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Laser Frequency Stabilization Design: How It Works

Detailed overview of the design process and experimental work in laser frequency stabilization, noise performances, and future activities led by François Bondu from CNRS-ARTEMIS in Nice.

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Laser Frequency Stabilization Design: How It Works

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  1. Laser Frequency Stabilization • How it works (Design) • Make it work (experimental work) • Noise performances • Next activities • François BONDU • CNRS – ARTEMIS, Nice • VIRGO 1

  2. HOW IT WORKS - DESIGN Complete Design in 2002 - early 2003 Designed to meet the requirements in the 10 Hz – 10 kHz band, Starting from the requirements. Design written, in Virgo Notes: Requirements for second stage VIR-NOT-OCA-1390-227 Advanced digital filters VIR-NOT-OCA-1390-233 Multiple servo loop systems VIR-NOT-OCA-1390-234 Description of the loops VIR-NOT-OCA-1390-247 THIS design functionalities successfully tried on the north arm this month 2

  3. HOW IT WORKS - DESIGN MC CMC laser Clas Clas2 OVERVIEW CEM ITF Common mode - or north arm - 3

  4. HOW IT WORKS - DESIGN MC CMC laser 2nd stage Clas Clas2 Second stage of frequency stabilization CEM Bs_IMC_DR_AC1 Pr_B1(p)_ACp Sc_IB_SSFS_Corr 4

  5. HOW IT WORKS - DESIGN MC CMC laser Pre-stabilization Clas Clas2 First stage of frequency stabilization (pre-stabilization) CEM Bs_IMC_DR_AC1 Bs_ML_Pz 5

  6. HOW IT WORKS - DESIGN MC CMC laser Clas Clas2 IMC locking CEM IMC Sc_MC_zCorrR Bs_IMC_DR_AC1 Sc_IB_SSFS_Corr 6

  7. HOW IT WORKS - DESIGN MC CMC laser Clas Clas2 ITF Common mode DC control Sc_IB_zErrGC CEM Sc_NE_zGc 7

  8. HOW IT WORKS - DESIGN Free running laser noise MODEL IB or MC motion Reference cavity length noise « frequcncy noise » inputs Stabilized laser frequency 8

  9. HOW IT WORKS - DESIGN SIMULINK MODEL With radiation pressure 9

  10. HOW IT WORKS - DESIGN Clas Clas2 Note on alternative topology (‘topo #1’) Sc_IB_zErrGC CEM MC CMC laser Sc_NE_zGc 10

  11. HOW IT WORKS - DESIGN Note on alternative topology (‘topo #1’) • ITF DC control necessary • reference cavity can not change its frequency easily • => ‘bad’ configuration (two loops sharing a same error signal) • => second stage can not have DC gain • Is not demonstrated to meet the requirements • See talks of april 2002, nov 2003 • Would have been a deceiving solution, according to today knowledge 11

  12. Experimental work • « 170 Hz » issue (december 2003) • analysis work • lock acquisition • transient during the lock acquisition / unlock of IMC • transient for lock with B1 / algo in Gc • resonances in the MC suspension 12

  13. Experimental work (1) Oscillation – saturation at about 170 Hz zGc not « hold » 13

  14. Experimental work (1) Leak-through due to phase modulation via IMC motion (cf. H. Trinquet) VIR-NOT-OCA-1390-178 Cf. also gouaty_09Nov03_sens.ppt Stability of second stage: crossing of these two TFs SUSPICION: 14

  15. Experimental work (1) Leak-through 15

  16. Experimental work (1) • Made the calculations taking into account this effect: • => loop stable • The problem was a loop oscillation • too much gain, due to the « horns » in the laser frequency noise 16

