Cryogenically cooled ultra low vibration silicon mirrors for gravitational wave observatories

Interferometric gravitational wave observatories recently launched a new field of gravitational wave astronomy with the first detections of gravitational waves in 2015. The number and quality of these detections is limited in part by thermally induced vibrations in the mirrors, which show up as noise in these interferometers. One way to reduce this thermally induced noise is to use low temperature mirrors made of high purity single-crystalline silicon. However, these low temperatures must be achieved without increasing the mechanical vibration of the mirror surface or the vibration of any surface within close proximity to the mirrors. The vibration of either surface can impose a noise inducing phase shift on the light within the interferometer or physically push the mirror through oscillating radiation pressure. This paper proposes a system for the Laser Interferometric Gravitational-wave Observatory (LIGO) to achieve the dual goals of low temperature and low vibration to reduce the thermally induced noise in silicon mirrors. Experimental results are obtained at Stanford University to prove that these dual goals can be realized simultaneously.     

Q measurements down to liquid helium temperatures for a gravitational wave aluminium bar antenna

To detect gravitational waves it is necessary to separate the signals due to these waves from thermal noise in the antenna. A possible way of achieving this would be to operate at liquid helium temperatures. The behaviour of aluminium bar antenna was studied at liquid helium temperatures with particular reference to Q values.     

Quality factors of quartz crystals for use as gravitational wave antennae

The Q of a large unpolished quartz crystal has been measured in the temperature interval 4–300 K and found to be similar in behaviour and magnitude to that of highly polished crystals previously studied. These results are of interest in the development of quartz crystal, gravitational, wave antennae the sensitivity of which increases in proportion with the mass. The data indicate that large raw quartz crystals are suitable for use as antennae.     

GRAIL: A 10 mk, 100 ton spherical gravitational wave antenna

Massive metallic spheres cooled to millikelvin temperatures could reach quantum-limited sensitivities high enough to detect gravitational waves from supernovae explosions up to 100–200 Mpc which would include millions of galaxies. They could provide sensitivity (in the frequency range above 700 Hz) and directionality, superior to the large interferometer arrays presently under construction, which will be better at lower frequencies and can have a larger bandwidth. World wide gravitational wave observatories will probably use both types of detectors. In this paper we give a brief overview of the problems involved in making a resonant spherical gravitational wave detector of very large mass working in the low millikelvin range.     

Monte Carlo simulation of the high energy cosmic muon background in a resonant gravitational wave antenna

We present the results of a Monte Carlo simulation for the energy loss distribution of high energy cosmic muons crossing a Weber-type gravitational wave (g.w.) antenna. The number of events per day of energy greater than an assigned value, generated in the antenna by the muons, is deduced.

The simulation shows that a rate of 60 events per week due to the cosmic background is expected in a sea-level g.w. detector with an energy sensitivity ten times greater than that of the present antennas. With the sensitivity of the resonant detectors approaching the quantum limit value the rate will increase to 5 × 10⁴ events per days. Therefore it seems unavoidable to carry on the experiment in an underground laboratory.     

The magnetic levitation of a gravitational antenna at low temperatures

Some levitation tests using superconducting coils on superconducting sheets are reported.These tests are used to provide preliminary data for the design of a levitation system for a gravitational antenna. Levitation tests on a small 60 kg bar are also reported. An empirical relation which enables displacement to be predicted as a function of the geometrical size, the weight, and the number of Ampere-turns of the coils is obtained from these tests.     

A two-channel circuit for protecting a resonant gravitational antenna from correlated non-Gaussian interference

A modernized circuit with a noninertial nonlinear element, a whitening filter and a matched filter, connected in series-parallel, for suppressing correlated non-Gaussian interference at the output of a cryogenic resonant gravitational antenna is considered. The algorithm is based on the use of optimum processing of vector signals. __________ Translated from Metrologiya, No. 5, pp. 3–9, May, 2008.     

Thermal noise of a laser gravitational antenna with an elastic clip

The behavior of the spectral density of the thermal noise of laser gravity antennas fastened by an elastic clip with dissipative losses in the mounting is investigated, using a smooth perturbations method based on the fluctuation-dissipation theorem. Translated from Izmeritel'naya Tekhnika, No. 3, pp. 3–5, March, 1998.     

Geophysical noise in the virgo gravitational antenna

The possibility of obtaining geophysical information from the system for controlling the position of the mirrors of the VIRGO laser-interferometric gravitational antenna and from angular perturbations of the vertical mirror lines is examined. Results from a study of tidal horizontal deformations are analyzed. Translated from Izmeritel’naya Tekhnika, No. 2, pp. 3–6, February, 2009.     

First-level Dulkyn gravitational wave detector

The functional-block diagram of the Dulkyn gravitational wave detector is described.     

