Experimental results for intracavity-laser intensity-noise suppression, or "squashing," manifested as reduced fluctuations on the transmitted field photodetector voltage are presented. It is experimentally demonstrated that a rigid optical cavity within the feedback loop is compatible with squashing. The observed closed loop detector noise floor is approximately 16 nV/sub rms///spl radic/Hz in the acoustic frequency range (/spl sim/100 Hz), well below the quantum limit due to shot noise of 148 nV/sub rms///spl radic/Hz. This corresponds to 19 dB of observed noise suppression below the quantum limit and is consistent with the measured disturbance suppression function of the feedback loop. We also present measurements demonstrating the orthogonality of the squashing and frequency-locking control loops.

The Australian Consortium for Gravitational Astronomy has built a High Optical Power Test Facility north of Perth, Western Australia. Current experiments in collaboration with LIGO are testing thermal lensing compensation, and suspension control on an 80m baseline suspended optical cavity. Future experiments will test radiation pressure instabilities and optical spring in a high power optical cavity with similar to200kW circulating power. Once issues of operation and control have been resolved, the facility will go on to assess the noise performance of the high optical power technology through operation of an advanced interferometer with sapphire tests masses, and high performance suspension and isolation systems. The facility combines research and development undertaken by all consortium members, which latest results are presented.

The Australian Consortium for Interferometric Gravitational wave Astronomy (ACIGA) is carrying out research on the detection of gravitational waves using laser interferometry. Here we discuss progress on each of the major sub systems: data analysis, lasers and optics, isolation suspension and thermal noise, and configurations, and report on the development of a high optical power test facility in Gingin, Western Australia.

This paper describes the investigation of the frequency stability of tilt locking, a technique which derives an error signal for locking a laser to an optical cavity by use of spatial-mode interference. By independently locking two lasers to the same optical cavity and measuring the beat frequency, a direct measurement of the stability of tilt locking was obtained. The beatnote exhibited a normal Allan deviation of 3.3 Hz over a time interval of 100 ms, yielding a relative frequency stability of 1.3 /spl times/ 10/sup -14/. This result implies at least a fractional locking stability of 1.3 /spl times/ 10/sup -14/. Moreover, this stability was limited by fluctuations in the cavity spacer length and not the tilt-locking technique.

Using a radio frequency coherent modulation and demodulation technique, we explicitly measure both the amplitude and the phase response of Fabry-Perot interferometers in reflection. This allows us to differentiate clearly between overcoupled and undercoupled cavities and allows a detailed measurement of the full width at half-maximum, the free spectral range, and the finesse of the cavities.