Development of optical techniques for space-borne laser interferometric gravitational wave detectors

QB Astronomy;QC Physics

McNamara, Paul William ; Ward, Harry

University:University of Glasgow

Department:School of Physics and Astronomy

关键词: QB Astronomy;    QC Physics;   

Others  :  http://theses.gla.ac.uk/8477/1/1998mcnamaraphd.pdf

来源: University of Glasgow

【 摘 要 】

This thesis deals with aspects of gravitational wave detection relating directlyto the proposed LISA mission.The thesis begins with a review of gravitational wave astrophysics, starting witha brief description of the prediction and nature of gravitational radiation as a consequenceof General Relativity. A short description of possible astrophysical sourcesis given along with current estimates of signal sources and strengths.The history of gravitational wave detectors is then briefly outlined, from theearly 1960s and the first resonant bar, through to the modern long baseline laserinterferometers currently under construction.Discussion then turns to the joint ESA/NASA space-borne interferometer, LISA.LISA involves picometre precision laser interferometry between spacecraft separatedby millions of kilometres. Among the considerable technical challenges involved arethe need for laser and clock frequency stabilisation schemes, active phase-lockedlaser transponders and precision telescope design.After an overview of the mission concept, the thesis deals with the issue ofgravitational wave signal extraction from the various interferometric data streamsproduced in the six LISA spacecraft. A scheme for obtaining the necessary transferof clock stability around the set of spacecraft is presented.LISA is planned to use diode-pumped solid state lasers. Experiments carried outto characterise the frequency noise of such a laser over the timescales of interest tothe LISA mission are then described. Active frequency stabilisation to a triangularFabry-Perot reference cavity is undertaken, with independent measurements ofresidual frequency noise obtained from a second analyser cavity.In LISA, the divergence of the laser beams as they propagate along the long armsof the interferometer means that only a very small amount of light is received by anyspacecraft. The phase locking system has to function with this low received intensityand should, ideally, produce a transponded beam with relative phase fluctuationsdetermined by the photon shot noise of the weak received light.A test and demonstration of the phase-locked laser transponder scheme for LISAis then presented. The frequency stabilised laser is used as the master oscillator, anda second identical laser is used as the slave. Results are obtained both from withinthe stabilisation system and also from out-of-Ioop measurements using an independentoptical path. At relative power levels approaching those in LISA, performanceclose to the shot noise limit was demonstrated over part of the frequency spectrumof interest. Some excess noise was, however, found at milliHertz frequencies, mostprobably due to thermal effects.The thesis then continues with an investigation of far-field wavefront aberrationscaused by errors in the transmitting telescopes originally planned for LISA. Anyphase variation across the near field wavefront (defined as the wavefront on the primarymirror), caused, for example, by a mis-alignment of the telescope mirrors, willproduce phase variation in the far-field wavefront. Coupled with pointing fluctuationsof the incoming light, these wavefront distortions can cause excess displacementnoise in the interferometer readout. The starting point of the investigation was to redesignthe LISA telescope in order to remove both spherical and coma aberrations.Using Gaussian ray tracing techniques, the effect of near field aberrations on the farfield phase was explored. A revised Ritchey-Chretien telescope design is describedand numerical simulations presented.Finally the thesis concludes with a summary of the work carried out, setting theresults in the context of the development of the LISA mission.