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Quantum Electronics

Study of transitions in thulium atoms in the 410–420-nm range for laser cooling

Alexey V. Akimov, K. Chebakov, Inga Yu. TOLSTIKHINA, А. В. Соколов, P B Rodionov, S. I. Kanorsky, В. Н. Сорокин, N. Kolachevsky

Published Oct 31, 2008• 4 citations
Publisher

Abstract

The possibility of laser cooling of thulium atoms is considered. The hyperfine structure of almost cyclic 4f 13 6s 2 ( J g = 7/2) ↔ 4f 12 5d 3/2 6s 2 ( J e = 9/2) and 4f 13 6s 2 ( J g = 7/2) ↔ 4f 12 5d 5/2 6s 2 ( J e = 9/2) transitions at 410.6 and 420.4 nm, respectively, is studied by the method of sub-Doppler saturation spectroscopy in counterpropagating laser beams. The hyperfine splitting of excited levels involved in these transitions is measured and the natural linewidths of these transitions are determined. The structure of the neighbouring 4f 13 6s6p ( J e = 5/2) and 4f 12 5d 5/2 6s 2 ( J e = 7/2) levels is studied for the first time by this method. The decay probabilities of the J e = 9/2 levels via channels removing atoms from the cooling cycle are calculated. It is found that the branching ratio for the strong transition at 410.6 nm ( A = 6 × 10 7 s -1 ) is smaller than 2 × 10 -5 , which makes this transition most promising for laser cooling. The laser cooling of atoms in a Zeeman cooler at this transition is simulated. The possibility of using a laser-cooled cloud of thulium atoms to study the metrological transition at 1.14 μm is discussed.

DOI
10.1070/qe2008v038n10abeh013794

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Russian Federation

We have studied possible candidates for laser cool- ing transitions in 169 Tm in the spectral region of 410-420 nm. By means of saturation absorption spectroscopy, we have meas- ured the hyperfine structure and rates of two nearly closed cy- cling transitions from the ground state 4 f 13 6s 2 ( 2 F0)(Jg = 7/2) to upper states 4 f 12 ( 3 H5)5d3/26s 2 (Je = 9/2) at 410. 6n m and 4 f 12 ( 3 F4)5d5/26s 2 (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. 6n m has an optical leak rate of less then 2 × 10 −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. 5n m 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 � = 5/2) of the ground state which can be con- sidered as a candidate for applications in atomic clocks.

•Jan 1, 2007•0 citations

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Daniil I. Provorchenko, Dmitry O. Tregubov, D. Mishin +5 more

Abstract A scheme is proposed for the third stage of laser cooling of thulium atoms at a wavelength of 506.2 nm, and a system for stabilising the laser radiation frequency is described, which provides the required characteristics. The transition at a wavelength of 506.2 nm is detected in a magneto-optical trap with the employment of the developed laser setup. The value of hyperfine splitting of the transition upper level is measured, and the single-dimension cooling at this wavelength is observed for the first time.

