1. LIGO Hanford Observatory
Gravity Waves
And
LIGO
Corey Gray
LIGO Hanford Observatory
LIGO Laboratory

2. Brief Outline Intro (astronomy & gravity waves) Waves & Gravity Waves
GW Detectors (Bar, Ifo = LIGO)
Current State & Future
Demonstrations
LIGO Laboratory

3. The Laser Interferometer Gravitational-Wave Observatory
Intro
LIGO =
The Laser Interferometer Gravitational-Wave Observatory
Laser = type of light used for our interferometer
Interferometer = Instrument/measuring device
Gravitational Wave = signal
LIGO Laboratory

4. Astronomy & Gravity Waves
Naked-eye observations
LIGO Laboratory

5. Astronomy & Gravity Waves (cont.)
Electromagnetic (EM) observations
(visible, microwave, IR, UV, X-ray, etc.)
Radio telescope array
Mauna Kea Observatories
LIGO Laboratory

6. Astronomy & Gravity Waves (cont.)
Gravity Wave Observations (soon to come!)
Orbiting black holes
Albert Einstein
LIGO Hanford Observatory
LIGO Laboratory

7. Waves & Gravity Waves Wave phenomena throughout nature/everyday life
Waves on a lake
Light
Sound
Familiar?
LIGO Laboratory

8. Waves & Gravity Waves (cont.)
Picture of a Wave
LIGO Laboratory

9. Waves & Gravity Waves (cont.)
Frequency is measured in Hz (cycles / wavelengths per sec)
| sec |
~3 3/4Hz
~5 3/4Hz
LIGO Laboratory

10. Waves & Gravity Waves (cont.)
SOUND
Movement of a medium (i.e. air particles) by vibrating matter (piano, drum, book dropping)
Our ears have range of ~20-20,000Hz
Wiggling of air vibrates our ear drum so we can detect sound
LIGO Laboratory

11. Waves & Gravity Waves (cont.)
VISIBLE LIGHT
Small band of frequencies in EM spectrum
These wiggling waves cause rods/cones in our eyes to wiggle
red
Wavelength = 700nm
violet
Wavelength = 400nm
LIGO Laboratory

12. Waves & Gravity Waves (cont.)
ELECTROMAGNETIC SPECTRUM
Waves composed of coupled electric and magnetic fields
Includes large family of waves: radio, microwaves, IR, visible, UV, X-rays, gamma rays
All travel at “c”  c = speed of light = 3 x 10 ^8 m/s
LIGO Laboratory

13. Waves & Gravity Waves (cont.)
LIGO Laboratory

14. Waves & Gravity Waves (cont.)
Examples of different signals/waves:
Distant earthquake = Hz
Microseism (ocean weather) = 0.15 Hz
Truck & car traffic = Hz
Computer monitor (fan?) = Hz
Human voice range = 100 – 1200Hz
LIGO Laboratory

15. Waves & Gravity Waves (cont.)
Einstein’s Theory of General Relativity
Concept of space-time---update on Newton’s law of gravity
Space and time tied together
Instead of having gravitational forces, matter curves space time
LIGO Laboratory

16. Waves & Gravity Waves (cont.)
Curved space-time Static example
This example shows a large object (big warp in spacetime), w/ an object orbiting it.
LIGO Laboratory

17. Waves & Gravity Waves (cont.)
Generated by accelerating matter/energy, but matter must be HUGE, because….
Signals are extremely weak
Only catastrophic events generate signals big enough to detect
Possible sources:
Binary systems (NS, BH,pulsar)
NS/NS
Supernova 
Stochastic background (Big Bang remnants)
LIGO Laboratory

18. Waves & Gravity Waves (cont.)
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:
BH/BH (no noise)
BH/BH (noise)
LIGO Laboratory

19. Waves & Gravity Waves (cont.)
Gravity Wave Characteristics:
Velocity = speed of light, c
Gravity waves shrink space along one axis as they stretch space along another axis (this is convenient for ifos!)
LIGO Laboratory

20. Waves & Gravity Waves (cont.)
Gravity Wave passing through a person:
LIGO Laboratory

21. Waves & Gravity Waves (cont.)
Gravity waves are completely different
from EM waves(macro vs. nuclear level)
Will offer a completely different way to
look at the cosmos
Gravity waves will hold completely
different types of information to
current EM signals
LIGO Laboratory

22. Detectors = LIGO How Will We Detect Gravity Waves??
Indirectly have already been discovered
Resonant Bar Detectors
Interferometers
LIGO Laboratory

