Table of contents

This issue is published as the Proceedings of the 6th Edoardo Amaldi Conference on Gravitational Waves, held on 20–24 June 2005 at Bankoku Shinryoukan in Okinawa, Japan. Since the first Amaldi conference was held in Frascati in 1994, eleven years have passed and the scale of the conference has grown with the increasing activity in the field of gravitational waves. As the centenary celebration of Einstein's `miracle year', 2005 was called `World Year of Physics'. Among his breakthroughs published in 1905, the special theory of relativity is recognized as the most significant revolution in physics, completely changing our views concerning time and space. Ten years later, Einstein proposed the general theory of relativity, by which he predicted the existence of gravitational waves (GWs). At that time, it was only a dream to observe a GW because its effect was so small. Efforts to detect GWs, pioneered by Weber, have continued for almost 40 years, yet their detection remained a dream. However, the presentations at this conference have convinced us that it is no longer a dream. The GW detector projects have made extraordinary advances; in particular, the significant sensitivity improvement of LIGO and the completion of the VIRGO detector mark the beginning of the new era of GW physics. Firm developments in theories and source estimations were also reported. In particular, the data analysis session was very active and various discussions were held. Elaborate experimental techniques were presented, some of them already achieving the requirements for the next generation of detectors, such as Advanced LIGO and LCGT. In addition to the earth-based detectors, many presentations concerning space detectors were contributed; they indicated that space would become the new stage for GW physics and astronomy.

This issue brings together the papers which were presented at this exciting conference. The proceedings comprise two volumes; the largest part is published as a volume of Journal of Physics: Conference Series and the other is a special issue of Classical and Quantum Gravity (CQG), presenting the highlights of the conference. This is the first time this format has been used and selecting the highlights for CQG was a difficult task as the quality of the papers submitted was so high. The issue has been published thanks to the excellent work of the reviewers who gave precise and appropriate comments to the Editors. We strongly believe this issue to be a milestone in the inception of GW astronomy.

The conference organizers would like to acknowledge the financial support of IUPAP, Okinawa prefecture, Inoue Foundation for Science, The Foundation for Promotion of Astronomy and a Grant-in-Aid for Scientific Research on Priority Areas (415) of the Ministry of Education, Culture, Sports, Science and Technology. The conference scientific programme was organized with the help of the session conveners. Their collaboration was indispensable for the success of the conference. We also appreciate the members of the international advisory committee and the local organizing committee; in particular, we thank Dr Akiteru Takamori for designing the fascinating poster of the conference and the image for the CD of this issue. The miscellaneous duties that were necessary for the conference were carried out with the help of ICS Convention Design Inc. with special thanks due to Ms Makiko Uwato and Mr Hiroyuki Suzuki. The proceedings are published by Institute of Physics Publishing; we would like to express our deep appreciation to Ms Judith Adams for her efficient management of the proceedings. Finally, we thank all of the excellent participants who made the conference so successful.

The Sixth Edoardo Amaldi Conference on Gravitational Waves was held on 20–24 June 2005 at Bankoku Shinryoukan in Okinawa, Japan. The bulk of the papers, after peer review, are published in Journal of Physics: Conference Series. However a selection of papers, chosen by the conference organisers, are published separately in a special issue of Classical and Quantum Gravity.

Neutron Stars (NSs) present a host of pulsation modes. Only a few of them, however, is of relevance from the gravitational wave (GW) point of view. Among the various possible modes the pulsation energy is mostly stored in the f-mode in which the fluid parameters undergo the largest changes. An important question is how the pulsation modes are excited in NSs. Here we consider the excitation of the f-mode in the accreting NSs belonging to Low Mass X-ray Binaries (LMXBs), which may well be a recurrent source of GWs, since the NSs are continuously receiving matter from their companion stars. We also discuss the detectability of the GWs for the scenario considered here.

We report about PHOEBUS (PHysics Of Events BUrsted by the Sun): a proposal for solar physics and space weather investigation with LISA (Laser Interferometer Space Antenna). Galactic and solar cosmic-ray particles with energies larger than 100 MeV(/n) penetrate and charge the LISA test masses. Spurious forces occur between the test masses and the surrounding electrodes mimicking gravitational wave signals. This process constitutes one of the major sources of acceleration noise for LISA. Silicon particle detectors will be placed on board the LISA-PF and LISA missions to monitor the overall energetic incident cosmic-ray fluxes. These telescopes can be also used to carry out a map of shock accelerated Solar Energetic Particle (SEPs) fluxes associated with evolving Coronal Mass Ejections (CMEs) at different steps in longitude. We discuss the role of protons, helium nuclei, galactic heavy nuclei and solar ions. We aim to contribute to the COST724 (European CO-operation in the field of Scientific and Technical Research) action inside WG1/WP13000 developing appropriate simulations of the dynamics of CMEs by using space-based data and theoretical models.

We present a method for detection and reconstruction of gravitational wave signals with a network of interferometric detectors. The method is based on the constraint maximization of the likelihood ratio functional. We discribe the method for the cases of white and colored detector noise.

The Mario Schenberg gravitational wave detector has been constructed at its site in the Physics Institute of the University of Sao Paulo as programmed by the Brazilian Graviton Project under full financial support from FAPESP (the Sao Paulo State Foundation for Research Support). We are ready to do a first test run of the spherical antenna at 4.2 K with three parametric transducers and an initial target sensitivity of h ∼ 10⁻²¹ Hz^−½ in a 60 Hz bandwidth around 3.2 kHz.

We have built a computer code for determining the source direction and the wave polarization (solution of the inverse problem) in real time acquisition for strong signal-to-noise ratio cases. The digital filter used is a simple bandpass filter.

The ''data'' used for testing our code was simulated, it had both the source signal and detector noise. The detector noise includes the antenna thermal, back action, phase noise, series noise and thermal from transducer coupled masses. The simulated noise takes into account all these noise and the antenna-transducers coupling. The detector transfer function was calculated for a spherical antenna with six two-mode parametric transducers.

