1. LIGO-G050251-00-W 2005 CLEO/QELS Joint Symposium on Gravitational Wave Detection 1 High-Power Stabilized Lasers and Optics of GW Detectors Rick Savage LIGO Hanford Observatory

2. LIGO-G050251-00-W 2005 CLEO/QELS Joint Symposium on Gravitational Wave Detection 2 Overview l In general, I will discuss issues and hardware solutions from a LIGO perspective because of familiarity. »Other GW interferometers (GEO, LCGT, TAMA, Virgo) face similar issues and have developed their own solutions as will be seen in subsequent talks in this session. l Lasers »Initial LIGO - ~10 watts –Requirements, performance, technical issues »Advanced LIGO ~ 200 watts –Concept, status l Optics »Initial LIGO core optics – test masses –Requirements, performance, technical issues »Advanced LIGO –Plans

3. LIGO-G050251-00-W 2005 CLEO/QELS Joint Symposium on Gravitational Wave Detection 3 GW detector – laser and optics Laser end test mass 4 km (2 km) Fabry-Perot arm cavity recycling mirror input test mass beam splitter Power Recycled Michelson Interferometer with Fabry-Perot Arm Cavities Power Recycled Michelson Interferometer with Fabry-Perot Arm Cavities signal

4. LIGO-G050251-00-W 2005 CLEO/QELS Joint Symposium on Gravitational Wave Detection 4 Closer look - more lasers and optics

5. LIGO-G050251-00-W 2005 CLEO/QELS Joint Symposium on Gravitational Wave Detection 5 Pre-Stabilized Laser System l Laser source l Frequency pre-stabilization and actuator for further stab. l Compensation for Earth tides l Power stab. in GW band l Power stab. at modulation freq. (~ 25 MHz)

6. LIGO-G050251-00-W 2005 CLEO/QELS Joint Symposium on Gravitational Wave Detection 6 Initial LIGO 10-W laser l Master Oscillator Power Amplifier configuration (vs. injection-locked oscillator) l Lightwave Model 126 non-planar ring oscillator (Innolight) l Double-pass, four-stage amplifier »Four rods - 160 watts of laser diode pump power l 10 watts in TEM 00 mode

7. LIGO-G050251-00-W 2005 CLEO/QELS Joint Symposium on Gravitational Wave Detection 7 LIGO PSL hardware l Running continuously since Dec. 1998 on Hanford 2k interferometer l Maximum output power has dropped to ~ 6 watts l Replacement of amplifier pump diode bars had restored performance in other units

8. LIGO-G050251-00-W 2005 CLEO/QELS Joint Symposium on Gravitational Wave Detection 8

9. 9 Concept for Advanced LIGO laser l Being developed by GEO/LZH l Injection-locked, end- pumped slave lasers l 180 W output with 1200 W of pump light

10. LIGO-G050251-00-W 2005 CLEO/QELS Joint Symposium on Gravitational Wave Detection 10 Frequency stabilization l Three nested control loops »20-cm fixed reference cavity »12-m suspended modecleaner »4-km suspended arm cavity l Ultimate goal:  f/f ~ 3 x 10 -22

11. LIGO-G050251-00-W 2005 CLEO/QELS Joint Symposium on Gravitational Wave Detection 11 Power stabilization l Sensors located before and after suspended modecleaner l Current shunt actuator controlling amplifier pump diode current l Pre-modecleaner for RIN measured upstream of MC

12. LIGO-G050251-00-W 2005 CLEO/QELS Joint Symposium on Gravitational Wave Detection 12 RIN at 20-30 MHz l Describe requirement l Give formula for filtering by PMC ala T. Ralph (from old CCD) l PMC parameters l Photo of optically contacted PMC

13. LIGO-G050251-00-W 2005 CLEO/QELS Joint Symposium on Gravitational Wave Detection 13 Tidal Compensation

14. LIGO-G050251-00-W 2005 CLEO/QELS Joint Symposium on Gravitational Wave Detection 14 Overall experience with LIGO I PSL l Reliability l Long locks l Pmc problems l Laser problems l Ref cav performance

