During the 1991–1997 window, the field coalesced around coherent generation and detection of terahertz radiation, driven by optical rectification in zinc telluride and gallium phosphide and by electro-optic sampling in transparent crystals. Researchers emphasized real-time, phase-sensitive measurement of broad THz spectra, enabling wideband spectroscopy, imaging, and practical sensing. Methodologically, the period favored ultrafast optical excitation, time-domain approaches, and non-destructive probing of materials and chemical samples, setting the stage for subsequent THz cameras and imaging techniques.