Magneto-optical studies of atomic thallium centers in KCl: Magnetic circular dichroism tagged by spin resonance

Abstract

We report measurement of the magnetic circular dichroism (MCD) of radiation-damaged crystals of KCl doped with Tl. By using microwaves resonant with ground-state magnetic splittings, we have been able to tag such MCD spectra to specific species. In particular, we have shown that bands peaking at 1040, 725, 550, 405, 340, and 254 nm all belong to the ${\mathrm{Tl}}^0$(1) center, where that center, as determined by earlier spin-resonance studies, consists of a neutral Tl atom perturbed by the field of an adjacent anion vacancy. Our experiment constitutes the first direct evidence that a recently discovered, thallium-associated, laser-active center whose pump band peaks at 1040 nm is indeed the ${\mathrm{Tl}}^0$(1) center; furthermore, the MCD of the two lowest energy bands are in rough quantitative agreement with predictions of a simple electronic model of that center. Finally, our technique has allowed the discovery of two other centers having distinctly different spin resonances, yet whose optical spectra bear some striking similarities to that of the ${\mathrm{Tl}}^0$(1) center. Because their fundamental bands overlap those of the ${\mathrm{Tl}}^0$(1) center, the new centers may affect the operation of ${\mathrm{Tl}}^0$(1)-center lasers.