Abstract:
The magnetic dipole transition between fine structure sublevels of the ground state of thulium atom $4f^{13}(^2F^o)6s^2$ has been directly excited in a cloud of ultra-cold atoms by a frequency-stabilised laser. This transition at the wavelength $\lambda=1.14\ \mu\mathrm m$ is planned to be used as the clock one in an optical frequency reference on laser-cooled thulium atoms.