1. Amaldi conference, June 2005 1 Lock acquisition scheme for the Advanced LIGO optical configuration Amaldi conference June24, 2005 O. Miyakawa, Caltech and the 40m collaboration

2. Amaldi conference, June 2005 2 Caltech 40 meter prototype interferometer Objectives  Develop lock acquisition procedure of detuned Resonant Sideband Extraction (RSE) interferometer, as close as possible to AdLIGO optical design BS PRM SRM X arm Dark port Bright port Y arm  Characterize noise mechanisms  Verify optical spring and optical resonance  Develop DC readout scheme  Extrapolate to AdLIGO via simulation

3. Amaldi conference, June 2005 3 AdLIGO signal extraction scheme  Arm cavity signals are extracted from beat between carrier and f 1 or f 2.  Central part (Michelson, PRC, SRC) signals are extracted from beat between f 1 and f 2, not including arm cavity information. f1f1 -f 1 f2f2 -f 2 Carrier (Resonant on arms) Single demodulation Arm information Double demodulation Central part information  Mach-Zehnder will be installed to eliminate sidebands of sidebands.  Only + f 2 is resonant on SRC.  Unbalanced sidebands of +/-f 2 due to detuned SRC produce good error signal for Central part. ETMy ETMx ITMy ITMx BS PRM SRM 4km f2f2 f1f1

4. Amaldi conference, June 2005 4 5 DOF for length control : L  =( L x  L y ) / 2 : L  = L x  L y : l  =( l x  l y ) / 2 =2.257m : l  = l x  l y = 0.451m : l s =( l sx  l sy ) / 2 =2.15m PortDem. Freq. LL LL ll ll l s SPf1f1 1-3.8E-9-1.2E-3-1.3E-6-2.3E-6 APf2f2 -4.8E-911.2E-81.3E-3-1.7E-8 SP f1  f2f1  f2 -1.7E-3-3.0E-41-3.2E-2-1.0E-1 AP f1  f2f1  f2 -6.2E-41.5E-37.5E-117.1E-2 PO f1  f2f1  f2 3.6E-32.7E-34.6E-1-2.3E-21 Signal Extraction Matrix (in-lock) Common of arms Differential of arms Power recycling cavity Michelson Signal recycling cavity Laser ETMy ETMx ITMy ITMx BS PRM SRM SP AP PO lxlx lyly l sx l sy L x =38.55m Finesse=1235 L y =38.55m Finesse=1235 Phase Modulation f 1 =33MHz f 2 =166MHz T =7% G PR =14.5

5. Amaldi conference, June 2005 5 Differences between AdvLIGO and 40m prototype  100 times shorter cavity length  Arm cavity finesse at 40m chosen to be = to AdvLIGO ( = 1235 ) »Storage time is x100 shorter.  Control RF sidebands are 33/166 MHz instead of 9/180 MHz »Due to shorter PRC length, less signal separation.  LIGO-I 10-watt laser, negligible thermal effects »180W laser will be used in AdvLIGO.  Noisier seismic environment in town, smaller stack »~1x10 -6 m at 1Hz.  LIGO-I single pendulum suspensions are used »AdvLIGO will use triple (MC, BS, PRM, SRM) and quad (ITMs, ETMs) suspensions.

6. Amaldi conference, June 2005 6 Lock acquisition procedure towards detuned RSE ITMy ITMx BS PRM SRM ETMx ETMy Shutter Carrier 33MHz 166MHz DRMI using DDM Off-resonant arms using DC lock (POX/TrX), (POY/TrY) SP166/PRC, AP166/PRC (POX/TrX) + (POY/TrY), (POX/TrX) – (POY/TrY) (TrX + TrY), (TrX – TrY) / (TrX + TrY) Ideas for arm control signal RSE Done In progress Done

7. Amaldi conference, June 2005 7 DRMI lock using double demodulation with unbalanced sideband by detuned cavity August 2004  DRMI locked with carrier resonance (like GEO configuration) November 2004  DRMI locked with sideband resonance (Carrier is anti resonant preparing for RSE.) Carrier 33MHz Unbalanced 166MHz Belongs to next carrier Belongs to next carrier Carrier 33MHz 166MHz ITMy ITMx BS PRM SRM OSA DDM PD Typical lock acquisition time : ~10sec Longest lock : 2.5hour

8. Amaldi conference, June 2005 8 Struggling lock acquisition for arm cavities Problems  High recycling gain of ~15 produces 94% coupling between two arms.  Very high coupled finesse of ~18000.  Slow sampling rate of 16kHz for direct lock acquisition. So, we have two steps  Each arm lock using transmitted light with DC offset. …done  Reduce offset to have full resonance of carrier. …in progress

9. Amaldi conference, June 2005 9 Error signal is produced by only transmitted light as Smaller coupling Wider linear range than RF error signal. Off-resonant DC lock scheme for arm cavity Off-resonant Lock point Resonant Lock

10. Amaldi conference, June 2005 10 All 5 degrees of freedom under controlled with DC offset on L + loop Both arms locked with DRMI  Lock acquisition time ~1 min  Lasts ~ 20 min  Can be switched to common/differential control L- : AP166 with no offset L+ : Trx+Try with DC offset Yarm lock Xarm lock Arm power Error signal Ideal lock point Offset lock Have started trying to reduce offset from L+ loop But…

11. Amaldi conference, June 2005 11 Peak changing due to reduction of offset Peak started from 1.6kHz and reached to ~450H. This peak introduces phase delay around unity gain frequency.

12. Amaldi conference, June 2005 12 CARM at 218 pm offset (~locking point) Unity Gain Frequency

13. Amaldi conference, June 2005 13 CARM at 118 pm offset Unity Gain Frequency

14. Amaldi conference, June 2005 14 CARM offset at 59 pm (losing lock) Unity Gain Frequency

15. Amaldi conference, June 2005 15 L- optical gain with RSE peak Optical gain of L- loop DARM_IN1/DARM_OUT,divided by pendulum transfer function No offset on L- loop 150pm offset on L+ loop Optical resonance of detuned RSE can be seen around the design RSE peak of 4kHz. Q of this peak is about 6. Design RSE peak ~ 4kHz

16. Amaldi conference, June 2005 16 DARM, operating point

17. Amaldi conference, June 2005 17 Summary  All 5DOFs are locked with some offset on L+.  RSE detuning peak was seen.  L + loop has a detuning peak with DC offset and it introduces phase delay around unity gain frequency with reducing offset.  Fortunately, Advanced LIGO will not have L + peak problem ! Cavity pole of single arm is around 16Hz from the beginning, far below from unity gain frequency of L + loop around 300Hz.  Fast frequency control or proper compensative digital filter may fix this problem for 40m. Hope we succeed in locking full RSE very soon!

18. Amaldi conference, June 2005 18 DC Readout at the 40m  DC Readout eliminates several sources of technical noise (mainly due to the RF sidebands): –Oscillator phase noise –Effects of unstable recycling cavity. –The arm-filtered carrier light will serve as a heavily stabilized local oscillator. –Perfect spatial overlap of LO and GW signal at PD.  DC Readout has the potential for QND measurements, without major modifications to the IFO.  We can use a 3 or 4-mirror OMC to reject RF sidebands. »Finesse ~ 500, In-vacuum, on a seismic stack.  The DC Detection diode »an aluminum stand to hold a bare photodiode, and verified that the block can radiate 100 mW safely. from SRM From SRM