Saturation of an optical transition by a phase-diffusing laser field

The dependence of the optical Autler-Townes effect on laser field phase fluctuations describable by a two-dimensional Markovian process (phase-diffusion model with a non-Lorentzian line shape) is investigated experimentally in atomic sodium. An intense cw laser tuned to near resonance with the ${3\mathrm{S}}_{1/2}$(F=2,${\mathrm{M}}_{\mathrm{F}}$=2)→${3\mathrm{P}}_{3/2}$(F=3,${\mathrm{M}}_{\mathrm{F}}$=3) transition was frequency modulated to generate phase fluctuations with the desired characteristics. A weak probe laser coupling to the 4$D_{5/2}$(F=4, $M_F$=4) state was used to obtain the double-peaked optical Autler-Townes absorption profiles in order to investigate their dependencies on band shape, bandwidth, intensity, and detuning of the intense fluctuating laser field. Reversals of the peak-height asymmetry and reversion to normal asymmetry with increased detuning were observed and measured. Quantitative studies of the spectral widths and splittings of the peaks are also reported. Measured absorption profiles are in excellent agreement with calculations based on previous theoretical work.