The installation of the new VIRGO Injection Bench Paolo La Penna for the VIRGO collaboration European Gravitational Observatory

Recombined configuration: first half of 2004 IB

Recycled interferometer: July 2004 IB

PR reflection inside IMC: frequency noise Black: PR misaligned Red: PR aligned

PR reflection scattering inside IMC MC scattering (10 ppm) IMC PR Cavity effect (10% fringes)

Plane Power Recycling mirror The old PR was made by two parts: a curved one inside an external cylindrical glass mass (it was a lens, part of the telescope for collimating inside the ITF) The curved part was fixed to the cylindrical by means of a steel ring and pression screws; There was evidence of mechanical resonances (drifting in time): problems in locking acquisition and in the future Frequency Stabilization: need of a monolitic mirror Decided to make it plane (get rid of transverse movements of the beam induced by the suspension displacements)

The RFC was more stable than IMC: the AA of the RFC worked quite well IMC and RFC alignment ABP OFF 10% ABP dismounted The beam was atomatically aligned on the RFC (fixed below the IB) with ABP The IMC was partly automatically aligned (feedback only on the MC mirror The RFC was more stable than IMC: the AA of the RFC worked quite well the poor AA of the IMC couldn’t correct the drifts

PR reflection: Input Beam Attenuation (temporary solution) IMC 10% M6 From the laser To the interferometer 700 mW (10% of the full power) Reference Cavity

The PR feedback inside the IMC (mid of 2004) Simulations on a lock acquisition technique developed following the LIGO experience Locking trials with this baseline technique failed (first half of July) Beam attenuation installed (summer)

HR M6 vs attenuated M6 HR M6 (Same y-scale) R=10% M6 Hz Hz

The PR feedback inside the IMC (end of 2004) Restart of the locking trials with the baseline technique (21st September) Establishement of theVariable Finesse lock acquisition technique (October) PR locking acquisition after one month (end of October 2004) CONFIRMATION OF THE BACKSCATTERING PROBLEM NEED OF AN OPTICAL ISOLATOR (FARADAY)

Resume: why to build a new Injection Bench The reflection of the light inside the Input Mode Cleaner increased the frequency noise, thus making it impossible to lock the recycling cavity The use of a Faraday isolator was necessary There was no way to accomodate a Faraday isolator and respective telescope on the old IB: the bench had to be replaced In addition to this: It was decided to replace the curved PR with a plane PR (less coupling with the transverse PR displacement): a short (parabolic) telescope on the IB was necessary It was decided to change the automatic alignment system of the injection system: separate alignment of the Input Mode Cleaner and Reference Cavity

The Faraday isolator was tested in Nice with the 20W laser How did we proceed The aforementioned problems were individuated in many data takings (C1-C4) The mechanical design of the bench was performed using essentially Autocad and Ansys The optical simulation of the bench was performed using mainly Zemax (simulation of optical aberrations and stray light), and by Optocad The Faraday isolator was tested in Nice with the 20W laser The new IB was mounted and prealigned in Class 10 room (after old IB dismounting) Once prealigned it has been inserted into the tower

Upper part layout Autocad drawing Optocad drawing

Lower (RFC) part layout Autocad drawing Optocad drawing

Autocad 3-D simulation (example)

ANSYS model Marionette Reference Cavity

Uy Tx Tz ANSYS simulation Probably Dihedron Susp. Legs Wire 30 40 50 60 70 80 90 Probably Dihedron Legs (measured in september 2005) Uy Susp. Wire couplers Tx Tz

Plane PR: Beam simulation with spherical mirrors Input mirrors End mirrors

Plane PR: Beam simulation with parabolic mirrors Input mirrors End mirrors

Plane PR: (new) 6 parabolic off-axis telescope With plane PR: a big magnification is needed, the telescope has to be short (about 700 mm) Parabolic mirrors are needed The computed curvature radius are not off-shelf: custom mirrors (Optical Surface) IMC: waist 4.9 mm Condensing telescope FI: waist 2.65 mm M5: f= 75 mm M6: f = 600 mm Ø  10 cm to PR: waist=20 mm d= 675 mm

Parabolic telescope mechanical mount Two open loop picomotors Three closed loop picomotors X and Z closed loop translators Mounts designed by ourselves and Machined by a workshop close to Virgo Mounting commercial actuators

