On a quartz wafer, the angular rhombic boron nitride crystal with a thickness of only 1 to 3 microns is as thin as cicada wings, but its energy efficiency is 100 to 10000 times higher than traditional optical crystals - this is the thinnest known optical crystal invented by Chinese scientists in the world. At the opening ceremony of the 2024 Zhongguancun Forum Annual Meeting held on April 25th, this crystal was released as a major achievement. Optical crystals are the "heart" of laser technology. "Laser technology is the cornerstone of our current technological civilization, shining brightly in fields such as micro nano processing, quantum light sources, and biological monitoring." Professor Liu Kaihui from the School of Physics at Peking University introduced that the breakthrough of laser technology highly relies on a special material - optical crystals. Integration, miniaturization, and multifunctionality are the development directions of future lasers. However, traditional optical crystals are difficult to efficiently produce lasers within a limited thickness, so the preparation of lighter and thinner optical crystals has become a focus of research and development by scientists from various countries. Chinese scientists have repeatedly combined and attempted to lock in lightweight boron nitride as the optimal choice. However, experiments have found that simply stacking boron nitride molecules layer by layer can cause "inconsistent step" or phase mismatch when the laser passes through, which hinders the efficient output of the laser and cannot be directly used as an optical crystal in laser manufacturing. Academician Wang Enge from the Center for Quantum Materials Science at the School of Physics, Peking University, Professor Liu Kaihui from the Institute of Condensed Matter Physics and Materials Physics, and Associate Researcher Hong Hao have created a new crystal design method: by rotating each rhombic boron nitride material at a specific angle like a twisted cube, the stacked optical crystals can reduce the energy consumption of laser penetration and efficiently produce the required laser. The combination of crystal design theory and preparation method pioneered by Chinese scientists has successfully slimmed down optical crystals to 1 to 3 micrometers. The thickness of traditional optical crystals ranges from millimeters to centimeters. The R&D team summarized this method as the interface rotation theory of two-dimensional materials. "The application of this theory is expected to reduce the size of lasers to the micrometer level. Some materials that were previously unable to manufacture optical crystals are also expected to revive in the rotation of material stacking angles," Liu Kaihui told reporters. (Lai Xin She)