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Abstract
This thesis details an experimental study of resonant photopumping in laser produced plasmas. Successful attempts were made to use the observed line coincidence between the 4s$\sp2$5s $\sp2$S$\sb{1/2}$ $-$ 4s$\sp2$4p $\sp2$P$\sb{3/2}$ transition in gallium like Mo XII at 136.499 A to enhance the population of the krypton like Mo VII 4s$\sp2$4p$\sp5$6s 1/2 (1/2) $\sb1$ level through resonant photoexcitation of the Mo VII 4s$\sp2$4p$\sp6$ $\sp1$S$\sb0$ $-$ 4s$\sp2$4p$\sp5$6s 1/2 (1/2) $\sb1$ transition at 136.507 A. The desire is to use this excitation process to produce a population inversion and gain for one of several 4s$\sp2$4p$\sp5$6s - 4s$\sp2$4p$\sp5$5p transitions as a means of developing a Vacuum Ultra Violet laser near 600 A.
A gated microchannel plate spectrometer system was developed to facilitate time resolved spectroscopic studies of expanding laser produced plasmas. A novel two laser interaction scheme that uses a 6 J ruby laser to preform a dense cold plasma which is subsequently heated by a 1/2 of the beam of a 10 J CO$\sb2$ laser was employed to produce a Mo XII pump plasma. The lasant plasma was created by line focusing the remaining half of the CO$\sb2$ laser on a planar Molybdenum target. The intensities for several Mo VII 6s-5p transitions were recorded for the two cases of the spectrometer viewing the lasant plasma alone, and when it viewed the lasant plasma exposed to Mo XII pump photons from a second simultaneously created pump plasma. At 5 times enhancement of the intensity of the MO VII 6s-5p lines was observed when the lasant plasma was exposed to the Mo XII radiation. A control experiment where a Zirconium pump plasma replaced the Mo pump plasma did not result in any enhancement of the MO VII line intensities supporting the conclusion that the measured population enhancement was as a result of photopumping and not other atomic processes. These results indicate that this pumping mechanism should be capable of producing a working 600 A laser.