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

Paolo La PennaThe New Virgo Injection BenchN5-WP1 4TH MEETING, Hannover, 7/04/2005

The New VIRGO Injection Bench

Paolo La Penna

European Gravitational Observatory


Recombined configuration: first half of 2004

Nd :YAG= 1064 nm

20 W

DETEC TIO NSYSTEM

WIp la ne

R= 0.88

NIp la ne

R= 0.88

WER = 3500 m

R= 0.99995c urv

NER = 3500

R= 0.99995c urv

PRp la ne

R= 0.925

BS

INPUTM O DE

C LEANER(144 m )

6 m 6.4 m

5.6

m

3 km

3 km

O M C

M o d ula to rsing le fre q ue nc y

6.26 M hz

Nd :YAG= 1064 nm

20 W

DETEC TIO NSYSTEM

WIp la ne

R= 0.88

NIp la ne

R= 0.88

WER = 3500 m

R= 0.99995c urv

NER = 3500

R= 0.99995c urv

PRp la ne

R= 0.925

BS

INPUTM O DE

C LEANER(144 m )

6 m 6.4 m

5.6

m

3 km

3 km

O M C


6.26 M hz


Recycled interferometer: July 2004

Nd :YAG= 1064 nm

20 W

DETEC TIO NSYSTEM

WIp la ne

R= 0.88

NIp la ne

R= 0.88

WER = 3500 m

R= 0.99995c urv

NER = 3500

R= 0.99995c urv

PRp la ne

R= 0.925

BS

INPUTM O DE

C LEANER(144 m )

6 m 6.4 m

5.6

m

3 km

3 km

O M C


6.26 M hz

Nd :YAG= 1064 nm

20 W

DETEC TIO NSYSTEM

WIp la ne

R= 0.88

NIp la ne

R= 0.88

WER = 3500 m

R= 0.99995c urv

NER = 3500

R= 0.99995c urv

PRp la ne

R= 0.925

BS

INPUTM O DE

C LEANER(144 m )

6 m 6.4 m

5.6

m

3 km

3 km

O M C


6.26 M hz


PR REFLECTION INSIDE IMC: FREQUENCY NOISE

Black: PR misaligned

Red: PR aligned


PR reflection scattering inside IMC

MC scattering (10 ppm)

PR

IMC

Cavity effect

(10% fringes)


The PR feedback inside the IMC (Summer 2004 - 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)


Temporary solution: Input Beam Attenuation

From the laser

To the interferometer

10% M6 IMC

Reference Cavity700 mW (10% of the

full power)

Final solution: Insert a Faraday Isolator


OLD M6 vs NEW M6

NEW M6OLD M6

HzHz

PR LOCKING ACQUIRED AFTER ONE MONTH

CONFIRMATION OF THE BACKSCATTERING PROBLEM

NEED OF AN ISOLATOR (FARADAY)

(Same y-scale)


Beam waist 5mm

Beam diameter 10 mm

If a Faraday is needed it will have a large aperture


EOTec Faraday Isolator

TGG (Terbium Gallium Garnet,) vacuum compatible;

20 mm maximum clear aperture : (25 and 50 mm would be “glass based” rotators, not reliable for 10 W power);

Weight: 7 kg, TGG rod length: 20 mm, isolator length: 25 cm

Extinction measured in Nice 41 db;

Absorption: less than 0.0025 cm-1;

EOTec uses vacuum compatible thin film polarizers at Brewsters angle:

BK7 Pulsed damage threshold >5J/cm2 10nsec pulse Extinction >1000:1 @1064 nm Transmission: 95-97% @1064 nm (97% maximum)


Faraday isolator: present bench

250 mm

670 mm

Not enough space on the

present bench


IB design with a Faraday Isolator

Even with a 20 mm clear aperture Faraday:

The IMC waist is 5 mm: the beam has to be reduced in size before entering in the Faraday

A telescope for reducing the beam to 2-3 mm in the Faraday has to be taken into account and designed

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 50-100 m

Induced (stationary) thermal lensing effects will be corrected acting on the matching telescope.


