Significance The main methods of controlled fusion are magnetic and inertial confinement. Between them, inertial - confinement fusion (ICF) uses a higher - power laser beam or higher - energy particle - beam irradiation to focus energy on a deuterium - tritium fuel target pellet with a diameter of only a few millimeters, which rapidly yields a temperature and pressure similar to the core of a star or nuclear explosion, followed by nuclear fusion. Basov. N. G. first proposed the concept of ICF in 1963, and then Chinese nuclear physicist Wang Ganchang proposed laser - driven ICF, which propelled investigations into ICF in China. The emergence and development of high - power lasers have enabled ICF. Currently, the worlds major stakeholders are investing significant resources into developing high - power laser devices, e.g., the world s largest laser device NOVA developed in the United States in 1985, the construction of a megajoule laser device at the United States National Ignition Facility (NIF), France, and the development of a series laser device by Shenguang, China. Short - wavelength laser beams have greater energy and couple more efficiently to the target pellet compared with long - wavelength laser beams. Therefore, for large ICF devices, high - quality electro - optical and nonlinear optical materials are required to convert the 1064 nm laser output wavelength of neodymium glass to 355 nm. Additionally, the materials must exhibit a large aperture, a high laser - damage threshold, large nonlinear optical and electro - optical coefficients, a wide transmission band, and low refractive - index inhomogeneity. KDP - class crystals are excellent nonlinear optical crystal materials with high resistance to laser damage, wide transmittance bands, high electro - optical coefficients, good optical uniformity, and the ability to grow into large crystals. Therefore, large KDP - class crystals are the only type of crystal that can be used for electro - optical switches and frequency - conversion devices in large - caliber high - power laser - driven devices. Progress To address the low efficiency of the conventional rapid growth of point - seed crystals at the cylindrical cone interface, an innovative process for the rapid growth of long - seeded crystals was proposed (Fig. 2). Compared with the conventional growth method, the rapid - growth method reduces the crystal growth time from 3 years to half a year. Additionally, the cutting efficiency is doubled and the column - cone interface is absent. The rapid - growth method revamps the entire process route from batching, point crystal, growth, cutting, to annealing. Additionally, a full set of production equipment and processes required for crystal growth, cutting, rough grinding, and annealing is independently developed, thus providing a solid foundation for the entire chain of DKDP components. Dynamic - light - scattering technology was developed to characterize the particle size of solutions prepared using DKDP crystals, which supports the rapid increase in the probability of the laser - damage threshold and provides technical support for obtaining high - quality DKDP crystals (Fig. 3). This technology involves the independent development of large - caliber DKDP crystal wirecutting equipment, requires fewer cutting process parameters, and achieves large - caliber crystal cutting flatness (0.2 mm), thus providing technical support for large - sized crystal cutting (Fig. 4). A precision annealing equipment for large - diameter DKDP crystals was independently developed (Fig. 5), and the damage threshold of 1-2 J/cm 2 increased after annealing (Fig. 6). Based on the freegrowth technology of long - seeded crystals, 320 mm long - seeded crystals were used to rapidly achieve 520 mmx521 mmx540 mm large - diameter DKDP crystals at 120 d of growth. The internal transparency of the crystal blank was favorable and satisfied the cutting requirements of large - diameter second - type mixing elements and did not present a conical column interface. The successful growth of the crystals validates the rapid - growth technique for long - seeded DKDP crystals. Owing to continuous research efforts, the growth success rate of DKDP crystals has exceeded 80%, and their optical performance has improved continuously, among which the core index of the crystal anti - laser damage ability has increased significantly and the anti - laser damage ability of the fundamental - frequency KDP component has reached 30 J/cm 2 (1 omega, 3 ns). The zero - probability laser - damage resistance of triple - frequency small - aperture DKDP crystals has reached 18 J/cm 2 (3 omega, 3 ns), and after subnanosecond pretreatment, it exceeded 20 J/cm 2 (3 omega, 3 ns), which is the highest level for DKDP crystals with 70% deuteration rate in China. Conclusions and Prospects To develop high - power laser drivers, four requirements are to be fulfilled: technology, quality, production capacity, and target cost, Additionally, two goals are to be achieved. First, the technology should be improved continuously and the quantitative and deterministic control of crystal growth should be realized. Second, the development of a full - link device for the growth of DKDP crystals should be promoted; the extremely limited growth, cutting, and annealing capabilities should be addressed; and large - caliber DKDP components should be mass produced.
