Much as natural historians search for the first roots of our human race, curiosity drives the laser scientist to pursue the roots of his or her own field. This is especially the case in this year where our community celebrates the 50th anniversary of the demonstration of the first laser. If the experiments of Maiman, Javan and other early laser pioneers represent the spark of energy that brought the field of laser physics to life, then the seed for the frequency comb was planted in 1964 with the introduction of the mode-locked laser. In fact, one could already recognize the distinct comb-like frequency structure in the optical spectra of that early helium-neon laser. While development of active and passive mode-locked sources continued over the intervening decade (Ippen72), the frequency comb seed began to germinate in the experiments of Haensch in the late 1970 s, but did not sprout into its presently-recognized form until nearly 20 years later. Tracing this development from the very first laser sources is a fascinating story, but it is not the goal of this article to re-tell the history of the birth of the frequency comb in the context optical frequency metrology. That history has already been wonderfully re-counted in several reviews and the Nobel lectures of H nsch and Hall. Rather, in this article we will focus our attention on the rapidly evolving developments of the past decade the story of the numerous applications that have sprouted (sometimes unexpectedly) and formed new branches indeed new areas of research in some cases.
Citation: Journal of the Optical Society of America B-Optical Physics
Pub Type: Journals
femtosecond laser, frequency comb, optical clock, oscillator, spectroscopy