Brewster dielectric polarizers

Rotator

Faraday Isolator


20W Pump

HeNe

Shack-Hartman

Faraday

2f2f

Thermal focal length measurement


Shack-Hartmann measurement


Plane Power Recycling mirror

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)

The curved part is fixed to the cylindrical by means of a steel ring and pression screws;

There is evidence of mechanical resonances: 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)


Plane PR: (new) 6 parabolic off-axis telescope

IMC: waist 4.9 mmCondensing 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


Plane PR: Beam simulation

Input mirrors End mirrors


Telescope tolerances

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

The global tolerancies for plane PR seem to be accettable


IB layout


Optical layout - 2

Detector table

IB input window(s)


Ref. cav.

MC

LC

IMC auto- alignment

-- ALIGNMENT SERVOPICOMOTORSPIEZOS

Laser

NFFF

NF

FF

h

v

ABP_U

M2

M3M5

M6

PZT

RFC auto- alignment

Beam drift control

ABP_D

MATRIX


IMC and RFC alignment

10% ABP OFF

ABPdismounted

RFC is more stable than IMC:

RFC is fully automatically alignmed

IMC is partially automatically aligned


ISYS alignment: modifications to the IB

Automatic alignment of the IMC on the beam: acting on the IB through the IB marionette;

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)


Ref. cav.

MC

LC

IMC auto- alignment

-- ALIGNMENT SERVOPICOMOTORSPIEZOS

Laser

NFFF

NF

FF

h

v

h

v

ABP_U

M2

M3M5

M6

MATRIX

PZT

RFC auto- alignment

Beam pre- alignment

Beam drift control

ABP_D

MATRIX


Input beam monitoring

NF telescope: conjugate ABP_D mount on NF_Quadrant (shifts)

FF telescope: locate quadrant at focus (tilts)


Suspended Bench

Reference

Cavity

Marionette


Reference Cavity alignment

The design of the RFC layout should not change

M11 and M12 will be mounted on piezosfor RFC separate alignment

(Closed loop Physik Instrumente piezos)


VIRGO OPTICAL SCHEME

Nd :YAG= 1064 nm

20 W

DETEC TIO NSYSTEM

WIp la ne

R= 0.88

NIp la ne

R= 0.88

WER = 3500 m

R= 0.99995c urv

NER = 3500

R= 0.99995c urv

PRp la ne

R= 0.925

BS

INPUTM O DE

C LEANER(144 m )

6 m 6.4 m

5.6

m

3 km

3 km

O M C


6.26 M hz

Nd :YAG= 1064 nm

20 W

DETEC TIO NSYSTEM

WIp la ne

R= 0.88

NIp la ne

R= 0.88

WER = 3500 m

R= 0.99995c urv

NER = 3500

R= 0.99995c urv

PRp la ne

R= 0.925

BS

INPUTM O DE

C LEANER(144 m )

6 m 6.4 m

5.6

m

3 km

3 km

O M C


6.26 M hz

Frontal modulation


Sidebands resonant in the IMC

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

lIMC (a.u.)

J- J+J0


Sidebands resonant in the IMC

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+J0


Modulation frequency tuning

B2_ACq signal: f = 6.264080 MHz f = 6.264150 MHz (tuned)


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).

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).

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?


Pockels cell on the Input Bench after the IMC

Contacted several companies One (Leysop) gave more detailed answers (but still not final one)

After discussion, a possible proposed EOM is:

LiNbO4 (possible occurrence of self focusing and astigmatism) 15 mm aperture (beam waist=2.65 mm) About 50mm40mm 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


Space reserved on the new IB

EOM


Problems

Is it possible to place the EOM after the IMC? Is it a good idea?

There are many questions:

thermal focussing effects, astigmatism, distortions high voltage for modulation, etc.


Other GW experiments

We have no experience on these problems

Which is the experience in the other GW experiments?

As far as we know:

TAMA: no EOM in vacuum (not on the main beam) LIGO: no EOM in vacuum (not on the main beam)

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

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

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