  17. Experimental work (2) 17

  18. Experimental work (2) SSFS_FFT_765549800_RFCACp.txt SSFS_FFT_766456300.gif SSFS_FFT_766456300_B1pd1ACp.txt SSFS_FFT_766456300_SSFSCorr.txt SSFS_FFT_766467000.gif SSFS_FFT_766467000_B1pd1ACp.txt SSFS_FFT_766467000_SSFSCorr.txt SSFS_FFT_766713000_B1ACp.txt SSFS_FFT_766713000_B1d6ACp.txt SSFS_FFT_766713000_B1d6_SSFSCorr.gif SSFS_FFT_766713000_RFC.gif SSFS_FFT_766713000_RFC_2.gif SSFS_FFT_766713000_RFC_3.gif SSFS_FFT_766713000_RFC_4.gif SSFS_FFT_766713000_SSFSCorr.txt SSFS_FFT_766713000_zErrGC_2.txt SSFS_FFT_766713000_zErrGCx30_2.txt SSFS_FFT_766713100_zErrGC.txt SSFS_FFT_766990000.gif SSFS_FFT_766990000_SSFSACp.txt SSFS_FFT_766990000_SSFSCorr.txt SSFS_FFT_766990000_zErrGCx30.txt SSFS_FFT_767040722_zErrGC_B1pACp.gif SSFS_JPC1.gif SSFS_JPC2.gif SSFS_RMS_765549800_RFCACp.txt SSFS_763560321_1.gif SSFS_763560321_2.gif SSFS_763561763_1.gif SSFS_763561763_2.gif SSFS_763561763_3.gif SSFS_763561763_4.gif SSFS_763566197_1.gif SSFS_763566896_1.gif SSFS_763575387_1.gif SSFS_763575387_2.gif SSFS_763575387_3.gif SSFS_763633937_1.gif SSFS_763633937_2.gif SSFS_763633937_3.gif SSFS_763633937_4.gif SSFS_763633937_5.gif SSFS_763643300_1.gif SSFS_763643300_2.gif SSFS_763643300_3.gif SSFS_763643301_1.gif SSFS_763647965.gif SSFS_763649282.gif SSFS_763649282_1.gif SSFS_763650999.gif SSFS_763726087.gif SSFS_763726087_2.gif SSFS_763726087_3.gif SSFS_763730743_1.gif SSFS_763730743_2.gif SSFS_763730743_3.gif SSFS_764023082_1.gif SSFS_764023082_2.gif SSFS_764023082_3.gif SSFS_764023082_4.gif SSFS_764023082_5.gif SSFS_764025420_1.gif SSFS_764025420_2.gif SSFS_764107509_1.gif SSFS_764107509_2.gif SSFS_764109486.gif SSFS_764109945.gif SSFS_764109945_2.gif SSFS_764110790.gif SSFS_764112941_1.gif SSFS_764114400_1.gif SSFS_764114409.gif SSFS_764184989.gif SSFS_764191160.gif SSFS_764191160_2.gif SSFS_764191160_3.gif SSFS_764191160_4.gif SSFS_764198517_1.gif SSFS_764237811.gif SSFS_764237811_2.gif SSFS_764240101.gif SSFS_764240101_2.gif SSFS_764242950_1.gif SSFS_764242950_2.gif SSFS_764255788.gif SSFS_764255788_3.gif SSFS_764257611_1.gif SSFS_764257611_2.gif SSFS_764257611_3.gif SSFS_764257611_4.gif SSFS_764332843_1.gif SSFS_764343670_1.gif SSFS_764343670_2.gif SSFS_764344270.gif SSFS_764344270_2.gif SSFS_764344706.gif SSFS_764344733.gif SSFS_764589302.gif SSFS_764589459_1.gif SSFS_764589459_2.gif SSFS_764589459_3.gif SSFS_764589459_4.gif SSFS_764589459_5.gif SSFS_764665294.gif SSFS_765302566_1.gif SSFS_765302566_2.gif SSFS_765302705_1.gif SSFS_765308183_1.gif SSFS_765308183_2.gif SSFS_765311654_1.gif SSFS_765311710_1.gif SSFS_765311732_1.gif SSFS_765318312_1.gif SSFS_765320955.gif SSFS_765327588.gif SSFS_765398187.gif SSFS_765398187_2.gif SSFS_765398305_1.gif SSFS_765398305_2.gif SSFS_765398306_1.gif SSFS_765398306_2.gif SSFS_765398306_3.gif SSFS_765398306_4.gif SSFS_765398306_5.gif SSFS_765475670.gif SSFS_765479098.gif SSFS_765484281.gif SSFS_765485180.gif SSFS_765485500.gif SSFS_765485500_2.gif SSFS_765536392.gif SSFS_765536392_2.gif SSFS_765545485.gif SSFS_765545485_2.gif SSFS_765549504.gif SSFS_765549517.gif SSFS_765549540.gif SSFS_765552348.gif SSFS_765968820.gif SSFS_765971138.gif SSFS_765971138_2.gif SSFS_766144998.gif SSFS_766149536.gif SSFS_766150426.gif SSFS_766150430.gif SSFS_766150558.gif SSFS_766151638.gif SSFS_766151639.gif SSFS_766417300.gif SSFS_766417306.gif SSFS_766417306_2.gif SSFS_766417436.gif SSFS_766426403.gif SSFS_766426460.gif SSFS_766426497.gif SSFS_766426552.gif SSFS_766430777.gif SSFS_766431882.gif SSFS_766466742.gif SSFS_766590206.gif SSFS_766709295.gif SSFS_766709295_2.gif SSFS_766712859.gif SSFS_766772044.gif SSFS_766779324.gif SSFS_766783915.gif SSFS_766784545.gif SSFS_COHE_765321000_1.gif SSFS_COHE_766713000_SSFSCorr_GxIB.gif SSFS_COHE_766713000_SSFSCorr_GxMC.gif SSFS_COHE_766713000_SSFSCorr_IBLCtx.gif SSFS_COHE_766713000_SSFSCorr_IBLCtytz.gif SSFS_COHE_766713000_SSFSCorr_ISYSAA.gif SSFS_COHE_766990000_PrRFCACp_ScNEzGC.gif SSFS_Calib_HG.gif SSFS_Calib_HG2.gif SSFS_Calib_LG.gif SSFS_FFT_763633900.gif SSFS_FFT_763633937_1.gif SSFS_FFT_763633937_2.gif SSFS_FFT_763633937_3.gif SSFS_FFT_763643302_1.gif SSFS_FFT_764113906.gif SSFS_FFT_764114430_1.gif SSFS_FFT_764114500_1.gif SSFS_FFT_764114500_B1pd1ACp.txt SSFS_FFT_764114500_SSFSCorr.txt SSFS_FFT_764589420.gif SSFS_FFT_764590250.gif SSFS_FFT_764597900.gif SSFS_FFT_765321000_B1pd1ACp.txt SSFS_FFT_765321000_SSFSCorr.txt SSFS_FFT_765489291_B1pd1ACp.txt SSFS_FFT_765489291_SSFSCorr.txt SSFS_FFT_765549800.gif SSFS_FFT_765549800_10.gif SSFS_FFT_765549800_11.gif SSFS_FFT_765549800_12.gif SSFS_FFT_765549800_2.gif SSFS_FFT_765549800_3.gif SSFS_FFT_765549800_4.gif SSFS_FFT_765549800_5.gif SSFS_FFT_765549800_6.gif SSFS_FFT_765549800_7.gif SSFS_FFT_765549800_8.gif SSFS_FFT_765549800_9.gif … careful analysis of 206 plots 18

