1,252 research outputs found
An all-optical trap for a gram-scale mirror
We report on a stable optical trap suitable for a macroscopic mirror, wherein
the dynamics of the mirror are fully dominated by radiation pressure. The
technique employs two frequency-offset laser fields to simultaneously create a
stiff optical restoring force and a viscous optical damping force. We show how
these forces may be used to optically trap a free mass without introducing
thermal noise; and we demonstrate the technique experimentally with a 1 gram
mirror. The observed optical spring has an inferred Young's modulus of 1.2 TPa,
20% stiffer than diamond. The trap is intrinsically cold and reaches an
effective temperature of 0.8 K, limited by technical noise in our apparatus.Comment: Major revision. Replacement is version that appears in Phy. Rev.
Lett. 98, 150802 (2007
Squeezed light for advanced gravitational wave detectors and beyond
Recent experiments have demonstrated that squeezed vacuum states can be injected into gravitational wave detectors to improve their sensitivity at detection frequencies where they are quantum noise limited. Squeezed states could be employed in the next generation of more sensitive advanced detectors currently under construction, such as Advanced LIGO, to further push the limits of the observable gravitational wave Universe. To maximize the benefit from squeezing, environmentally induced disturbances such as back scattering and angular jitter need to be mitigated. We discuss the limitations of current squeezed vacuum sources in relation to the requirements imposed by future gravitational wave detectors, and show a design for squeezed light injection which overcomes these limitations
Arm-length stabilisation for interferometric gravitational-wave detectors using frequency-doubled auxiliary lasers
Residual motion of the arm cavity mirrors is expected to prove one of the
principal impediments to systematic lock acquisition in advanced
gravitational-wave interferometers. We present a technique which overcomes this
problem by employing auxiliary lasers at twice the fundamental measurement
frequency to pre-stabilise the arm cavities' lengths. Applying this approach,
we reduce the apparent length noise of a 1.3 m long, independently suspended
Fabry-Perot cavity to 30 pm rms and successfully transfer longitudinal control
of the system from the auxiliary laser to the measurement laser
Precise calibration of LIGO test mass actuators using photon radiation pressure
Precise calibration of kilometer-scale interferometric gravitational wave
detectors is crucial for source localization and waveform reconstruction. A
technique that uses the radiation pressure of a power-modulated auxiliary laser
to induce calibrated displacements of one of the ~10 kg arm cavity mirrors, a
so-called photon calibrator, has been demonstrated previously and has recently
been implemented on the LIGO detectors. In this article, we discuss the
inherent precision and accuracy of the LIGO photon calibrators and several
improvements that have been developed to reduce the estimated voice coil
actuator calibration uncertainties to less than 2 percent (1-sigma). These
improvements include accounting for rotation-induced apparent length variations
caused by interferometer and photon calibrator beam centering offsets, absolute
laser power measurement using temperature-controlled InGaAs photodetectors
mounted on integrating spheres and calibrated by NIST, minimizing errors
induced by localized elastic deformation of the mirror surface by using a
two-beam configuration with the photon calibrator beams symmetrically displaced
about the center of the optic, and simultaneously actuating the test mass with
voice coil actuators and the photon calibrator to minimize fluctuations caused
by the changing interferometer response. The photon calibrator is able to
operate in the most sensitive interferometer configuration, and is expected to
become a primary calibration method for future gravitational wave searches.Comment: 13 pages, 6 figures, accepted by Classical and Quantum Gravit
Precise calibration of LIGO test mass actuators using photon radiation pressure
Precise calibration of kilometer-scale interferometric gravitational wave
detectors is crucial for source localization and waveform reconstruction. A
technique that uses the radiation pressure of a power-modulated auxiliary laser
to induce calibrated displacements of one of the ~10 kg arm cavity mirrors, a
so-called photon calibrator, has been demonstrated previously and has recently
been implemented on the LIGO detectors. In this article, we discuss the
inherent precision and accuracy of the LIGO photon calibrators and several
improvements that have been developed to reduce the estimated voice coil
actuator calibration uncertainties to less than 2 percent (1-sigma). These
improvements include accounting for rotation-induced apparent length variations
caused by interferometer and photon calibrator beam centering offsets, absolute
laser power measurement using temperature-controlled InGaAs photodetectors
mounted on integrating spheres and calibrated by NIST, minimizing errors
induced by localized elastic deformation of the mirror surface by using a
two-beam configuration with the photon calibrator beams symmetrically displaced
about the center of the optic, and simultaneously actuating the test mass with
voice coil actuators and the photon calibrator to minimize fluctuations caused
by the changing interferometer response. The photon calibrator is able to
operate in the most sensitive interferometer configuration, and is expected to
become a primary calibration method for future gravitational wave searches.Comment: 13 pages, 6 figures, accepted by Classical and Quantum Gravit
Benefits of Artificially Generated Gravity Gradients for Interferometric Gravitational-Wave Detectors
We present an approach to experimentally evaluate gravity gradient noise, a
potentially limiting noise source in advanced interferometric gravitational
wave (GW) detectors. In addition, the method can be used to provide sub-percent
calibration in phase and amplitude of modern interferometric GW detectors.
