Abstract
A simple analytic expression for the double optical resonance spectrum obtained when a two-level atom is excited by a noisy pump laser is derived for two different models of laser noise, the phase diffusion model, and a model in which the laser bandwidth arises from a random telegraph signal in the laser phase. The double optical resonance spectrum is identical for both models and therefore double optical resonance experiments cannot distinguish between them. The importance of transients in cases where the laser bandwidth is comparable with or less than the atomic linewidth is stressed. Experiments which can distinguish between the two sources of bandwidth are identified.