20 Years and 20 Decimal Digits: A Journey With Optical Frequency Combs
M. Giunta, M. Fischer, W. Hänsel, T. Steinmetz, M. Lessing, S. Holzberger, C. Cleff, Th. W. Hänsch, M. Mei, & R. Holzwarth
IEEE Photonics Technology Letters (2019); doi: 10.1109/LPT.2019.2955096
Precision measurements represent a cornerstone in fundamental science. The capability of observing and quantifying subtle phenomena and events allows new discoveries and it confirms or confutes the theories describing our understanding of nature. The optical frequency comb, providing hundreds of thousands of phase-locked and evenly spaced laser lines, is one of the most fascinating enabling optical technologies and it is the result of a continuous pursuit for precision. Within the two decades from its inception, it has become a key instrument in many laboratories and has revolutionized numerous fields, spanning from time, frequency and length metrology to attosecond physics, gas-sensing and molecular fingerprinting. In this letter we summarize some steps of an exciting journey started 20 years ago, with a certain focus on the authors’ contribution, finally leading to the demonstration of frequency measurements at the 20th decimal digit, and we show some prospective developments.