Collective excitations in solids have been the focus of studying quantum materials and understanding the underlying physics. One of the ways to probe these excitations is by using time-domain terahertz spectroscopy (TDTS). In the first part of the talk, I will briefly introduce how TDTS can be used in modern condensed matter to probe collective excitations in strongly correlated systems which leads to the recent discovery of massive phason in (TaSe4)2I. In the second part of the talk, I will focus more on new breakthroughs recently in TDTS which allows us to probe broader bandwidth and the relating new physics. I will also briefly introduce some other techniques that use light matter interactions to study emergent phenomena of quantum materials.
