Characterization of an optical frequency comb using modified direct frequency comb spectroscopy
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We introduce a method for determination of the absolute frequencies of comb lines within an optical frequency comb spectrum. The method utilizes the experimental and theoretical approach of the velocity-selective optical pumping of the atomic ground state hyperfine levels induced by resonant pulse-train excitation. The information on the laser pulse repetition frequency and carrier–envelope offset are physically mapped onto the 87Rb ground state hyperfine level population velocity distributions. Theoretical spectra are calculated using an iterative analytic solution of the optical Bloch equations describing the resonant pulse-train excitation of four-level 87Rb atoms. They are employed to fit the measured spectra and obtain the parameters of the frequency comb, thus providing a practical algorithm which can be used in real-time measurements.
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