Stable operation of a 300-m laser interferometer with sufficient sensitivity to detect gravitational-wave events within our galaxy

The influence of the Sc3+ dopant on the transmittance of (Y, Er)3Al5O12 ceramics

High erbium content yttrium aluminum garnet (Er:YAG) and yttrium scandium aluminum garnet (Er:YSAG) ceramics have been fabricated from Er:YAG and Er:YSAG powders, respectively. The powders have been synthesized via a reverse precipitation technique, processed by uniaxial pressing followed by cold isostatic pressing, and sintered in a vacuum. TEOS (tetraethoxysilane) was used as a sintering additive. After vacuum sintering, all of the samples were processed by annealing in air to increase the transmittance and polished on both sides. The influence of the Sc³⁺ content and the synthesis conditions on the microstructure and optical transparency of the Er:YAG and Er:YSAG ceramics have been investigated in detail. It has been found that changing Al³⁺ for the bigger Sc³⁺ ion leads to the transmittance increasing to up to 60% at a wavelength of about 1500 nm.

A three-dimensional laser interferometer gravitational-wave detector

The gravitational wave (GW) has opened a new window to the universe beyond the electromagnetic spectrum. Since 2015, dozens of GW events have been caught by the ground-based GW detectors through laser interferometry. However, all the ground-based detectors are L-shaped Michelson interferometers, with very limited directional response to GW. Here we propose a three-dimensional (3-D) laser interferometer detector in the shape of a regular triangular pyramid, which has more spherically symmetric antenna pattern. Moreover, the new configuration corresponds to much stronger constraints on parameters of GW sources, and is capable of constructing null-streams to get rid of the signal-like noise events. A 3-D detector of kilometer scale of such kind would shed new light on  the joint search of GW and electromagnetic emission.

Evaluation of resonance phenomena of mechanical oscillator by self-mixing solid-state laser Doppler vibrometry

We performed self-mixing laser Doppler vibrometry on a vibrating oscillator consisting of a rigid-body laser-light-scattering object attached to a piezoelectric element driven by low-frequency AC voltage to evaluate its motion. The sideband spectrum reflecting the motion of the oscillator is observed in the power spectrum of the modulated wave. The time dependence of the intensity of the sideband spectrum is explained by Newton's second law assuming that the oscillator has a mechanical resonance frequency and undergoes simple vibration under the driving force, which depends on the deformation velocity of the piezoelectric element. Our results indicate that the motion of a slowly moving target with sub-nanometer displacement, which is difficult to measure by general laser Doppler vibrometry, can be evaluated with high spatial and frequency resolutions by detecting the sideband signal, which changes periodically at the driving frequency of the piezoelectric element.

Quantum Measurement Theory in Gravitational-Wave Detectors

The fast progress in improving the sensitivity of the gravitational-wave detectors, we all have witnessed in the recent years, has propelled the scientific community to the point at which quantum behavior of such immense measurement devices as kilometer-long interferometers starts to matter. The time when their sensitivity will be mainly limited by the quantum noise of light is around the corner, and finding ways to reduce it will become a necessity. Therefore, the primary goal we pursued in this review was to familiarize a broad spectrum of readers with the theory of quantum measurements in the very form it finds application in the area of gravitational-wave detection. We focus on how quantum noise arises in gravitational-wave interferometers and what limitations it imposes on the achievable sensitivity. We start from the very basic concepts and gradually advance to the general linear quantum measurement theory and its application to the calculation of quantum noise in the contemporary and planned interferometric detectors of gravitational radiation of the first and second generation. Special attention is paid to the concept of the Standard Quantum Limit and the methods of its surmounting.

Relaxation time and viscosity of fused silica glass at room temperature

Cases of long-term deformation of fused silica glass at room temperature attributed to the action of gravity have been reported. Further experimental investigations now provide evidence of time-dependent viscous behavior, with a time constant of the order of 10 years. Data relating to a pair of fused silica reference plates are presented, showing the overall deformation occurred over the years; considerations on the pertaining viscosity with aging are also given. An account of the observed relaxation process in terms of the Kelvin-Voigt model for linear viscoelasticity is provided.

