laser frequency stabilization – 2004, may 04 1 laser frequency stabilization françois bondu cnrs...

1 Laser Frequency Stabilization – 2004, May 04

Laser Frequency Stabilization

François BONDU CNRS – ARTEMIS, Nice VIRGO

• How it works (Design)• Make it work (experimental work)• Noise performances• Next activities


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-1390-227Advanced digital filters VIR-NOT-OCA-1390-233Multiple servo loop systems VIR-NOT-OCA-1390-234Description of the loops VIR-NOT-OCA-1390-247

THIS design functionalities successfully tried on the north arm this month

HOW IT WORKS - DESIGN



MC

laser

Clas Clas2

CMC

CEM

OVERVIEW

ITF Common mode- or north arm -



MC

laser

Clas Clas2

CMC

2nd stage

CEM

Pr_B1(p)_ACp

Sc_IB_SSFS_Corr

Bs_IMC_DR_AC1

Second stage of frequency stabilization



MC

laser

Clas Clas2

CMC

Pre-stabilization

CEM

Bs_IMC_DR_AC1

Bs_ML_Pz

First stage of frequency stabilization(pre-stabilization)



MC

laser

Clas Clas2

CMC

IMC

CEM

Sc_IB_SSFS_Corr

Sc_MC_zCorrR

Bs_IMC_DR_AC1

IMC locking



MC

laser

Clas Clas2

CMC

CEM

Sc_NE_zGc

Sc_IB_zErrGC

ITF Common mode DC control



MODEL

« frequcncy noise » inputs

Stabilized laser frequency

Free running laser noise

IB or MC motion

Reference cavity length noise



SIMULINK MODEL

With radiation pressure



Note on alternative topology (‘topo #1’)

MC

laser

Clas Clas2

CMC

CEM

Sc_NE_zGc

Sc_IB_zErrGC


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


Note on alternative topology (‘topo #1’)


- « 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


Oscillation – saturation at about 170 Hz

zGc not « hold »

Experimental work (1)


Leak-through due to phase modulationvia IMC motion (cf. H. Trinquet)VIR-NOT-OCA-1390-178Cf. also gouaty_09Nov03_sens.ppt

Stability of second stage:crossing of these two TFs


SUSPICION:



Leak-through


• Made the calculations taking into account this effect:=> loop stable

• The problem was a loop oscillationtoo much gain, due to the « horns » in the laser frequency noise



Experimental work (2)SSFS_763560321_1.gifSSFS_763560321_2.gifSSFS_763561763_1.gifSSFS_763561763_2.gifSSFS_763561763_3.gifSSFS_763561763_4.gifSSFS_763566197_1.gifSSFS_763566896_1.gifSSFS_763575387_1.gifSSFS_763575387_2.gifSSFS_763575387_3.gifSSFS_763633937_1.gifSSFS_763633937_2.gifSSFS_763633937_3.gifSSFS_763633937_4.gifSSFS_763633937_5.gifSSFS_763643300_1.gifSSFS_763643300_2.gifSSFS_763643300_3.gifSSFS_763643301_1.gifSSFS_763647965.gifSSFS_763649282.gifSSFS_763649282_1.gifSSFS_763650999.gifSSFS_763726087.gifSSFS_763726087_2.gifSSFS_763726087_3.gifSSFS_763730743_1.gifSSFS_763730743_2.gifSSFS_763730743_3.gifSSFS_764023082_1.gifSSFS_764023082_2.gifSSFS_764023082_3.gifSSFS_764023082_4.gifSSFS_764023082_5.gifSSFS_764025420_1.gifSSFS_764025420_2.gifSSFS_764107509_1.gifSSFS_764107509_2.gifSSFS_764109486.gifSSFS_764109945.gifSSFS_764109945_2.gifSSFS_764110790.gifSSFS_764112941_1.gifSSFS_764114400_1.gif

SSFS_764114409.gifSSFS_764184989.gifSSFS_764191160.gifSSFS_764191160_2.gifSSFS_764191160_3.gifSSFS_764191160_4.gifSSFS_764198517_1.gifSSFS_764237811.gifSSFS_764237811_2.gifSSFS_764240101.gifSSFS_764240101_2.gifSSFS_764242950_1.gifSSFS_764242950_2.gifSSFS_764255788.gifSSFS_764255788_3.gifSSFS_764257611_1.gifSSFS_764257611_2.gifSSFS_764257611_3.gifSSFS_764257611_4.gifSSFS_764332843_1.gifSSFS_764343670_1.gifSSFS_764343670_2.gifSSFS_764344270.gifSSFS_764344270_2.gifSSFS_764344706.gifSSFS_764344733.gifSSFS_764589302.gifSSFS_764589459_1.gifSSFS_764589459_2.gifSSFS_764589459_3.gifSSFS_764589459_4.gifSSFS_764589459_5.gifSSFS_764665294.gifSSFS_765302566_1.gifSSFS_765302566_2.gifSSFS_765302705_1.gifSSFS_765308183_1.gifSSFS_765308183_2.gifSSFS_765311654_1.gifSSFS_765311710_1.gifSSFS_765311732_1.gifSSFS_765318312_1.gifSSFS_765320955.gifSSFS_765327588.gifSSFS_765398187.gif