Finally, we were able to check at what distance Schenberg would detected some known sources. Here we present the results of these simulations.

We present methods and results to reduce fake burst events induced by nonstationary noises. To reduce these fake events, we systematically surveyed monitor signals recorded with a main (or gravitational-wave) signal of a gravitational-wave detector so as to watch the detector. Our survey was to check whether or not there was a coincidence between the main and monitor signals when we found a burst event from the main signal. If there was a coincidence, we rejected this event as a fake event induced by nonstationary noises, regarding the main signal as being dominated by nonstationary noises. As a result, we succeeded to reject about 90% of the burst events of which the SNR values were larger than 10 as fake events, with an accidental probability of about 5% to reject burst-gravitational-wave candidates.

We report on the search for gravitational waves emitted by non-spinning binary black hole inspirals in the data taken during the third LIGO science run (S3). We give an overview of the data acquired during S3 and the target waveforms that we are searching for in this analysis. We briefly describe how the data was filtered using a BCV detection template family (using an hexagonal template bank placement in the mass parameter plane). Finally, we report on preliminary estimates of the sensitivity of the three LIGO detectors using software injections of effective one-body waveforms with component masses in the range 3-40 M_⊙ and total mass M ⩽ 40 M_⊙. We show that during S3, the three LIGO detectors have a detection efficiency of 50% up to several Mpc for L1 and H2, and up to 30 Mpc for H1.

The interferometric gravitational wave detector Virgo is currently completing its commissioning phase and it is close to start scientific observations. Among the signals to be searched for, those emitted by coalescing binary systems are particularly promising and require a considerable computational effort to optimally search the parameter space. The Virgo collaboration has decided to implement an on-line analysis strategy capable of processing the interferometer data in-time. In this communication we present a component of the analysis pipeline, a parallel computing system based on the Message Passing Interface (MPI). We describe its capabilities, underlining its strength and flexibility, and we illustrate its relation with the other components of the pipeline. The on-line analysis chain, including the presented parallel system, has been run for the first time successfully during the Virgo commissioning run C5 in December 2nd to December 6th 2004[1].

Presence of slow non-stationarities has been seen in a series of studies with LIGO engineering and science data. It is important to track these slow variations or 'drifts' to diagnose their origin and correct them, as nonstationary data can affect sensitivity of astrophysical searches. A DMT (Data Monitoring Tool) monitor has been built to track slow non-stationarities in LIGO data. The monitor, tested on S4 data, will be operational during LIGO S5 data run. Offline analysis will be performed to unearth details of patterns thus obtained in the output of the monitor.

An overview of the searches for gravitational waves from radio pulsars with LIGO and GEO is given. We give a brief description of the algorithm used in these targeted searches and provide end-to-end validation of the technique through hardware injections. We report on some aspects of the recent S3/S4 LIGO and GEO search for signals from several pulsars. The gaussianity of narrow frequency bands of S3/S4 LIGO data, where pulsar signals are expected, is assessed with Kolmogorov-Smirnov tests. Preliminary results from the S3 run with a network of four detectors are given for pulsar J1939+2134.

Techniques of evolutionary computing have proven useful for a diverse array of fields in science and engineering. Because of the expected low signal to noise ratio of LIGO data and incomplete knowledge of gravitational waveforms, evolutionary computing is an excellent candidate for LIGO data analysis studies. Using the evolutionary computing methods of genetic algorithms and genetic programming, we have developed, as a proof of principle, search algorithms that are effective at finding sine-gaussian signals hidden in noise while maintaining a small false alarm rate. Because we used realistic LIGO noise as a training ground, the algorithms we have evolved should be well suited to detecting signals in actual LIGO data, as well as in simulated noise. These algorithms have continuously improved during the five days of their evolution and are expected to improve further the more they are evolved. The top performing algorithms from generation 100 and 199 were benchmarked using gaussian white noise to illustrate their performance and the improvement over 100 generations.

During the S4 LSC science run, the gravitational-wave detector GEO600, the first large scale dual recycled interferometer, took 30 days of continuous data. An instrumental duty cycle greater than 96% and a peak sensitivity of 7 × 10⁻²²/√Hz around 1 kHz were achieved during this time. Detector commissioning and characterization work are essential to prepare the worldwide network of gravitational-wave detectors for future extended science runs. This paper describes the detector commissioning that was done in the run-up to S4. The focus is set on techniques used for the identification and removal of limiting noise sources. Furthermore we give some examples for the detector characterization work of GEO600.

The propagation mechanisms of noise imposed on the light used to illuminate complex optical systems, from the noise source to the signal readout, can be very complicated, such as gravitational wave detectors. It is very important to understand these mechanisms both qualitatively and quantitatively, in order to effectively suppress the noise contribution to the interferometer readout. In this article, a method for the systematic treatment of the noise propagation mechanisms, and a way to analyze a noise contributions in complex optical systems, is described.

The study of the external influences from environmental disturbances is a fundamental issue in interferometric detection of gravitational wave, both in locking and in normal operation. Virgo is continuously monitored by a large number of environmental sensors, ranging from seismometers to microphones to electromagnetic probes, up to a weather station. Using data collected during the engineering runs, we have studied the features of the main external noise sources, and the way they interfere with Virgo operation and expected sensitivity. In this paper we present the preliminary results obtained.

We describe the present status of a new read-out for the EXPLORER and NAUTILUS gravitational wave detectors. The read-out is based on a double-gap capacitive transducer and a double-SQUID amplifier. The transducer has been tested at liquid helium temperature and a Q of 1.0.10⁶ has been measured with a biasing field of 20 MV/m. The double- SQUID amplifier has been tested down to 2 K with a high-Q resonant input load, showing very good stability and energy resolution, of about 70ℏ. With the new read-out, NAUTILUS, cooled to 100 mK, could reach a peak sensitivity of 3 . 10⁻²²Hz^−½ and a bandwidth, at the level of 10⁻²¹Hz^−½, of about 35 Hz.

