1. LOGO Gravitational Waves 2009-20440 I.S.Jang

2. www.themegallery.com 1. Introduction Contents ii. Waves in general relativity iii. Gravitational wave detectors iv. LIGO v. Future detectors

3. www.themegallery.com 1. Waves in general relativity

4. www.themegallery.com 1. Introduction

5. 1.1 Gravitational wave www.themegallery.com Fluctuation in the curvature of spacetime which propagates as a wave, traveling outward from the source From Wikipidia 1. Introduction

6. Predicted to exist by Albert Einstein in 1916 where, www.themegallery.com 1. Introduction

7. www.themegallery.com 1. Introduction

8. www.themegallery.com ii. Waves in general relativity

9. www.themegallery.com 1.2 Gravitational amplitude - Usually denoted h -Differences between major and minor axis -Shown here is h = 0.5(50%) -Most of sources are weaker than h~10 -20 -Quantity h can be expressed as below ii. Waves in general relativity

10. www.themegallery.com 1.2 Gravitational amplitude Examples) Then, we can calculate using this eqn (17Mpc) By using a detector with a baseline of 10km, ( Electron radius=3 x 10 -15 ) “This is rather optimistic estimate” ii. Waves in general relativity

11. 1.3 Gravitational wave frequencies - G.W source can’t much smaller than - Therefore rotation period T is - Finally frequency f From this, we can estimate the maximum mass of G.W source! www.themegallery.com ( Schwarzshild radius) ii. Waves in general relativity

12. 1.3 Gravitational wave frequencies www.themegallery.com ii. Waves in general relativity

13. 1.4 Experimental evidence for G.W 1993 Nobel prize! ii. Waves in general relativity

14. www.themegallery.com iii. Gravitational wave detectors

15.  There are 2 kind of detectors www.themegallery.com Bar(Cylindrical) detector Laser interferometer detector iii. Gravitational wave detectors

16. Bar(cylindrical) detector www.themegallery.com Built in 1966 by J.Weber Measure the extremely small resistance difference Bar(Resistance) must cool it down to under the 20k Frequency range ~ 1kHz Sensitivity h~10 -16 Only sensitive to extremely powerful GWs! iii. Gravitational wave detectors

17. First-generation efforts -Weber 1960 ‘bar’ detectors -Weber (’69): Announced that two bar detectors (DC & Chicago) were being excited simultaneously -15 groups (~’77,78,79): No convincing evidence -Sensitivity in early 70s for kiloHz bursts: Weber 1960 iii. Gravitational wave detectors

18. Bar(cylindrical) detector www.themegallery.com iii. Gravitational wave detectors

19. Laser interferometer detector  Measure space-time distortions from light travel time difference  Compare time in two ortho directions transverse to GW  Measure interference phase difference  More sensitive, wider frequency range iii. Gravitational wave detectors

20. Laser interferometer detector www.themegallery.com Ground-based (VIRGO-Italy) Space-based iii. Gravitational wave detectors

21. Ground-based detector www.themegallery.com iii. Gravitational wave detectors

22. Space-based detector -Using 2 or 3 satellite -Possible to use very long base line -Sensitive to lower frequency range -LISA (Laser Interferometer Space Antenna) -Omega (OMnidirectional Experiments with Gravitational Antennas) www.themegallery.com iii. Gravitational wave detectors

23. www.themegallery.com iv. LIGO

24.  Laser Interferometer Gravitational wave Observatory  Two ground observatories, separated by 3000 km – use triangulation to locate source  L-shaped ultra-high vacuum, 4km, 2km on each side iv. LIGO

25. www.themegallery.com

26.  Interferometer There are many possible configurations! a)Simple michelson interferometer b)Michelson with delay lines c)Michelson with Fabry-Perot arm cavities d)Power recycled Michelson with Fabry- Perot arm cavities Current LIGO use ‘(d)’ configuration! www.themegallery.com iv. LIGO

27.  Interferometer Antenna response function www.themegallery.com iv. LIGO Ex) freq = 1kHz → length = 10000km!! → impossible! Problems (1) mirror accuracy (2) diffraction limit (3) storage time

28.  Interferometer Antenna response function www.themegallery.com iv. LIGO

29. www.themegallery.com iv. LIGO

30.  Suspended Mirrors Mirrors are hung in a pendulum -> ‘freely falling masses’ Provide 100x suppression above 1hz Provide ultraprecise control of mirror displacement (< 1pm) iv. LIGO

31. Arm (vacuum tube) www.themegallery.com iv. LIGO

32. Arm (vacuum tube) Diameter : 1.2m, 3mm thickness Material : special low-hydrogen steel Volume = 20,000 m 3 (most largest!) Pressure : 10 -8 ~ 10 -9 torr iv. LIGO Altitude of 400km! → I S S

33. Noise www.themegallery.com iv. LIGO

34. Noise Fundamental limit -Seismic at low freq -Thermal at mid freq -Shot noise at high freq Facility limit -Gravity gradient -Stray light -Residual gas www.themegallery.com iv. LIGO

35. www.themegallery.com iv. LIGO

36. Advanced LIGO www.themegallery.com iv. LIGO Initial LIGOAdvanced LIGO

37. www.themegallery.com iv. LIGO

38. Advanced LIGO www.themegallery.com iv. LIGO Reduced noise - Higher power laser - Signal recycling - Low loss optics - Active seismic isolation - Multiple suspensions Sensitivity → An order of magnitude improvements!

39. www.themegallery.com v. Future detectors

40. Space-based detectors  LISA (Laser Interferometer Space Antenna)  E.W (Einstein Gravitational Wave Telescope) www.themegallery.com v. Future detectors

41. www.themegallery.com v. Future detectors LISA  Launch due 2018  Arm length : 5 million km Advantages  Away from the earth  Laser interferometry over astronomical distances  Sensitive to lower frequencies  Two independent interferometers