SHG occurs in materials that lack inversion symmetry. When an intense light source, such as a laser, illuminates a nonlinear material, the electric field of the light induces a polarization in the material. This polarization generates a new electromagnetic field with a frequency that is double that of the incident light. The efficiency of SHG depends on factors such as the intensity of the incident light, the nonlinear susceptibility of the material, and the phase matching conditions.
