PRECISION LIFETIME MEASUREMENTS OF CS 6PP-2(1 2) AND 6PP-2(3/2) LEVELS BY SINGLE-PHOTON COUNTING/

Time-correlated single-photon counting is used to measure the lifetime s of the 6p 2P1/2 and 6p 2P3/2 levels in atomic Cs with accuracies alm ost-equal-to 0.2-0.3%. A high-repetition-rate, femtosecond, self-mode- locked Ti:sapphire laser is used to excite Cs produced in a well-colli mated atomic beam. The time interval between the excitation pulse and the arrival of a fluorescence photon is measured repetitively until th e desired statistics are obtained. The lifetime results are 34.75(7) a nd 30.41(10) ns for the 6p 2P1/2 and 6p 2P3/2 levels, respectively. Th ese lifetimes fall between those extracted from ab initio many-body pe rturbation-theory calculations by Blundell, Johnson, and Sapirstein [P hys. Rev. A 43, 3407 (1991)] and V. A. Dzuba et al. [Phys. Lett. A 142 , 373 (1989)] and are in all cases within 0.9% of the calculated value s. The measurement errors are dominated by systematic effects, and met hods to alleviate these and to approach an accuracy of 0.1% are discus sed. The technique is a viable alternative to the fast-beam laser appr oach for measuring lifetimes with extreme accuracy.