  Light-matter interaction in 2D and topological materials provides a
fascinating control knob for inducing emergent, non-equilibrium properties and
achieving new functionalities in the ultrafast time scale (from fs to ps). Over
the past decade, intriguing light-induced phenomena, e.g., Bloch-Floquet states
and photo-induced phase transitions, have been reported experimentally, but
many still await experimental realization. In this Review, we discuss recent
progress on the light-induced phenomena, in which the light field could act as
a time-periodic field to drive Floquet states, induce structural and
topological phase transitions in quantum materials, couple with spin and
various pseudospins, and induce nonlinear optical responses that are affected
by the geometric phase. Perspectives on the opportunities of proposed
light-induced phenomena as well as open experimental challenges are also
discussed.
