Infrared near-field study of a localised absorption in a thin film

¹ LURE, Bât. 209d, Université de Paris-Sud, 91405 Orsay Cedex, France
² Optique Submicronique, Univ. de Bourgogne, 9 avenue A. Savary, BP 400, 21011 Dijon, France
³ Laboratoire des Verres et Céramiques, Campus de Beaulieu, 35042 Rennes Cedex, France

Corresponding author: ortega@lure.u-psud.fr

Received: 17 January 2001
Revised: 13 July 2001
Accepted: 13 July 2001
Published online: 15 November 2001

Abstract

We study the conditions to perform micro-spectroscopy with a sub-wavelength lateral resolution in the wavelength spectral range from 3 to 20 μm, taking advantage of the infrared spectral signature of different chemical species. We utilised CLIO, a free electron laser, as the photon source. The transmitted photons were collected by either fluoride or chalcogenide glass fibres. Fibre tips were obtained through chemical etching by organic solvents. Metallisation of the tips permits to achieve lateral resolution of the order of the tip size. However, parasitic propagation of the light in the film reduces the contrast between irradiated and non-irradiated zones. We exemplify our set up with near-field infrared spectra obtained for polymer thin films deposited onto silicon wafers.