Deepankar Sri Gyan

1 Introduction Terahertz (THz) frequencies occupy the spectral gap between electronics and photonics, bridging microwave electronics on the low-frequency side and infrared/optical photonics at higher frequencies. The characteristic timescales of THz phenomena (sub-picosecond) and energies (few meV) match a broad class of low-energy degrees of freedom in solids, such as collective excitations in quantum materials, as well as resonant processes relevant to sub-THz wireless communications [1, 2].