V. P. Mitrofanov

The isolation of test masses for gravitational wave antennae

Abstract A method which permits one to reach a relaxation time of a mechanical pendulum oscillator longer than 4 × 10 7 s is described. The problem of the isolation of test masses for a gravitational wave antenna in order to reach a level of sensitivity of 1 × 10 -21 in units of the metric perturbation is discussed.

Investigations of the dynamics and mechanical dissipation of a fused silica suspension

The quality factor (Q) of a violin mode of a fiber under tension is related to the Q of the unloaded fiber by the dilution factor. We calculate this dilution factor from measurements of the Q’s and compare to measurements based on the shift of the violin mode frequencies with temperature, and to theoretical predictions. We also report supporting measurements of the temperature dependence of the Young’s modulus of fused silica. The Q’s of the violin modes are the highest yet measured in fused silica mechanical resonators.  2002 Published by Elsevier Science B.V.

Damping dilution factor for a pendulum in an interferometric gravitational waves detector

Mechanical loss in pendulums is a subject of great importance to gravitational waves detectors being built and being planned, as this determines the level of thermal noise associated with the detector suspensions. Relationships between the mechanical loss of the pendulum and the mechanical loss of the suspending fibres or wires can be derived in two apparently contradictory ways which give answers different by a factor of two. In this paper the differences are resolved and it is shown that both methods lead to the same answer.

On the thermal noise from the violin modes of the test mass suspension in gravitational wave antennae

Abstract The results of measurements of the quality factors of the violin modes in the test mass suspension are described. The measured values are between 1 × 10 7 and 4 × 10 7 . At this level of dissipation the thermal noise from the violin modes permits one to reach the standard quantum limit of the sensitivity in laser interferometric gravitational wave antennae.

Investigation of mechanical loss factors of some candidate materials for the test masses of gravitational wave detectors

This Letter describes the results of investigations into the mechanical losses of a selection of crystalline materials with the potential for use as the test masses in advanced gravitational wave detectors. We have measured loss factors of 3.7=10 y9 for HEM sapphire, to our knowledge the lowest measured loss factors of sapphire grown by a method suitable to produce test masses of the size and quality needed for use in advanced interferometric detectors. We also present the first measurements of the mechanical loss factors of YAG and Spinel at frequencies of interest for gravitational wave detection. q2000 Published by Elsevier Science B.V. All rights reserved.

Isolation of test masses in the advanced laser interferometric gravitational‐wave antennae

We analyze the experimental conditions required for the action of thermal, seismic, and excess noises on the test mass in the advanced LIGO experiment to be smaller than the uncertainty of the coordinate corresponding to the standard quantum limit. It is shown that the contribution of thermal noise can be made small enough if existing low‐dissipation materials are used for the suspension. On the other hand, the contribution of excess noise can be large and has to be examined thoroughly.

Technology for the next gravitational wave detectors

This paper reviews some of the key enabling technologies for advanced and future laser interferometer gravitational wave detectors, which must combine test masses with the lowest possible optical and acoustic losses, with high stability lasers and various techniques for suppressing noise. Sect. 1 of this paper presents a review of the acoustic properties of test masses. Sect. 2 reviews the technology of the amorphous dielectric coatings which are currently universally used for the mirrors in advanced laser interferometers, but for which lower acoustic loss would be very advantageous. In sect. 3 a new generation of crystalline optical coatings that offer a substantial reduction in thermal noise is reviewed. The optical properties of test masses are reviewed in sect. 4, with special focus on the properties of silicon, an important candidate material for future detectors. Sect. 5 of this paper presents the very low noise, high stability laser technology that underpins all advanced and next generation laser interferometers.

Damping of the test mass oscillations caused by multistrip electrostatic actuator

Abstract Multistrip electrostatic actuators are supposed to be used to provide fine control of the test mass position in laser interferometric gravitational wave detectors. This Letter describes the results of investigations into the damping Q e −1 of the torsion mode of bifilar all-fused silica pendulum caused by the electrostatic actuator. Our results show that the important source of losses is associated with properties of the pendulum mass surface that moves in the electric field of the actuator. The flame treatment of this surface allowed us to reduce the damping Q e −1 to the level of less than 3×10 −9 provided that forces up to 10 −4 N were exerted by the actuator on the suspended mass.

Controllable damping of high-Q violin modes in fused silica suspension fibers

Fused silica fiber suspension of the test masses will be used in the interferometric gravitational wave detectors of the next generation. This allows a significant reduction of losses in the suspension and thermal noise associated with the suspension. Unfortunately, unwanted violin modes may be accidentally excited in the suspension fibers. The Q-factor of the violin modes also exceeds 108. They have a ring-down time that is too long and may complicate the stable control of the interferometer. Results of the investigation of a violin mode active damping system are described. An original sensor and actuator were especially developed to realize the effective coupling of a thin, optically transparent, non-conducting fused silica fiber with an electric circuit. The damping system allowed the changing of the violin modes damping rate over a wide range.

Effect of heating on dissipation of mechanical energy in fused silica fibers

Abstract We present a study of the change of the Q-factors (Qs) of the bending modes of fused silica fibers caused by the heating of the fiber to 330 ° C and its subsequent cooling. Irreversible dependence of Qs on the temperature was observed. Baking the fiber resulted in the increase of Qs in a limited temperature range. Room temperature Qs did not vary after the baking of the fiber. We assume that these changes are caused by desorption of water molecules from the fiber surface. The possible mechanism of losses associated with adsorbed water is analyzed.