Transition isotope shift and hyperfine constant measurements in low-lying transitions in lead

We report high-precision measurements of transition isotope shifts and hyperfine structure constants for multiple low-lying states of Pb using two-step, Doppler-free laser spectroscopy. Measurements are performed on the four naturally abundant isotopes (²⁰⁸Pb, ²⁰⁷Pb, ²⁰⁶Pb, and ²⁰⁴Pb) at the sub-MHz-level, enabling improved determinations of isotope shifts and hyperfine splittings in transitions where existing experimental data are limited or incomplete.

The experiments employ a two-step laser excitation scheme using a pair of isotopically pure, high-temperature quartz vapor cells, where Doppler narrowing is achieved using rapid switching (>1 MHz) of the pump laser using an acousto-optic modulator. The first-step transitions for each of the two isotopes are excited on resonance with a single locked IR laser via FM modulation in a fiber-based electro-optic modulator with tunable RF driving frequency. By scanning the second step laser and comparing spectra for geometries where the two lasers co-propagate vs counter-propagate, we can determine isotope shifts for both transitions in a single set of spectra. Measurements are made on the following two-step transitions: the (6p²) ³P₀ → (6p²) ³P₁ M1 transition at 1279 nm followed by the (6p²) ³P₁ →  (6p7s) ³P₀ E1 transition at 368 nm, as well as the (6p²) ³P₀ → (6p²) ³P₂ E2 transition at 939 nm followed by the (6p²) ³P₂ → (6p7s) ³P₁ E1 transition at 406 nm.  Such high-precision data provide sensitive probes of short-range electronic wavefunction behavior in heavy, multivalence atoms, informing ab initio wavefunction calculations and providing nuclear structure information.  Current results will be reported.