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
But what are really the true requirements?

4. Optical Constrains
Thanks to: "Measurement of the optical parameters of the Virgo interferometer“ document
The same modulation frequency is used both for the longitudinal locking and for the alignment
This must be resonant in the recycling and in the mode cleaner cavity
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
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”
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:
Reff~Rend mirror
The modulation frequency fmod must correspond to the optimal one within the cavity linewidth (Df=500Hz):

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