Pressure shift and broadening of the resonance line of barium atoms in liquid helium

Abstract

We have measured the pressure broadening and shift of the excitation and emission lines of the 6${\mathit{s}}^2$ ${}_{}{}^1{}_{}{}^{}$ ${\mathit{S}}_0$→6s6p ${}_{}{}^1{}_{}{}^{}$ ${\mathit{P}}_1$ transition of Ba atoms implanted in liquid and solid helium at 1.5 K. The observed spectra are quantitatively explained within the adiabatic line-broadening theory by assuming a bubble structure of the trapping sites for the Ba atoms. The evolution of the bubble shape and size in the optical excitation-deexcitation cycle is modeled theoretically.