Absolute Transition Frequencies and Quantum Interference in a Frequency Comb Based Measurement of the ${}^{6,7}\mathrm{Li}$ $D$ Lines

Optical frequencies of the $D$ lines of ${}^{6,7}\mathrm{Li}$ were measured with a relative accuracy of $5\times {10}^{-11}$ using an optical comb synthesizer. Quantum interference in the laser induced fluorescence for the partially resolved $D2$ lines was found to produce polarization dependent shifts as large as 1 MHz. Our results resolve large discrepancies among previous experiments and between all experiments and theory. The fine-structure splittings for ${}^6\mathrm{Li}$ and ${}^7\mathrm{Li}$ are 10052.837(22) MHz and 10053.435(21) MHz. The splitting isotope shift is 0.599(30) MHz, in reasonable agreement with recent theoretical calculations.

Figure 1

Reported values of the ${}^{6,7}\mathrm{Li}$ SIS.

Figure 2

Typical data and fitted profiles that show the polarization dependence of the unresolved ${}^7\mathrm{Li}$ $D2$ line.