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"Colliding Black Holes"

Credit:National Center for Supercomputing Applications (NCSA)

LIGO for Chemists

Fred Raab,

LIGO Hanford Observatory

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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

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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:

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Basic Signature of Gravitational Waves for All Detectors

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Laser

Beam Splitter

End Mirror End Mirror

ScreenViewing

Sketch of a Michelson Interferometer

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LIGO (Washington) LIGO (Louisiana)

The Laser InterferometerGravitational-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.

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How Small is 10-18 Meter?

Wavelength of light, about 1 micron100

One meter, about 40 inches

Human hair, about 100 microns000,10

LIGO sensitivity, 10-18 meter000,1

Nuclear diameter, 10-15 meter000,100

Atomic diameter, 10-10 meter000,10

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How the atomic world affects LIGO

In the lasers In the evacuated beam tubes In the mirrors

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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

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Light Amplification by Stimulated Emission of Radiation

Pump

Lasing

Supply Energy

EquilibrationEquilibration

A four-level laser system

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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 10-12 atmospheres to mitigate this effect

+

-

Incident Light Wave

Induced Polarization Wave

Molecule

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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

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Background Forces in GW Band = Thermal Noise ~ kBT/mode

Strategy: Compress energy into narrow resonance outside band of interest require high mechanical Q, low friction

xrms 10-11 mf < 1 Hz

xrms 210-17 mf ~ 350 Hz

xrms 510-16 mf 10 kHz

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Thermal Noise Observed in 1st Violins on H2, L1 During S1

Almost good enough for tracking calibration.