Optical pump / terahertz probe spectroscopy determines the conductivity of a material on picosecond to nanosecond timescales after photoexcitation, and in a non-contact manner. It is ideal to examine the intrinsic photoresponse of semiconductor nanomaterials, without the complication of device fabrication. Further, it permits the formation of bound and free charges, and their subsequent transport and interaction with interfaces, to be tracked with exquisite detail. This will provide important insights into charge transport in monolayer semiconductors and their heterostructures, nanowires, and materials for photocatalytic processes such as solar water splitting. Further, studies of metamaterials coupled to 2D electron systems will permit strong light-matter coupling to be probed on picosecond timescales. WCUS will also have imaging capabilities with wide applicability across different material systems, for instance using scanning THz microprobes for micron length scales. Other modalities provided by the facility will also contribute to this theme, for instance mid-IR pump-probe studies of defect states in semiconductor photovoltaics.