SSFS_765398187_2.gifSSFS_765398305_1.gifSSFS_765398305_2.gifSSFS_765398306_1.gifSSFS_765398306_2.gifSSFS_765398306_3.gifSSFS_765398306_4.gifSSFS_765398306_5.gifSSFS_765475670.gifSSFS_765479098.gifSSFS_765484281.gifSSFS_765485180.gifSSFS_765485500.gifSSFS_765485500_2.gifSSFS_765536392.gifSSFS_765536392_2.gifSSFS_765545485.gifSSFS_765545485_2.gifSSFS_765549504.gifSSFS_765549517.gifSSFS_765549540.gifSSFS_765552348.gifSSFS_765968820.gifSSFS_765971138.gifSSFS_765971138_2.gifSSFS_766144998.gifSSFS_766149536.gifSSFS_766150426.gifSSFS_766150430.gifSSFS_766150558.gifSSFS_766151638.gifSSFS_766151639.gifSSFS_766417300.gifSSFS_766417306.gifSSFS_766417306_2.gifSSFS_766417436.gifSSFS_766426403.gifSSFS_766426460.gifSSFS_766426497.gifSSFS_766426552.gifSSFS_766430777.gifSSFS_766431882.gifSSFS_766466742.gifSSFS_766590206.gifSSFS_766709295.gif

SSFS_766709295_2.gifSSFS_766712859.gifSSFS_766772044.gifSSFS_766779324.gifSSFS_766783915.gifSSFS_766784545.gifSSFS_COHE_765321000_1.gifSSFS_COHE_766713000_SSFSCorr_GxIB.gifSSFS_COHE_766713000_SSFSCorr_GxMC.gifSSFS_COHE_766713000_SSFSCorr_IBLCtx.gifSSFS_COHE_766713000_SSFSCorr_IBLCtytz.gifSSFS_COHE_766713000_SSFSCorr_ISYSAA.gifSSFS_COHE_766990000_PrRFCACp_ScNEzGC.gifSSFS_Calib_HG.gifSSFS_Calib_HG2.gifSSFS_Calib_LG.gifSSFS_FFT_763633900.gifSSFS_FFT_763633937_1.gifSSFS_FFT_763633937_2.gifSSFS_FFT_763633937_3.gifSSFS_FFT_763643302_1.gifSSFS_FFT_764113906.gifSSFS_FFT_764114430_1.gifSSFS_FFT_764114500_1.gifSSFS_FFT_764114500_B1pd1ACp.txtSSFS_FFT_764114500_SSFSCorr.txtSSFS_FFT_764589420.gifSSFS_FFT_764590250.gifSSFS_FFT_764597900.gifSSFS_FFT_765321000_B1pd1ACp.txtSSFS_FFT_765321000_SSFSCorr.txtSSFS_FFT_765489291_B1pd1ACp.txtSSFS_FFT_765489291_SSFSCorr.txtSSFS_FFT_765549800.gifSSFS_FFT_765549800_10.gifSSFS_FFT_765549800_11.gifSSFS_FFT_765549800_12.gifSSFS_FFT_765549800_2.gifSSFS_FFT_765549800_3.gifSSFS_FFT_765549800_4.gifSSFS_FFT_765549800_5.gifSSFS_FFT_765549800_6.gifSSFS_FFT_765549800_7.gifSSFS_FFT_765549800_8.gifSSFS_FFT_765549800_9.gif

SSFS_FFT_765549800_RFCACp.txtSSFS_FFT_766456300.gifSSFS_FFT_766456300_B1pd1ACp.txtSSFS_FFT_766456300_SSFSCorr.txtSSFS_FFT_766467000.gifSSFS_FFT_766467000_B1pd1ACp.txtSSFS_FFT_766467000_SSFSCorr.txtSSFS_FFT_766713000_B1ACp.txtSSFS_FFT_766713000_B1d6ACp.txtSSFS_FFT_766713000_B1d6_SSFSCorr.gifSSFS_FFT_766713000_RFC.gifSSFS_FFT_766713000_RFC_2.gifSSFS_FFT_766713000_RFC_3.gifSSFS_FFT_766713000_RFC_4.gifSSFS_FFT_766713000_SSFSCorr.txtSSFS_FFT_766713000_zErrGC_2.txtSSFS_FFT_766713000_zErrGCx30_2.txtSSFS_FFT_766713100_zErrGC.txtSSFS_FFT_766990000.gifSSFS_FFT_766990000_SSFSACp.txtSSFS_FFT_766990000_SSFSCorr.txtSSFS_FFT_766990000_zErrGCx30.txtSSFS_FFT_767040722_zErrGC_B1pACp.gifSSFS_JPC1.gifSSFS_JPC2.gifSSFS_RMS_765549800_RFCACp.txt

… careful analysis of 206 plots



Large transient at lock acquisition


• 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


Transient / algo in Gc


• 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.


MC SUSPENSION RESONANCES


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 cavity2nd 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 cavitiesex: « north arm » (C2)North arm, IMC, reference cavity

cf VIR-NOT-OCA-1390-260


Noise performances


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 shifts1 shift

2 shifts1 shift4 shifts2-3 shifts

2-3 shifts½ shift???

(tentative durations)


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 weeks2-3 shifts1 shift

2 weeks

1-2 weeks

laser frequency stabilization – 2004, may 04 1 laser frequency stabilization françois bondu cnrs...

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