A. I. Hernandez-Serrano

Quality control of leather by terahertz time-domain spectroscopy

We use terahertz time-domain spectroscopy, combined with effective-medium theory, to measure the moisture content and thickness of leather simultaneously. These results demonstrate that this method could become a standard quality control test for the industrial tanning process.

Fabrication of gradient-refractive-index lenses for terahertz applications by three-dimensional printing

In this article we present the design, fabrication, and characterization of gradient-refractive-index lenses for terahertz (THz) applications. The fabrication was performed by three-dimensional printing. These new low-cost lenses were tested using THz time-domain spectroscopy and imaging in order to measure their optical properties. The results show a focusing capacity within the diffraction limit for frequencies below 700 GHz.

Modelling the carrier dynamics of semiconductors to understand their terahertz emission (Conference Presentation)

We use a Monte-Carlo model to simulate semi-classical photo-carrier dynamics on bulk InAs, InGaAs and GaAs that leads to terahertz emission after ultrafast photoexcitation. This detailed model has allowed us to understand various aspects of the THz emission process, including the near-field distribution which has been experimentally observed, the role of the excess excitation photon energy, and the relative importance of the surface field driven, diffusive (photo-Dember) and ballistic currents. In order to understand the near-field emission we coupled a finite-difference time-domain routine to the carrier dynamics simulation, by doing this, we were able to analyse the near terahertz field emission caused by the motion of such carriers even when the excitation is performed at normal incidence. We found that both the current parallel, which has traditionally been assumed not to take part in the emission, and normal to the interface take a relevant role in the terahertz generation. We performed another set of simulations for different bandgaps and excitation-photon energies in order to compare the emission power of all three semiconductors as function of excitation photon energy finding that the carrier excess excitation energy is more relevant to explain their performance difference than their motilities. We conclude that ballistic transport after photoexcitation is the dominant mechanism for terahertz emission instead of diffusion driven or surface field driven charge separation, which were traditionally considered the most relevant mechanisms.

Pancharatnam-Berry phase optical elements fabricated by 3D printing for shaping terahertz beams

The design, fabrication and characterization of space-variant Pancharatnam-Berry phase optical elements is presented for the terahertz regime (THz). These PBOEs are made out of polystyrene and were fabricated by commercially available three-dimensional printers, providing a simple and inexpensive solution for the generation of THz vector beams. The polarization structure was characterized by using a THz time-domain imaging system. These devices can find applications in future THz technologies and provide new tools for the study of polarization morphologies