Continuous-wave terahertz thickness measurement system based on photo-mixing

Abstract

In this thesis, we propose and demonstrate a terahertz thickness measurement system based on optical mixing. Continuous wave terahertz waves are generated based on optical mixing technology using UTC-PD (Uni-Traveling-Carrier Photodiode). The proposed continuous wave terahertz thickness measurement system can down convert a signal using a square-law detection method that does not require a local oscillation signal, which is a disadvantage of conventional homodyne or heterodyne coherent detection. In addition, unlike conventional thickness measurement systems, thickness measurements can be made at long distance locations without direct contact with the sample. Therefore, the proposed continuous wave terahertz thickness measurement system can be constructed much more efficiently than the conventional coherent detection system because there is no optical local oscillation signal. Next, we show the measurement results of the stability and phase linearity of the system to evaluate the proposed system. Finally, we introduce and analyze the thickness measurements of the tested samples.