An optical frequency comb is a controlled rainbow of individual lasers that span a large range of colours. It is both a powerful tool for diverse applications such as a measuring device for precise spectroscopy of molecular transitions such as for trace gas detection and atomic physics. It is at the same time an absolute reference for metrology, for transferring the standard meter, and can even be used as an optical clock.

In this talk, I will introduce the optical frequency comb as a powerful tool for many diverse scientific fields. I will give an appetizer of the many different applications, and will describe various implementations, from the initial invention to modern versions as well as our approach at DFM, The Danish National Metrology Institute.