Blue laser cooling transitions in Tm I

Abstract

We have studied possible candidates for laser cooling transitions in 169Tm in the spectral region of 410–420 nm. By means of saturation absorption spectroscopy, we have measured the hyperfine structure and rates of two nearly closed cycling transitions from the ground state 4f136s2(2F0)(Jg=7/2) to upper states 4f12(3H5)5d3/26s2(Je=9/2) at 410.6 nm and 4f12(3F4)5d5/26s2(Je=9/2) at 420.4 nm and evaluated the life times of the excited levels as 15.9(8) ns and 48(6) ns, respectively. Decay rates from these levels to neighboring opposite-parity levels are evaluated by means of Hartree–Fock calculations. We conclude that the strong transition at 410.6 nm has an optical leak rate of less then 2×10-5 and can be used for efficient laser cooling of 169Tm from a thermal atomic beam. The hyperfine structure of two other even-parity levels, which can be excited from the ground state at 409.5 nm and 418.9 nm, is also measured by the same technique. In addition, we give a calculated value of 7(2) s-1 for the rate of magnetic-dipole transition at 1.14 μm between the fine structure levels (Jg=7/2)↔(J’g=5/2) of the ground state which can be considered as a candidate for applications in atomic clocks.