Influence of noise on the characterization of materials by terahertz time-domain spectroscopy

TLDR

In THz time‑domain spectroscopy using photoswitch antennae, the transmitting antenna is the main noise source. The study analyzes how various error sources, particularly noise, contribute to uncertainty in far‑infrared optical constants measured by THz time‑domain spectroscopy. By measuring a thick transparent slab that produces temporal echoes from internal reflections, the authors extract data from each echo to characterize the noise sources. They find that uncertainty in the optical constants is markedly reduced when extraction uses echoes that have undergone many reflections.

Abstract

We analyze the contributions of various error sources to uncertainty in the far-infrared optical constants (refractive index and absorption coefficient) measured by terahertz (THz) time-domain spectroscopy. We focus our study on the influence of noise. This noise study is made with a thick slab of transparent material for which the THz transmitted signal exhibits temporal echoes owing to reflections in the sample. Extracting data from each of these time-windowed echoes allows us to characterize the noise sources. In THz time-domain spectroscopy experiments in which photoswitches are used as antennae, the transmitting antenna constitutes the principal noise source. The uncertainty in the far-infrared optical constants can be strongly reduced when the extraction is performed with THz echoes that have encountered many reflections in the sample.