Evanescent-wave infrared spectroscopy of solid materials using deformable silver-halide optical fibers

Silver-halide crystalline infrared optical fibers are used for infrared evanescent-wave spectroscopy of solid materials. The fiber is pressed onto the material to be studied and good contact is achieved either by elastic or plastic deformation of the ductile fiber. The absorption-signal level is determined by the length and pressure of contact. This method allows convenient measurement of the absorption signals in large samples that cannot be introduced into an IR spectrometer and in materials that are practically opaque so that their spectra cannot be obtained by conventional transmission measurements. Examples of measurements of hard polymers are given, and the evanescent-wave spectra of polyethylene are compared with conventional transmission measurements.