-modes numerical model with most parameters of the
model directly measured
“in2005
situ”. Left: current sensitivity. Rigth: foreseen sensitivity at ultracryogenic operation
Explorer
Antenna mechanical
with a moderate field increase
Transducer mechanical
Electrical+ SQUID backaction
SQUID additive
Total
10
-19
10 -19
10 -20
)
)
-1/2
-1/2
Shh (Hz
-20
Shh (Hz
10 -21
10 -22
800
10
Data 76
Nautilus 2005
Antenna mechanical
Electrical+ SQUID backaction
SQUID additive
Transducer mechanical
Total
10
10
850
900
Frequency (Hz)
950
1000
-21
-22
850
900
950
1000
1050
Frequency (Hz)
Figure 4 - Left: EXPLORER current sensitivity (black curve) and expected sensitivity (red curve) after
the upgrade of the readout. Rigth: NAUTILUS current sensitivity (black curve) and expected sensitivity
(red curve) after the upgrade of the readout and the cooling to 0.1K. The theoretical curves are computed
using a full three-modes numerical model.
Resonant spherical detector
MiniGRAIL
MiniGRAIL is close to start the first scientific run. The spheroidal modes will be monitored
by three or four capacitive transducers. In order to fully exploit the sphere capability to
reconstruct all the GW parameters and the arrival direction, the near term planned upgrade
will be the installation of the complete readout set up made of six transducers in the proper
geometrical configuration and, as for bar detectors, the use of quantum limited SQUID
amplifiers. The table below shows the expected MiniGRAIL strain amplitude and spectral
strain amplitude within a band of 230Hz for 100, 10 and 1 hυ SQUID sensitivity. A required
condition is to obtain a ratio T/βQ < 2TN where β is the coupling parameter, T is the
thermodynamic sphere temperature and Q is the mechanical quality factor of the spheretransducer system. At present the best values for MiniGRAIL were T=0.06K, β=10-2 and
Q=6x105 which gives T/βQ=1x10-5 and an expected spectral strain sensitivity of 3x10-22
within a band of ~200 Hz , requiring a SQUID with a noise of 20 hυ. This is quite close to
what the Auriga and ROG groups have already achieved. Our most immediate goal is now to
improve our SQUIDs to reach the above sensitivity and go beyond that by efficiently cooling
the electrons of the SQUID shunt resistances. A general improvement on stability and noise
will be achieved by lead-plating the two shields around the sphere and transformers and
covering them with high permeability “Glasmet”metal tape to produce a near-zero field
around the transducers. Further improvement of the T/βQ parameter will be possible by
lowering the temperature of the sphere, by improving the coupling β with higher capacitance
transducers and possibly higher Q of the transducers, since the sphere itself had Q>106.
EN
TN
Teff

f
h
h/√Hz
Initial goal
100 h
1.510-5
4.210-5
0.1
224
310-20
4.510-22
Advanced
10 h
1.510-6
4.210-6
0.1
224
9.510-21
1.610-22
Quantum limit
1 h
1.510-7
4.210-7
0.1
230
310-21
4.510-23
Table of expected spectral strain sensitivities for MiniGRAIL for a ~200Hz bandwidth.
2.2 Definition of the technologies to be shared between the different European detectors
Technology for laser interferometer
With GEO600 being a shorter interferometer than the VIRGO and LIGO detectors so called
2nd generation techniques have already been built into GEO600 in order to achieve a
comparable sensitivity. Some of these techniques could be modified and used for future stages
of VIRGO.
 GEO600 uses low loss quasi-monolithic fused silica suspensions for the last stage of a
triple pendulum mirror suspension. Advanced stages of VIRGO will also use such


quasi-monolithic fused silica stages. The thermal noise limit of interferometric
detectors, at low frequency, will be strongly reduced adopting this technology. In the
GEO collaboration the Glasgow group is leader in the realization of this kind of
suspension using a innovative production procedure based on a CO2 laser; in the
Virgo collaboration the Perugia group developed a completely automated machine,
computer driven, based on a more traditional H2-O2 flame system.
