Laser spectroscopic studies on collisional relaxation of Rydberg atoms

Broadening and shift of strontium 5s5p1P1-5snd1D2 (n=14-39) transitions as a function of helium pressure have been measured by monitoring the absorption of a probe laser by strontium ions. The ions were found to be produced due to the collisional ionization from Rydberg states. The magnitude of line broadening of the levels for n>15 does not increase as n becomes larger. This result has been interpreted by a mechanism that the perturber passes through the ion core-electron system with a reduced interaction. (author)