Determination of optical constants by using thz time-domain spectroscopy

The Terahertz (THz) time-domain spectroscopy represents the spectrum region between the microwave and the infrared with a range between 0.1-30 THz. In recent years, the THz spectrum have received great attention of the scientific community because of its non-destructive testing properties and its unique applications in various fields. In order to effectively use the functionality of THz spectroscopy, optical properties of materials should be extracted accurately and correctly. This thesis focuses on proposing a new method for extracting optical constants of low-loss or lossless materials using reflection-only signals. We applied the following steps for validation of our method. First, time-domain signals of the sample (Si or GaAs) with/out a perfect electric conductor (PEC) backing are simulated using a commercial 3D electromagnetic simulator program (CST Microwave Studio©). Then, appropriate windows are applied to sample out the required components of the reflected signal and transmitted signal (for comparison). Next, fast Fourier transform algorithm was implemented to transform the time-domain signal components into frequency-domain signal components. Finally, frequency-domain signal components are utilized to extract the optical properties of the analyzed sample. The advantages of the proposed method are that it doesn't require the application of any numerical technique with an appropriate initial guess, and it uses only reflection properties so that the proposed formula is applicable to optical characterization of samples backed by a PEC.