Within the GEO collaboration high power lasers and amplifier stages have been
developed and currently are under further development. As both detectors will need
high power lasers the expertise can be used to the advantage of both projects.
Within VIRGO most control loops are made from digital electronics whereas GEO600
mostly uses analogue electronics. As the servos tend to become more and more
complex the future of the control systems lies in the digital domain. GEO600 is
already converting some of the control loops to digital. This process will continue into
the future and can benefit from the knowledge within the VIRGO group where a
dedicated program has already started to develop more powerful DSP’s (with
integrated DAQ and timing units) and faster digital control systems.
Resonant detectors readout systems
The MiniGRAIL, Auriga and ROG detectors use SQUID based capacitive readouts. Many
experimental efforts are devoted to improve the present performances and are pursued in
strong collaboration among the different groups.
 One of the crucial improvements regards the energy resolution of the SQUID
amplifier. Up to now the best performance achieved on a bar detector is obtained with
a double SQUID amplifier and corresponds to about 700 hbar, but an energy
resolution of about a few quanta in SQUID amplifiers without input load has been
obtained and of about 25 hbar in a SQUID coupled with a high Q input resonant load.
Specific R&Ds are ongoing in Italy (INFN and CNR - Istituto di Fotonica e
Nanotecnologie), in the AURIGA and ROG collaborations, and The Netherlands
(Leiden University and Twente University) in the MiniGRAIL collaboration.
 Two parallel R&Ds are also ongoing on capacitive transducers, to improve the
transduction efficiency. One aims at the increase of the maximum bias voltage applied
to the transducer electrodes of about a factor of 10. At present, electrical fields in the
range of 10 MV/m are achievable. The goal of this R&D is to reach electrical bias
fields of the order of 100 MV/m, by studying the surface finishing effect, the
electrodes conditioning procedure and the effect of dielectric films. The second R&D
focuses on the study of a new geometry transducer, with the resonant mass enclosed
between two identically spaced electrodes, i.e. two identical gaps. This setup has the
net effect to double the total capacitance C of the transducer and thus to increase the
transduction efficiency.
 The AURIGA group is developing an optics-based resonant readout. It was tested on a
room temperature bar showing performances comparable to capacitive readouts, and
will soon be cooled to liquid helium temperatures.
 Parametric transducers in the r.f. to microwave region look promising, because of their
intrinsic wideband behavior. A parametric read-out is being developed by the ROG
collaboration.
2.3 First draft of a common document on short term upgrades
The Virgo collaboration is now designing the evolution of the Virgo detector. To realize the
white paper describing the evolution path, a group of 7 writers has been defined. In this group
a member of the GEO collaboration has been invited so that a more direct information
exchange can be performed. Furthermore, 4 working groups, devoted to the effective studies
of the needed upgrades, have been formed and GEO members appear in these groups as
coordinators or members. The 4 working groups are devoted to the following subjects:
 Thermal noise, mirrors and suspensions
 Laser and input optic
 Optical configuration
 Electronics and control
A first draft of this document is available and currently under evaluation of the Virgo
collaboration (VIR-NOT-DIR-1390-304).
2.4 Parallel development of the European detectors toward the realization of new GW
detectors
Advanced Virgo
The 4 working groups involving Virgo and GEO scientists must design the evolution of the
current Virgo detector toward the realization of the advanced design.
The main duty of the first group is the realization of a monolithic fused silica suspension for
the advanced Virgo Detector that could reduce the suspension thermal noise and the substrate
thermal noise. Furthermore the reduction of the coating mechanical dissipation will be
investigated in collaboration of the ILIAS-J3 activity. The second group is investigating the
possibility to use a ~200W laser watt in the advanced Virgo to reduce the shot noise. The
implications on the injection optics will be evaluated by this group. The “Optical
configuration” group will investigate the optimal topology for advanced Virgo: beam
topology, use of Signal recycling technique,.. The last group is designing the electronics and
the control strategies that permit the reaching of the nominal sensitivity.
In Figure 5 the expected sensitivity for advanced Virgo is reported. In Table 2 the detection
distance and rate expected for advanced Virgo is reported.
