Infrared laser radiation induced changes in the IR absorption spectra of thin polymer films

The presented work demonstrates that powerful laser radiation causes changes in absorbance spectra of epoxy resin and polyethylene. Thin polymer films were located between IR AgBrCL optical fibres and exposed to the radiation of a CO₂ laser. The output of the laser source was varied in the range 0-8.5 W. Absorbance spectra were measured by a Fourier transform IR spectrophotometer. It was revealed that characteristic absorbance peaks of polymers decay under the powerful IR light. The apparent dependence of peak magnitude on IR radiation power has been established. The mathematical theory of the observed effect was worked out. The authors suggest that the effect under discussion is caused by the oxygen-free thermal action of IR radiation on the chemical structure of polymer materials. The revealed effect could be effectively used for the lowering of losses in adhesive contacts of IR optic elements. The novelty of the proposed method lies in the fact that thermal treatment is localized strictly in the adhesive contact: optical elements to be contacted (fibres, lenses etc), which are highly transparent in the IR, do not experience the IR radiation, but the polymer adhesive is subjected to a temperature rise. The phenomenon could be effectively used for the lowering of losses in optical contacts and recording and storage of information in polymer films as well.