N N Kolachevsky

Blue laser cooling transitions in Tm I

We have studied possible candidates for laser cooling transitions in 169Tm in the spectral region of 410–420xa0nm. 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 410.6xa0nm and 4f12(3F4)5d5/26s2(Je=9/2) at 420.4xa0nm and evaluated the life times of the excited levels as 15.9(8)xa0ns and 48(6)xa0ns, 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 410.6xa0nm 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 409.5xa0nm and 418.9xa0nm, is also measured by the same technique. In addition, we give a calculated value of 7(2)xa0s-1 for the rate of magnetic-dipole transition at 1.14xa0μm 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.

Zeeman slowing of thulium atoms

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.

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

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.

Mass selective laser cooling of 229Th3+ in a multisectional linear Paul trap loaded with a mixture of thorium isotopes:

We consider an experiment on trapping and laser cooling of 229Th3+ ions in a linear Paul trap in the presence of undesirable impurities such as ions of the radioactive isotope 228Th3+. We suggest a method of separating these impurities by means of selective laser cooling utilizing the isotope shift of cooling transitions in 229Th3+ and 228Th3+ ions. According to our estimation, the isotope shift is equal to 3.4u2009GHZ and makes laser separation of these isotopes possible.

Secondary laser cooling of strontium-88 atoms

The secondary laser cooling of a cloud of strontium-88 atoms on the 1S0–3P1 (689 nm) intercombination transition captured into a magneto-optical trap has been demonstrated. We describe in detail the recapture of atoms from the primary trap operating on the strong 1S0–1P1 (461 nm) transition and determine the recapture coefficient κ, the number of atoms, and their temperature in the secondary trap as a function of experimental parameters. A temperature of 2 µK has been reached in the secondary trap at the recapture coefficient κ = 6%, which confirms the secondary cooling efficiency and is sufficient to perform metrological measurements of the 1S0–3P1 (698 nm) clock transition in an optical lattice.

Short-haul fibre-optic communication link with a phase noise compensation system for optical frequency signal transmission

A 5-m-long fibre link with a phase noise compensation system for optical frequency signal transmission at a wavelength of 1.14 μm is demonstrated. The stability of the noise compensation system in the presence of harmonic mechanical perturbations is assessed and the relative transmitted signal frequency instability is shown to be 3.8 × 10−15 at an averaging time of 1 s and 3.5 × 10−20 over 850 s.

Progress in optical frequency standards: ultracold Thulium, ions, and passive resonators

We report on different types of optical clocks and passive frequency references which are under development in our laboratories: optical lattice clock based on the inner-shell transition in the Tm atom at λ = 1.14μm, optical ion clock on single 27Al+ ion, and a family of lasers referenced to ultra-stable ULE and cryogenic silicon cavities.

Method of the production and trapping of thorium ions for nuclear transition investigation

This paper describes the techniques of production and trapping of thorium ions required to perform spectroscopic studies of thorium nuclear transition.

Loading of mass spectrometry ion trap with Th ions by laser ablation for nuclear frequency standard application

We describe an original multisectional quadrupole ion trap aimed to realize nuclear frequency standard based on the unique isomer transition in thorium nucleus. It is shown that the system effectively operates on Th+, Th2+ and Th3+ ions produced by laser ablation of metallic thorium-232 target. Laser intensity used for ablation is about 6u2009GW/cm2. Via applying a bias potential to every control voltage including the RF one, we are able not only to manipulate ions within the energy range as wide as 1–500u2009eV but to specially adjust trap potentials in order to work mainly with ions that belong to energy distribution maximum and therefore to effectively enhance the number of trapped ions. Measurement of energy distributions of 232Th+, 232Th2+, 232Th3+ ions obtained by laser ablation allows us to define optimal potential values for trapping process. Observed number of ions inside trap in dependence on trapping time is found to obey an unusually slow – logarithmic decay law that needs more careful study.

Spectroscopy of intercombination transition {sup 1}S{sub 0} – {sup 3}P{sub 1} for secondary cooling of strontium 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.