Integrated Optics and Raman Scattering: Molecular Orientation in Thin Polymer Films and Langmuir-Blodgett Monolayers

Studies of submicron films and molecular monolayers with infrared and Raman spectroscopy have been hampered by the inability of current spectroscopic techniques to detect the minute amount of material present in these thin-film assemblies. A method for overcoming this problem by using integrated optics has been successfully demonstrated. In the case of Raman studies, the material whose spectrum was desired was made into an asymmetric slab waveguide or a composite waveguide structure in which both the optical field intensity of the in-coupled laser source and the scattering volume of the sample have been significantly increased. Using this technique we have obtained Raman spectra of thin polymer films (<80 nm) and the resonant Raman spectra of single dye monolayers (2.7 nm). Estimates of molecular orientation within the two-dimensional films have been made based on the results of polarized Raman measurements. In addition, the results of overcoating experiments illustrate the versatility and applicability of this technique to a wide variety of surface and thin-film studies.