Showing papers by "Bernd M. Fischer published in 2022"

Spectral Shaping of a Superluminescent Diode for Terahertz Cross-Correlation Spectroscopy

Abstract: After 20 years of terahertz cross-correlation spectroscopy (THz-CCS), the performance of the systems has been improved to practical relevance by reaching a bandwidth of ~2 THz. For the development of high-performance THz-CCS systems, it is necessary to get a deeper knowledge of the signal generation from incoherent light sources. In this work, the bandwidth, dynamic range, and peak-to-peak amplitude of a THz-CCS systems using a superluminescent diode as light source and a programmable optical filter for spectral shaping was investigated to obtain a better understanding of the relationship between the optical spectrum and the generated terahertz spectrum. By a periodic structuring of the continuous optical spectrum, an enhancement of the peak dynamic range of more than 10 dB was achieved with a bandwidth of 1.6 THz. The experimental results are confirmed by numerical simulations.

An investigation of water diffusion in polymers with terahertz time-domain spectroscopy

Abstract: Water plays an important role in the degradation of polymers. Diffusion across bulk polymers is commonly investigated by gravimetric and capacitive techniques. Here, the water diffusion in polycarbonate (PC) and poly(methyl methacrylate) (PMMA) is studied by terahertz time-domain spectroscopy (THz-TDS) and gravimetric measurements. Time-resolved measurements of the THz refractive index and absorption coefficients show a good agreement to the gravimetrics and allow the contact-free extraction of the diffusion coefficients.