Detection of Quantum Properties of Liquid Helium by use of Atoms and Molecules as Optical Probes

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Spectra of Ca atoms implanted in liquid helium-3 and helium-4 have been investigated both experimentally and theoretically. Smaller atomic mass leads to the lower density of liquid for helium-3 compared with helium-4. And the statistic character of helium-3 as fermionic atoms results in the smaller surface tension for liquid helium-3 compared with bosonic liquid helium-4. Our model calculation based on the bubble theory has shown that these quantum mechanical and statistic character of liquid helium are manifested in these spectra as large differences in the spectral shift and width between liquid isotopes.Emission and excitation spectra of Mg atoms in pressurized liquid helium-3 and helium-4 have been observed. Emission spectra of Mg atom have almost no dependence on the pressure, which is in contrast to the fact that emission spectra for the other atomic species observed so far shifts to blue side and broaden with the pressure. Theoretical investigations have indicated that this spectral feature of Mg atom in liquid helium can be explained by the exciplex model of Mg-He_n.Emission spectra of Bay in cold helium gas have been observed as a function of helium pressure and temperature. Analysis based on rate equations have revealed the collision dynamics such as the formation, dissociation and vibrational relaxation of Ba^+He:.