Optical Lattice Clock: Precision Frequency Measurement

The paper discusses a concept and a projected performance of an "optical lattice clock" as a next generation time and frequency standard. Recent experiments on the absolute frequency measurement are presented. The measured Allan standard deviation shows that the fractional frequency instability of the Sr lattice clock has reached 3times10^-15 at an averaging time of 1000 s. A preliminary absolute frequency value of the Sr lattice clock is obtained to be 429,228,004,229,876(5) Hz