Laser Frequency Stabilization

1

• Laser Frequency Stabilization

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

• François BONDU
• CNRS ARTEMIS, Nice
• VIRGO

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 Descript
ion of the loops VIR-NOT-OCA-1390-247 THIS
design functionalities successfully tried on the
north arm this month
3
HOW IT WORKS - DESIGN
OVERVIEW
CEM
ITF Common mode - or north arm -
4
HOW IT WORKS - DESIGN
Second stage of frequency stabilization
CEM
Bs_IMC_DR_AC1
Pr_B1(p)_ACp
Sc_IB_SSFS_Corr
5
HOW IT WORKS - DESIGN
First stage of frequency stabilization (pre-stabil
ization)
CEM
Bs_IMC_DR_AC1
Bs_ML_Pz
6
HOW IT WORKS - DESIGN
IMC locking
CEM
IMC
Sc_MC_zCorrR
Bs_IMC_DR_AC1
Sc_IB_SSFS_Corr
7
HOW IT WORKS - DESIGN
ITF Common mode DC control
Sc_IB_zErrGC
CEM
Sc_NE_zGc
8
HOW IT WORKS - DESIGN
Free running laser noise
MODEL
IB or MC motion
Reference cavity length noise
 frequcncy noise  inputs
Stabilized laser frequency
9
HOW IT WORKS - DESIGN
SIMULINK MODEL With radiation pressure
10
HOW IT WORKS - DESIGN
Note on alternative topology (topo 1)
Sc_IB_zErrGC
CEM
MC
CMC
laser
Sc_NE_zGc
11
HOW IT WORKS - DESIGN
Note on alternative topology (topo 1)

• ITF DC control necessary
• reference cavity can not change its frequency
  easily
• gt bad configuration (two loops sharing a same
  error signal)
• gt 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

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

13
Experimental work (1)
Oscillation saturation at about 170 Hz
zGc not  hold 
14
Experimental work (1)
SUSPICION
15
Experimental work (1)
Leak-through
16
Experimental work (1)

• Made the calculations taking into account this
  effect
• gt loop stable
• The problem was a loop oscillation
• too much gain, due to the  horns  in the laser
  frequency noise

