In this colloquium, I will talk about how the extremely fast light, called “ultrafast” laser, is used to investigate “exciting” quantum properties of van der Waals materials. I will first introduce principles and applications of conventional ultrafast time-resolved spectroscopy. Then, a highly nonlinear optical spectroscopy will be introduced, where we were recently able to generate THz electric fields over 1 MV/cm.

Followed by the introductions, discussion will be made on the following topics. (i) Non-excitonic valley Hall effect in a heterostructure consisted of a monolayer semiconductor and 2D topological insulator. (ii) Ultrafast manipulation of many-body excitons in a gate-controlled 2D semiconductor.