Novel Fluorooxoborate Crystal, NH₄B₄O₆F (ABF), Revolutionizes VUV Light Generation
Researchers at the Chinese Academy of Sciences have developed a novel fluorooxoborate crystal, NH₄B₄O₆F (ABF), which facilitates the generation of vacuum ultraviolet (VUV) light. Published in Nature, this development addresses the scarcity of suitable nonlinear optical (NLO) crystals for VUV light production, demonstrating record efficiency and pulse energy for VUV second-harmonic generation (SHG).
Introduction to VUV Light and Challenges
Vacuum ultraviolet (VUV) light, spanning wavelengths from 100 to 200 nanometers, is crucial for various advanced scientific and industrial applications. These include spectroscopy, quantum research, and semiconductor lithography.
Historically, the generation of VUV light has faced limitations due to a lack of suitable nonlinear optical (NLO) crystals capable of efficient second-harmonic generation (SHG). SHG is a process where two input photons of the same frequency are combined to produce a single photon with twice the frequency, thereby generating shorter wavelength light.
Development of the ABF Crystal
A research team led by Professor Pan Shilie at the Xinjiang Technical Institute of Physics and Chemistry of the Chinese Academy of Sciences (CAS) has developed a new fluorooxoborate crystal, NH₄B₄O₆F, designated as ABF. The findings were published in the journal Nature on January 28, 2026, under the title “Vacuum Ultraviolet Second-Harmonic Generation in NH₄B₄O₆F Crystal.”
The team successfully achieved centimeter-scale, high-quality ABF crystal growth and advanced anisotropic crystal processing technologies. This innovative method utilizes widely available industrial chemicals, offering a significant alternative to traditional NLO crystal production, which can often be complex and reliant on rare raw materials.
Unique Properties and Structure
The ABF crystal is particularly notable for integrating several properties critical for VUV NLO materials that were previously considered conflicting. These include:
- Excellent VUV Transparency: Allowing VUV light to pass through with minimal absorption.
- Strong Nonlinear Optical Coefficient: Indicating its efficiency in converting light frequencies.
- Significant Birefringence: Essential for VUV phase-matching, a condition required for efficient SHG.
In addition to these optical characteristics, ABF also meets practical requirements for real-world applications. It can be grown to a large crystal size, exhibits stable physical and chemical properties, possesses a high laser-induced damage threshold, and demonstrates suitable processability. Prior crystals had not simultaneously met all these criteria.
The crystal's exceptional performance is attributed to its unique structure, which ingeniously incorporates fluorine into the borate system. This design strategy created specific fluorooxoborate groups and precisely regulated their arrangement, thereby enhancing the crystal's overall performance and providing a methodological approach for exploring new VUV NLO materials.
Performance and Applications
Through second-harmonic generation, the ABF crystal has demonstrated the ability to generate VUV light with wavelengths down to 158.9 nm.
The team recorded a maximum nanosecond pulse energy of 4.8 mJ at 177.3 nm, with a conversion efficiency of 5.9%. These figures represent new records for nanosecond pulse energy and conversion efficiency for VUV SHG devices.
Researchers anticipate that further refinements in crystal quality and device fabrication precision could lead to additional improvements in these performance metrics.
The development of ABF is expected to support new scientific exploration and industrial applications. It serves as an invaluable tool for researchers studying superconductivity, chemical reactions, quantum mechanics, and spectroscopy. Furthermore, it holds potential benefits for advanced chip manufacturing.
Impact and Future Prospects
The development of ABF crystals facilitates the creation of compact, efficient, all-solid-state VUV lasers. This advancement is expected to improve access to VUV light sources for a broad range of scientific research and industrial applications, potentially broadening the scope of investigations and technological development significantly.
The research received support from the CAS Strategic Priority Research Program, the National Natural Science Foundation of China, and other funding sources.