PRESSURE SHIFT AND BROADENING OF THE RESONANCE LINE OF BARIUM ATOMS IN LIQUID-HELIUM

We have measured the pressure broadening and shift of the excitation a nd emission lines of the 6s2 S-1(0) --> 6s6p P-1(1) transition of Ba a toms implanted in liquid and solid helium at 1.5 K. The observed spect ra are quantitatively explained within the adiabatic line-broadening t heory by assuming a bubble structure of the trapping sites for the Ba atoms. The evolution of the bubble shape and size in the optical excit ation-deexcitation cycle is modeled theoretically.