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10
(a) Advanced Virgo with SR
(b) Advanced Virgo without SR
(c) Virgo+ with NN
-19
10
h(f) [1/sqrt(Hz)]
-20
10
-21
10
(b)
-22
10
(c)
-23
10
(a)
-24
10
1
10
100
1000
10000
Frequency [Hz]
Figure 5 Sensitivities expected in advanced Virgo for three different cases: (a) Signal recycling
implemented, (b) without Signal recycling (c) comparison with Virgo+
Event Rate
Range (Mpc)
NS – NS
3/yr – 4/day
300
NS – BH
1/yr – 6/day
750
BH - BH
0.1 – 30/day
z = 0.45
SuperNovae
20/yr
100
Table 2 - Detection distance and rate for advanced Virgo
The Auriga, MiniGRAIL and ROG collaborations are designing the evolution of the resonant
detectors. The shortest term evolution of resonant detectors is considered in the direction of a
large spherical antenna: a sphere allows isotropic sky coverage, determination of the source
direction and wave polarization. It also has an intrinsic veto against non-GW signals
consisting in measuring the toroidal modes that do not couple to GWs. The needed
technology is defined and is currently under test in the MiniGrail detector.
SFERA proposal
The INFN ROG collaboration(Frascati, Genova, L’Aquila, Roma, Roma2), the university of
Geneva and the university of Leiden submitted a proposal for the realization of a spherical
resonant detector, named SFERA.
The proposed SFERA detector consists in a resonant-mass spherical detector with radius R =1
meter, made of a CuAl6% alloy. The mass of such a sphere will be 33 ton.Its first quadrupolar
spheroidal mode is monitored (about 1 kHz) using six transducers in the TIGA configuration.
At an advanced stage, also its first harmonics (about 2Khz) will be monitored. Thanks to the
large experience gained with resonant bars, as well as with MiniGRAIL, all intrinsic noise
sources are very well understood. The read-out system of the detector is studied to permits a
overall bandwidth of about 200Hz around the resonant frequency; obviously the noise
performances of the read-out system affects the sensitivity of the detector, as reported in
Figure 6 and Figure 7. The noise floor depends by the bandwidth of the read-out system and
by mechanical thermal noise. A possible improvement can be probably attained improving the
Q of the detector material (selecting CuBe10%, instead of CuAl10%) and reducing
consequently the detector bandwidth. The investigation of this possibility will be object of a
study in the next WP3 meetings.
Figure 6 - Calculated strain noise spectrum for a 2 meter diameter CuAl sphere. The sphere is equipped
with six transduction chains in the TIGA configuration, with a read-out at 20 h
Figure 7 - Calculated strain noise spectrum for a 2 meter diameter CuAl sphere. The sphere is equipped
with six transduction chains in the TIGA configuration, with noise at quantum limit.
The Dual detection scheme will give a further improvement in sensitivity and bandwidth, and
a challenging R&D program has started to improve the current readouts performances for the
use in the Dual configuration. The Dual scheme is proposed as the mid term evolution of
resonant detectors, and will profit from the cryostat design, the test mass production method
developed for the large spherical detector and the study of the noise induced by cosmic rays.
The main specific goals of the Dual R&D program concern:
The sensitivity. In order to guarantee such a wide frequency interval of high sensitivity, order
of many kHz, the deformation of the test masses which form the dual detector needs to be
measured by devices that are not in mechanical resonance. A wide-band readout cannot profit
from the displacement amplification at resonance of a conventional transducers; thus it is
necessary to develop an alternative and non-resonant device to amplify the differential
deformation of the massive bodies. Mechanical amplifiers based on the elastic deformation of
monolithic devices – compliant mechanisms – are well known for their applications in
mechanical engineering. However their application to gravitational wave detectors requires
the study of their thermal noise contributions.
The selectivity. Another relevant requirement for the transducer system is to sense the
deformation of the resonant masses on a wide surface, in order to be less sensitive to the
resonant modes of higher frequency, which do not carry any gravitational signal. In this way
the thermal noise of the detector is minimized, while preserving the sensitivity to the signal. A
further progress in this noise reduction can be achieved by a readout scheme which is
geometrically selective to the fundamental quadrupolar modes. This selectivity also allows to
clean the bandwidth from the spurious modes not sensitive to gravitational waves.
