  We investigate different methods to compute the DC conductance in a quantum
wire doped with some impuritied by exploiting the integrability of the theories
under consideration. As an essential ingredient in all methods we evaluate the
reflection and transmission amplitudes ofthe impurities for a variety of
defects. When the impurities inthe wire are coupled to an external three
dimensional laser field, we predict the generation of harmonic emission
spectra. We propose a modified version of the well-known Kubo formula, which
incorporates the impurities of the system and evaluate the current-current
two-point correlation function it involves with the help of a form factor
expansion. A comparison with the corresponding quantities computed in a
Landauer transport theory picture is carried out in part II.
