  In this paper we present the realization of further steps towards the
measurement of the magnetic birefringence of the vacuum using pulsed fields.
After describing our experiment, we report the calibration of our apparatus
using nitrogen gas and we discuss the precision of our measurement giving a
detailed error budget. Our best present vacuum upper limit is Dn < 5.0x10^(-20)
T^-2 per 4 ms acquisition time. We finally discuss the improvements necessary
to reach our final goal.
