Second harmonic imaging microscopy (SHIM) is based on a nonlinear optical effect known as second harmonic generation (SHG). SHIM has been established as a viable microscope imaging contrast mechanism for visualization of cell and tissue structure and function. A second harmonic microscope obtains contrasts from variations in a specimen s ability to generate second harmonic light from the incident light while a conventional optical microscope obtains its contrast by detecting variations in optical density, path length, or refractive index of the specimen. SHG requires intense laser light passing through a material with a noncentrosymmetric molecular structure. Second-harmonic light emerging from an SHG material is exactly half the wavelength (frequency doubled) of the light entering the material.