The stochastic nature induced by laser noise in narrow transitions

We use a probabilistic method to describe the effect of laser noise on the laser-atom interaction, in the case that the atom is a two level system without spontaneous emission. The stochastic differential equation for the laser-atom interaction is analyzed in the sense of perturbation approach, and we construct a stochastic process corresponding to the time evolution of the atom's wave function, whose extra randomness is induced by the laser noise. It also provides the layout of a theory for the possible experiment of measuring the laser line width by driving a narrow atomic transition.