Browsing by Subject "Ultrashort"
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Item Contact effects in light activated GaAs switches(Texas Tech University, 1985-05) Durkin, Peter SNot availableItem Photodetachment as a discharge control mechanism in gases containing oxygen(Texas Tech University, 1985-05) Thurmond, Leo ErasmusInterest in high voltage switches for pulsed power applications has increased significantly in the last several years. Inductive energy storage has space and weight advantages over capacitive energy storage, but requires the use of a high power opening switch. Opening switch technology has only recently started to be developed, and several concepts for opening switches are being studied. One of these concepts is the diffuse discharge switch, which shows several advantages over other types of opening switches. One major advantage of the diffuse discharge switch is that it may be controlled externally by an electron beam or by optical means. There are several processes possible for optical control of a diffuse discharge, one of which is photodetachment. In this paper, three experiments are presented which study the possibility of using photodetachment as a discharge control mechanism in gases containing 02 are presented. The first experiment shows the effect of photodetachment outside the discharge and the dependence of the effect on laser energy flux density. The second experiment demonstrates the feedback effect of photodetachment on a glow discharge. Operating conditions for the largest effect are presented. The last experiment simulates the conditions in a high power switching device, and the preliminary results of this study are given.Item Studies of solvent-solute interactions in the photophysics of laser dyes(Texas Tech University, 1988-12) Casey, Kelly GambleThe fluorescence lifetime of rhodamine B in the normal alcohols (C1-C10) and normal nitriles (C2,C5,C6,C8,C9) has been measured using a picosecond laser system. The lifetime measuring technique is time-correlated single photon counting (TCSPC). Absorption and emission spectra of rhodamine B in the alcohols and nitriles have also been determined, thus allowing calculation of quantum yields, radiative, and nonradiative rates. The rotation of the dye's diethylamino groups is related to the nonradiative rate. A decreasing nonradiative rate corresponds to a greater energy barrier to rotation. The behavior of the nonradiative rates, and thus the rotational energy barrier, is modelled as a function of (1) solvent viscosity and (2) solvent polarity. The polarity-dependent model shows better cortelation with the data. The nitrile data differs from the alcohol data in that the barrier appears to be constant and therefore independent of solvent viscosity and polarity. Hydrogen bonding is used to explain the differences between the alcohols and nitriles. Rotational relaxation times of two laser dyes (cresyl violet and oxazine-1) in polymer solution (poly(ethylene oxide) and methanol) has been measured using the transient absorption spectroscopy (TAS) method. TAS is a pump-probe technique using a picosecond laser system. The pump beam optically bleaches the sample and the probe beam monitors the transient response. The effect of increasing polymer concentration is seen as an increasing rotational relaxation time. This result is examined with respect to the Debye-Stokes-Einstein (DSE) equation governing viscosity-dependent, rotational reorientational times. The greater increase in the rotational times of cresyl violet is explained on the basis of increased polymer-dye interaaion, specifically hydrogen bonding.