Heavy IMC end payload requirements

1
Heavy IMC end payload requirements

• M.Punturo

2
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
3
February detector meeting

• P.Puppo shown a possible large payload design
  able to translate many cm
• http//wwwcascina.virgo.infn.it/collmeetings/prese
  ntations/2006/2006-02/DetectorMeeting/puppo_8Feb_D
  M.ppt
• But what are really the true requirements?

4
Optical Constrains
Thanks to "Measurement of the optical parameters
of the Virgo interferometer document

1. The same modulation frequency is used both for
   the longitudinal locking and for the alignment
2. This must be resonant in the recycling and in the
   mode cleaner cavity
3. The length of these cavities must be matched to
   the fmod or viceversa

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

1. 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

1. The Anderson frequency fAnd is the difference
   between the resonance frequencies of the TEM00
   and TEM01 modes and it is univocally defined by
   the cavity geometry

ReffRend mirror

1. The modulation frequency fmod must correspond to
   the optimal one within the cavity linewidth
   (Df500Hz)

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

6
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

7
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

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