15. LIGO-G050251-00-W 2005 CLEO/QELS Joint Symposium on Gravitational Wave Detection 15 Core Optics – Test Masses l Core optics requirements for initial and advanced ligo l Coating requirements l Q factor l Scattering/ absorption, etc. l Thermal noise – internal modes; noise due to coatings

16. LIGO-G050251-00-W 2005 CLEO/QELS Joint Symposium on Gravitational Wave Detection 16 LIGO I core optics Caltech data CSIRO data l Surface uniformity < 1 nm rms l Scatter < 50 ppm l Absorption < 2 ppm l ROC matched < 3% l Internal mode Q’s > 2 x 106

17. LIGO-G050251-00-W 2005 CLEO/QELS Joint Symposium on Gravitational Wave Detection 17 Advanced LIGO core optics

18. LIGO-G050251-00-W 2005 CLEO/QELS Joint Symposium on Gravitational Wave Detection 18 Preparation and installation challenges l Photos of cleaning and installation l Description of problems with etching coatings during cleaning.

19. LIGO-G050251-00-W 2005 CLEO/QELS Joint Symposium on Gravitational Wave Detection 19 Practical issues l Anamolous absorption l Vacuum incursions very costly – time and risky. l Need to make remote measuements due to water absorption in spring seats

20. LIGO-G050251-00-W 2005 CLEO/QELS Joint Symposium on Gravitational Wave Detection 20 Thermal compensation system CO 2 Laser ? Over-heat Correction Inhomogeneous Correction Under-heat Correction ZnSe Viewport Over-heat pattern Inner radius = 4cm Outer radius =11cm

21. LIGO-G050251-00-W 2005 CLEO/QELS Joint Symposium on Gravitational Wave Detection 21 Next-generation TCS PRM SRM ITM Compensation Plates l Design utilizes a fused silica suspended compensation plate l Actuation by a scanned CO2 laser (Small scale asymmetric correction) and nichrome heater ring (Large scale symmetric correction) l No direct actuation on ITMs for improved noise reduction, simplicity and lower power (Sapphire)

22. LIGO-G050251-00-W 2005 CLEO/QELS Joint Symposium on Gravitational Wave Detection 22 Kilometer-scale Fabry-Perot cavities l Free spectral range ~ 37.5 kHz l Plot of H_w(f) and H_L(f)

23. LIGO-G050251-00-W 2005 CLEO/QELS Joint Symposium on Gravitational Wave Detection 23 G-factor measurements

24. LIGO-G050251-00-W 2005 CLEO/QELS Joint Symposium on Gravitational Wave Detection 24 l Pre-stabilized laser »MOPA source »Frequency reference cavity »Pre-modecleaner cavity »Electro-optics modulators for stabilization and locking to cavities 15-m modecleaner cavity »Wavefront sensors and piezo- controlled input pointing l Faraday isolator l Mode-matching telescope l Core optics »Optical levers »Wavefront sensors l Output beams »modematching telescopes »Periscopes »Photodetectors

25. LIGO-G050251-00-W 2005 CLEO/QELS Joint Symposium on Gravitational Wave Detection 25 Pre-stabilized laser l Laser source and ancillary optical components and feedback control loops necessary to provide frequency and amplitude stabilized light to the interferometers (input optics subsystem). l Requirements »~ 10 watts of stabilized light (first generation) »Frequency pre-stabilization to the ?? Level (10 Hz to 100 kHz) »Power stabilization to the ?? level (10 Hz to 100 kHz). »Power stabilization at GW detection modulation freq. (20-30 MHz). »Availability – long (10s to 100s of hours continuous operation without loss of lock). l Insert schematic of PSL/photos

26. LIGO-G050251-00-W 2005 CLEO/QELS Joint Symposium on Gravitational Wave Detection 26 LIGO 10-W laser l Master oscillator power amplifier configuration l Developed under contract with Lightwave Electronics (model 126MOPA) l Oscillator – Non-planar ring oscillator »Monolithic design »Free-running frequency stability »Free-running RIN l Power amplifier »Four-rod, double-pass

27. LIGO-G050251-00-W 2005 CLEO/QELS Joint Symposium on Gravitational Wave Detection 27 Measurement Technique l Dynamic resonance of light in Fabry-Perot cavities ( Rakhmanov, Savage, Reitze, Tanner 2002 Phys. Lett. A, 305 239 ). Laser frequency to PDH signal transfer function, H  (s), has cusps at multiples of FSR and features at freqs. related to the phase modulation sidebands.

