  We demonstrate an optical frequency analysis method using the Fourier
transform of detection times of fluorescence photons emitted from a single
trapped 40Ca+ ion. The response of the detected photon rate to the relative
laser frequency deviations is recorded within the slope of a dark resonance
formed in the lambda-type energy level scheme corresponding to two optical
dipole transitions. This approach enhances the sensitivity to the small
frequency deviations and does so with reciprocal dependence on the fluorescence
rate. The employed lasers are phase locked to an optical frequency comb, which
allows for precise calibration of optical frequency analysis by deterministic
modulation of the analyzed laser beam with respect to the reference beam. The
attainable high signal-to-noise ratios of up to a MHz range of modulation
deviations and up to a hundred kHz modulation frequencies promise the
applicability of the presented results in a broad range of optical
spectroscopic applications.
