LIGO-G D 1 Status of Detector Commissioning LSC Meeting, March 2001 Nergis Mavalvala California Institute of Technology

LIGO-G D 2 Promises at Aug 00 LSC meeting  Power recycled Michelson locks Carrier or sideband resonance  Arm cavity locks Feedback to ITM or ETM  …get both locking at same time…  …add second arm cavity…  …full interferometer!

LIGO-G D 3 Livingston overview: what’s new  Installation/alignment of remaining in-vacuum components – Nov  Beam sighted down arm cavities – Jan Within < 3  rad of optic centers  Some realignment of input optics beam required  4 km arm cavity (longest ever!) locked – Feb  Full interferometer locking underway  Learning about differences in seismic environment between both sites  E3: first ‘coincidence’ run – Mar LLO X arm cavity locked for ~ 80% PEM channels acquired at both observatories

LIGO-G D 4 Hanford overview: what’s new  Initial full ifo locking – Oct Intentionally reduced buildup  E2: recombined interferometer – Nov  Full ifo locking with no intentional loss – Jan Carrier power recycling gain: 15 Hour long lock stretches Sensitivity spectra noisy as expected  Noise reduction studies Sensing noise PSL/IO frequency noise Electronics noise (low input power, less filtering)  Olympia earthquake – Feb Damage to magnets on several suspended optics Under repairs

LIGO-G D 5 Interferometer Locking: lock acquisition  Masterminded by Matt Evans (CIT grad student). His reward: PhD thesis Acquisition C code named for him: “Matt’s code”  Basic problem Sensing matrix goes through singularity as both arm cavities start building up power  Solution implemented Judicious use of light power levels to estimate when matrix determinant too small; turn of controller till dofs coast through singularity  LSC digital controls made it possible “Matt’s code” interfaced with “Rolf’s code”  All testing of actual C code was done using E2E model of full ifo Angular fluctuations not included had to rethink use of signals a few times

LIGO-G D 6 Length Sensing Matrix: very near resonance AS_Q: DARM REFL_I: CARM, PRC REFL_Q: MICH PO_I: CARM, PRC PO_Q: MICH Phase modulated light: C and SB Reflection and Pick-off I phase signals both dominated by CARM (~100x), but with different amounts of PRC => Matrix can be inverted! Reflection and Pick-off Q phase signals are clean MICH signals, but ~100x smaller than corresponding I phase signals Phase must be set accurately

LIGO-G D 7 Lock acquisition: the problem  Sensor signals, S, are related to degrees of freedom, D, via the optical gain matrix, Ĝ Ĝ depends on buildup of fields in the ifo, i.e. Ĝ(t) Ĝ must be invertible, i.e. det(Ĝ) = 0  Lock acquisition sequence: states State 2 State 3 State 4 Sideband resonance in arm cavity in State 2/3 kills lock Change in optical gain Matrix for separating CARM, PRC goes through singularity

LIGO-G D 8 Lock Acquisition Program a.k.a. Matt’s code DC and 2f SB Use DC power signals (total power) as well as 2f SB demodulated signals (sideband power) to determine state and optical gain Use measured optical gains in easily locked states (2 and 3) to estimate gain matrix in State 4 Determine occurrence of matrix singularity and turn off control of PRC dof in a carefully tuned window around that zero crossing DC

LIGO-G D 9 Matt’s Code in Action

LIGO-G D 10 Full Interferometer Locking S. Whitcomb

LIGO-G D 11 From “first lock” to stable high buildup lock  Optical lever damping for angular dof on several optics Mitigate 1.06  m light coupling problem  Improved signal-to-noise on critical light power signals (dynamic range)  Wavefront sensor on antisymmetric port  ETM angles differentially  Detour to run recombined configuration First look at ‘differential mode’ E2: >90% duty cycle for lock

LIGO-G D 12 Displacement Sensitivity M. Landry

LIGO-G D 13 What’s next? Near future  LHO 2km Repairs – expect to re-commission in 05/01 Improvements – new 1.06  m insensitive OSEMs  LHO 4km Expect to begin commissioning in 05/01  LLO 4km Characterize environmental noise better Proceed with full interferometer locking Identify in-vacuum problems that must be fixed in next vent Vent coordinated with installation/repair effort at LHO