  An original dispersion relation between the stationary coherent nonlinear
optical responses by current and polarisation is obtained. The dispersion
relation provides a new complimentary tool that can be employed to study
light-induced charge transport models and facilitate experimental data
analysis. It is shown that the origin of the coherent current and the
dc-polarisation induced in a noncentrosymmetric crystal under illumination is
related to the theory of the Berry phase and can be represented in terms of the
renormalised geometric potentials. This renormalisation originates from the
extra phase difference acquired by a carrier in the light field on the quantum
transition between the electronic bands. The gauge invariance of the
corresponding expressions for the current and the polarisation is demonstrated.
