The terahertz (THz) region is defined as frequencies between 0.1 THz and 10 THz. It lies between the microwave and infrared regions of the electromagnetic spectrum and has very low photon energy (4.1 meV) such that it will not cause ionization. What’s more, this radiation is strongly attenuated by water and is very sensitive to water content. These characteristics mean that terahertz imaging is suitable for uses in fields like biomedicine, security and telecommunication.

Terahertz 2D imaging has shown potential for diverse applications such as cancer and concealed weapon detection. Yet most existing terahertz imaging systems use raster scanning to move samples in front of a single pixel detector and this limits the acquisition time. Thus single pixel terahertz imaging system wi...[ Read more ]

The terahertz (THz) region is defined as frequencies between 0.1 THz and 10 THz. It lies between the microwave and infrared regions of the electromagnetic spectrum and has very low photon energy (4.1 meV) such that it will not cause ionization. What’s more, this radiation is strongly attenuated by water and is very sensitive to water content. These characteristics mean that terahertz imaging is suitable for uses in fields like biomedicine, security and telecommunication.

Terahertz 2D imaging has shown potential for diverse applications such as cancer and concealed weapon detection. Yet most existing terahertz imaging systems use raster scanning to move samples in front of a single pixel detector and this limits the acquisition time. Thus single pixel terahertz imaging system with compressed sensing theory is developed. In this system no mechanical scanning or detector-array is deployed and only a spatial light modulator is inserted behind sample position. This modulator consists of independent cells which have two states. In one state terahertz signal will pass through carrying sample information while in another state signal will be blocked. Each time the modulator generates a random pattern and compressed sensing technique is applied to the spatial signal received, largely reducing the number of measurements.

In this thesis, high birefringence liquid crystals and vanadium dioxide are explored as the switching material for the spatial light modulator (mask). The switching time between ‘blocking’ and ‘passing’ states of liquid crystals with electrical control, thermal control and frequency control are simulated and measured. The stability and complexity of each control method are also evaluated. Electrical control proves to be the most effective method with our ‘terahertz in-plane and terahertz out-of-plane’ electrode design. Vanadium dioxide is studied because it has an ‘insulating’ state (high transmission) below a critical temperature value and ‘metal’ state (low transmission) above that value. A patterned golden layer is added to increase the contrast between two states. The information we obtained will be used for fabricating the prototype spatial light modulator.

Keywords --- Terahertz radiation, Liquid crystal, Vanadium Dioxide, Modulation