Download LIGO4Chemists - Hanford Observatory

LIGO for Chemists
"Colliding Black Holes"
Credit:
National Center for Supercomputing
Applications (NCSA)
Fred Raab,
LIGO Hanford Observatory
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Mass Warps Space, Affecting
Paths of Objects and Light
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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
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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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Sketch of a Michelson
Interferometer
End Mirror
End Mirror
Beam Splitter
Viewing
Screen
Laser
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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.
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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
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LIGO sensitivity, 10-18 meter
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How the atomic world affects LIGO

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
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
Supply
Energy
Pump
Equilibration
Equilibration
Lasing
A four-level laser system
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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
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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
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Background Forces in GW Band =
Thermal Noise ~ kBT/mode
xrms  10-11 m
f < 1 Hz
xrms  210-17 m
f ~ 350 Hz
xrms  510-16 m
f  10 kHz
Strategy: Compress energy into narrow resonance outside
band of interest  require high mechanical Q, low friction
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Thermal Noise Observed in 1st
Violins on H2, L1 During S1
Almost good
enough for
tracking
calibration.
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