Quantum Electronics•May 19, 2021•3 citations
The possibility of laser cooling of thulium atoms is considered. The hyperfine structure of almost cyclic 4f 13 6s 2 ( J g = 7/2) ↔ 4f 12 5d 3/2 6s 2 ( J e = 9/2) and 4f 13 6s 2 ( J g = 7/2) ↔ 4f 12 5d 5/2 6s 2 ( J e = 9/2) transitions at 410.6 and 420.4 nm, respectively, is studied by the method of sub-Doppler saturation spectroscopy in counterpropagating laser beams. The hyperfine splitting of excited levels involved in these transitions is measured and the natural linewidths of these transitions are determined. The structure of the neighbouring 4f 13 6s6p ( J e = 5/2) and 4f 12 5d 5/2 6s 2 ( J e = 7/2) levels is studied for the first time by this method. The decay probabilities of the J e = 9/2 levels via channels removing atoms from the cooling cycle are calculated. It is found that the branching ratio for the strong transition at 410.6 nm ( A = 6 × 10 7 s -1 ) is smaller than 2 × 10 -5 , which makes this transition most promising for laser cooling. The laser cooling of atoms in a Zeeman cooler at this transition is simulated. The possibility of using a laser-cooled cloud of thulium atoms to study the metrological transition at 1.14 μm is discussed.
Full text: It has been shown recently that Yb and Er atoms from the lanthanides group can be efficiently laser-cooled using strong transitions near 400 nm. Degenerate Fermi gases of ytterbium have been also recently demonstrated using laser-cooling based technic. Our goal was to investigate the possibility of laser cooling of Tm atom. Among other lanthanides, thulium possesses relatively simple level structure.Moreover, it has only one stable isotope {sup 169}Tm with a nuclear spin of I = 1/2 which makes possible to use schemes for sub-Doppler cooling. Laser-cooled thulium is a favorable candidate for optical clocks applications, since the forbidden transition between the fine structure sublevels (J{sub g} 5=2) - (J'{sub g} = 7/2) of the ground state 4f{sup 13}6s{sup 2} ({lambda} = 1.14 micron) has a spectral width of approximately 1 Hz. The collisional shift of such kind of transitions in lanthanides is suppressed because of the outer closed 6s{sup 2} shell, which allows for precision spectroscopy in a dense atomic cloud. We studied two candidates for cooling transitions from the ground state 4f{sup 13}6s{sup 2} (J{sub g} 7/2) to the states 4f{sup 12}({sup 3}H{sub 5})5d{sub 3/2}6s{sup 2} (J{sub e} = 9/2) at 410.6 nm and 4f{sup 12}({sup 3}F{sub 4})5d{sub 5/2}6s{sup 2} (J{sub e} = 9/2) at 420.4 nm. By means of saturation absorption spectroscopy, we measured the hyperfine structure and rates of these transitions. We evaluated the life times of appropriate excited levels as 15.9(8) ns and 48(6) ns, respectively. Decay rates from these levels to neighboring opposite-parity levels were evaluated by means of Hartree-Fock calculations. The fraction of atoms which do not return to the ground state is about 10{sup -5} and 5 {center_dot} 10{sup -4} for the 410.6 nm and 420.4 nm transitions respectively. We conclude that the strong transition at 410.6 nm with relative slow leakage rate can be used for the efficient cooling of Tm I. We also measured hyperfine structure of two nearby transitions from the ground state to the states 4f{sup 13}({sup 2}F{sub 7/2})6s6p({sup 1}P{sub 1}) (J{sub e} 5/2) at 409.4 nm and 4f{sup 12}({sup 3}F{sub 4})5d{sub 5/2}6s{sup 2} (J{sub e} = 7/2) at 418.9 nm, which can be used for {lambda}-type excitation of {lambda} = 1.14 {mu}m transition. (author)
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 4f 13 6s 2 ( 2 F0)(Jg = 7/2) to upper states 4f 12 ( 3 H5)5d3/26s 2 (Je = 9/2) at 410.6 nm and 4f 12 ( 3 F4)5d5/26s 2 (Je = 9/2) at 420.4 nm and evaluated the life times of the excited levels as 16.1(8) ns and 40(4) 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 169 Tm from a thermal atomic beam. 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. Due to efficient shielding by the closed 6s 2 shell, this transition is insensitive to collisions which makes it a promising candidate for applications in atomic clocks. PACS numbers: I.
Sub-Doppler laser cooling in a magneto-optical trap for thulium atoms at a wavelength of 410.6 nm has been experimentally studied. Without any dedicated molasses period of sub-Doppler cooling, the cloud of 3 × 106 atoms at a temperature of 25(5) μK was observed. The measured temperature is significantly lower than the Doppler limit of 240 μK for the cooling transition at 410.6 nm. The high efficiency of the sub-Doppler cooling process is due to a near-degeneracy of the Landé g-factors of the lower 4f 136s 2 (J = 7/2) and the upper 4f 125d 3/26s 2 (J = 9/2) cooling levels.
We have studied possible candidates for laser cool- ing transitions in 169 Tm in the spectral region of 410-420 nm. By means of saturation absorption spectroscopy, we have meas- ured the hyperfine structure and rates of two nearly closed cy- cling transitions from the ground state 4 f 13 6s 2 ( 2 F0)(Jg = 7/2) to upper states 4 f 12 ( 3 H5)5d3/26s 2 (Je = 9/2) at 410. 6n m and 4 f 12 ( 3 F4)5d5/26s 2 (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. 6n m has an optical leak rate of less then 2 × 10 −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. 5n m 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 � = 5/2) of the ground state which can be con- sidered as a candidate for applications in atomic clocks.
Abstract A scheme is proposed for the third stage of laser cooling of thulium atoms at a wavelength of 506.2 nm, and a system for stabilising the laser radiation frequency is described, which provides the required characteristics. The transition at a wavelength of 506.2 nm is detected in a magneto-optical trap with the employment of the developed laser setup. The value of hyperfine splitting of the transition upper level is measured, and the single-dimension cooling at this wavelength is observed for the first time.