Influence of two-photon absorption and optical excitation size on the THz radiation via optical rectification

Although the ZnTe crystal used the generation of THz radiation has a favorable phase matching properties at 820nm, it has strong third-order nonlinearity, such as two-photon absorption effect. And we found experimentally that, the effect of two-photon absorption in ZnTe on the THz radiation was not neglect. In addition, due to optical rectification and diffraction effect, the generated efficiency of THz radiation is also related to the optical excitation size in the emitter. In this paper, by taking into account optical rectification, diffraction and two-photon absorption effects, the theoretical model is established to describe the emitting field intensity of THz radiation. There is excellent agreement between the theoretical results and the experimental data. The good agreement demonstrates that there is a trade-off between these three effects for THz radiation.