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  • LIGO Livingston Observatory News
    signals propagate i e the direction opposite to the source where northwards is at the top of the plot at 90 degrees and the radial direction indicates the velocity amplitude of the seismic motion The data show the distribution of events where the ground motion exceeded one micron per second during a three hour interval on a typical weekday It is apparent that the noise doesn t come from any single source but rather arises almost entirely from sources that are located to the south of the observatory Above Plot showing the distribution of ground motion events We are pursuing several technical approaches to surmount this obstacle Foremost is a new controller for the actuators that has been designed to supply significantly more current to the actuators for brief periods This allows the system to apply much more force by more than a factor of five to counteract impulsive seismic disturbances This apparatus designed by Ken Watts and Rai Weiss is now undergoing thorough testing earlier on the bench and then in the interferometer and initial results are promising We have been able to lock a single Fabry Perot cavity even during the day mid week and this is a significant improvement in the robustness of the overall system A safety circuit which is an integral part of this new controller design automatically disables the controller whenever the rms current exceeds about 150 mA This protects the actuators from heating up and outgassing into the interferometer vacuum while still allowing instantaneous currents which are a few times higher than this On a second front we are planning to implement a feed forward compensator for the seismic ground motion This effort conducted primarily by Joe Giaime and Ed Daw will sense the ground motion along the direction of the Fabry Perot arms using seismometers mounted on the floor near the suspended test masses The seismometer outputs will be used to control external positioners fine actuators essentially long stroke piezoelectric stacks that will compensate for the ground motion Initial testing will be done over the frequency band of the micro seismic peak about 0 14 Hz where simulations of the procedure indicate that such a simple one degree of freedom compensation technique appears likely to be quite successful The micro seismic motion is also about one order of magnitude larger in Livingston than it is at Hanford We will also experiment with extending this technique into the 1 to 10 Hz band to further reduce ground noise See the Livingston LIGO Electronic Log entry on this topic for additional explanation of the technical approach being pursued Enter reader for user and readonly for password at the security window Finally on a third front we are examining the possibility of pursuing an early implementation of some of the active seismic isolation techniques being developed for advanced LIGO For example the hydraulic actuator prototypes now being readied for testing in the LASTI interferometer at MIT could possibly be replicated for integration into the external

    Original URL path: http://www.ligo.caltech.edu/LIGO_web/0110news/0110liv.html (2015-06-02)
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  • LIGO Caltech News
    from Israel Sweden and all over the United States Caltech was represented by Mark Coles Steve Frautschi Dave Hitlin Frank Porter and John Schwarz Coles Hitlin and Schwarz spoke The complete program is listed below A reception and banquet at the Gant a condominium complex followed the lectures on the evening of August 25 There was a general feeling of warmth and camaraderie throughout About 95 people came to the reception and banquet including all of Syd s family and many physicist and non physicist friends of all ages After dinner Mike Simmons led a fairly gentle roasting of Syd read various congratulatory messages from Fred Gilman Myron Bander Gordon Shaw Dennis Silverman and others and introduced a variety of speakers These included Roy Schwitters former director of the SSC Laboratory Sally Mencimer who ran the Physics Center for 30 years before retiring just a few years ago DeeDee McCabe tennis instructor to generations of fizzies and a true Aspen character and Paul Fishbane a collaborator for many years The evening concluded with the presentation to Syd by Steve Pinsky of a Mac I book appropriately inscribed Pre conference activities included an ad hoc welcoming reception on Friday evening at Syd s apartment featuring wild mushrooms that Syd had picked and Alaskan smoked salmon and smoked halibut Scenes from Sydfest Above At left Mark Coles background and Pierre Ramond Next from left to right PAC Chairman Bill Frazer Frank Porter and Mark Coles At left above from left to right Arnold Perlmutter S Peter Rosen and Moshe Kugler Next from left to right Mark Coles Hiroshi Ooguri and Bill Frazer Above In celebration of Syd s 75th birthday an inscribed Mac I book is presented to him by Steve Pinsky Below Syd stands with family members at a picnic held

