Spectroscopic Investigations of the Ablation Plume of Several Inorganic Materials
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SPECTROSCOPIC INVESTIGATIONS OF THE ABLATION PLUME OF SEVERAL INORGANIC MATERIALS A. ROSENFELD, R. MITZNER, R. KONIG Max Born Institute of Non-linear Optics and Short Time Spectroscopy in Research System Berlin e.V. Rudower Chaussee 6,0-1199 Berlin-Adlershof, Germany ABSTRACT Time resolved absorption spectroscopic investigations of the KrF laser ablation of MgOceramics and sapphire on atmospheric conditions were carried out with a time resolution of about 5 ns and a two-dimensional space resolution of less than 100 pm. The time delay between the ablation pulse and the broad band probe pulse was varied from 10 ns up to 10 Ps. Absolute particle densities of the species were determined in dependence on the time delay and on the distance to the surface. The spatial and temporal behaviour of the particles in the ablation plume near the surface was found to be strongly affected both by air atmosphere and the reaction dynamic in the plasma zone. In the case of sapphire the time evolution of the densities of Al , AI+ and A10 species are discussed in comparison to measurements on vacuum conditions. INTRODUCTION The ablation of organic and inorganic material utilising pulsed uv lasers is of great practical interest, e.g. for the micro-material processing, for the preparation of super-conducting thin films or for the angioplastie. But the ablation processes at fluences of a few J/cm2 are so complex that they are not understood in detail until now. Therefore spectroscopic investigations of the plasma plume are so important. Many results were published about emission measurements of the ablation plume (e.g. Il3]). Because of the bright Bremsstrahlung-continuum up to 50 or 70 ns after the ablation pulse the emission spectroscopic investigations are restricted mainly to longer delay times 114] and are not suited for the examination of the primary reactions in the high temperature and high pressure plasma plume. An other disadvantage of the fluorescence method is the difficulty to determine absolute particle densities. Till now only few absorption investigations of the plasma plume were made, nearly all related to the problem of preparation of superconducting thin films [4,5,6]. While Geohegan and Mashburn [5] used a Xe lamp as probing continuum, Cheung and co-workers [6] used a cw Rhodamine 6G dye laser between 572 and 628 nm. Masuhara and co-workers [3,4] obtained information from self absorption lines in the bright Bremsstrahlung-continuum of the ablation plume at short delay times. Using the resonance absorption photography Ventzek et. al. [7] investigated the dependence of the plume on the surrounding gas pressure at the ablation of several materials. In time resolved absorption studies of excimer laser ablation of CaF 2 Mitzner et al. [8] investigated spatial and temporal behaviour of the particles in the ablation plume near the surface. In this paper results are given of ns time resolved absorption measurements of the KrF excimer laser ablation of MgO-ceramics and of sapphire (A120 3) on atmospheric conditions. These studie
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