Observation of spin polarized clock transition in ⁸⁷Sr optical lattice clock

We report our observation of the spin polarized ¹S₀ → ³P₀ clock transition spectrum in an optical lattice clock based on fermionic ⁸⁷Sr. The atoms are trapped and pre-cooled to about 2 μK with two stages of laser cooling at 461 nm and 689 nm, respectively. Then the atoms are loaded into an optical lattice formed by the interference of counter-propagating laser beams at 813 nm. An external cavity diode laser at 698 nm, which is stabilized to a high finesse cavity with a linewidth of about 5 Hz and a drift rate of less than 0.2 Hz/s, is used to excite the atoms to the ³P₀ state. The π-polarized clock transition spectrum of resolvable m_F states is obtained by applying a small bias magnetic field along the polarization axis of the probe beam. A spin polarized clock transition spectrum as narrow as 10 Hz with an 80 ms probe pulse is obtained.