Heavy IMC end payload requirements

Heavy IMC end payload requirements

M.Punturo

Translation of the IMC end mirror

• Current payload is made in such a way the suspension point can be translated by

11cm in the beam axis direction

Motorization

Counter-weight (800g)

360g mirror and ~5kg

reference mass

February detector meeting

• P.Puppo shown a possible large payload design able to translate many cm

– http://wwwcascina.virgo.infn.it/collmeetings/presentations/2006/2006 -02/DetectorMeeting/puppo_8Feb_DM.ppt

• But what are really the true requirements?

Optical Constrains

1. The same modulation frequency is used both for the longitudinal locking and for the alignment

1. This must be resonant in the recycling and in the mode cleaner cavity 1. The length of these cavities must be matched to the f

or viceversa

FP And

optimal

f n FSR

f

  

3. The Anderson frequency f

is the difference between the resonance

frequencies of the TEM

and TEM

modes and it is univocally defined by the cavity geometry:

eff FP FP

And

R

L L

f    c acos 1 

00

2

01

 



Thanks to: "Measurement of the optical parameters of the Virgo interferometer“ document

2. The use of the Anderson technique for the Angular alignment requires that “the TEM01 mode of the upper sideband is distant from the carrier by an exact number of free spectral range”

IMC optimal

k FSR

f

  For the recycling cavity the phase shift of the FP must be taken in account

R

~R

3. The modulation frequency fmod must correspond to the optimal one within the cavity linewidth (f=500Hz):

5 6

mod

10 10 8

26 . 6

500  

 

 

 f

f L

L 





























mm m

L

cm m

L

0 . 1 10

8 12

2 . 1 10

8 144

5 5

Mechanical displacements requirements

• The optical constrains require a mechanical displacement range smaller than two cm

• On the contrary, the initial position of the IMC end mirror must be well selected

– Passing from the current 3 cm thick mirror to a 10 cm thick the reflecting surface advances by 3.5 cm (and similarly the IMC cavity will be shortened by 3.5cm)

• The suspension point of the new payload must be off-

centered to take in account this offset

Conclusion

• The design of the new heavy payload for the end mirror of the IMC will take in

account a displacement system having a

range of ±3 cm

Large BS update

• J.Marque preliminary studies:

– Very large BS needed to reduce the scattered light

• Studied geometry is monstrous but what are our limits?

• L.Pinard contacted

– Heraeus can produce a 700 mm diameter BS (thickness is a

limitation)

– LMA can coat a mirror larger than 400 mm, but this is the upper limit for the

characterization facility

08/02/2006 European Gravitational Observatory 10

New BS geometry

Geometry:

t=135mm d=710mm

wedge=2.8mrad

J.Marque, Det. Meeting 8-2-2003