Excitation of magnetic dipole transition of Thulium atoms trapped in rare gas crystals

We performed single-laser direct excitation of the magnetic dipole transition of the ground state (²F_7/2 ↔²F_5/2) of ¹⁶⁹Tm atoms trapped in solid argon and neon and performed absorption and emission spectroscopy. The transition is split into multiple components, likely due to the crystal field effects of the host. With improved FTIR and absorption spectroscopy, a number of narrow linewidth features were resolved. We demonstrate sufficient driving amplitude to saturate the transition and find no evidence of inhomogeneous line broadening. This supports a picture where the linewidth (as narrow as 1.5 GHz) is determined by homogeneous broadening from photons, which is also supported by an observed temperature dependence. We will present the results from spectroscopy and attempts to assign features to specific transitions.