Alignment of the parabolic telescope (Class 10 room) Laser

Starting conditions: misaligned, mismatched AUTOCOLLIMATOR

1st autocollimator alignment REF. MIRROR AUTOCOLLIMATOR

2nd autocollimator alignment REF. MIRROR

Autocollimators aligned

1st mirror alignment AUTOCOLLIMATOR AUTOCOLLIMATOR

1st mount alignment AUTOCOLLIMATOR AUTOCOLLIMATOR

2nd mount alignment AUTOCOLLIMATOR AUTOCOLLIMATOR

2nd mount alignment AUTOCOLLIMATOR AUTOCOLLIMATOR

Mirror matching AUTOCOLLIMATOR AUTOCOLLIMATOR

Focussing AUTOCOLLIMATOR AUTOCOLLIMATOR

Off-axis AUTOCOLLIMATOR AUTOCOLLIMATOR

Off-axis AUTOCOLLIMATOR AUTOCOLLIMATOR

Off-axis AUTOCOLLIMATOR AUTOCOLLIMATOR

Autocollimation AUTOCOLLIMATOR AUTOCOLLIMATOR

Beam dumpers: aluminum boxes and buffle-glass plates

Beam dumpers and PSDs PSD Beam dumpers PSD PSD PSD

Resume of the main differences between new and old IB Different shape and strutcture of the bench (octagonal, larger, M6 grid of holes, …) Thinner suspension wires Presence of the Faraday isolator Presence of a collimating (reducing) telescope between the Input Mode Cleaner (two lenses) Presence of a short (less than 1-m-long) off-axis parabolic telescope (×8) Separate alignment of the IMC and the RFC RFC placed after the IMC (no beam on the RFC when the IMC is not locked): it should make the beam on the RFC more stable Use of several PSDs to monitor the beam on the bench Use of larger mirrors Use of specifically designed beam dumpers

Beam diameter  10 mm Beam diameter  40 mm

Actions after the recycling cavity locking Decision to revise the Injection Bench design (June 2004) Creation of a group charged to redesign the IB (July 2004) Choice of the Faraday isolator and simulation of several possible telescopes (autumn 2004) Decision to install a plane PR (and therefore an off-axis parabolic telescope) (November 2004) Develope of the IB optical and mechanical design and starting of orders and (first months of 2005) Arrival of the main part of the components (May 2005) Arrival of the bench (July 2005) Arrival (delayed) of the last parabolic mirror (M5, 75 mm focal length) (August 2005)

Actions after the recycling cavity locking Dismounting of the old IB and starting of the mounting of the new IB (September 2005) Insertion of the new IB into the IB tower (begin of november 2005) IB suspension tuning (november 2005) Bench prealignment and local controls tuning (end of November 2005) Mounting of the plane PR (end of November 2005) Local control of the bench (December 2005) Nd:YAG injection and beam alignment (December 2005) Alignment of the IB optics (now)

Brewster dielectric polarizers Rotator February 2005

Mid September 2005

Begin of October 2005

Main activities before inserting the bench into the tower Change of the input flange (larger windows) Change of the Brewster link (to accomodate a larger beam) Suspension tuning (filter 0 and 7 blades): the bench is heavier (about 150 kg) Adjustment of the wires length Full tuning and balancing of the suspension Mounting of the coils: close to the center of mass plane (more stable equilibrium of the bench) Cabling (of coils and bench actuators)

Insertion into the tower (begin November) Detector table

Insertion into the tower (begin November) Detector table

Begin of November 2005

Now

Now

Main activities after inserting the bench into the tower Bench heigth setting: some difficulties with the suspension point motors Balancing of the bench Orientation of the bench with an HeNe coming from the MC tower: some difficulties in the filter 7 rotation range Test of the coils: some problems in the frames interrupting RFC beams Orientation of the local controls target: quite difficult because the small angular range in its orientation

Local controls Beam diameter  10 mm Beam diameter  40 mm The IB local controls use a target, placed in front of the dihedron, with reference markers (bench translations) and reflecting HeNe beams (angles) The setup had not been changed with respect to the old IB Beam diameter  10 mm Beam diameter  40 mm

Old IB local controls

After the realignment of the reference beams and target: New IB local controls After the realignment of the reference beams and target: Closing of the coarse and fine with the old IB correction filters and essentially the same gains (end of November) Adjustment of the reference spots Fine alignment of the bench with the MC HeNe (begin of December) Measurement of the mechanical TF (last week)

Preliminary: New TF measurement (Henrich Heitmann and Paolo Ruggi)

Full alignment procedure After this first alignment in Class 100 room, the bench has been mounted inside the tower. The dummy dihedron is mounted, the LC target is realigned, the local controls of the bench are restarted. The IB is aligned using the HeNe coming from the MC tower The Nd:YAG beam is injected into the bench and aligned until a light spot is visible on the MC mirror The optics on the bench is realigned using the IB actuators The true dihedron is reinstalled, the IB is put in vacuum, the IMC aligned and locked After IMC locking, it should be possible to make the final tuning and alignment using the bench actuators.

Next steps Present status: The fake dihedron is still mounted on the bench The Nd:YAG beam (up to 5 W for the moment) has been sent into the bench: some light (with even some interference) is visible at the end of the MC The optics on the bench are being realigned using the IB actuators: we perform this operation staying inside the tower, with the laminar flux on and the LC closed (they are very robust) The true dihedron will be reinstalled this week, then the IMC will be aligned (we hope it will be possible in air, in order to be able check the RFC alignment) the IB will put in vacuum, the IMC aligned and locked After IMC locking, it should be possible to make the final tuning and alignment using the bench actuators. The beam will be aligned in the ITF