Optical rectification
![An electron (purple) is being pushed side-to-side by a sinusoidally-oscillating force, i.e. the light's electric field. But because the electron is in an anharmonic potential (black curve), the electron motion is not sinusoidal. The three arrows show the Fourier series of the motion: The blue arrow corresponds to ordinary (linear) susceptibility, the green arrow corresponds to second-harmonic generation, and the red arrow corresponds to optical rectification. (When there is no oscillating force, the electron sits at the potential minimum, but when there is an oscillating force, it is, on average, further to the right, by an amount shown by the red arrow.)](/Images/godic/202501/31/Electron_asymmetric_motion_animation5518.gif")
![A schematic of an ionic crystal with no applied electric field (top), and with a sinusoidal electric field caused by a light wave (bottom). The blurryness indicates the sinusoidal oscillation of the ions. The red arrow indicates optical rectification: The oscillating electric field causes a shift of the ions' average positions, which in turn changes the crystal's DC polarization.](/Images/godic/202501/31/Optical_rectification.svg5518.png")
Electro-optic rectification (EOR), also referred to as optical rectification, is a non-linear optical process that consists of the generation of a quasi-DC polarization in a non-linear medium at the passage of an intense optical beam. For typical intensities, optical rectification is a second-order phenomenon which is based on the inverse process of the electro-optic effect. It was reported for the first time in 1962, when radiation from a ruby laser was transmitted through potassium dihydrogen phosphate (KDP) and potassium dideuterium phosphate (KDdP) crystals.