We report on online monitoring of alignment noises in TAMA300 detector of Japan. The continuous monitoring of noise contributions is necessary for the veto analysis. To detect gravitational wave signals, fake events should be removed by veto analysis. We investigated a procedure for evaluating various noise contributions continuously. The procedure has been applied to several noise sources such as laser intensity and auxiliary length control. An investigation of alignment noises is the focus of this paper.

We measured the harmonic noise produced at the radio frequency mixer used to extract gravitational wave signal from a laser interferometer, and set an upper limit of the current sensitivity of TAMA300 applying this measurement to the mixer.

We present contributions of oscillator noises to the sensitivity of TAMA300. The oscillator is required for operating the interferometric detector. In order to estimate the contributions, phase and amplitude noises of the oscillator are measured, then transfer functions from these noises to the output of the interferometer are measured. The results show that neither phase nor amplitude noise limit the present sensitivity of TAMA300. Furthermore, models of the transfer functions are calculated to clarify how the noises pass through an interferometer. The frequency dependencies of the models agree with that of the measurement at the frequency above 200 Hz.

We present a completed prototype of the AIGO seismic vibration isolation system. The design has been developed to satisfy the isolation requirements for the next generation of interferometric GW detectors. The system relies on passive isolation and includes multiple Ultra Low Frequency (ULF) stages to achieve minimal low frequency residual motion. Two complete isolators are being installed at the high power test facility located in Gingin, Western Australia. The performance of individual mechanical stages is continually being tested and improved. Currently it is expected that residual motion close to 1 nm at 0.3 Hz will be achieved.

We describe the calibration and operation of the ST7 GRS capacitive sensor system. A novel optical interferometer, featuring both fiber optic delivery and readout, is used for calibration of the capacitive sensor system and as a witness sensor during testing. The capacitive sensor showed 1 nm/√Hz performance from 1 mHz to 10 Hz. Above 10 mHz the optical system showed significantly better performance than the capacitive sensor, with a noise floor at 2 × 10⁻¹¹ m/√Hz and a longer measurement standoff distance. The optical system was limited to 5 nm/√Hz at 1 mHz due to thermal disturbances of the laboratory environment, and could be reduced with a revised design and/or improved thermal stability.

This article demonstrates experimental results of a thermal control system developed for ST-7 gravitational reference sensor (GRS) ground verification testing which provides thermal stability δT < 1 mK/√Hz to f < 0.1 mHz, and which by extension is suitable for in-flight thermal control of the LISA spacecraft to compensate solar irradiate 1/f fluctuations. Although for ground testing these specifications can be met fairly readily with sufficient insulation and thermal mass, in contrast, for spacecraft the very limited thermal mass calls for an active control system which can simultaneously meet disturbance rejection and stability requirements in the presence of long time delay; a considerable design challenge. Simple control laws presently provide ∼ 1mK/√Hz for >24 hours. Continuing development of a model predictive feedforward control algorithm will extend performance to <1 mK/√Hz at f < 0.01 mHz and possibly lower, extending LISA coverage of super massive black hole mergers.

This paper gives an update on the status of the LISA technology package (LTP) which is to be launched in 2009 by ESA as a technology demonstration mission for the spaceborne gravitational wave observatory LISA. The dominant noise source in the interferometer prototype has been investigated and improved such that it is now comfortably below its budget at all frequencies.

We present the Modular GRS (previously named as Stand-Alone GRS), in which the laser light from the remote spacecraft does not illuminate the proof mass. The modular GRS uses only a single spherical proof mass on each spacecraft and optical, as opposed to capacitive, position sensing. The use of a single sphere as the test mass avoids the issue of cross coupling that is inherent for the cubic proof mass, and allows true drag free flight with no forcing. Together, the modular design, optical sensing and a single spherical proof mass reduce the disturbances and the number of degrees of freedom that must be managed for future LISA and BBO.

The assumptions used in developing the canonical Galacitic white dwarf binary background level for LISA are investigated. The differences between several models of the white dwarf binary population are described and a technique for comparing the onset of the confusion limit between different population models is introduced.

Over the next decade the gravitational physics community will benefit from dramatic improvements in many technologies critical to the tests of gravity and gravitational-wave detection. The highly accurate deep space navigation, interplanetary laser ranging and communication, interferometry and metrology, high precision frequency standards, precise pointing and attitude control, together with the drag-free technologies will revolutionize the field of the experimental gravitational physics. Deep-space laser ranging will be ideal for gravitational-wave detection, and testing relativity and measuring solar-system parameter to an unprecedented accuracy. ASTROD I is such a mission with single spacecraft; it is the first step of ASTROD (Astrodynamical Space Test of Relativity using Optical Devices) with 3 spacecraft. In this paper, we will present the progress of ASTROD and ASTROD I with emphases on the acceleration noises, mission requirement, charging simulation, drag-free control and low-frequency gravitational-wave sensitivity.

We employ a relatively simple experimental technique enabling mechanical-noise free, cavityenhanced spectroscopic measurements of an atomic transition and its hyperfine structure. We demonstrate this technique with the 532 nm frequency doubled output from a Nd:YAG laser and an iodine vapour cell. The resulting cavity-enhanced, noise-cancelled, iodine hyperfine error signal is used as a frequency reference with which we stabilise the frequency of the 1064nm Nd:YAG laser. Preliminary frequency stabilisation results are then presented.

The Laser Interferometer Space Antenna (LISA) and the Big Bang Observer (BBO) require angular sensing in their gravitational reference sensor (GRS), telescope pointing, and spacecraft control. The conventional angular sensing schemes utilize simple geometric reflections as the sensing mechanism.

