We describe an experimental apparatus capable of achieving a high loading rate of strontium atoms in a magneto-optical trap operating in a high vacuum environment. A key innovation of this setup is a two dimensional magneto-optical trap deflector located after a Zeeman slower. We find a loading rate of 6 × 109 s−1 whereas the lifetime of the magnetically trapped atoms in the 3P2 state is 54 s.

A high flux source of cold strontium atoms

We describe an experimental apparatus capable of achieving a high loading rate of strontium atoms in a magneto-optical trap operating in a high vacuum environment. A key innovation of this setup is a two dimensional magneto-optical trap deflector located after a Zeeman slower. We find a loading rate of 6x10^9/s whereas the lifetime of the magnetically trapped atoms in the 3P2 state is 54s.

The magnetic dipole transition between fine structure sublevels of the ground state of thulium atom 4f13(2Fo)6s2 has been directly excited in a cloud of ultra-cold atoms by a frequency-stabilised laser. This transition at the wavelength λ = 1.14 μm is planned to be used as the clock one in an optical frequency reference on laser-cooled thulium atoms.

https://iopscience.iop.org/article/10.1070/QE2015v045n05ABEH015749/pdf

Detection of the clock transition (1.14 μm) in ultra-cold thulium atoms

We review the current research on precision spectroscopy and quantum optics applications of laser-cooled lanthanides. We discuss the specific electronic structure of hollow atoms, which determine prospects for application in optical frequency standards and in quantum simulators based on spin interactions in optical lattices. Using the example of the thulium atom, we describe the specifics of laser cooling, optical lattice trapping techniques, and clock transition spectroscopy using spectrally narrow lasers.

Ultracold lanthanides: from optical clock to a quantum simulator

A laser system with a spectral linewidth less than 1 Hz for spectroscopy of the 1S0–3P0 clock transition in strontium atoms has been demonstrated. A semiconductor laser emitting at a wavelength of 698 nm was stabilised to an external high-finesse Fabry–Perot cavity with vibration and temperature compensation near the zero expansion point. After laser cooling to a temperature below 3 μK, 88Sr atoms were loaded into an optical lattice at a magic wavelength of 813 nm. The laser system was used to characterise the 88Sr clock transition by magnetically induced spectroscopy. The resonance spectral width was determined to be 130 ± 17 Hz, which corresponds to a quality factor of 3 × 1012.

https://iopscience.iop.org/article/10.1070/QEL16346/pdf

Ultrastable laser system for spectroscopy of the 1S0–3P0 clock transition in Sr atoms

A laser system with a narrow generation line for secondary laser cooling of 87Sr atoms has been developed and investigated. It is planned to use ultracold 87Sr atoms loaded in an optical lattice in an optical frequency standard. To this end, a 689-nm semiconductor laser has been stabilised using an external reference ultrastable cavity with vibrational and temperature compensation near the critical point. The lasing spectral width was 80 Hz (averaging time 40 ms), and the frequency drift was at a level of 0.3 Hz s-1. Comparison of two independent laser systems yielded a minimum Allan deviation: 2 × 10-14 for 300-s averaging. It is shown that this system satisfies all requirements necessary for secondary cooling of 87Sr atoms using the spectrally narrow 1S0 — 3P1 transition (λ = 689 nm).

Laser system for secondary cooling of 87Sr atoms

In the framework of the project aimed at creating an optical standard on cold Sr atoms we have realised sub-Doppler spectroscopy of the intercombination transition 1S0 – 3P1 (689 nm) in a cell with Sr vapour and in a cloud of atoms loaded in a magneto- optical trap (MOT). By measuring Zeeman splitting of the 3P1 level in the magnetic field of the MOT we have succeeded in fine adjustment of the MOT relative to a minimum of the magnetic field, which is necessary for successful secondary-stage cooling on the intercombination transition. In turn, absorption saturation spectroscopy in the vapour cell provides the long-term frequency stability of the second-stage cooling laser at λ = 689 nm.

http://iopscience.iop.org/article/10.1070/QE2015v045n02ABEH015638/pdf

G S Belotelov

Papers

Laser system for secondary cooling of 87Sr atoms

Spectroscopy of intercombination transition 1S0 – 3P1 for secondary cooling of strontium atoms

Microgravity Test Complex for Mobile and Portable Optical Frequency Standards