  Two-dimensional transition metal dichalcogenides (TMDC) have shown promise
for various applications in optoelectronics and so-called valleytronics. Their
operation and performance strongly depend on the stacking of individual layers.
Here, optical second-harmonic generation (SHG) in imaging mode is shown to be a
versatile tool for systematic time-resolved investigations of TMDC monolayers
and heterostructures in consideration of the material's structure. Large sample
areas can be probed without the need of any mapping or scanning. By means of
polarization dependent measurements, the crystalline orientation of monolayers
or the stacking angles of heterostructures can be evaluated for the whole field
of view. Pump-probe experiments then allow to correlate observed transient
changes of the second-harmonic response with the underlying structure. The
corresponding time-resolution is virtually limited by the pulse duration of the
used laser. As an example, polarization dependent and time-resolved
measurements on mono- and multilayer MoS$_2$ flakes grown on a SiO$_2$/Si(001)
substrate are presented.
