Designing a Terahertz Spatial Light Modulator

Abstract

This thesis presents the design, development, and characterisation of a novel spatial light modulator operating in the terahertz (THz) regime. It addresses key limitations in current THz technologies, including the scarcity of efficient modulators with high spatial resolution, fast response times, and integration compatibility with THz imaging systems. The device employs a high-resistivity (5000 Ohm·cm), 480 µm-thick silicon wafer modulated via photoexcitation at intensities up to 1.5 W/cm2 and wavelengths spanning 405–920 nm. Spatially patterned excitation is delivered using a digital micromirror device (DMD), enabling reconfigurable and high-resolution THz modulation. The modulator is integrated into a 550 GHz imaging system, where its performance is assessed in terms of spatial resolution, contrast, modulation depth, and frame rate. The system achieves real-time image formation with a diffraction-limited resolution of 340 µm and a modulation depth of 29%. Dynamic modulation tests demonstrate operational frame rates exceeding 10 kHz while maintaining consistent contrast. These results highlight the system’s potential for applications in security screening, non-destructive testing, and biomedical imaging. Ultimately, this work bridges disciplines across materials science, photonics, and semiconductor engineering, delivering a scalable and efficient platform that advances the capabilities of THz modulation and imaging.