    Original URL path: http://www.ligo.caltech.edu/LIGO_web/0110news/0110cit.html (2015-06-02)
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  • Special Report on Virgo
    input mirrors are substituted by totally reflecting mirrors and the so called Central InTerFerometer CITF is operated in the recycled Michelson configuration In this phase of commissioning the CITF is operated in the simple Michelson configuration shown in schematic outline in Figure 2 below The interferometer uses a low power Nd YAG laser as light source since the final laser is still being commissioned The input beam as well as all the interferometer mirrors and optical benches were aligned during the spring The interferometer was locked on the dark fringe for the first time in June 2001 Locking was acquired and maintained by controlling the optics position using electro magnetic actuators suspended behind the mirrors and attached to the same seismic isolator from which the mirrors are suspended Achieving lock was an important achievement for the fully digital control architecture used in VIRGO The goal of the run on 21 23 September was to collect a long stream of data with the interferometer operated in a well defined configuration Then the data would be used to help the detector characterization effort and to start a real data analysis activity The run was a big success The interferometer was in operation for three days 24 hours a day More than 30 people representing most of the VIRGO labs spent a part of their weekend on shift at Cascina Most of the software for interferometer control and data collection performed well The interferometer was kept locked on the dark fringe for most of the time Only four losses of lock occurred between Friday evening and Saturday morning and three of these were generated by human activity Starting from Saturday morning the Michelson interferometer was kept locked on the dark fringe until the end of the run for more than 51 hours later

    Original URL path: http://www.ligo.caltech.edu/LIGO_web/0110news/0110spr.html (2015-06-02)
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  • LIGO Hanford Observatory News
    upon us a description of this unique toy is Hanford s contribution to this issue of the newsletter The complete kit for building a replica Michelson interferometer pictured above costs about 120 This desktop model can readily measure mirror displacements of a few ten thousandths of a millimeter If you are a science hobbyist you may want to build one for yourself or give the parts and instructions to your science hobbyist friend And if you grow bored with it there s no need to let it sit on the shelf Your local high school science teacher would love to have one for classroom use The interferometer uses a laser light source split into two perpendicular beams that bounce off mirrors and return to the beam splitter The interference pattern created when the beams recombine on the beam splitter is projected by a lens onto a screen for viewing This pattern is sensitive to minute changes in the distances between the beam splitter and the mirrors The complete instructions for the kit can be found here and it includes internet addresses where you can buy any parts not available at your local hardware store The Michelson interferometer is an example of how the ever advancing frontier of knowledge transforms the Nobel Prize experiment of one era into a commonplace tool or even a demonstration model in future eras The American physicist Albert Michelson began developing his interferometer roughly 120 years ago before Edison invented the light bulb At that time it was a device on the cutting edge of research developed to investigate the propagation of light through space In fact we now recognize Michelson s experimental result in searching for the luminiferous ether as fundamental to modern theories connecting space time and gravitation He was awarded the Nobel Prize

    Original URL path: http://www.ligo.caltech.edu/LIGO_web/0112news/0112han.html (2015-06-02)
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  • LIGO Livingston Observatory News
    interferometer while locked You can now see a bright spot of light on the upper left and right images of the end mirrors of the X and Y arms This is from the kilowatt of laser light circulating in each arm cavity Since the interferometer is locked most of the light is circulating in the interferometer and there is little light reflected by the interferometer This can be seen in the dim image at the reflected port on the lower left On the lower right is seen an interference fringe on the Michelson dark port We are now working on keeping the interferometer locked for longer periods We also want to understand how to maintain the interferometer lock during the day when ground noise in the area is ten to one hundred times stronger than at night Feed Forward Reduction of the Micro Seismic Motion at LLO Contributed by Mark Coles from an edited presentation by Joe Giaime The surface of the earth is constantly vibrating with a period of about six to seven seconds This effect known as micro seismic motion is observed worldwide It is believed that most micro seismic motion is weather induced caused by the interaction of the wind with the ocean Huge storm waves change the loading on the ocean floor This time varying force produces waves which couple into deep geologic strata and from there they propagate around the world Here at Livingston Louisiana the amplitude of the micro seismic peak is typically around a few microns varying with weather conditions at sea The propagation velocity of the micro seismic peak in Livingston is around two kilometers per second so there can be a significant phase difference in the displacement of the input and end test masses of one of the interferometer arms depending on the relative direction of propagation of the micro seismic wave with respect to the interferometer orientation The micro seismic motion can therefore be larger than a wavelength of light and must be compensated for in order to maintain the interferometer in an optically resonant state The Fine Actuator System FAS incorporated into the LIGO design provides a means of compensating for this motion Piezo transducers with stroke lengths of about 90 microns allow displacement of the input and end test masses along the direction of each arm Joe Giaime and Ed Daw have developed a scheme by which the earth s micro seismic motion is sensed with high performance Streckheisen STS 2 three axis seismometers at the location of the input and end test masses A mathematical model was developed that provides a best estimate of the expected displacement along the interferometer axes of the suspended test masses due to the ground motion This model was decomposed into the interferometer degrees of freedom called CARM and DARM CARM refers to the common mode stretching of the interferometer arms while DARM is the differential change in arm length These are the degrees of freedom used by the interferometer s length

