Overview of LIGOOverview of LIGO Noise BudgetNoise Budget DevelopmentThermal NoiseCalculation of Thermal NoiseState of Thermal Noise ProtocolSeismic NoiseSeismic Noise CalculationState of Seismic Noise ProtocolDisplacement NoiseCalculation of the Displacement NoiseState of Displacement Noise ProtocolOutput Electronics NoiseCalculation of Output Electronics NoiseState of Output Electronics Noise ProtocolDARM noiseConclusionsCalibration of the LIGO 40m Bartington MagnetometerOverviewSet - UpTheoryDataExperimental valueRevised Seismic CodeLASER INTERFEROMETER GRAVITATIONAL WAVE OBSERVATORY- LIGO -CALIFORNIA INSTITUTE OF TECHNOLOGYMASSACHUSETTS INSTITUTE OF TECHNOLOGYTechnical Note LIGO-T080074-00-R 2008/09/26Automated Noise Characterizationfor the 40 m LIGO FacilityW. Max JonesDistribution of this document:ISC GroupCalifornia Institute of Technology Massachusetts Institute of TechnologyLIGO Project, MS 18-34 LIGO Project, Room NW22-295Pasadena, CA 91125 Cambridge, MA 02139Phone (626) 395-2129 Phone (617) 253-4824Fax (626) 304-9834 Fax (617) 253-7014E-mail: [email protected] E-mail: [email protected] Hanford Observatory LIGO Livingston ObservatoryRoute 10, Mile Marker 2 19100 LIGO LaneRichland, WA 99352 Livingston, LA 70754Phone (509) 372-8106 Phone (225) 686-3100Fax (509) 372-8137 Fax (225) 686-7189E-mail: [email protected] E-mail: [email protected]://www.ligo.caltech.edu/LIGO-T080074-00-R1 AbstractThe Laser Interferometer Gravitational Observatory (LIGO) is currently prototyping newtechnologies at the 40 m test bed facility at the California Institute of Technology. BecauseLIGO’s success depends critically on it’s ability to limit noise sources which may interferewith the detection of weakly interacting gravitational waves, much time and effort has beenspent on cataloguing various noise sources. This SURF represents an extension of that effort.A suite of matlab scripts has been developed to automatically compile such a noise catalogue,called a noise budget, for the LIGO sites in Livingston, Louisiana and Hanford, Washington.Efforts have been made in the past to adapt these methods for the 40 m site.The SURF focused on re-writting parts of the automated noise budget suite to make themcompatible with the 40 m facility. Efforts focused on the seismic, DARM, PRC, SRC, andMICH noise sources. Furthermore, a magnetometer was installed at the 40 m site to measurethe effect of nearly static magnetic fields on the beam splitter optic.2 Overview of LIGOGeneral relativity predicts that rapid changes in a local gravitational field will propagateoutward at the speed of light as gravitational waves. Gravitational waves take the form ofplane waves in space time which interact with matter by stretching space-time along oneaxis while simultaneously compressing space-time along a perpendicular axis. Due of therelative weakness of the gravitational force, gravitational waves do not interact strongly withmatter. This fact presents the ambitious observer with a unique opportunity. Because of theweak coupling, only very large masses moving rapidly will produce gravitational waves ofsignificant size. Among these types of sources are inspiraling black holes, inspiraling neutronstars, and pre-recombintation inflation. Furthermore, the weak coupling of gravitationalwaves to matter means that unlike electromagnetic waves, gravitational waves will not besignificantly absorbed or scattered by matter between the source and the observer. Thissignifies that an observer who can construct a device to measure the infinitesimal effects ofa passing gravitational wave will have a direct observational window to some of the mostinteresting and least understood phenomena in our universe.The Laser Interferometer Gravitational Wave Observatory (LIGO) project is a joint ven-ture between the Massachusetts Institute of Technology (MIT) and the California Instituteof Technology (Caltech) to design, develop, construct, and operate devices capable of de-tecting gravitational waves. To this end LIGO has constructed three interferometers: a 4km arm-length interferometer in Livingston, Louisiana and two interferometers in Hanford,Washington with arm-lengths of 2 km and 4 km respectively. A Michelson interferometer inits most basic form consist of a laser, a beamsplitter, two mirrors, and a photodetector. Alaser beam is directed to the beamsplitter. A fraction of the incident beam passes throughthe beam splitter to continue down the x-arm of the interferometer to the x-arm end testmass mirror (ETMX). There the light is reflected directly back along its incoming path tothe beam splitter. Simultaneously, the non-transmitted incident laser light is reflected alongthe orthogonal y-arm of the interferometer to an identical end test mass mirror ETMY thatagain reflects the beam directly back to the beam splitter. A fraction of each of the reflectedpage 1LIGO-T080074-00-Rbeams will interfere at the anti-symmetric port and produce a interference fringe pattern onthe photodetector. By carefully manipulating the optical lengths of both arms an operatorcan create total destructive interference at the anti-symmetric port. This is the manner thatthe LIGO interferometers are operated in. A passing gravitational wave will lengthen thearms differentially, disturbing the state of destructive interference in a manner that allowsone to determine the change in absolute arm-length difference, ∆l = |lx-arm− ly-arm|.The best predictions indicate that passing gravitational waves of interest to LIGO mayinduce a strain of amplitude as small as 10−21in the frequency range 40-7000 Hz [9]. Witharm-lengths on the order of 1 km this implies that to detect the presence of such waves LIGOinterferometers must be able to register a change in differential arm-length on the order of10−18m. This is one-thousand times smaller than the diameter of a proton. A traditionalinterferometer set-up would be incapable of measuring such infinitesimal changes.Pre-stabilizedlaserETMXETMYITMYITMXAnti-symmetric portphoto-detectorFabry-PerotCavitiesModeCleanerPRMSRMBSlylxLxLyFigure 1: Interferometer LayoutTo achieve these sensitivities LIGO implements several novel subsystems. For example, byplacing input test mass mirrors in each arm with mirrored sides facing away from the inputbeam each arm is turned into a Fabry-Perot cavity. Light in each arm becomes trapped inthe Fabry-Perot cavity which is created by keeping each ITM/ETM pair an integer number