I. First coincidence experiments between cryogenic resonant-mass gravitational wave detectors. II. Development of a thin film superconducting transducer for a gravitational wave antenna.

摘要

This dissertation is concerned with two aspects of detecting gravitational radiation from astrophysical sources.; First, the data collection and analysis for a coincidence experiment conducted in 1986 using gravitational wave detectors operated by Stanford University, the University of Rome, and Louisiana State University are described. This experiment was important for several reasons: (i) it was the first coincidence experiment between cryogenic resonant-mass detectors; (ii) it improved the observational upper limit on the flux of impulsive gravitational waves that impinge upon the Earth; and (iii) it lead to the development of a data analysis method for converting the experimental results into an astrophysically meaningful limit on the flux of gravitational radiation from impulsive events. With 95% confidence, the experiment established that the rate at which gravitational wave pulses with dimensionless wave amplitude h {dollar}geq{dollar} 3 {dollar}times{dollar} 10{dollar}sp{lcub}-17{rcub}{dollar} are impinging on the Earth from an isotropic source distribution is less than 1 event every 3 days.; Second, the development of a superconducting thin-film motion transducer intended for use on an ultra-low temperature detector now under construction is described. The sensitivity goal is h = 1 {dollar}times{dollar} 10{dollar}sp{lcub}-20{rcub}{dollar}. To reach this goal the physical temperature of the detector will be lowered to 40mK, a lower noise SQUID amplifier will be used, and a new motion transducer will be developed. The new transducer design described offers the possibility of less noise from electrical losses, wider bandwidth, and better reliability.; The design and fabrication process are described. The required fabrication technology includes depositing, patterning, and contacting niobium thin-films on silicon substrates; chemical machining of a high Q, large area, narrow gap, cantilever oscillator; and fabricating a thin-film heat switch for use in storing persistent currents in the superconducting circuits.; The experimental results obtained with the first prototype transducer are described. At low amplitudes of motion, the transducer's total mechanical and electrical Q was 9 {dollar}times{dollar} 10{dollar}sp5{dollar}. A lower bound on the electrical Q was set at 4 {dollar}times{dollar} 10{dollar}sp6{dollar}. These values should be sufficient to meet the sensitivity goal for the Stanford ultra-low temperature detector, and are especially encouraging since no design optimization has yet been done.