Nonlinear Optical Materials for Terahertz Generation

Terahertz (THz) radiation, occupying the spectral region between 0.1 and 10 THz, sits at a uniquely productive crossroads between microwaves and infrared light. Its applications now span spectroscopy, biomedical imaging, security screening, ultrafast communications, and condensed matter physics — yet the field remains constrained by a persistent bottleneck: the lack of efficient, compact, and tunable THz sources. Nonlinear optical (NLO) materials have become central to addressing this challenge, with mechanisms such as optical rectification, difference-frequency generation, and nonlinear frequency mixing under ultrafast laser excitation offering some of the most promising routes to practical THz emission. The performance of these sources, however, depends sensitively on a tightly coupled set of material properties — nonlinear susceptibility, phase-matching behavior, optical damage threshold, and absorption characteristics — which together determine whether a given material can deliver the bandwidth, power, and stability that real applications demand.Traditional workhorses such as ZnTe, GaP, and LiNbO₃ have shaped the field but are increasingly limited by narrow bandwidth, phonon absorption, and phase-matching constraints. Recent progress in crystal engineering, organic and hybrid compounds, semiconductors with tailored band structures, two-dimensional materials, metamaterials, and nanostructured systems is opening new design space, but the community still lacks a coherent picture of how structure, symmetry, and electronic properties translate into nonlinear response in the THz regime. This Research Topic aims to build that picture. By bringing together work on emerging material platforms alongside refined understanding of established ones, it seeks to clarify the structure–property–performance relationships that govern THz generation and to surface the design principles needed for the next generation of broadband, high-power, and tunable sources.Contributions are welcome across the full breadth of the field, including the development and characterization of inorganic crystals, organic NLO materials, semiconductors, low-dimensional systems, and hybrid architectures; analyses of second- and third-order nonlinear coefficients, dispersion, phonon resonances, and absorption losses at THz frequencies; comparative studies of generation mechanisms under femtosecond excitation; and investigations of how molecular alignment, crystal symmetry, and nano- or microstructuring shape emission efficiency and bandwidth. Theoretical, computational, and experimental perspectives are equally valued, as are benchmarking studies that situate new materials against the current state of the art in terms of output power, spectral coverage, stability, and scalability.Taken together, the collection is intended to provide a unified reference for researchers working on compact, high-performance THz sources — mapping the current landscape of nonlinear optical materials, identifying the parameters that most strongly govern efficient and broadband emission, and highlighting the platforms and directions most likely to define the field in the years ahead. Topic editors: Boomadevi Shanmugam, Barun Kumar Barman, Toijam Sunder Meetei Source: https://www.frontiersin.org/research-topics/79442/nonlinear-optical-materials-for-terahertz-generation