  We show that a single-mode squeeze operator S(z) being an unitary operator
with a purely continuous spectrum gives rise to a family of discrete real
generalized eigenvalues. These eigenvalues are closely related to the spectral
properties of S(z) and the corresponding generalized eigenvectors may be
interpreted as resonant states well known in the scattering theory. It turns
out that these states entirely characterize the action of S(z). This result is
then generalized to N-mode squeezing.