28. LIGO-G050251-00-W 2005 CLEO/QELS Joint Symposium on Gravitational Wave Detection 28 Misaligned cavity l Features appear at frequencies related to higher-order transverse modes. Transverse mode spacing: f tm = f 01 - f 00 = (f fsr /  acos (g 1 g 2 ) 1/2 l g 1,2 = 1 - L/R 1,2 l Infer mirror curvature changes from transverse mode spacing freq. changes. l This technique proposed by F. Bondu, Aug. 2002. Rakhmanov, Debieu, Bondu, Savage, Class. Quantum Grav. 21 (2004) S487-S492.

29. LIGO-G050251-00-W 2005 CLEO/QELS Joint Symposium on Gravitational Wave Detection 29 H1 data – Sept. 23, 2003 Lock a single arm Mis-align input beam (MMT3) in yaw Drive VCO test input (laser freq.) Measure TF to ASPD Q mon or I mon signal Focus on phase of feature near 63 kHz 2f fsr - f tm

30. LIGO-G050251-00-W 2005 CLEO/QELS Joint Symposium on Gravitational Wave Detection 30 Data and (lsqcurvefit) fits. Assume metrology value for R ETMx = 7260 m Metrology value for ITMx = 14240 m ITMx TCS annulus heating  decrease in ROC (increase in curvature) R = 14337 mR = 14096 m

31. LIGO-G050251-00-W 2005 CLEO/QELS Joint Symposium on Gravitational Wave Detection 31 To investigate heating via 1  m light … l Lock ifo. for > 2 hours w/o TCS; P laser = 2 W l Break full lock (t = 0) and quickly lock a single arm. l Misalign input beam (MMT3) in yaw Measure temporal evolution of H  (s) Note: 1  m light heats both ETM and ITM l H1 Xarm data Feb. 18, 2005

32. LIGO-G050251-00-W 2005 CLEO/QELS Joint Symposium on Gravitational Wave Detection 32 Yarm measurement Feb. 19, 2005

33. LIGO-G050251-00-W 2005 CLEO/QELS Joint Symposium on Gravitational Wave Detection 33 Comparison with model – Phil Willems l Time-dependent model based on Hello-Vinet formalism (J. Phys. France 51(1990) 2243-2261) l Free parameters: “cold” radius of curvature and power absorbed l Fits by eye (+,- 20%) Xarm surface absorption 33 mW  R ~ 370 m Xarm bulk absorption 76 mW  R ~ 320 m

34. LIGO-G050251-00-W 2005 CLEO/QELS Joint Symposium on Gravitational Wave Detection 34 Comparison with model - Yarm l Phil Willems – time-dependent Hello-Vinet model Yarm surface absorption 25 mW  R ~ 250 m Yarm bulk absorption 50 mW  R ~ 190 m

35. LIGO-G050251-00-W 2005 CLEO/QELS Joint Symposium on Gravitational Wave Detection 35 Calibration using TCS heaing results l TCS calibration Xarm: 220m / 37mW = 5.9 m/mW Yarm: 190m / 45mW = 4.2 m/mW »Surface (not bulk) absorption l 1064 nm heating Xarm: 293m / 5.9 m/mW = 49mW Yarm: 177m / 4.2 m/mW = 42 mW Assumes all heating on surface and no absorption in ETMs l Surface-equivalent, ITM-only absorption calibration 14.28 km 13.71 km 14.5 km 13.9 km  ~ 220 m  ~ 190 m

36. LIGO-G050251-00-W 2005 CLEO/QELS Joint Symposium on Gravitational Wave Detection 36 Issues – “cold” curvature differences l “Cold” values from 1064 nm meas. ITMX: 14.226 km difference ~ 50 m ITMY: 13.615 km difference ~ 100m l Systematic errors? »Alignment drifts – sampling different areas of TM surfaces l More complex, time-dependent behavior of surface distortions? »Phil Willems studying with time- dependent model of surface distortions »g factor measurements and reduced data available in LIGO-T050030-00-W 14.28 km 13.71 km 14.5 km 13.9 km  ~ 220 m  ~ 190 m