Fig. 3
From: Single ion fluorescence excited with a single mode of an UV frequency comb
Typical spectroscopy signal. a The longitudinal modes of the frequency comb are scanned over the 25Mg+ D2 resonance by changing the repetition rate while the fluorescence from an individual ion is collected. The signal is periodic just as the comb is. To convert the detuning of the repetition rate to optical frequency one needs to multiply with the mode number which is n = 2,871,702 for the central peak. The photon count rate at the peak of resonance was ~7 Hz. The signal was accumulated to give a larger signal count. The data are fitted with a series of Lorentzians as indicated by a solid red curve and the fit residuals are shown in b. The linewidth of the signal peaks is about 43 MHz in good agreement with the natural linewidth of 41.8 MHz40. The error bars are taken as the square root of the signal counts assuming Poissonian statistics for both a and b