Gravitational Wave Detection by Interferometry (Ground and Space)

Significant progress has been made in recent years on the development of gravitational-wave detectors. Sources such as coalescing compact binary systems, neutron stars in low-mass X-ray binaries, stellar collapses and pulsars are all possible candidates for detection. The most promising design of gravitational-wave detector uses test masses a long distance apart and freely suspended as pendulums on Earth or in drag-free spacecraft. The main theme of this review is a discussion of the mechanical and optical principles used in the various long baseline systems in operation around the world - LIGO (USA), Virgo (Italy/France), TAMA300 and LCGT (Japan), and GEO600 (Germany/U.K.) - and in LISA, a proposed space-borne interferometer. A review of recent science runs from the current generation of ground-based detectors will be discussed, in addition to highlighting the astrophysical results gained thus far. Looking to the future, the major upgrades to LIGO (Advanced LIGO), Virgo (Advanced Virgo), LCGT and GEO600 (GEO-HF) will be completed over the coming years, which will create a network of detectors with the significantly improved sensitivity required to detect gravitational waves. Beyond this, the concept and design of possible future "third generation" gravitational-wave detectors, such as the Einstein Telescope (ET), will be discussed.

Torsion-bar antenna for low-frequency gravitational-wave observations

We propose a novel type of gravitational-wave antenna, formed by two bar-shaped test masses and laser-interferometric sensors to monitor their differential angular fluctuations. This antenna has a fundamental sensitivity to low-frequency signals below 1 Hz, even with a ground-based configuration. In addition, it is possible to expand the observation band to a lower limit determined by the observation time, by using modulation and up-conversion of gravitational-wave signals by rotation of the antenna. The potential sensitivity of this antenna is superior to those of current detectors in a 1 mHz-10 Hz frequency band and is sufficient for observations of gravitational waves radiated from in-spiral and merger events of intermediate-mass black holes.

Shot-noise-limited control-loop noise in an interferometer with multiple degrees of freedom

Precise measurements, such as those made with interferometric gravitational-wave detectors, require the measurement device to be properly controlled so that the sensitivity can be as high as possible. Mirrors in the interferometer are to be located at specific operation points to isolate laser noise and to accumulate the signal in resonant cavities. On the other hand, rigid control of an auxiliary degree of freedom may result in imposing sensing noise of the control on the target object as excess force noise. Evaluation of this so-called loop noise is important in order to design a decent control scheme of the measurement device. In this paper, we show the method to calculate the level of loop noise, which has been recently implemented in simulation tools that are broadly used for designing gravitational-wave detectors.

Quantum enhancement of the zero-area Sagnac interferometer topology for gravitational wave detection

Only a few years ago, it was realized that the zero-area Sagnac interferometer topology is able to perform quantum nondemolition measurements of position changes of a mechanical oscillator. Here, we experimentally show that such an interferometer can also be efficiently enhanced by squeezed light. We achieved a nonclassical sensitivity improvement of up to 8.2 dB, limited by optical loss inside our interferometer. Measurements performed directly on our squeezed-light laser output revealed squeezing of 12.7 dB. We show that the sensitivity of a squeezed-light enhanced Sagnac interferometer can surpass the standard quantum limit for a broad spectrum of signal frequencies without the need for filter cavities as required for Michelson interferometers. The Sagnac topology is therefore a powerful option for future gravitational-wave detectors, such as the Einstein Telescope, whose design is currently being studied.

Exploring binary-neutron-star-merger scenario of short-gamma-ray bursts by gravitational-wave observation

We elucidate the feature of gravitational waves (GWs) from a binary-neutron-star merger collapsing to a black hole by general relativistic simulation. We show that GW spectrum imprints the coalescence dynamics, formation process of disk, equation of state for neutron stars, total masses, and mass ratio. A formation mechanism of the central engine of short-gamma-ray bursts, which are likely to be composed of a black hole and surrounding disk, therefore could be constrained by GW observation.

Long-term deformation at room temperature observed in fused silica

Cases of long-term deformation of fused silica flats are reported. The phenomenon is detected at the scale of the nanometer, and exhibits a time constant of the order of 9 years. The observed deformation appears related to gravity and constraints, but a change of physical properties locally resulting in non-homothetic behavior is also hypothesized.

