Optical Frequency Measurement Using Frequency Multiplication and Frequency Combs

Abstract

We review the development of phase-coherent optical frequency measurement from its start with the harmonic frequency chain to the present use of optical comb generators. We demonstrate that the frequency fluctuations of a femtosecond comb laser-used in optical frequency measurement-can be eliminated completely from the measurement process, allowing ultimate frequency measurement performance. This principle was applied to the frequency measurements of the Ca cloud standard and the single-ion standard. The latter measurements confirm the suitability of these optical standards as future atomic clocks.