Mode-locked femtosecond lasers emit tens of thousands of discrete laser lines with a frequency-spacing precisely given by the laser repetition rate fR. Their output is thus commonly referred to as a frequency comb where each tooth is essentially an integer multiple of fR. It is this simplicity by which a frequency comb directly links the optical (hundreds of terahertz) and the radio (hundreds of Megahertz) frequency domains separated by several decades and practically governed by very different technologies that has made frequency combs such powerful and invaluable tools to the science-community. Indeed, the Physics Nobel Prize has been awarded to Theodor Hänsch and John Hall in 2005 for developing this idea.
Today frequency combs enable precision optical frequency measurements much in the same way as a rule is used to measure a distance. They serve in many laboratories worldwide to perform fundamental physics experiments such as measurements of the drift of fundamental natural constants. They are used to perform massively parallel precision optical spectroscopy or to synthesize microwave signals with unprecedentedly low phase-noise. Frequency combs also support the development of novel superior optical atomic clocks, by functioning as their clockwork, which may eventually lead to such practical advances as a more precise GPS navigation.
Laser Quantum’s femtosecond lasers have enabled optical frequency measurements with 20 significant figures, the highest accuracy demonstrated to date. There are three compelling reasons for the success of our GHz femtosecond technology: