Laser Frequency Stabilization – 2004, May 04 1 Laser Frequency Stabilization François BONDU CNRS – ARTEMIS, Nice VIRGO How it works (Design) Make it work (experimental work) Noise performances Next activities

Laser Frequency Stabilization – 2004, May 04 2 Complete Design in 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 stageVIR-NOT-OCA Advanced digital filtersVIR-NOT-OCA Multiple servo loop systemsVIR-NOT-OCA Description of the loopsVIR-NOT-OCA THIS design functionalities successfully tried on the north arm this month HOW IT WORKS - DESIGN

Laser Frequency Stabilization – 2004, May 04 3 HOW IT WORKS - DESIGN MC laser C las C las2 C MC C EM OVERVIEW ITF Common mode - or north arm -

Laser Frequency Stabilization – 2004, May 04 4 HOW IT WORKS - DESIGN MC laser C las C las2 C MC 2 nd stage C EM Pr_B1(p)_ACp Sc_IB_SSFS_Corr Bs_IMC_DR_AC1 Second stage of frequency stabilization

Laser Frequency Stabilization – 2004, May 04 5 HOW IT WORKS - DESIGN MC laser C las C las2 C MC Pre-stabilization C EM Bs_IMC_DR_AC1 Bs_ML_Pz First stage of frequency stabilization (pre-stabilization)

Laser Frequency Stabilization – 2004, May 04 6 HOW IT WORKS - DESIGN MC laser C las C las2 C MC IMC C EM Sc_IB_SSFS_Corr Sc_MC_zCorrR Bs_IMC_DR_AC1 IMC locking

Laser Frequency Stabilization – 2004, May 04 7 HOW IT WORKS - DESIGN MC laser C las C las2 C MC C EM Sc_NE_zGc Sc_IB_zErrGC ITF Common mode DC control

Laser Frequency Stabilization – 2004, May 04 8 HOW IT WORKS - DESIGN MODEL « frequcncy noise » inputs Stabilized laser frequency Free running laser noise IB or MC motion Reference cavity length noise

Laser Frequency Stabilization – 2004, May 04 9 HOW IT WORKS - DESIGN SIMULINK MODEL With radiation pressure

Laser Frequency Stabilization – 2004, May HOW IT WORKS - DESIGN Note on alternative topology (‘topo #1’) MC laser C las C las2 C MC C EM Sc_NE_zGc Sc_IB_zErrGC

Laser Frequency Stabilization – 2004, May 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 2003april 2002nov 2003  Would have been a deceiving solution, according to today knowledge HOW IT WORKS - DESIGN Note on alternative topology (‘topo #1’)

Laser Frequency Stabilization – 2004, May « 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 Experimental work

Laser Frequency Stabilization – 2004, May Oscillation – saturation at about 170 Hz zGc not « hold » Experimental work (1)

Laser Frequency Stabilization – 2004, May Leak-through due to phase modulation via IMC motion (cf. H. Trinquet) VIR-NOT-OCA Cf. also gouaty_09Nov03_sens.pptgouaty_09Nov03_sens.ppt Stability of second stage: crossing of these two TFs Experimental work (1) SUSPICION :

