  New experimental techniques based on non-linear ultrafast spectroscopies have
been developed over the last few years, and have been demonstrated to provide
powerful probes of quantum dynamics in different types of molecular aggregates,
including both natural and artificial light harvesting complexes. Fourier
transform-based spectroscopies have been particularly successful, yet
'complete' spectral information normally necessitates the loss of all
information on the temporal sequence of events in a signal. This information
though is particularly important in transient or multi-stage processes, in
which the spectral decomposition of the data evolves in time. By going through
several examples of ultrafast quantum dynamics, we demonstrate that the use of
wavelets provide an efficient and accurate way to simultaneously acquire both
temporal and frequency information about a signal, and argue that this greatly
aids the elucidation and interpretation of physical process responsible for
non-stationary spectroscopic features, such as those encountered in coherent
excitonic energy transport.
