Miniaturization of terahertz spectroscopy

Abstract

The use of terahertz waves in medical research has gained attention in recent years due to the non-ionizing energy levels and non-destructive properties. Despite having promising capabilities comparable to existing medical spectroscopy and imaging techniques, the technology remains confined to research settings primarily due to challenges associated with generating and detecting terahertz waves.

In this thesis, we document the process building a miniaturized terahertz spectroscopy machine using photoconductive antennas. Due to the complexity of generating and detecting terahertz waves in our fiber-based setup, several challenges had to be addressed before we could observe the first experimental terahertz pulse. Additionally, our apparatus's limitations made it difficult to achieve a high-resolution spectrum and high scan rate simultaneously. To address this, we developed two scan modes using LabVIEW. The absolute scan mode was optimized for resolution of the spectrum and achieved a bandwidth of 1.7𝑇𝐻𝑧. However, the scan time was long, taking an estimated one hour for a full scan of 660𝑝𝑠 at 0.05 resolution (13,200 𝑠𝑡𝑒𝑝𝑠). On the other hand, the rapid scan mode was designed to optimize scan rate and was able to achieve two scans per second after resolving synchronization issues between delay line movement and data acquisition. However, this mode produced a lower bandwidth of 1.2𝑇𝐻𝑧 due to higher noise levels.

Future enhancement to our setup may include downsizing of dimensions, replacing the source meter with an independent power supply unit, integration of a single-board computer, and using a two-tier enclosure to achieve full miniaturization. In addition, dispersion compensating fibers and lock-in detection can be added to optimize the signal. For polarization control, the inclusion of metamaterial is another feature that can be added to the setup.