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Optical frequency comb with submillihertz linewidth and more than 10 W average power


Growing demands for high average and peak powers in extreme nonlinear optics1, attosecond-pulse2,3 and extreme ultraviolet comb generation experiments4,5 can find a powerful solution in fibre-based mode-locked lasers. Using passive enhancement cavities6, fibre lasers have produced high-repetition-rate femtosecond pulse trains with multikilowatt average powers and peak powers reaching hundreds of megawatts7. One major challenge for novel high-resolution spectroscopy and precision measurement in suboptical wavelength regions8,9,10 is to transfer the state-of-the-art optical phase coherence into the extreme ultraviolet domain through the extreme nonlinear optics enabled by these high-power systems. We demonstrate here that optical frequency combs produced by high-power fibre lasers reach unprecedented levels of performance in both precision and average power. We achieve a record low relative linewidth of <1 mHz between a traditional Ti:sapphire frequency comb and a novel 10 W average power fibre comb, at the same time demonstrating all the necessary elements for power scaling precision comb technology to beyond 10 kW.

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Figure 1: Experimental set-up of the fibre comb.
Figure 2: Optical spectrum of the frequency comb and carrier-envelope offset frequency.
Figure 3: Experimental set-up for precise phase comparison of combs.
Figure 4: Out-of-loop comb comparison.


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We gratefully acknowledge technical assistance from M. Miranda with the Ti:sapphire comb, and G. Campbell and A. Ludlow with the subhertz linewidth 698 nm reference laser and the noise-cancelled fibre links. We thank F.X. Kärtner and C. Menyuk for technical discussions with regards to modelocked laser noise. We acknowledge funding support from the Defense Advanced Research Project Agency, the Air Force Office of Scientific Research, and the National Institute of Standards and Technology.

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T.R.S. is responsible for the design and the overall execution of the experiment; T.R.S. and D.C.Y. for the stabilization of the Yb:fibre comb; M.J.M. for stabilization of the octave spanning Ti:sapphire comb and the 1,064 nm Nd:YAG laser; J.Y. for the overall laboratory infrastructure and concept development in precision measurement and phase control of fs combs; and I.H., A.M. and M.E.F. for the design and construction of the Yb:fibre laser.

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Correspondence to T. R. Schibli.

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Schibli, T., Hartl, I., Yost, D. et al. Optical frequency comb with submillihertz linewidth and more than 10 W average power. Nature Photon 2, 355–359 (2008).

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