Nonlinear interactions of light with light are well known in quantum
electronics, and it is quite common to generate harmonic or subharmonic beams
from a primary laser with photonic crystals. One suprising result of quantum
electrodynamics is that because of the quantum fluctuations of charged fields,
the same can happen in vacuum. The virtual charged particle pairs can be
polarized by an external field and vacuum can thus become birefringent: the
PVLAS experiment was originally meant to explore this strange quantum regime
with optical methods. Since its inception PVLAS has found a new, additional
goal: in fact vacuum can become a dichroic medium if we assume that it is
filled with light neutral particles that couple to two photons, and thus PVLAS
can search for exotic particles as well. PVLAS implements a complex signal
processing scheme: here we describe the double data acquisition chain and the
data analysis methods used to process the experimental data.Comment: presented by E. Milotti to the WSEAS-ISCGAV '05 Conference, Malta,
15-17/9/200