NLO CRYSTALS FOR DEEP-UV PHOTONICS: FROM FUNDAMENTAL PRINCIPLES TO ADVANCED FREQUENCY CONVERSION DEVICES

The interaction between light and matter remains a foundation of classical optics and continues to inspire intense research interest, particularly with the rapid advancements in nonlinear optics. As fixed-wavelength lasers increasingly fall short of meeting the stringent demands of modern scientific and technological applications, deep-ultraviolet (DUV) nonlinear optical (NLO) crystals have emerged as a powerful solution, offering short wavelength and high photon energy that enable spectral high-resolution, selective material excitation, and advanced NLO processes beyond the capabilities of conventional lasers. However, achieving efficient short-wavelength DUV lasers, especially from fundamental laser sources, demands a series of critical and technically challenging steps, including rational single-crystal design, bulk crystal growth, comprehensive physicochemical and optical characterization, and device-level implementation. Each of these stages involves complex and time-consuming processes, underscoring the need for a clear understanding of the fundamental objectives and technical prerequisites required to satisfy the performance benchmarks of next-generation DUV photonic technologies. This chapter places particular emphasis on how intrinsic optical properties are strategically leveraged to enable cutting edge DUV applications. Furthermore, recent breakthroughs in DUV material are highlighted, demonstrating how these advancements collectively accelerate innovation and shape the future landscape of this dynamic and influential industry field.