We propose and demonstrate the use of grating diffraction orders as angular sensing signal beams. The grating angular sensor can be far more sensitive than a simple reflection scheme for two reasons. First, the diffractive angles can vary more than the incident angle when the grating rotates. The grating thus magnifies the variation of the input angle. Second, the cross section of the diffracted beam is compressed by the oblique projection, resulting in a higher energy density. These two favorable effects become more pronounce for a normal incidence beam to diffract at grazing angles. We have conducted a preliminary experiment and demonstrated an angular sensitivity below 10 nanoradians per root hertz over a short working distance, meeting the Space Technology 7 (ST-7) GRS and LISA requirements for proof mass angular sensing.

Our proposed grating-based angular measurement does not introduce additional optical elements between the sensed surface and the photodiode. Thus, it eliminates measurement uncertainty due to in-path optics. The proposed grating sensor can be generalized to build an integrated sensor for both angular and displacement sensing.

On-ground tests are required to study the couplings between LISA test masses and the spacecraft that host them. Very interesting and useful results have already been obtained with a 1 DoF torsion pendulum. In order to study couplings that might act between two or more degrees of freedom in measuring the position and acting on the position of each test mass, a many degrees of freedom facility is needed. Here we present a new 2 DoF double torsion pendulum that will be used to test LISA Gravitational Reference Sensor (GRS) on the ground. The facility will be located at INFN Laboratory at Gran Sasso (LNGS), in order to reduce the local ambient noise that limits the sensitivity of the system.

The Astrodynamical Space Test of Relativity using Optical Devices (ASTROD) mission consists of three spacecraft in separate solar orbits and carries out laser interferometric ranging. ASTROD aims at testing relativistic gravity, measuring the solar system and detecting gravitational waves. Because of the larger arm length, the sensitivity of ASTROD to gravitational waves is estimated to be about 30 times better than Laser Interferometer Space Antenna (LISA) in the frequency range lower than about 0.1 mHz. ASTROD I is a simple version of ASTROD, employing one spacecraft in a solar orbit. It is the first step for ASTROD and serves as a technology demonstration mission for ASTROD. In addition, several Scientific results are expected in the ASTROD I experiment. The allowed acceleration noise level of ASTROD I is 10⁻¹³ m s⁻² Hz^−½ at the frequency of 0.1 mHz. In this paper, we focus on local gravity gradient noise that could be one of the largest acceleration disturbances in the ASTROD I experiment. We have carried out gravitational modelling for the current test-mass design and simplified configurations of ASTROD I by using an analytical method and the Monte Carlo method. Our analyses can be applied to figure out the optimal designs of the test mass and the constructing materials of the spacecraft, and the configuration of compensation mass to reduce local gravity gradients.

The classical delta filters used in the current resonant bar experiments for detecting GW bursts are viable when the bandwidth of resonant bars is few Hz. In that case, the incoming GW burst is likely to be viewed as an impulsive signal in a very narrow frequency window. After making improvements in the read-out with new transducers and high sensitivity dc-SQUID, the Explorer-Nautilus have improved the bandwidth (∼20 Hz) at the sensitivity level of 10⁻²⁰/√Hz. Thus, it is necessary to reassess this assumption of delta-like signals while building filters in the resonant bars as the filtered output crucially depends on the shape of the waveform. This is presented with an example of GW signals - stellar quasi-normal modes, by estimating the loss in SNR and the error in the timing, when the GW signal is filtered with the delta filter as compared to the optimal filter.

The recently upgraded AURIGA detector and the LIGO observatory were simultaneously acquiring data for the first time in a 2-weeks period during the LIGO S3 run. This coincidence run motivated a collaborative effort to test search methods for gravitational wave bursts on real data. The adopted method uses broad-band cross correlation for the LIGO interferometers triggered by AURIGA events in the 850-950 Hz band. This paper describes the analysis technique and gives a status report on the search, with emphasis on the tuning procedure. Preliminary network performance and background estimates will be provided.

We describe an improved version of the Hough transform search for continuous gravitational waves from isolated neutron stars assuming the input to be short segments of Fourier transformed data. The method presented here takes into account possible nonstationarities of the detector noise and the amplitude modulation due to the motion of the detector. These two effects are taken into account for the first stage only, i.e. the peak selection, to create the time-frequency map of our data, while the Hough transform itself is performed in the standard way.

We examine the benefits of performing a joint LIGO-Virgo search for transient signals. We do this by adding burst and inspiral signals to 24 hours of simulated detector data. We find significant advantages to performing a joint coincidence analysis, above either a LIGO only or Virgo only search. These include an increased detection efficiency, at a fixed false alarm rate, to both burst and inspiral events and an ability to reconstruct the sky location of a signal.

While the current interferometric gravitational wave detectors are approching their nominal sensitivity, the new generation of detectors is in an advanced design phase. The Virgo collaboration is de.ning now the path to arrive to a complete design of the advanced version of the detector within about two years. The upgrades needed to obtain a detector with improved sensitivity in a relatively short time are here discussed.

We report on the status of the R & D towards a dual detector. We discuss the experimental advances for a broadband mechanical amplifier equipped with a Fabry-Perot cavity and for an increase of the breakdown voltage in capacitive transducers.

The Q & A experiment, first proposed and started in 1994, provides a feasible way of exploring the quantum vacuum through the detection of vacuum birefringence effect generated by QED loop diagram and the detection of the polarization rotation effect generated by photon-interacting (pseudo-)scalar particles. Three main parts of the experiment are: (1) Optics System (including associated Electronic System) based on a suspended 3.5-m high finesse Fabry-Perot cavity, (2) Ellipsometer using ultra-high extinction-ratio polarizer and analyzer, and (3) Magnetic Field Modulation System for generating the birefringence and the polarization rotation effect. In 2002, the Q & A experiment achieved the Phase I sensitivity goal. During Phase II, we set (i) to improve the control system of the cavity mirrors for suppressing the relative motion noise, (ii) to enhance the birefringence signal by setting-up a 60-cm long 2.3 T transverse permanent magnet rotatable to 10 rev/s, (iii) to reduce geometrical noise by inserting a suspended polarization-maintaining optical fiber (PM fiber) as a mode cleaner, and (iv) to use ultra-high extinction-ratio (10⁻⁹) polarizer and analyzer for ellipsometry. Here we report on (iii) & (iv); specifically, we present the properties of the PM-fiber modecleaner, the transfer function of its suspension system, and the result of our measurement of high extinction-ratio polarizer and analyzer.

