Chinese researchers have developed a new type of optical crystal that addresses existing supply bottlenecks and opens new possibilities in superconducting and quantum research.
The most cutting-edge work in spectroscopy, quantum mechanics, and semiconductor production relies on vacuum ultraviolet light generated with scarce nonlinear optical crystals (NLOs).
In a recent paper published in Nature, Professor Pan Shilie’s team at the Xinjiang Technical Institute of Physics and Chemistry of the Chinese Academy of Sciences (CAS) revealed their new fluorooxoborate crystal, NH₄B₄O₆F (ABF), offering an alternative to traditional NLOs for producing vacuum ultraviolet light.
Growing ABR Crystals
The researchers’ advancements focus on crystal growth and processing. They developed a new centimeter-scale, high-quality growth technique that enables crystals to be produced from chemicals already widely used in industrial applications. Current NLO crystal production methods are limited by extreme complexity and reliance on rare raw materials, which are typically useful only in their purest forms.
The crystals have a unique structure. Borates—boron-oxygen compounds commonly used in glass, flame retardants, and cleaning agents—form the base. Fluorine is then introduced into the borate system, allowing the researchers to create fluorooxoborate groups. The CAS team arranged these groups into configurations designed to maximize the crystal’s desired properties. Importantly, this design approach is viable for larger-scale production.
Crystal Properties
ABF crystals are defined by a set of important, yet often competing, properties. One is birefringence, a phenomenon in which a crystal splits light into two beams with slightly different polarizations and paths, which is critical for vacuum ultraviolet phase matching. Another is the strength of its nonlinear optical response, as measured by an NLO coefficient. Finally, the material must be highly transparent to vacuum ultraviolet light.
These characteristics must be balanced with practical constraints for ABF crystals to function in real-world devices. The crystals must meet specific size requirements to achieve precise phase-matching angles. They must also be physically and chemically stable, with a high threshold for laser-induced damage. Before the CAS team’s work, no crystal had simultaneously demonstrated all of these properties.
Improving Applications
Through a process called second-harmonic generation (SHG), the crystal combines two input photons of the same frequency into a single photon with twice the frequency, producing vacuum ultraviolet light with a wavelength of 158.9 nanometers. Such a short wavelength provides a powerful new tool for researchers studying superconductivity and chemical reactions.
In addition to producing short wavelengths, the crystal can also generate extremely high-energy vacuum ultraviolet light. The team measured a maximum nanosecond pulse energy of 4.8 mJ at 177.3 nm, with a conversion efficiency of 5.9%. This represents the highest nanosecond pulse energy and conversion efficiency in a vacuum ultraviolet SHG device reported to date. The researchers plan further refinements to crystal quality and device fabrication that could push these figures even higher.
By producing ABF crystals in the laboratory, the team says compact, all-solid-state vacuum ultraviolet lasers could become much more accessible. This would empower researchers working in areas such as chip manufacturing, quantum mechanics, and spectroscopy.
The paper, “Vacuum Ultraviolet Second-Harmonic Generation in NH4B4O6F Crystal,” appeared in Nature on January 28, 2026.
Ryan Whalen covers science and technology for The Debrief. He holds an MA in History and a Master of Library and Information Science with a certificate in Data Science. He can be contacted at ryan@thedebrief.org, and follow him on Twitter @mdntwvlf.