Thulium atoms are trapped in a magneto-optical trap using a strong transition at 410 nm with a small branching ratio. We trap up to 7 × 10 4 atoms at a temperature of 0.8(2) mK after deceleration in a 40 cm long Zeeman slower. Optical leaks from the cooling cycle influence the lifetime of atoms in the MOT which varies between 0.3 -1.5 s in our experiments. The lower limit for the leaking rate from the upper cooling level is measured to be 22(6) s −1 . The repumping laser transferring the atomic population out of the F=3 hyperfine ground-state sublevel gives a 30% increase for the lifetime and the number of atoms in the trap.

We have studied possible candidates for laser cooling transitions in $^{169}$Tm in the spectral region 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 $4\textrm{f}^{13}6\textrm{s}^2(^2\textrm{F}_0)(J_g=7/2)$ to upper states $4\textrm{f}^{12}(^3\textrm{H}_5)5\textrm{d}_{3/2}6\textrm{s}^2(J_e=9/2)$ at 410.6 nm and $4\textrm{f}^{12}(^3\textrm{F}_4)5\textrm{d}_{5/2}6\textrm{s}^2(J_e=9/2)$ 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 $2\cdot10^{-5}$ and can be used for efficient laser cooling of $^{169}$Tm 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 $\mu$m between the fine structure levels $(J_g=7/2)\leftrightarrow(J'_g=5/2)$ of the ground state which can be considered as a candidate for applications in atomic clocks.Comment: 8 pages, 5 figure

We demonstrate laser slowing of a hot thulium atomic beam using the nearly closed cycling transition 4f(13)6s(2)((2)F(o))(J=7/2)<-->4f(12)((3)H(5))5d(3/2)6s(2)(J=9/2) at 410.6 nm. Atoms are decelerated to velocities around 25 m/s by a 40 cm Zeeman slower. The flux of slowed atoms is evaluated as 10(7) s(-1)cm(-2). The experiment explicitly indicates the possibility of trapping Tm atoms in a magneto-optical trap.

We have experimentally studied sub-Doppler laser cooling in a magneto-optical trap for thulium atoms working at the wavelength of 410.6 nm. Without any dedicated molasses period of sub-Doppler cooling, the cloud of 3 × 10 6 atoms at the temperature of 25(5) µK was observed. The measured temperature is significantly lower than the Doppler limit of 240µK for the cooling transition at 410.6 nm. High efficiency of the sub-Doppler cooling process is due to a near-degeneracy of the Landé-g factors of the lower 4f 13 6s 2 (J = 7/2) and the upper 4f 12 5d 3/2 6s 2 (J = 9/2) cooling levels.

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