Gravitational wave forms for two- and three-body gravitating systems

Different numbers of self-gravitating particles (in different types of periodic motion) are most likely to generate very different shapes of gravitational waves, some of which, however, can be accidentally almost the same. One such example is a binary and three-body system for Lagrange's solution. To track the evolution of these similar wave forms, we define a chirp mass to the triple system. Thereby, we show that the quadrupole wave forms cannot distinguish the sources. It is suggested that wave forms with higher lth multipoles will be important for classification of them (with a conjecture of l<or=N for N particles).

Spectral-domain optical coherence phase microscopy for label-free multiplexed protein microarray assay

Quantitative measurement of affinities and kinetics of various biomolecular interactions such as protein-protein, protein-DNA and receptor-ligand is central to our understanding of basic molecular and cellular functions and is useful for therapeutic evaluation. Here, we describe a laser-scanning quantitative imaging method, referred to as spectral-domain optical coherence phase microscopy, as an optical platform for label-free detection of biomolecular interactions. The instrument is based on a confocal interferometric microscope that enables depth-resolved quantitative phase measurements on sensor surface with high spatial resolution and phase stability. We demonstrate picogram per square millimeter surface mass sensitivity, and show its sensing capability by presenting static and dynamic detection of multiplexed protein microarray as immobilized antigens capture their corresponding antibodies.

Reduction and possible elimination of coating thermal noise using a rigidly controlled cavity with a quantum-nondemolition technique

Thermal noise of a mirror is one of the most important issues in high-precision measurements such as gravitational-wave detection or cold damping experiments. It has been pointed out that thermal noise of a mirror with multilayer coatings can be reduced by mechanical separation of the layers. In this Letter, we introduce a way to further reduce thermal noise by locking the mechanically separated mirrors. The reduction is limited by the standard quantum limit of control noise, but it can be overcome with a quantum-nondemolition technique, which finally raises a possibility of complete elimination of coating thermal noise.

Resonant speed meter for gravitational-wave detection

Gravitational-wave detectors have been well developed and operated with a high sensitivity. However, they still suffer from mirror displacement noise. In this Letter, we propose a resonant speed meter as a displacement noise-canceled configuration based on a ring-shaped synchronous recycling interferometer. The remarkable feature of this interferometer is that, at certain frequencies, gravitational-wave signals are amplified, while displacement noises are not.

Label-free and dynamic detection of biomolecular interactions for high-throughput microarray applications

Direct monitoring of primary molecular-binding interactions without the need for secondary reactants would markedly simplify and expand applications of high-throughput label-free detection methods. A simple interferometric technique is presented that monitors the optical phase difference resulting from accumulated biomolecular mass. As an example, 50 spots for each of four proteins consisting of BSA, human serum albumin, rabbit IgG, and protein G were dynamically monitored as they captured corresponding antibodies. Dynamic measurements were made at 26 pg/mm(2) SD per spot and with a detectable concentration of 19 ng/ml. The presented method is particularly relevant for protein microarray analysis because it is label-free, simple, sensitive, and easily scales to high-throughput.

Detuned Twin-Signal-Recycling for ultrahigh-precision interferometers

We propose a new interferometer technique for high-precision phase measurements such as those in gravitational wave detection. The technique utilizes a pair of optically coupled resonators that provide identical resonance conditions for the upper as well the lower phase modulation signal sidebands. This symmetry significantly reduces the noise spectral density in a wide frequency band compared with single-sideband recycling topologies of current and planned gravitational wave detectors. Furthermore, the application of squeezed states of light becomes less demanding.

Demonstration of a squeezed-light-enhanced power- and signal-recycled Michelson interferometer

We report on the experimental combination of three advanced interferometer techniques for gravitational wave detection, namely, power recycling, detuned signal recycling, and squeezed field injection. For the first time, we experimentally prove the compatibility of especially the latter two. To achieve a broadband nonclassical sensitivity improvement, we applied a filter cavity for compensation of quadrature rotation. The signal-to-noise ratio was improved by up to 2.8 dB beyond the coherent state's shot noise. The complete setup was stably locked for arbitrary times and characterized by injected single-sideband modulation fields.

Development of a frequency-detuned interferometer as a prototype experiment for next-generation gravitational-wave detectors

We report on our prototype experiment that uses a 4-m detuned resonant sideband extraction interferometer with suspended mirrors, which has almost the same configuration as the next-generation, gravitational-wave detectors. We have developed a new control scheme and have succeeded in the operation of such an interferometer with suspended mirrors for the first time ever as far as we know. We believe that this is the first such instrument that can see the radiation pressure signal enhancement, which can improve the sensitivity of next-generation gravitational-wave detectors.