17
Experimental work (2)
18
Experimental work (2)
SSFS_FFT_765549800_RFCACp.txt SSFS_FFT_766456300.g
if SSFS_FFT_766456300_B1pd1ACp.txt SSFS_FFT_766456
300_SSFSCorr.txt SSFS_FFT_766467000.gif SSFS_FFT_7
66467000_B1pd1ACp.txt SSFS_FFT_766467000_SSFSCorr.
txt SSFS_FFT_766713000_B1ACp.txt SSFS_FFT_76671300
0_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_76671
3000_RFC_4.gif SSFS_FFT_766713000_SSFSCorr.txt SSF
S_FFT_766713000_zErrGC_2.txt SSFS_FFT_766713000_zE
rrGCx30_2.txt SSFS_FFT_766713100_zErrGC.txt SSFS_F
FT_766990000.gif SSFS_FFT_766990000_SSFSACp.txt SS
FS_FFT_766990000_SSFSCorr.txt SSFS_FFT_766990000_z
ErrGCx30.txt SSFS_FFT_767040722_zErrGC_B1pACp.gif
SSFS_JPC1.gif SSFS_JPC2.gif SSFS_RMS_765549800_RFC
ACp.txt
SSFS_763560321_1.gif SSFS_763560321_2.gif SSFS_763
561763_1.gif SSFS_763561763_2.gif SSFS_763561763_3
.gif SSFS_763561763_4.gif SSFS_763566197_1.gif SSF
S_763566896_1.gif SSFS_763575387_1.gif SSFS_763575
387_2.gif SSFS_763575387_3.gif SSFS_763633937_1.gi
f SSFS_763633937_2.gif SSFS_763633937_3.gif SSFS_7
63633937_4.gif SSFS_763633937_5.gif SSFS_763643300
_1.gif SSFS_763643300_2.gif SSFS_763643300_3.gif S
SFS_763643301_1.gif SSFS_763647965.gif SSFS_763649
282.gif SSFS_763649282_1.gif SSFS_763650999.gif SS
FS_763726087.gif SSFS_763726087_2.gif SSFS_7637260
87_3.gif SSFS_763730743_1.gif SSFS_763730743_2.gif
SSFS_763730743_3.gif SSFS_764023082_1.gif SSFS_76
4023082_2.gif SSFS_764023082_3.gif SSFS_764023082_
4.gif SSFS_764023082_5.gif SSFS_764025420_1.gif SS
FS_764025420_2.gif SSFS_764107509_1.gif SSFS_76410
7509_2.gif SSFS_764109486.gif SSFS_764109945.gif S
SFS_764109945_2.gif SSFS_764110790.gif SSFS_764112
941_1.gif SSFS_764114400_1.gif
SSFS_764114409.gif SSFS_764184989.gif SSFS_7641911
60.gif SSFS_764191160_2.gif SSFS_764191160_3.gif S
SFS_764191160_4.gif SSFS_764198517_1.gif SSFS_7642
37811.gif SSFS_764237811_2.gif SSFS_764240101.gif
SSFS_764240101_2.gif SSFS_764242950_1.gif SSFS_764
242950_2.gif SSFS_764255788.gif SSFS_764255788_3.g
if SSFS_764257611_1.gif SSFS_764257611_2.gif SSFS_
764257611_3.gif SSFS_764257611_4.gif SSFS_76433284
3_1.gif SSFS_764343670_1.gif SSFS_764343670_2.gif
SSFS_764344270.gif SSFS_764344270_2.gif SSFS_76434
4706.gif SSFS_764344733.gif SSFS_764589302.gif SSF
S_764589459_1.gif SSFS_764589459_2.gif SSFS_764589
459_3.gif SSFS_764589459_4.gif SSFS_764589459_5.gi
f SSFS_764665294.gif SSFS_765302566_1.gif SSFS_765
302566_2.gif SSFS_765302705_1.gif SSFS_765308183_1
.gif SSFS_765308183_2.gif SSFS_765311654_1.gif SSF
S_765311710_1.gif SSFS_765311732_1.gif SSFS_765318
312_1.gif SSFS_765320955.gif SSFS_765327588.gif SS
FS_765398187.gif
SSFS_765398187_2.gif SSFS_765398305_1.gif SSFS_765
398305_2.gif SSFS_765398306_1.gif SSFS_765398306_2
.gif SSFS_765398306_3.gif SSFS_765398306_4.gif SSF
S_765398306_5.gif SSFS_765475670.gif SSFS_76547909
8.gif SSFS_765484281.gif SSFS_765485180.gif SSFS_7
65485500.gif SSFS_765485500_2.gif SSFS_765536392.g
if SSFS_765536392_2.gif SSFS_765545485.gif SSFS_76
5545485_2.gif SSFS_765549504.gif SSFS_765549517.gi
f SSFS_765549540.gif SSFS_765552348.gif SSFS_76596
8820.gif SSFS_765971138.gif SSFS_765971138_2.gif S
SFS_766144998.gif SSFS_766149536.gif SSFS_76615042
6.gif SSFS_766150430.gif SSFS_766150558.gif SSFS_7
66151638.gif SSFS_766151639.gif SSFS_766417300.gif
SSFS_766417306.gif SSFS_766417306_2.gif SSFS_7664
17436.gif SSFS_766426403.gif SSFS_766426460.gif SS
FS_766426497.gif SSFS_766426552.gif SSFS_766430777
.gif SSFS_766431882.gif SSFS_766466742.gif SSFS_76
6590206.gif SSFS_766709295.gif
SSFS_766709295_2.gif SSFS_766712859.gif SSFS_76677
2044.gif SSFS_766779324.gif SSFS_766783915.gif SSF
S_766784545.gif SSFS_COHE_765321000_1.gif SSFS_COH
E_766713000_SSFSCorr_GxIB.gif SSFS_COHE_766713000_
SSFSCorr_GxMC.gif SSFS_COHE_766713000_SSFSCorr_IBL
Ctx.gif SSFS_COHE_766713000_SSFSCorr_IBLCtytz.gif
SSFS_COHE_766713000_SSFSCorr_ISYSAA.gif SSFS_COHE_
766990000_PrRFCACp_ScNEzGC.gif SSFS_Calib_HG.gif S
SFS_Calib_HG2.gif SSFS_Calib_LG.gif SSFS_FFT_76363
3900.gif SSFS_FFT_763633937_1.gif SSFS_FFT_7636339
37_2.gif SSFS_FFT_763633937_3.gif SSFS_FFT_7636433
02_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 SSF
S_FFT_765321000_SSFSCorr.txt SSFS_FFT_765489291_B1
pd1ACp.txt SSFS_FFT_765489291_SSFSCorr.txt SSFS_FF
T_765549800.gif SSFS_FFT_765549800_10.gif SSFS_FFT
_765549800_11.gif SSFS_FFT_765549800_12.gif SSFS_F
FT_765549800_2.gif SSFS_FFT_765549800_3.gif SSFS_F
FT_765549800_4.gif SSFS_FFT_765549800_5.gif SSFS_F
FT_765549800_6.gif SSFS_FFT_765549800_7.gif SSFS_F
FT_765549800_8.gif SSFS_FFT_765549800_9.gif
careful analysis of 206 plots
19
Experimental work (4)
Large transient at lock acquisition
20
Experimental work (5)
Transient / algo in Gc

• Algo in Gc start SSFS when correction signal is
  zero, and holds this zero
• gt error signal is generally not null
• gt excites the step response (large transient)
• NEW Algo in Gc to be implemented start SSFS
  when error signal is null
• gt then switch off the filter
• gt decay slowly correction signal to zero

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.

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

23
Noise performances
24
Noise performances
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
trigger0 in the sequence Gc lock of RFC
without intermediate steps test Coulons
filter (NINE) increase of UG of SSFS test
with Virgo final corrector stage SSFS -gt 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 ???
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