Virgo Characteristics by GatorFace


									               The Virgo Experiment: Characteristics

The scheme of the Virgo interferometer is shown in fig. 1. We define l1 , l2 the lenghts
of the Michelson interferometer arms (distances from the beam splitter to the input
mirrors of the FP cavities), L1, L2 the lenghts of the cavities and lr the distances
between the beam splitter and the recycling mirror.

                           Fig 1: The Virgo Interferometer

The principal characteristics are:
    Laser: it is a Nd:Yag emitting at λ = 1064 nm. Its output power in the TEM00
       mode is about 20 W. The stability requirement are:

                        "P $ 3*10 / Hz
                           &                   for f = 10Hz
           -   power:     <%
                         P & 3*10#7 / Hz
                           '                   for 100 < f < 1000Hz

                        "v $10 / Hz
                           & #4                for f = 10Hz
           - frequency:   <%
            !            v &10#6 / Hz
                           '                   for 100 < f < 1000Hz

           This level of frequency stability requires a gain of about 107 in the control
    Input bench: it is under vacuum and suspended from a short superattenuator. It
     is equipped with a rigid triangular referente cavità for the frequency pre-
     stabilization, the input and output mirrors of the mode cleaner and the main
     beam expansion and alignment optronics.
 Mode cleaner: it is a triangular cavità 144 m long. Two mirrors (input and
  output) are mounted on the input bench. The third mirror is suspended from a
  short tower, connected to the input bench tower by a dedicated pipe.
 Power recycling: the recycling cavity is made by the recycling mirror and the
  interferometer itself. The cavità length is defined as lr = l0+(l1+l2)/2. The
  foreseen recycling factor is about 50: a power of about 1 kW is expected on
  the beam splitter.
 Fabry-Perot cavities: the FP will be 3 km long and will have a finesse F = 50.
  The interferometer output i sto be kept on the dark fringe for the carrier, while
  the sidebands are to be transmitted to carry the signal.
 Detector system: it is composed of a detection bench, suspended from a short
  tower and a optical table (outside the vacuum vessel). The bench supports the
  output mode cleaner (a small monolithic triangular cavità, designed to increase
  the contrast by filtering the spurious mode) and the optics for splitting and
  collimatine the beam on the photodiodes. The table supports the photodiodes
  (InGaAs, quantum efficiency η = 0.85) for the locking and the signal

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