Microwave to visible frequency synthesis

The helium‐neon methane‐stabilized laser frequency at 88 THz (3.39 μm) and higher frequencies (148 and 197 THz, frequencies of the Xe (2.03 μm) and Ne (1.52 μm) lasers) have been measured by comparison with the cesium frequency standard using a microwave to visible frequency synthesis chain. This paper will report on the techniques of laser frequency measurements, the nonlinear devices used for these measurements, and the different methods for laser frequency synthesis with emphasis on microwave and laser generators. The extension of laser frequency measurements to the visible will also be discussed.