Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
X-ray fluorescence wikipedia , lookup
Tight binding wikipedia , lookup
Wave function wikipedia , lookup
Ultrafast laser spectroscopy wikipedia , lookup
Double-slit experiment wikipedia , lookup
Atomic theory wikipedia , lookup
Matter wave wikipedia , lookup
Wave–particle duality wikipedia , lookup
Theoretical and experimental justification for the Schrödinger equation wikipedia , lookup
LIGO for Chemists "Colliding Black Holes" Credit: National Center for Supercomputing Applications (NCSA) Fred Raab, LIGO Hanford Observatory LIGO-G060033-00-W Mass Warps Space, Affecting Paths of Objects and Light Presence of mass gives space the appearance of lumpy glass as evidenced by the bending of light 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-G060033-00-W Raab: Relativity 2 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 LIGO-G060033-00-W Rendering of space stirred by two orbiting black holes: Raab: Relativity 3 Basic Signature of Gravitational Waves for All Detectors LIGO-G060033-00-W Raab: Relativity 4 Sketch of a Michelson Interferometer End Mirror End Mirror Beam Splitter Viewing Screen Laser LIGO-G060033-00-W Raab: Relativity 5 The Laser Interferometer Gravitational-Wave Observatory LIGO (Washington) LIGO (Louisiana) 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-G060033-00-W Raab: Relativity 6 How Small is 10-18 Meter? One meter, about 40 inches 10,000 100 Human hair, about 100 microns Wavelength of light, about 1 micron 10,000 Atomic diameter, 10-10 meter 100,000 Nuclear diameter, 10-15 meter 1,000 LIGO-G060033-00-W LIGO sensitivity, 10-18 meter Raab: Relativity 7 How the atomic world affects LIGO In the lasers In the evacuated beam tubes In the mirrors LIGO-G060033-00-W Raab: Relativity 8 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-G060033-00-W Raab: Relativity 9 Light Amplification by Stimulated Emission of Radiation Supply Energy Pump Equilibration Equilibration Lasing A four-level laser system LIGO-G060033-00-W Raab: Relativity 10 Beam tubes Incident Light Wave + Molecule Induced Polarization Wave - •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 10-12 atmospheres to mitigate this effect LIGO-G060033-00-W Raab: Relativity 11 Molecules physadsorbed onto beam tube walls Molecule Van der Waals bond Beam tube wall 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 LIGO-G060033-00-W Raab: Relativity 12 Background Forces in GW Band = Thermal Noise ~ kBT/mode xrms 10-11 m f < 1 Hz xrms 210-17 m f ~ 350 Hz xrms 510-16 m f 10 kHz Strategy: Compress energy into narrow resonance outside band of interest require high mechanical Q, low friction LIGO-G060033-00-W Raab: Relativity 13 Thermal Noise Observed in 1st Violins on H2, L1 During S1 Almost good enough for tracking calibration. LIGO-G060033-00-W Raab: Relativity 14