Research On Electro-optical Properties Of Several Crystals In The Terahertz Range

With the rapid development of the microwave technology and laser technology, terahertz band has gradually become the band with great potential in the electromagnetic spectrum. Besides, the electro-optical properties of crystal materials are one of the bases for all kinds of functional devices in the terahertz range. Although comparatively more researches and wider applications have been done to all kinds of electro-optical crystal materials in the optical band, in the terahertz band, few studies of specific experiments have been done to the electro-optic properties of materials. However, the applications based on the electro-optic materials, such as the detection and generation of terahertz wave, terahertz electro-optical imaging, a variety of terahertz functional devices, and etc., are crucial for the terahertz system researches. It is of great significance to research the electro-optical properties of materials in the terahertz range. The proper use of the properties of crystals, the adjustment and control of crystals'vital parameters through controllable electromagnetic field, will make the terahertz functional devices and terahertz system performances improve a lot.This article summarizes the researches and applications of electro-optic materials from three aspects, in the terahertz generation, detection and terahertz imaging. Combined index-ellipsoid theory with the crystal structure theory, theoretical analysis and determination have been made about the optimal direction of the outside electric fields applied on the crystal ZnTe, GaAs and LiNbO3. Transmission-type THz-TDS system was used to obtain the refractive index dispersion curves and other important parameters of several crystalline materials. The results are meaningful, which can contribute to the researches on terahertz devices using these materials. The main research results are listed as follows:First of all, for ZnTe and GaAs, When the outside bias voltage takes the direction of the y' axis, terahertz polarization takes the direction of the y' axis or z' axis, the changes in the crystal refractive index are the largest, the direction of the bias electric field at this time is optimal, and the direction is always perpendicular to the z axis the crystal; the optimal direction of the bias electric field for LiNbO3 is the z axis direction of the crystal, which is also the direction on which the changes in the crystal refractive index are largest with voltages, the direction of terahertz polarization also take this direction to sense the larger changes in the refractive index of crystals.In addition, a rotatable electrode mold has been made. Compared to former molds, the rotatable electrode moid can adjust the angles of the crystals more accurately, and make it convenient for the bias voltage to be applied. Electric field simulations have been done to the mold to make the crystals work normally in the mold.Thirdly, the transmission-type THz-TDS system was used to obtain the refractive index dispersion curves and other important parameters of several crystalline materials under different bias voltages:the refraciive index of GaAs had comparatively obvious changes around 0.0932 in the frequency from 800 GHz to 2 THz, the refractive index of ZnTe has smaller changes around 0.015, and the refractive index of Si barely changes for the reason that Si is not the electro-optic materials. and it was used in the experiments mainly for testing the system stability and system noise. At last, the error sources analysis was done as a practical matter.