Deployable stable lasers for gravitational wave interferometers.
Date
2009
Authors
Hosken, David John
Editors
Advisors
Veitch, Peter John
Munch, Jesper
Munch, Jesper
Journal Title
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Type:
Thesis
Citation
Statement of Responsibility
Conference Name
Abstract
The most promising technique for the direct, ground-based detection of gravitational waves is the use of advanced interferometric gravitational wave detectors. These detectors use long-baseline Michelson interferometers, where the critical enabling component is the laser. The laser required for these interferometers must provide a low noise, single frequency, diffraction limited, high power TEM₀₀ beam. Very importantly, the laser beam must be available continuously and without the need for operator intervention.
In this thesis I describe the development and characterisation of injection-locked 10 W Nd:YAG lasers, designed specifically for use at the Australian Consortium for Interferometric Gravitational Astronomy (ACIGA) High Power Test Facility (HPTF) in Western Australia, and on the Japanese TAMA 300 gravitational wave interferometer (GWI). The starting point was a 5 W laboratory laser that had demonstrated the proof-of-principle; however this laser had insufficient power, inadequate reliability, and was not suitable for deployment to a remote site. I describe the development of this laser technology and design to realise reliable, longterm operation and field deployability, while satisfying the requirements for a GWI, with the final laser system bearing little resemblance to the proof-of-principle system. Injection-locked lasers were successfully installed at the ACIGA HPTF and at TAMA 300 in June 2004 and September 2005 respectively.
The 10 W laser uses a Nd:YAG Coplanar Pumped Folded Slab (CPFS) gain medium. The slab is side-pumped using a temperature controlled, fast-axis collimated, custom laser diode array, and conduction cooled in the orthogonal direction. Interferometry is used to measure the thermal lensing within the gain medium; these
measurements are used to design a single-mode, travelling-wave slave resonator. The entire slave laser is temperature controlled and mounted on an integrated, air-cooled base. The thermal design is validated by extensive thermal testing.
Long-term and robust injection-locking is achieved by using a servo system based on the Pound-Drever-Hall technique. I describe the development of a split feedback servo system to provide increased frequency stabilisation loop bandwidth and show that long-term injection-locking of the slave laser to a low power non-planar ring oscillator (NPRO) master laser produces a single frequency output at ~ 10 W with M²[subscript]x.y approx ≤ 1.1.
Finally, the noise of the injection-locked laser is characterised. Relative intensity noise measurements demonstrate stability comparable to current GWI laser sources, while the results of a heterodyne beat measurement show that the 10 W injectionlocked laser output has frequency noise limited by the NPRO input.
The laser installed at the ACIGA HPTF has been used to investigate the effects of increased intracavity laser powers on next-generation interferometers, with the laser described in this thesis being the key enabling component of this research.
School/Discipline
School of Chemistry and Physics : Physics
Dissertation Note
Thesis (Ph.D.) - University of Adelaide, School of Chemistry and Physics, 2009
Provenance
Copyright material removed from digital thesis. See print copy in University of Adelaide Library for full text.