Patent ID: 8514482

Claim:
A terahertz electromagnetic wave generating element comprising: a generating layer made of nonlinear optical substance which emits terahertz electromagnetic wave from a surface when another surface is illuminated by light; and a multiple pairs of layer structures provided on the both sides of the generating layer, wherein each of the multiple pairs of layer structures comprises; a first layer; a second layer provided on a side of the first layer, the side being opposite to the side of the generating layer; a first grating provided on a surface on the generating layer side of the second layer, the first grating having a first period smaller than wavelength of used terahertz electromagnetic wave and a first height; and a second grating provided on a surface on the side opposite to the generating layer of the second layer, the second grating having the first period and the first height; wherein refractive index of a medium of the first layer (a first refractive index) is smaller than refractive index of a medium of the second layer (a second refractive index), the first grating and the second grating are constructed in such a way that refractive index between the first layer and the second layer gradually changes between the first refractive index and the second refractive index and thickness of the first layer, thickness of the second layer and the first height are determined in such a way that terahertz electromagnetic wave having a desired band width is generated around the center wavelength of the generated terahertz electromagnetic wave.