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The characteristics of laser lithotripsy of biliary calculi are compared for a flashlamp pumped dye laser (lambda = 640 nm) and a Cr:Tm:Ho-YAG laser (lambda = 2.1 microns). Data on fragmentation efficiency with respect to laser power and pulse repetition rate are presented for different types of stones. It is shown that both lasers can produce effective stone fragmentation. The laser power required for efficient fragmentation characteristics is significantly less for the visible wavelength laser. However, the problems associated with damage to the fiber tips of the delivery system during operation were found to be less with the near infrared wavelength. The laser power for efficient fragmentation with the dye laser varies significantly for different types of stones while the power for efficient fragmentation with the holmium laser is the same for all stones.

Natural radiative lifetimes in the perturbed 6sns ~D 2 (n= 12-30) sequence of barium have been measured using the PUMOLS (PUlse-MOdulated Laser Spectroscopy) method, which incorporates pulse-modulation of a CW dye-laser beam and delayed coincidence techniques. Principal perturbers are the 5d 7d 3F 2 and ~D 2 states. Lifetimes were also measured for these shortlived valence states, which through configuration mixing cause drastic decreases in lifetime values in the region of perturbation of the 6snd 1D z sequence. Two-step laser excitation from the ground 6s 2 ~So state via the 6s 6p 1p~ state was employed. Special care was taken to determine the influence of black-body radiation transitions on the measured lifetimes.

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A new study of the even-parity spectrum of Ca I is reported. The term assignments of the 3d2 doubly excited configuration are discussed in relation to those of the isoelectronic sequence and to the corresponding assignments in Ti I . The significance of term-dependent contraction of the 3d orbitals in Ca I, not considered in earlier studies of this spectrum, is demonstrated from ab initio Hartree-Fock calculations, and the energies of the missing terms are estimated. We show that recent data for the members n = 62 to 85 of 4snd ID, do not agree as well as originally surmised with earlier MQDT extrapolations, indicating the presence of a further perturbation. We have investigated the breakdown of the AJ selection rule in the presence of collisions with a foreign gas. A collision-induced perturbation around n = 63 of 4snd 'D, is used to locate the missing 'G, term of 3d2.