Space-time description of squeezing

We present a field-theoretical description of the squeezed states of the electromagnetic field. A definition of the squeezed state is introduced that is a natural generalization of the definition for one or two modes. We show that the squeezing produced by the medium with spaceand time-dependent material coefficients e and is directly related to the photon-pair production. In Appendix A we describe the time evolution of the Gaussian squeezed states in terms of the field variables.