RAPID GENERATION OF APPROXIMATE OPTICAL-SPECTRA OF DENSE COOL PLASMAS

In recent experiments uniform plasmas have been generated at high dens ities and low temperatures, (typically electron densities of 10(19) cm (-3) and T similar to 2 - 5 eV). Additionally, such plasmas are also p roduced during free laser ablation - a topic of relevance to the depos ition of thin solid films. Standard methods used to diagnose plasmas a re difficult to apply at these conditions, as there is significant ove rlap of the broad spectral lines from different elements and ion stage s. It is therefore of interest to attempt to calculate the entire spec trum in the appropriate wavelength regime. For most elements, the numb er of individual spectral line profiles that have been calculated as a , function of density and temperature using the semi-classical method is very small, hindering such a synthesis of the full spectra. However , a technique for approximating line shapes simply and rapidly (the mo dified semi-empirical method) has previously been developed for indivi dual lines. We utilise this method, coupled with an accurate database, to generate a large number of density dependent line profiles, and he nce an approximation to the full spectrum. We evaluate the accuracy an d utility of such an approach by comparison with the few extant semi-c lassical calculations. The method described facilitates the rapid gene ration of approximate spectra. It can also be used as a post processor to a hydrodynamic code to obtain both time dependent and time integra ted spectra in the approximation that the laser-ablated plasma is both optically thin and in LTE. (C) 1997 Elsevier Science Ltd. All rights reserved.