Optical rectification in an area with a diameter comparable to or smaller than the center wavelength of terahertz radiation.

We report the measurement of optically rectified terahertz (THz) wave power relative to the optical excitation area. Rectified THz wave power reaches its maximum when radius r of the optical excitation area is comparable to the center wavelength of the rectified THz radiation. When r is smaller than the center wavelength of the rectified THz radiation, an r(2) relationship is demonstrated. A model based on optical rectification and Bethe's diffraction theory is used to describe this relationship.