Paolo La Penna The New Virgo Injection BenchN5-WP1 4 TH MEETING, Hannover, 7/04/2005 The New VIRGO Injection Bench Paolo La Penna European Gravitational Observatory

Paolo La Penna The New Virgo Injection BenchN5-WP1 4 TH MEETING, Hannover, 7/04/2005 Recombined configuration: first half of 2004

Paolo La Penna The New Virgo Injection BenchN5-WP1 4 TH MEETING, Hannover, 7/04/2005 Recycled interferometer: July 2004

Paolo La Penna The New Virgo Injection BenchN5-WP1 4 TH MEETING, Hannover, 7/04/2005 PR REFLECTION INSIDE IMC: FREQUENCY NOISE Black: PR misaligned Red: PR aligned

Paolo La Penna The New Virgo Injection BenchN5-WP1 4 TH MEETING, Hannover, 7/04/2005 PR reflection scattering inside IMC MC scattering (10 ppm) PR IMC Cavity effect (10% fringes)

Paolo La Penna The New Virgo Injection BenchN5-WP1 4 TH MEETING, Hannover, 7/04/2005 The PR feedback inside the IMC (Summer now) Simulations on a lock acquisition technique developed following the LIGO experience Locking trials with this baseline technique failed (first half of July) Attenuator installed (summer) Restart of the locking trials with the baseline technique (21st September) Establishement of theVariable Finesse lock acquisition technique (October) PR cavity locking (end of October)

Paolo La Penna The New Virgo Injection BenchN5-WP1 4 TH MEETING, Hannover, 7/04/2005 Temporary solution: Input Beam Attenuation From the laser To the interferometer 10% M6 IMC Reference Cavity 700 mW (10% of the full power) Final solution: Insert a Faraday Isolator

Paolo La Penna The New Virgo Injection BenchN5-WP1 4 TH MEETING, Hannover, 7/04/2005 OLD M6 vs NEW M6 NEW M6OLD M6 Hz PR LOCKING ACQUIRED AFTER ONE MONTH CONFIRMATION OF THE BACKSCATTERING PROBLEM NEED OF AN ISOLATOR (FARADAY) (Same y-scale)

Paolo La Penna The New Virgo Injection BenchN5-WP1 4 TH MEETING, Hannover, 7/04/2005 Beam waist  5mm Beam diameter  10 mm If a Faraday is needed it will have a large aperture

Paolo La Penna The New Virgo Injection BenchN5-WP1 4 TH MEETING, Hannover, 7/04/2005 EOTec Faraday Isolator l TGG (Terbium Gallium Garnet,) vacuum compatible; l 20 mm maximum clear aperture : (25 and 50 mm would be “glass based” rotators, not reliable for 10 W power); l Weight: 7 kg, TGG rod length: 20 mm, isolator length: 25 cm l Extinction measured in Nice 41 db; l Absorption: less than cm -1 ; l EOTec uses vacuum compatible thin film polarizers at Brewsters angle:  BK7  Pulsed damage threshold >5J/cm 2 10nsec pulse  Extinction nm  Transmission: nm (97% maximum)

Paolo La Penna The New Virgo Injection BenchN5-WP1 4 TH MEETING, Hannover, 7/04/2005 Faraday isolator: present bench 250 mm 670 mm Not enough space on the present bench

Paolo La Penna The New Virgo Injection BenchN5-WP1 4 TH MEETING, Hannover, 7/04/2005 IB design with a Faraday Isolator Even with a 20 mm clear aperture Faraday: l The IMC waist is 5 mm: the beam has to be reduced in size before entering in the Faraday l A telescope for reducing the beam to 2-3 mm in the Faraday has to be taken into account and designed l Thermal lensing: no plan to correct it (using FK51 for example) with present input power (about 10 W): the induced focal length should be of the order of m l Induced (stationary) thermal lensing effects will be corrected acting on the matching telescope.

Paolo La Penna The New Virgo Injection BenchN5-WP1 4 TH MEETING, Hannover, 7/04/2005 Brewster dielectric polarizers Rotator Faraday Isolator

Paolo La Penna The New Virgo Injection BenchN5-WP1 4 TH MEETING, Hannover, 7/04/ W Pump HeNe Shack- Hartman Faraday 2f Thermal focal length measurement

Paolo La Penna The New Virgo Injection BenchN5-WP1 4 TH MEETING, Hannover, 7/04/2005 Shack-Hartmann measurement

Paolo La Penna The New Virgo Injection BenchN5-WP1 4 TH MEETING, Hannover, 7/04/2005 Plane Power Recycling mirror l The present PR is made by two parts: a curved one inside an external cylindrical glass mass (t’s a lens, part of the telescope for collimating inside the ITF) l The curved part is fixed to the cylindrical by means of a steel ring and pression screws; l There is evidence of mechanical resonances: problems in locking acquisition and in the future Frequency Stabilization: need of a monolitic mirror l Decided to make it plane (get rid of transverse movements of the beam induced by the suspension displacements)

Paolo La Penna The New Virgo Injection BenchN5-WP1 4 TH MEETING, Hannover, 7/04/2005 Plane PR: (new) 6  parabolic off-axis telescope 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 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 on-shelf: custom mirrors

Paolo La Penna The New Virgo Injection BenchN5-WP1 4 TH MEETING, Hannover, 7/04/2005 Plane PR: Beam simulation Input mirrors End mirrors

Paolo La Penna The New Virgo Injection BenchN5-WP1 4 TH MEETING, Hannover, 7/04/2005 Telescope tolerances l A tolerance study for the whole telescope (Faraday collimating and off-axis parabolic telescope) has been performed using Zeemax in the case of plane PR l The global tolerancies for plane PR seem to be accettable

