Spectroscopy of thulium atoms trapped in solid argon and neon

We present a detailed study of excitation-emission spectroscopy for the magnetic dipole transitionbetween the ground state fine levels in thulium atoms trapped in crystals of argon and neon at cryogenic temperatures. We observed narrow transitions near 1140 nm when excited with visible light and also observe visible fluorescence when directly excited with infrared light. In the presence of an external magnetic field, the lines are split into multiple components. We excited the sample with circularly polarized light and preliminary results suggest the right and left polarized light have different effect in the fluorescence signal at those transitions. We will discuss efforts to identify the observed transitions with theoretical models of crystal-field-split levels.