Selective Absorption of Circularly Polarized Light in Broad Bands by the Zeeman Components of Divalent Thulium in Calcium Fluoride

The paramagnetic circular dichroism of the 4f-5d absorption bands of CaF₂:Tm²⁺ was investigated at 2.0^∘{}K and 9.0kG. Using group theory it is shown that the bands can be separated into E5/2 and G3/2 character. Experimentally it was found that in this case the bands are primarily G3/2 in character. Optical pumping experiments were performed where changes as large as ±{}20% were easily observed in the electron-paramagnetic-resonance absorption signal at X-band frequencies and 1.5^∘{}K by changing the polarization of the pump light from right to left circular. A method for optically monitoring the difference in the population of the two Zeeman components of the ground state is also reported on.