High Quality Content by WIKIPEDIA articles! Electromagnetically induced grating (EIG) is an optical interference phenomenon where an interference pattern is used to build a dynamic spatial diffraction grating in matter. EIGs are dynamically created by light interference on optically resonant materials and rely on population inversion and/or optical coherence properties of the material. They were first demonstrated with population gratings on atoms. EIGs can be used for purposes of atomic/molecular velocimetry, to probe the material optical properties such as coherence and population life-times, and switching and routing of light. Related but different effects are thermally induced gratings and photolithography gratings.