Jean-Paul Richard

Sensor and suspensions for a low‐temperature gravitational wave antenna

A dc‐biased resonant capacitor sensor for cylindrical gravitational antennas is discussed. For appropriate tuning and Q, its noise is found to be below the thermal noise of such antennas down to millidegree temperatures. ’’Ring’’ and ’’knife edge’’ suspensions of antennas are also discussed as possible alternates to wire and magnetic suspensions.

Cryogenic monocrystalline silicon Fabry–Perot cavity for the stabilization of laser frequency

A 1.6 kg silicon monocrystal was used to make a Fabry–Perot optical cavity operated at cryogenic temperatures. High‐resolution thermal expansion measurements were made as the silicon cooled to 4.2 K in order to characterize the cavity as a length reference standard. A helium–neon laser was then locked to a transmission resonance at liquid‐helium temperatures, and the laser frequency tracked the cavity resonance with error fluctuations at the level of 10 Hz/√Hz in the bandwidth dc to 1 Hz. Implications of the combined set of data, thermal expansion plus frequency‐tracking fluctuations, for using such a system as a frequency standard are discussed.

Laser instrumentation for one‐phonon sensitivity and wide bandwidth with multimode gravitational radiation detectors

In a multimode detector of gravitational radiation, the displacements induced in the antenna by the gravitational field can be amplified by many orders at the last resonator. Detection of the displacements of that resonator with a Fabry–Perot interferometer is considered. Quantum and classical sources of noise are analyzed and specifications for laser instrumented massive wideband systems operating at the level of δh=2.6×10−20 and 3×10−22/(Hz)1/2 are given. Three detectors could be used to cover the frequency range ≊400–≊1200 Hz with approximately uniform sensitivity.

Fabry-Perot Optical Resonator at Low Temperatures

Results of an experimental study of an optical Fabry-Perot resonant cavity operated between temperatures of 77 and 300 K are presented. In particular, measurements of the cavity finesse and thermal expansion are discussed in terms of new and current applications for such a device. These include energy sensors for Weber-bar type gravitational wave antennas, high-stability laser oscillators, and high-sensitivity thermal-expansion studies of condensed matter.

Sensitivity of a 1200-kg three-mode gravitational radiation detector instrumented with a Clarke or IBM dc SQUID

An analysis is made of a three‐mode 1200‐kg gravitational radiation detector operating at 1660 Hz and instrumented with a Clarke or IBM dc SQUID. The sensitivity projected for the detection of short pulses at 4.2 K and with optimum filtering is at the level of dh∼10−18 over a bandwidth of approximately 150 Hz.

Instrumentation of a resonant gravitational radiation detector with a planar thin-film dc SQUID

The instrumentation of a low‐temperature three‐mode gravitationa1 radiation antenna incorporating a low‐noise dc SQUID provided by IBM is described. The feedback circuitry necessary to maintain the linearity and dynamic range of the SQUID was found to drive the resonant system due to high coupling between the input coil and the feedback coil of the SQUID. In order for this type of planar thin‐film dc SQUID to be useful for gravitational radiation detectors and other applications requiring high Q input circuits, a solution to this feedback problem is needed. To this end, the nonlinear equations describing the dc SQUID with linear feedback are solved in terms of an isolated SQUID. The important feedback parameters for a high Q resonant system are found to be the slew rate of the electronics and the coupling constant ratio α2if/α2f, where α2if is the energy coupling efficiency between the feedback coil and input coil and α2f is the energy coupling efficiency between the feedback coil and the SQUID loop. Meth...

Room-temperature tests of an optical transducer for resonant gravitational wave detectors

A two-oscillator transducer incorporating a laser-illuminated Fabry-Perot cavity with a finesse of 77,500 and a power dissipation of 1.2 µW was tested at room temperature. The energy of the last resonator with a mass of 1.25 g was measured to be k(B)T within 8%, and no back action from the sensor could be detected. The lowest value of the noise measured away from resonance was 1.0 × 10(-15)m/√Hz, and the electronic noise was 3.2 × 10(-17) m/√Hz. That transducer is designed for a 2400-kg gravitational wave antenna operating at cryogenic temperatures. At 4.2 K and for mechanical quality factors of 3 × 10(6), the measured thermal and electronic noise levels would translate into a sensitivity in h equal to 7.0 × 10 (-19) and 1.5 × 10(-19), respectively.

Recent developments in the measurement of space time curvature

The theoretical sensitivity of a gravitational radiation antenna instrumented with a resonant capacitor transducer is considered. An expression for the sensitivity limit resulting from the preamplifier noise is derived. Experimental development and preliminary testing of a transducer is reported. Instrumentation of very high Q antennas is also discussed. In the Appendix, general aspects of the instrumentation of an antenna are studied.

Frequency noise induced by fiber perturbations in a fiber-linked stabilized laser

The effects of acoustic perturbations on an optical fiber that links a stabilized laser to its reference cavity are studied. An extrapolation indicates that 69 dB of acoustic noise impinging on a 1-m segment of the 10-m fiber contribute frequency noise at the level of 1 Hz/(Hz) ((1/2)) in the 1100- 21 00-Hz band.

Optical motion sensor for resonant-bar gravitational wave antennas

An experiment is described in which an optical method was used to measure fluctuations in the separation between two mirrors of a Fabry-Perot sensor cavity. Noise measurements were made to determine the sensitivity of this device to vibration amplitudes in the frequency range 1.1-2.1 kHz, which is of interestfor resonant-bar gravitational wave antennas. The rms spectral noise density for length fluctuations inthis range was 3.7 x 10(15-) m/Hz((1/2)) and can be related to electronic noise of the circuitry plus vibrationalnoise from the environment. The cavity finesse was relatively low at 117, and the power dissipated in the mirrors was estimated to be 1.9 muW. On a multimode gravitational wave detector, the sensor cavity would be formed by one reference mirror and by one mirror mounted on the last resonator. For a 1200-kg bar, 1.2-g last resonator system operating at 1600 Hz, the sensor described here would exhibit a noise temperature of 18 muK; the resolution in h in the case of negligible thermal noise from the mechanical system would be 3.7 x 10(-18)/Hz((1/2)). Improvements in the sensitivity in a quiet antenna-like environment should be possible with higher finesse mirrors.