High-resolution two-photon resonant three-photon spectroscopy was applied to investigate the 3
snf Rydberg series of Mg. Hyperfine-induced level shifts were detected for the
1,3F states of the odd isotope
25Mg. From these measurements the hyperfine coupling constant
a3s of the
25Mg+-ion ground state was derived.
The diamagnetic shifts of the
mJ=0 and ${m}_{J}=\ifmmode\pm\else\textpm\fi{}1$ components of
6snp1P1 (
n=40,55,70,85,100) and
6s55p3P0,1 Rydberg states of
172,174Yb have been measured in external magnetic fields up to ≌3 kG by high-resolution three-photon spectroscopy. The diamagnetic shifts have been analyzed to yield the singlettriplet mixing due to spin-orbit interaction. At
n=40, the singlet-triplet mixing derived from diamagnetic shifts and hyperfine-structure data are in excellent agreement.
Here we report atomic structure calculations and experimental observations of the two-photon
6s21S0→6s23s1S0 transition in Yb. The unique level structure of Yb places the
6s6p1P1 state's energy at
≈49.7% of the ionization energy, which facilitates two-photon Doppler-free excitation of the
6s23s1S0 Rydberg state from the
6s21S0 ground state at a relatively low optical intensity. This
J=0→J=0 transition is immune to first-order Zeeman and electric quadrupole shifts, has reduced sensitivity to higher-order Zeeman shifts, and is further predicted to have relatively low sensitivity to density shifts. Using configuration interaction theory, we compute relevant properties of the
6s23s1S0 Rydberg state for sensing, including the
C6 coefficient, dc polarizability, blackbody radiation (BBR) shift, and BBR depopulation rate. As a first experimental step, we demonstrate two-photon Doppler-free spectroscopy of the
6s21S0→6s23s1S0 transition. From our experimental spectra, we estimate the natural linewidth (lifetime) of the
6s23s1S0 state to be 90 kHz (1.8
μs). We believe this transition, or other
6s21S0→6sns1S0 transitions in Yb with
n≈23, may find use in a variety of sensing applications, potentially including a two-photon clock, electrometer, or BBR thermometer.
The ionization of
6sns1S0 Rydberg states of
138Ba has been investigated by high-resolution electron spectroscopy. The Rydberg states were excited by two cw dye lasers via the
6s6p1P1 level. The electron spectra show rich structure between 0.025 and 3 eV, largely attributable to collisional (Penning) ionization, photoionization, and autoionizing transitions. The first process might be interpreted as superelastic scattering of the Rydberg electron by optically pumped
Ba(6s6p1P1) or
Ba(6s5d1D2) atoms.
Doppler-free two-photon spectroscopy was applied to excite hyperfine-induced transitions from the $5{s}^{2}^{1}S_{0}$ ground state to the
F=I component of the hyperfine multiplet of the
5sns3S1 Rydberg series of
87Sr (
n=50,…,85). The experimental data confirm the interpretation of hyperfine-induced singlet-triplet mixing which is related to the singlet-triplet energy separation.
A combined experimental and theoretical spectroscopic study of high-$n, 30\ensuremath{\lesssim}n\ensuremath{\lesssim}100$, triplet
S and
D Rydberg states in
87Sr is presented.
87Sr has a large nuclear spin
I=9/2, and at high-
n the hyperfine interaction becomes comparable to, or even larger than, the fine structure and singlet-triplet splittings, which poses a considerable challenge both for precision spectroscopy and for theory. For high-
nS states, the hyperfine shifts are evaluated nonperturbatively, taking advantage of earlier spectroscopic data for the
I=0 isotope
88Sr, which results in good agreement with the present measurements. For the
D states, this procedure is reversed by first extracting from the present
87Sr measurements the energies of the
3D1,2,3 states to be expected for isotopes without hyperfine structure (
88Sr), which allows the determination of corrected quantum defects in the high-
n limit.