The Q & A experiment, aiming at the detection of vacuum birefringence predicted by quantum electrodynamics, consists mainly of a suspended 3.5 m Fabry-Perot cavity, a rotating permanent dipole magnet and an ellipsometer. The 2.3 T magnet can rotate up to 10 rev/s, introducing an ellipticity signal at twice the rotation frequency. The X-pendulum gives a good isolation ratio for seismic noise above its main resonant frequency 0.3 Hz. At present, the ellipsometry noise decreases with frequency, from 1 × 10⁻⁵ rad.Hz^−½ at 5 Hz, 2×10⁻⁶ rad.Hz^−½ at 20 Hz to 5×10⁻⁷ rad.Hz^−½ at 40 Hz. The shape of the noise spectrum indicates possible improvement can be made by further reducing the movement between the cavity mirrors. From the preliminary result of yaw motion alignment control, it can be seen that some peaks due to yaw motion of the cavity mirror was suppressed. In this paper, we first give a schematic view of the Q & A experiment, and then present the measurement of transfer function of the compound X-pendulum-double pendulum suspension. A closed-loop control was carried out to verify the validity of the measured transfer functions. The ellipsometry noise spectra with and without yaw alignment control and the newest improvement is presented.

In this paper, we propose a passive method to suppress parametric instabilities. This method requires the design of a test mass mirror with appropriate loss distribution. We show that localized losses can significantly reduce the parametric gain without degrading the thermal noise for the advanced LIGO configuration. The method can be use individually or in conjunction with other active feed-back methods. We present numerical analysis for both spherical and non-spherical mirrors.

Cryogenic Laser Interferometer Observatory (CLIO) is a laser interferometric gravitational wave detector using cryogenic cooled mirrors. In order to cool the mirrors, cryogenic environment is necessary. We made four vacuum chambers with cryogenic cooled shields inside. The mirror is suspended by a mirror suspension system with a heat path for transferring heat from the mirror to the shield. Test cooling of the chambers and the mirror suspension system has been done. After one week cooling, the chambers was cooled from 8K to 10K and the mirror were cooled at 21K successfully.

The lock acquisition scheme for the Advanced LIGO optical configuration, which makes use of ''resonant sideband extraction'', is under investigation in the 40 meter prototype interferometer at Caltech. The 40m has a similar optical configuration to the one planned for Advanced LIGO which has 5 degrees of freedom for length control. So far we have succeeded in locking the 5 degrees of freedom routinely. The differential mode of arm cavities was locked in the same state as the final setup, and the peak of optical resonance was verified to be around 4 kHz. Currently, since an offset remains in the common mode of the arm cavities, another optical resonance can be seen in common mode optical gain.

Second generation gravitational wave detectors require high power lasers with several 100W of output power and with very low temporal and spatial fluctuations. In this paper we discuss possible setups to achieve high laser power and describe a 200W prestabilized laser system (PSL). The PSL noise requirements for advanced gravitational wave detectors will be discussed in general and the stabilization scheme proposed for the Advanced LIGO PSL will be described. Special emphasis will be given to the most demanding power stabilization requiremets and new results (RIN ⩽ 4×10⁻⁹/√Hz) will be presented.

We have built a 100-W injection-locked Nd:YAG laser for a Japanese next generation gravitational wave detector. A 2-W master laser was directly injected to a high-power slave laser, which led to coherent radiation of 100 W at 1064 nm.

High frequency parametric instabilities in optical cavities are radiation pressure induced interactions between test mass mechanical modes and cavity optical modes. The parametric gain depends on the cavity power and the quality factor of the test mass internal modes (usually in ultrasonic frequency range), as well as the overlap integral for the mechanical and optical modes. In advanced laser interferometers which require high optical power and very low acoustic loss test masses, parametric instabilities could prevent interferometer operation if not suppressed. Here we review the problem of parametric instabilities in advanced detector configurations for different combinations of sapphire and fused silica test masses, and compare three methods for control or suppression of parametric instabilities-thermal tuning, surface damping and active feedback.

We have developed an experiment of ultrasensitive interferometric measurement of small displacements based on a high-finesse Fabry-Perot cavity. We have observed the internal thermal noise of mirrors and fully characterized their acoustics modes. We describe recent progress in our experimental setup in order to reach a sensitivity better than 10⁻²⁰m/√Hz. This unique sensitivity is a step towards the first observation of the radiation pressure effects and the resulting standard quantum limit in interferometric measurements. Our experiment may become a powerful facility to test quantum noise reduction schemes such as the use of squeezed light or quantum locking of mirrors. We also present a new scheme where a cavity detuning changes the mirror dynamics in such a way that the gravitational signal is amplified by the optomechanical coupling and the interferometer sensitivity is improved.

The design of cryogenic interferometers and quantum limited ultra-cryogenic resonators (3rd generation Advanced Gravitational Wave Detectors) is driving the R&D activities in the area of thermal noise reduction at low temperature. The project Strega coordinates the R&D activities of 18 labs in Europe involved in Interferometric, Resonant and Electromagnetic Detectors. The aim of the collaboration is to develop a technology that will reduce the thermal noise in the third generation detectors 10 times with respect to the second generation (advanced resonators and advanced room temperature interferometers). The work carried out in Strega, in the areas of Materials, Cryogenics and Thermal Noise specific Studies after 14 months since the project started, will be reviewed.

