  Multitime correlation functions provide useful probes for the ensembles of
trajectories underlying the stochastic dynamics of complex systems. These can
be obtained by measuring their optical response to sequences of ultrashort
optical pulse. Using the continuous time random walk model for spectral
diffusion, we analyze the signatures of anomalous relaxation in two-dimensional
four wave mixing signals. Different models which share the same two point joint
probability distribution show markedly different lineshapes and may be
distinguished. Aging random walks corresponding to waiting time distributions
with diverging first moment show dependence of 2D lineshapes on initial
observation time, which persist for long times.