    Original URL path: http://www.ligo.caltech.edu/LIGO_web/0112news/0112liv.html (2015-06-02)
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  • LIGO MIT News
    fundamental reason is that because of the coefficient of thermal expansion very small random temperature fluctuations turn directly into very small random fluctuations of the optic s surface Since LIGO is trying to detect gravity waves which induce length changes of about 10 18 meters a coefficient of thermal expansion of 5x10 6 K means that mean temperature fluctuations greater than 10 12 K will be seen instead of gravity waves Statistical physics along with the well known quantities of heat capacity and density for sapphire predicts temperature variations typically less than 10 14 degrees K in the measured volume of a LIGO test mass so it is clear that this thermoelastic noise will not ruin everything but it will most certainly enforce a limit on the sensitivity of the detector Exactly where this limit lies depends on the value taken for thermal expansion which depending on who you ask varies by a factor of 2 Here at MIT we re trying to pin down a much more precise value for the thermal expansion coefficient of sapphire in addition to other parameters such as thermal conductivity and the thermo optic coefficient dn dT To measure these parameters we look at how a thermally isolated sapphire optic distorts when we abruptly begin to heat it with an external laser beam We then compare the measured distortion with a computer simulation we ve made of the optic s thermo mechanical response and adjust the material parameters in the model until the calculated behavior matches what we observe Figure 1 at left above shows a snapshot of the numerical model and Figure 2 at right is a photograph of the heating laser table a 10 Watt carbon dioxide laser typically used in industry for soldering Then Figures 3 and 4 below show some

    Original URL path: http://www.ligo.caltech.edu/LIGO_web/0112news/0112mit.html (2015-06-02)
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  • Reader Alert - LIGO Invades Your Local Newsstand!
    Sky Telescope feature we have a little more information chiefly because the scribe behind it is none other than than our own LIGO Deputy Director Dr Gary Sanders with a little help dotting the i s and crossing the t s from yours truly The article gives a concise overview of the history of gravitational wave detection and follows the path that led to the decision to construct LIGO It also presents a no holds barred look at the formidable engineering challenges LIGO confronts in its quest and explains the technological remedies devised to overcome these barriers Dr Sanders s article also briefly describes the other members of the gravitational wave detection family those interferometer projects underway in Europe in Asia even in space In Sky and Telescope the LIGO story is part of a suite of articles on the search for gravity waves and the interferometer community Insist on Quality LIGO Articles in Your Books Journals and Magazines It s Your Guarantee of Fine Reading Of course we realize that most of our loyal readers prefer to get all their LIGO info right here on the Newsletter Website But it s also true that many of you have grown

    Original URL path: http://www.ligo.caltech.edu/LIGO_web/0008news/0008ep.html (2015-06-02)
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  • LIGO Hanford Observatory News
    the system which is basically the full interferometer minus the end mirrors To understand how this works pretend the recycling mirror is absent If there was no recycling mirror light from the laser would be split by the beam splitter forming two beams that reflect off the input mirrors and then return to the beam splitter If the distances between these mirrors and the beam splitter are exactly the same the light returning to the beam splitter will recombine into a beam that returns toward the laser leaving the photodetector in the dark If we move the mirror on the right farther away from the beam splitter some light will spill onto the photodetector and less light will go back toward the laser The total of the energy going toward the laser and the energy going toward the photodetector will stay the same due to energy conservation If we continue moving the mirror on the right away from the beam splitter the light hitting the photodetector will increase until the distances between the beam splitter and the two mirrors is different by a quarter of the light s wavelength For our infrared light sources the wavelength is 1 1000th of a mm so a difference of 1 4000th of a mm will cause all of the light returning to the beam splitter to fall on the photodetector This process of switching light between the two directions toward the laser or toward the photodetector depending on the mirror distances is called interference If a laser is used for the light source we call the device a laser interferometer We operate our interferometer with the photodetector in the dark by using feedback to keep the mirrors in the correct places The forces we feed back to the mirrors to maintain the photodetector

    Original URL path: http://www.ligo.caltech.edu/LIGO_web/0008news/0008han.html (2015-06-02)
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