Two-photon laser excitation of trapped 232Th+ ions via the 402 nm resonance line

Abstract

Experiments on one- and two-photon laser excitation of 232Th+ ions in a radiofrequency ion trap are reported. As the first excitation step, the strongest resonance line at 402 nm from the 6d^2 7s J=3/2 ground state to the 6d7s7p J=5/2 state at 24874 cm^{-1} is driven by radiation from an extended cavity diode laser. Spontaneous decay of the intermediate state populates a number of low-lying metastable states, thus limiting the excited state population and fluorescence signal obtainable with continuous laser excitation. We study the collisional quenching efficiency of helium, argon, and nitrogen buffer gases, and the effect of repumping laser excitation from the three lowest-lying metastable levels. The experimental results are compared with a four-level rate equation model, that allows us to deduce quenching rates for these buffer gases. Using laser radiation at 399 nm for the second step, we demonstrate two-photon excitation to the state at 49960 cm^{-1}, among the highest-lying classified levels of Th+. This is of interest as a test case for the search for higher-lying levels in the range above 55000 cm^{-1} which can resonantly enhance the excitation of the 229Th+ nuclear resonance through an inverse two-photon electronic bridge process.

8 pages, 8 figures

References in corpus (6)

• Wigner Crystals of 229Th for Optical Excitation of the Nuclear Isomer
• Excitation of the isomeric ^{229m}Th nuclear state via an electronic bridge process in ^{229}Th^+
• Electronic bridge process in 229Th^+
• Laser ablation loading of a radiofrequency ion trap
• Exponential increase of energy level density in atoms: Th and Th II
• Charge Exchange and Chemical Reactions with Trapped Th${}^{3+}$

Cited by in corpus (16)

• Laser spectroscopic characterization of the nuclear clock isomer ${}^{229m}$Th
• Nuclear clocks based on resonant excitation of gamma-transitions
• Radiative lifetime and energy of the low-energy isomeric level in ${}^{229}$Th
• Electronic bridge excitation in highly charged Th-229 ions
• The ${}^{229}$Th isomer: prospects for a nuclear optical clock
• Energy levels of Th+ between 7.3 and 8.3 eV
• Nuclear charge radii of ${}^{229}$Th from isotope and isomer shifts
• Laser-induced electronic bridge for characterization of the ${}^{229\mathrm{m}}\mathrm{Th}\to {}^{229\mathrm{g}}\mathrm{Th}$ nuclear transition with a tunable optical laser
• The electric quadrupole channel of the 7.8 eV ${}^{229}\mathrm{Th}$ transition
• Excitation of the ${}^{229}$Th nucleus via a two-photon electronic transition
• Internal conversion from excited electronic states of ${}^{229}\mathrm{T}h$ ions
• Prospects for measuring the 229Th isomer energy using a metallic magnetic microcalorimeter
• Hyperfine interaction with the ${}^{229}$Th nucleus and its low lying isomeric state
• Observation of an unexpected negative isotope shift in 229Th+ and its theoretical explanation
• Electronic level structure of ${\mathrm{Th}}^{+}$ in the range of the ${}^{229m}\mathrm{Th}$ isomer energy
• Studies of thorium and ytterbium ion trap loading from laser ablation for gravity monitoring with nuclear clocks