23. Detectors = LIGO (cont.)
1974—Taylor & Hulse
Indirectly discover existence of gravity waves emitted from pulsar/neutron star system.
Energy seeping away from binary system directly correlated to emission of gravity waves
Nobel Prize in 1993
LIGO Laboratory

24. Detectors = LIGO (cont.)
RESONANT BAR DETECTORS
First Instrument designed for gravity wave detection (1960s)
Developed by Joseph Weber (right)
LIGO Laboratory

25. Detectors = LIGO (cont.)
Bar is basically a bell
Designed to resonate at one frequency by a gravity wave
Consist of
Al bar (hundreds of lbs)
Seismic isolation
Motion detectors (piezos)
Limitations
Only one frequency
Hard to improve sensitivity
LIGO Laboratory

26. Detectors = LIGO (cont.)
INTERFEROMETERS (a.k.a. “ifo”)
Background
How it works
Current ifos = LIGO
Noise
Michelson Einstein Millikan
LIGO Laboratory

27. Detectors = LIGO (cont.)
IFO BACKGROUND
Interferometers were born from Michelson-Morley experiment of the late 1800s
High precision instrument used in many fields of science
Uses wave nature of light to detect small changes in lengths
interferes light w/ itself
LIGO Laboratory

28. Detectors = LIGO (cont.)
Rai Weiss (MIT) began work w/
use of an ifo as a gravity wave
detector (‘70s)
Resonating the arms of an ifo was
developed by Ron Drever (’70s); this
is birth of current LIGO set up
In the 80s Caltech developed a 40m experimental ifo & VIRGO begins
Mid 80s – present, Caltech/MIT join for current LIGO project
LIGO Laboratory

29. Detectors = LIGO (cont.)
How An Ifo Works
LIGO Laboratory

30. Detectors = LIGO (cont.)
LIGO Interferometer: Ideal GW Instrument
Technology improvements of last 30+ years
Geometry of an ifo is perfect for the orthogonal (90 deg) nature of gravity waves
Ifos can detect signals over a wide range of frequencies (tens to thousands of Hz)
Able to improve on sensitivity in many different ways (consists of several sub-systems)
LIGO Laboratory

31. Detectors = LIGO (cont.)
Locked on dark fringe
Acquiring w/ 1-arm locks
Locked
LIGO Laboratory

32. Detectors = LIGO (cont.)
How’s LIGO Unique?
Biggest Interferometers (one 2km and two 4km)
Two observatories
High power laser ( >6W)
Resonant arm cavities ( >2500W)
Seismic Isolation System
One of the largest vacuum systems
LIGO Laboratory

33. Detectors = LIGO (cont.)
How’s LIGO Unique?
1) Three of the Biggest Interferometers (one 2km and two 4km)
LIGO (Washington)
LIGO (Louisiana)
LIGO Laboratory

34. How’s LIGO Unique? (cont.)
Observatories at Hanford, WA (LHO) & Livingston, LA (LLO)
Support Caltech & MIT campuses
LIGO Laboratory

35. How’s LIGO Unique? (cont.)
High power (>6W) laser and Mode Cleaning Cavity
Custom-built
10 W Nd:YAG Laser
Cavity for defining beam geometry
LIGO Laboratory

36. How’s LIGO Unique? (cont.)
Resonant arm cavities (resonating > 2500W)
LIGO Laboratory

37. How’s LIGO Unique? (cont.)
Seismic Isolation System
LIGO Laboratory

38. How’s LIGO Unique? (cont.)
damped spring cross section
LIGO Laboratory

39. How’s LIGO Unique? (cont.)
Seismic noise over ~40Hz attenuated
Supports all internal components
LIGO Laboratory

40. How’s LIGO Unique? (cont.)
One of the largest vacuum systems
Vacuum down to 10^-9torr (vs. ~7.6x10^2 torr )
LIGO Laboratory

41. How’s LIGO Unique? (cont.)
Inside the Corner Station
Beam splitter chamber
LIGO Laboratory

42. How’s LIGO Unique? (cont.)
Specialized And Custom Optics
Massive optics (to reduce thermal noise)
Precisely polished surfaces
Specially coated
LIGO Laboratory

43. How’s LIGO Unique? (cont.)
Layers of Isolation:
Damped Table
Suspended Optic
Electronically damped/
controlled optic
LIGO Laboratory

44. Noise Issues Seismic Electrical Brownian/thermal
Microseism, tidal, cultural,
logging, etc.
Electrical
Brownian/thermal
Hurricane in North Atlantic
LIGO Laboratory

45. LIGO’s Future LIGO will have overall upgrade around 2007
Increased sensitivity
Increased range
LIGO2
LIGO1
LIGO Laboratory

46. Excitement at LIGO
LIGO Laboratory