1. 1 Locking in Virgo Matteo Barsuglia ILIAS, Cascina, July 7 th 2004

2. 2 Introduction: optical scheme, terms, etc… Actors: Hardware, software, simulation Results: Experience with a single arm (cavity locking, frequency stabilization, ouput-mode cleaner locking) The recombined interferometer (almost all the controls working) Full detector lock acquisition (preparation and first results) Outline

3. 3 Virgo optical scheme West cavity F=50 North cavity F=50 Recycling cavity G=50 Dark fringe Fabry-Perot Michelson Power recycling

4. 4 Standard base MICH = l n -l w PRC= l rec +(l N + l w )/2 CARM= L N +L W DARM= L N -L W LNLN LwLw lwlw lNlN l rec

5. 5 Intro: photodiode names 3 signals for each photodiode: DC, ACp, Acq 7 8 21 5 and 5_2f In- phase quadrature reflectionAntisymetric port Transmission north Transmission west

6. 6 Detection system InGaAs photodiodes 6.26 MHz (only 1 modulation) 16 bits ADC

7. 7 Last stage Digital controls Control signals (DOL’s) Photodiodes signals (DOL’s) Alignment Locking 3 for each suspension trigger, signal processing, filtering 10 kHz sampling VME based, homemade software in C

8. 8 Mirror actuators Reference mass 4 coils 40 mN Beam splitter

9. 9 Real time simulation package of the Virgo experiment Written in C, configuration cards produces frames Can be interfaced to the real time control system (global control) Siesta

10. 10 SIESTA Control signals Photodiodes signals Algorithms running in the global control Siesta

11. 11 Control signals Photodiodes signals Algorithms running in the global control VIRGO Siesta

12. 12 North cavity locking north arm Test: Locking Autoalignment Frequency stabilization tidal control

13. 13 Linearized error signal No Linearized error signal m Lock acquisition speed threshold ~ 10 m/s Signals and linearization

14. 14 Signals and simulation Correction Transmitted power Time domain Simulation (Siesta)

15. 15 Cavity first locking Locking at the first trial first lock ~ 1 hour frequency noise Transmitted power Frequency noise reduction

16. 16 Lock acquisition statistics  24 locking events collected locking and delocking the cavity  23 lock acquisition at the first attempt, only 1 failed locking attempt

17. 17 Relative velocity between the mirrors computed for each locking attempt 8  m/s: maximum velocity for the lock acquisition success 12.5  m/s: velocity of the failed event Failed locking attempt v ~ 12.5 8 2.5  m/s: mean value of the velocity Lock acquisition statistics

18. 18 Cavity locking accuracy 3 picometers RMS

19. 19 Output mode-cleaner locking 1. Cavity locked with ~ 1% of the light 2. Mode-cleaner locked 3. Control transferred to this phd ~ 99% of the light After OMC Before OMC Sensitivity (m/  Hz)

20. 20 Output mode-cleaner locking Transmitted P Reflected P  2 StateTemperatureError signal 2 min

21. 21 Frequency stabilization - North cavity error signal sent to the input mode-cleaner (below 200 Hz) and to the laser (above 200 Hz) - Reference cavity error signal used to control cavity length at DC

22. 22 Recombined ITF north arm west arm

23. 23 Recombined ITF 10 W ~ 1W Sensitivity ~ (500 W) 3 d.o.f. decoupled fields are not mixed lock acquisition easy no “dynamical effects”

24. 24 Lock Acquisition – Overview B8_phase/B8_DC B5_phase/B7_DC B2_quad NE WE BS  Lock of the two cavities (independently) Corrections sent to NE and WE  Lock of the michelson length Corrections sent to BS 3 Steps lock acquisition: North arm West arm Michelson length

25. 25 Linear Locking - Overview ⊗ B1p_phase B2_quad North arm West arm B2_phase Michelson length

26. 26 Complete scheme

27. 27 Run C4

28. 28 reach the Virgo sensitivity: recycling

29. 29 Technique choosen: use the LIGO one (developed by Evans et al.) VIRGO and LIGO have the same optical scheme, and similar optical parameters. VIRGO and LIGO have similar control systems (digital, quite similar sampling frequencies,…). VIRGO and LIGO have similar simulation packages (real time, etc…) pragmatic point of view …the LIGO approach works Few differences between LIGO and VIRGO Pick-off signal different Arm finesse in LIGO = 200 (Virgo =50) Suspension and local controls system simpler in LIGO Reproduce the LIGO technique with SIESTA only optics (TEMO00, no saturation, no superattenuators) Include fine effects (saturations, etc…) Full Virgo lock acq approach

30. 30 Full virgo lock acq approach very difficult to have the 4 d.o.f. satisfied, in a linear regime Sequencial & Statistical (the states are not stable) used in LIGO, works well in 3 itf’s lot of signal processing (linearization, dynamical matrix inversion) simulation crucial central cavity locked central cavity + first arm all ITF locked

31. 31 Optical characherization parameters of the optical matix (~ 10 ) determined by simulation very important to reproduce in simulation the optical behaviour of the interferometer During the CITF the locking parameters (2) what dermined in this way optical characterization is a strategic item Each element = K P(measured throughB7/B8/B5_2f)

32. 32 Simulation West cavity Trans power North cavity Trans power Power inside the rec cavity Sidebands power inside the rec cavity

33. 33 “step 3” locking Lock of the central cavity (CITF) on the sidebands + lock of the north arm (on the carrier) B2_Q B2_P B1_Q

34. 34 Lock acquisition state3

35. 35 Experience with a single cavity and recombined very interesting to understand the hardware/software/signals/simulations Real time simulation crucial tool (understand signals, test algos, save commissioning time) Hardware and software tested and performant (algos in C++, parameter in a database, etc…) This summer: try to lock the recycled interferometer and prepare linear lock and final frequency stabilization. Conclusions and next steps