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					            Laser Frequency Stabilization


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


             1               Laser Frequency Stabilization – 2004, May 04
                                       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                          Laser Frequency Stabilization – 2004, May 04
                   HOW IT WORKS - DESIGN

OVERVIEW
                                       CEM


                  MC


                                             ITF Common mode
                       CMC                   - or north arm -

laser




           Clas                Clas2




              3              Laser Frequency Stabilization – 2004, May 04
                                            HOW IT WORKS - DESIGN

Second stage of frequency stabilization

                                                               CEM


                                          MC



                                               CMC

 laser

                                          2nd stage
                            Bs_IMC_DR_AC1                       Pr_B1(p)_ACp
                   Clas                                Clas2
                                     Sc_IB_SSFS_Corr




                      4                              Laser Frequency Stabilization – 2004, May 04
                                              HOW IT WORKS - DESIGN

First stage of frequency stabilization
(pre-stabilization)
                                                               CEM


                                         MC



                                               CMC

 laser

          Pre-stabilization

                              Bs_IMC_DR_AC1
                    Clas                               Clas2
   Bs_ML_Pz




                       5                             Laser Frequency Stabilization – 2004, May 04
                                     HOW IT WORKS - DESIGN

IMC locking

                                                       CEM
                                        IMC
                                MC     Sc_MC_zCorrR




                                      CMC

 laser



                     Bs_IMC_DR_AC1
              Clas                             Clas2
                             Sc_IB_SSFS_Corr




                 6                          Laser Frequency Stabilization – 2004, May 04
                                       HOW IT WORKS - DESIGN

ITF Common mode DC control
                       Sc_IB_zErrGC
                                                           CEM


                                      MC



                                           CMC

 laser
                                                                                 Sc_NE_zGc




                Clas                               Clas2




                   7                             Laser Frequency Stabilization – 2004, May 04
            HOW IT WORKS - DESIGN
                            Free running laser noise
MODEL




                           IB or MC motion


                           Reference cavity length noise

                     « frequcncy noise » inputs




                                    Stabilized laser frequency
        8        Laser Frequency Stabilization – 2004, May 04
                              HOW IT WORKS - DESIGN

SIMULINK MODEL

With radiation pressure




                          9        Laser Frequency Stabilization – 2004, May 04
                                             HOW IT WORKS - DESIGN

Note on alternative topology (‘topo #1’)
                             Sc_IB_zErrGC
                                                              CEM


                                            MC



                                                 CMC

 laser
                                                                                       Sc_NE_zGc




                 Clas                              Clas2




                        10                             Laser Frequency Stabilization – 2004, May 04
                                           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                         Laser Frequency Stabilization – 2004, May 04
                                            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                            Laser Frequency Stabilization – 2004, May 04
                Experimental work (1)




     Oscillation – saturation at about 170 Hz




       zGc not « hold »




13                 Laser Frequency Stabilization – 2004, May 04
                  Experimental work (1)


SUSPICION:



                        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



             14      Laser Frequency Stabilization – 2004, May 04
     Experimental work (1)




           Leak-through




15      Laser Frequency Stabilization – 2004, May 04
                                            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                          Laser Frequency Stabilization – 2004, May 04
     Experimental work (2)