Figure 8 - Predicted spectral strain SQL sensitivities of different
These evolutions of the current resonant detectors could permit these devices to complement,
in specific frequency ranges, the advanced interferometric detectors, allowing a precise
reconstruction of the gravitational wave signal.
A document concerning the road map of the resonant mass detectors was submitted to the
GWIC in June 2005 and positively evaluated.
2.4 International workshop on European GW detectors evolution
An international workshop has been organized co-supported by the European Science
Foundation, under the Exploratory Workshop programme. The event occurred in Perugia (2123 September 2005) and it has been inserted in an entire week devoted to the collaboration
between the European Gravitational Wave detectors. In fact this joint WP3-ESF workshop
has been preceded by a WP1 meeting and followed by the Executive Board of N5. At this
workshop important members of the European GW scientific community and a few scientists
coming from the American experiment LIGO participated. The outcome of this meeting has
been the decision to have a common effort to present a joint project for a design study in the
future FP7 European programme.
3. Other activities
A Memorandum of Understanding between the GEO and Virgo collaboration has been
formulated and it will be signed shortly. The purpose of this Memorandum of Understanding
(MOU) is to establish and define the participation of GEO scientists in the study of an
advanced version of the Virgo antenna. The GEO and Virgo members of the WP3 group are
working on the realization of this collaboration between the two experiments; once the MOU
has be signed it will be included in the next report to the European Commission.
4. Conclusion
The activity of the working group is reaching the original target of opening a collaboration
between the European groups, studying the upgrade of the detectors in a collaborative way
and planning the evolution of the European detectors in a common scenario.
List of publications and conference proceedings
L. Baggio et al.
3-Mode Detection for Widening the Bandwidth of Resonant Gravitational Wave
Detectors
Phys. Rev. Lett. 94 241101 (2005)
M. Bignotto et al.
New suspension system for the gravitational wave bar detector AURIGA
Rev. Sci. Instrum. 76 084502 (2005)
M. Bonaldi et al.
Wide bandwidth dual acoustic gravitational wave detectors
Nuclear Physics B - Proceedings Supplements 138 443 (2005)
M. Bassan et al.
A new capacitive readout for EXPLORER and NAUTILUS
Proceedings of the 6th Edoardo Amaldi Conference on Gravitational waves, Bankoku
Shinryoukan Kise Nago, Okinawa Japan, June 20-24 (2005)
to be published in Journal of Physics: Conference Series
V. Fafone
Developments in Resonant-mass Detectors
Proceedings of the 6th Edoardo Amaldi Conference on Gravitational waves, Bankoku
Shinryoukan Kise Nago, Okinawa Japan, June 20-24, 2005
to be published in Class. Quantum Grav. Special Issue
V. Fafone
SFERA: a new spherical gravitational wave detector
IX International Conference on Topics in Astroparticle and Underground Physics, Zaragoza,
Spain, September 10-14, 2005
to be published in Journal of Physics: Conference Series
B. Willke et al.
The GEO-HF project
Proceedings of the 6th Edoardo Amaldi Conference on Gravitational waves, Bankoku
Shinryoukan Kise Nago, Okinawa Japan, June 20-24, 2005
to be published in Journal of Physics: Conference Series.
M. Punturo et al.
Virgo upgrade investigations
Proceedings of the 6th Edoardo Amaldi Conference on Gravitational waves, Bankoku
Shinryoukan Kise Nago, Okinawa Japan, June 20-24, 2005
to be published in Journal of Physics: Conference Series.
Proposals (Manuscripts)
SFERA, Proposal for a Spherical Gravitational Wave Detector, INFN ROG Collaboration
(Frascati, Genova, L’Aquila, Roma, Roma 2), University of Geneva, University of Leiden
(September 2005)
The Advanced Virgo White Paper, VIR-NOT-DIR-1390-304, the Virgo collaboration (12
November 2005)