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.
We present a technique for the stable transfer of an optical frequency reference over a kilometer-scale optical fiber link. This technique implements phase measurements and laser feedback to cancel ...out the phase fluctuations that are introduced to an optical frequency standard as it passes through the fiber. We also present results for a bench top experiment, developed for the Advanced LIGO lock acquisition system, where this technique is implemented to phase-lock two Nd:YAG lasers, through a 4.6 km optical fiber. The resulting differential optical frequency noise reaches a level as low as 0.5 mHz/ radical Hz for Fourier frequencies between 5 Hz and 20 Hz, which is equal to a fractional frequency stability of 1.7 x 10(-18)/ radical Hz.
We present the first demonstration of real-time closed-loop control and deterministic tuning of an independently suspended Fabry-Perot optical cavity using digitally-enhanced heterodyne ...interferometry, realising a peak sensitivity of \(\sim\)10 pm\(/\sqrt{\mathrm{Hz}}\) over the 10-1000 Hz frequency band. The methods presented are readily extensible to multiple coupled cavities. As such, we anticipate that refinements of this technique may find application in future interferometric gravitational-wave detectors.
Recent gravitational-wave observations from the LIGO and Virgo observatories have brought a sense of great excitement to scientists and citizens the world over. Since September 2015,10 binary black ...hole coalescences and one binary neutron star coalescence have been observed. They have provided remarkable, revolutionary insight into the "gravitational Universe" and have greatly extended the field of multi-messenger astronomy. At present, Advanced LIGO can see binary black hole coalescences out to redshift 0.6 and binary neutron star coalescences to redshift 0.05. This probes only a very small fraction of the volume of the observable Universe. However, current technologies can be extended to construct "\(3^\mathrm{rd}\) Generation" (3G) gravitational-wave observatories that would extend our reach to the very edge of the observable Universe. The event rates over such a large volume would be in the hundreds of thousands per year (i.e.tens per hour). Such 3G detectors would have a 10-fold improvement in strain sensitivity over the current generation of instruments, yielding signal-to-noise ratios of 1000 for events like those already seen. Several concepts are being studied for which engineering studies and reliable cost estimates will be developed in the next 5 years.
Interferometric gravitational wave detectors operate with high optical power in their arms in order to achieve high shot-noise limited strain sensitivity. A significant limitation to increasing the ...optical power is the phenomenon of three-mode parametric instabilities, in which the laser field in the arm cavities is scattered into higher order optical modes by acoustic modes of the cavity mirrors. The optical modes can further drive the acoustic modes via radiation pressure, potentially producing an exponential buildup. One proposed technique to stabilize parametric instability is active damping of acoustic modes. We report here the first demonstration of damping a parametrically unstable mode using active feedback forces on the cavity mirror. A 15,538 Hz mode that grew exponentially with a time constant of 182 sec was damped using electro-static actuation, with a resulting decay time constant of 23 sec. An average control force of 0.03 nNrms was required to maintain the acoustic mode at its minimum amplitude.
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