17      Laser Frequency Stabilization – 2004, May 04
                                                                             Experimental work (2)
                                                                                                                 SSFS_FFT_765549800_RFCACp.txt
SSFS_763560321_1.gif   SSFS_764114409.gif     SSFS_765398187_2.gif   SSFS_766709295_2.gif                        SSFS_FFT_766456300.gif
SSFS_763560321_2.gif   SSFS_764184989.gif     SSFS_765398305_1.gif   SSFS_766712859.gif                          SSFS_FFT_766456300_B1pd1ACp.txt
SSFS_763561763_1.gif   SSFS_764191160.gif     SSFS_765398305_2.gif   SSFS_766772044.gif                          SSFS_FFT_766456300_SSFSCorr.txt
SSFS_763561763_2.gif   SSFS_764191160_2.gif   SSFS_765398306_1.gif   SSFS_766779324.gif                          SSFS_FFT_766467000.gif
SSFS_763561763_3.gif   SSFS_764191160_3.gif   SSFS_765398306_2.gif   SSFS_766783915.gif                          SSFS_FFT_766467000_B1pd1ACp.txt
SSFS_763561763_4.gif   SSFS_764191160_4.gif   SSFS_765398306_3.gif   SSFS_766784545.gif                          SSFS_FFT_766467000_SSFSCorr.txt
SSFS_763566197_1.gif   SSFS_764198517_1.gif   SSFS_765398306_4.gif   SSFS_COHE_765321000_1.gif                   SSFS_FFT_766713000_B1ACp.txt
SSFS_763566896_1.gif   SSFS_764237811.gif     SSFS_765398306_5.gif   SSFS_COHE_766713000_SSFSCorr_GxIB.gif       SSFS_FFT_766713000_B1d6ACp.txt
SSFS_763575387_1.gif   SSFS_764237811_2.gif   SSFS_765475670.gif     SSFS_COHE_766713000_SSFSCorr_GxMC.gif       SSFS_FFT_766713000_B1d6_SSFSCorr.gif
SSFS_763575387_2.gif   SSFS_764240101.gif     SSFS_765479098.gif     SSFS_COHE_766713000_SSFSCorr_IBLCtx.gif     SSFS_FFT_766713000_RFC.gif
SSFS_763575387_3.gif   SSFS_764240101_2.gif   SSFS_765484281.gif     SSFS_COHE_766713000_SSFSCorr_IBLCtytz.gif   SSFS_FFT_766713000_RFC_2.gif
SSFS_763633937_1.gif   SSFS_764242950_1.gif   SSFS_765485180.gif     SSFS_COHE_766713000_SSFSCorr_ISYSAA.gif     SSFS_FFT_766713000_RFC_3.gif
SSFS_763633937_2.gif   SSFS_764242950_2.gif   SSFS_765485500.gif     SSFS_COHE_766990000_PrRFCACp_ScNEzGC.gif    SSFS_FFT_766713000_RFC_4.gif
SSFS_763633937_3.gif   SSFS_764255788.gif     SSFS_765485500_2.gif   SSFS_Calib_HG.gif                           SSFS_FFT_766713000_SSFSCorr.txt
SSFS_763633937_4.gif   SSFS_764255788_3.gif   SSFS_765536392.gif     SSFS_Calib_HG2.gif                          SSFS_FFT_766713000_zErrGC_2.txt
SSFS_763633937_5.gif   SSFS_764257611_1.gif   SSFS_765536392_2.gif   SSFS_Calib_LG.gif                           SSFS_FFT_766713000_zErrGCx30_2.txt
SSFS_763643300_1.gif   SSFS_764257611_2.gif   SSFS_765545485.gif     SSFS_FFT_763633900.gif                      SSFS_FFT_766713100_zErrGC.txt
SSFS_763643300_2.gif   SSFS_764257611_3.gif   SSFS_765545485_2.gif   SSFS_FFT_763633937_1.gif                    SSFS_FFT_766990000.gif
SSFS_763643300_3.gif   SSFS_764257611_4.gif   SSFS_765549504.gif     SSFS_FFT_763633937_2.gif                    SSFS_FFT_766990000_SSFSACp.txt
SSFS_763643301_1.gif   SSFS_764332843_1.gif   SSFS_765549517.gif     SSFS_FFT_763633937_3.gif                    SSFS_FFT_766990000_SSFSCorr.txt
SSFS_763647965.gif     SSFS_764343670_1.gif   SSFS_765549540.gif     SSFS_FFT_763643302_1.gif                    SSFS_FFT_766990000_zErrGCx30.txt
SSFS_763649282.gif     SSFS_764343670_2.gif   SSFS_765552348.gif     SSFS_FFT_764113906.gif                      SSFS_FFT_767040722_zErrGC_B1pACp.gif
SSFS_763649282_1.gif   SSFS_764344270.gif     SSFS_765968820.gif     SSFS_FFT_764114430_1.gif                    SSFS_JPC1.gif
SSFS_763650999.gif     SSFS_764344270_2.gif   SSFS_765971138.gif     SSFS_FFT_764114500_1.gif                    SSFS_JPC2.gif
SSFS_763726087.gif     SSFS_764344706.gif     SSFS_765971138_2.gif   SSFS_FFT_764114500_B1pd1ACp.txt             SSFS_RMS_765549800_RFCACp.txt
SSFS_763726087_2.gif   SSFS_764344733.gif     SSFS_766144998.gif     SSFS_FFT_764114500_SSFSCorr.txt
SSFS_763726087_3.gif   SSFS_764589302.gif     SSFS_766149536.gif     SSFS_FFT_764589420.gif
SSFS_763730743_1.gif   SSFS_764589459_1.gif   SSFS_766150426.gif     SSFS_FFT_764590250.gif
SSFS_763730743_2.gif   SSFS_764589459_2.gif   SSFS_766150430.gif     SSFS_FFT_764597900.gif
SSFS_763730743_3.gif   SSFS_764589459_3.gif   SSFS_766150558.gif     SSFS_FFT_765321000_B1pd1ACp.txt
SSFS_764023082_1.gif   SSFS_764589459_4.gif   SSFS_766151638.gif     SSFS_FFT_765321000_SSFSCorr.txt
SSFS_764023082_2.gif
SSFS_764023082_3.gif
                       SSFS_764589459_5.gif
                       SSFS_764665294.gif
                                              SSFS_766151639.gif
                                              SSFS_766417300.gif
                                                                     SSFS_FFT_765489291_B1pd1ACp.txt
                                                                     SSFS_FFT_765489291_SSFSCorr.txt
                                                                                                            … careful analysis of 206 plots
SSFS_764023082_4.gif   SSFS_765302566_1.gif   SSFS_766417306.gif     SSFS_FFT_765549800.gif
SSFS_764023082_5.gif   SSFS_765302566_2.gif   SSFS_766417306_2.gif   SSFS_FFT_765549800_10.gif
SSFS_764025420_1.gif   SSFS_765302705_1.gif   SSFS_766417436.gif     SSFS_FFT_765549800_11.gif
SSFS_764025420_2.gif   SSFS_765308183_1.gif   SSFS_766426403.gif     SSFS_FFT_765549800_12.gif
SSFS_764107509_1.gif   SSFS_765308183_2.gif   SSFS_766426460.gif     SSFS_FFT_765549800_2.gif
SSFS_764107509_2.gif   SSFS_765311654_1.gif   SSFS_766426497.gif     SSFS_FFT_765549800_3.gif
SSFS_764109486.gif     SSFS_765311710_1.gif   SSFS_766426552.gif     SSFS_FFT_765549800_4.gif
SSFS_764109945.gif     SSFS_765311732_1.gif   SSFS_766430777.gif     SSFS_FFT_765549800_5.gif
SSFS_764109945_2.gif   SSFS_765318312_1.gif   SSFS_766431882.gif     SSFS_FFT_765549800_6.gif
SSFS_764110790.gif     SSFS_765320955.gif     SSFS_766466742.gif     SSFS_FFT_765549800_7.gif
SSFS_764112941_1.gif   SSFS_765327588.gif     SSFS_766590206.gif     SSFS_FFT_765549800_8.gif
SSFS_764114400_1.gif   SSFS_765398187.gif     SSFS_766709295.gif     SSFS_FFT_765549800_9.gif


