Several large-scale interferometric gravitational-wave detectors use resonant arm cavities to enhance the light power in the interferometer arms. These cavities are based on different optical ...designs: One design uses wedged input mirrors to create additional optical pick-off ports for deriving control signals. The second design employs input mirrors without wedge and thus offers the possibility of using the etalon effect inside the input mirrors for tuning the finesse of the arm cavities. In this paper, we introduce a concept of maximum flexibility that combines both of these options, by featuring wedges at the input mirrors and using the etalon effect instead in the end mirrors. We present a design for the arm cavities of Advanced Virgo. The paper focusses on evaluating the influence of etalon imperfections onto the overall Advanced Virgo performance. We use numerical simulations to derive requirements for the manufacturing accuracy of an end mirror etalon for Advanced Virgo. Furthermore, we give analytical approximations for the achievable tuning range of an imperfect etalon depending on the curvature and orientation mismatch of the two etalon surfaces. We evaluate the displacement noise originating from temperature driven optical phase noise of the etalon. In addition the influence of the etalon effect onto other Advanced Virgo subsystems such as the alignment sensing and control is analysed.
Gravitational wave (GW) interferometers are complex instruments, requiring years of commissioning to achieve the required sensitivities for the detection of GWs, of order 10−21 in dimensionless ...detector strain, in the tens of Hz to several kHz frequency band. Investigations carried out by the GEO 600 detector characterization group have shown that detector characterization techniques are useful when planning for commissioning work. At the time of writing, GEO 600 is the only large scale laser interferometer currently in operation running with a high duty factor, , limited chiefly by the time spent commissioning the detector. The number of observable GW sources scales as the product of the volume of space to which the detector is sensitive and the observation time, so the goal of commissioning is to improve the detector sensitivity with the least possible detector down-time. We demonstrate a method for increasing the number of sources observable by such a detector, by assessing the severity of non-astrophysical noise contaminations to efficiently guide commissioning. This method will be particularly useful in the early stages and during the initial science runs of the aLIGO and adVirgo detectors, as they are brought up to design performance.
The output mode cleaner of GEO 600 Prijatelj, M; Degallaix, J; Grote, H ...
Classical and quantum gravity,
03/2012, Letnik:
29, Številka:
5
Journal Article
Recenzirano
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The German-British interferometric gravitational wave detector GEO 600 is currently undergoing upgrades within the GEO-HF upgrade program. The goal of this program is to enhance the sensitivity of ...GEO 600, in particular at frequencies above 500 Hz. At these frequencies, the detector is limited by shot noise. An important element of the upgrade is the implementation of an output mode cleaner (OMC). This filtering cavity suppresses higher order spatial and temporal modes in the interferometer's output beam, thereby reducing the shot noise and enhancing sensitivity. Fully automated lock acquisition for the OMC was developed in order to ensure a high duty cycle of GEO 600. To maintain optimum sensitivity, the resonance condition of the OMC must be matched to the output beam from the interferometer. This requires continuous control of the resonance frequency of the OMC to the light, and alignment of the beam to the OMC. We describe the design and implementation of the OMC with special attention to the control techniques employed. We present results from the experience gained during the S6/VSR3 science run. Furthermore, we describe an upper limit measurement of the internal displacement noise of a piezoelectric actuator.
Novel asymmetric metallocene catalysts lead to low isotactic polypropylenes (iPP) with randomly distributed stereo irregularities. The polypropylenes are low crystalline and show elastic mechanical ...behavior due to physical crosslinking. The morphology of such iPP, which is responsible for the observed mechanical properties, is still sparsely resolved. In the present work a low isotactic, low crystalline metallocene iPP containing randomly distributed stereoerrors was investigated. The influence of the chain microstructure in the elastic properties was studied using two complementary investigation methods, X-ray diffraction and scanning force microscopy (SFM). For a better understanding of the unique mechanical properties, microscopic changes in morphology and strain-induced variation in chain orientation were monitored during uniaxial stretching using SFM and wide angle X-ray scattering measurements. For quantitative analysis and discussion the polymer chain orientations were calculated. The correlation between the orientation, the arrangements of the amorphous and crystalline phases observed by SFM, and the mechanical properties of the material at different elongation ratios allowed an interpretation of the macroscopic behavior on the microscopic scale. It was shown that the deformation behavior of low isotactic polypropylene with randomly distributed stereoerrors is in agreement with existing structural models, which proposed that small crystalline domains act as physical crosslinks for the amorphous matrix.
The AEI 10 m prototype interferometer Goßler, S; Bertolini, A; Born, M ...
Classical and quantum gravity,
04/2010, Letnik:
27, Številka:
8
Journal Article, Conference Proceeding
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A 10 m Prototype Interferometer facility is currently being set up at the AEI in Hannover, Germany. The Protoype Interferometer will be housed inside a 100 m 3 ultra-high vacuum envelope. Seismically ...isolated optical tables inside the vacuum system will be interferometrically interconnected via a Suspension Platform Interferometer. Advanced isolation techniques will be used, such as inverted pendulums and geometrical anti-spring filters in combination with multiple-cascaded pendulum suspensions, containing an all-silica monolithic last stage. The light source is a 35 W Nd:YAG laser, geometrically filtered by passing it through a photonic crystal fibre and a rigid pre-modecleaner cavity. Laser frequency stabilisation will be achieved with the aid of a high finesse suspended reference cavity in conjunction with a molecular iodine reference. Coating thermal noise will be reduced by the use of Khalili cavities as compound end mirrors. Data acquisition and control of the experiments is based on the AdvLIGO digital control and data system. The aim of the project is to test advanced techniques for GEO 600 as well as to conduct experiments in macroscopic quantum mechanics. Reaching standard quantum-limit sensitivity for an interferometer with 100 g mirrors and subsequently breaching this limit, features most prominently among these experiments. In this article we present the layout and current status of the AEI 10 m Prototype Interferometer project.
This work provides a new method for the absolute amplitude calibration of the GEO 600 interferometric gravitational wave detector. It is motivated by ongoing data analysis efforts carried out by the ...LIGO Scientific and Virgo Collaborations. Previously, arm length difference measurements of GEO 600 have been calibrated against the length of the first mode cleaner. Here, we re-evaluate this process, providing new measurements, and add a much simpler and more elegant method which calibrates against the laser wavelength. Since our calibration measurements involve injections of signals at least five orders of magnitude larger than possible gravitational wave signals, we also carry out a linearity check of the electrostatic drive (ESD) actuators used to make the injections. We find that these actuators exhibit no more than a 0.3% deviation from linearity over nearly six orders of magnitude. The new absolute amplitude calibration method that uses the laser wavelength as a length standard is shown here to be superior to the old one. Using this method, we show that the ESD gain over a two-year period varies by less than 4%.
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