Combs with Tunable Teeth

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Science  19 Sep 2008:
Vol. 321, Issue 5896, pp. 1607
DOI: 10.1126/science.321.5896.1607b

The generation of optical combs—broadband light made up of individual frequency components, equally spaced and spanning many orders of magnitude—has revolutionized metrology and spectroscopy because it provides an exact ruler with which to compare and measure wavelengths and spectroscopic signals. The spacing between the teeth of these optical combs, however, tends to be fixed for the system being used for light generation.

Savchenkov et al. introduce a generation method that allows the frequency spacing to be tuned. Using a calcium fluoride optical whispering-gallery-mode resonator, which sustains a family of resonant modes, they show that the nonlinear interaction of the laser light pumped into the cavity of the resonator generates a comb of equally spaced frequencies. By tuning the frequency of the pump laser with a particular resonant mode of the resonator, the frequency spacing of the output light comb can be shifted in a controlled manner, thereby providing an additional degree of flexibility in the generation of bespoke light.— ISO

Phys. Rev. Lett. 101, 93902 (2008).

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