Frequency comb

A frequency comb is a spectrum consisting of a series of discrete, equally spaced elements. Frequency combs can be generated by a number of mechanisms, including amplitude modulation (AM) of a continuous wave laser or stabilization of the pulse train generated by a mode locked laser. Much work has been devoted to the latter mechanism, which was developed around the turn of the twenty-first century and ultimately led to one half of the Nobel Prize in Physics being shared by John L. Hall and Theodor W. Hänsch in 2005.

The frequency domain representation of a perfect frequency comb is a series of delta functions spaced according to

where ${\displaystyle n}$ is an integer, ${\displaystyle f_{r}}$ is the comb tooth spacing (equal to the mode locked laser's repetition rate or, alternatively, the AM frequency), and ${\displaystyle f_{0}}$ is the carrier offset frequency, which is less than ${\displaystyle f_{r}}$.

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