LIGO Commissioning Update LSC Meeting March 16 2004

LIGO Commissioning Update LSC Meeting, March 16, 2004 Peter Fritschel G 040066 -00 -D LIGO I

S 3: peak sensitivities G 040066 -00 -D LIGO I 2

S 3: reliability & stability G 040066 -00 -D LIGO I 3

Major Goals and Tasks After S 3 q Sensitivity Ø Operate at high power: achieve designed optical gain v Laser v Thermal compensation system (TCS) v Output mode cleaner (OMC) Ø Manage noise in auxiliary degrees-of-freedom Ø Finish acoustic mitigation Ø Clean up electronics: RFI mitigation q Reliability & Stability Ø Seismic retrofit at LLO: HEPI Ø Auto-alignment system: all degrees-of-freedom, at full bandwidth Ø Address causes of lock-loss G 040066 -00 -D LIGO I 4

Acoustic Mitigation q Recall: significant improvements between S 2 & S 3 Ø Ø Problem: acoustical vibrations of optical elements in the output beam path No acoustic peaks left in S 3 spectra Acoustic enclosures around AS port sensing tables: ~10 x reduction Improvements and simplifications to beam sensing path: ~10 x q Original goals: 100 x-1000 x reduction, reached for H 1 G 040066 -00 -D LIGO I 5

Acoustic Mitigation (2) q Raise the bar at LHO: H 1 -H 2 stochastic b. g. potential Ø H 1 sensitivity now dominated by reflection port table: continue improvement/simplifications of this beam path Ø Reduce continuous sources: house or move electronics cabinets q New data on lower frequencies: seismic/acoustic Ø HVAC the main source: no easy improvements Ø Investigating ‘floating’ the detection tables on low-frequency mounts G 040066 -00 -D LIGO I 6

More environmental effects Dust monitor at AS port table 1 day q Dust in table enclosures Ø Gets stirred up by entries, takes a while to settle down Ø Causes glitches when it falls through the beam Ø To be addressed with HEPA filters, and/or covers over the beam path q HVAC in-duct heaters Ø Pulsing produces ~1 Hz sidebands around 60 Hz; couples magnetically to AS_Q G 040066 -00 -D LIGO I 7

Optical gain: “ 10 W” laser q Current input power levels H 1 H 2 L 1 Design Mode cleaner input 3. 6 W 3. 7 W 6 W 8 W Recycling mirror input 2. 3 W 2. 6 W 3. 6 W 6 W q Plan Ø Get LWE lasers back up to spec: LWE may be able to rebuild for somewhat higher power, 10 W 12 -15 W Ø Diagnose pre-mode cleaner loss (typically 10 -15% lost) Ø Diagnose suspended mode cleaner loss (20 -30% lost) Ø Input electro-optic modulators: reduce number from 3 to 1 G 040066 -00 -D LIGO I 8

Thermal Compensation ITM CO 2 Laser ? Over-heat Correction Under-heat Correction Zn. Se Viewport Inhomogeneous Correction Over-heat pattern Inner radius = 4 cm Outer radius =11 cm Ø Cold power recycling cavity is unstable: poor buildup and mode shape for the RF sidebands Ø ITM thermal lens power of ~0. 00003 diopters needed to achieve a stable, mode-matched cavity v intended to be produced by ~25 m. W absorbed from 1μm beam G 040066 -00 -D LIGO I 9

Two CO 2 lasers installed on H 1 To ITM HR surface G 040066 -00 -D LIGO I 10

TCS on the power recycled Michelson: beam images at AS port No Heating 30 m. W 60 m. W 90 m. W Best match 120 m. W G 040066 -00 -D 150 m. W 180 m. W LIGO I Input beam 11

Full Interferometer Results Sideband power gain 25 A. Lock interferometer at 1 Watt B. Apply 45 m. W Common central heating 16. 5 C B 8. 3 A C. Increase to 60 m. W D D. Increase to 90 m. W E 0 Optical gain E. Turn off TCS Ø AS_Q gain: increases by 40% v doesn’t increase as fast as expected Ø PRC & MICH (pick-off) gains increase by factor of 4 v gain scales as (GSB)2 G 040066 -00 -D LIGO I 12

Summary of TCS Results State GSB --------------------------------------State 2 cold 7. 0 State 2 hot (90 m. W CO 2) 12. 5 State 2 max (t. RM / (1 - r. RM r. ITM))2 14 --------------------------------------State 4 cold 13 State 4 warm (0. 8 W input) 16 State 4 hot (2. 3 W input, no TCS) 20 State 4 hot (0. 8 W input, 45 m. W CO 2) 26. 5 State 4 max (t. RM / (1 - r. RM r. M))2 30 --------------------------------------G 040066 -00 -D LIGO I 13

