The calculation is given of the spectral distribution of resonance fluorescence from an atom that is driven near a
j=21 to
j=21 transition by a monochromatic,
x-polarized electric field and that is subject to radiation damping only. In accordance with Mollow's results for a two-level system, the power spectrum of the scattered radiation corresponding to the
x component of the dipole moment contains a coherent part for all driving-field intensities. The coherent part is absent in the fluorescence radiation corresponding to the
y and
z components of the dipole moment. For weak driving fields all power scattered by these latter components is present in a narrow Lorentzian. Consistent with energy conservation, the width of the Lorentzian corresponds to the probability of excitation of the atom out of its ground level due to the presence of the driving field. For strong driving fields the power spectra corresponding to the
x component and to the
y or
z component mainly differ in the heights and widths of their central incoherent band and their Rabi-precession-frequency-shifted side bands.
Working with a beam of two-level--atom--like
174Yb, we have measured the temporal evolution of strong-field resonance fluorescence spectra during square-pulse excitation. In the case of resonant excitation, it is found that driving-field phase shifts transform the normal three-peaked Mollow spectrum into a transient doublet spectrum asymmetric with respect to the atomic transition frequency. This qualitatively new type of spectrum provides fundamental insight into the connection between atomic dynamics and spectra, and results from a nearly perfect polarization of the dressed atom-field states.
We have investigated the two basic types of Hanle fluorescence spectra, distinguished by the direction of observation, from a V-type atom with a
Jg =0\ensuremath{\leftrightarrows}
Je =1 transition excited by a linearly polarized laser. In the absence of a magnetic field to lift the Zeeman degeneracy of the sublevels, the incoherent fluorescence spectrum
GXinc(\ensuremath{\omega}) is dark for all Rabi frequencies, while the incoherent fluorescence spectrum
GYinc(\ensuremath{\omega}) exhibits a single peak for small Rabi frequencies and a Mollow-like triplet for large Rabi frequencies. However, if a magnetic field is applied, the incoherent spectra are composed, in general, of five peaks. When ${\mathrm{\ensuremath{\omega}}}_{\mathrm{B}}$ \ensuremath{\ll}\ensuremath{\Omega}, the incoherent spectrum
GXinc(\ensuremath{\omega}) has four peaks, while
GYinc(\ensuremath{\omega}) has a Mollow-like triplet, and the integrated area (i.e., the fluorescence intensity) under the spectrum
GXinc(\ensuremath{\omega}) is much less than that of
GYinc(\ensuremath{\omega}). When ${\mathrm{\ensuremath{\omega}}}_{\mathrm{B}}$ \ensuremath{\gg}:\ensuremath{\Omega}, both incoherent spectra have a two-peak structure similar to that of a two-level atom far off resonance, but the integrated area under the spectrum
GXinc(\ensuremath{\omega}) is much greater than that of
GYinc(\ensuremath{\omega}). When ${\mathrm{\ensuremath{\omega}}}_{\mathrm{B}}$ =\ensuremath{\Omega}\ensuremath{\gg}:\ensuremath{\gamma}, both spectra have a similar five-peak structure, and the same integrated area. The results obtained are interpreted in the dressed atomic state representation. In the strong-field limit, the secular approximation is invoked, and analytical expressions of the resonance fluorescence spectra are derived which demonstrate the dependence of the peak heights and widths of the resonance fluorescence spectra on the intensities of the magnetic and linear polarized laser fields in a more transparent way.
The interaction of a strong bichromatic field with a two-level atom has been the subject of numerous experimental and theoretical investigations. We performed an experimental study of the Interaction of an intense 100% amplitude-modulated (AM) field with an ensemble of homogeneously broadened two-level atoms. An optically pumped sodium atomic beam is used as the atomic medium. The field is created by interfering two intense frequency-stabilized laser fields. The frequency of one field is held fixed while another field of equal amplitude is scanned in frequency. The beat frequency produced by interfering the two laser fields is equal to twice the modulation frequency of a 100% AM field. We monitor the time-averaged fluorescent intensity of the atoms as the frequency separation between the two fields is varied. A similar experiment was done in the past in the rf regime.1 For the first time, we report the observation of multiple, well-resolved resonances in the absorption spectrum of the field in the optical regime. We present data and theory for several values of detuning between the fixed field and atomic resonance. The experimental results are in good agreement with theory.