Abstract : VIRGO is a gravitational wave detector based on a Michelson interferometer with arms
which are 3 km long. This thesis fouses on the study of the interferometer signal detection
system i.e. the system which detects the gravitational wave signal by measuring the ITF
transmitted beam power.
By means of a simulation of the interferometer, it is shown that the optical filtering
of the transmitted beam with a ring cavity gives an improvement in the interferometer
sensitivity. The performance of this cavity is tested with a table-top interferometer. An
automatic locking procedure of the cavity is then developed using a beam profile analysis
with a CCD camera.
The light detection system is studied to deal with the signal dynamic range without
degrading the VIRGO sensitivity. First the signal shaping needed before digitization is
defined. Then a calibration procedure is developed to measure the dispersion between the
different readout channels and to correct it on line.
Finally the measurement of the detection system noise is performed and it's contribution
to the VIRGO sensitivity is discussed. A coalescing binary search algorithm is
implemented and used to study the detection system noise contribution to this kind of