Second harmonic generation is also relevant to characterize organic or inorganic crystals since is one of the most discriminant and rapid technique to detect non-centrosymmetry. In addition, this technique can be used on single crystal as well as on powdered samples.

Second harmonic generation (SHG), also called frequency doubling, is a nonlinear optical process, in which photons interacting with a nonlinear material are effectively 'combined' to form new photons having twice the frequency of initial photons.

THG, or Third Harmonic Generation, is a remarkable process where the frequency of a laser beam is tripled through nonlinear interactions within an optical medium. In this dynamic interplay of light, a new beam materializes, featuring double the initial frequency and a halved wavelength.

SHG requires intense laser light passing through a material with a noncentrosymmetric molecular structure, either inherent or induced externally, for example by an electric field. Second-harmonic light emerging from an SHG material is exactly half the wavelength (frequency doubled) of the light entering the material.