Broadband CARS Microscopy

A major challenge in optical microscopy is to develop techniques with high spatial resolution, sensitivity, and chemical specificity. The latter, chemical specificity, is typically achieved through some form of labeling, which has potential to alter the nature of the sample under investigation. Raman or infrared (IR) microscopy can be utilized to image samples in their natural form using molecular vibrations as a contrast mechanism. IR microscopy suffers from spatial resolution issues, and spontaneous Raman microscopy suffers from low scattering cross-sections, so that high laser power is often required, introducing the possibility of sample photo-damage. Scattering cross-sections for Coherent Anti-Stokes Raman Scattering (CARS) are typically several orders of magnitude greater than those of spontaneous Raman Scattering. This, in addition to the high spatial resolution inherent in nonlinear optical microscopy, has led CARS microscopy to begin emerging as a powerful, noninvasive technique for biological and material imaging.