Doppler-free two-photon (DFTP) spectroscopy is a standard technique for precision measurement of transition frequencies of dipole-forbidden transitions. Here, we report the observation of quantum interference (QI) of optical transition pathways in DFTP spectroscopy of the cesium $6S\text{\ensuremath{-}}7D$ transitions chosen as a prototype system. The QI manifests itself as asymmetric line shapes of the hyperfine lines of the
7D states, observed through spontaneous emission following excitation by a narrow-linewidth cw laser. The interference persists despite the lines being spectrally well resolved. Ignoring the effect and fitting the spectrum to a Voigt profile causes large systematic shifts in the determination of the line centers, while accounting for QI resolves the apparent line shift and enables the precise determination of hyperfine splitting in the
7D states. We calculate the spectral line shape including the effect of QI and show that it agrees with the experimental observations. Our results are broadly applicable to other species and have implications for portable secondary optical clocks and precision measurements of hyperfine splittings, isotope shifts, and transition frequencies.
The frequency shifts of the (F = 2, m = 0)--(F = 3, m = 0) transition in the 5 /sup 2/S/sub 1//sub ///sub 2/ state have been calculated for the /sup 85/Rb isotope on perturbation of the unpolarized light of the D1 line (lambda = 794.7 nm) of a spectral lamp as functions of the temperature of the absorbing vapor, the pressure of the buffer gas, and the length of the cell. The change in intensity and spectral distribution in the emitted light as it passes through the cell, containing rubibium vapor, has been taken into account. Experimentally measured contour lines of standard spectral lamps were used in the calculations.
Abstract Using a Rb cell and a wavemeter, with a Doppler-free two-photon transition near 993 nm, we have measured the four hyperfine components (two isotopes, Δ F = 0) of the 5S–6S transition, finding the absolute energies of those transitions to a spectral resolution of 0.002 cm −1 = 60 MHz. We find the (87 minus 85) isotope shift of the 5S–6S transition to be +94(12) MHz. Using our single frequency cw laser with focused intensity up to 10 4 W cm −2 at the cell, we find no AC Stark or light shift of the lines at 6 MHz spectral resolution. We find no density shift of the lines at 6 MHz spectral resolution, for a range of Rb atom densities from 3 × 10 11 to 5 × 10 13 atoms/cm 3 .