Frequency measurements of optical radiation

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Abstract
Among the remarkable facts of modern technology, one of the most striking is that the possibility is at hand of making an exact count of cyclical events that occur at a rate of over 500 million in a microsecond; this will be the likely result of present work on the measurement of the frequency of optical radiation and the use of optical resonances at frequency standards. The actual counting of the exact frequency of optical radiation or locking its oscillations to microwave standards is still very much in the development stage; however, its feasibility has already been demonstrated in experiments such as a recent measurement of the frequency of a visible laser emission, a feat that gained a recognition not often accorded scientists: mention in the Guinness Book of Records for the highest frequency measured! A number of laboratories are actively engaged in setting up systems for precisely relating optical and microwave standards. The Institute for Semiconductor Physics in Novosibirsk, for example, has announced the first “optical clock,” in which microwaves were locked to the 3.39‐micron absorption line in methane.