We investigate the dual-frequency Doppler-free resonance in the ${\mathrm{D}}_1$ line of alkali-metal atoms for any accessible value of the nuclear spin $I$ by considering the symmetries of the dipole operator. We show that there is the absence of optical pumping in the scheme with parallel polarizations for the center of the crossover, resulting in its smallest width. Secondly, the growth in absorption for the center of the peak with $F_e=I-1/2$ and the decrease of its width with the two-photon detuning in the case of orthogonal polarizations is explained. Particular attention is paid to the special case of $I=3/2$, where this effect is the most pronounced. Experimental results with ${}^{85}\mathrm{Rb}$ and ${}^{133}\mathrm{Cs}$ atoms are in agreement with the analysis.

Close

PrevNext

View figure in article

• Atomic spectra
• Atomic, optical & lattice clocks
• Optical pumping
• Atomic gases
• Dipole approximation
• Optical spectroscopy