  Optical micro-manipulation techniques has evolved into powerful tools to
efficiently steer the motion of microscopical particles on periodic and
quasi-periodic potentials, driven by the external electromagnetic field. Here,
the dynamics of molecular diffusion on optical lattices is analysed within the
framework of the theory of open systems, for polar molecules coupled to a
transient electromagnetic field. Using the normal mode expansion of the field,
we derive an effective, generalised Langevin equation which describes the
motion of the system along the molecular degrees of freedom. The present
approach is universally applicable (for molecules with non-vanishing permanent
dipole moment) and it opens a wide spectrum of applications in the control of
the molecular transport mechanisms on optical lattices. The numerical analysis
of suitable model external fields demonstrates the feasibility of neglecting
memory terms in the resulting Langevin equation.
