Transcript F. Cavalier (LAL IN2P3/CNRS)

CALVA : A test facility for Lock Acquisition
F.Cavalier1 on behalf of CALVA team :
M.-A.Bizouard1, V.Brisson1, M.Davier1, P.Hello1, N.Leroy1, N.Letendre2, V.Loriette3, I.Maksimovic3, A.Masserot2,
C.Michel4, B.Mours2, L.Pinard4, F.Robinet1, M.Vavoulidis1, M.Was1
1) LAL, Université Paris-Sud, IN2P3/CNRS, F-91898 Orsay, France
2) Laboratoire d'Annecy-le-Vieux de Physique des Particules (LAPP), IN2P3/CNRS, Université de Savoie, F-74941
Annecy-le-Vieux, France
3) ESPCI, CNRS, F-75005 Paris, France
4) Laboratoire des Matériaux Avancés (LMA), IN2P3/CNRS, F-69622 Villeurbanne, Lyon, France
• Principle and Layout
• Status of the infrastructure
• First lock acquisition with the short cavity
• Perspectives
CALVA motivation
• The acquisition of lock for advanced detectors will be a crucial problem :
• more coupled dofs with Signal Recycling
• higher finesse for FP cavities
• effect of radiation pressure
• question about the maximal possible force, acquisition vs sensitivity problem
• Set-up a middle-scale infrastructure dedicated to Locking R&D for Advanced Virgo and
beyond (CALVA stands for “Cavité(s) pour l’Acquisition du Lock de Virgo Avancé ”)
CALVA Principle
Lock the long cavity using an auxiliary laser with a different
wavelength and bring it to the main laser resonance in a
deterministic way
The mirror reflectivity seen by the auxiliary laser
can be much lower than for the main laser
 the cavities have a lower finesse
 easier lock acquisition
 requires less force (FMax  F )
 the cavities are much less coupled
Infrastructure status
FP1
Optical
Table
FP2
Vacuum tanks
for mirrors
Vacuum Pipe
7m
5.5 m
Room 2
Room 1
10 m
• Two rooms operational:
• Cleanliness between 10000 and 100000
• Class 10 air flux in each room
• 1o C stability
• Vacuum tanks:
• Connected by a 25-cm diameter tube
• Reached pressure: 10-6 mbar
• Housing a 80x80 cm2 breadboard
45 m
5.5 m
CALVA set-up
• Lasers from Innolight:
• 1 W @ 1064 nm  same radiation pressure effect than in AdV
• 100 mW @ 1319 nm
• Electronics & Software:
• LAPP components built for Virgo+ (ADC, Timing system, Optical Links, Control
software and DAQ)
• Other parts homemade or commercial
• Control loops running at 10 kHz
• Mirrors coated by LMA
Suspensions and
Local control performances
Local control laser
Local control bench
• Motion of free mirror in quiet conditions:
• z ~ 1-2 microns
• q ~ 10-20 microradians
• Local Controls Range:
• z ~ 400 microns
• q ~ 0.5 milliradians
• Local controls sensitivity:
• z ~ few tens of nanometers
• q ~ fraction of microradians
Lock of the short high finesse cavity
• Parameters:
•L=5m
• ROC1=ROC2 = 33 m (mirrors foreseen for the long cavity)
• Reflectivities at 1064 nm:
• R1 = 0.9909
 F = 680
• R2 = 0.99974
• Reflectivities at 1319 nm:
• R1= 0.3
 F = 3.3
• R2 = 0.55
• 1064-nm laser operated at low power (~200 mW) in order to avoid radiation pressure effects
Lock sequence:
• cool angular motion with local controls
• cool longitudinal motion with local controls
• release local controls on z and switch on the cavity lock using DC (reflected or transmitted)
for 1319 nm laser (with F = 3.3, DC and Pound-Drever signals are quite similar)
• When locked on 1319 nm, typical motion for the cavity is about 3 nm (supposing that error
signal is due to mirror motion)
• No coherence has been seen with laser power or angular motion of the mirrors
• Coherence with frequency noise has to be evaluated
• Resonance crossing time for 1064-nm laser is about 100 ms
M1 z-motion
M2 z-motion
Transmitted DC
power @ 1319 nm
Lock sequence (cont’d):
• Wait for resonance crossing for 1064-nm laser due to natural frequency drifts of the two lasers
(trigger on transmitted power). Controlled search for the resonance to be implemented acting on
DC offset or 1319-nm laser frequency
• Switch on 1064-nm laser Pound-Drever signal
Reflected DC
power @ 1319 nm
Reflected PD
signal @ 1064 nm
Transmitted DC
power @ 1064 nm
Trigger level
• Lock routinely obtained with this procedure even starting with very excited mirrors
• Error signal amplitude corresponds to a motion of 100 picometers
• Force for lock acquisition has the same order of magnitude as the force needed to keep the lock
on 1064-nm laser. More statistics must be acquired
• Error signal spectrum to be understood
• Coherence seen with angular motion and laser power
• Coherence with frequency noise to be evaluated
Next steps
• Characterization of lock and power increase of the main laser (up to June)
• Installation of the 50-m cavity
• Lock of long cavity with same optical parameters (this summer)
• Addition of the short cavity (F ~ 15)
• Lock of coupled cavities (this autumn)
Needs for Advanced Virgo
• Check that it is still mandatory for Adv (recent change of finesse)
• Frequency of auxiliary laser has to be stabilized. Two paths under evaluation :
• rigid cavity
• fiber ITF
Conclusion
• CALVA infrastructure has been set-up and is working properly
• First lock has been acquired using an auxiliary laser on a short (5 meters) cavity with a
finesse about 700 for the main laser and 3 for the auxiliary laser
• Longer cavity and coupled cavities will be locked before the end of the year
• Application to AdV under reevaluation
• Use of Laguerre-Gauss beams as possible next step in collaboration with APC