Summary of the meeting held in Cascina, 05.04.06

AdVirgo, Optical Configuration Working Group

In the following I have tried to summarise the main 
items discussed and actions proposed during the meeting.
Please let me know if I have forgotten something
or if your summary differs from what I understood.

I should be noted that no volunteers were found for
the task list circulated earlier. Apparently no-one
present is currently working on related tasks not mentioned
in that list.

Main items:

o first of all a starting set of IFO parameters 
  should be compiled and provided. This allows to
  compare the results from various people/groups 
  investigating specific features of a new topology 
  (this is underway, I will send around some data
  soon)

o the design should start out with spherical beams
  and mirrors; the inclusion of other beam geometries 
  (see below) can be based on a working spherical design

o One of the main issues are the optical losses upon 
  reflection on the main optical surfaces. The following
  tasks have been identified:
  - compute the expected losses due to 'scattering' from mirror 
    distortions of large spatial wavelength 
  - compute realistic values for losses of non-spherical
    geometries (including misalignment and contrast defects)
  - compute specifications for optical losses, especially
    for the signal recycling topologies or quantum-non-
    demolition techniques (e.g. using squeezed vacuum)
  
o Non-spherical beams and the respective interferometer
  topologies require a considerable experimental R+D process
  which should be started immediately if this option should
  be kept.

Some independent points raised during the meeting:

o Spherical ring-type higher-order Gaussian modes could possibly be used
  to achieve a similar reduction of thermal noise as flat beams
  but without the problems related to the non-spherical mirror
  surfaces. (Under investigation by J.Y. Vinet)

o The feasibility of squeezed vacuum injections could be tested
  using the low-frequency facility but requires collaboration
  with GEO. 

o The envisaged larger beam size in the central interferometer
  might require changes to the tubes connecting the central tank
  with the input and output optics. Currently the dimensions
  are: tube diameter 400mm (not taking into account the baffles), 
  valve diameter 250mm

o Wedges in the input test masses and the BS can be vertical,
  this would minimise the impact on the vacuum system. Realistic
  wedge angles should be computed and specifications for 
  vertical seismic noise at the mirror level should be 
  computed.

Open points:

o The status of SIESTA with respect to signal recycling simulations
  with realistic parameters (including higher order modes and 
  mirror maps)

o The status of the simulation of J. LeBars and J.M. Courty

o The availability of DarkF to other people (a question of FORTRAN
  compilers)