Ž . Spectrochimica Acta Part B 56 2001 567586 Modelling of LIBS plasma expansion  G. Colonna  , A. Casavola, M. Capitelli Centro Studi per la Chimica dei Plasmi, Cnr and Dipartimento di Chimica, Uni  ersita degli Studi di Bari, V. Orabona 4, ` 70126 Bari, Italy Received 12 October 2000; accepted 20 April 2001 Abstract A one-dimensional time-dependent fluid dynamic model has been developed to describe the expansion of the plume produced by laser ablation. The model includes chemical reactions considered in local thermodynamic equilibrium to describe the expansion of a TiO plasma. The results are discussed in connection with LIBS plasmas.  2001 Elsevier Science B.V. All rights reserved. Keywords: LIBS; Modelling; Equilibrium; Thermodynamic; Fluid dynamic 1. Introduction Laser ablation is a powerful technique to de- posit good quality thin films. The characteristics of the deposited material depend on the expan- sion of the plume and the theoretical study of the deposition should consider the properties of the mass flow from the target to the substrate. To understand the characteristics of a thin film  This paper was presented at the 1st International Congress on Laser Induced Plasma Spectroscopy and Applications, Pisa, Italy, October 2000, and is published in the Special Issue of Spectrochimica Acta Part B, dedicated to that conference.  Corresponding author. Tel.: 39-080-544-3563; fax: 39- 080-544-2024. Ž . E-mail address: cscpgc08@area.ba.cnr.it G. Colonna . deposited by laser ablation, a theoretical model has been developed. To obtain quantitative re- sults the model should describe the target evap- oration, the Knudsen-layer formation, the plume expansion, and the absorption of the ablated ma-  terial 1 . This approach is too complicated involv- ing poorly understood concepts. So a partial model has been developed, which only deals with plume expansion. The mechanisms of the laser  surface interaction are not included in the model, and the evaporated material is formed either instanta- neously or continuously with a given density and temperature. Various expansion conditions have been studied, including different temperatures of the newly formed material at various buffer pres- sures. Moreover, the role of the production rate of matter released from the target and the loss 0584-854701$ - see front matter  2001 Elsevier Science B.V. All rights reserved. Ž . PII: S 0 5 8 4 - 8 5 4 7 01 00230-0