Large-scale Gravitational Wave Detectors Research Articles

Enhanced effects of variation of the fundamental constants in laser interferometers and application to dark-matter detection

We outline new laser interferometer measurements to search for variation of the electromagnetic fine-structure constant $\alpha$ and particle masses (including a non-zero photon mass). We propose a strontium optical lattice clock -- silicon single-crystal cavity interferometer as a novel small-scale platform for these new measurements. Multiple passages of a light beam inside an interferometer enhance the effects due to variation of the fundamental constants by the mean number of passages ($N_{\textrm{eff}} \sim 10^2$ for a large-scale gravitational-wave detector, such as LIGO, Virgo, GEO600 or TAMA300, while $N_{\textrm{eff}} \sim 10^5$ for a strontium clock -- silicon cavity interferometer). Our proposed laser interferometer measurements may be implemented as an extremely precise tool in the direct detection of scalar dark matter that forms an oscillating classical field or topological defects.

Time evolution of parametric instability in large-scale gravitational-wave interferometers

We present a study of three-mode parametric instability in large-scale gravitational-wave detectors. Previous work used a linearized model to study the onset of instability. This paper presents a nonlinear study of this phenomenon, which shows that the initial stage of an exponential rise of the amplitudes of a higher-order optical mode and the mechanical internal mode of the mirror is followed by a saturation phase, in which all three participating modes reach a new equilibrium state with constant oscillation amplitudes. Results suggest that stable operation of interferometers may be possible in the presence of such instabilities, thereby simplifying the task of suppression.

Length sensing and control of a Michelson interferometer with power recycling and twin signal recycling cavities

The techniques of power recycling and signal recycling have proven as key concepts to increase the sensitivity of large-scale gravitational wave detectors by independent resonant enhancement of light power and signal sidebands within the interferometer. Developing the latter concept further, twin signal recycling was proposed as an alternative to conventional detuned signal recycling. Twin signal recycling features the narrow-band sensitivity gain of conventional detuned signal recycling but furthermore facilitates the injection of squeezed states of light, increases the detector sensitivity over a wide frequency band and requires a less complex detection scheme for optimal signal readout. These benefits come at the expense of an additional recycling mirror, thus increasing the number of degrees of freedom in the interferometer which need to be controlled.In this article we describe the development of a length sensing and control scheme and its successful application to a tabletop-scale power recycled Michelson interferometer with twin signal recycling. We were able to lock the interferometer in all relevant longitudinal degrees of freedom and thus laid the foundation for further investigations of this interferometer configuration to evaluate its viability for the application in gravitational wave detectors.

High-vacuum-compatible high-power Faraday isolators for gravitational-wave interferometers

Faraday isolators play a key role in the operation of large-scale gravitational-wave detectors. Second-generation gravitational-wave interferometers such as the Advanced Laser Interferometer Gravitational-Wave Observatory (LIGO) and Advanced Virgo will use high-average-power cw lasers (up to 200 W) requiring specially designed Faraday isolators that are immune to the effects resulting from the laser beam absorption–degraded isolation ratio, thermal lensing, and thermally induced beam steering. In this paper, we present a comprehensive study of Faraday isolators designed specifically for high-performance operation in high-power gravitational-wave interferometers.

THE AIGO PROJECT

The AIGO project is the proposed southern hemisphere advanced large scale gravitational wave detector. With this southern hemisphere detector, the global array of ground based gravitational wave detectors will be substantially improved. Here we summarize the current plans for the AIGO detector.

Preparing a Mechanical Oscillator in Non-Gaussian Quantum States

We propose a protocol for coherently transferring non-Gaussian quantum states from an optical field to a mechanical oscillator. We demonstrate its experimental feasibility in future gravitational-wave detectors and tabletop optomechanical devices. This work not only outlines a feasible way to investigate nonclassicality in macroscopic optomechanical systems, but also presents a new and elegant approach for solving non-Markovian open quantum dynamics in general linear systems.

Prospects of higher-order Laguerre-Gauss modes in future gravitational wave detectors

The application of higher-order Laguerre Gauss (LG) modes in large-scale gravitational wave detectors has recently been proposed. In comparison to the fundamental mode, some higher-order Laguerre Gauss modes can significantly reduce the contribution of coating Brownian noise. Using frequency domain simulations we give a detailed analysis of the longitudinal and angular control signals derived with a LG33 mode in comparison to the fundamental TEM00 mode. The performance regarding interferometric sensing and control of the LG33 mode is found to be similar, if not even better in all aspects of interest. In addition, we evaluate the sensitivity gain of the implementation of LG33 modes into the Advanced Virgo instrument. Our analysis shows that the application of the LG33 mode results in a broadband improvement of the Advanced Virgo sensitivity, increasing the potential detection rate of binary neutron star inspirals by a factor 2.1.

DC-readout of a signal-recycled gravitational wave detector

All first-generation large-scale gravitational wave detectors are operated at the dark fringe and use a heterodyne readout employing radio frequency (RF) modulation–demodulation techniques. However, the experience in the currently running interferometers reveals several problems connected with a heterodyne readout, of which phase noise of the RF modulation is the most serious one. A homodyne detection scheme (DC-readout), using the highly stabilized and filtered carrier light as a local oscillator for the readout, is considered to be a favourable alternative. Recently a DC-readout scheme has been implemented on the GEO 600 detector. We describe the results of first measurements and give a comparison of the performance achieved with homodyne and heterodyne readout. The implications of the combined use of DC-readout and signal recycling are considered.

