Study on terahertz generation from LiNbO 3 crystal with density function theory

Abstract

Terahertz(THz) wave, which lies between infrared and microwave in electromagnetic spectrum, belongs to far-infrared band. THz-wave covers the frequency range from 0.1THz to 10THz. The physical mechanism of terahertz generation was discussed in this paper. It provided theoretical foundation for designing terahertz-generator of LiNbO₃ crystal and optimizing output property of terahertz through the analysis of internal mechanism. The polariton dispersion characteristic was mainly reflected by its dispersion curve. Density functional theory (DFT) was used to calculate Raman spectrum and dispersion curve for LiNbO₃ in this paper. The polariton dispersion curve of LiNbO₃ indicated that the frequencies between 0THz and 7.5THz (the wave numbers were 0cm^-1 250cm^-1) were generated from LiNbO₃ crystal when the scattering angle were about 0 - 5 degree. This predicted theoretically that terahertz was generated from LiNbO₃. It was very obvious that the Raman vibration modes of crystal model were more than molecular structure. Intermolecular vibrations were depicted by molecular structure and parts of vibration modes were simulated. But whole vibration-rotation of unit cell was depicted by crystal model and all atoms were concerned with vibration. It was more accurate that the prediction about generated THz-wave and the range of THz-wave by crystal model than by molecular structure based on the analysis of polariton dispersion curves because crystal model was close to the experimental sample.