  We present a topological quantization of free massive bosonic fields as the
first example of a classical field theory with a quantum counterpart to be
studied under this formalism. First, we identify certain harmonic map as a
geometric representation of this physical system. We take as a concrete example
the case of free massive bosonic fields in two dimensions represented by the
minimal embedding of a two dimensional surface into a pp-wave spacetime. We use
this geometric representation to construct the fiber bundle corresponding to
some specific field configurations and then find their topological spectra,
defined in terms of the Euler invariant. We discuss the results for some
particular configurations and their consequences for the energy of the system.