A quantum-enhanced prototype gravitational-wave detector

Substantial improvements, through the use of squeezed light, in the sensitivity of a prototype gravitational-wave detector built with quasi-free suspended optics represents the next step in moving such devices out of the lab and into orbit. The quantum nature of the electromagnetic field imposes a fundamental limit on the sensitivity of optical precision measurements such as spectroscopy, microscopy and interferometry1. The so-called quantum limit is set by the zero-point fluctuations of the electromagnetic field, which constrain the precision with which optical signals can be measured2,3,4. In the world of precision measurement, laser-interferometric gravitational-wave detectors4,5,6 are the most sensitive position meters ever operated, capable of measuring distance changes of the order of 10−18 m r.m.s. over kilometre separations caused by gravitational waves from astronomical sources7. The sensitivity of currently operational and future gravitational-wave detectors is limited by quantum optical noise6. Here, we demonstrate a 44% improvement in displacement sensitivity of a prototype gravitational-wave detector with suspended quasi-free mirrors at frequencies where the sensitivity is shot-noise-limited, by injecting a squeezed state of light1,2,3. This demonstration is a critical step towards implementation of squeezing-enhancement in large-scale gravitational-wave detectors.

Demonstration and comparison of tuned and detuned signal recycling in a large-scale gravitational wave detector

The British/German gravitational wave detector GEO 600 located near Hannover in Germany is the first large-scale gravitational-wave detector using the advanced technique of signal recycling. Currently the instrument operates in detuned signal recycling mode. Several problems arise due to the fact that the signal recycling cavity changes amplitude and phase of all light fields (carrier and sidebands) present at the dark-port. In addition, in the case of detuned signal recycling this leads to unbalanced sideband fields at the detector output. The large amplitude modulation caused by this asymmetry does not carry any gravitational wave information, but might be the cause of saturation and nonlinearities on the main photodiode. We developed and demonstrated a new control method to realize tuned signal recycling operation in a large-scale gravitational wave detector. A detailed comparison of tuned and detuned signal recycling operation is given. The response function of the system (optical gain) was measured and compared, as was the size of amplitude modulation on the main photodiode. Some important noise couplings were measured and partly found to be strongly reduced in the case of tuned signal recycling operation.

Adaptive control of laser modal properties

An adaptive optical system for precise control of a laser beam's mode structure has been developed. The system uses a dynamic lens based on controlled optical path deformation in a dichroic optical element that is heated with an auxiliary laser. Our method is essentially aberration free, has high dynamic range, and can be implemented with high average power laser beams where other adaptive optics methods fail. A quantitative model agrees well with our experimental data and demonstrates the potential of our method as a mode-matching and beam-shaping element for future large-scale gravitational wave detectors.

H∞ Control of a Gravitational Wave Detector Using Normalized Coprime Factor Plant Descriptions

This paper deals with large-scale gravitational-wave detector control. These detectors use multiple optical cavities and require a coherent control of several suspended mirror positions. In fact the mirrors forming the detector are oscillating around their equilibrium positions under the influence of the earth seismic noise. Hence a control system is needed in order to control the mirror positions at a certain precision level specified by the detection sensitivity.We present in this paper a H∞ control approach of the detector, based on the H∞ loop shaping design method of Glover and Mc-Farlane (D.McFarlane and K.Glover, 1992). The design method is first discussed and then the simulation results, obtained with the suspension simulation program, are commented.

The GEO600 project

GEO600, an interferometric gravitational-wave detector with an arm length of 600 m, is currently being built in northern Germany close to Hannover. GEO600 incorporates an externally modulated fourfold delay-line Michelson interferometer giving a round-trip optical length of 2400 m. A master - slave combination of a monolithic diode-pumped Nd:YAG ring laser and an injection-locked amplifier will give a light power of about 10 W at a wavelength of 1064 nm. Power recycling increases the light power inside the interferometer to a level of about 10 kW. The use of both power and signal recycling will yield a sensitivity of the same order of magnitude as the first stages of the other large-scale gravitational-wave detectors LIGO and VIRGO currently under construction. High signal recycling factors allow the sensitivity to be increased at a chosen frequency while reducing the bandwidth of the detector. This gives an advantage over broad-band detectors in detecting narrow-band periodic sources such as pulsars. The 25 cm diameter mirrors will be suspended as double pendulums from a platform supported by vibration-reduction systems. The passive filtering properties of this system sufficiently reduce the seismic noise in the frequency range of interest, i.e. 50 - 1000 Hz. The detector will start taking data in the year 2000.

Demonstration of a power-recycled Michelson interferometer with Fabry–Perot arms by frontal modulation

Large-scale gravitational-wave detectors currently under construction such as the LIGO detectors use multiplemirror resonant optical systems containing several surfaces at which the relative phase of interfering light beams must be controlled. We describe a tabletop experiment that demonstrates a scheme for extracting signals in such an interferometer corresponding to deviations from perfect interference.