Manufacture of a 10-km-scale radius-of-curvature surface by use of a thin-film coating technique

We tried a method of making a 10-km-class large-radius-of-curvature surface that would satisfy both low microroughness (0.1 nm rms) and low waviness (lambda/100) by forming a spherically curved film with a low-loss coating technique on a flat surface produced by mechanical (chemical) polishing. We obtained a SiO2 surface with a 10255 +/- 250-m radius of spherical curvature that had less than lambda/30 waviness and 0.4-nm micro-roughness over a 9-cm-diameter area.

Parametric instabilities and their control in advanced interferometer gravitational-wave detectors

A detailed simulation of Advanced LIGO test mass optical cavities shows that parametric instabilities will excite 7 acoustic modes in each fused silica test mass, with parametric gain R up to 7 and only 1 acoustic mode with R approximately 2 for alternative sapphire test masses. Fine-tuning of the test mass radii of curvature causes the instabilities to sweep through various modes with R as high as approximately 2000. Sapphire test mass cavities can be tuned to completely eliminate instabilities using thermal g-factor tuning. In the case of fused silica test mass, instabilities can be minimized but not eliminated.

Squeezing in the audio gravitational-wave detection band

We demonstrate the generation of broadband continuous-wave optical squeezing from 280 Hz-100 kHz using a below-threshold optical parametric oscillator (OPO). The squeezed state phase was controlled using a noise locking technique. We show that low frequency noise sources, such as seed noise, pump noise, and detuning fluctuations, present in optical parametric amplifiers, have negligible effect on squeezing produced by a below-threshold OPO. This low frequency squeezing is ideal for improving the sensitivity of audio frequency measuring devices such as gravitational-wave detectors.

Analytic Black Hole Perturbation Approach to Gravitational Radiation

We review the analytic methods used to perform the post-Newtonian expansion of gravitational waves induced by a particle orbiting a massive, compact body, based on black hole perturbation theory. There exist two different methods of performing the post-Newtonian expansion. Both are based on the Teukolsky equation. In one method, the Teukolsky equation is transformed into a Regge-Wheeler type equation that reduces to the standard Klein Gordon equation in the flat-space limit, while in the other method (which was introduced by Mano, Suzuki, and Takasugi relatively recently, the Teukolsky equation is used directly in its original form. The former's advantage is that it is intuitively easy to understand how various curved space effects come into play. However, it becomes increasingly complicated when one goes to higher and higher post-Newtonian orders. In contrast, the latter's advantage is that a systematic calculation to higher post-Newtonian orders can be implemented relatively easily, but otherwise, it is so mathematical that it is hard to understand the interplay of higher order terms. In this paper, we review both methods so that their pros and cons may be seen clearly. We also review some results of calculations of gravitational radiation emitted by a particle orbiting a black hole.

Evaluation of the performance of polished mirror surfaces for the TAMA gravitational wave detector by use of a wave-front tracing simulation

We evaluated the performance of polished mirror surfaces for the TAMA interferometric gravitational wave detector by comparing the experimental results with a wave-front tracing simulation. The TAMA mirror surfaces were polished to a roughness of a few nanometer rms. We confirmed that these polished mirrors do not limit the present TAMA sensitivity and that the target shot-noise sensitivity will be achieved with these mirrors, even if a power-recycling technique is introduced in the next stage of the TAMA.

Possibility of direct measurement of the acceleration of the universe using 0.1 Hz band laser interferometer gravitational wave antenna in space

It may be possible to construct a laser interferometer gravitational wave antenna in space with h(rms) approximately 10(-27) at f approximately 0.1 Hz in this century. Using this antenna, (1) typically 10(5) chirp signals of coalescing binary neutron stars per year may be detected with S/N approximately 10(4); (2) we can directly measure the acceleration of the universe by a 10 yr observation of binary neutron stars; and (3) the stochastic gravitational waves of Omega(GW) > or similar to 10(-20) predicted by the inflation may be detected by correlation analysis. Our formula for phase shift due to accelerating motion might be applied for binary sources of LISA.