Raman spectroscopy is based on vibrational transitions that yield very narrow spectral features that are characteristic of the investigated sample. us, it has long been regarded as a valuable tool for the identication of chemical and biological samples as well as the elucidation of molecular structure, surface processes, and interface reactions. Despite such advantages, Raman scattering suers the disadvantage of extremely poor eciency. Compared to luminescence-based processes, Raman spectroscopy has an inherently small cross section (e.g., 10−30 cm2 per molecule), thus precluding the possibility of analyte detection at low concentration levels without special enhancement processes. Some modes of signal enhancement have included resonance Raman scattering and nonlinear processes such as coherent anti-Stokes Raman scattering. However, the need for high-power, multiple-wavelength excitation sources has limited the widespread use of these techniques.