Hyperfine structure of 5I8-->5F5 optical transitions within the trigonal center of CaF2:Ho3+

Abstract

The origin of extra hyperfine lines in two optical transitions in the $^{5}$${\mathit{I}}_{8}$${\ensuremath{\rightarrow}}^{5}$${\mathit{F}}_{5}$ region of the trigonal center of ${\mathrm{Ho}}^{3+}$ in ${\mathrm{CaF}}_{2}$ has been investigated by using optically detected nuclear magnetic resonance and two-laser hole burning. Specific mixing of the excited-state hyperfine wave functions is established by the experimental measurements and, in a theoretical analysis, it is shown that such a mixing can arise from the off-diagonal hyperfine interaction between adjacent E and A states. Normally forbidden transitions gain intensity from the mixing and lead to the appearance of the extra hyperfine lines in the optical spectra. The strengths of the quadrupole, hyperfine, and off-diagonal hyperfine interaction in the ground and excited states are obtained in the analysis.