Three-mode optomechanical interactions have been predicted to allow the creation of very high sensitivity transducers in which very strong optical self-cooling and strong optomechanical quantum ...entanglement are predicted. Strong coupling is achieved by engineering a transducer in which both the pump laser and a single signal sideband frequency are resonantly enhanced. Here we demonstrate that very high sensitivity can be achieved in a very simple system consisting of a Fabry-Perot cavity with CO{sub 2} laser thermal tuning. We demonstrate a displacement sensitivity of {approx}1x10{sup -17} m/{radical}(Hz), which is sufficient to observe a thermally excited acoustic mode in a 5.6 kg sapphire mirror with a signal-to-noise ratio of more than 20 dB. It is shown that a measurement sensitivity of {approx}2x10{sup -20} m/{radical}(Hz) limited by the quantum shot noise is achievable with optimization of the cavity parameters.
Three-mode opto-acoustic interactions in advanced laser interferometer gravitational wave detectors have high sensitivity to thermally excited ultrasonic modes in their test masses. Three mode ...interaction signal gain can change by 100% for thermally induced radius of curvature variations ~ 10-5, allowing the monitoring of thermal distortions corresponding to wavefront changes ~2 x 10-13m. We show that the three-mode gain for single cavity interactions can be monitored by observing beat signals in the transmitted or reflected light due to the thermal excitation of the many hundreds of detectable acoustic modes. We show that three mode interaction signals can be used at low optical power to predict parametric instabilities that could occur at higher power. In addition, at any power, the observed mode amplitudes can be used to control the interferometer operating point against slow environmental perturbations. We summarize data on an 80m cavity that demonstrates these effects and propose testing on full scale interferometer cavities to evaluate whether the technique has practical benefits that can be extended from single cavities to dual recycling interferometers.
We present the results of a LIGO search for gravitational waves (GWs) associated with GRB 051103, a short-duration hard-spectrum gamma-ray burst (GRB) whose electromagnetically determined sky ...position is coincident with the spiral galaxy M81, which is 3.6 Mpc from Earth. Possible progenitors for short-hard GRBs include compact object mergers and soft gamma repeater (SGR) giant flares. A merger progenitor would produce a characteristic GW signal that should be detectable at the distance of M81, while GW emission from an SGR is not expected to be detectable at that distance. We found no evidence of a GW signal associated with GRB 051103. Assuming weakly beamed gamma-ray emission with a jet semi-angle of 30 deg we exclude a binary neutron star merger in M81 as the progenitor with a confidence of 98%. Neutron star-black hole mergers are excluded with > 99% confidence. If the event occurred in M81 our findings support the the hypothesis that GRB 051103 was due to an SGR giant flare, making it the most distant extragalactic magnetar observed to date.
The physical mechanisms responsible for pulsar timing glitches are thought to excite quasi-normal mode oscillations in their parent neutron star that couple to gravitational wave emission. In August ...2006, a timing glitch was observed in the radio emission of PSR B0833-45, the Vela pulsar. At the time of the glitch, the two co-located Hanford gravitational wave detectors of the Laser Interferometer Gravitational-wave observatory (LIGO) were operational and taking data as part of the fifth LIGO science run (S5). We present the first direct search for the gravitational wave emission associated with oscillations of the fundamental quadrupole mode excited by a pulsar timing glitch. No gravitational wave detection candidate was found. We place Bayesian 90% confidence upper limits of 6.3e-21 to 1.4e-20 on the peak intrinsic strain amplitude of gravitational wave ring-down signals, depending on which spherical harmonic mode is excited. The corresponding range of energy upper limits is 5.0e44 to 1.3e45 erg.
We present a search for periodic gravitational waves from the neutron star in the supernova remnant Cassiopeia A. The search coherently analyzes data in a 12-day interval taken from the fifth science ...run of the Laser Interferometer Gravitational-Wave Observatory. It searches gravitational wave frequencies from 100 to 300 Hz, and covers a wide range of first and second frequency derivatives appropriate for the age of the remnant and for different spin-down mechanisms. No gravitational wave signal was detected. Within the range of search frequencies, we set 95% confidence upper limits of 0.7--1.2e-24 on the intrinsic gravitational wave strain, 0.4--4e-4 on the equatorial ellipticity of the neutron star, and 0.005--0.14 on the amplitude of r-mode oscillations of the neutron star. These direct upper limits beat indirect limits derived from energy conservation and enter the range of theoretical predictions involving crystalline exotic matter or runaway r-modes. This is the first gravitational wave search to present upper limits on r-modes.
The Laser Interferometer Gravitational Wave Observatory (LIGO) is a network of three detectors built to detect local perturbations in the space-time metric from astrophysical sources. These ...detectors, two in Hanford, WA and one in Livingston, LA, are power-recycled Fabry-Perot Michelson interferometers. In their fifth science run (S5), between November 2005 and October 2007, these detectors accumulated one year of triple coincident data while operating at their designed sensitivity. In this paper, we describe the calibration of the instruments in the S5 data set, including measurement techniques and uncertainty estimation.
Three-mode opto-acoustic interactions can excite acoustic modes of the mirrors of an optical cavity. This was achieved when the frequency difference between the fundamental and higher order optical ...mode matches the frequency of appropriate acoustic mode of the mirror. The excitation also critically depends on the spatial overlap between acoustic and optical modes. In this Letter, we use a controlled CO2 laser to thermally change the radius of curvature of one mirror of an 80 m Fabry–Pérot cavity for three-mode interaction. Several acoustic modes of the cavity end mirror were observed with quality factors of ∼105–106 at the thermal noise level.
•CO2 laser heating.•Spectrum of ultrasonic modes.•Thermal relaxation time of Sapphire mirror.•Resolution of acoustic modes.•Parametric instability control.
Three-mode parametric instabilities may compromise stable operation of gravitational wave detectors. Instabilities manifest as varying radiation pressure distributions, derived from beating between ...two optical modes, exciting mirror acoustic modes in Fabry–Pérot cavities. Here we report the first demonstration of radiation pressure driving of ultrasonic acoustic modes via pairs of optical modes in gravitational wave type optical cavities. In this experiment ∼0.4 W of TEM01 mode and ∼1 kW of TEM00 mode circulated inside the cavity, an ∼181.6 kHz excitation was observed with amplitude ∼5×10−13 m. The results verify the driving force term in the parametric instability feedback model (Braginsky et al., 2001) 1. The interaction parametric gain was (3.8±0.5)×10−3 and mass-ratio scaled opto-acoustic overlap 2.7±0.4.
•Three mode parametric instability investigation.•Investigation in gravitation wave detector type optical cavity.•Demonstrate the radiation pressure driving term in parametric instability theory.•Proposition of method to characterize parametric instability susceptibility.
Three mode interactions could induce parametric instability in advanced gravitational wave detectors with high optical power circulating in the cavities. One of the conditions for parametric ...instability to occur is when the cavity frequency difference between fundamental mode and the high order mode matches the test mass acoustic mode frequency. The optical mode spacing is a function of cavity g-factor (radius of curvature). At the Gingin High Optical Power Facility, we have an 80 meter optical cavity particularly designed for studying high optical power effects in advanced gravitational wave detectors such as parametric instabilities. Here we present the recent results of thermal tuning the cavity g-factor by heating the test mass surface with a CO sub(2) laser to investigate the 3-mode interactions. Observation of test mass thermal noise peaks above 160 kHz enhanced by 3 mode interaction is presented.
PDF
