Laser spectroscopic investigation of Ca atoms in liquid helium: Comparison between spectral properties for liquid helium-3 and helium-4

Excitation and emission spectra of the 4s21S0 - 4s4p1P1 and 4s4p3PJ(J = 0, 1, 2) - 4s5s3S1 transitions of Ca atoms implanted not only in liquid 4He but also in liquid 3He have been measured. It has been found that the excitation spectra for liquid 3He show considerably smaller widths and peak shifts from transition wavelengths of a free Ca atom, in comparison with those for liquid 4He. These spectral characteristics have been well reproduced by our theoretical calculation based on a vibrating bubble model. This calculation has shown that, due to a significant difference in surface tension between the two liquids, the radius of a bubble formed around Ca in liquid 3He is larger than the one in 4He, and that this fact as well as the smaller number density of He atoms in liquid 3He cause weaker perturbation for Ca, resulting in the smaller peak shift and width for liquid 3He.