Measurements of the quality factor of a quartz crystal gravitational radiation antenna

For an optimally matched detector of gravitational radiation pulses, the sensitivity depends largely on the quality factor, Q, of the antenna material. Although in general the Q's of many materials tend to increase at low temperatures, their temperature dependence is marked by relative minima that can affect the sensitivity of the detector. The determination of these minima is therefore of great importance in the selection of the useful temperature range in which to operate the detector. The measurements reported here refer in particular to the first quartz antenna developed by the Regina Group. Its resonant frequency is 25.2 kHz and the measurements span the range from 300 K down to 1 K.     

Mirror-orientation noise in a Fabry-Perot interferometer gravitational wave detector

The influence of angular mirror-orientation errors on the length of a Fabry-Perot resonator is analyzed geometrically. Under conditions in which dominant errors are static or vary slowly over time, the analysis permits a simple prediction of the spectrum of short-term cavity length fluctuations resulting from mirror-orientation noise. The resulting model is applicable to the design of mirror control systems for the Laser Interferometer Gravitational-Wave Observatory, which will monitor separations between mirrored surfaces of suspended inertial test bodies as a way to measure astrophysical gravitational radiation. The analysis is verified by measuring the response of the Laser Interferometer Gravitational- Wave Observatory's 40-m interferometer test-bed to the rotation of its mirrors.     

Vacuum control system for the AIGO gravitational wave detector

In this article a vacuum control system for the Australian International Gravitational Observatory (AIGO) research facility is described. The very large UHV vacuum system requires ultra-low hydrocarbon partial pressures and must be protected in order to prevent contaminations due to accidents. The system utilizes an Ethernet based remote automated system and supports dynamic monitoring of the entire vacuum system from any work station on the Local Area Network. The control system uses simple hardware and can be easily expanded for the proposed 4 km AIGO detector.     

Vacuum-system design for the large-scale cryogenic gravitational wave telescope

The large-scale cryogenic gravitational wave telescope (LCGT) requires ultra-high vacuum tubes which the laser beams pass through. Two 3-km vacuum tubes are kept in ∼10⁻⁷ Pa of vacuum pressure so as to reduce scattering-effects due to residual gas molecules. The stainless-steel material with electro-chemical buffing is the most available for use as long tubes of 1 m in diameter. To reduce noises due to scattered light from the surface of tubes, a lot of baffles are inserted into the tubes.     

Sampling the output signal from a resonant gravitational antenna with fast filtering

The scope for coherent digital processing is considered for the narrow-band random process at the output of a resonant gravitational antenna operating with fast filtering and low-frequency sampling. __________ Translated from Izmeritel’naya Tekhnika, No. 7, pp. 7–10, July, 2007.     

Peculiarities of the response of a laser interference gravitational antenna to low-frequency disturbances

Translated from Izmeritel'naya Tekhnika, No. 10, pp. 26–28, October, 1990.     

空间引力波探测干涉仪探测模式比较研究

为了实现毫赫兹频段的引力波信号测量,基于激光干涉体制的空间引力波探测计划要求干涉系统硬件本底噪声低于星间散粒噪声极限,这对光机设计及相应干涉载荷提出了严苛的工程指标。本文从探测模式选择的角度出发,推导了在单探测器模式和平衡模式下读出噪声和杂散光噪声在干涉信号中的表达形式,并就科学干涉仪的弱光干涉过程进行了详细讨论。结果表明,平衡模式可以跨量级的抑制激光功率涨落和后向杂散光引起的干涉相位噪声,但其抑制能力受限于合束器的不等比分光性质。为此引入相对增益因子来补偿合束器的不等比分光特性,进一步的分析表明,电子学手段的增益补偿只能消除不等比分光对两者之一的影响,不能同时兼顾,需要在激光功率涨落噪声和杂散光噪声的抑制之间平衡选择增益补偿。即便如此,平衡模式下的跨量级的噪声抑制能力,仍然可望降低对激光功率涨落和望远镜杂散光的工程指标要求。

     

Alignment of an interferometric gravitational wave detector

Interferometric gravitational wave detectors are designed to detect small perturbations in the relative lengths of their kilometer-scale arms that are induced by passing gravitational radiation. An analysis of the effects of imperfect optical alignment on the strain sensitivity of such an interferometer shows that to achieve maximum strain sensitivity at the Laser Interferometer Gravitational Wave Observatory requires that the angular orientations of the optics be within 10(-8) rad rms of the optical axis, and the beam must be kept centered on the mirrors within 1 mm. In addition, fluctuations in the input laser beam direction must be less than 1.5 x 10(-14) rad/ radicalHz in angle and less than 2.8 x 10(-10) m/ radicalHz in transverse displacement for frequencies f > 150 Hz in order that they not produce spurious noise in the gravitational wave readout channel. We show that seismic disturbances limit the use of local reference frames for angular alignment at a level approximately an order of magnitude worse than required. A wave-front sensing scheme that uses the input laser beam as the reference axis is presented that successfully discriminates among all angular degrees of freedom and permits the implementation of a closed-loop servo control to suppress the environmentally driven angular fluctuations sufficiently.