Fig 1: Reducing gradiants- collisionally confine the ablated plasma Variation in the microdot spectroscopy I=1x10^8 W/cm^2 Fig 2: Collisonal confinement All in the visable range Real and virtual image Nikon camera lens depth of field centered in the plume Fig 3: Time resolved - nonminally identical experiments instruments gated at different times. All recorded after the end of the laser pulse. Real and Virtual Images. Visable range All neutral lines (2 Li and 2Ag) Expanding plasma Broadened Lines at high density, narrow for low density Fig 4: 2-Li and 2Ag (fine structure spliting) All neutral - Plasma? Broadening -> Plasma Self-reversal -> gradients (not always) Pt contamination H contamination Ox contamination (LiO; LiOH) 2s2 2p3 4d -> 2s2 2p3 3p Fig 5: Contamination Li: 3p-2s Ag: 5d(3/2)-5p(3/2) Contamination in F - complex Nearly all energy levels of neutral Pt is unknown. Pure Pt no Ox. Fig 6: We used the Los Alamos TAPs suite of codes to produce both the atomic structure and collisional data needed for this work. Compression in the energy level structure for high-Z neutral and near neutral systems is common for most code that can compute neutrals. To solve this problem we employed the RCE procedure into CATS: This procedure varies in an iterative fashion the radial energy parameters Eav, Fk, Gk, zeta, Rk in a manner that produces the best least-squared fit between the theoretical and experimental energy levels. These modified radial energy parameters are are the used to compute new wavefunctions with there corresponding energies. Fig 7. Typical allowed and forbidden electron impact cross sections. The over estimate of the DW cross section is very typical for neutral and the corrected wavefunctions has moved the cross sections in the right direction. Fig 8. How does this effect the rates? Free electron temperature vs the rate coefficient. Following the cross sections we see a depression in the rate by a factor of 2. Fig 9. This plot shows the interplay between the Li and Ag for two temperatures - recall that level populations of Li and Ag are solved self-consistently in a common free-electron pool. *describe the level indexes* *frac. pop* At low temperature Li ionizes first 5.3 eV ioniziation threshold providing as compared to Ag's 7.5 eV threshold. At 3 eV, Li populations shows little change due to its 60.9 eV first excited state jump while Ag shows ionization through Ag+3. Fig 10. In order to describe the various qualities found in the line shapes I will use this grotrian diagram for neutral silver. The predominant effect on the lineshapes are due to stark broadening due to plasma electro-microfiles. Besides the typical shifting of energy levels of the radiator by the local microfile the leads to the accumulative broadening of the lines, energy levels of different parity begin to mix and take on opposite parity qualities and allow an otherwise forbidden transition. The lineshape for all three transitions were computed together since the upper levels were spaced so close together. Fig 11. Normalized Ag lineshapes. The narror lineshapes are related to the low electron density and the high electron density is associated the broad lineshapes. These lineshapers are insensitive to the plasma temperature. Fig 12. Similar situation for the Li and a predominant 3p-2p tranistion is appearent. In addition the is a slight asymetry in the in the line profile that will become apparpent later on. Fig 13. Shows the effects of radiation transport in the spectra. For all these figures the Ne is constant so the lineshape is constant and the plasma is represened as one zone. The red lines are optically thin The black are optically thick The closes match to the experimental spectra is the lower right - where the temperature is low enough that both Ag lines are visable (recall that Ag ionizes very quickly) and the importance of opacity in lowering the 3d-2p line. Fig 14. This is the optical depth associated with the previous slides. These slides emphisises the importance of the lineshapes on the optical depth. This study was the first revield to us that a very accurate radiation transport code was necessary to transport these spectral lines with such large variation in optical depth. An optical depth less that 1 is usually considered to be optically thin and greater then 1 is optically thick. Fig 15. This next 3 plates describes the effects of plasma gradients on the spectra. We now construct a large series of temperture and density profiles to compute the synthetic spectra and compare them with the experimental spectra. The plasma is divided into symetric zones, inparticular 1,4,6 zones. The next 3 spectral images represent the best fit to the experimental data. The overal hights compare vary well however, the widths need improving. Notice the Li 4d-2p contribution in the f-complex of lines - it is not being used to determine the best fit. Lines a and c appear to be underestimating the exp. lines however, recall that these lines contained Pt contamination. Notice also that no self-reversal feature is present. Fig 16. 4-zone comparision with a visable improvement in the width and a asymetric self-reversal feature. Fig 17. 6-zone comparision showing good comparison with experimental spectra. Notice the effects of forbiddent transition are visable in the theoretical spectra. Fig 18 The lower left hand side plate represents the optical depth of the last, 6-zone ,case. Notice the variation in optical depth from ~1 to 400! Fig 19 The fundemental result follow the opposite to the intuitive notion of opacity. Typically opacity increases as density density increases. This is not the case here. The two upper panels show the temperature and density profile results for the 1,4, and 6 zone cases. We may consider the x-axis of this historgram to be the physical width of the LiAg plasm. *red - 1 zone* *black - hatched 4 zone* *blue - 6 zone * *purple - corresponding atom number density in 1 zone *black - hatched 4 zone* *tan - 6 zone* The first thing to note is the symetry- the profiles were defined in this manner in the beginning. Next the single zone case corresponds to the values of the outer zones of the 4 and 6 zone cases for both Te and Na. Why are the outer zones so important? Recall that the low density low temperature zones have smaller Ne. The line profiles associated with low Ne for Li inparticular, are very narrow and inturn produce a very high opacity at line centers. This reduces the line intensity of the 3d-2p and 2p-2s Li lines. The higher core densities and temperatures have broader lineshapes associated with them and are needed to fill out the lines.