A non-Gaussian, flat-top laser beam profile, also called Mesa Beam Profile, supported by non spherical mirrors known as Mexican Hat (MH) mirrors, has been proposed as a way to depress the mirror thermal noise and thus improve the sensitivity of future interferometric Gravitational Wave detectors, including Advanced LIGO [1]. Non-Gaussian beam configurations have never been tested before [2] hence the main motivation of this project is to demonstrate the feasibility of this new concept. A 7m rigid suspended Fabry-Perot (FP) cavity which can support a scaled version of a Mesa beam applicable to the LIGO interferometers has been developed. The FP cavity prototype is being designed to prove the feasibility of actual MH mirror profiles, determine whether a MH mirror cavity is capable of transforming an incoming Gaussian beam into a flat top beam profile, study the effects of unavoidable mirror imperfections on the resulting beam profile and gauge the difficulties associated with locking and maintaining the alignment of such an optical cavity. We present the design of the experimental apparatus and simulations comparing Gaussian and Mesa beams performed both with ideal and current (measured) mirror profiles. An overview of the technique used to manufacture this kind of mirror and initial results showing Mesa beam properties are presented.

In order to design a suspension for large cryogenic mirror, we have measured thermal conductance and shear strength of sapphire bonding in comparison with direct bonding and hydroxide-catalysis bonding. Thermal conductance per unit area of 4 [W/K/mm²] for the direct bonding and 0.3 [W/K/mm²] for the hydroxide-catalysis bonding were obtained around 20K. Shear strength of 28[MPa] for the direct bonding and 6.5 [MPa] for the hydroxide-catalysis bonding were measured at 300K. Based on those values, an estimated area that support a weight of a mirror produces a temperature step of less than 1% of a difference of temperature in between the main mirror and a mirror of Suspension Point Interferometer.

"Mario Schenberg" is a spherical resonant-mass gravitational wave (GW) detector that will be part of a GW detection array of two detectors. Another one is been built in The Netherlands. Their resonant frequencies will be around 3.2 kHz with a bandwidth of about 200 Hz. This range of frequencies is new in a field where the typical frequencies lay below 1 kHz, making the transducer development much more complex. Some studies indicated that using low mass mechanical resonators (used for impedance matching to the parametric transducer, in a cold damping regime) allow the detector to reach the standard quantum limit. In this work we describe the procedures that are being developed to quickly test the mechanical quality factor of a very small resonator in the quest to find the best machining method and thermal annealing for the impedance matching resonator, one key part that makes a good coupling between the sphere and the transducer. The main goal is to optimize the mechanical quality factor in a reasonable time.

``Mario Schenberg'' is a spherical resonant-mass gravitational wave (GW) detector that is expected to be part of a GW detection array of two detectors. Another one is been built in The Netherlands. Their resonant frequencies will be around 3 kHz with a bandwidth of about 200 Hz. This range of frequencies is new in a field where the typical frequencies lay below 1 kHz, making the transducer development much more complex. Some studies indicated that the use of low mass mechanical resonators (used for impedance matching to the parametric transducer, in a cold damping regime) allows the detector to reach the standard quantum limit. In this work we describe the study of a new shape for the impedance matching resonator used to obtain a better coupling between the sphere and the transducers and a better use of the space inside the experimental chamber.

There is in the literature a number of papers addressing the stochastic background of gravitational waves (GWs) generated by an ensemble of astrophysical sources. The main ingredient in such studies is the so called star formation rate density (SFRD), which gives the density of stars formed per unit time. Some authors argue, however, that there is, in the equation that determines the amplitude of the stochastic background of GWs, an additional (1 + z) term dividing the SFRD, which would account for the effect of cosmic expansion onto the time variable. We argue here that the inclusion of this additional term is wrong. In order to clarify where the inclusion of the (1 + z) term is really necessary, we briefly discuss the calculation of event rates in the study of GRBs (gamma ray bursts) from cosmological origin.

We are developing a small-scale interferometer in order to observe radiation pressure noise. This radiation pressure noise interferometer is composed of two cavities whose mirror mass is less than 1g. In this system, radiation pressure noise is dominant around at a few hundred Hz. The design and the current status of our prototype system are described.

All-reflective interferometry based on nano-structured diffraction gratings offers new possibilities for gravitational wave detection. We investigate an all-reflective Fabry-Perot interferometer concept in 2nd order Littrow mount. The input-output relations for such a resonator are derived treating the grating coupler by means of a scattering matrix formalism. A low loss dielectric reflection grating has been designed and manufactured to test the properties of such a grating cavity.

Parametric transducers, such as superconducting rf cavities, can boost the bandwidth and sensitivity of the next generation resonant antennas, thanks to a readily available technology. We have developed a fully coupled dynamic model of the system ''antenna- transducer'' and worked out some estimates of signal-to-noise ratio and the stability conditions in various experimental configurations. We also show the design and the prototype of a rf cavity which, together with a suitable read-out electronic, will be used as a test bench for the parametric transducer.

The Low Frequency Facility consists of a 1 cm Fabry-Perot cavity suspended to a single SuperAttenuator, which is the mechanical system adopted to isolate the test masses of the Virgo interferometer. In this paper we present the preliminary results of measurements performed with a cavity of finesse 4000 and lasting 1-2 hours in different working conditions. The analysis presented here is focused mainly on the region below 100 Hz, and uses data collected with longitudinal control bandwidth below 150 Hz. A calibration test confirmed that the collected data are in good agreement with the model of the longitudinal control loop based on the open loop measurements. In addition to this, above 2 Hz the power spectrum of the two mirrors relative displacement shows a stationary noise floor and few peaks with high mechanical quality factor. Studying these peaks in the time domain, it has been observed that the energy associated with a single peak is Boltzman distributed, whether the oscillations are not excited. The measured upper limit of the seismic noise contamination at 10 Hz is around 2 × 10⁻¹⁴m/√Hz.

We discuss the possibility of significantly reducing the number and Q-factor of violin string modes in the mirror suspension. Simulations of a bar-flexure suspension and an orthogonal ribbon have shown a reduction in the number of violin string modes when compared to a normal ribbon suspension. By calculating the expected suspension thermal noise, we find that the orthogonal ribbon provides a promising suspension alternative. A lower number of violin modes oscillating in the direction of the laser and a reduction in violin mode peak values of at least 23dB can be achieved with a slight increase in thermal noise above 40Hz.