  19. Experimental work (4) Large transient at lock acquisition 19

  20. Experimental work (5) Transient / algo in Gc • Algo in Gc: start SSFS when correction signal is zero, and holds this zero • => error signal is generally not null • => excites the step response (large transient) • NEW Algo in Gc to be implemented: start SSFS when error signal is null • => then switch off the filter • => decay slowly correction signal to zero 20

  21. Experimental work (6) MC SUSPENSION RESONANCES • While working, we found in-loop resonances in the MC suspension at • 18 Hz, 25 Hz, 53 Hz, 128 Hz, 333 Hz, … • The reference mass is not holded by its wires, but by the coil wires! • MC reference mass wires are not stresses and may • have random resonance frequencies, varying in time. 21

  22. Noise performances • 1 laser, 1 FP cavity, lock with high unity gain • error signal = readout noise • correction signal = beating note of laser cavity and FP cavity, • Usually dominated by laser cavity (« free running laser noise ») • 1 laser locked on a FP cavity, lock of another cavity • 2nd cavity error signal = beating note of the 2 FP cavities • ex: experiment in Orsay in 95, • ex: « ISYS »: IMC and reference cavity • 1 laser, 3+ FP cavities • ex: « north arm » (C2) • North arm, IMC, reference cavity • cf VIR-NOT-OCA-1390-260 22

  23. Noise performances 23

  24. Noise performances 24

  25. Next activities (1/2) (tentative durations) SSFS on north arm * update saturation in SSFS rack (+ RAMPEAUTO) * new algo in Gc (trigger condition) * check of IB-DSP/MC-DSP DOL * Gc: trigger=0 in the sequence * Gc: lock of RFC without intermediate steps * test Coulon’s filter (NI+NE) * increase of UG of SSFS * test with Virgo final corrector stage * SSFS -> ISYS reliability SSFS on « recombined » interferometer * ready Input MC control * TF measurement (again) (z,Tx,Ty) * control from 2 coils * change coil wires of MC suspension? 1-2 shifts 1 shift 2 shifts 1 shift 4 shifts 2-3 shifts 2-3 shifts ½ shift ??? 25

  26. Next activities (2/2) Lock of recycling cavity * improve rms of IMC length noise? * improve 50 Hz level on reference cavity * detune recycling cavity of 25 nm (1/10th linewidth) SSFS on virgo Noise and requirements * cabling of « pertub » input * calibration sequence Simulation * Siesta simulation of SSFS (fs = 200 kHz, does not include IMC error signal saturation) 3-4 weeks 2-3 shifts 1 shift 2 weeks 1-2 weeks 26

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