Frequency-Chain

From Qwiki

This technique has been superseded by optical frequency combs. A frequency-chain is used to generate a high frequency (optical, infrared, terahertz etc...) reference from a precision RF source, i.e. a cesium atomic clock. A frequency-chain operates by successively doubling the RF reference through various nonlinear processes. The high frequency signal of interest is compared to the reference generated by the frequency doubling chain. Generating a frequency-chain is extremely cumbersome and the resulting chain can be tuned only over an extremely limited range of frequencies. These problems have been overcome with optical frequency combs.