We present the preliminary results for an experiment that aims to perform direct measurements of suspension thermal noise. The experiment is based on a niobium flexure membrane approximately 200 µm thickness that is operated as a stable inverted pendulum. A 0.25 g mirror suspended by this flexure membrane is used as the end mirror of a Fabry-Perot test cavity. This test cavity has a length of 12mm and a finesse of about 800. It is mounted at the lowest stage of a quadruple cascaded pendulum suspension, enclosed in a high-vacuum envelope. The length of test cavity is stabilized with 1Hz bandwidth to a Nd:YAG laser, which itself is stabilized with high bandwidth to the length of a suspended Zerodur reference cavity of finesse 6000.

The Australian Consortium for Gravitational Wave Astronomy (ACIGA) in collaboration with LIGO is developing a high optical power research facility at the AIGO site, Gingin, Western Australia. Research at the facility will provide solutions to the problems that advanced gravitational wave detectors will encounter with extremely high optical power. The problems include thermal lensing and parametric instabilities. This article will present the status of the facility and the plan for the future experiments.

A new generation of gravitational wave interferometers is under study with the main goal to improve the sensitivity of the present detectors which are taking data now. Two of the dominant noises which limit the actual sensitivity of the interferometers are the thermal noise of the suspended optics and the thermal lensing process. At low temperature it is possible to reduce both the effects. However, lowering the temperature of the test masses without injecting vibration noise from the cooling system is a technological challenge. We present the first results on a new active system to dampen the vibrations from a pulse tube refrigerator coupled to a suspended mirror.

The 4m Resonant Sideband Extraction (RSE) interferometer is a planned prototype of the LCGT interferometer. The aim of the experiment is to operate a powerrecycled Broadband RSE interferometer with suspended optics and to achieve diagonalization of length signals of the central part of the interferometer directly through the optical setup. Details of the 4m RSE interferometer control method as well as the design of the experimental setup will be presented.

The proposed upgrade to the LIGO detectors to form the Advanced LIGO detector system is intended to incorporate a low thermal noise monolithic fused silica final stage test mass suspension based on developments of the GEO 600 suspension design. This will include fused silica suspension elements jointed to fused silica test mass substrates, to which dielectric mirror coatings are applied.

The silica fibres used for GEO 600 were pulled using a Hydrogen-Oxygen flame system. This successful system has some limitations, however, that needed to be overcome for the more demanding suspensions required for Advanced LIGO. To this end a fibre pulling machine based on a CO₂ laser as the heating element is being developed in Glasgow with funding from EGO and PPARC.

At the moment a significant limitation for proposed detectors like Advanced LIGO is expected to come from the thermal noise of the mirror coatings. An investigation on mechanical losses of silica/tantala coatings was carried out by several labs involved with Advanced LIGO R&D. Doping the tantala coating layer with titania was found to reduce the coating mechanical dissipation. A review of the results is given here.

The results on cosmic rays detected by the gravitational wave antenna NAUTILUS have motivated an experiment (RAP) based on a suspended cylindrical bar, which is made of the same aluminum alloy as NAUTILUS and is exposed to a high energy electron beam. Mechanical vibrations originate from the local thermal expansion caused by warming up due to the energy lost by particles crossing the material. The aim of the experiment is to measure the amplitude of the fundamental longitudinal vibration at different temperatures. We report on the results obtained down to a temperature of about 4 K for an Al 5056 bar, which agree at the level of 10% with the predictions of the model describing the underlying physical process. Very preliminary results for a Niobium bar at temperatures below and above the transition temperature are also reported.

For the design and commissioning of the LIGO interferometer, simulation tools have been used explicitly and implicitly. The requirement of the advanced LIGO interferometer is much more demanding than the first generation interferometer. Development of revised simulation tools for future interferometers are underway in the LIGO Laboratory. The outline of those simulation tools and applications are discussed.

A comparison between sapphire and silicon as test mass substrate regarding the sensitivity of advanced laser interferometers with transmissive optics has been performed. Our simulations include thermal noise magnitude and shot noise level from 5K to 300K. The thermal noise is dominated by thermoelastic noise from room to low temperature. At cryogenic temperature, the coating loss is the predominant source of noise. On the other hand, the shot noise level is strongly dependent on thermal lensing effect due to the substrate and coating optical absorption. Thermal lensing becomes negligible below 90 K for sapphire and below 50K for silicon. Even if silicon has a lower absorption than sapphire, this benefit is canceled due to its higher thermo-optic coefficient. Both thermal noise and shot noise demonstrates the advantage of using sapphire test mass over silicon below 200K

Interferometric gravitational wave detectors use test masses made by large mirrors whose coating is usually made by multiple layers of dielectric materials, most commonly alternating layers of SiO₂ (silica) and Ta₂O₅ (tantala). It is foreseeable that in future interferometric gravitational wave detector projects (LCGT, EGO, VIRGO,), the mirrors will be cooled down to cryogenic temperature in order to reduce the noise generated by the thermally activated motion of the masses. However, low temperature mechanical losses in the Ta₂O₅/SiO₂ coatings might limit the design sensitivity for such cryogenic detectors by setting a lower limit for the expected thermal noise. Here we present some measurements of mechanical losses in the TiO₂/SiO₂ coatings at room and low temperature (80K-300K).

In the LCGT and CLIO projects for the interferometric gravitational wave detectors of Japan, the mirrors and a part of the suspension systems are cooled by cryocoolers to reduce the thermal noise. For the CLIO, extremely small vibration cryocoolers were specially developed by improving a commercial Gifford-McMahon type pulse tube cryocooler. We measured the vibration at the top of the suspension base in the CLIO interferometer while operating these cryocoolers. Although the seismic motion of 10⁻⁹(1 Hz/f)² m/Hz^½ at the site of the CLIO and LCGT in the Kamioka mine is 100-times smaller than that around Tokyo, these cryocoolers did not seriously increase the vibration. Consequently, a reduction of thermal noise by the cooled mirrors and suspension fibers using these cryocoolers is expected to be observed without any additional fluctuation disturbance due to the cryocoolers.

