DEVELOPMENT OF AN APPARATUS FOR ULTRAFAST THz SPECTROSCOPY

Abstract

<p>This thesis details the development of a multi-functional THz system capable<br />of operating in three different geometrical configurations: transmission, reflection<br />and attenuated total reflection (ATR). This apparatus can be used to collect THz<br />time-domain spectroscopic data or it can be used to study the carrier dynamics of a<br />system following optical excitation. These two functions categorize the two types of<br />experiments presented in this thesis.<br />THz time-domain spectroscopy (TDS) was performed with the transmission and<br />reflection configurations to determine the feasibility of using THz radiation to study<br />thin polymer films. This technique was also performed in an ATR configuration<br />with the use of a high purity Si prism. The THz ATR method was developed to<br />extend the capabilities of the system to accommodate liquid samples. '!\fater was the<br />primary sample of interest, however methanol, ethanol and sucrose solutions were<br />also examined. Although the results obtained regarding water are inconsistent with<br />the literature, it has led to valuable insight as to ho\', the current experimental setup<br />may be improved.<br />The optical-pump THz-probe technique was also incorporated \\ ith each of the<br />configurations of the system. In transmission mode, the carrier dynamics of ZnSe<br />nanowires were studied. In reflection mode, the optical-pump, THz-probe capabilities<br />were tested using a Si wafer sample. In the ATR configuration, the carrier dynamics<br />of the Si prism itself were examined. It is necessary to characterize the response of<br />the prism to optical excitation if this technique is to be applied to samples placed<br />on the surface of the prism. Efforts were made to control the free carrier lifetime of<br />the near surface region of the Si prism, by irradiating the surface of the prism with<br />a high energy proton beam to create defects in the Si. The results from this initial<br />experiment, along with suggestions for future follow-up experiments, are presented.</p>