This thesis deals with aspects of gravitational wave detection relating directlyudto the proposed LISA mission.udThe thesis begins with a review of gravitational wave astrophysics, starting withuda brief description of the prediction and nature of gravitational radiation as a consequenceudof General Relativity. A short description of possible astrophysical sourcesudis given along with current estimates of signal sources and strengths.udThe history of gravitational wave detectors is then briefly outlined, from theudearly 1960s and the first resonant bar, through to the modern long baseline laserudinterferometers currently under construction.udDiscussion then turns to the joint ESA/NASA space-borne interferometer, LISA.udLISA involves picometre precision laser interferometry between spacecraft separatedudby millions of kilometres. Among the considerable technical challenges involved areudthe need for laser and clock frequency stabilisation schemes, active phase-lockedudlaser transponders and precision telescope design.udAfter an overview of the mission concept, the thesis deals with the issue ofudgravitational wave signal extraction from the various interferometric data streamsudproduced in the six LISA spacecraft. A scheme for obtaining the necessary transferudof clock stability around the set of spacecraft is presented.udLISA is planned to use diode-pumped solid state lasers. Experiments carried outudto characterise the frequency noise of such a laser over the timescales of interest toudthe LISA mission are then described. Active frequency stabilisation to a triangularudFabry-Perot reference cavity is undertaken, with independent measurements ofudresidual frequency noise obtained from a second analyser cavity.udIn LISA, the divergence of the laser beams as they propagate along the long armsudof the interferometer means that only a very small amount of light is received by anyudspacecraft. The phase locking system has to function with this low received intensityudand should, ideally, produce a transponded beam with relative phase fluctuationsuddetermined by the photon shot noise of the weak received light.udA test and demonstration of the phase-locked laser transponder scheme for LISAudis then presented. The frequency stabilised laser is used as the master oscillator, anduda second identical laser is used as the slave. Results are obtained both from withinudthe stabilisation system and also from out-of-Ioop measurements using an independentudoptical path. At relative power levels approaching those in LISA, performanceudclose to the shot noise limit was demonstrated over part of the frequency spectrumudof interest. Some excess noise was, however, found at milliHertz frequencies, mostudprobably due to thermal effects.udThe thesis then continues with an investigation of far-field wavefront aberrationsudcaused by errors in the transmitting telescopes originally planned for LISA. Anyudphase variation across the near field wavefront (defined as the wavefront on the primaryudmirror), caused, for example, by a mis-alignment of the telescope mirrors, willudproduce phase variation in the far-field wavefront. Coupled with pointing fluctuationsudof the incoming light, these wavefront distortions can cause excess displacementudnoise in the interferometer readout. The starting point of the investigation was to redesignudthe LISA telescope in order to remove both spherical and coma aberrations.udUsing Gaussian ray tracing techniques, the effect of near field aberrations on the farudfield phase was explored. A revised Ritchey-Chretien telescope design is describedudand numerical simulations presented.udFinally the thesis concludes with a summary of the work carried out, setting theudresults in the context of the development of the LISA mission.
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