in absorption in the vicinity of 83 nm. Predissociative widths as narrow as 0.3 cm have been measured, and profile analyses based on the theory of Pano are performed on these predissociated states. The importance of overlap integrals in the predissociation of B" is shown, and the absorption cross section o = (7.2 +0. 7) &(10 " cm' for the B"~X(2,0) is determined. Anomalous behavior observed in the D (v = 5) states of 0, is analyzed in terms of an accidental perturbation by the D" (v = 0) states.

Single-pulse irradiation of Au and Ag suspensions of nanospheres and nanodisks with 532-nm 4-ns pulses has identified complex optical nonlinearities while minimizing material damage. For all materials tested, we observe competition between saturable absorption (SA) and reverse SA (RSA), with RSA behavior dominating for intensities above ∼50 MW/cm2. Due to reduced laser damage in single-pulse experiments, the observed intrinsic nonlinear absorption coefficients are the highest reported to date for Au nanoparticles. We find size dependence to the nonlinear absorption enhancement for Au nanoparticles, peaking in magnitude for 80-nm nanospheres and falling off at larger sizes. The nonlinear absorption coefficients for Au and Ag spheres are comparable in magnitude. On the other hand, the nonlinear absorption for Ag disks, when corrected for volume fraction, is several times higher. These trends in nonlinear absorption are correlated to local electric field enhancement through quasi-static mean-field theory. Through variable size aperture measurements, we also separate nonlinear scattering from nonlinear absorption. For all materials tested, we find that nonlinear scattering is highly directional and that its magnitude is comparable to that of nonlinear absorption. These results indicate methods to improve the efficacy of plasmonic nanoparticles as optical limiters in pulsed laser systems.

Sequential two-photon photoexcitation of SO2 at 248 nm is found to lead to a number of primary fragments including S(3P) and SO(X 3Σ−). Further excitation of some of these photoproducts was also observed, occurring by both linear and two-quantum mechanisms. The resulting molecular X←B (v\,2) ultraviolet fluorescence from SO and the atomic 3P←3S vacuum ultraviolet emission from S atoms were detected and an analysis of the energy flow patterns was made.

Photolytic studies performed at 193 nm demonstrate that NO in the highly excited D(v = 1,5) and E(v = 0) states is generated from N2O during irradiation in three sequential steps involving photodissociation, chemical reaction, and photoexcitation. The resulting NO fluorescence (160–230 nm) was analyzed with a system of rate equations, and the temporal behavior, intensity dependence, and pressure dependence were found to be consistent with a simple kinetic model. The quenching coefficient of NO by N2, Ar, and N2O were determined in this analysis to be qN2 = (2.7±0.8)×10−11 cm3 sec−1, qAr = (6.6±1.4)×10−11 cm3 sec−1, and qN2O = (1.5±0.4)×10−10 cm3 sec−1. Finally, dramatic changes in the spectral distribution of the ultraviolet NO fluorescence due to collisions with He were observed, which contrasts with the absence of spectral redistribution in collisions involving N2, Ar, and N2O.

High-spectral-brightness coherent XUV radiation has been produced by third-harmonic generation of a transformlimited- bandwidth KrF* laser in gaseous xenon. The observed XUV output, which was continuously tunable from 82.8 to 83.3 nm, had a peak power of 40 mW, a bandwidth <0.01 cm(-1), and absolute frequency control to within 0.04 cm(-1). The utility of this XUV source for high-resolution spectroscopic applications is demonstrated by absorption studies in molecular hydrogen.

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