Frequency Measurement of an Optical Lattice Clock

A frequency measurement system is developed away from a National Metrological Institute with a frequency link to International Atomic Time (TAI). The absolute frequency of the 1S0 -3P0 clock transition of the 87Sr lattice clock is determined to be 429,228,004,229,875(4) Hz. The frequency measurement system is being further improved by introducing an optical fiber link and by upgrading the GPS link.