Terahertz Time-Domain Spectroscopy of Thin Material Samples
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- Institutt for fysikk 
This thesis describes the techniques used in terahertz time-domain spectroscopy to determine the optical properties of layers that are thin compared to the length of the terahertz pulse. An iterative procedure is used to minimize thedifference between the measured transfer function and the expression for a Fabry-Pérot etalon when calculating the complex refractive index while simultaneously determining the thickness of the medium. Measurements were performed on slabs of silicon withthicknesses of 50, 10 and 2 microns to test this approach. For all the samples, the determined thickness was larger than expected and the optical parameters deviated from the expected values. This could be caused by the rough surfaces of the samples, which are not accounted for in the models presented here. Absorbing media were simulated using the finite-difference time-domain scheme to calculate a modeled THz pulse shape after propagation through thin layers. Use of these modeled pulse shapes allowed retrieval of the optical parameters and thickness in a self-consistent manner.