By bouncing eye-safe laser pulses off a mirror on a
hillside, researchers at the National Institute of Standards and Technology
(NIST) have transferred ultraprecise time signals through open air with
unprecedented precision equivalent to the "ticking" of the world's
best next-generation atomic clocks.
Described in Nature Photonics,* the demonstration shows how
next-generation atomic clocks at different locations could be linked wirelessly
to improve geodesy (altitude mapping), distribution of time and frequency
information, satellite navigation, radar arrays and other applications. Clock
signals of this type have previously been transferred by fiber-optic cable, but
a wireless channel offers greater flexibility and the eventual possibility of
transfer to and from satellites.