A novel sample interface has been developed to acquire the unenhanced external reflection Raman spectra of Langmuir-Blodgett thin films deposited onto solid substrates. This interface does not rely on a surface or resonance enhancement to amplify the monolayer signal, but rather uses fiber optics and gradient-index lenses for collection of the scattered light, thus providing an efficient collection mechanism for the Raman scattered radiation in an external reflection arrangement. This design is relatively inexpensive and straightforward to implement, resulting in a sensitive and fast tool for obtaining high-quality Raman spectra of ultrathin films (greater than or equal to 2.5 nm thickness). The results of this study show that a fiber-optic bundle provides an efficient mechanism for transfer of the scattered Raman radiation from the sample to the monochromator. The optical design also incorporates gradient-index lenses for image transfer onto the fiber bundle, thereby significantly reducing chromatic and spherical aberrations in the transfer of the image of the sample onto the fiber. Using this optical design, the spectrum of a single cadmium arachidate (Cd:Ar) monolayer transferred onto CaF2 results in a signal-to-noise ratio of similar to 400:1 in the v(C-H) stretching region. Additionally, a high reflectivity dielectric mirror can be used as an alternative substrate to acquire Raman spectra below 2000 cm(-1). By use of this dielectric substrate, the unenhanced external reflection Raman spectrum of a Cd:Ar monolayer in the v(C-C) spectral region was obtained for the first time.