Study Of ZnCdTe<110> Crystals As Terahertz Wave Emitters

In the last decade, rapid progress in ultrafast laser technology provides a steady and reliable optical source for the terahertz (THz) pulses generation, which greatly promotes the research in the THz waveband that is difficult to access before. THz spectra of materials contain abundant physical and chemical information. Therefore, THz technology has been widely used in many domains, including foundational research, industrial and military applications.Effective generation of THz wave is a basic issue in experiments evolving THz radiation. Scientists have studied different electro-optic crystals as a THz waves emitter, and they found that the ZnTe crystal is the best for THz wave generation. Therefore, ZnTe crystal has been the most common material for pulsed THz wave sensing and imaging applications. Kai Liu et al have studied <110>-oriented Zn1-xCdxTe crystals with various composition ratios and different doping levels to find optimal materials' parameters for high performance THz radiation emitters. They explained their experimental results from the points of view of crystal quality and crystal DC resistivity. In this thesis, we study the THz pulse generation efficiency of the <110>-oriented Zn1-xCdxTe crystals with various composition ratios and doping levels, using THz time-domain spectroscopy. It is found that both absorption and phase matching condition play important role.It is the first time to systematically study <110>-oriented Zn1-xCdxTe crystals with various composition ratios and different doping levels using THz time-domain spectroscopy. Our results explain the mechanisms of the composition and doping dependent THz radiation efficiency for the different crystals. Experimental results in this thesis are useful for growing EO crystals with high performance, and suggest that more parameters are required for better characterization of this kind of crystals as THz wave emitters.The main results and conclusions are listed as follows:1) Experimental measurements with low Cd composition Zn1-xCdxTe<110>crystals(0 crystals (0-oriented Zn1-xCdxTe crystals is the key factor which affects the generation efficiency of THz waves.3) The phase matching condition in the <110>-oriented Zn1-xCdxTe crystal with x=0 is the best, but the average transmittance of THz wave in the crystal is lower. As a result, its generation efficiency of THz waves is not the best. The observation reconfirms that introduction of a small amount of Cd (3%-5%) into ZnTe can significantly improve the crystal quality and enhances the generation efficiency of THz waves.4) The THz resistivity of doped Zn0.95Cd0.05Te<110> crystals changes withdifferent doping following the similar way as the DC resistivity, which results in different THz wave generation efficiency. Experimental measurements from differentdoped Zn0.95Cd0.05Te<110> crystals suggest that the DC resistivity of the crystal forTHz emitter application should be greater than 102O-cm.5) Optical rectification in a set of doped Zn0.95Cd0.05Te<110> crystals show an increasing efficiency of THz beam generation with the increasing crystal resistivity, but the efficiency saturates and descended when the doped crystal resistivity goes beyond 106 O-m.6) The self-absorption of THz waves in doped Zn0.95Cd005Te<110> crystals is the main factor which affects the generation efficiency of THz waves.This thesis is composed of six sections, including the introduction and five chapters organized as follows:Introduction gives a brief view on the background and significance of studying THz radiation.Chapter One is a survey of THz radiation, including the character of THz ra...