Scientists in Xinjiang have created the world’s first crystal that can produce the ultraviolet light needed for future thorium nuclear clocks, which could one day guide submarines and deep-space probes without GPS.
The fluorinated borate compound could push laser light to a record 145.2 nanometres (nm) – a wavelength short enough to meet a key requirement for these ultra-precise, portable clocks being developed in the United States, China and elsewhere, the team reported in Advanced Materials in January.
The result surpassed previous benchmarks set by potassium beryllium fluoroborate, a crystal developed in China in the 1990s that has long dominated the field but can only reach about 150nm – just short of the 148.3nm target needed for such clocks.
The work offers a new way to design next-generation deep-ultraviolet materials and “paves the way for the practical development of the thorium-229 nuclear clock”, the team led by Pan Shilie at the Xinjiang Technical Institute of Physics and Chemistry wrote in the paper.
A nuclear clock keeps time using vibrations inside an atomic nucleus, rather than the electrons used in atomic clocks. Because the nucleus is far less affected by its surroundings, a nuclear clock could deliver much higher precision, enabling navigation in places where the Global Positioning System does not work, such as deep space or underwater.
Like other advanced clocks, it uses thorium atoms, a laser to probe them and a detector to read the signal. The laser must be tuned to a very specific wavelength to “tick” the nucleus, with timing set by how regularly it responds.
