Difference-frequency combs in cold atom physics

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Russell Kliese, Nazanin Hoghooghi, Thomas Puppe, Felix Rohde, Alexander Sell, Armin Zach, Patrick Leisching, Wilhelm Kaenders, Niamh C. Keegan, Alistair D. Bounds, Elizabeth M. Bridge, Jack Leonard, Charles S. Adams, Simon L. Cornish, Matthew P. A. Jones


Eur. Phys. J. Special Topics 225, 2775–2784 (2016)



Optical frequency combs provide the clockwork to relate optical frequencies
to radio frequencies. Hence, combs allow to measure optical frequencies
with respect to a radio frequency where the accuracy is limited
only by the reference signal. In order to provide a stable link between the
radio and optical frequencies, the two parameters of the frequency comb
must be fixed: the carrier envelope offset frequency fceo and the pulse
repetition-rate frep. We have developed the first optical frequency comb
based on difference frequency generation (DFG) that eliminates fceo by design
- specifically tailored for applications in cold atom physics. An fceo-free
spectrum at 1550 nm is generated from a super continuum spanning more
than an optical octave. Established amplification and frequency conversion
techniques based on reliable telecom fiber technology allow generation of
multiple wavelength outputs. In this paper we discuss the frequency comb
design, characterization, and optical frequency measurement of Sr Rydberg
states. The DFG technique allows for a compact and robust, passively
fceo stable frequency comb significantly improving reliability in practical