1. CALVA : A test facility for Lock Acquisition F.Cavalier 1 on behalf of CALVA team : M.-A.Bizouard 1, V.Brisson 1, M.Davier 1, P.Hello 1, N.Leroy 1, N.Letendre 2, V.Loriette 3, I.Maksimovic 3, A.Masserot 2, C.Michel 4, B.Mours 2, L.Pinard 4, F.Robinet 1, M.Vavoulidis 1, M.Was 1 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

2. 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 ”)

3. CALVA Principle 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 (F Max  F )  the cavities are much less coupled Lock the long cavity using an auxiliary laser with a different wavelength and bring it to the main laser resonance in a deterministic way

4. Infrastructure status Two rooms operational: Cleanliness between 10000 and 100000 Class 10 air flux in each room 1 o C stability Vacuum tanks: Connected by a 25-cm diameter tube Reached pressure: 10 -6 mbar Housing a 80x80 cm 2 breadboard 10 m 45 m 5.5 m 7 m 5.5 m Room 1 Room 2 Vacuum Pipe Optical Table Vacuum tanks for mirrors FP1 FP2

5. 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 CALVA set-up

6. Suspensions and Local control performances Motion of free mirror in quiet conditions: z ~ 1-2 microns  ~ 10-20 microradians Local Controls Range: z ~ 400 microns  ~ 0.5 milliradians Local controls sensitivity: z ~ few tens of nanometers  ~ fraction of microradians Local control bench Local control laser

7. Lock of the short high finesse cavity Parameters: L = 5 m ROC1=ROC2 = 33 m (mirrors foreseen for the long cavity) Reflectivities at 1064 nm: R1 = 0.9909 R2 = 0.99974 Reflectivities at 1319 nm: R1= 0.3 R2 = 0.55 1064-nm laser operated at low power (~200 mW) in order to avoid radiation pressure effects  F = 3.3  F = 680

8. 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-motionM2 z-motion Transmitted DC power @ 1319 nm

9. 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 Trigger level Reflected DC power @ 1319 nm Reflected PD signal @ 1064 nm Transmitted DC power @ 1064 nm

10. 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

11. Coherence seen with angular motion and laser power Coherence with frequency noise to be evaluated

12. 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

13. 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