The ability to observe samples qualitatively at the microscopic scale has greatly enhanced our understanding of the physical and biological world throughout the 400 year history of microscopic imaging, but there are relatively few techniques that can truly claim the ability to quantify the local concentration and composition of a sample. We review coherent anti-Stokes Raman scattering (CARS) as a quantitative, chemically specific, and label-free microscopy. We discuss the complicating influence of the nonresonant response on the CARS signal and the various experimental and mathematical approaches that can be adopted to extract quantitative information from CARS. We also review the uses to which CARS has been employed as a quantitative microscopy to solve challenges in material and biological science.
J. Phys. Chem. B

Day, J. P. R., Domke, K. F., Rago, G., Kano, H., Hamaguchi, H., Vartiainen, E. M., & Bonn, M. (2011). Quantitiative Coherent Anti-stokes Raman Scattering (CARS) microscopy. J. Phys. Chem. B, 115(24), 7713–7725. doi:10.1021/jp200606e