China's new crystal smashes vacuum ultraviolet laser record at 158.9nm

Chinese researchers at the Chinese Academy of Sciences (CAS), led by Pan Shilie, have developed a new nonlinear optical crystal called ammonium fluorooxoborate (ABF), enabling the creation of the world’s shortest-wavelength solid-state vacuum ultraviolet (VUV) laser at 158.9 nanometers (nm). This breakthrough surpasses previous records by using direct frequency doubling with the ABF crystal, which offers high transparency in the VUV range, strong nonlinear optical response, and sufficient birefringence for phase matching at extremely short wavelengths. Unlike the previously used potassium beryllium fluoroborate (KBBF) crystal, ABF overcomes growth and fabrication limitations, making it suitable for practical laser devices. The ABF crystal, synthesized in 2016 and refined over a decade to achieve centimeter-scale high optical quality, achieved a nanosecond pulse energy of 4.8 millijoules and a conversion efficiency near six percent—both new records for