Investigation of congruent lithium niobate crystal dispersion properties in the terahertz frequency range

Dispersion curves of the refraction index of a congruent lithium niobate (cLN) crystal cut perpendicular to the x and z axes in the terahertz frequency range are considered. In the study, the method of terahertz time domain spectroscopy with time resolution is used passed through an initially isotropic detecting crystal which becomes birefringent when exposed to a terahertz field. The magnitude of the induced birefringence is proportional to the amplitude of the terahertz field. Using Fourier analysis of a terahertz pulse passing through a cLN crystal and a reference pulse that does not interact with the object, the frequency dependences of the refractive index and the absorption coefficient of the object under study are constructed. Dispersion curves are presented for the real part of the refractive index of a cLN crystal cut along the planes (100) and (001), in the frequency range 0.25–1.25 THz. Simulation of the propagation of a one-and-a-half-cycle pulse in media with dispersion is performed based on the data of scientific papers by other authors. As a result, the temporal forms of the output signals are found. Conclusion about the inaccuracy of the dispersion curves from the selected works is made. The parameters has been identified whose optimization made it possible to eliminate inaccuracies in the display of the dispersion dependence for the high-frequency region of the terahertz spectrum were identified. The results obtained are very important for the design of devices based on nonlinear optical effects. These data will be useful for the generation of difference frequencies, optical rectification and generation of terahertz radiation as well as for areas where accurate data on the terahertz dispersion properties of nonlinear crystals, including cLN, are required.