LIGO-G W "Colliding Black Holes" Credit: National Center for Supercomputing Applications (NCSA) LIGO for Chemists Fred Raab, LIGO Hanford Observatory

LIGO-G W Raab: Relativity2 Mass Warps Space, Affecting Paths of Objects and Light l Presence of mass gives space the appearance of lumpy glass as evidenced by the bending of light l First observed during the solar eclipse of 1919 by Sir Arthur Eddington, when the Sun was silhouetted against the Hyades star cluster A massive object shifts apparent position of a star Einstein Cross Photo credit: NASA and ESA

LIGO-G W Raab: Relativity3 The Frontier of Relativity: Gravitational Waves Gravitational waves are ripples in space when it is stirred up by rapid motions of large concentrations of matter or energy Rendering of space stirred by two orbiting black holes:

LIGO-G W Raab: Relativity4 Basic Signature of Gravitational Waves for All Detectors

LIGO-G W Raab: Relativity5 Laser Beam Splitter End Mirror Screen Viewing Sketch of a Michelson Interferometer

LIGO-G W Raab: Relativity6 LIGO (Washington)LIGO (Louisiana) The Laser Interferometer Gravitational-Wave Observatory Brought to you by the National Science Foundation; operated by Caltech and MIT; the research focus for more than 500 LIGO Scientific Collaboration members worldwide.

LIGO-G W Raab: Relativity7 How Small is Meter? Wavelength of light, about 1 micron One meter, about 40 inches Human hair, about 100 microns LIGO sensitivity, meter Nuclear diameter, meter Atomic diameter, meter

LIGO-G W Raab: Relativity8 How the atomic world affects LIGO In the lasers In the evacuated beam tubes In the mirrors

LIGO-G W Raab: Relativity9 Lasers Quantum mechanics tells us that particles are described by wave functions. »Measurable properties depend on the square of the wave function. »So, if I have a system of identical particles and I interchange two of them, then the square of the wave function is not affected. That means the wave function itself either »does not change at all under interchange »or it does change sign These two possibilities correspond to two different types of particles »Fermions, like electrons, protons and neutrons can never share the same state »Bosons, like photons, can all share the same state A laser beam is composed of identical photons all in the same state

LIGO-G W Raab: Relativity10 Light Amplification by Stimulated Emission of Radiation Pump Lasing Supply Energy Equilibration A four-level laser system

LIGO-G W Raab: Relativity11 Beam tubes Polarization wave retards incident wave causing a phase shift As atoms move the incident light encounters varying numbers of atoms This causes a fluctuating phase shift proportional to the density and polarizability of the gas in the tubes Need vacuum of atmospheres to mitigate this effect + - Incident Light Wave Induced Polarization Wave Molecule

LIGO-G W Raab: Relativity12 Molecules physadsorbed onto beam tube walls Van der Waals bonds are weak (~0.1 eV), but they keep molecules from being pumped out Occasionally the bonds do break, releasing molecules into gas phase and ruining vacuum quality To remove these molecules, need to raise temperature of the walls while pumping; this provides energy to break the Van der Waals bonds and allow the pumps to remove these molecules Beam tube wall Van der Waals bond Molecule

LIGO-G W Raab: Relativity13 Background Forces in GW Band = Thermal Noise ~ k B T/mode Strategy: Compress energy into narrow resonance outside band of interest  require high mechanical Q, low friction x rms  m f < 1 Hz x rms  2  m f ~ 350 Hz x rms  5  m f  10 kHz

LIGO-G W Raab: Relativity14 Thermal Noise Observed in 1 st Violins on H2, L1 During S1 Almost good enough for tracking calibration.