Knowledge of calibration to such certainties shall enhance the scientific
output of the instruments in case of an eventual detection of GWs. The method
relies on a rotating symmetrical two-body mass, a Dynamic gravity Field
Generator (DFG). The placement of the DFG in the proximity of one of the
interferometer's suspended test masses generates a change in the local
gravitational field detectable with current interferometric GW detectors.Comment: 16 pages, 4 figure
A Gravitational Wave Detector with Cosmological Reach
Twenty years ago, construction began on the Laser Interferometer
Gravitational-wave Observatory (LIGO). Advanced LIGO, with a factor of ten
better design sensitivity than Initial LIGO, will begin taking data this year,
and should soon make detections a monthly occurrence. While Advanced LIGO
promises to make first detections of gravitational waves from the nearby
universe, an additional factor of ten increase in sensitivity would put
exciting science targets within reach by providing observations of binary black
hole inspirals throughout most of the history of star formation, and high
signal to noise observations of nearby events. Design studies for future
detectors to date rely on significant technological advances that are
futuristic and risky. In this paper we propose a different direction. We
resurrect the idea of a using longer arm lengths coupled with largely proven
technologies. Since the major noise sources that limit gravitational wave
detectors do not scale trivially with the length of the detector, we study
their impact and find that 40~km arm lengths are nearly optimal, and can
incorporate currently available technologies to detect gravitational wave
sources at cosmological distances
Perturbative framework for the pi(+)pi(-) atom
The perturbative framework is developed for the calculation of the pi(+)pi(-)
atom characteristics on the basis of the field-theoretical Bethe-Salpeter
approach. A closed expression for the first-order correction to the pi(+)pi(-)
atom lifetime has been obtained.Comment: 8 pages, LaTeX-fil
The Goldberger-Miyazawa-Oehme sum rule revisited
The Goldberger-Miyazawa-Oehme sum rule is used to extract the pion-nucleon
coupling constant from experimental N information. Chiral perturbation
theory is exploited in relating the pionic hydrogen s-wave level shift and
width results to the appropriate scattering lengths. The deduced value for the
coupling is , where the largest source of uncertainty is
the determination of the s-wave scattering length from the atomic
level shift measurement.Comment: 4 pages, 1 figure. v2: Revised the second last paragraph of 5th
section and clarified the electromagnetic corrections (Tromborg vs.
PT). Also removed the KH80 slope from the fig.
Journal of African Christian Biography: v. 4, no. 3
A publication of the Dictionary of African Christian Biography with U.S. offices located at the Center for Global Christianity and Mission at Boston University. This issue focuses on: 1. African Christian Biography Volume, Serialized: "Pointillist History and the Essential Role of Biography in the Dictionary of African Christian Biography,” by M. Sigg; 2. Biographies of I. Ababio by E. Acolatse and C. Y. Yeboa-Korie by T. Oduro; 3. A Tribute to J. Cone, by J. N. K. Mugambi; 4. Reviews of African Christian Biography Volume by E. Sibanda and the Africa Study Bible by J-C Loba Mkole; 5. Book Notes, compiled by B. Restric
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