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We present the full implementation of a room-temperature gravitational wave bar detector equipped with an optomechanical readout. The bar mechanical vibrations are read by a Fabry-Pérot interferometer whose length changes are compared with a stable reference optical cavity by means of a resonant laser. The detector performance is completely characterized in terms of spectral sensitivity and statistical properties of the fluctuations in the system output signal. This kind of readout technique allows for wide-band detection sensitivity and we can accurately test the model of the coupled oscillators for thermal noise. Our results are very promising for cryogenic operation and represent an important step towards significant improvements in the performance of massive gravitational wave detectors. [ABSTRACT FROM AUTHOR]

Presents information on a study which analyzed the 1/frequency magnetization noise of thermal origin in amorphous ferromagnets at liquid-helium temperatures. Investigation of the low-temperature behavior; Description of the oscilloscope technique; Measurement of the superconducting quantum interference device background noise; Evaluation of the quality of noise spectra.

Presents a model for the thermal magnetic noise in a radio frequency superconducting quantum interference device (SQUID) coupled to a ferromagnetic core via a superconducting direct current flux transformer. Uses of ferromagnetic cores; Factor that introduces hysteresis, nonlinearity and delays in relation to ferromagnets; Effect of flux noise on the SQUID behavior.

Deals with a study which determined the measurements of the magnetic reversible complex permeability and the related thermal noise for a few cobalt-based soft ferromagnetic amorphous alloys. Information on the use of ferromagnetic cores in low-level signal circuits; Methodology of the study; Results and discussion.

Presents a study that measured thermal magnetic noise in a strip wound crystalline ferromagnetic core at 4.2 Kelvin. Details on the development of a dc SQUID magnetometer-based system to measure thermal magnetic noise; Schematic of the equivalent electrical circuit of the dc SQUID-based measuring system; Bilateral noise spectrum density of the measuring system.

Presents a study on thermal equilibrium noise with 1/f spectrum in a ferromagnetic alloy. Introduction to frequency-independent imaginary susceptibility; Experimental methods; Characteristics of the spectral noise density.

Reports the magnetization noise and imaginary susceptibility for the random anisotropy amorphous alloy DyNi[1.32]. Experiment conducted; Results; Discussion.

Presents a study which investigated the magnetic properties of soft ferromagnetic cores in the low field linear regime at low temperature. Discussion of thermal activation processes and quantum tunneling; Emphasis on the noise properties of amorphous and polycrystalline alloys; Application of Laplace transformation.

A setup for measuring mechanical losses of silicon wafers has been fully characterized from room temperature to 4 K in the frequency range between 300 Hz and 4 kHz: it consists of silicon wafers with nodal suspension and capacitive and optical vibration sensors. Major contributions to mechanical losses are investigated and compared with experimental data scanning the full temperature range; in particular, losses due to the thermoelastic effect and to the wafer clamp are modeled via finite element method analysis; surface losses and gas damping are also estimated. The reproducibility of the measurements of total losses is also discussed and the setup capabilities for measuring additive losses contributed by thin films deposited on the wafers or bonding layers. For instance, assuming that additive losses are due to an 80-nm-thick wafer bond layer with Young modulus about ten times smaller than that of silicon, we achieve a sensitivity to bond losses at the level of 5×10-3 at 4 K and at about 2 kHz. [ABSTRACT FROM AUTHOR]

Proposes an optical transduction chain for gravitational wave bar detectors. Generation of a signal transduction through a Fabry-Perot cavity; Detection of bar vibrations at harmonics simultaneously; Comparison between transducer and sensing cavities; Sources of noise in the detection system.

Electrical LC resonators with superconducting coils of ≈3.5 H inductance, operating in the frequency range 250-1500 Hz with quality factors up to Q ≈ 1.6×10[sup 6] are presented here. The coil has a reduced, < 100 pF, stray capacitance and is housed in a superconducting case. Measurements are made with a low coupling SQUID readout. Some possible applications of the device are briefly discussed. [ABSTRACT FROM AUTHOR]

Ultrahigh frequency rf-SQUID magnetometer employing a cryogenic preamplifier and a commercially available thin film rf-SQUID sensor have been designed, manufactured, and tested. The system has been operated at 316 MHz, which is the maximum pump frequency accepted by the thin film sensor. The cryogenic preamplifier has been built around a microwave high-electron-mobility transistor which was made unconditionally stable at ultrahigh frequency band by means of an appropriate circuit design, namely, a cascode configuration. The total flux noise of the magnetometer has been found to be 8.4 × 10-6[uppercase_phi_synonym]0/[Square_Root]Hz at 4.2 K and 5.8× 10-6[uppercase_phi_synonym]0/[Square_Root]Hz at 1.4 K. The temperature dependence of the fractional step rise α of the current-voltage rf characteristic has been measured to be proportional to the 2/3 power of the SQUID sensor temperature. The noise performance of the system at 4.2 K has been limited by the intrinsic SQUID noise only, in good agreement with theoretical predictions. [ABSTRACT FROM AUTHOR]

From measurements of additive and back action noise, we estimate the noise temperature of a two-stage superconducting quantum interference device (SQUID) amplifier developed for the acoustic wide-band gravitational wave detectors of the next generation. The minimum noise temperature evaluated at 8.9 kHz and T≤0.3 K is about 4 μK and corresponds to 10 times the quantum-limited noise temperature. As the high-Q electrical resonator used for the back action noise measurements behaves in many respects like the input load constituted by an acoustic gravitational wave detector, this SQUID amplifier is expected to keep the same noise performance once installed on the detector. [ABSTRACT FROM AUTHOR]

Presents abstracts of two studies on applied physics. Abstract of a study that examined the cryogenic valve developments for the European space launcher ARIANES; Abstract of a study that showed that the noise in ferromagnetic cores at liquid helium temperatures is limited by thermal fluctuation of the magnetization.

The energy sensitivity of a direct current (dc) superconducting quantum interference device (SQUID) can be improved if it is operated in a two-stage configuration. Employing this technique, a commercial dc SQUID system was modified and made competitive with other sensors especially designed for very low noise applications. We report the noise measurements performed in the temperature range 4.2 K–25 mK. At 4.2 K, the coupled energy sensitivity obtained with the two-stage dc SQUID was approximately ten times better than with a conventional readout electronics. The noise energy decreases linearly until approximately 300 mK, in good agreement with theoretical previsions. At lower temperature the hot-electron effect produces a saturation and the best energy sensitivity measured with open input coil is 35 h. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]