Paolo La Penna The New Virgo Injection BenchN5-WP1 4 TH MEETING, Hannover, 7/04/2005 IB layout

Paolo La Penna The New Virgo Injection BenchN5-WP1 4 TH MEETING, Hannover, 7/04/2005 Optical layout - 2 Detector table IB input window(s)

Paolo La Penna The New Virgo Injection BenchN5-WP1 4 TH MEETING, Hannover, 7/04/2005 Ref. cav. MC LC IMC auto- alignment -- ALIGNMENT SERVO PICOMOTORS PIEZOS Laser NFFF NF FF h v ABP_U M2 M3 M5 M6 PZT RFC auto- alignment Beam drift control ABP_D MATRIX

Paolo La Penna The New Virgo Injection BenchN5-WP1 4 TH MEETING, Hannover, 7/04/2005 IMC and RFC alignment 10% ABP OFF ABP dismounted RFC is more stable than IMC: RFC is fully automatically alignmed IMC is partially automatically aligned

Paolo La Penna The New Virgo Injection BenchN5-WP1 4 TH MEETING, Hannover, 7/04/2005 ISYS alignment: modifications to the IB l Automatic alignment of the IMC on the beam: acting on the IB through the IB marionette; l Separate automatic alignment of the Reference Cavity on the beam:  Actuators on the bench are necessary  Replacement of the present RC fixed steering mirrors with other actuators (piezos)

Paolo La Penna The New Virgo Injection BenchN5-WP1 4 TH MEETING, Hannover, 7/04/2005 Ref. cav. MC LC IMC auto- alignment -- ALIGNMENT SERVO PICOMOTORS PIEZOS Laser NFFF NF FF h v h v ABP_U M2 M3 M5 M6 MATRIX PZT RFC auto- alignment Beam pre- alignment Beam drift control ABP_D MATRIX

Paolo La Penna The New Virgo Injection BenchN5-WP1 4 TH MEETING, Hannover, 7/04/2005 Input beam monitoring NF telescope: conjugate ABP_D mount on NF_Quadrant (shifts) FF telescope: locate quadrant at focus (tilts)

Paolo La Penna The New Virgo Injection BenchN5-WP1 4 TH MEETING, Hannover, 7/04/2005 Suspended Bench Reference Cavity Marionette

Paolo La Penna The New Virgo Injection BenchN5-WP1 4 TH MEETING, Hannover, 7/04/2005 Reference Cavity alignment The design of the RFC layout should not change M11 and M12 will be mounted on piezos for RFC separate alignment (Closed loop Physik Instrumente piezos)

Paolo La Penna The New Virgo Injection BenchN5-WP1 4 TH MEETING, Hannover, 7/04/2005 VIRGO OPTICAL SCHEME Frontal modulation

Paolo La Penna The New Virgo Injection BenchN5-WP1 4 TH MEETING, Hannover, 7/04/2005 Sidebands resonant in the IMC l EOM for the 6.26… MHz is now before the IMC: sidebands and carrier have to be resonant at the same time inside the IMC to get into the ITF l IMC (a.u.) J-J- J+J+ J0J0

Paolo La Penna The New Virgo Injection BenchN5-WP1 4 TH MEETING, Hannover, 7/04/2005 Sidebands resonant in the IMC l If the modulation frequency is not exactly a multiple of the IMC FSR there can be an amplitude change in the sidebands and a signal on the photodiodes signals (in particular on the ITF reflection) J-J- J+J+ J0J0

Paolo La Penna The New Virgo Injection BenchN5-WP1 4 TH MEETING, Hannover, 7/04/2005 Modulation frequency tuning B2_ACq signal: f = MHz  f = MHz (tuned)

Paolo La Penna The New Virgo Injection BenchN5-WP1 4 TH MEETING, Hannover, 7/04/2005 Pockels Cell on the Input Bench after the IMC The IMC length is apparently drifting. A feedback is needed to keep the modulation frequency matched with the IMC length (or correct the IMC length drift). l This problem could be also solved placing the EOM after the IMC (on the IB, in vacuum, on the main beam going into the ITF). l In this case the first basic question is : where could an EOM be placed? That is, how could this EOM look like, and where is there space on the bench?

Paolo La Penna The New Virgo Injection BenchN5-WP1 4 TH MEETING, Hannover, 7/04/2005 Pockels cell on the Input Bench after the IMC l Contacted several companies l One (Leysop) gave more detailed answers (but still not final one) l After discussion, a possible proposed EOM is:  LiNbO4 (possible occurrence of self focusing and astigmatism)  15 mm aperture (beam waist=2.65 mm)  About 50mm  40mm  40mm external dimensions  Half wavelength voltage: 1295 V  Price: about € 4000  Delivery time: no answer yet For the moment we are trying to design the layout reserving space for possible accomodation of an EOM

Paolo La Penna The New Virgo Injection BenchN5-WP1 4 TH MEETING, Hannover, 7/04/2005 Space reserved on the new IB EOM

Paolo La Penna The New Virgo Injection BenchN5-WP1 4 TH MEETING, Hannover, 7/04/2005 Problems l Is it possible to place the EOM after the IMC? l Is it a good idea? l There are many questions:  thermal focussing effects,  astigmatism,  distortions  high voltage for modulation,  etc.

Paolo La Penna The New Virgo Injection BenchN5-WP1 4 TH MEETING, Hannover, 7/04/2005 Other GW experiments We have no experience on these problems Which is the experience in the other GW experiments? As far as we know: l TAMA: no EOM in vacuum (not on the main beam) l LIGO: no EOM in vacuum (not on the main beam) l GEO:  there are several EOM in vacuum and at least one EOM after the last IMC on the main beam  GEO experience could be very useful to understand the opportunity of putting this EOM after the IMC