Double-Pass Terahertz Time-Domain Spectroscopy of 2D Materials

Terahertz time-domain spectroscopy (THz-TDS) is a nondestructive imaging and characterization technique. It is currently used in the field of material science to obtain the surface conductivity and transmittance of bulk and 2D materials in the range from hundreds of GHz up to few THz. In this research, an alternative setup of the THz-TDS technique is proposed, based on a Michelson interferometer, with a double pass through the sample using a mirror and a semitransparent wafer. A single-branch configuration is used to characterize a few-layer WS2 sample on a fused quartz substrate. The objectives of the experiment are to demonstrate that the configuration is viable for obtaining the parameters of the sample and the substrate, to present the models and equations used, and to explain the advantages and limitations of the method compared to the transmission configuration. The optical transmittance and surface conductivity of WS2 are obtained with the new configuration in the frequency range from 0.2 to 1.2 THz. Raman spectroscopy is used to analyze the sample quality before performing the measurements.