Development and optimization of a PCA-based terahertz time-domain spectroscopy system for high-resolution material characterization

Abstract

Terahertz time-domain spectroscopy (THz-TDS) is a powerful technique for material characterization, providing amplitude and phase information across a broad frequency range. This study details the design, development, and optimization of the first homemade THz-TDS system in Thailand, addressing the high cost and limited accessibility of commercial systems. The system features in-house-developed photoconductive antennas (PCAs) fabricated from electron-beam-irradiated SI-GaAs and a Ti:Sapphire femtosecond laser oscillator, achieving great signal-to-noise ratios and broad bandwidth. Through careful tuning of operational parameters including laser power, bias voltage, scan range, and resolution, the system achieves high signal quality and broad spectral coverage. The system’s performance was validated through material characterization experiments, including accurate measurements of refractive index and thickness of a silicon wafer. Additionally, challenges in liquid-phase measurements, such as window material selection and internal reflections, were systematically addressed. Integration of the system into a dry-air-filled box minimized moisture absorption, allowing precise characterization of moisture-sensitive materials. This work addresses critical gaps in the THz-TDS field by offering systematic system design, parameter optimization, and liquid-phase analysis. It provides practical guidelines and advancements that enable researchers to develop cost-effective, high-performance THz-TDS systems, in resource-limited settings.