Large Cryogenic Gravitational wave Telescope (LCGT) is the future Japanese gravitational-wave detector. It will employ the broadband resonant sideband extraction (RSE) as its optical configuration. We compared four signal extraction schemes that have been proposed so as to downselect one of them as the scheme for LCGT. The selected scheme uses the phase and amplitude modulation sidebands: the phase modulation sidebands transmitting to the antisymmetric port (AP) and the amplitude modulation sidebands reffected to the symmetric port (SP) by the functions of the Michelson asymmetry. Using these sidebands, a new technique called 'delocation' is applicable. One advantage is that the control signals of the undesired signals do not appear at the AP, where the differential signals appear.

We developed an automatic measuring device of birefringence inhomogeneity in synthetic sapphire substrates to evaluate their crystal quality suitable for laser interferometric gravitational wave (GW) detectors. The orientation of the projection of the c-axis on a plane orthogonal to the beam was measured with an accuracy of 2 × 10⁻² rad. The phase retardation was measured with an accuracy of 7 × 10⁻⁴ rad, which was equivalent to 4 × 10⁻¹⁰ in terms of the fluctuation of the refractive index for samples of 150mm thickness. The reproducibility was 1% for both the orientation and phase retardation. The automatic measuring device meets the requirements of the LCGT project, which is a next-generation laser interferometer project for GW detection.

We have constructed the Mario Schenberg gravitational wave detector at the Physics Institute of the University of Sao Paulo as programmed by the Brazilian Graviton Project, under the full support of FAPESP (the São Paulo State Foundation for Research Support). We are ready to do a first test run of the spherical antenna at 4.2K with three parametric transducers and an initial target sensitivity of h∼10⁻²¹Hz^−½ in a 60Hz bandwidth around 3.2kHz. The parametric transducers to be used on the Mario Schenberg detector consist of reentrant klystron copper-aluminum cavities covered with a thin layer of niobium on the walls and on the oscillating membrane. The gap between the central conical post and the membrane is about 40µm. Here we present a progress report on this transducer development related with niobium layer deposition in the transducer cavities and on the design of silicon membranes for the last transducer mechanical mode.

Upcoming generations of interferometric gravitational wave detectors are likely to be operated at cryogenic temperatures because one of the sensitivity limiting factors of the present generation is the thermal noise of optical components (e.g. end mirrors, cavity couplers, beam splitters). The main contributions to this noise are due to the substrate, the optical coating, and the suspension. The thermal noise can be reduced by cooling to cryogenic temperatures. In addition the overall mechanical quality factor should preferable increase at low temperatures. The experimental details of a new cryogenic apparatus for investigations of the temperature dependency of the Q-factor of several substrate materials in the range of 5 to 300 K are presented. To perform a ring down recording an electrostatic mode excitation of the samples and an interferometric read-out of the amplitude of the vibrations was used.

A suspension point interferometer (SPI) is a high-performance active vibrationisolation scheme for laser interferometric gravitational wave detectors. By making use of auxiliary interferometers installed at the suspension points of the interferometer's mirrors, this technique helps to reduce the seismic noise and to improve the stability of the interferometer. We are now constructing a Fabry-Perot interferometer equipped with an SPI to test the effectiveness of the SPI. We report on the current status of the experiment and preliminary results that demonstrate about 20 dB of vibration attenuation by the SPI below 2 Hz.

Using a conventional mode-cleaner with the output beam taken through a diagonal mirror it is impossible to achieve a non-astigmatic output. The geometrical astigmatism of triangular mode-cleaners for gravitational wave detectors can be self-compensated by thermally induced astigmatism in the mirrors substrates. We present results from finite element modelling of the temperature distribution of the suspended mode-cleaner mirrors and the associated beam profiles. We use these results to demonstrate and present a self-compensated mode-cleaner design. We show that the total astigmatism of the output beam can be reduced to 5×10⁻³ for ±10% variation of input power about a nominal value when using the end mirror of the cavity as output coupler.

We developed a control scheme of homodyne detection. To operate the homodyne detector as easy as possible, a simple Michelson interferometer is used. Here a motivation that the control scheme of the homodyne detection is developed is for our future experiment of extracting the ponderomotively squeezed vacuum fluctuations. To obtain the best signalto- noise ratio using the homodyne detection, the homodyne phase should be optimized. The optimization of the homodyne phase is performed by changing a phase of a local oscillator for the homodyne detection from a point at which a signal is maximized. In fact, in this experiment, using the developed control scheme, we locked the Michelson interferometer with the homodyne detector and changed the phase of the local oscillator for the homodyne detection. Then, we measured signals quantity changed by changing the phase of the local oscillator for the homodyne detection. Here we used the output from the homodyne detection as the signal.

For a broadband-operated RSE interferometer, a simple and smart length sensing and control scheme was newly proposed. The sensing matrix could be diagonal, owing to a simple allocation of two RF modulations and to a macroscopic displacement of cavity mirrors, which cause a detuning of the RF modulation sidebands. In this article, the idea of the sensing scheme and an optimization of the relevant parameters will be described.

Outgassing velocities and optical absorption coefficients of black colored optical absorbers (UB-NiP, Phosblack II, Raydent, ECB+DLC and Alumite) were studied to reduce scattered and strayed light in interferometric gravitational wave detectors. The measured results showed that the UB-NiP had the largest optical absorption coefficient of 99.89% for 1064nm wavelength of light. For the outgassing velocity, the ECB+DLC had the lowest value, which was 1 × 10⁻⁸ Pam³/s/m² at 20 hours. This value was about two orders of magnitude smaller than that of the UB-NiP, however, its optical absorption coefficient was only 65 %. Therefore, we concluded that the UB-NiP is suitable as an optical dumper with small area and high efficiency, and the ECB+DLC is suitable as large area coating such as a use for vacuum chamber walls.