Laser Frequency Stabilization – 2004, May Experimental work (1) Leak-through

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

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

Laser Frequency Stabilization – 2004, May Experimental work (2) SSFS_ _1.gif SSFS_ _2.gif SSFS_ _1.gif SSFS_ _2.gif SSFS_ _3.gif SSFS_ _4.gif SSFS_ _1.gif SSFS_ _1.gif SSFS_ _1.gif SSFS_ _2.gif SSFS_ _3.gif SSFS_ _1.gif SSFS_ _2.gif SSFS_ _3.gif SSFS_ _4.gif SSFS_ _5.gif SSFS_ _1.gif SSFS_ _2.gif SSFS_ _3.gif SSFS_ _1.gif SSFS_ gif SSFS_ gif SSFS_ _1.gif SSFS_ gif SSFS_ gif SSFS_ _2.gif SSFS_ _3.gif SSFS_ _1.gif SSFS_ _2.gif SSFS_ _3.gif SSFS_ _1.gif SSFS_ _2.gif SSFS_ _3.gif SSFS_ _4.gif SSFS_ _5.gif SSFS_ _1.gif SSFS_ _2.gif SSFS_ _1.gif SSFS_ _2.gif SSFS_ gif SSFS_ gif SSFS_ _2.gif SSFS_ gif SSFS_ _1.gif SSFS_ _1.gif SSFS_ gif SSFS_ gif SSFS_ gif SSFS_ _2.gif SSFS_ _3.gif SSFS_ _4.gif SSFS_ _1.gif SSFS_ gif SSFS_ _2.gif SSFS_ gif SSFS_ _2.gif SSFS_ _1.gif SSFS_ _2.gif SSFS_ gif SSFS_ _3.gif SSFS_ _1.gif SSFS_ _2.gif SSFS_ _3.gif SSFS_ _4.gif SSFS_ _1.gif SSFS_ _1.gif SSFS_ _2.gif SSFS_ gif SSFS_ _2.gif SSFS_ gif SSFS_ gif SSFS_ gif SSFS_ _1.gif SSFS_ _2.gif SSFS_ _3.gif SSFS_ _4.gif SSFS_ _5.gif SSFS_ gif SSFS_ _1.gif SSFS_ _2.gif SSFS_ _1.gif SSFS_ _1.gif SSFS_ _2.gif SSFS_ _1.gif SSFS_ _1.gif SSFS_ _1.gif SSFS_ _1.gif SSFS_ gif SSFS_ gif SSFS_ gif SSFS_ _2.gif SSFS_ _1.gif SSFS_ _2.gif SSFS_ _1.gif SSFS_ _2.gif SSFS_ _3.gif SSFS_ _4.gif SSFS_ _5.gif SSFS_ gif SSFS_ gif SSFS_ gif SSFS_ gif SSFS_ gif SSFS_ _2.gif SSFS_ gif SSFS_ _2.gif SSFS_ gif SSFS_ _2.gif SSFS_ gif SSFS_ gif SSFS_ gif SSFS_ gif SSFS_ gif SSFS_ gif SSFS_ _2.gif SSFS_ gif SSFS_ gif SSFS_ gif SSFS_ gif SSFS_ gif SSFS_ gif SSFS_ gif SSFS_ gif SSFS_ gif SSFS_ _2.gif SSFS_ gif SSFS_ gif SSFS_ gif SSFS_ gif SSFS_ gif SSFS_ gif SSFS_ gif SSFS_ gif SSFS_ gif SSFS_ gif SSFS_ _2.gif SSFS_ gif SSFS_ gif SSFS_ gif SSFS_ gif SSFS_ gif SSFS_COHE_ _1.gif SSFS_COHE_ _SSFSCorr_GxIB.gif SSFS_COHE_ _SSFSCorr_GxMC.gif SSFS_COHE_ _SSFSCorr_IBLCtx.gif SSFS_COHE_ _SSFSCorr_IBLCtytz.gif SSFS_COHE_ _SSFSCorr_ISYSAA.gif SSFS_COHE_ _PrRFCACp_ScNEzGC.gif SSFS_Calib_HG.gif SSFS_Calib_HG2.gif SSFS_Calib_LG.gif SSFS_FFT_ gif SSFS_FFT_ _1.gif SSFS_FFT_ _2.gif SSFS_FFT_ _3.gif SSFS_FFT_ _1.gif SSFS_FFT_ gif SSFS_FFT_ _1.gif SSFS_FFT_ _1.gif SSFS_FFT_ _B1pd1ACp.txt SSFS_FFT_ _SSFSCorr.txt SSFS_FFT_ gif SSFS_FFT_ gif SSFS_FFT_ gif SSFS_FFT_ _B1pd1ACp.txt SSFS_FFT_ _SSFSCorr.txt SSFS_FFT_ _B1pd1ACp.txt SSFS_FFT_ _SSFSCorr.txt SSFS_FFT_ gif SSFS_FFT_ _10.gif SSFS_FFT_ _11.gif SSFS_FFT_ _12.gif SSFS_FFT_ _2.gif SSFS_FFT_ _3.gif SSFS_FFT_ _4.gif SSFS_FFT_ _5.gif SSFS_FFT_ _6.gif SSFS_FFT_ _7.gif SSFS_FFT_ _8.gif SSFS_FFT_ _9.gif SSFS_FFT_ _RFCACp.txt SSFS_FFT_ gif SSFS_FFT_ _B1pd1ACp.txt SSFS_FFT_ _SSFSCorr.txt SSFS_FFT_ gif SSFS_FFT_ _B1pd1ACp.txt SSFS_FFT_ _SSFSCorr.txt SSFS_FFT_ _B1ACp.txt SSFS_FFT_ _B1d6ACp.txt SSFS_FFT_ _B1d6_SSFSCorr.gif SSFS_FFT_ _RFC.gif SSFS_FFT_ _RFC_2.gif SSFS_FFT_ _RFC_3.gif SSFS_FFT_ _RFC_4.gif SSFS_FFT_ _SSFSCorr.txt SSFS_FFT_ _zErrGC_2.txt SSFS_FFT_ _zErrGCx30_2.txt SSFS_FFT_ _zErrGC.txt SSFS_FFT_ gif SSFS_FFT_ _SSFSACp.txt SSFS_FFT_ _SSFSCorr.txt SSFS_FFT_ _zErrGCx30.txt SSFS_FFT_ _zErrGC_B1pACp.gif SSFS_JPC1.gif SSFS_JPC2.gif SSFS_RMS_ _RFCACp.txt … careful analysis of 206 plots

Laser Frequency Stabilization – 2004, May Experimental work (4) Large transient at lock acquisition

Laser Frequency Stabilization – 2004, May 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 Experimental work (5) Transient / algo in Gc

Laser Frequency Stabilization – 2004, May 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. Experimental work (6) MC SUSPENSION RESONANCES

Laser Frequency Stabilization – 2004, May 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

Laser Frequency Stabilization – 2004, May Noise performances

Laser Frequency Stabilization – 2004, May Noise performances

Laser Frequency Stabilization – 2004, May Next activities (1/2) 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 ½ shift ??? (tentative durations)

Laser Frequency Stabilization – 2004, May 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 (1/10 th 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