                                       18                                           Laser Frequency Stabilization – 2004, May 04
             Experimental work (4)




     Large transient at lock acquisition




19               Laser Frequency Stabilization – 2004, May 04
                                              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                           Laser Frequency Stabilization – 2004, May 04
                                          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                           Laser Frequency Stabilization – 2004, May 04
                                                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                               Laser Frequency Stabilization – 2004, May 04
     Noise performances




23     Laser Frequency Stabilization – 2004, May 04
     Noise performances




24     Laser Frequency Stabilization – 2004, May 04
                                                 Next activities (1/2)
                                                            (tentative durations)
SSFS on north arm
         * update saturation in SSFS rack (+ RAMPEAUTO)            1-2 shifts
         * new algo in Gc (trigger condition)                      1 shift
         * 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)                            2 shifts
         * increase of UG of SSFS                                  1 shift
         * test with Virgo final corrector stage                   4 shifts
         * SSFS -> ISYS reliability                                2-3 shifts

SSFS on « recombined » interferometer
         * ready

Input MC control
         * TF measurement (again) (z,Tx,Ty)                        2-3 shifts
         * control from 2 coils                                    ½ shift
         * change coil wires of MC suspension?                     ???




                    25                             Laser Frequency Stabilization – 2004, May 04
                                                    Next activities (2/2)


Lock of recycling cavity
         * improve rms of IMC length noise?                             3-4 weeks
         * improve 50 Hz level on reference cavity                      2-3 shifts
         * detune recycling cavity of 25 nm (1/10th linewidth)          1 shift

SSFS on virgo                                                           2 weeks

Noise and requirements
         * cabling of « pertub » input
         * calibration sequence                                         1-2 weeks

Simulation
         * Siesta simulation of SSFS
         (fs = 200 kHz, does not include IMC error signal saturation)




                    26                                Laser Frequency Stabilization – 2004, May 04

				
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