Waveguide Raman spectroscopy (WRS) has shown considerable potential for investigating the chemistry of thin films and interfaces in a number of fields, including microelectronics, imaging, optics, and coating technology. One of the major problems associated with Raman spectroscopy has been the presence of fluorescence, greatly limiting the investigation of thin films which are colored. To circumvent this difficulty, WRS sampling techniques have been extended to Fourier transform Raman spectroscopy where near-IR excitation is used. In doing this, the increase in wavelenght and the resulting decrease in the refractive index of the film combine to restrict the film thicknesses which can be studied. The effect of the excitation wavelength on the distribution of the optical field in the waveguide and its effect on WRS measurements are discussed. © 1991.