  We present a general analysis of the state obtained by subjecting the output
from a continuous-wave (cw) Gaussian field to non-Gaussian measurements. The
generic multimode state of cw Gaussian fields is characterized by an infinite
dimensional covariance matrix involving the noise correlations of the source.
Our theory extracts the information relevant for detection within specific
temporal output modes from these correlation functions . The formalism is
applied to schemes for production of non-classical light states from a squeezed
beam of light.