Output mode cleaner: motivation q Reduction of AS_I signal Ø Power in orthogonal phase limits the amount of power per AS port photodetector & AS_I servo is noisy Ø Produced by alignment fluctuations: TEM 01/10 modes would be removed by an OMC q Improvement in shot noise sensitivity Ø Reduction of noise-producing (higher-order mode) power q Potential saturation at 2 fm at higher power G 040066 -00 -D LIGO I 14

OMC design overview 30 Cavity finesse (maximum mode suppression of 300 x) 10 cm / 100 MHz Cavity round-trip path/bandwidth (keep short/wide to pass SBs on same resonance) Geometry Triangular ring cavity; fixed spacer with bonded mirrors g-parameter Approx. 0. 4 Mounting & isolation In-vacuum, single stage suspension Locking and control PZT-mounted end mirror, dither lock in transmission G 040066 -00 -D LIGO I 15

OMC plans T = 10% q GEO output mode cleaner a good fit for initial testing Ø On loan from GEO for several months q Installation and testing on H 1 Ø Beginning mid-April Ø Will be put into the beam path of one of the AS port detection PDs 50/50 AS port beam PZT LSC PD G 040066 -00 -D LIGO I 16

Alignment Control q Continued incremental progress on WFS/QPDs … Ø Goals: v Sufficient gain/bandwidth to reduce power fluctuations to ~1% v Turn off optical lever angular control: too noisy v Manage WFS/QPD noise coupling to AS_Q Ø Status, H 1 (post-S 3 progress) v Bandwidth now at 2. 2 Hz for all but one WFS: effect not fully characterized v Some noise reductions made, still an active issue v Initial alignment steps now fully automated Ø Upcoming v Controls software upgrade: sensor input matrix; compensate radiation torques; compensate for optical gain change v WFS feedback to mode cleaner mirrors v Beam centering … G 040066 -00 -D LIGO I 17

Beam centering q Transmission QPDs hold the beam position fixed at the ETMs Ø Need to independently find the right spot (w/in 1 mm of center) q WFS control all mirror angles: only DOF left is the beam position in the corner q New servo: Ø Capture image of beam scatter from BS face Ø Image processing to determine position of beam center Ø Slow feedback to input telescope to fix BS beam position ON Pitch fb Sign fixed G 040066 -00 -D LIGO I 18

Auxiliary degrees-of-freedom: small coupling, but very noisy X-cplg to ASQ: 0. 01 @100 Hz X-cplg to ASQ: 0. 001 @100 Hz Excess noise G 040066 -00 -D LIGO I 19

Excess noise: optical gain modulation q Signal (sideband field)·(length deviation) Intermodulation Reduce these by increasing loop gain Effect of increasing the MICH bandwidth from 10 Hz to 50 Hz: > 10 x lower noise at 40 Hz > able to detect higher power pick-off beam for reduced shot noise Similar noise reduction for PRC, and for the WFS error signals G 040066 -00 -D LIGO I 20

Impact on noise Low gain High gain G 040066 -00 -D LIGO I 21

Seismic retrofit at LLO q Currently ~2 weeks into installation q Recent best performance data from LASTI, on a HAM chamber: G 040066 -00 -D LIGO I 22

High-f noise bump: mystery solved Mechanism: possibly coupling through the DC AS_I signal RF Oscillator phase noise Ø Modulation phase noise appears on demodulation signal (LO) too – no big deal Ø True at low frequencies, but mode cleaner pole shifts phase of modulation fields – doesn’t cancel out at higher frequencies Ø Solutions: v Low phase noise crystal oscillator v Pass LO through an electronic filter to equalize paths G 040066 -00 -D LIGO I 23

Miscellaneous q New low-noise D-A converters from Freq. Devices Inc. Ø 30 -40 d. B lower noise q New Faraday isolator for H 2 Ø Larger aperture to reduce clipping Ø Lower absorption for higher power operation q Photon calibrators Ø Reproducing first-article: in place for S 4 q Phase cameras on all interferometers Ø Introducing a reference field so that any field component can be mapped q Dual ETM transmission photodetectors Ø To handle larger dynamic range with higher power q Upgrade DAQ reflective memory network: higher capacity q Micro-seismic feedforward system at LHO G 040066 -00 -D LIGO I 24

Major Post-S 3 Steps First ~6 months after S 3 L 1 ► Thermal lens studies ► Seismic upgrade: HEPI installation & commiss. ► Electronics rack relocation ► Thermal comp. H 1 ► Manage noise in auxiliary degrees-of-freedom ►Thermal compensation trial ► Wideband WFS control ► Laser power increase ► Output mode cleaner ► Duty cycle H 2 ► Wideband WFS control G 040066 -00 -D LIGO I 25