A new model that keeps track of the dynamics of single dipoles is suggested for the photoinduced formation of a surface relief grating on azobenzene polymer films by two optical fields. Interfering optical fields provide a single dipole of an azobenezene molecule with two dynamical resources: rotation of the molecule caused by the torque, leading to an induced dipole, and its subsequent migration because of the electric force. Explicit development of the induced dipole of the molecule and its real-time migration, which depend on the details of the optical fields such as polarization and wavelength, can be understood self-consistently within the model.