Sub-Doppler laser cooling of thulium atoms in a magneto-optical trap and trapping thulium atoms in a magnetic trap with low gradient of magnetic field

We have studied sub-Doppler laser cooling of thulium atoms in a magneto-optical trap (MOT) operated at 410.6 nm. Without any additional sub-Doppler cooling cycles the sub- Doppler temperature of 25(5) microK have been achieved (the number of atoms was 3$\times 10^6$). This temperature is one order of magnitude lower than the Doppler limit for used transition (240 microK). The high efficiency of sub-Doppler cooling is accounted for by equality of Lande g-factors of high and lower levels of cooling transition. We have implemented trapping of ultracold thulium atoms in a magnetic trap (MT) formed by a MOT quadruple magnetic field (field gradient is about 20 G/cm). Loading of MT has been performed from the cloud contained 4$\times 10^5$ thulim atoms previously cooled in the MOT down to the sub-Doppler temperature of 80 microK. About 4$\times 10^4$ atom have been trapped in MT at the temperature 40 microK. By analysing MT population decay process the lifetime has been determined (0.5 s) and the constrain on the rate constant of inelastic binary collision of spin-polarized thulim atoms in the ground state ($g_{in}<10^{-11}$ cm$^3$ s$^{-1}$) has been imposed.