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Desorption induced by femtosecond laser: nonlinear regime through indirect coupling

D. BEJAN1,* , G. RASEEV2

Affiliation

  1. Faculty of Physics, University of Bucharest, P.O. Box M.G.11, Bucarest, Magurele, Romania
  2. Laboratoire de Photophysique Moléculaire du CNRS, bât. 210, 91405 Orsay, France

Abstract

The photodesorption of molecular adsorbates from metallic surfaces has been studied by wave packet propagation of the Schrödinger equation, using a non-conservative three-state phenomenological model. The three-state diabatic model includes the surface band structure, the laser-matter interaction and the interstate coupling. The non-conservative fluctuation/dissipation coupling with the bath is introduced through the third state |3> and its interactions: (i) a delay time (expressed as a phase difference) between |1>↔|3> excitation/de-excitation events related to the fluctuation of the energy with the bath and (ii) a quenching of the electron population of this state |3> related to the dissipation. The desorption yield (Y) is obtained as an average over the desorption probability calculated from a sampling of delays or phase differences. The study of the photodesorption of CO from Cu(111) showed that the model displays: (i) a Gaussian distribution of the desorption probability with the phase difference indicating a random, incoherent character of the coupling between the system and the metal bath; (ii) a nonlinear dependence of the photodesorption yield with the laser fluence governed by a single parameter, the amplitude of the |1>↔|3> transition probability. We obtained a Y≈F4.9 dependence of the desorption yield with the laser fluence, in agreement with the experimental findings..

Keywords

Nonlinear photodesorption, Cu, CO, Metal bath, Delay time, Electronic quenching.

Submitted at: Jan. 27, 2006
Accepted at: July 20, 2006

Citation

D. BEJAN, G. RASEEV, Desorption induced by femtosecond laser: nonlinear regime through indirect coupling, Journal of Optoelectronics and Advanced Materials Vol. 8, Iss. 4, pp. 1331-1340 (2006)